Controlling signal chirp in LIDAR systems

Abstract

The LIDAR system includes a light source that outputs an outgoing LIDAR signal. The LIDAR system also includes a plurality of phase difference generators, each of which combines a first optical signal and a second optical signal to generate a pulsation control signal. Each of the first optical signal and each of the second optical signals includes light from the outgoing LIDAR signal. The phase difference generators generate each pulsation control signal having a phase difference between the contribution of the first optical signal to the pulsation control signal and the contribution of the second optical signal to the pulsation control signal. The phase difference is different for each pulsation control signal from a different phase difference generator. Electronics apply the light source control signal to the light source to chirp the frequency of the outgoing LIDAR signal. The electronics are configured to modify the light source control signal in response to changes in the frequency of baseline crossings of the pulsation control signal.

Description

Field

[0001] The present invention relates to optical devices, and in particular to LIDAR systems.

[0002] There is growing commercial demand for LIDAR systems that can be deployed in applications such as ADAS (Advanced Driver Assistance Systems) and AR (Augmented Reality). LIDAR (Light Detection and Ranging) systems typically provide a system output signal that is reflected by objects outside the LIDAR system. At least a portion of the reflected optical signal returns to the LIDAR system. The LIDAR system directs the received optical signal to an optical sensor that converts the optical signal into an electrical signal. Electronics can use the output of the optical sensor to quantify LIDAR data indicative of the radial velocity and / or distance between the object and the LIDAR system.

[0003] Many LIDAR systems chirp the frequency of the system output signal linearly or with other well-defined waveforms over time to ensure accurate measurement of LIDAR data. In these cases, the LIDAR system can monitor the frequency of the system output signal and adjust the frequency accordingly to achieve a desired waveform shape. Systems used to monitor the frequency of the system output signal may require one or more delay waveguides used to create a time delay between an optical signal carried in one delay waveguide and an optical signal carried in another. These delay waveguides often need to be undesirably long to achieve the desired results. Increasing the length of the delay waveguides typically improves the quality of monitoring and adjusting the system output signal. However, the length of these delay waveguides often means that they occupy an undesirably large percentage of the available space in the LIDAR system. The length of these delay waveguides can also result in undesirably high levels of signal loss. High levels of loss in the arm waveguides can degrade signal quality. As a result, the lengths of the waveguides are often shortened to a level that degrades the chirp quality of the system output signal. As a result, there is a need for an improved system for controlling frequency chirp in LIDAR system output signals.

[0004] The LIDAR system includes a light source that outputs an outgoing LIDAR signal. The LIDAR system also includes a plurality of phase difference generators, each combining a first optical signal and a second optical signal to generate a pulsation control signal. Each of the first optical signals and each of the second optical signals include light from the outgoing LIDAR signal. The phase difference generators generate each pulsation control signal having a phase difference between the contribution of the first optical signal to the pulsation control signal and the contribution of the second optical signal to the pulsation control signal. The phase difference is different for each pulsation control signal from a different phase difference generator. Electronics apply the light source control signal to the light source to chirp the frequency of the outgoing LIDAR signal. The electronics are configured to modify the light source control signal in response to changes in the frequency of baseline crossings of the pulsation control signal.

[0005] A method of operating a LIDAR includes outputting an outgoing LIDAR signal from a light source. The method also includes generating a plurality of different pulsation control signals, each including a contribution from a first optical signal and a contribution from a second optical signal. Each of the first optical signals and each of the second optical signals includes light from the outgoing LIDAR signal. Each of the pulsation control signals is generated with a phase difference between the contribution of the first optical signal to the pulsation control signal and the contribution of the second optical signal to the pulsation control signal. The phase difference is different for each pulsation control signal from a different phase difference generator. The method also includes applying a light source control signal to the light source to chirp the frequency of the outgoing LIDAR signal. The light source control signal is altered in response to changes in the frequency of baseline crossings of the pulsation control signal. [Brief explanation of the drawings]

[0006] FIG. 1A is a top view of a schematic diagram of a LIDAR system including or consisting of a LIDAR chip that outputs a LIDAR output signal and receives a LIDAR input signal on a common waveguide.

[0007] FIG. 1B is a top view of a schematic diagram of a LIDAR system including or consisting of a LIDAR chip that outputs a LIDAR output signal and receives a LIDAR input signal on a different waveguide.

[0008] FIG. 1C is a top view of a schematic diagram of another embodiment of a LIDAR system that includes or is configured with a LIDAR chip that outputs a LIDAR output signal and receives multiple LIDAR input signals on different waveguides.

[0009] FIG. 2 is a top view of an example LIDAR adapter suitable for use with the LIDAR chip of FIG. 1B.

[0010] FIG. 3 is a top view of an example of a LIDAR adapter suitable for use with the LIDAR chip of FIG. 1C.

[0011] FIG. 4 is a top view of an example of a LIDAR system including the LIDAR chip of FIG. 1A and the LIDAR adapter of FIG. 2 on a common support.

[0012] FIG. 5A shows an example of an optical signal processor suitable for use in a LIDAR system.

[0013] FIG. 5B shows a schematic diagram of electronics suitable for use in an optical signal processor constructed according to FIG. 5A.

[0014] FIG. 5C is a frequency versus time graph of the system output signal with triangular frequency regulation.

[0015] FIG. 5D shows another example of an optical signal processor suitable for use in a LIDAR system.

[0016] FIG. 5E shows a schematic diagram of electronics suitable for use in an optical signal processor constructed according to FIG. 5D.

[0017] Figures 6A and 6B show an example of a control signal processor suitable for use as all or part of the control signal processor disclosed in the context of Figures 1A-1C. Figure 6A shows an interface between optical components and a light sensor that may be located on a LIDAR chip.

[0018] FIG. 6B is a schematic diagram of an example of the relationship between electronics and light sensors that may be included in a LIDAR chip.

[0019] FIG. 6C is a graph showing baseline crossings of the electrical pulsatile control signal versus time.

[0020] FIG. 6D is a schematic diagram of an example of another relationship between electronics and light sensors that may be included in a LIDAR chip.

[0021] Figure 6E is a graph of several different error signals over the duration of a frequency chirp. Figure 6E also is a graph of a composite error signal over the duration of a frequency chirp, where the composite error signal is generated from the illustrated error signals.

[0022] FIG. 6F is a graph of the composite error signal.

[0023] FIG. 6G shows an example of waveforms of the light source control signal and modified light source control signal for chirp durations in multiple data periods each associated with the same period index.

[0024] FIG. 7A is a schematic diagram of an example of the relationship between electronics and light sensors that may be included in a LIDAR chip.

[0025] FIG. 7B is a graph of the error signal over the duration of the frequency chirp.

[0026] FIG. 7C is a graph of the composite error signal.

[0027] FIG. 7D shows an example of waveforms of the light source control signal and modified light source control signal for chirp durations in multiple data periods each associated with the same period index.

[0028] FIG. 8 is a process flow for a method of operating an electronic device constructed as shown in FIG. 6D or FIG. 7A.

[0029] FIG. 9 is a voltage versus time graph illustrating example voltage levels of a light source control signal and a modified light source control signal.

[0030] Figure 10 is a cross-sectional view of a portion of a LIDAR chip containing a waveguide on a silicon-on-insulator platform.

[0031] FIG. 11 is a top view of a portion of a waveguide including a spiral waveguide.

[0032] The LIDAR system outputs a system output signal, at least a portion of which is reflected by an object outside the LIDAR system and returns to the LIDAR system. The LIDAR system can then use the reflected light to generate LIDAR data of the object. The LIDAR data indicates the radial velocity and / or distance between the object and the LIDAR system.

[0033] The LIDAR system includes a light source that outputs an outgoing LIDAR signal, the system output signal includes or consists of light from the outgoing LIDAR signal, and electronics that apply a light source control signal to the light source to chirp the frequency of the outgoing LIDAR signal.

[0034] The LIDAR system also includes a plurality of phase difference generators. Each phase difference generator combines the first optical signal and the second optical signal to generate a pulsating signal. The first optical signals from different phase difference generators include light from the outgoing LIDAR signal. The second optical signals from different phase difference generators include light from the outgoing LIDAR signal. Each phase difference generator is configured such that there is a phase difference between the contribution of the first optical signal to the pulsating signal and the contribution of the second optical signal to the pulsating signal. The phase difference is different for each pulsating signal from a different phase difference generator.

[0035] Each pulsatile signal includes a series of baseline crossings, such as zero crossings. The baseline crossings of the multiple pulsatile signals occur at a certain frequency. The electronics modify the light source control signal in response to changes in the frequency of the collective baseline crossings. For example, the electronics can modify the light source control signal in response to changes in the time difference between the baseline crossings of the pulsatile signals, where the time difference between the two baseline crossings can be measured between the baseline crossings of two different pulsatile signals.

[0036] The presence of multiple distinct pulsating signals increases the number and frequency of baseline crossings. Increasing the frequency of baseline crossings improves the resolution of the feedback used by the electronics to modify the light source control signal. As a result, increasing the number of baseline crossings results in a more reliable chirp of the outgoing LIDAR signal and the resulting system output signal. This increased reliability is achieved without the need for multiple delay waveguides, which would occupy an undesirably large amount of space on a semiconductor chip.

[0037] 1A is a top view of a schematic diagram of a LIDAR chip that can function as a LIDAR system or can be included in a LIDAR system that includes components in addition to the LIDAR chip. The LIDAR chip can include a photonic integrated circuit (PIC) or can be a photonic integrated circuit chip. The LIDAR chip includes a light source 4 that outputs a preliminary output LIDAR signal. Suitable light sources 4 include, but are not limited to, semiconductor lasers such as external cavity lasers (ECLs), distributed feedback lasers (DFBs), discrete mode (DM) lasers, and distributed Bragg reflector lasers (DBRs).

[0038] The LIDAR chip includes a utility waveguide 12 that receives the outgoing LIDAR signal from the light source 4. The utility waveguide 12 terminates at a facet 14 and conveys the outgoing LIDAR signal to the facet 14. The facet 14 can be positioned such that the outgoing LIDAR signal passing through the facet 14 exits the LIDAR chip and functions as the LIDAR output signal. For example, the facet 14 can be positioned at the end of the chip such that the outgoing LIDAR signal passing through the facet 14 exits the chip and functions as the LIDAR output signal. In some cases, a portion of the LIDAR output signal exiting the LIDAR chip can also be considered a system output signal. As an example, if the exit for the LIDAR output signal from the LIDAR chip is also the exit for the LIDAR output signal from the LIDAR system, then the LIDAR output signal can also be considered a system output signal.

[0039] The LIDAR output signal travels away from the LIDAR system through free space in the atmosphere and / or environment in which the LIDAR system is located. 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 returns toward the LIDAR chip as a LIDAR input signal. In some cases, the LIDAR input signal may also be considered a system return signal. As an example, if the exit of the LIDAR output signal from the LIDAR chip is also the exit of the LIDAR output signal from the LIDAR system, the LIDAR input signal may also be considered a system return signal.

[0040] A LIDAR input signal can be incident on utility waveguide 12 through facet 14. The portion of the LIDAR input signal incident on utility waveguide 12 serves as the incident LIDAR signal. Utility waveguide 12 carries the incident LIDAR signal to splitter 16. Splitter 16 transfers a portion of the outgoing LIDAR signal from utility waveguide 12 onto comparison waveguide 18 as a comparison signal. Comparison waveguide 18 carries the comparison signal to optical signal processor 22 for further processing. While FIG. 1A shows a directional coupler operating as splitter 16, other signal taps can also be used as splitter 16. Suitable splitters 16 include, but are not limited to, directional couplers, star couplers, optical couplers, y-junctions, tapered couplers, and multi-mode interference (MMI) devices.

[0041] The utility waveguide 12 also carries the outgoing LIDAR signal to a splitter 16. The splitter 16 transfers a portion of the outgoing LIDAR signal as a reference signal from the utility waveguide 12 onto a reference waveguide 20. The reference waveguide 20 carries the reference signal to an optical signal processor 22 for further processing.

