OPTICAL SWITCHING IN LIDAR SYSTEMS

Abstract

A LIDAR system is configured to generate an outgoing light signal that exits from the LIDAR system. The LIDAR system is configured to receive an incoming light signal that enters the LIDAR system and that includes light from the outgoing light signal. The LIDAR system also includes an optical switch that receives the outgoing light signal and the incoming light signal and is configured to be operated in different modes. The incoming light signal and/or the outgoing light signal are routed along different optical paths through the LIDAR system in response to the optical switch being in different modes.

Description

FIELD

The invention relates to optical devices. In particular, the invention relates to LIDAR systems.

BACKGROUND

LIDAR technologies are being applied to a variety of applications. One LIDAR technique makes use of a LIDAR system that generates an outgoing light signal. The LIDAR system also outputs from the system a LIDAR output signal that includes a portion of the light from the outgoing light signal. The LIDAR output signal is reflected off of an object and at least a portion of the reflected light returns to the LIDAR system as a LIDAR input signal. The LIDAR system combines the LIDAR input signal with a reference signal so as to generate a composite signal. The reference signal includes a second portion of the light from the outgoing light signal that did not exit from the LIDAR system and was not reflected by the object. The LIDAR system uses the composite signal to generate LIDAR data for the object (distance and/or radial velocity between the source of a LIDAR output signal and a reflecting object).

It is often desirable for the LIDAR input signal to be received through the same facet through which the LIDAR output signal is transmitted (sometimes called a coaxial configuration). Accordingly, a portion of the path traveled by the LIDAR input signal and the LIDAR output signal through the LIDAR system can be the same (common optical path); however, the LIDAR system can separate the path of the LIDAR input signal from the path of the LIDAR output signal in order to combine the LIDAR input signal with the reference signal. The signals are often separated by technologies such as couplers and circulators.

It is desirable to build these LIDAR systems on optical chips using platforms such as the silicon-on-insulator platform. However, circulators are not practical for integration onto these optical chips. Additionally, since optical couplers spilt a signal, optical couplers are a source of power loss for the LIDAR input signal. As a result, there is a need for a LIDAR system that can separate a LIDAR input signal and the LIDAR output signal that travel on the same optical path.

SUMMARY

A LIDAR system is configured to generate an outgoing light signal that exits from the LIDAR system. The LIDAR system is configured to receive an incoming light signal that enters the LIDAR system and that includes light from the outgoing light signal. The LIDAR system also includes an optical switch that receives the outgoing light signal and the incoming light signal and is configured to be operated in different modes. The incoming light signal and/or the outgoing light signal are routed along different optical paths through the LIDAR system in response to the optical switch being in different modes.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic of a LIDAR system.

FIG. 2A illustrates an example of a frequency versus time schedule for an outgoing light signal and an incoming light signal at an exit from a LIDAR system.

FIG. 2B illustrates another example of a frequency versus time schedule for an outgoing light signal and an incoming light signal at an exit from a LIDAR system.

FIG. 2C illustrates another example of a frequency versus time schedule for an outgoing light signal and an incoming light signal at an exit from a LIDAR system.

FIG. 2D illustrates a separation threshold (ST) as a function of a receive ratio.

FIG. 3 illustrates multiple light sources configured to generate an outgoing light signal that includes multiple channels.

FIG. 4 illustrates a light source that includes multiple laser sources.

FIG. 5 illustrates one example of a structure configured to generate a light signal that includes multiple channels.

FIG. 6A illustrates an example of a processing unit.

FIG. 6B provides a schematic of electronics that are suitable for use with a processing unit constructed according to FIG. 6A.

FIG. 6C provides another schematic of electronics that are suitable for use with a processing unit constructed according to FIG. 6A.

FIG. 7 illustrates an example of an optical port that includes beam steering capability.

FIG. 8 illustrate construction of an optical switch that is suitable for use in planar optical devices.

DESCRIPTION

The LIDAR system generates an outgoing light signal and outputs a LIDAR output signal that includes a first portion of the light from the outgoing light signal. The LIDAR output signal is reflected off of an object and at least a portion of the reflected light returns to the LIDAR system as a LIDAR input signal. The LIDAR system combines the LIDAR input signal with a reference signal so as to generate a composite signal. The reference signal includes a portion of the light from the outgoing light signal that did not exit from the LIDAR system and was not reflected by the object. The LIDAR system uses the composite signal to generate LIDAR data for the object (distance and/or radial velocity between the source of a LIDAR output signal and a reflecting object).

The LIDAR input signal and the LIDAR output signal travel along the same path between a signal-directing component and a facet of a waveguide. The signal-directing component is an optical switch that is operated so as to separate the pathway of the LIDAR input signal from the pathway of the LIDAR output signal. Optical switches can be integrated into optical chip platforms such as the silicon-on-insulator platform. Additionally, the switch does not significantly reduce the power of the LIDAR input signal. As an additional and unexpected advantage, the optical switch can greatly reduce the amount of laser energy that exits from the LIDAR system and enters the environment. As a result, the optical switch provides a LIDAR system that can provide protection for the environment and the eyes of users and bystanders.

FIG. 1 is a schematic of a LIDAR system. The system includes a light source 10 such as a laser that outputs an outgoing light signal. The outgoing light signal includes one or more different channels that are each at a different wavelength. When the outgoing light signal includes multiple channels, the wavelengths of the channels can be periodically spaced in that the wavelength increase from one channel to the next channel is constant or substantially constant. A suitable light source 10 for generating an outgoing light signal with a single channel includes semiconductor lasers, solid-state lasers, gas lasers, and liquid lasers. A suitable light source 10 for generating multiple channels with periodically spaced wavelengths includes, but is not limited to, comb lasers, multiple single wavelength lasers multiplexed into to single optical waveguide, and sources such as that described in U.S. patent application Ser. No. 11/998,846, filed on Nov. 30, 2017, grated patent number U.S. Pat. No. 7,542,641, entitled “Multi-Channel Optical Device,” and incorporated herein in its entirety.

The LIDAR system also includes a utility waveguide 12 that receives the outgoing light signal from the light source 10. A modulator 14 is optionally positioned along the utility waveguide 12. The modulator 14 is configured to modulate the power of the outgoing light signal and accordingly the LIDAR output signal(s). The electronics can operate the modulator 14. Accordingly, the electronics can modulate the power of the outgoing light signal and accordingly the LIDAR output signal(s). Suitable modulators 14 include, but are not limited to, PIN diode carrier injection devices, Mach-Zehnder modulator devices, and electro-absorption modulator devices. When the modulator 14 is constructed on a silicon-on-insulator platform, a suitable modulator is disclosed in U.S. Patent application Ser. No. 617,810, filed on Sep. 21 1993, entitled Integrated Silicon PIN Diode Electro-Optic Waveguide, and incorporated herein in its entirety.

An amplifier 16 is optionally positioned along the utility waveguide 12. Since the power of the outgoing light signal is distributed among multiple channels, the amplifier 16 may be desirable to provide each of the channels with the desired power level on the utility waveguide 12. Suitable amplifiers include, but are not limited to, semiconductor optical amplifiers (SOAs).

The utility waveguide 12 carries the outgoing light signal from the modulator 14 to a signal-directing component 18. The signal-directing component 18 can direct the outgoing light signal to a LIDAR branch 20 and/or a data branch 22. The LIDAR branch outputs LIDAR output signals and receives LIDAR input signals. The data branch processes the LDAR input signals for the generation of LIDAR data (distance and/or radial velocity between the source of the LIDAR output signal and a reflecting object).

The LIDAR branch includes a LIDAR signal waveguide 24 that receives at least a portion of the outgoing light signal from the signal-directing component 18. The LIDAR signal waveguide 24 carries at least a portion of the outgoing light signal to an optical port 26 through which light signals enter and/or exit from the LIDAR system. In some instances, the optical port 26 is a facet positioned at an edge of an LIDAR chip. When the outgoing light signal includes multiple different channels at different wavelengths, the optical port 26 can have demulitplexer functionality and/or can include or consist of a demulitplexer that separates the outgoing light signal into multiple LIDAR output signals that are each at a different wavelength (channel) and are directed to different sample regions in a field of view. The optical port 26 outputs the LIDAR output signals which can be reflected by a reflecting object (not shown) located outside of the LIDAR system. The reflected LIDAR output signals return to the optical port 26 as LIDAR input signals. The optical port 26 combines the LIDAR input signals and outputs the result on the LIDAR signal waveguide 24 as an incoming light signal.

In some instances, the optical port 26 includes beam steering functionality. In these instances, the optical port 26 can be in electrical communication with electronics (not shown) that can operate the optical port 26 so as to steer the LIDAR output signals to different sample regions in a field of view. The optical port 26 and/or electronics can be configured such that the different LIDAR output signals are steered independently or are steered concurrently.

Although the optical port 26 is illustrated as a single component, the optical port 26 can include multiple optical components and/or electrical components. Suitable optical ports include, but are not limited to, optical phased arrays (OPAs), transmission diffraction gratings, reflection diffraction gratings, and Diffractive Optical Elements (DOE). Suitable optical port 26 with beam steering capability include, but are not limited to, optical phased arrays (OPAs) with active phase control elements on the array waveguides.

