Patent Application
20240264289
The invention relates to imaging systems. In particular, the invention relates to data refinement in imaging systems.
LIDAR systems output a system output signal that is reflected by objects located outside of the LIDAR system. The reflected light returns to the LIDAR system as a system return signal. The LIDAR system includes electronics that use the system return signal to determine LIDAR data (radial velocity and/or distance between the LIDAR system and the objects) for sample regions that are illuminated by the system output signal.
In order for a LIDAR system to generate an image of a scene, the system output signal is scanned across the scene. During the scan, the LIDAR data is generated for multiple different sample regions within the scene. Each of the sample regions is illuminated for a regional time period in order to generate the LIDAR data for the sample region. However, the scanning of the system output signal continues during the regional time period. As a result, the system output signal can illuminate one object at the start of a regional time period and then move so the system output signal illuminates another object before the regional time period has expired. Changing the object that is illuminated during a regional time period is a source of errors in the LIDAR data. As a result, there is a need for LIDAR systems that can provide more reliable LIDAR data.
Operating a LIDAR system includes transmitting a system output signal from the LIDAR system such that a sample region is illuminated by the system output signal. During illumination of the sample region, the system output signal includes a check data period and multiple subject data periods. A frequency of the system output signal changes at different rates during the subject data periods. Light that returns to the LIDAR system from the system output signal is combined with light from a reference signal so as to generate a beating signal beating at a beat frequency. The reference signal includes light that has not exited from the LIDAR system. A comparative beat frequency is calculated. The comparative beat frequency approximates a value of the beat frequency of the beating signal during the check data period. Additionally, the comparative beat frequency is calculated from the beat frequencies of the beating signal during the subject data periods.
A LIDAR system is configured to output a system output signal such that a sample region is illuminated by the system output signal. During illumination of the sample region, the system output signal includes a check data period and multiple subject data periods. A frequency of the system output signal changes at different rates during the subject data periods. The LIDAR system includes a light-combining component that combines light that returns to the LIDAR system from the system output signal with light from a reference signal so as to generate a beating signal beating at a beat frequency. The reference signal includes light that has not exited from the LIDAR system. The system also includes electronics configured to calculate a comparative beat frequency that approximates a value of the beat frequency of the beating signal during the check data period. The comparative beat frequency is calculated from the beat frequencies of the beating signal during the subject data periods.
A LIDAR system outputs a system output signal. The frequency of the system output signal changes in a series of repeated cycles. Each of the cycles includes a check data period and multiple subject data periods. A light-combining component combines light that returns to the LIDAR system from the system output signal with light from a reference signal so as to generate a beating signal that is beating at a beat frequency. The reference signal includes light that has not exited from the LIDAR system.
Electronics can use the beat frequency of the beating signal during multiple different subject data periods to calculate candidate LIDAR data for a sample region that is illuminated by the system output signal during a subject one of the cycles. The candidate LIDAR data indicates a potential radial velocity and/or a potential distance between the LIDAR system and an object external to the LIDAR system.
The electronics can also use the beat frequency of the beating signal during multiple different subject data periods to calculate a comparative beat frequency. The comparative beat frequency approximates the value of the beat frequency of the beating signal during the check data period in the subject cycle.
The comparative beat frequency can be calculated such that when the system output signal is incident on the same surface during the subject data periods and the check data period, the value of the comparative beat frequency matches, or substantially matches, the beat frequency during the check data period. However, when the system output signal is not incident on the same surface during the subject data periods and the check data period, the comparative beat frequency and the beat frequency during the check data period do not match. For instance, the comparative beat frequency and the beat frequency during the check data period can match, or substantially match, when the candidate LIDAR data stays constant, or substantially constant, for durations of the subject and check data periods. The candidate LIDAR data staying constant through the subject and check data periods indicates that the radial velocity and/or distance between the LIDAR system and the object stayed constant through the subject and check data periods. As a result, the constant candidate LIDAR data indicates that the system output signal has remained incident on the same surface object during at least the subject data periods. Accordingly, a match, or substantial match, between the comparative beat frequency and the beat frequency during the check data period indicates that the system output signal has remained incident on the same surface of the object during at least the subject data periods.
The values of the comparative beat frequency and the beat frequency during the check data period can be compared to determine whether the system output signal has remained incident on the same surface of the object during the subject data periods. LIDAR data for the sample region can be classified as unavailable when the comparison indicates that the system output signal was not incident on the same surface during the subject data periods. In contrast, the candidate LIDAR data for the sample region can be classified as valid when the comparison indicates that the system output signal remained on the same surface during the subject data periods. As a result, the LIDAR data for the sample region can be set equal to the candidate LIDAR date for the sample region. Accordingly, LIDAR data for sample regions where the system output signal changes surfaces can be removed from the LIDAR data for the collection of sample regions within the system's field of view. As a result, the LIDAR data for the sample regions within the system's field of view can be processed with reduced interference from edge effect errors.
The above method for refining LIDAR data has also been shown to reduce other errors that occur in the generation of LIDAR data for the sample regions within a system's field of view. Outliers occur where the LIDAR data for a sample region is not consistent with the LIDAR data for surrounding sample regions. Outliers do not necessarily occur at a transition between surfaces but can occur in the middle of a surface. As a result, an outlier can be LIDAR data from a surface that is not consistent with LIDAR data at other locations on that surface. Removing candidate LIDAR data that does not remain constant or substantially constant during illumination of a sample region has been shown to reduce the presence of outliers. Aliasing will also be reduced by the extraction of these candidate LIDAR data values from the final LIDAR data values in the field of view.