[0042] The fraction of light redirected from the utility waveguide 12 by the splitter 16 can be fixed or substantially fixed. For example, the splitter 16 can be configured so that the power of the reference signal redirected to the reference waveguide 20 is an outgoing fraction of the power of the outgoing LIDAR signal, or so that the power of the comparison signal redirected to the comparison waveguide 18 is an incoming fraction of the power of the incoming LIDAR signal. In many splitters 16, such as directional couplers or multimode interferometers (MMIs), the outgoing fraction is equal to or substantially equal to the incoming fraction. In some cases, the outgoing fraction is greater than 30%, 40%, or 49% and / or less than 51%, 60%, or 70%; and / or the incoming fraction is greater than 30%, 40%, or 49% and / or less than 51%, 60%, or 70%. Splitters 16, such as multimode interferometers (MMIs), typically provide outgoing and incoming fractions of 50% or approximately 50%. However, multimode interferometers (MMIs) can be more easily fabricated in platforms such as silicon-on-insulator platforms than some other alternatives. In one example, splitter 16 is a multimode interferometer (MMI), and the outgoing and incoming fractions are 50% or substantially 50%. As described in more detail below, optical signal processor 22 combines the comparison signal and the reference signal to form a composite signal carrying LIDAR data for a sample area on the field of view. Thus, the composite signal can be processed to extract LIDAR data for the sample area (e.g., radial velocity and / or distance between the LIDAR system and an object external to the LIDAR system).

[0043] The LIDAR chip can include a control branch for controlling the 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 combined portion of the outgoing LIDAR signal serves as a tapped signal. While FIG. 1A shows a directional coupler acting as the splitter 26, other signal tapping elements can also be used as the splitter 26. Suitable splitters 26 include, but are not limited to, directional couplers, optical couplers, star couplers, y-junctions, tapered couplers, and multi-mode interference (MMI) devices.

[0044] The control waveguide 28 carries the tapped signal to a plurality of phase difference generators 29. Each phase difference generator 29 is associated with a phase difference generator index n (n=1 to N). Each phase difference generator 29 includes a control divider 30 that transfers a portion of the tapped signal from the control waveguide 28 onto a first waveguide 31. The combined portion of the tapped signal serves as a first control signal. The first waveguide 31 carries the first control signal to a control signal processor 36. While FIG. 1A shows a directional coupler operating as the control divider 30, other signal tapping sections can also be used as the control divider 30. Suitable control dividers 30 include, but are not limited to, directional couplers, star couplers, optical couplers, y-junctions, tapered couplers, and multimode interference (MMI) devices. Suitable numbers (N) of phase difference generators 29 include, but are not limited to, 2, 3, or 5 or more, but less than 6, 8, or 10 phase difference generators 29.

[0045] The utility waveguides 12 also carry the outgoing LIDAR signals to phase difference generators 29. Each phase difference generator 29 includes a utility divider 33 that moves a portion of the outgoing LIDAR signal from the utility waveguide 12 to a second waveguide 34. The combined portion of the outgoing LIDAR signal serves as a second control signal. The second waveguide 34 carries the second control signal to a control signal processor 36. The control signal processor 36 can be in electrical communication with the electronics 32 and / or all or a portion of the control signal processor 36 can be included in the electronics 32.

[0046] 1A shows a directional coupler operating as the utility divider 33, other signal tap sections can also be used as the utility divider 33. Suitable utility dividers 33 include, but are not limited to, directional couplers, star couplers, optical couplers, y-junctions, tapered couplers, and multi-mode interference (MMI) devices.

[0047] The control waveguide 28 may optionally be terminated with a signal dump 35 configured to prevent and / or reduce reflection of the tapped signal back into the control waveguide 28 .

[0048] LIDAR systems can be modified so that the incoming and outgoing LIDAR signals are carried on different waveguides. For example, FIG. 1B shows a top view of the LIDAR chip of FIG. 1A modified so that the incoming and outgoing LIDAR signals are carried on different waveguides. The outgoing LIDAR signal exits the LIDAR chip through facet 14 and serves as the LIDAR output signal. When light from the LIDAR output signal is reflected by an object external to the LIDAR system, at least a portion of the reflected light returns to the LIDAR chip as the first LIDAR input signal. The first LIDAR input signal enters comparison waveguide 18 through facet 35 and serves as the comparison signal. Comparison waveguide 18 carries the comparison signal to optical signal processor 22 for further processing. As described in the context of FIG. 1A, reference waveguide 20 carries the reference signal to optical signal processor 22 for further processing. As described in more detail below, optical signal processor 22 combines the comparison signal and the reference signal to form a composite signal that carries LIDAR data for the sample area within the field of view.

[0049] The LIDAR chip can be modified to receive multiple LIDAR input signals. For example, FIG. 1C shows the LIDAR chip of FIG. 1B modified to receive two LIDAR input signals. The splitter 40 is configured to place a portion of the reference signal carried on the reference waveguide 20 onto a first reference waveguide 42 and another portion of the reference signal onto a second reference waveguide 44. Thus, the first reference waveguide 42 carries the first reference signal, and the second reference waveguide 44 carries the second reference signal. The first reference waveguide 42 carries the first reference signal to a first optical signal processor 46, and the second reference waveguide 44 carries the second reference signal to a second optical signal processor 48. Examples of suitable splitters 40 include, but are not limited to, a y-junction, an optical coupler, and a multi-mode interference coupler (MMI).

[0050] The outgoing LIDAR signal exits the LIDAR chip through facet 14 and serves as the LIDAR output signal. When light from this LIDAR output signal is reflected by one or more objects external to the LIDAR system, at least a portion of the reflected light returns to the LIDAR chip as a first LIDAR input signal. This first LIDAR input signal enters comparison waveguide 18 through facet 35 and serves as a first comparison signal. Comparison waveguide 18 conveys the first comparison signal to first optical signal processor 46 for further processing.

[0051] Additionally, when light from the LIDAR output signal is reflected by one or more objects external to the LIDAR system, at least a portion of the reflected signal returns to the LIDAR chip as a second LIDAR input signal, which passes through facet 52 into second comparison waveguide 50 and serves as a second comparison signal carried by second comparison waveguide 50. Second comparison waveguide 50 carries the second comparison signal to second optical signal processor 48 for further processing.

[0052] Although the light source 4 is shown as being located on the LIDAR chip, the light source 4 can also be located off the LIDAR chip. For example, the utility waveguide 12 can terminate at a second facet that allows the outgoing LIDAR signal to enter the utility waveguide 12 from a light source 4 located off the LIDAR chip.

[0053] 1B or 1C is used in combination with a LIDAR adapter. In some cases, the LIDAR adapter can be physically and optically positioned between the LIDAR chip and one or more reflective objects and / or a field of view through which the first LIDAR input signal and / or LIDAR output signal travel an optical path from the LIDAR chip to the field of view through the LIDAR adapter. Additionally, the LIDAR adapter can be configured to operate on the first LIDAR input signal and the LIDAR output signal such that the first LIDAR input signal and the LIDAR output signal travel different optical paths between the LIDAR adapter and the LIDAR chip but travel the same optical path between the LIDAR adapter and reflective objects in the field of view.

[0054] An example of a LIDAR adapter suitable for use with the LIDAR chip of FIG. 1B is shown in FIG. 2. The LIDAR adapter includes multiple components disposed on a base. For example, the LIDAR adapter includes a circulator 100 disposed on a base 102. The illustrated optical circulator 100 includes three ports, such that light entering one port exits the next port. For example, the illustrated optical circulator includes a first port 104, a second port 106, and a third port 108. The LIDAR output signal enters the first port 104 from the utility waveguide 12 of the LIDAR chip and exits the second port 106.

[0055] The LIDAR adapter can be configured such that the output of the LIDAR output signal from the second port 106 also serves as the output of the LIDAR output signal from the LIDAR adapter, and thus from the LIDAR system. As a result, the LIDAR output signal can be output from the LIDAR adapter to travel toward a sample area within the field of view. Thus, in some cases, the portion of the LIDAR output signal output from the LIDAR adapter can also be considered a system output signal. As an example, if the output of the LIDAR output signal from the LIDAR adapter is also the output of the LIDAR output signal from the LIDAR system, the LIDAR output signal can also be considered a system output signal.

[0056] 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. Thus, the LIDAR output signal output from the LIDAR adapter may be the same as 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 example, the LIDAR output signal may experience optical loss as it passes through the LIDAR adapter, and / or the LIDAR adapter may optionally include an amplifier configured to amplify the LIDAR output signal as it passes through the LIDAR adapter.

[0057] When one or more objects within the sample volume reflect the LIDAR output signal, at least a portion of the reflected light returns to the circulator 100 as a system return signal. The system return signal enters the circulator 100 through a second port 106. Figure 2 shows how the LIDAR output signal and the system return signal travel along the same optical path between the LIDAR adapter and the sample volume.

[0058] The system return signal exits the circulator 100 through a third port 108 and is directed to a comparison waveguide 18 on the LIDAR chip. Thus, all or a portion of the system return signal can serve as the first LIDAR input signal, which can include or consist of light from the system return signal. Thus, the LIDAR output signal and the first LIDAR input signal travel along different optical paths between the LIDAR adapter and the LIDAR chip.

[0059] As is apparent from Figure 2, the LIDAR adapter may include optical components in addition to the circulator 100. For example, the LIDAR adapter may include components for directing and controlling the optical paths of the LIDAR output signal and the system return signal. As an example, the adapter of Figure 2 includes an optional amplifier 110 positioned to receive and amplify the LIDAR output signal before it enters the circulator 100. The amplifier 110 may be operated by the electronics 32, allowing the electronics 32 to control the power of the LIDAR output signal.

[0060] FIG. 2 also illustrates a LIDAR adapter including an optional first lens 112 and an optional second lens 114. The first lens 112 can be configured to couple the LIDAR output signal to a desired location. In some cases, the first lens 112 is configured to focus or collimate the LIDAR output signal to a desired location. In one example, if the LIDAR adapter does not include an amplifier 110, the first lens 112 can be configured to couple the LIDAR output signal onto the first port 104. As another example, if the LIDAR adapter includes an amplifier 110, the first lens 112 can be configured to couple the LIDAR output signal onto the input port to the amplifier 110. The second lens 114 can be configured to couple the LIDAR output signal to a desired location. In some cases, the second lens 114 is configured to focus or collimate the LIDAR output signal to a desired location. For example, the second lens 114 can be configured to couple the LIDAR output signal onto facet 35 of the comparison waveguide 18.

[0061] The LIDAR adapter may also include one or more redirectors, such as mirrors. Figure 2 shows a LIDAR adapter including a mirror as a redirector 116 that redirects the system return signal from the circulator 100 to the facet 20 of the comparison waveguide 18.

[0062] The LIDAR chip includes one or more waveguides that restrict the optical path of one or more optical signals. While the LIDAR adapter can include waveguides, the optical paths along which the system return signals and LIDAR output signals travel between components on the LIDAR adapter and / or between the LIDAR chip and components on the LIDAR adapter can be free space. For example, the system return signals and / or LIDAR output signals can travel through the air in which the LIDAR chip, LIDAR adapter, and / or base 102 are disposed as they travel between various components on the LIDAR adapter and / or between components on the LIDAR adapter and the LIDAR chip. As a result, optical components such as lenses and redirectors can be used to control the characteristics of the optical paths along which the system return signals and LIDAR output signals travel on, to, and from the LIDAR adapter.

[0063] Suitable bases 102 for LIDAR adapters include, but are not limited to, substrates, platforms, and plates. Suitable substrates include, but are not limited to, glass, silicon, and ceramic. The components can be discrete components attached to the substrate. Suitable techniques for attaching discrete components to the base 102 include, but are not limited to, epoxy, solder, and mechanical clamps. 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.

[0064] LIDAR systems can be configured to compensate for polarization. Light from a laser source is typically linearly polarized, and therefore the LIDAR output signal is typically linearly polarized as well. Reflection from an object can change the polarization angle of the returned light. Thus, the system return signal can contain light with different linear polarization states. For example, a first portion of the system return signal can contain light with a first linear polarization state, and a second portion of the system return signal can contain light with a second linear polarization state. The strength of the resulting composite signal is proportional to the cosine squared of the angle between the comparison signal polarization field and the reference signal polarization field. If this angle is 90 degrees, LIDAR data can be lost in the resulting composite signal. However, LIDAR systems can be modified to compensate for changes in the polarization state of the LIDAR output signal.