The LIDAR signal waveguide 24 carries the incoming light signal to the signal-directing component 18. Since the outgoing light signal also travels between the optical port 26 and the signal-directing component 18 on the LIDAR signal waveguide 24, the incoming light signal and the outgoing light signal travel a common optical path between the optical port 26 and the signal-directing component 18. The outgoing light signal travels away from the signal-directing component 18 along the common optical pathway and the incoming light signal travels toward the signal-directing component 18 along the common optical pathway. The signal-directing component 18 directs the incoming light signal to the utility waveguide 12 and/or a comparative signal waveguide 28. The portion of the incoming light signal-directed to the comparative signal waveguide 28 serves as a comparative incoming light signal.

The comparative signal waveguide 28 carries the comparative incoming light signal to a comparative demultiplexer 30. When the comparative light signal includes multiple channels, the comparative demultiplexer 30 divides the comparative incoming light signal into different comparative signals that each has a different wavelength. The comparative demultiplexer 30 outputs the comparative signals on different comparative waveguides 32. The comparative waveguides 32 each carry one of the comparative signals to different processing components 34.

The signal-directing component 18 is configured such that when the signal-directing component 18 directs at least a portion of the incoming light signal to the comparative waveguide 32, the signal-directing component 18 also directs at least a portion of the outgoing light signal to a reference signal waveguide 36. The portion of the outgoing light signal received by the reference signal waveguide 36 serves as a reference light signal.

The reference signal waveguide 36 carries the reference light signal to a reference demultiplexer 38. When the reference light signal includes multiple channels, the reference demultiplexer 38 divides the reference light signal into different reference signals that each has a different wavelength. The reference demultiplexer 38 outputs the reference signals on different reference waveguides 40. The reference waveguides 40 each carry one of the reference signals to a different one of the processing components 34.

The comparative waveguides 32 and the reference waveguides 40 are configured such that a comparative signal and the corresponding reference signal are received at the same processing component 34. For instance, the comparative waveguides 32 and the reference waveguides 40 are configured such that the comparative signal and the corresponding reference signal of the same wavelength are received at the same processing component 34.

As will be described in more detail below, the processing components 34 each combines a comparative signal with the corresponding reference signal to form a composite signal that carries LIDAR data for a sample region on the field of view. Accordingly, the composite signal can be processed so as to extract LIDAR data for the sample region. The signal-directing component 18 can be an optical switch such as a cross-over switch. A suitable cross-over switch can be operated in a switched mode or a pass mode. In the pass mode, the outgoing light signal is directed to the LIDAR signal waveguide 24 and an incoming light signal would be directed to the utility waveguide 12. In the switched mode, the outgoing light signal is directed to the reference signal waveguide 36 and the incoming light signal is directed to the comparative signal waveguide 28. Accordingly, the incoming light signal or a portion of the incoming light signal can serve as the comparative light signal and the outgoing light signal or a portion of the outgoing light signal can serve as the reference light signal.

The different modes of switch operation described above are configured such that the outgoing light signal exits from the LIDAR system when the optical switch is in the pass mode (first mode) but does not exit from the LIDAR system when the optical switch is in the switched mode (second mode). The incoming light signal and the outgoing light signal both travel along the common optical path when the optical switch is in the pass mode. The incoming light signal travels along the common optical path when the optical switch is in the switched mode but the outgoing light signal does not travel along the common optical path when the optical switch is in the pass mode. The incoming light signal travels away from the optical switch along a first optical path that includes all or a portion of the comparative signal waveguide 28 when the optical switch is in the pass mode and the outgoing light signal travels away from the optical switch along a second optical path that includes all or a portion of the reference signal waveguide 36 when the optical switch is in the switched mode. The first optical path, the second optical path and the common optical path are separate from one another. Light from the outgoing light signal is mixed with light from the incoming light signal so as to generate the composite light signal when the optical switch is in the switched mode. The composite light signal is not generated when the optical switch is in the first mode.

An optical switch such as a cross-over switch can be controlled by the electronics. For instance, the electronics can control operate the switch such that the switch is in the switched mode or a pass mode. When the LIDAR output signal is to be transmitted from the LIDAR system, the electronics operate the switch such that the switch is in the pass mode. When the LIDAR input signal is to be received by the LIDAR system, the electronics operate the switch such that the switch is in the switched mode. The use of a switch can provide lower levels of optical loss than are associated with the use of an optical coupler as the signal-directing component 18.

In the above descriptions of the operation of the signal-directing component 18, the comparative light signals and the reference light signals are concurrently directed to the data branch. As a result, the processing components 34 can each combine a comparative signal with the corresponding reference signal.

In some instances, an optical amplifier 42 is optionally positioned along the LIDAR signal waveguide 24 and is configured to provide amplification of the outgoing light signal and/or of the incoming light signal. Accordingly, the effects of optical loss at the signal-directing component 18 can be reduced.

During operation of the LIDAR system, the generation of LIDAR data is divided into a series of cycles where LIDAR data is generated for each cycle. In some instances, each of the cycles corresponds to a different sample region in a field of view. Accordingly, different cycles can generate LIDAR data for different regions in a field of view.

The cycles can be performed such that the time for each cycle can be divided into different time periods. The electronics can add chirp to the frequency of the outgoing light signal and accordingly to the LIDAR output signal(s). The chirp can be different during adjacent periods in a cycle. For instance, the electronics can increase the frequency of the outgoing light signal during a first period and decrease the frequency of the outgoing light signal during a second period.

The following FIG. 2A through FIG. 2D illustrate the results of operating a LIDAR system using the optical switch disclosed. In order to simplify the illustration, FIG. 2A through FIG. 2D are directed to a single channel in an outgoing light signal or treat the LIDAR system as generating an outgoing light signal with a single channel.

FIG. 2A illustrates an example of a possible frequency versus time schedule for the frequency of the outgoing light signal at the facet and the incoming light signal at the facet. The schedule is shown for several different cycles labeled cycle, through cycle_i+2. As noted above, different cycles can correspond to different sample regions in a field of view. As a result, the LIDAR system can steer the LIDAR output signal(s) from one sample region in the field of view to another sample region in the field of view between different cycles.

Each cycle includes a first period labeled “Period,” and a second period labeled “Period₂.” The illustrated chirp is different for different periods in a cycle. Accordingly, the outgoing light signal is a different function of time than the incoming light signal. For instance, the frequency of the outgoing light signal increases during the first period and decreases during the second period. Although each of the cycles is shown in FIG. 2A as having two periods, the cycles can include one, two, or more than two periods.

Each period includes multiple time segments. The electronics can operate the signal-directing component 18 in different modes during different time segments. For instance, in FIG. 2A, each period includes a transmit segment and a receive segment. During the transmit segment, the electronics can operate a signal-directing component 18 such as an optical switch in the pass mode where the outgoing light signal is directed to the LIDAR signal waveguide 24 as illustrated by the solid line labeled “outgoing light signal” in FIG. 2A. As a result, one or more LIDAR output signals are output from the LIDAR system during the transmit segment.

During the receive segment, the electronics can operate a signal-directing component 18 such as an optical switch in the switched mode where the outgoing light signal is directed to the reference signal waveguide 36 so the outgoing light signal or a portion of the outgoing light signal can serve as the reference light signal. As a result, the outgoing light signal is not received at the facet during the receive segment. In order to illustrate this result, the portion of the LIDAR output signal in the receive segment is shown as a dashed line in FIG. 2A. Accordingly, during the receive segment, the “outgoing light signal” continues to be generated by the LIDAR system but is not output as the one or more LIDAR output signals. Since the one or more LIDAR output signals are not output from the LIDAR system during the receive segment, the amount of laser energy introduced into the atmosphere is reduced and the possibility of eye damage from the LIDAR system is reduced. Additionally, during the receive segment, the incoming light signal is directed to the comparative signal waveguide 28 allowing the incoming light signal or a portion of the incoming light signal to serve as the comparative light signal.

During subsequent transmit segments, previously transmitted LIDAR output signal may continue returning to the LIDAR system as LIDAR input signals. The resulting incoming light signal can still be received on the LIDAR signal waveguide 24, however, since the electronics operate the signal-directing component 18 in the pass mode during the transmit segments, the received incoming light signal are not passed to a data branch 22. For instance, in the LIDAR system of FIG. 1, the incoming light signal is directed to the utility waveguide 12 where it generally does not have enough power to affect operation of the light source(s). In instances, where it is desirable to reduce the intensity of the incoming light signal on the utility waveguide 12, it is possible to reduce the power of the outgoing light signal through one or more mechanisms selected from the group consisting of reducing amplification provided by an amplifier 16, tuning the output from the light source and operating an optical attenuator (not shown) on the utility waveguide 12. Since the incoming light signal is directed to the utility waveguide 12 during the transmit segments, the electronics do not generate LIDAR data from incoming light signals received during the transmit segments. This result is illustrated by the portion of the incoming light signals shown by dashed lines during the transmit segments of FIG. 2A.

