Monitoring signal chirp in LIDAR output signals

Abstract

The LIDAR system has at least one optical component configured to output a system output signal that travels away from the LIDAR system and that can be reflected by objects located external to the LIDAR system. The LIDAR system also has a control mechanism configured to control one or more process variables in the system output signal. The control mechanism controls the process variables using an electrical process variable signal. The process variable signal has in-phase and quadrature components.

Description

Related Applications

[0001] This application is a continuation of U.S. Patent Application No. 16 / 867,987, filed May 16, 2020, entitled "Monitoring Signal Chirp in a LIDAR Output Signal," which is incorporated in its entirety. [Technical Field]

[0002] The present invention relates to optical devices. In particular, the present invention relates to LIDAR systems.

[0003] There is increasing commercial demand for LIDAR systems that can be deployed in applications such as Advanced Driver Assistance Systems (ADAS) and Augmented Reality (AR). Light Detection and Ranging (LIDAR) systems typically generate a system output signal that is reflected by an object located outside the LIDAR system. At least a portion of the reflected light signal returns to the LIDAR system. The LIDAR system directs the received light signal to a light sensor that converts the light signal into an electrical signal. Electronic circuitry can use the light sensor output to quantify LIDAR data indicative of the radial velocity and / or distance between the object and the LIDAR system.

[0004] Many LIDAR systems adjust the frequency of the system output signal linearly with respect to time or with other well-defined waveforms to enable accurate measurement of LIDAR data. In these examples, the LIDAR system monitors the frequency of the system output signal to achieve a desired waveform shape and can adjust the frequency accordingly. Systems used to monitor the frequency of the system output signal can require one or more waveguides that are unnecessarily long to achieve the desired result. As a result of this waveguide length, these systems often occupy a large percentage of the available space on the LIDAR chip. As a result, there is a need for an improved system for monitoring the frequency of a LIDAR system output signal. Abstract

[0005] The LIDAR system includes at least one optical component configured to output a system output signal that travels away from the LIDAR system and that can be reflected by objects located external to the LIDAR system. The LIDAR system also includes a control mechanism configured to control one or more process variables in the system output signal. The control mechanism controls the process variables using an electrical process variable signal. The process variable signal has an in-phase component and a quadrature component. [Brief explanation of the drawings]

[0006] FIG. 1A is a schematic plan view of a LIDAR system having or comprising a LIDAR chip that outputs a LIDAR output signal and receives a LIDAR input signal on a common waveguide.

[0007] FIG. 1B is a schematic plan view of a LIDAR system having or comprising a LIDAR chip that outputs a LIDAR output signal and receives a LIDAR input signal on a different waveguide.

[0008] FIG. 1C is a schematic plan view of another embodiment of a LIDAR system having or comprising a LIDAR chip that outputs a LIDAR output signal and receives a LIDAR input signal on a different waveguide.

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

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

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

[0012] FIG. 5A illustrates an example of a processing component suitable for use with a LIDAR system.

[0013] FIG. 5B provides a schematic of electronic circuitry suitable for use with a processing component configured according to FIG. 5A.

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

[0015] FIG. 5D illustrates another example of a processing component suitable for use with a LIDAR system.

[0016] FIG. 5E provides a schematic of electronic circuitry suitable for use with a processing component configured according to FIG. 5D.

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

[0018] FIG. 6B is a schematic diagram of the relationship between the electronic circuitry and the light sensor that may be included in a LIDAR chip.

[0019] FIG. 6C is a graph showing the amplitudes of the in-phase and quadrature components of a signal on the same time axis as the frequency of the system output signal.

[0020] FIG. 6D illustrates an example of a process variable identification component suitable for use in the electronics portion of a LIDAR system.

[0021] FIG. 6E illustrates another example of a process variable identification component suitable for use in the electronics portion of a LIDAR system.

[0022] Figure 7 shows a cross section of a portion of a LIDAR chip with a waveguide on a silicon-on-insulator platform.