[0065] FIG. 3 shows the LIDAR system of FIG. 3 modified so that the LIDAR adapter is suitable for use with the LIDAR chip of FIG. 1C. The LIDAR adapter includes a beam splitter 120 that receives a system return signal from the circulator 100. The beam splitter 120 splits the system return signal into a first portion of the system return signal and a second portion of the system return signal. Suitable beam splitters include, but are not limited to, a Wollaston prism and a MEMS-based beam splitter.

[0066] A first portion of the system return signal is directed to a comparison waveguide 18 on the LIDAR chip and serves as the first LIDAR input signal described in the context of Figure 1C. A second portion of the system return signal is directed to a polarization rotator 122, which outputs a second LIDAR input signal that is directed to a second input waveguide 76 on the LIDAR chip and serves as the second LIDAR input signal.

[0067] The beam splitter 120 can be a polarizing beam splitter. One example of a polarizing beam splitter is constructed so that a first portion of the system return signal has a first polarization state but is free or substantially free of a second polarization state, and a second portion of the system return signal has a second polarization state but is free or substantially free of the first polarization state. The first and second polarization states can be linear polarization states, with the second polarization state being different from the first polarization state. For example, the first polarization state can be TE and the second polarization state can be TM. Alternatively, the first polarization state can be TM and the second polarization state can be TE. In some cases, the laser source can be linearly polarized such that the LIDAR output signal has the first polarization state. Suitable beam splitters include, but are not limited to, Wollaston prisms and MEMs-based polarizing beam splitters.

[0068] The 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 example, the polarization rotator 122 shown in FIG. 3 can be configured to change the polarization state of the second portion of the system return signal from the second polarization state to the first polarization state. As a result, the second LIDAR input signal has the first polarization state but does not have, or is substantially not having, the second polarization state. Thus, the first LIDAR input signal and the second LIDAR input signal each have the same polarization state (the first polarization state in this example). Despite carrying light of the same polarization state, the first LIDAR input signal and the second LIDAR input signal are associated with different polarization states as a result of the use of the polarizing beam splitter. For example, the first LIDAR input signal carries light reflected with the first polarization state, and the second LIDAR input signal carries light reflected with the second polarization state. As a result, the first LIDAR input signal is associated with the first polarization state, and the second LIDAR input signal is associated with the second polarization state.

[0069] Because the first LIDAR input signal and the second LIDAR input signal carry light of the same polarization state, the comparison signal resulting from the first LIDAR input signal has the same polarization angle as the comparison signal resulting from the second LIDAR input signal.

[0070] Suitable polarization rotators include, but are not limited to, polarization-maintaining fiber rotation, Faraday rotators, half-wave plates, MEMs-based polarization rotators, and integrated optical polarization rotators using asymmetric y-branches, Mach-Zehnder interferometers, and multimode interference couplers.

[0071] Because the outgoing LIDAR signal is linearly polarized, the first reference signal can have the same linear polarization state as the second reference signal. Additionally, components on the LIDAR adapter can be selected such that the first reference signal, the second reference signal, the comparison signal, and the second comparison signal each have the same polarization state. In the example disclosed in the context of FIG. 3, the first comparison signal, the second comparison signal, the first reference signal, and the second reference signal can each have light of a first polarization state.

[0072] As a result of the above configuration, the first composite signal generated by the first optical signal processor 46 and the second composite signal generated by the second optical signal processor 48 each result from combining a reference signal and a comparison signal in the same polarization state, thereby providing a desired pulsation between the reference signal and the comparison signal. For example, the composite signal may result from combining a first reference signal and a first comparison signal in a first polarization state, excluding or substantially excluding light in a second polarization state. Alternatively, the composite signal may result from combining a first reference signal and a first comparison signal in a second polarization state, excluding or substantially excluding light in the first polarization state. Similarly, the second composite signal includes a second reference signal and a second comparison signal in the same polarization state, thereby providing a desired pulsation between the reference signal and the comparison signal. For example, the second composite signal may result from combining a second reference signal and a second comparison signal in a first polarization state, excluding or substantially excluding light in the second polarization state. Alternatively, the second composite signal is produced from a combination of a second reference signal and a second comparison signal of a second polarization state, and excludes or substantially excludes light of the first polarization state.

[0073] With the above configuration, LIDAR data for a single sample area within the field of view is generated from multiple different composite signals (i.e., a first composite signal and a second composite signal) from the sample area. In some cases, measuring the LIDAR data for the sample area includes the electronics combining the LIDAR data from the different composite signals (i.e., the composite signal and the second composite signal). Combining the LIDAR data can include obtaining a mean, median, or mode of the LIDAR data generated from the different composite signals. For example, the electronics can average a distance between the LIDAR system and a reflecting object measured from the composite signal with a distance measured from the second composite signal, and / or the electronics can average a radial velocity between the LIDAR system and a reflecting object measured from the composite signal with a radial velocity measured from the second composite signal.

[0074] In some cases, measuring LIDAR data for the sample area includes the electronics identifying one or more composite signals (i.e., the composite signal and / or the second composite signal) as a source of LIDAR data that most closely represents reality (representative LIDAR data). The electronics can then use the LIDAR data from the identified composite signals as the representative LIDAR data for further processing. For example, the electronics can identify a signal (the composite signal or the second composite signal) with a larger amplitude as the representative LIDAR data and use the LIDAR data from the identified signal for further processing by the LIDAR system. In some cases, the electronics combine identifying the composite signal with the representative LIDAR data and combining LIDAR data from different LIDAR signals. For example, the electronics can identify each composite signal with an amplitude above an amplitude threshold as having representative LIDAR data, and if two or more composite signals are identified as having representative LIDAR data, the electronics can combine the LIDAR data from each of the identified composite signals. If one composite signal is identified as having representative LIDAR data, the electronics may use the LIDAR data from that composite signal as the representative LIDAR data. If none of the composite signals are identified as having representative LIDAR data, the electronics may discard the LIDAR data for the sample regions associated with those composite signals.

[0075] While FIG. 3 is described in the context of components being arranged such that the first comparison signal, the second comparison signal, the first reference signal, and the second reference signal each have a first polarization state, other configurations of components in FIG. 3 can be arranged such that the composite signal is the result of combining the reference signal and the comparison signal with the same linear polarization state, and the second composite signal is the result of combining the reference signal and the comparison signal with the same linear polarization state. For example, beam splitter 120 can be configured such that the second portion of the system return signal has a first polarization state, the first portion of the system return signal has a second polarization state, the polarization rotator receives the first portion of the system return signal, and the output LIDAR signal has a second polarization state. In this example, the first LIDAR input signal and the second LIDAR input signal each have a second polarization state.

[0076] The above system configuration directs the first portion of the system return signal and the second portion of the system return signal into different composite signals, such that the first portion of the system return signal and the second portion of the system return signal are associated with different polarization states, and the electronics can process each composite signal, such that the LIDAR system compensates for changes in the polarization state of the LIDAR output signal in response to reflections of the LIDAR output signal.

[0077] The LIDAR adapter of FIG. 3 can include additional optical components, including passive optical components. For example, the LIDAR adapter can include an optional third lens 126. The third lens 126 can be configured to couple the second LIDAR output signal to a desired location. In some cases, the third lens 126 can focus or collimate the second LIDAR output signal to a desired location. For example, the third lens 126 can be configured to focus or collimate the second LIDAR output signal onto facet 52 of the second comparison waveguide 50. The LIDAR adapter also includes one or more redirecting elements 124, such as mirrors or prisms. FIG. 3 illustrates a LIDAR adapter including a mirror as the redirecting element 124, which redirects a second portion of the system return signal from the circulator 100 to facet 52 of the second comparison waveguide 50 and / or the third lens 126.

[0078] When the LIDAR system includes a LIDAR chip and a LIDAR adapter, the LIDAR chip, electronics, and LIDAR adapter can be disposed 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, FIG. 4 is a top view of a LIDAR system including the LIDAR chip and electronics 32 of FIG. 1A and the LIDAR adapter of FIG. 2 mounted on a common support 140. While the electronics 32 is shown disposed on the common support, all or a portion of the electronics can be disposed remotely from the common support. When the light source 4 is disposed remotely from the LIDAR chip, the light source can be disposed on or remotely from the common support 140. Suitable approaches for mounting the LIDAR chip, electronics, and / or LIDAR adapter on the common support include, but are not limited to, epoxy, solder, and mechanical clamps.

[0079] A LIDAR system may include components including additional passive and / or active optical components. For example, a LIDAR system may include one or more components that receive a LIDAR output signal from a LIDAR chip or a LIDAR adapter. A portion of the LIDAR output signal from the one or more components may function as a system output signal. As an example, a LIDAR system may include one or more beam steering units that receive a LIDAR output signal from a LIDAR chip or a LIDAR adapter and output all or a portion of the LIDAR output signal that functions as a system output signal. For example, FIG. 4 shows a beam steering unit 142 that receives a LIDAR output signal from a LIDAR adapter. While FIG. 4 shows the beam steering unit disposed on the common support 140, the beam steering unit may be disposed on the LIDAR chip, on the LIDAR adapter, outside the LIDAR chip, or outside the common support 140. Suitable beam steering components include, but are not limited to, movable mirrors, MEMS mirrors, optical phased arrays (OPAs), and actuators that move the LIDAR chip, LIDAR adapter, and / or common support.

[0080] The electronics can operate one or more beam steering units 142 to steer the system output signal to different sample areas 144. The sample areas can extend away from the LIDAR system up to a maximum distance configured for the LIDAR system to provide reliable LIDAR data. The sample areas can be stitched together to define a field of view. For example, the field of view of a LIDAR system can include or consist of the space occupied by a combination of the sample areas.

[0081] 5A-5C illustrate an example of an optical signal processor suitable for use as all or part of an optical signal processor selected from the group consisting of optical signal processor 22, first optical signal processor 46, and second optical signal processor 48. The optical signal processor receives a comparison signal from a comparison waveguide 196 and a reference signal from a reference waveguide 198. The comparison waveguide 18 and reference waveguide 20 shown in FIGS. 1A and 1B can function as the comparison waveguide 196 and reference waveguide 198, the comparison waveguide 18 and first reference waveguide 42 shown in FIG. 1C can function as the comparison waveguide 196 and reference waveguide 198, or the second comparison waveguide 50 and second reference waveguide 44 shown in FIG. 1C can function as the comparison waveguide 196 and reference waveguide 198.

[0082] The optical signal processor includes a second splitter 200 that splits the comparison signal carried on the comparison waveguide 196 between a first comparison waveguide 204 and a second comparison waveguide 206. The first comparison waveguide 204 carries a first portion of the comparison signal to an optical signal combiner 211. The second comparison waveguide 208 carries a second portion of the comparison signal to an optical signal combiner 212.

[0083] The optical signal processor includes a first splitter 202 that splits a reference signal carried on reference waveguide 198 between a first reference waveguide 204 and a second reference waveguide 206. First reference waveguide 204 carries a first portion of the reference signal to optical signal combiner 211. Second reference waveguide 208 carries a second portion of the reference signal to optical signal combiner 212.

[0084] The optical signal combiner 212 combines the second portion of the comparison signal with the second portion of the reference signal to generate a second composite signal, where the second composite signal pulsates between the second portion of the comparison signal and the second portion of the reference signal due to the difference in frequency between the second portion of the comparison signal and the second portion of the reference signal.

[0085] The optical signal combiner 212 splits the resulting second composite signal into a first detector waveguide 214 and a second detector waveguide 216. The first detector waveguide 214 carries a first portion of the second composite signal to a first optical sensor 218, which converts the first portion of the second composite signal into a first auxiliary electrical signal. The second detector waveguide 216 carries a second portion of the second composite signal to a second optical sensor 220, which converts the second portion of the second composite signal into a second auxiliary electrical signal. Examples of suitable optical sensors include germanium photodiodes (PDs) and avalanche photodiodes (APDs).