The LIDAR chip includes a utility waveguide 12 that receives an outgoing LIDAR signal from a light source 4. The utility waveguide 12 terminates at a facet 14 and carries the outgoing LIDAR signal to the facet 14. The facet 14 can be positioned such that the outgoing LIDAR signal traveling through the facet 14 exits the LIDAR chip and serves as a LIDAR output signal. For instance, the facet 14 can be positioned at an edge of the chip so the outgoing LIDAR signal traveling through the facet 14 exits the chip and serves as the LIDAR output signal. In some instances, the portion of the LIDAR output signal that has exited from the LIDAR chip can also be considered a system output signal. As an example, when the exit of the LIDAR output signal from the LIDAR chip is also an exit of the LIDAR output signal from the LIDAR system, the LIDAR output signal can also be considered a system output signal.
The LIDAR output signal travels away from the LIDAR system through free space in the atmosphere in which the LIDAR system is positioned. The LIDAR output signal may be reflected by one or more objects in the path of the LIDAR output signal. When the LIDAR output signal is reflected, at least a portion of the reflected light travels back toward the LIDAR chip as a LIDAR input signal. In some instances, the LIDAR input signal can also be considered a system return signal. As an example, when the exit of the LIDAR output signal from the LIDAR chip is also an exit of the LIDAR output signal from the LIDAR system, the LIDAR input signal can also be considered a system return signal.
The LIDAR input signals can enter the utility waveguide 12 through the facet 14. The portion of the LIDAR input signal that enters the utility waveguide 12 serves as an incoming LIDAR signal. The utility waveguide 12 carries the incoming LIDAR signal to a splitter 16 that moves a portion of the outgoing LIDAR signal from the utility waveguide 12 onto a comparative waveguide 18 as a comparative signal. The comparative waveguide 18 carries the comparative signal to a processing component 22 for further processing. Although
The utility waveguide 12 also carrier the outgoing LIDAR signal to the splitter 16. The splitter 16 moves a portion of the outgoing LIDAR signal from the utility waveguide 12 onto a reference waveguide 20 as a reference signal. The reference waveguide 20 carries the reference signal to the processing component 22 for further processing.
The percentage of light transferred from the utility waveguide 12 by the splitter 16 can be fixed or substantially fixed. For instance, the splitter 16 can be configured such that the power of the reference signal transferred to the reference waveguide 20 is an outgoing percentage of the power of the outgoing LIDAR signal or such that the power of the comparative signal transferred to the comparative waveguide 18 is an incoming percentage of the power of the incoming LIDAR signal. In many splitters 16, such as directional couplers and multimode interferometers (MMIs), the outgoing percentage is equal or substantially equal to the incoming percentage. In some instances, the outgoing percentage is greater than 30%, 40%, or 49% and/or less than 51%, 60%, or 70% and/or the incoming percentage is greater than 30%, 40%, or 49% and/or less than 51%, 60%, or 70%. A splitter 16 such as a multimode interferometer (MMI) generally provides an outgoing percentage and an incoming percentage of 50% or about 50%. However, multimode interferometers (MMIs) can be easier to fabricate in platforms such as silicon-on-insulator platforms than some alternatives. In one example, the splitter 16 is a multimode interferometer (MMI) and the outgoing percentage and the incoming percentage are 50% or substantially 50%. As will be described in more detail below, the processing component 22 combines the comparative signal with the 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 (radial velocity and/or distance between a LIDAR system and an object external to the LIDAR system) for the sample region.
The LIDAR chip can include a control branch for controlling operation of the light source 4. The control branch includes a splitter 26 that moves a portion of the outgoing LIDAR signal from the utility waveguide 12 onto a control waveguide 28. The coupled portion of the outgoing LIDAR signal serves as a tapped signal. Although
The control waveguide 28 carries the tapped signal to control components 30. The control components can be in electrical communication with electronics 32. All or a portion of the control components can be included in the electronics 32. During operation, the electronics can employ output from the control components 30 in a control loop configured to control a process variable of one, two, or three loop controlled light signals selected from the group consisting of the tapped signal, the system output signal, and the outgoing LIDAR signal. Examples of the suitable process variables include the frequency of the loop controlled light signal and/or the phase of the loop controlled light signal.
The LIDAR system can be modified so the incoming LIDAR signal and the outgoing LIDAR signal can be carried on different waveguides. For instance,
The LIDAR chips can be modified to receive multiple LIDAR input signals. For instance,
The outgoing LIDAR signal exits the LIDAR chip through the facet 14 and serves as the LIDAR output signal. When light from the LIDAR output signal is reflected by one or more object located external to the LIDAR system, at least a portion of the reflected light returns to the LIDAR chip as a first LIDAR input signal. The first LIDAR input signals enters the comparative waveguide 18 through the facet 35 and serves as a first comparative signal. The comparative waveguide 18 carries the first comparative signal to a first processing component 46 for further processing.
Additionally, when light from the LIDAR output signal is reflected by one or more object located external to the LIDAR system, at least a portion of the reflected signal returns to the LIDAR chip as a second LIDAR input signal. The second LIDAR input signals enters a second comparative waveguide 50 through a facet 52 and serves as a second comparative signal carried by the second comparative waveguide 50. The second comparative waveguide 50 carries the second comparative signal to a second processing component 48 for further processing.
Although the light source 4 is shown as being positioned on the LIDAR chip, the light source 4 can be located off the LIDAR chip. For instance, the utility waveguide 12 can terminate at a second facet through which the outgoing LIDAR signal can enter the utility waveguide 12 from a light source 4 located off the LIDAR chip.
In some instances, a LIDAR chip constructed according to
An example of a LIDAR adapter that is suitable for use with the LIDAR chip of
The LIDAR adapter can be configured such that the output of the LIDAR output signal from the second port 106 can also serve as the output of the LIDAR output signal from the LIDAR adapter and accordingly from the LIDAR system. As a result, the LIDAR output signal can be output from the LIDAR adapter such that the LIDAR output signal is traveling toward a sample region in the field of view. Accordingly, in some instances, the portion of the LIDAR output signal that has exited from the LIDAR adapter can also be considered the system output signal. As an example, when the exit of the LIDAR output signal from the LIDAR adapter is also an exit of the LIDAR output signal from the LIDAR system, the LIDAR output signal can also be considered a system output signal.