[0023] The LIDAR system has a control mechanism configured to control a process variable of the system output signal. In some cases, the control mechanism is a control loop, such as a feedback control loop. The system output signal is an optical signal output by the LIDAR system that is reflected by an object located outside the LIDAR system and then returns to the LIDAR system. The LIDAR system can then use the reflected light to generate LIDAR data about the object. Examples of process variables that the control mechanism can control include the frequency and / or phase of the system output signal.

[0024] The control mechanism generates a control signal that carries data indicating the value of the process variable. The control signal is generated from a process variable signal that has an in-phase component and a quadrature component. The process variable signal is a beat signal resulting from contributions from signals of different frequencies. By using the quadrature component, the frequency of the control signal can be increased relative to the frequency of the control signal that would result if the process variable signal had only an in-phase component. Increasing the frequency of the control signal reduces the beat frequency of the process variable signal required to determine the value of the process variable. In conventional systems, the beat frequency was increased by increasing the length of one waveguide in the Mach-Zehnder interferometer. Because the quadrature component reduces the required beat frequency, the quadrature component also reduces the required length of one waveguide in the Mach-Zehnder interferometer. Therefore, the quadrature component can reduce the amount of space on the LIDAR chip occupied by the control mechanism.

[0025] FIG. 1A is a schematic plan view of a LIDAR chip that can function as a LIDAR system or can be included in a LIDAR system having 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 has a light source 4 that outputs a pre-emitted 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).

[0026] The LIDAR chip has 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 carries the outgoing LIDAR signal to the facet 14. The facet 14 can be located at the end of the chip such that the outgoing LIDAR signal traveling through the facet 14 exits the chip and also functions as the LIDAR output signal. For example, the facet 14 can be located at the end of the chip, such that the outgoing LIDAR signal traveling through the facet 14 exits the chip and also 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 exiting of the LIDAR output signal from the LIDAR chip also exits the LIDAR output signal from the LIDAR system, the LIDAR output signal can also be considered a system output signal.

[0027] The LIDAR output signal travels away from the LIDAR system through free space in the atmosphere where 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 the LIDAR input signal. In some examples, the LIDAR input signal may also be considered a system return signal. As an example, if the LIDAR output signal emanating from the LIDAR chip also emanates from the LIDAR system, the LIDAR input signal may also be considered a system return signal.

[0028] A LIDAR input signal can enter utility waveguide 12 through facet 14. A portion of the LIDAR input signal entering utility waveguide 12 serves as the incident LIDAR signal. Utility waveguide 12 carries the incident LIDAR signal to splitter 16, which passes a portion of the outgoing LIDAR signal from utility waveguide 12 to comparison waveguide 18 as a comparison signal. Comparison waveguide 18 carries the comparison signal to processing component 22 for further processing. While FIG. 1A shows a directional coupler as splitter 16, other signal tap components can be used as splitter 16. Suitable splitters 16 include, but are not limited to, directional couplers, optical couplers, y-couplers, tapered couplers, and multi-mode interference (MMI) devices.

[0029] Utility waveguide 12 also carries the outgoing LIDAR signal to splitter 16. Splitter 16 moves a portion of the outgoing LIDAR signal from utility waveguide 12 as a reference signal to reference waveguide 20. Reference waveguide 20 carries the reference signal to processing component 22 for further processing.

[0030] The fraction of light redirected by splitter 16 from utility waveguide 12 can be fixed or substantially fixed. For example, splitter 16 can be configured so that the power of the reference signal redirected to reference waveguide 20 is the ratio of the power of the outgoing LIDAR signal, or so that the power of the comparison signal redirected to comparison waveguide 18 is the ratio of the power of the incoming LIDAR signal. In many splitters 16, such as directional couplers and multimode interferometers (MMIs), the ratio of the outgoing light is equal to or substantially equal to the ratio of the incoming light. In some examples, the ratio of the outgoing light is greater than 30%, 40%, or 49% and / or less than 51%, 60%, or 70% and / or the ratio of the incoming light is greater than 30%, 40%, or 49% and / or less than 51%, 60%, or 70%. Splitters 16, such as multimode interferometers (MMIs), typically provide a 50% or approximately 50% exit and entrance ratio. However, multimode interferometers (MMIs) are easier to fabricate in platforms such as silicon-on-insulator platforms than other alternatives. In one example, splitter 16 is a multimode interferometer (MMI) and the exit and entrance ratios are 50% or substantially 50%. As described in more detail below, processing component 22 combines the comparison signal with the reference signal to form a composite signal carrying LIDAR data about a sample region of the field of view. Thus, the composite signal can be processed to extract LIDAR data about the sample region (e.g., radial velocity and / or distance between the LIDAR system and an object external to the LIDAR system).