[0086] In some cases, optical signal combiner 212 splits the second composite signal such that the portion of the comparison signal included in the first portion of the second composite signal (i.e., the second portion of the comparison signal) is phase-shifted 180 degrees relative to the portion of the comparison signal in the second portion of the second composite signal, but the portion of the reference signal in the second portion of the second composite signal (i.e., the second portion of the reference signal) is not phase-shifted relative to the portion of the reference signal in the first portion of the second composite signal. Alternatively, optical signal combiner 212 splits the second composite signal such that the portion of the reference signal in the first portion of the second composite signal (i.e., the second portion of the reference signal) is phase-shifted 180 degrees relative to the portion of the reference signal in the second portion of the second composite signal, but the portion of the comparison signal in the first portion of the second composite signal (i.e., the second portion of the comparison signal) is not phase-shifted relative to the portion of the comparison signal in the second portion of the second composite signal. Examples of suitable optical sensors include germanium photodiodes (PDs) and avalanche photodiodes (APDs).

[0087] The first optical signal combiner 211 combines the first portion of the comparison signal with the first portion of the reference signal to generate a first composite signal. Due to the difference in frequency between the first portion of the comparison signal and the first portion of the reference signal, the first composite signal pulsates between the first portion of the comparison signal and the first portion of the reference signal.

[0088] The first optical signal coupler 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 optical sensor 223, which converts the first portion of the second composite signal into a first electrical signal. The second detector waveguide 222 carries a second portion of the second composite signal to a second optical sensor 224, which converts the second portion of the second composite signal into a second electrical signal. Examples of suitable optical sensors include germanium photodiodes (PDs) and avalanche photodiodes (APDs).

[0089] In some cases, the optical signal combiner 211 splits the first composite signal such that a portion of the comparison signal included in the first portion of the composite signal (i.e., a portion of the first portion of the comparison signal) is phase-shifted 180 degrees relative to a portion of the comparison signal in the second portion of the composite signal (i.e., a portion of the first portion of the comparison signal), but a portion of the reference signal in the first portion of the composite signal (i.e., a portion of the first portion of the reference signal) is not phase-shifted relative to a portion of the reference signal in the second portion of the composite signal (i.e., a portion of the first portion of the reference signal). Alternatively, the optical signal combiner 211 splits the composite signal such that a portion of the reference signal in the first portion of the composite signal (i.e., a portion of the first portion of the reference signal) is phase-shifted 180 degrees relative to a portion of the reference signal in the second portion of the composite signal (i.e., a portion of the first portion of the reference signal), but a portion of the comparison signal in the first portion of the composite signal (i.e., a portion of the first portion of the comparison signal) is not phase-shifted relative to a portion of the comparison signal in the second portion of the composite signal (i.e., a portion of the first portion of the comparison signal).

[0090] When optical signal combiner 212 splits the second composite signal such that the portion of the comparison signal in the first portion of the second composite signal is phase-shifted 180 degrees relative to the portion of the comparison signal in the second portion of the second composite signal, optical signal combiner 211 also splits the composite signal such that the portion of the comparison signal in the first portion of the composite signal is phase-shifted 180 degrees relative to the portion of the comparison signal in the second portion of the composite signal. When optical signal combiner 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 180 degrees relative to the portion of the reference signal in the second portion of the second composite signal, optical signal combiner 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 180 degrees relative to the portion of the reference signal in the second portion of the composite signal.

[0091] 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 example, the first reference waveguide 210 and the second reference waveguide 208 can be constructed 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. Thus, one reference signal portion can be a sine function and the other reference signal portion can be a cosine function. As an example, the first reference waveguide 210 and the second reference waveguide 208 are constructed so that the first reference signal portion is a cosine function and the second reference signal portion is a sine function. Thus, the reference signal portion in the second composite signal is phase-shifted relative to the reference signal portion in the first composite signal. However, the comparison signal portion in the first composite signal is not phase-shifted relative to the comparison signal portion in the second composite signal.

[0092] The first optical sensor 223 and the second optical sensor 224 can be connected as a balanced detector, and the first optical sensor 218 and the second optical sensor 220 can also be connected as a balanced detector. For example, FIG. 5B is a schematic diagram showing the relationship between the electronics, the first optical sensor 223, the second optical sensor 224, the first optical sensor 218, and the second optical sensor 220. Although photodiode symbols are used to represent the first optical sensor 223, the second optical sensor 224, the first optical sensor 218, and the second optical sensor 220, one or more of these sensors may have other configurations. In some cases, all of the components shown in the schematic diagram of FIG. 5B are included on the LIDAR chip. In some cases, the components shown in the schematic diagram of FIG. 5B are distributed between the LIDAR chip and the electronics external to the LIDAR chip.

[0093] The electronics connect first photosensor 223 and second photosensor 224 as a first balanced detector 225, and connect first photosensor 218 and second photosensor 220 as a second balanced detector 226. Specifically, first photosensor 223 and second photosensor 224 are connected in series. Also, first photosensor 218 and second photosensor 220 are connected in series. The series connection in the first balanced detector communicates with a first data line 228, which carries the output from the first balanced detector as a first data signal. The series connection in the second balanced detector communicates with a second data line 232, which 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. Thus, the first data signal includes contributions from the first waveform and the second waveform, and the second data signal is a composite of the first waveform and the second waveform. A portion of a first waveform in the first data signal is phase-shifted relative to a portion of the first waveform in the first data signal, while a portion of a second waveform in the first data signal is in phase with a portion of the second waveform in the first data signal. For example, the second data signal includes a portion of a reference signal that is phase-shifted relative to another portion of the reference signal included in the first data signal. The second data signal also includes a portion of a comparison signal that is in phase with another portion of the comparison signal included in the first data signal. The first and second data signals pulsate as a result of the pulsation between the comparison signal and the reference signal, i.e., the pulsation in the first and second composite signals.

[0094] The electronics 32 includes a mathematical transformer 238 configured to perform a mathematical transform on the first and second data signals. For example, the mathematical transform may be a complex Fourier transform with the first and second data signals as inputs. The first data signal is the in-phase component and the second data signal is its quadrature component, such that the first and second data signals together function as a complex data signal, with the first data signal being the real component of the input and the second data signal being its imaginary component.

[0095] The mathematical converter 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 analog to digital format and outputs a first digital data signal. The mathematical converter 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 analog to digital format 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. Thus, the first digital data signal and the second digital data signal together function as a composite signal, with the first digital data signal functioning as the real component of the composite signal and the second digital data signal functioning as the imaginary component of the composite data signal.

[0096] The mathematical converter 238 includes a transform unit 268 that receives the composite data signal. For example, the transform unit 268 receives as input a first digital data signal from a first analog-to-digital converter (ADC) 264 and also receives as input a second digital data signal from a second analog-to-digital converter (ADC) 266. The transform unit 268 can be configured to perform a mathematical transform on the composite signal to convert it 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 explicit solution for the shift in frequency of the LIDAR input signal relative to the LIDAR output signal caused by the radial velocity between the reflecting object and the LIDAR tip. The electronics use one or more frequency peaks output from the transform unit 268 to generate LIDAR data (range and / or radial velocity between the reflecting object and the LIDAR tip or LIDAR system) for further processing. The converter 268 may use firmware, hardware, software, or a combination thereof to perform the specified functions.

[0097] FIG. 5C shows an example of the relationship between frequency, time, cycle, and data period of the system output signal. The fundamental frequency (f o ) may be the frequency of the system output signal at the start of the cycle.

[0098] Figure 5C shows the cycle j and cycle j+1 5C shows frequency versus time for a sequence of two cycles labeled "1" and "2." In some cases, the frequency versus time pattern is repeated for each cycle, as shown in FIG. 5C. The illustrated cycles do not include relocation periods and / or no relocation periods are interspersed between cycles. As a result, FIG. 5C shows the results of successive scans.

[0099] Each cycle is associated with a period index k, and k In the example of FIG. 5C, each cycle contains K data periods, denoted as DP k (k=1 and 2). In some cases, the frequency-versus-time patterns of corresponding data periods in different cycles are the same, as shown in FIG. 5C. Corresponding data periods are data periods with the same period index. As a result, each data period DP1 can be considered a corresponding data period, and the associated frequency-versus-time patterns in FIG. 5C are the same. At the end of the cycle, the electronics returns the frequency to the same frequency level as at the start of the previous cycle.

[0100] During data period DP1 and data period DP2, the electronics operate the light source so that the frequency of the system output signal changes as a linear function of time. The direction of the frequency change during data period DP1 is opposite to the direction of the frequency change during data period DP2. In some cases, the target rate of frequency change during data period DP1 is a constant represented by α, and the target rate of frequency change during data period DP2 is a constant represented by −α.

[0101] The frequency output from the complex Fourier transform represents the beat frequency of a composite signal that includes comparison signals that each beat relative to a reference signal. The beat frequencies (f LDP ) can be combined to generate LIDAR data. For example, the measured beating frequency from DP1 in FIG. 5C can be combined with the measured beating frequency from DP2 in FIG. 5C to measure LIDAR data. As an example, the following formula applies during a data period where the electronics increase the frequency of the outgoing LIDAR signal during the data period, as occurs in data period DP1 in FIG. 5C: f ub =-f d +ατ, where f ub is the frequency provided by the converter 268 (in this case, f measured from DP1). LDP ) and f d is the Doppler shift (f d =2υf c / c), where f c is the optical frequency (f o ), where c represents the speed of light, and υ is the radial velocity between the reflecting object and the LIDAR system, where the direction from the reflecting object toward the LIDAR system is assumed to be the positive direction and c is the speed of light. The following equation applies during data periods when the electronics reduce the frequency of the outgoing LIDAR signal, as occurs during data period DP2 in Figure 5C: f db =-f d -ατ, where f db is the frequency provided by the converter 268 (in this case, f measured from DP2) i,LDP ) In these two equations, f d and τ are unknowns. The electronics solve these two equations for the two unknowns. The radial velocity in the sample volume is then calculated as the Doppler shift (ν=c*f d / (2f c )) and the separation distance of the sample regions is c*f d It can be quantified from / 2.

[0102] In some cases, multiple objects are present in the sample volume. In some cases, when multiple objects are present in the sample volume, the transform outputs multiple frequencies, with each frequency associated with a different object. Frequencies arising from the same object in different data periods of the same cycle can be considered corresponding frequency pairs. For each corresponding frequency pair output by the transform, LIDAR data can be generated. As a result, separate LIDAR data can be generated for each object in the sample volume.

[0103] 5A-5B show an optical signal combiner that combines a portion of the reference signal with a portion of the comparison signal, the optical signal processor may include a single optical signal combiner that combines the reference signal with a portion of the comparison signal to form a composite signal. As a result, at least a portion of the reference signal and at least a portion of the comparison signal may be combined to form a composite signal. The portion of the reference signal that is combined may be the entire reference signal or a portion of the reference signal, and the portion of the comparison signal that is combined may be the entire comparison signal or a portion of the comparison signal.

[0104] As an example of an optical signal processor that combines a reference signal with a comparison signal to form a composite signal, Figures 5D-5E show the optical signal processor of Figures 5A-5B modified to include a single optical signal combiner. Comparison waveguide 196 carries the comparison signal directly to first optical signal combiner 211, and reference waveguide 198 carries the reference signal directly to first optical signal combiner 211.

[0105] The first optical signal coupler 211 combines the comparison signal and the reference signal into a composite signal. Due to the frequency difference between the comparison signal and the reference signal, the first composite signal pulsates between the comparison signal and the reference signal. The first optical signal coupler 211 also splits the composite signal into a first detector waveguide 221 and a second detector waveguide 222. The first detector waveguide 221 carries a first portion of the composite signal to a first optical sensor 223, which converts a first portion of the second composite signal into a first electrical signal. The second detector waveguide 222 carries a second portion of the composite signal to a second optical sensor 224, which converts a second portion of the second composite signal into a second electrical signal.

[0106] 5E shows a schematic diagram of the relationship between the electronics, first optical sensor 223, and second optical sensor 224. Although a photodiode symbol is used to represent first optical sensor 223 and second optical sensor 224, one or more of these sensors may have other configurations. In some cases, all of the components shown in the schematic diagram of FIG. 5E are included on the LIDAR chip. In some cases, the components shown in the schematic diagram of FIG. 5E are distributed between the LIDAR chip and electronics remote from the LIDAR chip.

[0107] The electronics connects the first photosensor 223 and the second photosensor 224 as a first balanced detector 225. In particular, the first photosensor 223 and the second photosensor 224 are connected in series. The series connection in the first balanced detector communicates with a first data line 228 that carries the output from the first balanced detector as a first data signal. This first data signal is an electrical representation of the composite signal.