The LIDAR output signal output from the LIDAR adapter includes, consists of, or consists essentially of light from the LIDAR output signal received from the LIDAR chip. Accordingly, the LIDAR output signal output from the LIDAR adapter may be the same or substantially the same as the LIDAR output signal received from the LIDAR chip. However, there may be differences between the LIDAR output signal output from the LIDAR adapter and the LIDAR output signal received from the LIDAR chip. For instance, the LIDAR output signal can experience optical loss as it travels through the LIDAR adapter and/or the LIDAR adapter can optionally include an amplifier configured to amplify the LIDAR output signal as it travels through the LIDAR adapter.
When one or more objects in the sample region reflect the LIDAR output signal, at least a portion of the reflected light travels back to the circulator 100 as a system return signal. The system return signal enters the circulator 100 through the second port 106.
The system return signal exits the circulator 100 through the third port 108 and is directed to the comparative waveguide 18 on the LIDAR chip. Accordingly, all or a portion of the system return signal can serve as the first LIDAR input signal and the first LIDAR input signal includes or consists of light from the system return signal. Accordingly, the LIDAR output signal and the first LIDAR input signal travel between the LIDAR adapter and the LIDAR chip along different optical paths.
As is evident from
The LIDAR adapter can also include one or more direction changing components such as mirrors.
The LIDAR chips include one or more waveguides that constrains the optical path of one or more light signals. While the LIDAR adapter can include waveguides, the optical path that the system return signal and the LIDAR output signal travel between components on the LIDAR adapter and/or between the LIDAR chip and a component on the LIDAR adapter can be free space. For instance, the system return signal and/or the LIDAR output signal can travel through the atmosphere in which the LIDAR chip, the LIDAR adapter, and/or the base 102 is positioned when traveling between the different components on the LIDAR adapter and/or between a component on the LIDAR adapter and the LIDAR chip. As a result, optical components such as lenses and direction changing components can be employed to control the characteristics of the optical path traveled by the system return signal and the LIDAR output signal on, to, and from the LIDAR adapter.
Suitable bases 102 for the LIDAR adapter include, but are not limited to, substrates, platforms, and plates. Suitable substrates include, but are not limited to, glass, silicon, and ceramics. The components can be discrete components that are attached to the substrate. Suitable techniques for attaching discrete components to the base 102 include, but are not limited to, epoxy, solder, and mechanical clamping. In one example, one or more of the components are integrated components and the remaining components are discrete components. In another example, the LIDAR adapter includes one or more integrated amplifiers and the remaining components are discrete components.
The LIDAR system can be configured to compensate for polarization. Light from a laser source is typically linearly polarized and hence the LIDAR output signal is also typically linearly polarized. Reflection from an object may change the angle of polarization of the returned light. Accordingly, the system return signal can include light of different linear polarization states. For instance, a first portion of a system return signal can include light of a first linear polarization state and a second portion of a system return signal can include light of a second linear polarization state. The intensity of the resulting composite signals is proportional to the square of the cosine of the angle between the comparative and reference signal polarization fields. If the angle is 90 degrees, the LIDAR data can be lost in the resulting composite signal. However, the LIDAR system can be modified to compensate for changes in polarization state of the LIDAR output signal.
The first portion of the system return signal is directed to the comparative waveguide 18 on the LIDAR chip and serves as the first LIDAR input signal described in the context of
The beamsplitter 120 can be a polarizing beam splitter. One example of a polarizing beamsplitter is constructed such that the first portion of the system return signal has a first polarization state but does not have or does not substantially have a second polarization state and the second portion of the system return signal has a second polarization state but does not have or does not substantially have the first polarization state. The first polarization state and the second polarization state can be linear polarization states and the second polarization state is different from the first polarization state. For instance, the first polarization state can be TE and the second polarization state can be TM or the first polarization state can be TM and the second polarization state can be TE. In some instances, the laser source can linearly polarized such that the LIDAR output signal has the first polarization state. Suitable beamsplitters include, but are not limited to, Wollaston prisms, and MEMs-based polarizing beamsplitters.
A polarization rotator can be configured to change the polarization state of the first portion of the system return signal and/or the second portion of the system return signal. For instance, the polarization rotator 122 shown in
Since the first LIDAR input signal and the second LIDAR carry light of the same polarization state, the comparative signals that result from the first LIDAR input signal have the same polarization angle as the comparative signals that result from the second LIDAR input signal.
Suitable polarization rotators include, but are not limited to, rotation of polarization-maintaining fibers, Faraday rotators, half-wave plates, MEMs-based polarization rotators and integrated optical polarization rotators using asymmetric y-branches, Mach-Zehnder interferometers and multi-mode interference couplers.
Since the outgoing LIDAR signal is linearly polarized, the first reference signals can have the same linear polarization state as the second reference signals. Additionally, the components on the LIDAR adapter can be selected such that the first reference signals, the second reference signals, the comparative signals and the second comparative signals each have the same polarization state. In the example disclosed in the context of
As a result of the above configuration, first composite signals generated by the first processing component 46 and second composite signals generated by the second processing component 48 each results from combining a reference signal and a comparative signal of the same polarization state and will accordingly provide the desired beating between the reference signal and the comparative signal. For instance, the composite signal results from combining a first reference signal and a first comparative signal of the first polarization state and excludes or substantially excludes light of the second polarization state or the composite signal results from combining a first reference signal and a first comparative signal of the second polarization state and excludes or substantially excludes light of the first polarization state. Similarly, the second composite signal includes a second reference signal and a second comparative signal of the same polarization state will accordingly provide the desired beating between the reference signal and the comparative signal. For instance, the second composite signal results from combining a second reference signal and a second comparative signal of the first polarization state and excludes or substantially excludes light of the second polarization state or the second composite signal results from combining a second reference signal and a second comparative signal of the second polarization state and excludes or substantially excludes light of the first polarization state.