[0031] The LIDAR chip can have 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 to a control waveguide 28. The combined portion of the outgoing LIDAR signal serves as a tap signal. While FIG. 1A shows a directional coupler acting as the splitter 26, other signal tap components can be utilized as the splitter 26. Suitable splitters 26 include, but are not limited to, directional couplers, optical couplers, y-couplers, tapered couplers, and multi-mode interference (MMI) devices.

[0032] The control waveguide 28 carries the tap signal to a control component 30. The control component 30 can be in electrical communication with an electronic circuitry 32. All or a portion of the control component 30 can be included in the electronic circuitry 32. In operation, the electronic circuitry can utilize the output from the control component 30 at a control component 34 that is configured to control process variables of one, two, or three controlled optical signals selected from the group consisting of the tap signal, the system output signal, and the emitted LIDAR signal. Examples of suitable process variables include the frequency of the controlled optical signal and / or the phase of the controlled optical signal.

[0033] LIDAR systems can be modified so that the incident and outgoing LIDAR signals are carried in different waveguides. For example, FIG. 1B is a plan view of the LIDAR chip of FIG. 1A modified to carry the incident and outgoing LIDAR signals in 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 processing component 22 for further processing. As described in connection with FIG. 1A, reference waveguide 20 carries the reference signal to processing component 22 for further processing. As will be described in more detail below, processing component 22 combines the comparison signal with the reference signal to form a composite signal that carries LIDAR data about the sample area on the field of view.

[0034] 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. Splitter 40 is configured to place a portion of the reference signal carried in reference waveguide 20 in first reference waveguide 42 and another portion of the reference signal in second reference waveguide 44. Thus, first reference waveguide 42 carries the first reference signal, and second reference waveguide 44 carries the second reference signal. First reference waveguide 42 carries the first reference signal to first processing component 46, and second reference waveguide 44 carries the second reference signal to second processing component 48. Examples of suitable splitters 40 include, but are not limited to, y-couplers, optical couplers, and multimode interference couplers (MMIs).

[0035] 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 one or more objects located external to the LIDAR system, at least a portion of the reflected light returns to the LIDAR chip as a first LIDAR input signal. The first LIDAR input signal enters comparison waveguide 18 through facet 35 and serves as a first comparison signal. Comparison waveguide 18 carries the first comparison signal to first processing component 46 for further processing.

[0036] Additionally, when light from the LIDAR output signal is reflected by one or more objects located external to the LIDAR system, at least a portion of the reflected signal returns to the LIDAR chip as a second LIDAR input signal. The second LIDAR input signal enters the second comparison waveguide 50 through facet 52 and serves as a second comparison signal carried by the second comparison waveguide 50. The second comparison waveguide 50 carries the second comparison signal to the second processing component 48 for further processing.

[0037] Although the light source 4 is shown as being located on the LIDAR chip, the light source 4 can be located off the LIDAR chip. For example, the utility waveguide 12 can terminate at a second facet where the outgoing LIDAR signal can enter the utility waveguide 12 from the light source 4 located off the LIDAR chip.

[0038] 1B or 1C is used with a LIDAR adapter. In some examples, the LIDAR adapter can be physically and optically positioned between the LIDAR chip and one or more reflective objects and / or the field of view such that the optical path along which the first LIDAR input signal and / or the LIDAR output signal travel from the LIDAR chip to the field of view passes through the LIDAR adapter. Furthermore, the LIDAR adapter can be configured to manipulate the first LIDAR input signal and the LIDAR output signal so 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.

[0039] 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 located on a base. For example, the LIDAR adapter includes a circulator 100 disposed on a base 102. The illustrated optical circulator 100 has three ports and is configured so 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.