[0108] The electronics 32 includes a mathematical transformer 238 configured to perform a mathematical transform on the first data signal. This mathematical transform may be a real Fourier transform with the first data signal as an input. The electronics can extract the LIDAR data using the frequencies output from the transform as described above.

[0109] Each of the balanced detectors disclosed in the context of Figures 5A through 5E can be replaced with a single optical sensor. As a result, the optical signal processor can include one or more optical sensors, each receiving at least a portion of the composite signal. This received portion of the composite signal can be the entire composite signal or a portion of the composite signal.

[0110] As described in the context of FIG. 5C , the electronics 32 adjusts the frequency of the system output signal. If the light source 4 is a gain element or laser chip, the electronics 32 can adjust the voltage applied to the light source to modulate the current through the light source. The voltage applied over time can serve as a light source control signal selected to achieve a desired frequency versus time pattern in the optical signal, including the light from the outgoing LIDAR signal. Additionally or alternatively, the light source 4 can include a modulator (not shown) configured to modulate the frequency of the outgoing LIDAR signal. If the light source 4 includes a modulator, the light source controller can apply the light source control signal to the modulator to achieve a desired frequency versus time pattern in the optical signal, including the light from the outgoing LIDAR signal. Suitable modulators include, but are not limited to, phase modulators. If the light source is or includes a resonator, the modulator can be located external to the resonator along the utility waveguide 12. Alternatively, if the light source is or includes a laser resonator, such as an external laser resonator (ECL), the modulator can be located externally within the resonator.

[0111] FIG. 6A illustrates the structure of a portion of a phase difference generator suitable for use as all or part of the phase difference generator 29 disclosed in the context of FIGS. 1A-1C and 4. As previously described, a first waveguide 31 carries a first control signal to a control signal processor 36, and a second waveguide 34 carries a second control signal to the control signal processor 36. The control signal processor 36 includes an optical signal combiner 286. The optical signal combiner 286 combines the first and second control signals into a pulsation control signal. The phase difference between the contribution of the first control signal to the pulsation control signal and the contribution of the second control signal to the pulsation control signal is different for different phase difference generators 29. For example, the contribution of the first control signal to the pulsation control signal and the contribution of the second control signal to the pulsation control signal may be Φ n where Φ n =π(n-1) / N, and Φ n represents the phase difference of the phase difference generator 29 associated with the phase difference generator index n, and N represents the number of phase difference generators 29 associated with the phase difference generator index. As a result, the phase difference (Φ n ) is between 0 and π, and the adjacent phase difference (Φ n ) can be π / N.

[0112] A first optical path taken by the light included in the first control signal from the splitter 26 to the optical signal combiner 286 can have a different length than a second optical path taken by the light included in the second control signal from the splitter 26 to the optical signal combiner 286. As a result, the first optical path, the second optical path, the splitter 26, and the optical signal combiner 286 in each phase difference generator 29 can function as a Mach-Zehnder interferometer.

[0113] The lengths of the first and second optical paths are set to provide the desired phase difference (Φ n For example, the phase difference (Φ n) is a function of the length of the first optical control path from the divider 26 to the utility divider 33 of the phase difference generator 29, the length of the second optical control path from the divider 26 to the control divider 30 of the phase difference generator 29, the length of the first waveguide 31, and the length of the second waveguide 34. Thus, the lengths of the optical control paths and / or waveguides are determined to provide the desired phase difference (Φ n ) The control waveguide 28 may include a delay section 37 that may be used to increase the length of the control waveguide 28. For example, the delay section 37 shown in FIG. 1A may represent a spiral arrangement of the control waveguide 28 to reduce the amount of space that the delay section 37 takes up on the LIDAR chip.

[0114] The electronics can adjust the frequency of the light source outgoing LIDAR signal contained in the first control signal and the second control signal, so that the second control signal has a different frequency than the first control signal due to the delay caused by the phase difference. Due to the difference in frequency between the second control signal and the first control signal, the pulsating control signal pulsates between the first control signal and the second control signal.

[0115] The optical signal combiner 286 also splits the pulsatile control signal into a first detector waveguide 294 and a second detector waveguide 296. The first detector waveguide 294 carries a first portion of the pulsatile control signal to a first optical sensor 298. The first optical sensor 298 converts the first portion of the pulsatile control signal into a first electrical signal. The second detector waveguide 296 carries a second portion of the pulsatile control signal to a second optical sensor 300. The second optical sensor 300 converts the second portion of the pulsatile control signal into a second electrical signal. Examples of suitable optical sensors include germanium photodiodes (PDs) and avalanche photodiodes (APDs).

[0116] In some cases, the optical signal combiner 286 splits the pulsation control signal so that the portion of the first signal included in the first portion of the pulsation control signal is phase shifted by 180 degrees relative to the portion of the first signal included in the second portion of the pulsation control signal.

[0117] An example of a suitable optical signal combiner 286 is a multi-mode interference (MMI) device, such as a 2x2 MMI device. Other suitable optical signal combiners 286 include, but are not limited to, adiabatic splitters and directional couplers. In some cases, the functionality of the illustrated optical signal combiner 286 is performed by multiple optical components or combinations of optical components.

[0118] FIG. 6B is a schematic diagram illustrating the relationship between the electronics and the different phase difference generators 29. Photodiode symbols are used to represent the first light sensor 298 and the second light sensor 300, although one or more of these sensors may have other configurations. In some cases, all of the components shown in the schematic diagram of FIG. 6B are included on the LIDAR chip. In some cases, the components shown in the schematic diagram of FIG. 6B are distributed between the LIDAR chip and electronics that are off the LIDAR chip.

[0119] The first optical sensor 298 and the second optical sensor 300 can be connected as a balanced detector. For example, in Figure 6B, the electronics connect the first optical sensor 298 and the second optical sensor 300 as a balanced detector 314. In particular, the first optical sensor 298 and the second optical sensor 300 are connected in series. The series connection in the balanced detector communicates with a data line 318 that carries the output from the balanced detector as an electrical beat control signal.

[0120] The electrical pulsatile control signal is an electrical representation of the pulsatile control signal and therefore pulsates at the pulsatile frequency of the pulsatile control signal.

[0121] The electrical pulse control signal is received by a waveform converter 320, which outputs a converted signal. The waveform converter 320 is configured to convert the waveform of the electrical pulse control signal from a sinusoidal current to a square wave voltage or a substantially square wave voltage. Thus, the waveform converter 320 outputs the converted signal. In one example, the waveform converter includes an amplifier 322 connected in series with a comparator 324, such that the amplifier 322 receives the electrical pulse control signal and the comparator outputs the converted signal. Suitable waveform converters 320 include, but are not limited to, a linear transimpedance amplifier (TIA) followed by a voltage comparator, a nonlinear limiting TIA followed by a comparator, and a current-mode comparator.

[0122] Each of the phase difference generators 29 outputs a different converted signal. The electronics 32 includes a digital logic gate 329 that receives the converted signals from the phase difference generators 29. Suitable digital logic gates 329 include, but are not limited to, combinational logic-based edge combiners, such as XOR gates and dedicated OR gates, and cascade logic-based edge combiners. As a result, the digital logic gate outputs a falling edge or a rising edge depending on which of the converted signals has a baseline crossing. Otherwise, the output of the digital logic gate does not undergo conversion. In some cases, the baseline crossing of the converted signal is a zero crossing of the converted signal.

[0123] Figure 6C shows the Φ n =π(n-1 / N) according to the phase difference (Φ n 2 shows a schematic diagram of the time variation of the amplitude of the logic signal of the N=4 phase difference generator 29 that provides the phase difference (Φ n) represent the phase difference between the first and second signals in the pulsation control signals of the different phase difference generators 29. The voltage transitions indicated by the arrows in FIG. 6C each occur at the time of one baseline crossing of the converted signal, and thus at the time of a baseline crossing of the electrical pulsation control signal. As a result, FIG. 6C can represent a graph of the timing of the baseline crossings of the converted signal. Because the converted signal is a transformation of the electrical pulsation control signal, the baseline crossings of the converted signal can represent the baseline crossings of the electrical pulsation control signal. For example, FIG. 6C can represent a graph of the zero crossings of the converted signal and / or the zero crossings of the electrical pulsation control signal over time. Each falling or rising edge indicated by an arrow is labeled with the phase difference generator index (n), which is the source of the baseline crossing that caused the high voltage value.

[0124] Each first signal and each second signal includes, consists of, or consists essentially of light from the outgoing LIDAR signal. As a result, if the frequency of the outgoing LIDAR signal has a linear chirp, the phase difference (Φ n ) are spaced apart by a constant π / N (π / 4 in this example). Thus, if the frequency chirp of the outgoing LIDAR signal is linear, the time difference between adjacent edges in the logic signal (denoted as g in FIG. 6C) remains constant over the duration of the chirp. As a result, if the frequency chirp of the outgoing LIDAR signal is linear, the time difference between baseline crossings is constant over the duration of the chirp. However, if the actual chirp rate (α a ) deviates from the target chirp rate (α), the time difference between adjacent edges in the logic signal (denoted by g in FIG. 6C) changes over time. As a result, the change in the time difference between adjacent edges indicates a nonlinear chirp and a variable chirp rate. Therefore, the time difference between adjacent edges in the logic signal, and the time difference between baseline crossings in the pulsatile signal, varies with the actual chirp rate (α a ) is a function of the actual chirp rate (α aIncreasing the chirp rate (α ) decreases the time difference between adjacent edges and baseline crossings in the logic signal (denoted by g in Figure 6C). a ), the time difference between adjacent edges and baseline crossings in the logic signal (denoted by g in FIG. 6C) increases.

[0125] The time difference is related to the frequency of baseline crossings of the pulsatile signal. For example, the frequency can be approximated as 1 / g. If the frequency chirp of the outgoing LIDAR signal is linear, the frequency of the baseline crossings remains constant over the duration of the chirp. If the frequency chirp of the outgoing LIDAR signal is linear, the time difference between baseline crossings remains constant over the duration of the chirp. However, the actual chirp rate (α a As the chirp rate (α) deviates from the target chirp rate (α), the frequency changes over time. As a result, the change in frequency of the baseline crossings indicates a nonlinear chirp and a variable chirp rate. Therefore, the frequency of the baseline crossings in the pulsatile signal is a function of the actual chirp rate (α) of the outgoing LIDAR signal. For example, a ) increases the frequency of crossings of the pulsatile signal, while decreasing the actual chirp rate (α) increases the frequency of these crossings.

[0126] The chirp rate (α) represents the target chirp rate of the outgoing LIDAR signal during the data period. The actual time difference between adjacent edges (g a ) is the actual chirp rate (α a ), the target chirp rate is a function of the target time difference (g t ) because the time difference between adjacent edges also represents the time difference between baseline crossings. a ) can represent the actual time difference between baseline crossings of the pulsatile signal, and the target time difference (g t ) can represent the target time difference between the beat signals. a ) can represent a function of multiple actual time differences. For example, the actual time difference (g a) can represent the averaged time difference value of several different time differences. Similarly, the actual frequency (f a ) can represent a function of multiple baseline crossings. For example, the actual frequency (f a ) can each represent a frequency averaged over multiple baseline crossings.

[0127] Target frequency (f t ) can each be associated with a particular data period. For example, data periods with the same period index k have a target chirp rate and an associated target frequency (f t ) can be associated with a target chirp rate and associated target frequency (f) associated with data periods with different period indices (k). t ) may be different or the same. The system determines the target frequency (f) associated with the data period having period index k. t ), the outgoing LIDAR signal can be maintained at a desired chirp rate for a data period having period index k.

[0128] Each target chirp rate and associated target time difference can be associated with a particular data period. For example, data periods having the same period index k can be associated with a target chirp rate and associated target time difference. The target chirp rates and associated target time differences associated with data periods having different period indexes (k) can be different or the same. As previously mentioned, the system can determine the target frequency (f) associated with a data period having period index k. t ), the outgoing LIDAR signal can be maintained at a desired chirp rate for a data period having period index k. In one example, the system measures the actual time difference between adjacent edges (g a ), or the actual time difference between adjacent baseline crossings (g a ) as the target time difference (g t) associated with a data period having period index k, by operating the system to maintain or substantially maintain a target frequency (f t ) to maintain or substantially maintain the frequency of baseline crossings.

