The disclosure relates to LIDAR system and methods, particularly but not exclusively, to a LIDAR transmitter system, a LIDAR system, and a method for emitting a LIDAR signal.
LIDAR is a technique of measuring a distance to a target. The target is illuminated with laser light and the reflected laser light is detected with a sensor. A time-of-flight measurement is made to establish the distance between the LIDAR system and different points on the target to build up a three-dimensional representation of the target.
An example of a known LIDAR transmitter system 100 is illustrated in
The VCSEL array 101 of
Some problems associated with known LIDAR transmitter systems 100 of the type shown in
(i) The fluctuation in the output signal voltage or current from the external detector 103 can be very high, making it difficult to establish a cause of malfunction of the LIDAR transmitter. For example, a fluctuating output signal may be caused by any one of: a prism, mirror or other optical component becoming misaligned (for example due to a moving component or motor breaking down), individual VCSELs malfunctioning and/or having reduced efficiency due to aging effects. It is very challenging to establish which of these is the cause of a transmitter malfunction based solely on the output signal current or voltage of the external detector 103.
(ii) The output signal voltage or current from the external detector 103 cannot determine the presence of hot or dark spots in the output beam. The terms hot spot and dark spot are used herein to portions of an output beam which have respectively higher or lower power than the rest of the beam.
(iii) The output signal voltage or current from the external detector 103 cannot distinguish between the output of individual emitters of the array.
It is an aim of the present disclosure to provide a LIDAR transmitter system, LIDAR system, and a method for emitting a LIDAR signal that addresses one or more of the problems above or at least provides a useful alternative.
In general terms, this disclosure proposes to overcome the above problems by arranging a photodetector with each laser energy source of the laser energy source array of the LIDAR transmitter system. This arrangement provides at least one or more of the following advantages over known LIDAR transmitter systems:
(i) With a photodetector arranged with each laser energy source, there are no prisms, mirrors or other optical components, or moving parts. Thus, any change in output signal voltage or current from the photodetectors can be immediately attributed to the laser energy sources rather than to any other component of the array. For example, when a drop in one or more photodetector outputs is detected, its cause can be directly attributed to a malfunction or decrease in efficiency in that corresponding laser energy source rather than to a problem with a prism, mirror, or other component of the transmitter.
(ii) Together, the output signal voltages or currents of the photodetectors provide a much higher resolution or granularity with which to monitor the array, for example up to individual emitter resolution. This permits, for example, the detection of hot (i.e. high intensity) or dark (i.e. low intensity) spots in the energy output to be made accurately and efficiently. If required, the detected hot or dark spots can also be compensated for more effectively than in known transmitter systems by controlling the corresponding laser energy source or laser energy sources of the array at the same, higher resolution. A scenario where this may be particularly useful is where a LIDAR transmitter system is required to output a high power beam when visibility is low in mist or fog. In such a scenario, any unexpected hot spots in the higher power beam could result in a risk to eye safety so monitoring the output beam is important. With the LIDAR transmitter system disclosed herein, the hot spots can immediately be compensated for by deactivating or reducing the output of laser energy sources contributing to the hotspots. Arranging a photodetector with each laser energy source of the array thus provides a means to guarantee eye safety and functional safety at higher power operation.
(iii) The malfunction or failure of individual emitters and/or rows or columns of emitters can be established more easily because any change in output signal voltage or current from individual photodetectors, or rows or columns thereof may directly indicate that the corresponding emitter and/or row of column of emitters is malfunctioning and/or not working as intended.
(iv) By integrating the respective photodetectors into the laser energy sources, any stray energy propagating in the array that could interfere with the LIDAR operation can be detected and compensated for. For example, if internal reflections and/or other noise can be measured at emitter level resolution at the transmitter, a much wider variety of noise reducing algorithms become available to use on the output of a corresponding LIDAR receiver. The photodetectors thus provide a powerful, built-in diagnostic tool not available in a transmitter system with an external detector.
(v) With space in LIDAR systems being at a premium, integrating the respective photodetectors into the laser energy sources reduces the reliance on prisms, optical components, motors and/or other moving parts all of which take up valuable space.
According to one aspect of the present disclosure, there is provided a LIDAR transmitter system comprising: an array of laser energy sources, each laser energy source comprising a corresponding photodetector, wherein the laser energy sources are configured to emit laser energy towards a LIDAR target, and wherein each respective photodetector is configured to detect the laser energy emitted by a corresponding energy source of the array.
Optionally, the array of laser energy sources comprises an array of vertical cavity surface emitting lasers (VCSELs) arranged on a wafer.
Optionally, each respective photodetector is arranged in, on or under a respective VCSEL.