In a LIDAR system, the roundtrip signal time τ represents the time for a LIDAR output signal to travel to a reflecting object and to return to the LIDAR system. As a result, the roundtrip signal time (τ) can be represented by τ=2D/c where D represents the displacement distance between the reflecting object and the location where the LIDAR output signal exits from the LIDAR system. LIDAR systems are generally associated with a maximum distance (D_max). The maximum distance is the largest separation between an object and the LIDAR system for which the LIDAR system generates LIDAR data. FIG. 2A is generated using the assumption that the displacement distance (D) is equal to the maximum displacement distance (D_max). When the displacement distance (D) is equal to the maximum displacement distance (D_max), the time between a LIDAR output signal exiting the LIDAR system and returning to the LIDAR system can be represented by τ_max (τ_max=2D_max/c where c is the speed of light). FIG. 2A represents the situation where τ=τ_max. As a result, the duration of the transmit segment is equal to the time needed for a LIDAR output signal to travel from the LIDAR system to an object located at the maximum distance and then back to the LIDAR system. As a result, the LIDAR system begins to receive the incoming light at the end of the transmit segment. Accordingly, the line labeled “incoming light signal” in FIG. 2A represents the receipt of the “incoming light signal” at the start of each receive segment.

FIG. 2B illustrates the frequency versus time schedule of FIG. 2A modified to show the results when the reflecting object is located closer to the LIDAR system than in FIG. 2A. In particular FIG. 2B represents the situation where τ=the duration of the receive segment (T_rs). Accordingly, in period 1 of cycle i, the incoming light signal resulting from a LIDAR output signal transmitted in cycle 1 first shows up in the transmit segment after passage of an amount of time equal to the duration of the receive segment as shown by the time labeled t_rs.

The electronics use data generated from the incoming light signal during the receive segment to generate the LIDAR data. The reliability of the LIDAR data increases the longer that the incoming light signal is available to the electronics. As is evident in FIG. 2A and FIG. 2B, the incoming light signal is available to the electronics for generating the LIDAR data during the entire duration of the receive segment.

As the distance between the LIDAR system and the object becomes close enough that the roundtrip signal time (τ) becomes less than duration of the receive segment (T_rs), the incoming light signal becomes available to the electronics for generating the LIDAR data for a fraction of the duration of the receive segment (i.e. <100% T_rs). For instance, FIG. 2C illustrates the frequency versus time schedule of FIG. 2A modified to show the results when the reflecting object is located closer to the LIDAR system than in FIG. 2A. In particular FIG. 2C represents the situation where τ<T_rs. Accordingly, in period 1 of cycle i, the incoming light signal resulting from a LIDAR output signal transmitted in cycle 1 first shows up in the transmit segment before passage of the amount of time equal to the duration of the receive segment (t_rs).

During the transmit segments in FIG. 2C, the close proximity of the LIDAR system and the reflecting object causes the incoming light signal to return to the LIDAR system quickly. Additionally, the frequency of the outgoing light signals that exit from the LIDAR system does not exceed an upper frequency labeled f_max in FIG. 2C because f_max corresponds to the frequency where the electronics change the signal-directing component 18 from the pass mode to the switched mode. As a result, the highest frequency of the incoming light signal corresponds to incoming light signal generated from the outgoing light signal with a frequency of f_max. The quick return of the incoming light signal combined with the frequency cut-off at f_max reduces the availability of the incoming light signal to the electronics during the receive segment. For instance, the portion of the incoming light signal illustrated at the solid line in FIG. 2C illustrates the portion of the incoming light signal that is available to the electronics. As shown in FIG. 2C, the incoming light signal is only available to the electronics a portion of the entire duration of the receive segment. The LIDAR data becomes less reliable as the percentage of the receive segment for which the incoming light signal is available decreases. Accordingly, the incoming light signal becomes available to the electronics for less than 100% of the receive segment in response to the LIDAR system and the reflecting object becoming closer than a separation threshold, but the incoming light signal is available to the electronics for 100% of the receive segment in response to the LIDAR system and the reflecting object becoming closer than a separation threshold.

FIG. 2D illustrates the separation threshold (ST) as a function of the receive segment duration where the receive segment duration is shown as the percentage of the period (100*t_rs/t_p). In FIG. 2D, the y-axis represents the radial distance between the LIDAR system and the reflecting object (R) and is expressed as a percentage of the maximum distance (100*R/D_max). The curve labeled ST represents the separation threshold and can be expressed as 100*A/(1−A) where A represents the receive ratio (t_rs/t_p). Accordingly, for radial distances at or above the separation threshold (ST), the incoming light signal is available to the electronics for 100% of the receive segment and for radial distances below the separation threshold (ST), the incoming light signal is available to the electronics for less than 100% of the receive segment.

As is evident from FIG. 2D, the incoming light signal is not available to the electronics for 100% of the receive segment when the receive segment is more than 50% of the period. Accordingly, the duration of the receive segment (t_rs) is selected to be less than or equal to 50% of the period (t_p). Suitable receive ratios (the percentage of a period that is the receive segment, t_rs/t_p) include, but are not limited to, receive ratios greater than 10%, 20%, or 30% and/or less than 40%, 45%, or 50%.

The electronics can tune the value of the transmit segment duration (t_ts) and/or the receive segment duration (t_rs) so as to increase the reliability of the LIDAR data. For instance, the electronics can tune the value of the transmit segment duration (t_ts) and/or the receive segment duration (t_rs) such that the LIDAR signal is available to the electronics for more than 90% or 100% of the receive segment when the receive segment is more than 50% of the period. For instance, the electronics can tune the value of the transmit segment duration (t_ts) such that the roundtrip signal time (τ) is greater than or equal to the duration of the receive segment (t_rs). For instance, when the displacement distance (D) decreases, the roundtrip signal time (τ=2D/c) also decreases. In response to the roundtrip signal time (τ) being or becoming less than the duration of the receive segment (t_rs), the electronics can reduce the value of the duration of the receive segment (t_rs) to a value that is less than or equal to the roundtrip signal time (τ). In some instances, the duration of the receive segment (t_rs) can be decreased to levels that are undesirably short for proper generation of the LIDAR data. As a result, the electronics can also adjust the duration of the receive segment (t_rs) upwards. For instance, in response to the roundtrip signal time (τ) being or becoming greater than the duration of the receive segment (t_rs)*adjustment factor₁, the electronics can increase the value of the duration of the receive segment (t_rs) to a value that is greater than or equal to the duration of the receive segment (t_rs)*adjustment factor₂. Suitable values for adjustment factor₁ include values greater than or equal to 1, 1.2, or 1.4 and/or less than 1.6, 1.8, or 2. Suitable values for adjustment factor₂ include values greater than or equal to 1, 1.2, or 1.4 and/or less than 1.6, 1.8, or 2. Adjustment factor₁ can be the same or different from adjustment factor₂. In the above examples, the value of the duration of the receive segment is tuned. Accordingly, the receive ratio is tuned in response to changes in the displacement distance. In the above examples, for a given displacement distance, the receive ratios are effectively tuned to provide a result located at or above the curve labeled ST in FIG. 2D. For instance, the value of t_rs is tuned to provide a receive ratio (t_rs/t_p) that is below the value of the receive ratio provided by D′/(1+D′) where D′=D/D_max. In one example, the value of t_rs is tuned in response to changes in the value of D. In another example, the value of t_rs is tuned in response to the receive ratio (t_rs/t_p) increasing to a value above D′/(1+D′). In another example, the value of t_rs is tuned in response to changes in the value of D where the receive ratio (t_rs/t_p) increases to a value above D′/(1+D′) but is not tuned when the change to the value of D results in a receive ratio (t_rs/t_p) remains below D′/(1+D′).

The above discussion discloses the displacement distance (D and D_max) as representing a distance between a reflecting object and an exit through which the outgoing light signal exits from the LIDAR system. However, in many LIDAR applications, the distance of the reflecting object changes during operation of the LIDAR system. As a result, in addition or as an alternative to representing the distance between the reflecting object and the exit, the displacement distance (D and D_max) can represent the distance of the field of view from the exit through which the outgoing light signal exits from the LIDAR system.

As noted above, the roundtrip time (τ) is a function of the displacement distance (τ=2D/c). Accordingly, electronics that know the roundtrip time are also effectively aware of displacement distance (D). The electronics can use a variety of different mechanisms for identifying the displacement distance that is to be used in tuning the transmit segment duration (t_ts) and/or the receive segment duration (t_rs). For instance, a device that includes the LIDATR system can have different mode setting that are each associated with a different displacement distance. As an example, a device such as a phone or camera can have a facial recognition mode and a room-scan mode. When the device is in facial recognition mode, the electronics can use a first displacement distance associated with the facial recognition mode. When the device is in room-scan mode, the electronics can use a second displacement distance associated with the room-scan mode. Additionally or alternately, an operator can enter the displacement distance into the device using a user interface. Additionally or alternately, the device can include an auto-focus mechanism that measures displacement distance. The auto-focus can be included in the electronics or can be part of an alternate application in the device. For instance, the auto-focus can be the auto-focus of a camera included in device. The displacement distance determined from the auto-focus can be provided to the electronics from the alternate application. The electronics can use the provided displacement distance as the displacement distance for the field of view in the LIDAR application or can perform additional processing of the provided displacement distance to determine the field that is used as the displacement distance for the field of view in the LIDAR application. As an example, the electronics can use the result of multiplying the provided displacement distance by a factor to generate the displacement distance of the field of view in the LIDAR application.