[0040] The LIDAR adapter can be configured such that the output of the LIDAR output signal from the second port 106 can also function as an output of the LIDAR output signal from the LIDAR adapter, and therefore the LIDAR system. As a result, the LIDAR output signal can be output from the LIDAR adapter such that the LIDAR output signal travels toward a sample area within the field of view. Thus, in some examples, a portion of the LIDAR output signal that exits the LIDAR adapter can also be considered a system output signal. As an example, if the exit of the LIDAR output signal from the LIDAR adapter is also an exit of the LIDAR output signal from the LIDAR system, the LIDAR output signal can also be considered a system output signal.

[0041] The LIDAR output signal output from the LIDAR adapter comprises, consists of, or essentially consists of light derived from the LIDAR output signal received from the LIDAR chip. Thus, the LIDAR output signal output from the LIDAR adapter will be the same or substantially the same as the LIDAR output signal received from the LIDAR chip. However, there may be differences between the LIDAR output signal output from the LIDAR adapter and the LIDAR output signal received from the LIDAR chip. For example, the LIDAR output signal may experience optical loss as the LIDAR output signal travels through the LIDAR adapter, and / or the LIDAR adapter may optionally include an amplifier configured to amplify the LIDAR output signal as it travels through the LIDAR adapter.

[0042] When one or more objects in the sample area reflect the LIDAR output signal, at least a portion of the reflected light travels back to the circulator 100 as a system return signal. The system return signal enters the circulator 100 through the second port 106. Figure 2 shows the LIDAR output signal and the system return signal traveling along the same optical path between the LIDAR adapter and the sample area.

[0043] The system return signal exits the circulator 100 through the third port 108 and is directed to the comparison waveguide 18 on the LIDAR chip. Thus, all or a portion of the system return signal can function as the first LIDAR input signal, and the first LIDAR input signal comprises or comprises light derived 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.

[0044] As is apparent from Figure 2, the LIDAR adapter can include optical components in addition to the circulator 100. For example, the LIDAR adapter can include components that direct and control 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 that is positioned to receive and amplify the LIDAR output signal before it enters the circulator 100. The electronic circuitry 32 can operate the amplifier 110 such that the electronic circuitry 32 can control the power of the LIDAR output signal.

[0045] FIG. 2 also illustrates a LIDAR adapter having 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 can be configured to focus or collimate the LIDAR output signal at 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 to 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 to an entrance 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 can be configured to focus or collimate the LIDAR output signal at a desired location. For example, the second lens 114 can be configured to couple the LIDAR output signal to facet 35 of the comparison waveguide 18.

[0046] The LIDAR adapter may also have one or more redirecting components, such as a mirror. Figure 2 shows a LIDAR adapter with a mirror as the redirecting component 116 that redirects the system return signal from the circulator 100 to the facet 20 of the comparison waveguide 18.

[0047] The LIDAR chip includes one or more waveguides that constrain the optical path of one or more optical signals. While the LIDAR adapter includes waveguides, the optical paths along which the system return signal and the LIDAR output signal travel between components of the LIDAR adapter and / or between the LIDAR chip and components of the LIDAR adapter can be free space. For example, the system return signal and / or the LIDAR output signal can travel through the environment in which the LIDAR chip, LIDAR adapter, and / or base 102 are disposed as they travel between different components of the LIDAR adapter and / or between components of the LIDAR adapter and the LIDAR chip. As a result, optical components such as lenses and redirecting components can be used to control the characteristics of the optical paths along which the system return signal and the LIDAR output signal travel on, toward, and from the LIDAR adapter.

[0048] 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 separate components attached to the substrate. Suitable techniques for attaching separate components to the base 102 include, but are not limited to, epoxy, solder, and mechanical clamps. In one example, one or more components are integrated components and the remaining components are separate components. In another example, the LIDAR adapter has one or more integrated amplifiers and the remaining components are separate components.

[0049] LIDAR systems can be configured to compensate for polarization. Light from a laser light source is typically linearly polarized, and therefore the LIDAR output signal is also typically linearly polarized. Reflection from an object may change the polarization angle of the returning light. Thus, the system return signal may contain light of different linear polarization states. For example, a first portion of the system return signal may have light of a first linear polarization state, and a second portion of the system return signal may have light of 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 the angle is 90 degrees, LIDAR data may 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.