Optionally, each VCSEL comprises a resonator comprising a first reflector at a first end and a second reflector at a second end opposite the first end, the laser energy emitted towards the LIDAR target is emitted from the first end, and the laser energy detected by the photodetector is emitted from the second end.
Optionally, the first and second reflectors comprise distributed Bragg reflectors.
Optionally, each respective photodetector comprises a photodiode arranged in, on or under a corresponding second reflector.
Optionally, the LIDAR transmitter system comprises a processor configured to: calculate a two-dimensional energy intensity profile of the array of laser energy sources from an output of the photodetectors; and determine from the two-dimensional energy intensity profile the presence of one or more energy intensity hot spots, energy intensity dark spots, and/or malfunctioning laser energy sources.
Optionally, the processor is configured to: control one or more of the laser energy sources to compensate for said energy intensity hots spots, energy intensity dark spots, and/or malfunctioning laser energy sources by: activating, deactivating, increasing and/or decreasing the energy output of one or more of the laser energy sources.
Optionally, each photodetector is configured to detect laser energy emitted from one or more other laser energy sources of the array of laser energy sources.
Optionally, the laser energy sources comprise edge emitters, LEDs and/or integrated laser energy sources.
According to a second aspect of the present disclosure, there is provided a LIDAR system, the LIDAR system comprising: the LIDAR transmitter system described above; and a LIDAR receiver system.
Optionally, the LIDAR system is configured to receive information from the LIDAR receiver system, combine said information with an output of the photodetectors, and control one or more of the laser energy sources by: activating, deactivating, increasing and/or decreasing the energy output of one or more of the laser energy sources.
Optionally, said information comprises driving condition information of a vehicle and/or ambient or environmental lighting information.
According to a third aspect of the present disclosure, there is provided a method for emitting laser energy towards a LIDAR target, the method comprising: emitting laser energy from an array of laser energy sources, each laser energy source comprising a photodetector;
Optionally, the array of laser energy sources comprises an array of VCSELs arranged on a wafer.
Optionally, each respective photodetector comprises a photodetector arranged in, on or under a respective VCSEL.
Thus, embodiments of this disclosure provide the above described advantages.
Some embodiments of the disclosure will now be described by way of example only and with reference to the accompanying drawings, in which:
In general terms, this disclosure provides a LIDAR transmitter system comprising an array of laser energy sources each comprising a corresponding photodetector. The photodetectors together provide a means to measure laser energy output at an individual emitter resolution and thus provide a means to more accurately measure and control the output of the array compared to known LIDAR transmitter systems.
Some examples of the solution provided by this disclosure are given in the accompanying figures.
Whilst an array of VCSELs is described herein as the array laser energy sources, it is envisaged that the present disclosure is equally applicable to any array of laser energy sources suitable for use with a LIDAR transmitter system such as arrays of edge emitters, integrated laser sources, LEDs and/or any combination thereof alone or together with VCSELs.
As described above, the array 201 of laser energy sources may comprise an array of VCSELs. The array of VCSELs may be arranged on a wafer and may be manufactured in an epitaxial process or integrated using wafer-bonding
The photodetector 304 may be arranged in, on or under one or more of the other layers of the VCSEL. The example shown in
All of the above described layers may further be arranged on a printed circuit board (PCB) 305 optionally connected by one or more readouts 306. The readouts 306 may comprise one or more electrical contacts to provide an interface to one or more processors configured to receive the photodetector output signals and/or control the VCSEL driving voltage or current signals applied through the electrical contacts. The interface provided hereby may comply with one or more known international standards and may be for example, a Mobile Industry Processor Interface (MIPI) interface. Typically, VCSELs in an array are addressable (i.e. controllable) on a column or row level however it is envisaged that they may also be addressed individually, or by region.
In both the examples of
Each photodetector 304 may comprise a photodiode, such as a pin diode, single photon avalanche diode, avalanche diode, or phototransistor.
The above described VCSEL layers and photodetectors may be formed and integrated as part of a single wafer manufacturing process, thus simplifying the manufacturing requirements of the LIDAR transmitter because no additional external components are required. For example, the VCSEL layers and photodetectors may be grown epitaxially or the photodetectors may be integrated into the VCSEL using wafer-bonding.