Although the above LIDAR systems are illustrated as having a single light source 10, the LIDAR system can have multiple light sources 10 as illustrated in FIG. 3. The light source 10 includes M light sources 10 that each generates N channels. The channels are each received on a channel waveguide 80. The channel waveguides carry the channels to a channel multiplexer 82 that combines the channels so as to form the outgoing light signal that is received on the utility waveguide 12.

In FIG. 3, each of the channels is labeled λ_i,j where i is the number of the light source 10 and is from 1 to M and j is the number of the channel for light source 10 j and is from 1 to N. As noted above, the light sources 10 can be configured such that the wavelengths of the channels are periodically spaced in that the wavelength increase from one channel to the next channel (Δλ) is constant or substantially constant. In some instances, the light sources 10 are configured such that channels with adjacent wavelengths are generated by different light sources 10. For instance, the light sources 10 can be configured such that λ_i,j=λ_o+((i−1)+(j−1)(M))(Δλ). Suitable light sources 10 for this configuration include, but are not limited to, comb lasers. In this configuration, the channel multiplexer can be a cyclic multiplexer designed with the wavelength spacing ((N−1)*Δλ) equal to a multiple of the Free Spectral Range (FSR) of the channel multiplexer. Accordingly, the channel multiplexer can be designed to cycle over the wavelength range ((N−1)*Δλ). A suitable cyclic multiplexer includes, but is not limited to, the ‘colorless’ AWG from Gemfire (8-Channel Cyclic Arrayed Waveguide Grating, 2018).

Suitable values for the number of light sources 10 (M) include, but are not limited to, values greater than or equal to 2, 4, or 8, and/or less than 16, 32, or 64. Suitable values for the number of channels provided by a light sources 10 (N) include, but are not limited to, values greater than or equal to 2, 4, or 8, and/or less than 16, 32, or 64. Suitable values for the wavelength increase from one channel to the next channel (Δλ) include, but are not limited to, values greater than or equal to 0.2 nm, 0.4 nm, or 0.6 nm, and/or less than 0.8 nm, 1.0 nm, or 1.5 nm. Suitable values for the wavelength of the channel with the shortest wavelength include, but are not limited to, values greater than or equal to 1.3 μm, 1.4 μm, or 1.5 μm, and/or less than 1.6 μm, 1.7 μm, or 1.8 μm. In one example, the LIDAR system includes M greater than or equal to 2, 4, or 8, and/or less than 16, 32, or 64; N greater than or equal to 2, 4, or 8, and/or less than 16, 32, or 64; and Δλ greater than or equal to 0.2 nm, 0.4 nm, or 0.6 nm, and/or less than 0.8 nm, 1 nm, or 1.5 nm.

In some instances, the light sources 10 are configured such that at least a portion of the light sources 10 each generates two or more channels with adjacent wavelengths. For instance, the light sources 10 can be configured such that λ_i,j=λ_o+((j−1)+(i−1)(N))(Δλ). Suitable light sources 10 for this configuration include, but are not limited to, comb lasers. In this configuration, the channel multiplexer can be a broadband multiplexer with a bandwidth of at least NΔλ. Suitable broadband multiplexers include, but are not limited to, arrayed waveguide gratings (AWG) and thin film filters.

As noted above, one or more of the light sources 10 can be a comb laser. However, other constructions of the light source 10 are possible. For instance, FIG. 4 illustrates an example of a light source 10 that includes multiple laser sources 84. The light source 10 illustrated in FIG. 4 includes multiple laser sources 84 that each outputs one of the channels on a source waveguide 86. The source waveguides 86 carry the channels to a laser multiplexer 88 that combines the channels so as to form a light signal that is received on a channel waveguide or the utility waveguide 12. The electronics can operate the laser sources 84 so the laser sources 84 concurrently output each of the channels. Suitable lasers for use with a light source 10 constructed according to FIG. 4 include, but are not limited to, external cavity lasers, distributed feedback lasers (DFBs), and Fabry-Perot (FP) lasers. External cavities lasers are advantageous in this embodiment because of their generally narrower linewidths, which can reduce noise in the detected signal.

FIG. 5 illustrates another example of a possible light source 10 construction. The light source 10 includes a gain element 90 such as the gain element of a semiconductor laser. A gain waveguide 92 is optically aligned with the gain element so as to receive a light signal from the gain element. In some instances, the gain waveguide excludes the gain medium included in the gain element. For instance, the gain waveguide can be a ridge waveguide on a silicon-on-insulator chip. Multiple partial return devices 94 are positioned along the gain waveguide such that the partial return devices interact with the light signal.

During operation, electronics operate the gain element such that the gain medium outputs the light signal. The partial return devices 94 each passes a portion of the light signal. The portion of the light signal that the utility waveguide 12 receives from the partial return devices serves as the outgoing light signal. The partial return devices also return a portion of the light signal to the gain element such that the returned portion of the light signal travels through the gain element. The gain element can include a fully or partially reflective layer that receives returned portion of the light signal from the gain element and reflects the returned portion of the light signal back to the gain element allowing the returned portion of the light signal to amplify and lase. Accordingly, the light source 10 can be an external cavity laser.

The partial return devices can be configured such that the each partial return device returns a different wavelength of light. For instance, the partial return devices can be configured such that the wavelength of each one of the channels that is to be output by the light source 10 is returned by at least one of the partial return devices. As a result, each of the desired channels will lase and be present in the outgoing light signal. Suitable partial return devices include, but are not limited to, Bragg gratings.

FIG. 6A through FIG. 6B illustrate an example of a suitable processing components for use in the above LIDAR systems. A first splitter 102 divides a reference signal carried on a reference waveguide 40, 52, or 58 onto a first reference waveguide 110 and a second reference waveguide 108. The first reference waveguide 110 carries a first portion of the reference signal to a light-combining component 111. The second reference waveguide 108 carries a second portion of the reference signal to a second light-combining component 112.

A second splitter 100 divides the comparative signal carried on the comparative waveguide 30, 72, or 74 onto a first comparative waveguide 104 and a second comparative waveguide 106. The first comparative waveguide 104 carries a first portion of the comparative signal to the light-combining component 111. The second comparative waveguide 108 carries a second portion of the comparative signal to the second light-combining component 112.

The second light-combining component 112 combines the second portion of the comparative signal and the second portion of the reference signal into a second composite signal. Due to the difference in frequencies between the second portion of the comparative signal and the second portion of the reference signal, the second composite signal is beating between the second portion of the comparative signal and the second portion of the reference signal. The light-combining component 112 also splits the resulting second composite signal onto a first auxiliary detector waveguide 114 and a second auxiliary detector waveguide 116.

The first auxiliary detector waveguide 114 carries a first portion of the second composite signal to a first auxiliary light sensor 118 that converts the first portion of the second composite signal to a first auxiliary electrical signal. The second auxiliary detector waveguide 116 carries a second portion of the second composite signal to a second auxiliary light sensor 120 that converts the second portion of the second composite signal to a second auxiliary electrical signal. Examples of suitable light sensors include germanium photodiodes (PDs), and avalanche photodiodes (APDs).

The first light-combining component 111 combines the first portion of the comparative signal and the first portion of the reference signal into a first composite signal. Due to the difference in frequencies between the first portion of the comparative signal and the first portion of the reference signal, the first composite signal is beating between the first portion of the comparative signal and the first portion of the reference signal. The light-combining component 111 also splits the first composite signal onto a first detector waveguide 121 and a second detector waveguide 122.

The first detector waveguide 121 carries a first portion of the first composite signal to a first light sensor 123 that converts the first portion of the second composite signal to a first electrical signal. The second detector waveguide 122 carries a second portion of the second composite signal to a second auxiliary light sensor 124 that converts the second portion of the second composite signal to a second electrical signal. Examples of suitable light sensors include germanium photodiodes (PDs), and avalanche photodiodes (APDs).

The first reference waveguide 110 and the second reference waveguide 108 are constructed to provide a phase shift between the first portion of the reference signal and the second portion of the reference signal. For instance, the first reference waveguide 110 and the second reference waveguide 108 can be constructed so as to provide a 90 degree phase shift between the first portion of the reference signal and the second portion of the reference signal. As an example, one reference signal portion can be an in-phase component and the other a quadrature component. Accordingly, one of the reference signal portions can be a sinusoidal function and the other reference signal portion can be a cosine function. In one example, the first reference waveguide 110 and the second reference waveguide 108 are constructed such that the first reference signal portion is a cosine function and the second reference signal portion is a sine function. Accordingly, the portion of the reference signal in the second composite signal is phase shifted relative to the portion of the reference signal in the first composite signal, however, the portion of the comparative signal in the first composite signal is not phase shifted relative to the portion of the comparative signal in the second composite signal.