The above configuration results in the LIDAR data for a single sample region in the field of view being generated from multiple different composite signals (i.e. first composite signals and the second composite signal) from the sample region. In some instances, determining the LIDAR data for the sample region includes the electronics combining the LIDAR data from different composite signals (i.e. the composite signals and the second composite signal). Combining the LIDAR data can include taking an average, median, or mode of the LIDAR data generated from the different composite signals. For instance, the electronics can average the distance between the LIDAR system and the reflecting object determined from the composite signal with the distance determined from the second composite signal and/or the electronics can average the radial velocity between the LIDAR system and the reflecting object determined from the composite signal with the radial velocity determined from the second composite signal.
In some instances, determining the LIDAR data for a sample region includes the electronics identifying one or more composite signals (i.e. the composite signal and/or the second composite signal) as the source of the LIDAR data that is most represents reality (the representative LIDAR data). The electronics can then use the LIDAR data from the identified composite signal as the representative LIDAR data to be used for additional processing. For instance, the electronics can identify the signal (composite signal or the second composite signal) with the larger amplitude as having the representative LIDAR data and can use the LIDAR data from the identified signal for further processing by the LIDAR system. In some instances, the electronics combine identifying the composite signal with the representative LIDAR data with combining LIDAR data from different LIDAR signals. For instance, the electronics can identify each of the composite signals with an amplitude above an amplitude threshold as having representative LIDAR data and when more than two composite signals are identified as having representative LIDAR data, the electronics can combine the LIDAR data from each of identified composite signals. When one composite signal is identified as having representative LIDAR data, the electronics can use the LIDAR data from that composite signal as the representative LIDAR data. When none of the composite signals is identified as having representative LIDAR data, the electronics can discard the LIDAR data for the sample region associated with those composite signals.
Although
The above system configurations result in the first portion of the system return signal and the second portion of the system return signal being directed into different composite signals. As a result, since the first portion of the system return signal and the second portion of the system return signal are each associated with a different polarization state but electronics can process each of the composite signals, the LIDAR system compensates for changes in the polarization state of the LIDAR output signal in response to reflection of the LIDAR output signal.
The LIDAR adapter of
When the LIDAR system includes a LIDAR chip and a LIDAR adapter, the LIDAR chip, electronics, and the LIDAR adapter can be positioned on a common mount. Suitable common mounts include, but are not limited to, glass plates, metal plates, silicon plates and ceramic plates. As an example,
The LIDAR systems can include components including additional passive and/or active optical components. For instance, the LIDAR system can include one or more components that receive the LIDAR output signal from the LIDAR chip or from the LIDAR adapter. The portion of the LIDAR output signal that exits from the one or more components can serve as the system output signal. As an example, the LIDAR system can include one or more beam steering components that receive the LIDAR output signal from the LIDAR chip or from the LIDAR adapter and that output all or a fraction of the LIDAR output signal that serves as the system output signal. For instance,
The electronics can operate the one or more beam steering component 142 so as to steer the system output signal to different sample regions 144. The sample regions can extend away from the LIDAR system to a maximum distance for which the LIDAR system is configured to provide reliable LIDAR data. The sample regions can be stitched together to define the field of view. For instance, the field of view of for the LIDAR system includes or consists of the space occupied by the combination of the sample regions.
The processing component includes a second splitter 200 that divides the comparative signal carried on the comparative waveguide 196 onto a first comparative waveguide 204 and a second comparative waveguide 206. The first comparative waveguide 204 carries a first portion of the comparative signal to the light-combining component 211. The second comparative waveguide 208 carries a second portion of the comparative signal to the second light-combining component 212.
The processing component includes a first splitter 202 that divides the reference signal carried on the reference waveguide 198 onto a first reference waveguide 204 and a second reference waveguide 206. The first reference waveguide 204 carries a first portion of the reference signal to the light-combining component 211. The second reference waveguide 208 carries a second portion of the reference signal to the second light-combining component 212.
The second light-combining component 212 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 second light-combining component 212 also splits the resulting second composite signal onto a first auxiliary detector waveguide 214 and a second auxiliary detector waveguide 216. The first auxiliary detector waveguide 214 carries a first portion of the second composite signal to a first auxiliary light sensor 218 that converts the first portion of the second composite signal to a first auxiliary electrical signal. The second auxiliary detector waveguide 216 carries a second portion of the second composite signal to a second auxiliary light sensor 220 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).
In some instances, the second light-combining component 212 splits the second composite signal such that the portion of the comparative signal (i.e. the portion of the second portion of the comparative signal) included in the first portion of the second composite signal is phase shifted by 180° relative to the portion of the comparative signal (i.e. the portion of the second portion of the comparative signal) in the second portion of the second composite signal but the portion of the reference signal (i.e. the portion of the second portion of the reference signal) in the second portion of the second composite signal is not phase shifted relative to the portion of the reference signal (i.e. the portion of the second portion of the reference signal) in the first portion of the second composite signal. Alternately, the second light-combining component 212 splits the second composite signal such that the portion of the reference signal (i.e. the portion of the second portion of the reference signal) in the first portion of the second composite signal is phase shifted by 180° relative to the portion of the reference signal (i.e. the portion of the second portion of the reference signal) in the second portion of the second composite signal but the portion of the comparative signal (i.e. the portion of the second portion of the comparative signal) in the first portion of the second composite signal is not phase shifted relative to the portion of the comparative signal (i.e. the portion of the second portion of the comparative signal) in the second portion of the second composite signal. Examples of suitable light sensors include germanium photodiodes (PDs), and avalanche photodiodes (APDs).