[0050] 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 the 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.

[0051] 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, as described in connection with FIG. 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.

[0052] The beam splitter 120 can be a polarizing beam splitter. An example of a polarizing beam splitter is configured 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, and the second polarization state can be different from the first polarization state. For example, the first polarization state can be TE and the second polarization state can be TM, or the first polarization state can be TM and the second polarization state can be TE. In some cases, the laser light source can be linearly polarized so 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.

[0053] 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 substantially or substantially does not have 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 reflected light with the first polarization state, and the second LIDAR input signal carries reflected light with the second polarization state. As a result, the first LIDAR input signal is associated with a first polarization state and the second LIDAR input signal is associated with a second polarization state.

[0054] Because the first LIDAR input signal and the second LIDAR 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.

[0055] Suitable polarization rotators include, but are not limited to, polarization-maintaining fiber rotators, Faraday rotators, half-wave plates, MEMS-based polarization rotators, and integrated optics polarization rotators using asymmetric y-branchers, Mach-Zehnder interferometers, and multimode interference couplers.

[0056] 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, the components of the LIDAR adapter can be selected so 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 connection with 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.

[0057] As a result of the above configuration, the first composite signal generated by first processing component 46 and the second composite signal generated by second processing component 48 each result from combining a reference signal and a comparison signal of the same polarization state and provide a desired beat between the reference signal and the comparison signal. For example, the composite signal may be the result of combining the first reference signal and the first comparison signal of a first polarization state and excluding or substantially excluding light of a second polarization state, or the result of combining the first reference signal and the first comparison signal of a second polarization state and excluding or substantially excluding light of the first polarization state. Similarly, the second composite signal may include the second reference signal and the second comparison signal of the same polarization state, thus providing a desired beat between the reference signal and the comparison signal. For example, the second composite signal may be the result of combining a second reference signal of a first polarization state with a second comparison signal and excluding or substantially excluding light of the second polarization state, or the second composite signal may be the result of combining a second reference signal of a second polarization state with a second comparison signal and excluding or substantially excluding light of the first polarization state.

[0058] The above configuration results in LIDAR data for a single sample area of ​​the field of view generated from multiple different composite signals (i.e., the first composite signal and the second composite signal) from the sample area. In some examples, determining the LIDAR data for the sample area includes electronic circuitry combining the LIDAR data from the different composite signals (i.e., the first composite signal and the second composite signal). Combining the LIDAR data can include taking the mean, median, or mode of the LIDAR data generated from the different composite signals. For example, the electronic circuitry can average a distance between the LIDAR system and a reflecting object determined from a composite signal having a distance determined from the second composite signal, and / or the electronic circuitry can average a radial velocity between the LIDAR system and a reflecting object determined from a composite signal having a radial velocity determined from the second composite signal.

[0059] In some examples, determining LIDAR data for the sample area includes electronic circuitry identifying one or more composite signals (i.e., the composite signal and / or the second composite signal) as the source of the most representative LIDAR data (representative LIDAR data). The electronic circuitry can then use the LIDAR data from the identified composite signals as the representative LIDAR data for further processing. For example, the electronic circuitry can identify a signal (the composite signal or the second composite signal) having a larger amplitude as having the representative LIDAR data and use the LIDAR data from the identified signal for further processing by the LIDAR system. In some examples, the electronic circuitry combines identifying the composite signal with the representative LIDAR data with combining LIDAR data from different LIDAR signals. For example, the electronic circuitry 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 electronic circuitry can combine the LIDAR data of each identified composite signal. If one composite signal is identified as having representative LIDAR data, the electronics can use the LIDAR data from that composite signal as the representative LIDAR data. If none of the composite signals are identified as having representative LIDAR data, the electronics can discard the LIDAR data for the sample areas associated with those composite signals.

[0060] Although Figure 3 is described with reference to components 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 the components of Figure 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, beamsplitter 120 can be configured such that the second portion of the system return signal has a first polarization state and 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.