The first light sensor 123 and the second light sensor 124 can be connected as a balanced detector and the first auxiliary light sensor 118 and the second auxiliary light sensor 120 can also be connected as a balanced detector. For instance, FIG. 6B provides a schematic of the relationship between the electronics, the first light sensor 123, the second light sensor 124, the first auxiliary light sensor 118, and the second auxiliary light sensor 120. The symbol for a photodiode is used to represent the first light sensor 123, the second light sensor 124, the first auxiliary light sensor 118, and the second auxiliary light sensor 120 but one or more of these sensors can have other constructions. In some instances, all of the components illustrated in the schematic of FIG. 6B are included on the LIDAR system. In some instances, the components illustrated in the schematic of FIG. 6B are distributed between the LIDAR system and electronics located off of the LIDAR system.

The electronics connect the first light sensor 123 and the second light sensor 124 as a first balanced detector 125 and the first auxiliary light sensor 118 and the second auxiliary light sensor 120 as a second balanced detector 126. In particular, the first light sensor 123 and the second light sensor 124 are connected in series. Additionally, the first auxiliary light sensor 118 and the second auxiliary light sensor 120 are connected in series. The serial connection in the first balanced detector is in communication with a first data line 128 that carries the output from the first balanced detector as a first data signal. The serial connection in the second balanced detector is in communication with a second data line 132 that carries the output from the first balanced detector as a second data signal. The first data signal and the second data signal are beating as a result of the beating between the comparative signal and the reference signal, i.e. the beating in the first composite signal and in the second composite signal.

The first data line 128 carries the first data signal to a first switch 134. The first switch can be in a first configuration where the first data signal is carried to a distance branch 136 or in a second configuration where the first data signal is carried to a velocity branch 138. In FIG. 6B, the first switch 134 is shown in the first configuration. The second data line 132 carries the second data signal to a second switch 140. The second switch can be in a first configuration where the second data signal is carried to the distance branch 136 or in a second configuration where the second data signal is carried to a velocity branch 138. In FIG. 6B, the second switch 140 is shown in the first configuration. A suitable switch for use as the first switch and/or second switch includes, but is not limited to, an electromechanical switch, and a solid state MOSFET or PIN diode switch.

The electronics operate the first switch and the second switch such that they are in the same configuration during the first period and during the second period. For instance, the electronics can operate the first switch and the second switch such that the first switch and the second switch are both in the first configuration during the first period and both in the second configuration during the second period. In this example, the first data signal and the second data signal are carried to the distance branch 136 during the first period and to the velocity branch 138 during the second period.

During operation of the LIDAR system, the generation of LIDAR data is divided into a series of cycles where LIDAR data is generated for each cycle. In some instances, each of the cycles corresponds to a different sample region in the field of view. Accordingly, different cycles can generate LIDAR data for different regions in a field of view.

The cycles can be performed such that the time for each cycle can be divided into different time periods that include a distance time period (first period) and a velocity time period (second period). The distance between the reflecting object and the LIDAR chip can be determined in the distance period and the radial velocity between the reflecting object and the LIDAR chip can be determined in the velocity period.

The electronics are configured to use the first data signal and the second data signal to determine or approximate at least the distance between the LIDAR system and the reflecting object. For instance, during the first period, the electronics can operate the modulator 14 so as to add chirp to the amplitude of the outgoing light signal and accordingly the LIDAR output signal. Adding chirp to the amplitude can include modulating the amplitude of the outgoing light signal such that the amplitude of the outgoing light signal is a function of a sinusoid. In one example, the amplitude of the outgoing light signal is modulated such that the amplitude of the outgoing light signal is a square root of a function that includes a sinusoid and/or is a square root of a sinusoid. For instance, the outgoing light signal can be modulated so as to produce a modulated outgoing light signal and LIDAR output signal mathematically represented by Equation 1: (M+N*cos(C*t+D*t²)^1/2cos(F*t) where M, N, C, D and F are constants, t represents time, M>0, N>0, and M≥N in order to prevent the radicand from becoming negative, C>0, D≠0. As will become evident below, F can be a function of the frequency of the LIDAR output signal (f_c). In Equation 1, F and C can be selected such that F>>C.

The distance branch includes a first distance branch line 142. During the first period, the first distance branch line 142 carries the first data signal to a first multiplier 144. In FIG. 6B, the first multiplier 144 is configured to square the amplitude of the first data signal and to output a first multiplied data signal. The distance branch includes a second distance branch line 146. During the first period, the second distance branch line 146 carries the second data signal to a second multiplier 148. In FIG. 6B, the second multiplier 148 is configured to square the amplitude of the second data signal and to output a second multiplied data signal. Suitable first multipliers and/or second multipliers include, but are not limited to, RF mixers such as a Gilbert cell mixer.

The distance branch includes an adder 150 that sums the first multiplied data signal and the second multiplied data signal. The adder outputs a summed data signal. Suitable adders include, but are not limited to, RF combiners including resistive or hybrid combiners. The distance branch includes a low-pass filter 152 that receives the summed data signal and outputs a beating data signal. The low-pass filter is selected to remove higher frequency contributions to the summed data signal that are artifacts of the mixing of the reference and return signals. The low-pass filter can be selected to have a bandwidth greater than or equal to: f_dmax/2+ατ_0max where f_dmax represents the maximum level of the Doppler shift of the LIDAR input signal relative to the LIDAR input signal for which the LIDAR system is to provide reliable results, τ_0max represents maximum delay between transmission of the LIDAR output signal and the receipt of the LIDAR input signal, and a represents the rate of change in the frequency of the chirp added to the amplitude of the modulated outgoing light signal during the duration of the sample period (i.e. the first period). In some instances, a is determined from B/T where B represents the change in the frequency of the chirp added to the amplitude of the modulated outgoing light signal during the duration of the sample period and T is the duration of the sample period. In some instances, T is determined from

$T=\frac{{\lambda }_c}{2\Delta v_{\min }}+{\tau }_{0\max }$

where λ_c represents the wavelength of the outgoing light signal, Δv_min: represents velocity resolution and B can be determined from

$B=\frac{\mathrm{cT}}{2\left(T-{\tau }_{0\max }\right)\Delta R_{\min }}$

where c represents the speed of light and represents distance resolution. In some instances, the filter has a bandwidth greater than 0.1 GHz, 0.2 GHz, or 0.3 GHz and/or less than 0.4 GHz, 0.5 GHz, or 1 GHz. Corresponding values for the sweep period (T) can be 10 μs, 8 μs, 4 μs, 3 μs, 2 μs, and 1 μs.

The distance branch includes an Analog-to-Digital Converter (ADC) 154 that receives the beating data signal from the filter. The Analog-to-Digital Converter (ADC) 154 converts the beating data signal from an analog form to digital form and outputs the result as a digital LIDAR data signal. As discussed above, the conversion of the beating data signal includes sampling the beating data signal at a sampling rate. The addition of the chirp to the amplitude of the LIDAR output signal substantially reduces or removes the effects of radial velocity from the beating of the composite signal and the resulting electrical signals. For instance, the frequency shift of the LIDAR output signal relative to the LIDAR input signal (“frequency shift,” Δf) can be written as Δf=Δf_d+Δf_s where Δf_d represents the change in frequency due to the Doppler shift and Δf_s is the change in frequency due to the separation between the reflecting object and the LIDAR system. The outgoing light signal can be modulated so as to produce a modulated outgoing light signal and accordingly, a LIDAR output signal that is also modulated, where the change in frequency due to the Doppler shift (Δf_d) is less than 10%, 5%, 1%, or even 0.1% of the Doppler shift that would occur from a sinusoidal LIDAR output signal serving as the LIDAR and having a constant amplitude and the same frequency as the modulated outgoing light signal and/or the LIDAR output signal. For instance, the outgoing light signal and/or the LIDAR output signal can be modulated so as to produce a modulated outgoing light signal and/or a LIDAR output signal where the change in frequency due to the Doppler shift (Δf_d) is less than 10%, 5%, 1%, or even 0.1% of the Doppler shift that would occur from a continuous wave serving as the LIDAR output signal and having the same frequency as the modulated outgoing light signal and/or the LIDAR output signal. In another example, the outgoing light signal and/or the LIDAR output signal are modulated so as to produce a modulated outgoing light signal and/or a LIDAR output signal where the change in frequency due to the Doppler shift (Δf_d) is less than 10%, 5%, 1%, or even 0.1% of the Doppler shift that would occur from the outgoing light signal before modulation (the unmodulated outgoing light signal) serving as the LIDAR output signal. These results can be achieved by increasing the value of the Equation 1 variable F relative to C. For instance, F can represent 2πf_c and C can represent 2πf₁ where f₁ denotes the base frequency of the frequency-chirp in the amplitude of the modulated outgoing light signal. Accordingly, F can be increased relative to C by increasing the value of the frequency of the LIDAR output signal (f_c) relative to the chirp base frequency (f₁). As an example, f_c and f₁ can be selected such that f_c>>f₁. In some instances, f_c and f₁ are selected such that a ratio of f_c:f₁ is greater than 2:1, 10:1, 1×10⁴:1, 5×10⁴, or 1×10⁵:1 and/or less than 5×10⁵, 1×10⁶, 5×10⁶ or 5×10⁸. Accordingly, the variables F and C can also have these same values for a ratio of F:C. The reduction and/or removal of the change in frequency due to the Doppler shift (Δf_d) from the frequency shift lowers the beat frequency and accordingly reduces the required sampling rate.