The first light-combining component 211 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 first light-combining component 211 also splits the first composite signal onto a first detector waveguide 221 and a second detector waveguide 222. The first detector waveguide 221 carries a first portion of the first composite signal to a first light sensor 223 that converts the first portion of the second composite signal to a first electrical signal. The second detector waveguide 222 carries a second portion of the second composite signal to a second light sensor 224 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).
In some instances, the light-combining component 211 splits the first composite signal such that the portion of the comparative signal (i.e. the portion of the first portion of the comparative signal) included in the first portion of the composite signal is phase shifted by 180° relative to the portion of the comparative signal (i.e. the portion of the first portion of the comparative signal) in the second portion of the composite signal but the portion of the reference signal (i.e. the portion of the first portion of the reference signal) in the first portion of the composite signal is not phase shifted relative to the portion of the reference signal (i.e. the portion of the first portion of the reference signal) in the second portion of the composite signal. Alternately, the light-combining component 211 splits the composite signal such that the portion of the reference signal (i.e. the portion of the first portion of the reference signal) in the first portion of the composite signal is phase shifted by 180° relative to the portion of the reference signal (i.e. the portion of the first portion of the reference signal) in the second portion of the composite signal but the portion of the comparative signal (i.e. the portion of the first portion of the comparative signal) in the first portion of the composite signal is not phase shifted relative to the portion of the comparative signal (i.e. the portion of the first portion of the comparative signal) in the second portion of the composite signal.
When the second light-combining component 212 splits the second composite signal such that the portion of the comparative signal in the first portion of the second composite signal is phase shifted by 180° relative to the portion of the comparative signal in the second portion of the second composite signal, the light-combining component 211 also splits the composite signal such that the portion of the comparative signal in the first portion of the composite signal is phase shifted by 180° relative to the portion of the comparative signal in the second portion of the composite signal. When the second light-combining component 212 splits the second composite signal such that the portion of the reference signal in the first portion of the second composite signal is phase shifted by 180° relative to the portion of the reference signal in the second portion of the second composite signal, the light-combining component 211 also splits the composite signal such that the portion of the reference signal in the first portion of the composite signal is phase shifted by 180° relative to the portion of the reference signal in the second portion of the composite signal.
The first reference waveguide 210 and the second reference waveguide 208 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 210 and the second reference waveguide 208 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 210 and the second reference waveguide 208 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 223 and the second light sensor 224 can be connected as a balanced detector and the first auxiliary light sensor 218 and the second auxiliary light sensor 220 can also be connected as a balanced detector. For instance,
The electronics connect the first light sensor 223 and the second light sensor 224 as a first balanced detector 225 and the first auxiliary light sensor 218 and the second auxiliary light sensor 220 as a second balanced detector 226. In particular, the first light sensor 223 and the second light sensor 224 are connected in series. Additionally, the first auxiliary light sensor 218 and the second auxiliary light sensor 220 are connected in series. The serial connection in the first balanced detector is in communication with a first data line 228 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 232 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 32 includes a transform mechanism 238 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 238 includes a first Analog-to-Digital Converter (ADC) 264 that receives the first data signal from the first data line 228. The first Analog-to-Digital Converter (ADC) 264 converts the first data signal from an analog form to a digital form and outputs a first digital data signal. The transform mechanism 238 includes a second Analog-to-Digital Converter (ADC) 266 that receives the second data signal from the second data line 232. The second Analog-to-Digital Converter (ADC) 266 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 238 includes a transform component 268 that receives the complex data signal. For instance, the transform component 268 receives the first digital data signal from the first Analog-to-Digital Converter (ADC) 264 as an input and also receives the second digital data signal from the second Analog-to-Digital Converter (ADC) 266 as an input. The transform component 268 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 electronics use the one or more frequency peaks output from the transform component 268 for further processing to generate the LIDAR data (distance and/or radial velocity between the reflecting object and the LIDAR chip or LIDAR system). The transform component 268 can execute the attributed functions using firmware, hardware or software or a combination thereof.
The electronics 32 includes a peak finder 270 that receives output from the transform component 268. The peak finder 270 is configured to find a peak in output of the transform component 268 in order to identify the beat frequency of the composite optical signal. 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 beat frequency of the composite optical signal. In some instances, the peak finder 270 can store the beat frequencies in a memory 271 for later use by a LIDAR data generator 274. As will be described in more detail below, the beat frequencies can each be stored as fm where m represents a period index. The LIDAR data generator 274 uses the beat frequencies to generate the LIDAR data (distance and/or radial velocity between the reflecting object and the LIDAR chip or LIDAR system). Suitable memories 271 include, but are not limited to, buffers. The peak finder 270 can execute the attributed functions using firmware, hardware or software or a combination thereof.
Although
The electronics tune the frequency of the system output signal over time. The system output signal has a frequency versus time pattern with a repeated cycle.
Each cycle includes M data periods that are each associated with a period index m and are labeled DPm. Suitable values for M include M≥3. In the example of
During the data period DPm, the electronics operate the light source such that the frequency of the system output signal changes linearly as a function of time. For instance, during data period DPm, the frequency of the system output signal can change at a constant or substantially constant rate αm (the chirp rate). The chirp rate can continue for all or a portion of the duration of the data period. For instance, during the data periods labeled DP1 the electronics operate the light source such that the frequency of the system output signal changes at a linear rate α1, during the data periods labeled DP2 the electronics operate the light source such that the frequency of the system output signal changes at a linear rate α2 and during the data periods labeled DP3 the electronics operate the light source such that the frequency of the system output signal changes at a linear rate α3. In some instances, α1 through αM are selected such that the sum of α1 through αM is zero. For instance, when M is equal to three, α1, α2, and α3 can be selected such that α1+α2+α3=0 as shown in
The frequency output from the Complex Fourier transform represents the beat frequency of the composite signals that each includes a comparative signal beating against a reference signal. The beat frequencies from two or more different data periods that are associated with the same sample region can be combined to generate the LIDAR data. For instance, the beat frequency determined from DP1 during the illumination of sample region SRk can be combined with the beat frequency determined from DP2 during the illumination of sample region SRk to determine the LIDAR data for sample region SRk. As an example, the beat frequency during data period DPm can be written as the following Equation 1: fm=2αmR/c−2ν/λ where m is period index, R represents the distance between the LIDAR system and the object, c represents the speed of light, ν represents the radial velocity between the reflecting object and the LIDAR system, λ represents the wavelength of the system output signal, and the direction from the reflecting object toward the LIDAR system is assumed to be the positive direction.