[0129] The system uses a feedback loop, such as a phase-locked loop (PLL), to measure the actual time difference (g a ) to the target time difference (g t The system can be operated to maintain or substantially maintain the phase difference (g) of the logic signal. An example phase-locked loop can lock the phase of the logic signal to the phase of a local oscillator. The error signal generator can generate an error signal that is proportional to the actual time difference (g a ) and target time difference (g t ) and outputs an error signal having one or more characteristics indicative of the level and direction of mismatch between the chirp rate (α a ) and the target chirp rate (α).

[0130] For example, the electronics 32 shown in FIG. 6B includes a schematic diagram of an example error signal generator 330, which may be an analog error signal generator. The error signal generator 330 includes a phase detector 332 that receives a logic signal and outputs an example error signal. The phase detector 332 may be an analog phase detector. As a result, the error signal may be an analog signal.

[0131] The error signal generator 330 includes a local oscillator 334 that outputs a local signal that is also received by the phase detector 332. The local signal may be a continuous wave of fixed frequency and phase. The frequency of the local signal is determined by the frequency at which the local signal reaches the target time difference (g t ) are selected to have baseline crossings separated by a target time difference (g t) separated by . In one example, the frequency of the local signal is selected to be the same as the frequency of the logic signal shown in FIG. 6C. As a result, when the phase of the logic signal matches the phase of the local signal, the edges in the logic signal align with the baseline crossings of the local signal. Therefore, when the phase of the local signal matches the phase of the logic signal, the sign and magnitude of the error signal do not indicate an error in the logic signal. However, the actual chirp rate (α) of the outgoing LIDAR signal a ) moves away from the target chirp rate (α), the magnitude and sign of the error signal change with the actual chirp rate (α a ) and the target chirp rate (α). Therefore, the local oscillator 334 t ) as a reference. Suitable local oscillators include, but are not limited to, a MEMS oscillator, a crystal oscillator, or an electronic phase-locked loop locked to a MEMS or crystal oscillator.

[0132] The error signal generator 330 may optionally include a filter 338, such as a low-pass filter, that receives the error signal and outputs a filtered version of the error signal.

[0133] Suitable phase detectors include, but are not limited to, analog mixed-base phase detectors, digital phase detectors, or flip-flop-based phase frequency detectors. Suitable local oscillators include, but are not limited to, MEMS oscillators, crystal oscillators, or electronic phase-locked loops locked to MEMS or crystal oscillators. Suitable filters 338 include, but are not limited to, analog RC filters and digital filters.

[0134] The error signal is received by a control signal generator 340, which uses the error signal to modify a light source control signal that a light source controller 342 applies to the light source 4 to cause the light source to output light that is included in the emitted LIDAR signal. For example, the light source control signal may indicate the level of voltage applied to the light source 4 for the duration of the frequency chirp, or the level of voltage applied to a modulator included in the light source.

[0135] The control signal generator 340 can modify the light source control signal to modify the magnitude and direction of the error indicated by the error signal. For example, if the error signal modifies the actual time difference (g a ) is the target time difference (g t ), the control signal generator 340 will calculate the actual time difference (g a ) and target time difference (g t ) difference. In one example, the control signal generator 340 may modify the light source control signal to reduce the actual time difference (g a The light source control signal can be changed so that the actual time difference (g a ) can be achieved by changing the light source control signal to decrease the voltage applied to the light source by about 10%.

[0136] The modified light source control signal is received by light source controller 342. Light source controller 342 applies the modified light source control signal to light source 4 as a light source control signal that can later be modified by control signal generator 340. As a result, the light source control signal can be changed multiple times during a data period. Thus, the modification of the light source control signal can be performed in real time and / or "on the fly."

[0137] As mentioned above, the light source control signal is applied to the light source to determine the actual time difference (g a ) and target time difference (g t) is changed to reduce the difference between it and the local signal. Reducing this difference locks the phase of the logic signal to the phase of the local signal. Because the phase of the local signal is constant, the phase of the logic signal also remains constant. Because a linear chirp produces a logic signal with constant phase, the constant phase of the logic signal indicates the presence of a linear chirp. As a result, the light source control signal is controlled by a feedback loop in which the phase of the logic signal is locked to the phase of the local signal.

[0138] The control signal generator 340 and the light source controller 342 may be the same component or different components. In some cases, the control signal generator 340 and the light source controller 342 are integrated into the same component. Examples of suitable control signal generators 340 include, but are not limited to, DSP chips, FPGAs, and microprocessors. Examples of suitable control signal generators 340 perform their functions using firmware, hardware, software, or a combination thereof. Examples of suitable light source controllers 342 include, but are not limited to, a current-mode DAC or a voltage DAC followed by a transconductance amplifier.

[0139] FIG. 6D illustrates the electronics and relationship of the phase difference generator 29 of FIG. 6B modified for use with a digital error signal generator 330. The error signal generator 330 may include a digital phase detector 332 and a filter 338. The error signal output from the phase detector 332 may be a digital signal received by a storage device 344. Once the filter 338 receives the error signal, the filtered error signal from the filter 338 may be a digital signal received by the storage device 344. The storage device stores the error signals from multiple different data periods for the duration of a frequency chirp in the data period. As an example, the solid lines in FIG. 6E illustrate an example of error signals stored for four different data periods, each associated with k=1 (DP1). The y-axis represents the direction and magnitude of the error indicated by the error signal. For example, the error shown on the y-axis may be the actual time difference (g) between adjacent edges in a logic signal. a ) and target time difference (g t) in a logic signal. In one example, the error shown on the y-axis is the actual time difference between adjacent edges in the logic signal (g a ) and the target time difference between adjacent edges in the logic signal (g t ) Suitable storage devices 344 include random access memory (RAM).

[0140] The control signal generator 340 accesses signals stored in memory device 344. The control signal generator 340 can generate one or more composite error signals from all or a portion of the stored error signals, depending on a threshold number of error signals from data periods having the same period index k stored in memory device 344. For example, the control signal generator 340 can average error signals from different data periods, each having the same period index k, to generate a composite error signal that is an average of the error signals as a function of time. As an example, the dashed line in FIG. 6E can represent the average of the stored error signals from data periods associated with the same period index (k=1). This dashed line can represent the composite error signal over the duration of the frequency chirp during the data period.

[0141] The solid line in Figure 6E is associated with period index k=1 (DP1), and therefore the resulting composite error signal is also associated with period index k=1 (DP1). Accordingly, the dashed lines shown in Figure 6E are each associated with a data period associated with k=1 (DP1). However, the control signal generator 340 can generate composite error signals for all or some of the different period indices (k). In some cases, the control signal generator 340 stores the composite error signals over time in the storage device 344 for one or more of the different period indices (k).

[0142] While the signals in FIG. 6E appear to be analog signals, these signals may also be digital signals. As a result, the time axis may be divided into time segments, each having a fixed duration. For purposes of illustration, the time segments in the signals in FIG. 6E are short enough so that the digital signal appears continuous over time. For purposes of illustration, FIG. 6F depicts the composite error signal of FIG. 6E as a digital signal divided into multiple time segments. The time segments shown in FIG. 6F are longer than those in FIG. 6E so that the digital nature of the composite error signal is more readily apparent in the image.

[0143] In some cases, the control signal generator 340 determines whether to generate a modified light source control signal. The control signal generator 340 can calculate a composite error level of the composite error signal. For example, the control signal generator 340 can calculate the deviation or root mean square of the composite error signal over the duration of the chirp. The control signal generator 340 can compare the composite error level to one or more error criteria to determine whether to generate a modified light source control signal. For example, the control signal generator 340 can compare the composite error level to an error threshold. If the composite error level exceeds the error threshold, the control signal generator 340 can generate a modified light source control signal. If the composite error level falls below the error threshold, the control signal generator 340 can refrain from generating the modified light source control signal.

[0144] The control signal generator 340 can modify the waveform of the light source control signal to modify the magnitude and direction of the error indicated by the composite error signal. Figure 6G shows an example of the waveform of the light source control signal during the duration of a chirp in different data periods, each associated with the same period index (k). Each voltage level shown indicates the voltage applied to the light source 4 during the associated time segment. The voltage level labeled V0 represents the waveform of the light source control signal. Thus, a series of digital signals or bits representing the series of voltage levels labeled V0 over the duration of the chirp can serve as a digital representation of the light source control signal.

[0145] The control signal generator 340 changes the waveform of the light source control signal (V0) to change the voltage level (V m ) can be expressed as follows: m represents the waveform of the modified light source control signal. As a result, V m A series of digital signals or bits representing a series of voltage levels, denoted as , can serve as a digital representation of the modified light source control signal.

[0146] Altering the light source control signal can modify the magnitude and direction of the error indicated by the composite error signal. For example, control signal generator 340 can alter the light source control signal to generate an altered light source control signal that reduces the magnitude of the error level indicated by the composite error signal. As an example, FIG. 6F can represent a composite error signal obtained by applying the light source control signal of FIG. 6G to the light source during a data period having the same period index associated with the composite error signal. The error on the y-axis of FIG. 6F can represent the percentage difference, where the percentage difference is the actual time difference (g) between adjacent edges in the logic signal. a ) and the target time difference (g t ) represents a percentage difference from the actual time difference (g) for that time segment. The light source control signal can be changed so that the applied voltage during each time segment is changed by the percentage difference for that time segment, but in the opposite direction. For example, a ) is the target time difference (g t ) is 10% less than the V m The value is V m =V0*(1-(er / 100)), where er represents the percentage difference and V m , V o , and er values ​​are associated with the same time interval. m The error value denoted as V can represent the modified waveform of the light source control signal.m The digital signal representing the series of error values, denoted as , can serve as a modified light source control signal.

[0147] Each light source control signal is associated with a different data period, and therefore a different period index, such that control signal generator 340 can generate different modified light source control signals associated with different period indexes.

[0148] While the above example of modifying the light source control signal modifies the light source control signal in proportion to the level of error indicated by the composite error signal, other relationships or more complex filtering and signal shaping may be used. For example, an association between changes in the light source control signal and different error values ​​may be stored in storage device 344. For a particular composite error, control signal generator 340 may modify the light source control signal as indicated by the change in the light source control signal associated with the particular composite error. The association between the composite error and changes in the light source control signal may be represented by a data structure such as a lookup table, a mathematical formula, a filter, and / or an adaptive filter.

[0149] The modified light source control signal is received by light source controller 342. Light source controller 342 may include a digital-to-analog converter that receives the modified light source control signal and converts the modified light source control signal to an analog signal. The digital-to-analog converter outputs an analog version of the modified light source control signal, and light source controller 342 applies the analog version of the modified light source control signal to light source 4. Because different light source control signals are associated with different data periods and therefore different period indices, light source controller 342 applies the modified light source control signal such that the data periods and the light source control signal applied to the light source are associated with the same period indices. As a result, different light source control signals can be applied to the light source for different data periods within a cycle. Furthermore, the same light source control signal can be applied to data periods for multiple different cycles. Therefore, the light source control signal does not need to be applied in-place.

[0150] The digital version of the modified light source control signal can be stored in a memory device and can serve as a light source control signal that can later be modified by the control signal generator 340 .

[0151] After generating a composite error signal associated with a data period index, the control signal generator 340 may clear the memory to store another set of error signals associated with that data period index. The control signal generator 340 and light source controller 342 may repeat the process of generating and applying modified light source control signals once the number of error signals in the set exceeds a threshold number.

[0152] FIG. 7A is a schematic diagram illustrating another example of the relationship between the electronics and the different phase difference generators 29. Each phase generator includes a counter 346 that receives the converted signal from the waveform converter 320. Each counter also receives an event signal from a clock 348, such as a time-to-digital converter. The event signal may indicate the occurrence of an event, such as the arrival of an incoming electrical pulse. Each counter 346 may count the number of baseline crossings in the converted signal during a time interval. For example, each counter 346 may count the number of zero crossings in the converted signal during a time interval. Suitable counters include, but are not limited to, synchronous counters.

[0153] Each counter outputs a counter data signal indicative of the number of baseline crossings during a different time interval. The counter data signals output from the different phase difference generators 29 are received by an error signal generator 330. The error signal generator 330 can be a digital component, such as a digital controller, processor, or microprocessor. As a result, the error signal generator 330 can include and / or perform the functionality of the control signal generator 340 disclosed in the context of FIG. 6D. Alternatively, the electronics of FIG. 7A can include the control signal generator 340 in addition to the error signal generator 330.