The distance branch includes a transform module 156 that receives the digital LIDAR data signal from the Analog-to-Digital Converter (ADC) 154. The transform module 156 is configured to perform a real transform on the digital LIDAR data signal so as to convert from the time domain to the frequency domain. This conversion provides an unambiguous solution for the shift in frequency of the shift of the LIDAR input signal relative to the LIDAR input signal that is caused by the distance between the reflecting object and the LIDAR system. A suitable real transform is a Fourier transform such as a Fast Fourier Transform (FFT). The classification of the transform as a real transform distinguishes the transform from complex transforms such as complex Fourier transforms. The transform module can execute the attributed functions using firmware, hardware or software or a combination thereof.

Since the frequency provided by the transform module does not have input from, or does not have substantial input from, a frequency shift due to relative movement, the determined frequency shift can be used to approximate the distance between the reflecting object and the LIDAR system. For instance, the electronics can approximate the distance between the reflecting object and the LIDAR system (R₀) using Equation 3: R₀=c*Δf/(2α) where Δf can be approximated as the peak frequency output from the transform module, and c is the speed of light.

The velocity branch can be configured to use the first data signal and the second data signal to determine or approximate at least the radial velocity of the LIDAR system and the reflecting object. The LIDAR output signal with a frequency that is a function of time disclosed in the context of FIG. 1 through FIG. 2 can be replaced by a LIDAR output signal where the frequency of the LIDAR output signal is not a function of time. For instance, the LIDAR output signal can be a continuous wave (CW). For instance, during the second period, the modulated outgoing light signal, and accordingly the LIDAR output signal, can be an unchirped continuous wave (CW). As an example the modulated outgoing light signal, and accordingly the LIDAR output signal, can be represented by Equation 2: G*cos(H*t) where G and H are constants and t represents time. In some instances, G represents the square root of the power of the outgoing light signal and/or H represents the constant F from Equation 1. In instances where the output of the light source has the waveform that is desired for the modulated outgoing light signal, the electronics need not operate the modulator 14 so as to modify the outgoing light signal. In these instances, the output of the light source(s) can serve as the modulated outgoing light signal and accordingly the LIDAR output signal. In some instances, the electronics operate the modulator 14 so as to generate a modulated outgoing light signal with the desired form.

Since the frequency of the LIDAR output signal is constant in the second period, changing the distance between reflecting object and LIDAR system does not cause a change to the frequency of the LIDAR input signal. As a result, the separation distance does not contribute to the shift in the frequency of the LIDAR input signal relative to the frequency of the LIDAR output signal. Accordingly, the effect of the separation distance has been removed or substantially from the shift in the frequency of the LIDAR input signal relative to the frequency of the LIDAR output signal.

The velocity branch includes a first velocity branch line 160 and a second velocity branch line 160. During the second period, the first velocity branch line 160 carries the first data signal to an Analog-to-Digital Converter (ADC) 164 which converts the first data signal from an analog form to a digital form and outputs a first digital data signal. As discussed above, the conversion of the first data signal is done by sampling the first data signal at a sampling rate. The use of a continuous wave as the LIDAR output signal substantially removes the effects of distance between the reflecting object and LIDAR system from the beating of the composite signal and the resulting electrical signals. Accordingly, the beating frequency is reduced and the required sampling rate is reduced.

The second velocity branch line 162 carries the second data signal to an Analog-to-Digital Converter (ADC) 166 which converts the second data signal from an analog form to a digital form and outputs a second digital data signal. As discussed above, the conversion of the second data signal includes sampling the second data signal at a sampling rate. The use of a continuous wave as the LIDAR output signal substantially reduces or removes the effects of distance between the reflecting object and LIDAR system from the beating of the second composite signal and the resulting electrical signals. Accordingly, the beating frequency is reduced and the required sampling rate is reduced.

The sampling rate for the Analog-to-Digital Converter (ADC) 164 can be the same or different from the sampling rate for the Analog-to-Digital Converter (ADC) 166.

The velocity branch includes a transform module 168 that receives the first digital data signal from the Analog-to-Digital Converters (ADC) 164 and the second digital data signal from the Analog-to-Digital Converters (ADC) 166. Since the first data signal is an in-phase component and the second data signal its quadrature component, the first data signal and the second data signal together act as a complex velocity data signal where the first data signal is the real component and the second data signal is the imaginary component. As a result, the first digital data signal can be the real component of a digital velocity data signal and the second data signal can be the imaginary component of the digital velocity data signal. The transform module 168 can be configured to perform a complex transform on the digital velocity data signal so as to convert from the time domain to the frequency domain. This conversion provides an unambiguous solution for the shift in frequency of LIDAR input signal relative to the LIDAR input signal that is caused by the radial velocity between the reflecting object and the LIDAR system. A suitable complex transform is a Fourier transform such as a complex Fast Fourier Transform (FFT). The transform module can execute the attributed functions using firmware, hardware or software or a combination thereof.

Since the frequency shift provided by the transform module 168 does not have input from a frequency shift due to the separation distance between the reflecting object and the LIDAR system, and because of the complex nature of the velocity data signal, the output of the transform module 168 can be used to approximate the radial velocity between the reflecting object and the LIDAR system. For instance, the electronics can approximate the radial velocity between the reflecting object and the LIDAR system (v) using Equation 4: v=c*f_d/(2*f_c) where f_d is approximated as the peak frequency output from the transform module 168, c is the speed of light, and f_c represents the frequency of the LIDAR output signal.

Additional components can be added to the schematic of FIG. 6B. For instance, when the LIDAR system generates multiple LIDAR output signals or is used with other LIDAR systems that generate LIDAR output signals (i.e., by means of frequency or wavelength division multiplexing, FDM/WMD), the LIDAR system can include one or more filters to remove interfering signals from the real and/or imaginary components of the beating data signal and/or of the velocity data signal. Accordingly, the LIDAR system can include one or more filters in addition to the illustrated components. Suitable filters include, but are not limited to, lowpass filters. In the case of the optical design, if the frequency of the interfering components fall outside the bandwidth of the balance detector(s), additional filtering may not be necessary as it may be effectively provided by the balance detector(s).

The sampling rate that is used during the first period and the second period can be selected to have a value that is greater than or equal to the larger of two values selected from the group consisting of the minimum sampling rate for the first period and the minimum sampling rate for the second period. For instance, during the first period the range of rates for the first period sampling rate (f_s1) can be determined by where τ_0max represents the maximum amount of time between the transmission of the LIDAR output signal and the receipt of the LIDAR input signal. During the second period the range of rates for the second period sampling rate (f_s2) can be determined by where f_dmax represents the maximum level of the Doppler shift of the LIDAR input signal relative to the LIDAR input signal for which the LIDAR system is to provide reliable results. The maximum is determined by the largest level for which the LIDAR system is to provide reliable results. Accordingly, the maximum distance generally corresponds to the distance for the field of view set in the LIDAR specifications and the maximum Doppler shift generally corresponds to the Doppler shift that would occur at the maximum radial velocity values set in the specifications. These two equations show that the minimum sampling rate for the first period is 2ατ_0max and the minimum sampling rate for the second period is 2f_dmax. As a result, the sampling rate is selected to have a value that is greater than or equal to the larger of 2ατ_0max and 2f_dmax. In other words, the sample rate used during the first period and the second period (f_s) is f_s≥max(2ατ_0max, 2f_dmax). In some instances, the sample rate used during the first period and the second period (f_s) is greater than or equal to 0.1 GHz, 0.2 GHz, or 0.5 GHz and/or less than 1 GHz, 2 GHz, or 4 GHZ.

FIG. 6C provides another example of a schematic of electronics that are suitable for extracting LIDAR data with a processing unit constructed according to FIG. 7A. The electronics connect the first light sensor 123 and the second light sensor 124 as a first balanced detector 125 and the first auxiliary light sensor 118 and the second auxiliary light sensor 120 as a second balanced detector 126. In particular, the first light sensor 123 and the second light sensor 124 are connected in series. Additionally, the first auxiliary light sensor 118 and the second auxiliary light sensor 120 are connected in series. The serial connection in the first balanced detector is in communication with a first data line 128 that carries the output from the first balanced detector as a first data signal. The serial connection in the second balanced detector is in communication with a second data line 132 that carries the output from the second balanced detector as a second data signal. The first data signal is an electrical representation of the first composite signal and the second data signal is an electrical representation of the second composite signal. Accordingly, the first data signal includes a contribution from a first waveform and a second waveform and the second data signal is a composite of the first waveform and the second waveform. The portion of the first waveform in the first data signal is phase-shifted relative to the portion of the first waveform in the first data signal but the portion of the second waveform in the first data signal being in-phase relative to the portion of the second waveform in the first data signal. For instance, the second data signal includes a portion of the reference signal that is phase shifted relative to a different portion of the reference signal that is included the first data signal. Additionally, the second data signal includes a portion of the comparative signal that is in-phase with a different portion of the comparative signal that is included in the first data signal. The first data signal and the second data signal are beating as a result of the beating between the comparative signal and the reference signal, i.e. the beating in the first composite signal and in the second composite signal.