The data periods associated with a sample region include multiple subject data periods and at least one check data period. In
The frequency of the system output signal can increase during one of the subject data periods associated with a sample region as is evident from the data period DP1 of
The beat frequency of the composite signal in a check data period can be represented by fchk and the rate of frequency change can be written as αchk. As noted above, the data periods labeled DP3 in
In the above Equation 1 (fm=2αmR/c−2ν/λ), the values of ν and R are unknown. As a result, the results of Equation 1 from two different data periods associated with the sample region can be used to calculate the values of ν and R for the data period. Solving these equations for the distance between the LIDAR system and the object (R) provides Equation 2: R=c(fub−fdb)/(2(αub−αdb)). Additionally, solving these equations for the radial velocity between the reflecting object and the LIDAR system (ν) provides Equation 3: ν=λ(αdbfub−αubfdb)/(2(αub−αdb)). As shown in
The electronics can include a LIDAR data validator 276 that receives the candidate LIDAR data from the LIDAR data generator 274. The LIDAR data validator 276 can also receive beat frequencies such as the check period beat frequency (cfchk) from the memory 271 and/or peak finder 270.
The LIDAR data validator 276 can use the check data period associated with a sample region to determine whether the associated candidate LIDAR data is valid for that sample region. For instance, the LIDAR data validator 276 can calculate a comparative check period beat frequency (cfchk) for a sample region from the candidate LIDAR data associated with the sample region. The comparative check period beat frequency (cfchk) can be determined by substituting the rate of frequency change during the check data period αchk into Equation 1 to provide Equation 4: cfchk=2αchkR/c−2ν/λ. As a result, the LIDAR data validator 276 can calculate the comparative check period beat frequency (cfchk) for a sample region from cfchk=2αchkR/c−2ν/λ where R represents the candidate distance and ν represents the candidate radial velocity for the sample region.
The LIDAR data validator 276 can use the comparative check period beat frequency (cfchk) for a sample region to determine whether the candidate LIDAR data for the sample region is valid. For instance, the LIDAR data validator 276 can apply one or more check criteria to the comparative check period beat frequency (cfchk). As an example, the LIDAR data validator 276 can compare the values of the check data period (fchk) and the comparative check period beat frequency (cfchk) from the same data period. For instance, when the LIDAR data validator 276 determines that comparative check period beat frequency (cfchk) is within a window of values that include the check period beat frequency (fchk), the LIDAR data validator 276 determines that the candidate LIDAR data for the sample region is valid. Accordingly, the LIDAR data validator can classify the candidate LIDAR data for the sample region as the LIDAR data for the sample region. When the LIDAR data validator 276 determines that comparative check period beat frequency (cfchk) is outside the window, the candidate LIDAR data can be found to be invalid for the sample region. As a result, the LIDAR data validator 276 can classify the candidate LIDAR data for the sample region as unavailable. The candidate LIDAR data classified as unavailable is essentially removed from the final LIDAR data for the sample regions in the field of view for the LIDAR system. The LIDAR data validator 276 can execute the attributed functions using firmware, hardware or software or a combination thereof.
An example of the window of values that include the check period beat frequency (fchk) is values in a range of fchk −C1 to fchk+C2 where C1 and C2 are positive constants and none, one, or both of C1 and C2 can be zero. Accordingly, an example of comparing the values of the check period beat frequency (fchk) and the comparative check period beat frequency (cfchk) includes making a determine whether the comparative check period beat frequency (cfchk) is within a range of fchk −C1 to fchk +C2. For instance, is fchk −C1≤cfchk≤fchk +C2 true? When fchk −C1≤cfchk≤fchk +C2 is true the LIDAR data validator can classify the candidate LIDAR data for the sample region as the LIDAR data for the sample region and when fchk −C1≤cfchk≤fchk +C2 is false, the candidate LIDAR data can be found to be invalid for the sample region. The values of C1 and C2 can be the same or different. Suitable values for C1 and/or C2, include, but are not limited to, values greater than or equal to 0.01 MHz, or 0.5 MHz, and less than or equal to 2 MHz, or 100 MHz. The selected values of C1 and C2 can be a function of the LIDAR system.
The validation performed by the LIDAR data validator 276 can reduce the presence of edge errors in the LIDAR data for a field of view.