[0154] In addition to receiving the counter data signal, the error signal generator 330 can receive the duration of each time interval from the clock. The error signal generator 330 can measure the period between baseline crossings in each of the different converted signals by dividing the number of baseline crossings during the time interval by the duration of the time interval. Furthermore, by accumulating the time intervals, the error signal generator 330 can identify the time at which the leading edge of each converted signal, and accordingly each electrical beat control signal, occurs. The time of the leading edge of each converted signal combined with the period between the baseline crossings of the converted signals indicates the time at which each baseline crossing occurs. The timing of baseline crossings from different converted signals plotted on the same timeline provides a graph such as the graph in FIG. 2C. As a result, the error signal generator 330 can combine the timing of baseline crossings from the different converted signals to determine the actual time difference between baseline crossings (g a ) is calculated.

[0155] The error signal generator 330 calculates the actual time difference between baseline crossings (g a ) and the target time difference between baseline crossings (g t ) can be calculated. For example, the error can be calculated as the actual time difference between baseline crossings (g a ) and target time difference (g t ) can also be calculated as the difference between the target time difference (g t ) to the actual time difference (g a ) can also be calculated as a percentage change to the target time difference (g). A series of error values ​​calculated over the duration of the chirp can serve as an error signal as disclosed in the context of FIG. 6E and shown in FIG. 7B. As previously mentioned, the target time difference (g t ) is associated with a period index. Thus, a series of error values ​​calculated over the duration of the chirp and capable of serving as an error signal is associated with one of the period indexes. The error signal generator 330 can access a memory 344 and can store the error values ​​and the resulting error signal in the memory 344.

[0156] Depending on whether a threshold number of error signals from data periods having the same period index k are stored in the storage device 344, the error signal generator 330 can generate a composite error value from all or a portion of the stored error values. Thus, the error signal generator 330 can generate one or more composite error signals from all or a portion of the stored error signals. For example, the error signal generator 330 can average error signals from multiple data periods, each having the same period index k, to generate a composite error value that is an average of the error signals as a function of time. As an example, the error value in FIG. 7C can represent an average of the stored error values ​​from data periods associated with the same period index (i.e., k=1), and the average error value for a time segment is the average of all the error values ​​for that time segment. A digital signal carrying a composite error value over the duration of a frequency chirp can function as a composite error signal.

[0157] Because the composite error value and resulting error signal are associated with a period index, i.e., k=1 (DP1), the error value and resulting composite error signal are also associated with period index k=1 (DP1). As a result, error signal generator 330 can generate composite error values ​​and / or composite error signals for all or some of the different period indices (k). In some cases, error signal generator 330 stores the composite error values ​​and / or composite error signals in storage device 344 for one or more of the different period indices (k) over the duration of the frequency chirp.

[0158] In some cases, the error signal generator 330 determines whether to generate a modified light source control signal. The error signal generator 330 can calculate a composite error level of the composite error signal. For example, the error signal generator 330 can calculate the deviation or root mean square of the composite error value over the duration of the chirp. The error signal generator 330 can compare the composite error level to one or more error criteria to determine whether to generate a modified light source control signal. For example, the error signal generator 330 can compare the composite error level to an error threshold. If the composite error level exceeds the error threshold, the error signal generator 330 can generate a modified light source control signal. If the composite error level falls below the error threshold, the error signal generator 330 can refrain from generating a modified light source control signal.

[0159] The error signal generator 330 can modify the waveform of the light source control signal to modify the magnitude and direction of the error indicated by the composite error signal. FIG. 7D shows an example of the waveform of the light source control signal for the duration of a chirp in different data periods each associated with the same period index (k). Each voltage level shown indicates the voltage applied to the light source 4 during the associated time segment. The voltage level labeled V0 represents the waveform of the light source control signal. The error signal generator 330 modifies the waveform of the light source control signal (V0) by V m The waveform can be changed to one represented by voltage levels denoted as V. m The voltage levels labeled represent the waveform of the modified light source control signal.

[0160] The light source control signal can be modified to modify the magnitude and direction of the error indicated by the composite error signal. For example, the error signal generator 330 can modify the light source control signal to generate a modified light source control signal that reduces the magnitude of the error level indicated by the composite error signal. As an example, FIG. 7D can represent a composite error signal obtained by applying the light source control signal of FIG. 7C to the light source during a data period having the same period index associated with the composite error signal. The y-axis in FIG. 7C can represent the percentage difference. This percentage difference is the actual time difference (g) between adjacent high voltage values ​​in the logic signal. a ) and the target time difference (g t ) represents a percentage difference from the actual time difference (g) for that time segment. The light source control signal can be changed so that the voltage applied during each time segment is changed by the percentage difference for that time segment, but in the opposite direction. For example, a ) is the target time difference (g t ) is 10% less than the V m The value is V m =V0*(1-(er / 100)), where er represents the percentage difference and V m , V0, and er values ​​are associated with the same time interval.

[0161] Each light source control signal is associated with a different data period, and therefore a different period index, such that error signal generator 330 can generate different modified light source control signals associated with different period indexes.

[0162] Although the above example of modifying the light source control signal modifies the light source control signal in proportion to the level of error indicated by the composite error signal, other relationships can be used. For example, an association between changes in the light source control signal and different error values ​​can be stored in memory 344. For a given composite error, error signal generator 330 can modify the light source control signal as indicated by the change in the light source control signal associated with the given composite error. The association between the composite error and changes in the light source control signal can be represented by a data structure, such as a lookup table, a mathematical formula, one or more filters, and one or more adaptive filters.

[0163] The modified light source control signal is received by light source controller 342. Light source controller 342 may include a digital-to-analog converter that receives the modified light source control signal and converts the modified light source control signal to an analog signal. The digital-to-analog converter outputs an analog version of the modified light source control signal, and light source controller 342 applies the analog version of the modified light source control signal to light source 4. Because different light source control signals are associated with different data periods and therefore different period indices, light source controller 342 applies the modified light source control signal such that the data periods and the light source control signal applied to the light source are associated with the same period indices. As a result, different light source control signals can be applied to the light source for different data periods within a cycle. Furthermore, the same light source control signal selection can be applied to data periods in multiple different cycles. Thus, the light source control signal does not need to be applied on the fly.

[0164] The digital version of the modified light source control signal can be stored in a memory device and can serve as a light source control signal that can later be modified by the error signal generator 330 .

[0165] After generating a composite error signal associated with a data period index, the error signal generator 330 may clear the storage device to store another set of error signals associated with that data period index. The error signal generator 330 may repeat the process of generating and applying modified light source control signals once the number of error signals in the set exceeds a threshold number.

[0166] FIG. 8 is a process flow method for operating an electronic device according to FIG. 7A or 6D. In process block 360, error signal generator 330 may generate error signals and store the error signals in storage device 344. Error signals may be generated for one or more different period indices, with each error signal associated with one of the period indices. In decision block 362, error signal generator 330 may determine whether a threshold number of error signals associated with the same period indices have been stored. This determination may be made for all or a portion of the period indices. If negative determinations are made for all period indices, error signal generator 330 may return to process block 360. If a positive determination is made for one or more period indices, each period indices for which a positive determination is made serves as a period indices of interest. If a positive determination is made, the error signal generator 330 proceeds to process block 364, where memory may be cleared so that additional error signal sets for each period indices of interest can be stored. The threshold numbers for different period indices may be the same or different. Examples of suitable threshold numbers include, but are not limited to, threshold numbers of 1 or greater than 2.

[0167] From process block 364, the error signal generator 330 may proceed to process block 366. In process block 366, the error signal generator 330 may generate a composite error signal for each of the time period indexes of interest. The error signal generator 330 may optionally store the composite error signal for each of the time period indexes of interest in a storage device. From process block 366, the error signal generator 330 may proceed to decision block 368. In decision block 368, for each of the time period indexes of interest, the error signal generator 330 and / or the control signal generator 340 may determine whether the level of error indicated by the composite error signal generated in process block 336 is sufficient to generate a modified light source control signal for that time period index of interest. For example, for each of the time period indexes of interest, the error signal generator 330 and / or the control signal generator 340 may determine whether the level of error indicated by the composite error signal generated in process block 336 exceeds an error threshold. As another example, for each of the period indices of interest, the error signal generator 330 may determine whether the root mean square of the composite error signal generated in process block 336 exceeds an error threshold. If a negative determination is made for all period indices, the error signal generator 330 and / or the control signal generator 340 may return to process block 360. If a positive determination is made for one or more of the time period of interest indices, each of the time period of interest indices for which a positive determination was made can function as an erroneous time period of interest indices. If a positive determination is made for one or more of the time period of interest indices, the error signal generator 330 and / or the control signal generator 340 proceed to process block 370, where the error signal generator 330 and / or the control signal generator 340 can generate a modified light source control signal for each of the erroneous time period of interest indices.

[0168] Process flow may proceed from process block 370 to process block 372. In process block 373, during the data period of each erroneous time period of interest index, light source controller 342 may apply to the light source an analog version of the modified light source control signal generated in process block 370 for the data period index. The analog version of the modified light source control signal for the erroneous time period of interest index may be applied in place of the light source control signal previously associated with that erroneous time period of interest index. The light source control signal previously applied to the light source to generate the error signal in process block 360 for the period indexes that did not result in the time period of interest index may continue to be applied to the light source during the data periods of those period indexes.

[0169] As mentioned above, the control waveguide 28 shown in FIGS. 1A-1C can include a delay section 37 that can be used to increase the length of the control waveguide 28. Increasing the length of the control waveguide 28 increases the difference in length between the first and second optical paths. Increasing the length difference between these paths increases the pulsating frequency of the pulsating control signal. Increasing the pulsating frequency increases the number of baseline crossings that provide the time differences disclosed above. Consequently, increasing the length difference between these paths reduces the size of these time differences, thereby improving the resolution in modifying the light source control signal.

[0170] As an alternative to, or in addition to, the delay section 37 in the control waveguide 28, a delay section 37 can be included in the first waveguide 31 or the second waveguide 34 in all or part of the phase difference generator 29. However, the delay section 37 can occupy an undesirably large amount of space on a semiconductor chip, such as a LIDAR chip. As a result, a single delay section 37 can be provided, as shown in Figures 1A-1C, allowing for more efficient use of the available space on the LIDAR chip.

[0171] Although the digital versions of the light source control signal and the modified light source control signal are disclosed above as having voltage levels at fixed time intervals, the light source control signal and the modified light source control signal may have voltage levels separated by fixed voltage increments of variable duration. As an example, FIG. 9 is a voltage versus time graph illustrating example voltage levels of the light source control signal and the modified light source control signal. The fixed voltage increments are represented by v i The graph shows a voltage level (V) of varying duration, as shown on the time axis. m and V0). m The duration of the voltage levels labeled as are shown in brackets rather than lines.

[0172] The voltage level labeled V0 represents the waveform of the light source control signal. Thus, a series of digital signals or bits representing the duration of the voltage level labeled V0 over the duration of the chirp can serve as a digital representation of the light source control signal. The control signal generator 340 and / or the error signal generator 330 use the composite error signal disclosed above to modify the waveform of the light source control signal (V0) and generate a V m Therefore, we can obtain a waveform represented by a voltage level expressed as V m The voltage level labeled V represents the waveform of the modified light source control signal. m A series of digital signals or bits representing the duration of the voltage levels denoted as , can serve as a digital representation of the modified light source control signal.

[0173] Figure 9 shows the digital-to-analog converter V m Included is a solid curve that may represent an example of an analog version of the modified light source control signal that may be generated from the voltage levels labeled . Thus, light source controller 342 may apply the analog version of the modified light source control signal to light source 4 as an analog light source control signal.

[0174] The electronic device 32 disclosed in the context of Figures 6A through 8 may include components in addition to those shown. As an example, the electronic device 32 disclosed in Figures 6D, 6D, and 7A may include a mathematical converter 238 in addition to the components shown.