The electronics 62 include a transform mechanism 138 configured to perform a mathematical transform on the first data signal and the second data signal. For instance, the mathematical transform can be a complex Fourier transform with the first data signal and the second data signal as inputs. Since the first data signal is an in-phase component and the second data signal its quadrature component, the first data signal and the second data signal together act as a complex data signal where the first data signal is the real component and the second data signal is the imaginary component of the input.

The transform mechanism 138 includes a first Analog-to-Digital Converter (ADC) 164 that receives the first data signal from the first data line 128. The first Analog-to-Digital Converter (ADC) 164 converts the first data signal from an analog form to a digital form and outputs a first digital data signal. The transform mechanism 138 includes a second Analog-to-Digital Converter (ADC) 166 that receives the second data signal from the second data line 132. The second Analog-to-Digital Converter (ADC) 166 converts the second data signal from an analog form to a digital form and outputs a second digital data signal. The first digital data signal is a digital representation of the first data signal and the second digital data signal is a digital representation of the second data signal. Accordingly, the first digital data signal and the second digital data signal act together as a complex signal where the first digital data signal acts as the real component of the complex signal and the second digital data signal acts as the imaginary component of the complex data signal.

The transform mechanism 138 includes a transform component 168 that receives the complex data signal. For instance, the transform component 168 receives the first digital data signal from the first Analog-to-Digital Converter (ADC) 164 as an input and also receives the second digital data signal from the first Analog-to-Digital Converter (ADC) 166 as an input. The transform component 168 can be configured to perform a mathematical transform on the complex signal so as to convert from the time domain to the frequency domain. The mathematical transform can be a complex transform such as a complex Fast Fourier Transform (FFT). A complex transform such as a complex Fast Fourier Transform (FFT) provides an unambiguous solution for the shift in frequency of LIDAR input signal relative to the LIDAR output signal that is caused by the radial velocity between the reflecting object and the LIDAR chip. The transform component 168 can execute the attributed functions using firmware, hardware or software or a combination thereof.

The Complex Fourier transform converts the input from the time domain to the frequency domain, the Complex Fourier transform outputs a single frequency peak for each object located in the sample region. The frequency associated with this peak is used by the electronics as the shift in frequency of LIDAR input signal relative to the LIDAR output signal is caused by the radial velocity between the reflecting object and the LIDAR chip and/or the distance between the reflecting object and the LIDAR chip. Prior methods of resolving the frequency of the LIDAR input signal made use of real Fourier transforms rather than the Complex Fourier transform technique disclosed above. These prior methods output multiple frequency peaks for each object in a sample region. Accordingly, the prior methods output multiple different frequencies that are both associated with each object in the sample region in that each of the associated frequencies would not be present if the object were removed from the sample region. As noted above, when using LIDAR applications, it can become difficult to identify the correct peak. Since the above technique for resolving the frequency generates a single solution for the frequency, the ambiguity with the frequency solution has been resolved.

The electronics can use each frequency peak output from the transform to generate LIDAR data. For instance, the electronics can operate the light source such that the LIDAR output signal alternates periods with an increasing frequency and periods with a decreasing frequency as shown in FIG. 2C. The following equation applies during a data period where the electronics increase the frequency of the LIDAR output during the data period such as occurs with the LIDAR output signal 2C during the first period: where f_ub is the frequency provided by the transform component, f_d represents the Doppler shift

$\left(f_d=2{\mathrm{vf}}_c/c\right)$

where f_c is the frequency of the LIDAR output signal at the start of the data period (i.e. t=0), v is the radial velocity between the reflecting object and the LIDAR chip where the direction from the reflecting object toward the chip is assumed to be the positive direction, and c is the speed of light, α represents the rate at which the frequency of the outgoing light signal is increased or decreased during the period, and τ₀ is the roundtrip delay (time between the LIDAR output signal exiting from the LIDAR chip and the associated LIDAR input signal returning to the LIDAR chip) for a stationary reflecting object. The following equation applies during a data period where electronics decrease the frequency of the LIDAR output signal during the period such as occurs with the LIDAR output signal of FIG. 2C during the second period:

$-f_{\mathrm{db}}=-f_d-{\mathrm{\alpha \tau }}_0$

where f_db is the frequency provided by the transform mechanism. In these two equations, f_d and τ₀ are unknowns. These two equations are solved for the two unknowns f_d and τ₀. The values of f_db and f_ub that are substituted into the solution come from the same channel and accordingly the same processing units (labeled 34 in FIG. 1), but during different data periods in the same cycle. Since the cycles is associated with a sample region in the field of view, the solution yields the values of f_d and τ₀ for a sample region in the field of view. The radial velocity for that sample region can then be determined from the Doppler shift (v=c*f_d/(2f_c)) and the separation distance for that sample region can be determined from c*τ₀/2. As a result, the LIDAR data for a sample regions is determined for a single LIDAR output signal (channel) that illuminates the sample region.

As discussed above, the LIDAR system can output more than two LIDAR output signals that each carries a different channel. For instance, the LIDAR system can output multiple LIDAR output signals that have frequency versus time waveforms according to FIG. 2C. The LIDAR output signals can be concurrently directed to the same sample region in a field of view or different portions of the LIDAR output signals can be directed to different sample regions in the field of view. Additionally, the LIDAR output signals can be sequentially scanned across the sample regions such that each sample region is illuminated by at least one of the LIDAR output signals.

The above descriptions of the LIDAR system operation assumes that a modulator is present on the utility waveguide 12; however, in some instances, the modulator is optional. In these instances, the electronics can operate the light source(s) 10 so as to tune the frequency of the LIDAR output signal as desired. Since one or more of the light sources can output multiple channels, tuning the frequency of one light sources can concurrently tune the frequency of multiple channels and accordingly multiple LIDAR output signals. For instance, tuning the frequency of a comb laser concurrently tunes the frequency of the channels output from that comb laser and accordingly tunes the LIDAR output signals that carry the channels output from that comb laser. The electronics can tune the frequency of a light source such as a comb laser by tuning the electrical current driven through the comb laser. In some instances, the electronics can tune the frequency of a light source such as a comb laser by 10 GHz, 100 GHz, and 1 THz.

The above descriptions of the LIDAR system operation assumes that a modulator is present on the utility waveguide 12; however, the modulator is optional. In these instances, the electronics can operate the light source(s) 10 so as to increase the frequency of the outgoing light signal during the first period and during the second period the electronics can decrease the frequency of the outgoing light signal as shown in FIG. 2C. Other examples of methods for extracting the LIDAR data from the resulting composite signals are disclosed in U.S. Patent Application Ser. No. 62/671,913, filed on May 15, 218, entitled “Optical Sensor Chip,” and incorporated herein in its entirety.

FIG. 7 illustrates an example of a suitable optical port 26 that includes demultiplexing functionality and beam steering capability. The optical port 26 includes a splitter 184 that receives the outgoing light signal from the LIDAR signal waveguide 24. The splitter divides the outgoing light signal into multiple output signals that are each carried on a steering waveguide 186. Each of the steering waveguides ends at a facet 188. The facets are arranged such that the output signals exiting the chip through the facets combine to form the LIDAR output signal.

The splitter and steering waveguides can be constructed such that there is not a phase differential between output signals at the facet of adjacent steering waveguides. For instance, the splitter can be constructed such that each of the output signals is in-phase upon exiting from the splitter and the steering waveguides can each have the same length. Alternately, the splitter and steering waveguides can be constructed such that there is a linearly increasing phase differential between output signals at the facet of adjacent steering waveguides. For instance, the steering waveguides can be constructed such that the phase of steering waveguide number j is f_o+(j−1)f where j is an integer from 1 to N and represents the number associated with a steering waveguide when the steering waveguides are sequentially numbered as shown in FIG. 5, f is the phase differential between neighboring steering waveguides when the phase tuners (discussed below) do not affect the phase differential, and f_o is the phase of the output signal at the facet of steering waveguide k=1. Because the channels can have different wavelengths, the values of f and f_o can each be associated with one of the channels. In some instances, this phase differential is achieved by constructing the steering waveguides such that the steering waveguides have a linearly increasing length differential. For instance, the length of steering waveguide j can be represented by l_o+(k−1)Δl where k is an integer from 1 to K and represents the number associated with a steering waveguide when the steering waveguides are sequentially numbered as shown in FIG. 7, Δl is the length differential between neighboring steering waveguide, and L_o is the length of steering waveguide k=1. Because Δl is a different percent of the wavelength of different channels included in the output signals, each of the different LIDAR output signals travels away from LIDAR chip in a different direction (θ). When the steering waveguides are the same length, the value of Δl is zero and the value of f is zero. Suitable Δl include, but are not limited to, Δl greater than 0, or 5 and/or less than 10, or 15 μm. Suitable f include, but are not limited to, f greater than 0π, or 7π and/or less than 15π, or 20π. Suitable N include, but are not limited to, N greater than 10, or 500 and/or less than 1000, or 2000. Suitable splitters include, but are not limited to, star couplers, cascaded Y-junctions and cascaded 1X2 MMI couplers.