The collection of sample regions that are scanned by the system output signal make up the field of view for the LIDAR system. The object(s) in the field of view can change with time. As a result, the locations of the sample regions are determined relative to the LIDAR system rather than relative to the atmosphere in which the LIDAR system is positioned. For instance, the sample regions can be defined as being located within a range of angles relative to the LIDAR system. The dashed line in
The portion of each sample region that corresponds to one of the data periods are each labeled DP1, DP2, or DP2 in
The movement of the system output signal causes the system output signal to go from being incident on object 1 during illumination of the sample region labeled SRk−1 to being incident on object 2 during illumination of the sample region labeled SRk. During illumination of the sample region labeled SRk−1, the system output signal is incident on different objects during a portion of data period DP1 and a portion of data period DP2. The change in the object that receives the system output signal during the illumination of sample region SRk+1 can be a source of error in the LIDAR data that is generated for sample region SRk−1. For instance,
The source of the LIDAR data error illustrated in
The application of the one or more check criteria reduces errors from the edge effect. For instance, the comparative check period beat frequency (cfchk) is an approximation of the value of the check period beat frequency (fchk) but rather than being a function of the value of the beat frequency in the check period, the comparative check period beat frequency (cfchk) is a function of the beat frequencies from multiple different subject data periods. As a result, the comparative check period beat frequency (cfchk) in the check period is calculated from the beat frequencies in multiple different subject data periods. For instance, in the above examples, the comparative check period beat frequency (cfchk) is calculated from the beat frequencies during an increasing data period and a decreasing data period. As a result, the comparative check period beat frequency (cfchk) is a function of the distance (R) and radial velocity (ν) values during data periods other than a check data period. In contrast, the check period beat frequency (fchk) is a function of the distance (R) and radial velocity (ν) values during the check data period. Accordingly, the value of the comparative check period beat frequency (cfchk) matches the value of the associated check period beat frequency (fchk) when the distance (R) and radial velocity (ν) values match during both the check data period and during the other associated data periods. For instance, the value of the comparative check period beat frequency (cfchk) matches the value of the associated check period beat frequency (fchk) when the distance (R) and radial velocity (ν) remain constant or substantially constant during the check data period, the associated increasing data period, and the associated decreasing data period. Removing candidate LIDAR data where the distance (R) and radial velocity (ν) do not remain constant or substantially constant during illumination of a sample region from the final LIDAR data values in the field of view, removes candidate LIDAR data that may result from the system output signal changing surfaces during the illumination of the sample region and accordingly reduces the presence of the edge error effect.
Filtering out candidate LIDAR data where the distance (R) and radial velocity (ν) substantially change during illumination of a sample region has proven to reduce the presence of other errors that occur in the generation of LIDAR data for a field of view. For instance, outliers occur where the LIDAR data for a sample region is not consistent with the LIDAR data for surrounding sample regions. Outliers do not necessarily occur at a transition between surfaces but can occur in the middle of a surface. As a result, an outlier can be LIDAR data for a sample region where the system output signal is incident on a surface, but that LIDAR data is not consistent with LIDAR data from adjacent sample regions where the system output signal is incident on the same surface. Removing candidate LIDAR data where the distance (R) and radial velocity (ν) do not remain constant or substantially constant during illumination of a sample region has been shown to reduce the presence of outliers. Aliasing will also be reduced by the extraction of these candidate LIDAR data values from the final LIDAR data values in the field of view.
At process block 312, the candidate LIDAR data is calculated from the beat frequency that result from the output of the system output signal during each one of multiple different subject data periods. The candidate LIDAR data need not be a function of the beat frequency that result from the output of the system output signal during the check data period. As a result, the calculation of the candidate LIDAR data can exclude the use of the beat frequency that result from the output of the system output signal during the check data period as a variable. For instance, the LIDAR data generator 274 can use the received beat frequencies in combination with the above Equation 1 and/or Equation 2 to calculate a potential value for the distance between the LIDAR system and an object in the sample region (R) and/or a potential value for the radial velocity between the LIDAR system and an object in the sample region. In an example where the system output signal has a frequency versus time pattern according to
At process block 314, the beat frequency of the composite signal in the check data period (comparative check period beat frequency, cfchk) is calculated. The comparative check period beat frequency (cfchk) can be calculated from the beat frequency that result from the output of the system output signal during each one of multiple different subject data periods. The comparative check period beat frequency (cfchk) need not be a function of the beat frequency that result from the output of the system output signal during the check data period. As a result, the calculation of the comparative check period beat frequency (cfchk) can exclude the use of the beat frequency that result from the output of the system output signal during the check data period as a variable. For instance, the LIDAR data validator 276 can receive the candidate LIDAR data from the LIDAR data generator 274 and can use the results in combination with Equation 4 to calculate the comparative check period beat frequency (cfchk). Alternately, the LIDAR data validator 276 can receive the beat frequencies from the memory 271 and/or peak finder 270 and can use the received beat frequencies in combination with Equation 2, Equation 3, and Equation 4 to calculate the comparative check period beat frequency (cfchk).
At determination block 316, a determination is made whether the comparative check period beat frequency (cfchk) matches the beat frequency during the check period (the check period beat frequency, fchk). In an example where the system output signal has a frequency versus time pattern according to
When the LIDAR data validator 276 determines that comparative check period beat frequency (cfchk) matches the beat frequency during the check period, the LIDAR data validator 276 proceeds to process block 318 where the candidate LIDAR data for the subject sample region is classified as valid. As a result, the candidate LIDAR data for the subject sample region serves as the actual LIDAR data for the subject sample region. The actual LIDAR data for the subject sample region is the value of the distance between the LIDAR system and an object in the sample region (R) and/or a value for the radial velocity between the LIDAR system and an object in the sample region. As a result, when the LIDAR data for the sample regions in the field of view for the LIDAR system is made available to an application for further processing, the candidate LIDAR data for the subject sample region is included as the actual LIDAR data for the sample region.
When the LIDAR data validator 276 determines that comparative check period beat frequency (cfchk) does not match the beat frequency during the check period, the LIDAR data validator 276 proceeds to process block 320 where the candidate LIDAR data for the subject sample region is classified as unavailable. As a result, the candidate LIDAR data for the subject sample region does not serve as the actual LIDAR data for the subject sample region. The classification effectively removes the candidate LIDAR data for the subject sample region from the collection of LIDAR data results for the sample regions in the field of view of the LIDAR system. As a result, when the LIDAR data results for the sample regions in the field of view of the LIDAR system are made available to a LIDAR application for further processing, the candidate LIDAR data for the subject sample region is excluded from the LIDAR data results for the field of view.