[0061] The above system configuration results in the first portion of the system return signal and the second portion of the system return signal being directed into different composite signals, such that the first portion of the system return signal and the second portion of the system return signal are each associated with a different polarization state, but the electronic circuitry can process each composite signal so 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.

[0062] 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 at a desired location. In some cases, the third lens 126 focuses or collimates the second LIDAR output signal at a desired location. For example, the third lens 126 can be configured to focus or collimate the second LIDAR output signal at the facet 52 of the second comparison waveguide 50. The LIDAR adapter also includes one or more redirecting components 124, such as mirrors and prisms. FIG. 3 illustrates a LIDAR adapter with a mirror as the redirecting component 124 that redirects the second portion of the system return signal from the circulator 100 to the facet 52 of the second comparison waveguide 50 and / or the third lens 1266.

[0063] If 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, metal, silicon, and ceramic plates. As an example, FIG. 4 is a plan view of a LIDAR system including the LIDAR chip of FIG. 1A, electronics 32, and the LIDAR adapter of FIG. 2 mounted on a common support 140. While the electronics 32 is shown as being disposed on the common support, all or part of the electronics can be disposed outside the common support. If the light source 4 is disposed outside the LIDAR chip, the light source can be disposed on the common support 240 or outside the common support 140. Suitable approaches for attaching the LIDAR chip, electronics, and / or LIDAR adapter to the common support include, but are not limited to, epoxy, solder, and mechanical clamps.

[0064] A LIDAR system can include components with additional passive and / or active optical components. A portion of the LIDAR output signal from one or more components can serve as the system output signal. For example, a LIDAR system can include one or more beam steering components that receive the LIDAR output signal from the LIDAR chip or from the LIDAR adapter and output all or a portion of the LIDAR output signal that serves as the system output signal. For example, FIG. 4 shows a beam steering component 142 that receives the LIDAR output signal from the LIDAR adapter. While FIG. 4 shows the beam steering component located on the common support 140, the beam steering components can be located on the LIDAR adapter, on the LIDAR chip, or outside of 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, the LIDAR adapter, and / or the common support.

[0065] The electronic circuitry can operate one or more beam steering components 142 to steer the system output signal to different sample areas 144. The sample areas can extend up to a maximum distance away from the LIDAR system that the LIDAR system is configured to provide reliable LIDAR data. The sample areas can be stitched together to define a field of view. For example, the field of view for a LIDAR system includes or comprises the space occupied by the combination of the sample areas.

[0066] 5A-5C illustrate examples of suitable processing components for use as all or part of a processing component selected from the group consisting of processing component 22, first processing component 46, and second processing component 48. The processing components receive a comparison signal from comparison waveguide 196 and a reference signal from reference waveguide 198. Comparison waveguide 18 and reference waveguide 20 shown in FIGS. 1A and 1B can function as comparison waveguide 196 and reference waveguide 198, comparison waveguide 18 and first reference waveguide 42 shown in FIG. 1C can function as comparison waveguide 196 and reference waveguide 198, or second comparison waveguide 50 and second reference waveguide 44 shown in FIG. 1C can function as comparison waveguide 196 and reference waveguide 198.

[0067] The processing component includes a second splitter 200 that splits the comparison signal carried in the comparison waveguide 196 into 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 combining component 211. The second comparison waveguide 208 carries a second portion of the comparison signal to a second optical combining component 212.

[0068] The processing component includes a first splitter 202 that splits a reference signal carried in the reference waveguide 196 into a first reference waveguide 204 and a second reference waveguide 206. The first reference waveguide 204 carries a first portion of the reference signal to an optical coupling component 211. The second reference waveguide 208 carries a second portion of the reference signal to a second optical coupling component 212.

[0069] The second optical combining component 212 combines the second portion of the comparison signal and the second portion of the reference signal into a second composite signal, which beats between the second portion of the comparison signal and the second portion of the reference signal due to the frequency difference between the second portion of the comparison signal and the second portion of the reference signal.