A phase tuner 190 can be positioned along at least a portion of the steering waveguides. Although a phase tuner is shown positioned along the first and last steering waveguide, these phase tuners are optional. For instance, the chip need not include a phase tuner on steering waveguide j=1.

The electronics can be configured to operate the phase tuners so as to create a phase differential between the output signals at the facet of adjacent steering waveguides. The electronics can operate the phase tuners such that the phase differential is constant in that it increases linearly across the steering waveguides. For instance, electronics can operate the phase tuners such that the tuner-induced phase of steering waveguide number k is (k−1)α where k is an integer from 1 to N and represents the number associated with a steering waveguide when the steering waveguides are sequentially numbered as shown in FIG. 7, a is the tuner-induced phase differential between neighboring steering waveguides. Accordingly, the phase of steering waveguide number k is f_o+(k−1)f+(k−1)α. FIG. 5 illustrates the chip having only 4 steering waveguides in order to simplify the illustration, however, the chip can include more steering waveguides. For instance, the chip can include more than 4 steering waveguides, more than 100 steering waveguides, or more than 1000 steering waveguides and/or less than 10000 steering waveguides.

The electronics can be configured to operate the phase tuners so as to tune the value of the phase differential α. Tuning the value of the phase differential α changes the direction that the LIDAR output signal travels away from the chip (θ). Accordingly, the electronics can scan the LIDAR output signal by changing the phase differential α. The range of angles over which the LIDAR output signal can be scanned is ϕ_R and, in some instances, extends from ϕ_v to −ϕ_v with ϕ=0° being measured in the direction of the LIDAR output signal when α=0. When the value of Δl is not zero, the length differential causes diffraction such that light of different wavelengths travels away from chip in different directions (θ). Accordingly, there may be some spreading of the outgoing light signal as it travels away from the chip. Further, changing the level of diffraction changes the angle at which the outgoing light signal travels away from the chip when α=0°. However, providing the steering waveguides with a length differential (Δl≠0) can simplify the layout of the steering waveguides on the chip.

Additional details about the construction and operation of an optical port 26 constructed according to FIG. 7 can be found in U.S. Provisional Patent Application Ser. No. 62/680,787, filed on Jun. 5, 2018, and incorporated herein in its entirety.

The above LIDAR systems can be integrated on a single chip. A variety of platforms can be employed for a chip that includes the above LIDAR systems. A suitable platform includes, but is not limited to, a silicon-on-insulator wafer. One or more of the above components and/or portions of the above components can be integral with the chip or can be placed on the chip with technologies such as flip-chip bonding technologies. For instance, a light source 10 can include a gain element and one or more other components such as waveguides. The waveguide can be integral with the chip and the gain element can be a component that is separate from the chip but attached to the chip with a flip-chip bonding. Alternately, the above LIDAR system can be constructed with discrete components. For instance, all or a portion of the waveguides can be optical fibers connecting discrete components, including a fiber optical switch. Alternately, one or more portions of the LIDAR system can be integrated on a chip while other portions are discrete components. For instance, the utility waveguide 12 can be or include an optical fiber that provides optical communication between a light source 10 and an optical chip that includes the remainder of the LIDAR system.

A variety of optical switches that are suitable for use with the LIDAR system can be constructed on planar device optical platforms such as silicon-on-insulator platforms. Examples of suitable optical switches for integration into the silicon-on-insulator platform include, but are not limited to, Mach-Zehnder interferometers. FIG. 8 is a schematic of a Mach-Zehnder interferometer. The switch includes a first switch waveguide 200 that connects the comparative signal waveguide 28 and the reference signal waveguide 36. A second switch waveguide 202 connects the utility waveguide 12 and the LIDAR signal waveguide 24. The first switch waveguide 200 and the second switch waveguide 202 are included in a first optical coupler 204 and in a second optical coupler 206. A phase shifter 208 is positioned along the first switch waveguide 200 or the second switch waveguide 200 between the first optical coupler 204 and the second optical coupler 206. Suitable phase shifters include, but are not limited to, PIN diodes, PN junctions operated in carrier depletion mode, and thermal heaters. The electronics can operate the phase shifter so as to change the switch between the pass mode and the switched mode.

The optical switches are disclosed above as being configured such that the outgoing light signal is directed to the LIDAR signal waveguide 24 and an incoming light signal would be directed to the utility waveguide 12 in the pass mode and such that the outgoing light signal is directed to the reference signal waveguide 36 and the incoming light signal is directed to the comparative signal waveguide 28 in the switched mode. However, the waveguides can optionally be arranged such that the outgoing light signal is directed to the LIDAR signal waveguide 24 and an incoming light signal would be directed to the utility waveguide 12 in the switched mode and such that the outgoing light signal is directed to the reference signal waveguide 36 and the incoming light signal is directed to the comparative signal waveguide 28 in the pass mode. In these instances, the LIDAR system can be operated as disclosed above but with the switched mode and pass mode switched so as to achieve the same results described above. As a result, the terms pass mode and switched mode need to refer to specific operational mode but instead to different modes of switch operation such as a first mode and a second mode.

Other embodiments, combinations and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.

Claims

1. A LIDAR system, comprising: a common optical pathway through a LIDAR system that is traveled by an outgoing light signal that exits the LIDAR system and also by an incoming light signal that enters the LIDAR system after being reflected by an object and that includes light from the outgoing light signal;an optical switch positioned along the common optical pathway and configured to be operated in different modes, the incoming light signal and/or the outgoing light signal being routed along a different optical path through the LIDAR system in response to the optical switch being in a different mode.

2. The LIDAR system of claim 1, further comprising: electronics configured to switch the optical switch between the different modes.

3. The LIDAR system of claim 1, wherein the outgoing light signal exits from the LIDAR system when the optical switch is in a first one of the modes but does not exit from the LIDAR system when the optical switch is in a second one of the modes.

4. The LIDAR system of claim 3, wherein light from the outgoing light is mixed with light from the incoming light signal so as to generate a composite light signal when the optical switch is in the second mode.

5. The LIDAR system of claim 4, wherein the composite light signal is not generated when the optical switch is in the first mode.

6. The LIDAR system of claim 4, wherein the incoming light signal and the outgoing light signal both travel along the common optical path when the optical switch is in the first mode.

7. The LIDAR system of claim 4, wherein the incoming light signal travels along the common optical path when the optical switch is in the second mode but the outgoing light signal does not travel along the common optical path when the optical switch is in the second mode.

8. The LIDAR system of claim 4, wherein the incoming light signal travels away from the optical switch along a first optical path when the optical switch is in the second mode, the outgoing light signal travels away from the optical switch along a second optical path when the optical switch is in the second mode,the first optical path being separate from the second optical path, andthe common optical path being separate from the first optical path being separate from the second optical path.

9. The LIDAR system of claim 1, wherein the outgoing light signal travels away from the optical switch along the common optical pathway and the incoming light signal travels toward the optical switch along the common optical pathway.

10. The LIDAR system of claim 1, wherein the optical switch is a cross-over switch.

11. The LIDAR system of claim 1, further comprising: electronics that switch the optical switch between the different modes, the different modes including a first mode and a second mode, the electronics operating the switch through a series or periods that each includes a transmit segment and a receiver period, the electronics operating the switch in the first mode during the transmit segment and in the second mode during the receive segment.

12. The LIDAR system of claim 11, wherein the electronics tune a duration of the transmit segment and/or the receive segment.

13. The LIDAR system of claim 12, wherein the duration of the transmit segment and/or the receive segment is tuned in response to a change in a distance between the LIDAR system and an object that is located remotely from the LIDAR system but reflects the outgoing light signal after the outgoing light signal exits from the LIDAR system.

14. The LIDAR system of claim 12, wherein the duration of the transmit segment and/or the receive segment is tuned in response to a change in a distance between the LIDAR system and a field of view associated with the LIDAR system.

15. The LIDAR system of claim 12, wherein the duration of the transmit segment (tts) and/or the receive segment (trs) is tuned such that a value of (trs/(trs+trs)) is less than D′/(1+D′) where D′=D/Dmax where D represents a distance between the LIDAR system and an object that is located remotely from the LIDAR system or a distance between the LIDAR system and a field of view and Dmax represents a maximum value for D for which the LIDAR system is configured to generate LIDAR data.

16. A LIDAR system, comprising: a light source configured to generate an outgoing light signal that exits from the LIDAR system, the LIDAR system configured to receive an incoming light signal that enters the LIDAR system from outside of the LIDAR system and that includes light from the outgoing light signal;an optical switch that receives the outgoing light signal and the incoming light signal and configured to be operated in different modes, the incoming light signal and/or the outgoing light signal being routed along a different optical path through the LIDAR system in response to the optical switch being in a different mode.

17. The LIDAR system of claim 16, wherein the outgoing light signal exits from the LIDAR system when the optical switch is in a first one of the modes but does not exit from the LIDAR system when the optical switch is in a second one of the modes.

18. The LIDAR system of claim 17, wherein light from the outgoing light is mixed with light from the incoming light signal so as to generate a composite light signal when the optical switch is in the second mode.

19. The LIDAR system of claim 18, wherein the composite light signal is not generated when the optical switch is in the first mode.