[0175] Suitable electronics 32 can include an electronic controller that includes or consists of analog electrical circuitry, digital electrical circuitry, application specific integrated circuits (ASICs), processors, microprocessors, digital signal processors (DSPs), field programmable gate arrays (FPGAs), computers, microcomputers, or any combination suitable for performing the above-described operation, control, and control functions. In some cases, electronics 32 includes one or more memory devices that store instructions executed by the electronic controller in performing the above-described operation, control, and control functions. Although the electronics is shown as a single component in a single location, the electronics can include multiple different components located independently of each other and / or in different locations. Also, as noted above, all or a portion of the disclosed electronics can be included on a chip, including electronics integrated with the chip.

[0176] The phase detector 332 as disclosed in the context of FIG. 6B may be or include an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), or a microprocessor. The analog phase detector 332 may perform the attribute function using discrete circuitry or an analog integrated circuit. The digital phase detector 332 as disclosed in the context of FIG. 6D may be an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), or a microprocessor. The digital phase detector 332 may perform the attribute function using a time-to-digital converter or other digital implementation.

[0177] The analog control signal generator 340, as disclosed in the context of FIG. 6B, can be an application-specific integrated circuit (ASIC) and / or an individual electronic device, or can include them. The digital control signal generator 340, as disclosed in the context of FIG. 6D, can be an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), a microprocessor, or can include them.

[0178] The light source controller 342, as disclosed in the context of FIG. 6B, can be an application-specific integrated circuit (ASIC) or an individual electronic device, or can include them. In some cases, the analog light source controller 342 uses a digital / analog converter, a transconductance amplifier, a current-mode digital / analog converter, and combinations thereof to perform the attribute functions.

[0179] The error signal generator 330, as disclosed in the context of FIG. 7A, can be a controller, a processor, or a microprocessor, an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), or can include them. In some cases, the digital error signal generator 330 uses a time / digital converter or other implementations using digital gates to perform the attribute functions.

[0180] Suitable platforms for LIDAR chips include, but are not limited to, silica, indium phosphide, and silicon-on-insulator wafers. Figure 10 shows a cross-sectional view of a portion of a chip constructed from a silicon-on-insulator wafer. A silicon-on-insulator (SOI) wafer includes a buried layer 410 between a substrate 412 and an optically transmissive medium 414. In a silicon-on-insulator wafer, the buried layer 410 is silica, while the substrate 412 and optically transmissive medium 414 are silicon. The substrate 412 of an optical platform such as an SOI wafer can serve as the base for the entire LIDAR chip. For example, the optical components shown on the LIDAR chips in Figures 1A-1C can be located on the top and / or sides of the substrate 412.

[0181] The portion of the LIDAR chip in Figure 10 includes a waveguide structure suitable for use in a LIDAR chip constructed from a silicon-on-insulator wafer. A ridge 416 of optically transmissive medium extends away from a slab region 418 of optically transmissive medium. The optical signal is confined between the top of the ridge 416 and the buried oxide layer 410.

[0182] The dimensions of the ridge waveguide are labeled in FIG. 10. For example, the width of the ridge is labeled w and the height is labeled h. The thickness of the slab region is labeled T. For LIDAR applications, these dimensions may be more important than other dimensions due to the need to use higher levels of optical power than in other applications. The ridge width (labeled w) is greater than 1 μm and less than 4 μm, the ridge height (labeled h) is greater than 1 μm and less than 4 μm, and the thickness of the slab region is greater than 0.5 μm and less than 3 μm. These dimensions may apply to straight or substantially straight sections of the waveguide, curved sections of the waveguide, and tapered sections of the waveguide. Therefore, these sections of the waveguide are single-mode. However, in some cases, these dimensions may apply to straight or substantially straight sections of the waveguide. Additionally or alternatively, the thickness of the slab in the curved sections of the waveguide may be reduced to reduce optical loss in the curved sections of the waveguide. For example, the curved portion of the waveguide can have a ridge extending away from the slab region, with a thickness of at least 0.0 μm but less than 0.5 μm. The above dimensions generally provide a single-mode structure in the straight or substantially straight portions of the waveguide, while resulting in multimode tapered and / or curved portions. Coupling between multimode and single-mode shapes can be achieved using a taper that does not substantially excite higher-order modes. Thus, the waveguide can be constructed such that signals carried in the waveguide are single-mode, even when carried in portions of the waveguide with multimode dimensions. The waveguide structure disclosed in the context of FIG. 10 is suitable for all or a portion of the waveguides on LIDAR chips constructed according to FIGS. 1A-1C.

[0183] As mentioned above, the control waveguide 28 can include a delay section 37 that can be used to increase the length of the control waveguide 28. The delay section 37 can represent a helical arrangement of the control waveguide 28. The helical arrangement is selected to reduce the amount of space occupied by a longer waveguide. FIG. 11 shows a portion of the control waveguide 28 having a helical arrangement. Near the center of the helical arrangement, the waveguide folds back. While the helical arrangement is shown as approximating a circle, the helical arrangement can also have other shapes, such as approximating an ellipse, a rectangle, or a triangle. As a result, the helical arrangement can include straight and / or substantially straight waveguide sections.

[0184] The optical sensor that interfaces with the waveguide on the LIDAR chip can be a component separate from the chip and then attached to the chip. For example, the optical sensor can be a photodiode or an avalanche photodiode. Examples of suitable optical sensor components include, but are not limited to, an InGaAs PIN photodiode manufactured by Hamamatsu Seisakusho Co., Ltd., Hamamatsu, Japan, or an InGaAs APD (avalanche photodiode) manufactured by Hamamatsu Seisakusho Co., Ltd., Hamamatsu, Japan. These optical sensors can be located in the center of the LIDAR chip. Alternatively, all or a portion of the waveguide that terminates in the optical sensor can terminate in a facet at the edge of the chip, and the optical sensor can be attached to the edge of the chip on this facet. In this way, the optical sensor receives light that passes through the facet. The use of a light sensor separate from the chip is suitable for all or some of the light sensors selected from the group consisting of first light sensor 218, second light sensor 220, first light sensor 223, second light sensor 224, first light sensor 298, and second light sensor 300.

[0185] As an alternative to a separate optical sensor, all or part of the optical sensor can be integrated on the chip. For example, examples of optical sensors interfaced with ridge waveguides on chips constructed from silicon-on-insulator wafers are described in Optics Express Vol. 15, No. 21, pp. 13965-13971 (2007); U.S. Patent No. 8,093,080 issued January 10, 2012; U.S. Patent No. 8,242,432 issued August 14, 2012; and U.S. Patent No. 6,108,472 issued August 22, 2000, each of which is incorporated herein in its entirety. The use of an optical sensor integrated on the chip is suitable for all or part of the optical sensors selected from the group consisting of auxiliary optical sensor 218, second optical sensor 220, first optical sensor 223, second optical sensor 224, second optical sensor 224, first optical sensor 298, and second optical sensor 300.

[0186] The light source 4 that interfaces 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 example, the light source 4 can be a laser chip that is attached to the chip using a flip-chip arrangement. The use of a flip-chip arrangement is appropriate when the light source 4 interfaces with a ridge waveguide on a chip constructed from a silicon-on-insulator wafer. Alternatively, the utility waveguide 12 can include an optical grating (not shown), such as a Bragg grating, that serves as a reflector for an external cavity laser. In these examples, 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 wafers are described in U.S. Pat. No. 9,705,278, issued July 11, 2017, and U.S. Pat. No. 5,991,484, issued November 23, 1999, each of which is incorporated herein in its entirety. If light source 4 is a gain element or laser chip, electronics 32 can change the frequency of the outgoing LIDAR signal by changing the level of current applied to the gain element or laser resonator.

[0187] The LIDAR system described above includes multiple optical components, such as a LIDAR chip, a LIDAR adapter, a light source, a light sensor, a waveguide, and an amplifier. In some cases, the LIDAR system includes one or more passive optical components in addition to or in place of the optical components shown. Passive optical components can be solid-state components with no moving parts. Suitable passive optical components include, but are not limited to, lenses, mirrors, optical gratings, reflective surfaces, splitters, demultiplexers, multiplexers, polarizers, polarization splitters, and polarization rotators. In some cases, the LIDAR system includes one or more active optical components in addition to or in place of the optical components shown. Suitable active optical components include, but are not limited to, optical switches, phase tuners, attenuators, steerable mirrors, steerable lenses, tunable demultiplexers, and tunable multiplexers.

[0188] Other embodiments, combinations, and modifications of the present invention will occur to those skilled in the art in light of these teachings. Accordingly, the present invention is 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, including: a light source that outputs an outgoing LIDAR signal; a plurality of phase difference generators, each of which combines the first optical signal and the second optical signal to generate a pulsation control signal; wherein the first optical signal includes light from the outgoing LIDAR signal; wherein the second optical signal includes light from the outgoing LIDAR signal; which of the pulsation control signals is generated with a phase difference between the contribution of the first optical signal to the pulsation control signal and the contribution of the second optical signal to the pulsation control signal; the phase difference is different for each pulsation control signal from a different phase difference generator; any of the pulsatile signals having multiple baseline crossings; and a phase difference generator, wherein baseline crossings of the pulsatile signal occur at a frequency; and 1. An electronic device applying a light source control signal to the light source to chirp the frequency of the emitted LIDAR signal, Electronics configured to modify the light source control signal in response to changes in a frequency of baseline crossings of the pulsatile control signal.

2. 10. The LIDAR system of claim 1, wherein there are more than three phase difference generators.

3. 3. The LIDAR system of claim 2, wherein the phase difference generator is configured such that the difference between each pair of numerically adjacent phase differences is a constant.

4. 4. The LIDAR system of claim 3, wherein the phase difference generators are configured such that the difference between each pair of numerically adjacent phase differences is π / N, where N represents the number of phase difference generators.

5. Any of the phase difference generators may be associated with a phase difference generator index n, where n is an integer having a value from 1 to N, and the phase difference may be Φ ｎ =π(n-1) / N, where Φ ｎ 5. The LIDAR system of claim 4, wherein n represents the phase difference of a phase difference generator associated with the phase difference generator index n.

6. 10. The LIDAR system of claim 1, wherein light in the first optical signal and the second optical signal does not exit the LIDAR system.

7. 7. The LIDAR system of claim 6, wherein a LIDAR chip includes a photonic integrated circuit with a utility waveguide that carries the outgoing LIDAR signal, and wherein light in the first optical signal and the second optical signal does not exit the LIDAR chip.

8. 10. The LIDAR system of claim 1, wherein the LIDAR system is configured to output a system output signal that includes light from the outgoing LIDAR signal.

9. 10. The LIDAR system of claim 1, wherein the LIDAR system is configured to output a system output signal that includes light from the outgoing LIDAR signal.

10. 10. The LIDAR system of claim 9, further comprising an optical signal combiner configured to combine the comparison optical signal and the reference optical signal to generate a pulsatile signal, the comparison light signal includes light from the system output signal that has been reflected by an object external to the LIDAR system and returned to the LIDAR system; and the reference light signal includes light from an exit LIDAR signal that does not exit the LIDAR system; LIDAR system.

11. 11. The LIDAR system of claim 10, wherein the electronics are configured to calculate LIDAR data from a pulsatile frequency of the pulsatile signal, the LIDAR data being indicative of a radial velocity and / or a distance between the object and the LIDAR system.

12. 2. The LIDAR system of claim 1, wherein either of the phase difference generators includes an optical signal coupler that receives the first optical signal from a first waveguide and the second optical signal from a second waveguide, and wherein either of the first waveguides receives the first optical signal from a control waveguide.

13. The LIDAR system of claim 12 , wherein the control waveguide comprises a helical waveguide.

14. 13. The LIDAR system of claim 12, wherein any of the first waveguides receives the first optical signal from a utility waveguide that carries the outgoing LIDAR signal.

15. 15. The LIDAR system of claim 14, wherein the control waveguide receives a portion of the outgoing LIDAR signal from the utility waveguide.

16. 10. The LIDAR system of claim 1, wherein the electronics are configured to modify the light source control signal such that a chirp in frequency of the outgoing LIDAR signal is a linear chirp.

17. 2. The LIDAR system of claim 1, wherein the electronics are configured to modify the light source control signal such that the time difference is a constant.

18. 2. The LIDAR system of claim 1, wherein the electronics being configured to modify the light source control signal in response to changes in frequency of baseline crossings of the pulsatile control signal includes the electronics being configured to modify the light source control signal in response to changes in time difference between baseline crossings of the pulsatile signal.

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