The array 201 of
The beam output by the array 400 may in some instances have one or more energy intensity hot spots and/or energy intensity dark spots caused by, for example, one or more malfunctioning laser energy sources 401. In the illustrative example of
Unlike in the case of known LIDAR transmitter systems which have an external detector and for which it would not be possible to distinguish between malfunctioning and/or correctly functioning individual laser energy sources, the presence of a photodetector for each laser energy source provides a diagnostics tool to determine, for example, that the laser energy sources 401 in the first region 402 are functioning correctly, but that the laser energy sources 401 in the second and third regions 403, 404 are not. This determination may be made on an individual laser energy source level resolution, on a row/column level resolution, and/or on a region level resolution as is shown in the example of
In the example of
From the example energy intensity profile of
For example, the laser energy sources in the second region 403 which produce a hot spot may be controlled to decrease output or be deactivated to compensate for or eliminate the hotspot. This could be achieved by reducing the driving current or voltage. Similarly, the laser energy sources in the third region 404 which produce a dark spot may be controlled to increase output (and/or the output laser energy sources in neighbouring rows, columns, regions or at individual level may be increased if the emitters causing the dark spot are dead and their output cannot be increased). This may be achieved by increasing the driving current or voltage. In this way, the hot spots and dark spots in the output beam and/or malfunctioning emitters can be compensated for accurately and without the need for any external sensors or other components.
Whilst the energy intensity profile 406 shown in the example of
The LIDAR system 500 may operate as a flash LIDAR where the LIDAR transmitter system 501 emits laser pulses (for example sub-nanosecond light pulses), or as a scanning LIDAR where the LIDAR transmitter system 501 emits a continuous, directed beam.
The LIDAR receiver system 502 may comprise a plurality of photodetectors, for example photodiodes, such as pin diodes, single photon avalanche diodes, avalanche diodes, or phototransistors configured to detect the laser energy reflected from the LIDAR target. Each photodetector of the LIDAR receiver system 502 acts as a detection pixel typically corresponding to one emitter in the array of the LIDAR transmitter system 501. The one-to-one pixel-emitter correspondence may be used to calculating a time-of-flight histogram which may be used to detect and compensate for any internal reflections 506 from, for example, optional cover glass 507 of the LIDAR system 500, or any cross-talk between laser energy sources of the array and a plurality of different detection pixels.
Typically, the signals detected by the LIDAR receiver system 502 show some fluctuation which may be caused by, for example, the above described hot spots, dark spots, and/or malfunctioning emitters, or by noise, internal reflections, cross-talk and/or other interference. In known LIDAR systems, it is difficult to determine when a fluctuation at a LIDAR receiver system pixel is due to noise, cross-talk or other interference, malfunctions or dead emitters in the LIDAR transmitter system. In known systems, it can thus be difficult to establish what actions need to be taken to improve the gain of the system. In contrast, the LIDAR system 500 provided herein may solve this problem by combining the output signal of the photodetectors in each laser energy source of the LIDAR transmitter system 501 with information received from the LIDAR receiver system 502 to provide automatic gain control.
For example, information from the LIDAR receiver system 502 indicating that a detection pixel has a weak detection signal may be combined with information from the photodetectors of the LIDAR transmitter system 501 indicating that the output beam has a dark spot corresponding to that detection pixel. The driving voltage or current to one or more laser energy sources may consequently be increased to eliminate the dark spot, improving the detection signal at the detection pixel.
Conversely, information from the LIDAR receiver system 502 indicating that one or more detection pixels are showing very strong signals may be combined with information from the photodetectors of the LIDAR transmitter system 501 indicating the presence of a hotspot in the output beam which is causing significant cross-talk. The driving voltage or current to one or more laser energy sources may consequently be decreased to eliminate the hot spot, reducing the cross-talk effect at the detection pixels.
The above described examples of automatic gain control provided by combining information received from the LIDAR receiver system 502 with the output of the photodetectors of the LIDAR transmitter system 501 are not intended to be limiting and it will be appreciated that other scenarios and combinations of receiver information being combined with light source photodetector output fall within the scope of the appended claims.
For example, the information received from the LIDAR receiver system 502 may comprise driving condition information of a vehicle on which the LIDAR system 500 is mounted and/or ambient or environmental lighting information. Thus, if driving conditions are bad (for example because visibility is low due to fog, mist, or adverse ambient or environmental lighting), this information may be used to increase the power of the output beam of the LIDAR transmitter system 501 to compensate. In this way, the power of the output beam may be controlled dynamically.
Embodiments of the present disclosure can be employed in many different applications including, for example, for 3D facial recognition, proximity detection, presence detection, object detection, distance measurements, and/or collision avoidance for example in the field of automotive vehicles or drones, and other fields and industries.
The skilled person will understand that in the preceding description and appended claims, positional terms such as ‘above’, ‘along’, ‘side’, etc. are made with reference to conceptual illustrations, such as those shown in the appended drawings. These terms are used for ease of reference but are not intended to be of limiting nature. These terms are therefore to be understood as referring to an object when in an orientation as shown in the accompanying drawings.
Although the disclosure has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in any embodiments, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.
Filing Document | Filing Date | Country | Kind |
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PCT/SG2020/050638 | 11/5/2020 | WO |
Number | Date | Country | |
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62931270 | Nov 2019 | US |