The electronics can return to process block 310 from process block 318 or process block 320. At process block 310, the beat frequencies are received for the next subject sample region. For instance, the LIDAR data generator 274 can receive the beat frequencies for sample region SRk+1. When each of the sample regions in the field of view that is to serve as one of the subject sample regions has served as the subject sample region, the collection of LIDAR data results for the sample regions in the field of view can be made available to a LIDAR application for further processing. A first portion of the sample regions in the field of view will not have LIDAR data results due to the application of the one or more check criteria to the comparative beat frequencies for these sample regions providing a first result indicating a mismatch between the comparative check period beat frequency (cfchk) and the measured beat associated with the sample region. In contrast, a second portion of the sample regions in the field of view will each have LIDAR data results due to the application of the one or more check criteria to the comparative beat frequencies for these sample regions providing a second result indicating a match between the comparative check period beat frequency (cfchk) and the measured beat associated with the sample region. Examples of LIDAR applications include, but are not limited to, self-driving cars, robotics, and industrial applications.
Although the mathematical transformer 268 is disclosed as performing complex transforms on a complex signal, the complex transforms can be replaced with real transforms performed on real signals. As a result, the optical-to-electrical assembly of
Suitable electronics 32 can include, but are not limited to, a controller that includes or consists of analog electrical circuits, digital electrical circuits, processors, microprocessors, digital signal processors (DSPs), Field Programmable Gate Arrays (FPGAs), computers, microcomputers, or combinations suitable for performing the operation, monitoring and control functions described above. In some instances, the controller has access to a memory that includes instructions to be executed by the controller during performance of the operation, control and monitoring functions. In some instances, the functions of the LIDAR data generator, the data correction component 272, peak finder can be executed by Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), Application Specific Integrated Circuits, firmware, software, hardware, and combinations thereof. Although the electronics are illustrated as a single component in a single location, the electronics can include multiple different components that are independent of one another and/or placed in different locations. Additionally, as noted above, all or a portion of the disclosed electronics can be included on the chip including electronics that are integrated with the chip.
Suitable platforms for the LIDAR chips include, but are not limited to, silica, indium phosphide, and silicon-on-insulator wafers.
The portion of the chip illustrated in
The dimensions of the ridge waveguide are labeled in
Light sensors that are interfaced with waveguides on a LIDAR chip can be a component that is separate from the chip and then attached to the chip. For instance, the light sensor can be a photodiode, or an avalanche photodiode. Examples of suitable light sensor components include, but are not limited to, InGaAs PIN photodiodes manufactured by Hamamatsu located in Hamamatsu City, Japan, or an InGaAs APD (Avalanche Photo Diode) manufactured by Hamamatsu located in Hamamatsu City, Japan. These light sensors can be centrally located on the LIDAR chip. Alternately, all or a portion the waveguides that terminate at a light sensor can terminate at a facet located at an edge of the chip and the light sensor can be attached to the edge of the chip over the facet such that the light sensor receives light that passes through the facet. The use of light sensors that are a separate component from the chip is suitable for all or a portion of the light sensors selected from the group consisting of the first auxiliary light sensor 218, the second auxiliary light sensor 220, the first light sensor 223, and the second light sensor 224.
As an alternative to a light sensor that is a separate component, all or a portion of the light sensors can be integrated with the chip. For instance, examples of light sensors that are interfaced with ridge waveguides on a chip constructed from a silicon-on-insulator wafer can be found in Optics Express Vol. 15, No. 21, 13965-13971 (2007); U.S. Pat. No. 8,093,080, issued on Jan. 10, 2012; U.S. Pat. No. 8,242,432, issued Aug. 14, 2012; and U.S. Pat. No. 6,108,472, issued on Aug. 22, 2000 each of which is incorporated herein in its entirety. The use of light sensors that are integrated with the chip are suitable for all or a portion of the light sensors selected from the group consisting of the auxiliary light sensor 218, the second auxiliary light sensor 220, the first light sensor 223, and the second light sensor 224.
The light source 4 that is interfaced with the utility waveguide 12 can be a laser chip that is separate from the LIDAR chip and then attached to the LIDAR chip. For instance, the light source 4 can be a laser chip that is attached to the chip using a flip-chip arrangement. Use of flip-chip arrangements is suitable when the light source 4 is to be interfaced with a ridge waveguide on a chip constructed from silicon-on-insulator wafer. Alternately, the utility waveguide 12 can include an optical grating (not shown) such as Bragg grating that acts as a reflector for an external cavity laser. In these instances, the light source 4 can include a gain element that is separate from the LIDAR chip and then attached to the LIDAR chip in a flip-chip arrangement. Examples of suitable interfaces between flip-chip gain elements and ridge waveguides on chips constructed from silicon-on-insulator wafer can be found in U.S. Pat. No. 9,705,278, issued on Jul. 11, 2017 and in U.S. Pat. No. 5,991,484 issued on Nov. 23, 1999; each of which is incorporated herein in its entirety. When the light source 4 is a gain element or laser chip, the electronics 32 can change the frequency of the outgoing LIDAR signal by changing the level of electrical current applied to through the gain element or laser cavity.
The above LIDAR systems include multiple optical components such as a LIDAR chip, LIDAR adapters, light source, light sensors, waveguides, and amplifiers. In some instances, the LIDAR systems include one or more passive optical components in addition to the illustrated optical components or as an alternative to the illustrated optical components. The passive optical components can be solid-state components that exclude moving parts. Suitable passive optical components include, but are not limited to, lenses, mirrors, optical gratings, reflecting surfaces, splitters, demulitplexers, multiplexers, polarizers, polarization splitters, and polarization rotators. In some instances, the LIDAR systems include one or more active optical components in addition to the illustrated optical components or as an alternative to the illustrated optical components. Suitable active optical components include, but are not limited to, optical switches, phase tuners, attenuators, steerable mirrors, steerable lenses, tunable demulitplexers, tunable multiplexers.
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.