[0070] The second optical combining component 212 also splits the resulting second composite signal into a first auxiliary detection waveguide 214 and a second auxiliary detection waveguide 216. The first auxiliary detection waveguide 214 carries a first portion of the second composite signal to a first auxiliary optical sensor 218, which converts the first portion of the second composite signal into a first auxiliary electrical signal. The second auxiliary detection waveguide 216 carries a second portion of the second composite signal to a second auxiliary 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).

[0071] In some cases, the second optical combining component 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., part of the second portion of the comparison signal) is 180° out of phase with the portion of the comparison signal in the second portion of the second composite signal (i.e., part of the second portion of the comparison signal), but the portion of the reference signal in the second portion of the second composite signal (i.e., part of the second portion of the reference signal) is not out of phase with the portion of the reference signal in the first portion of the second composite signal (i.e., part of the second portion of the reference signal). Alternatively, the second optical combining component 212 splits the second composite signal such that the portion of the reference signal in the first portion of the second composite signal (i.e., a portion of the second portion of the reference signal) is 180° out of phase with the portion of the reference signal in the second portion of the second composite signal (i.e., a portion of the second portion of the reference signal), but the portion of the comparison signal in the first portion of the second composite signal (i.e., a portion of the second portion of the comparison signal) is not out of phase with the portion of the comparison signal in the second portion of the second composite signal (i.e., a portion of the second portion of the comparison signal). Examples of suitable optical sensors include germanium photodiodes (PDs) and avalanche photodiodes (APDs).

[0072] The first optical coupling component 211 couples the first portion of the comparison signal and the first portion of the reference signal into a first composite signal, and the first composite signal oscillates between the first portion of the comparison signal and the first portion of the reference signal due to the frequency difference between the first portion of the comparison signal and the first portion of the reference signal.

[0073] The first optical combining component 211 also splits the first composite signal into a first detection waveguide 221 and a second detection waveguide 222. The first detection waveguide 221 carries a first portion of the first 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 detection waveguide 222 carries a second portion of the second composite signal to a second optical sensor 224, which converts a 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).

[0074] In some cases, the optical combining component 211 splits the first composite signal such that the 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 180° out of phase with the 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 the portion of the reference signal in the first portion of the composite signal (i.e., a portion of the first portion of the comparison signal) is not out of phase with the 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 combining component 211 splits the composite signal such that the 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 180° out of phase with the 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 the 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 out of phase with the 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).

[0075] When the second optical combining component 212 splits the second composite signal such that the portion of the comparison signal in the first portion of the second composite signal is 180° out of phase with the portion of the comparison signal in the second portion of the second composite signal, the optical combining component 211 also splits the composite signal such that the portion of the comparison signal in the first portion of the composite signal is 180° out of phase with the portion of the comparison signal in the second portion of the composite signal. When the second optical combining component 212 splits the second composite signal such that the portion of the reference signal in the first portion of the second composite signal is 180° out of phase with the portion of the reference signal in the second portion of the second composite signal, the optical combining component 211 also splits the composite signal such that the portion of the reference signal in the first portion of the composite signal is 180° out of phase with the portion of the reference signal in the second portion of the composite signal.

[0076] The first reference waveguide 210 and the second reference waveguide 208 are configured 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 configured 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. In one 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 out of phase with respect to the reference signal portion in the first composite signal, while the comparison signal portion in the first composite signal is out of phase with respect to the comparison signal portion in the second composite signal.

[0077] The first optical sensor 223 and the second optical sensor 224 can be connected as a balanced detector, and the first auxiliary optical sensor 218 and the second auxiliary optical sensor 220 can also be connected as a balanced detector. For example, FIG. 5B provides a schematic of the relationship between the electronic circuitry, the first optical sensor 223, the second optical sensor 224, the first auxiliary optical sensor 218, and the second auxiliary optical sensor 220. Although symbols for photodiodes are used to represent the first optical sensor 223, the second optical sensor 224, the first auxiliary optical sensor 218, and the second auxiliary optical sensor 220, one or more of these sensors can 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 electronic circuitry located off the LIDAR chip.

[0078] The electronic circuitry connects the first and second optical sensors 223 and 220 as a first balanced detector 225 and the first and second auxiliary optical sensors 218 and 220 as a second balanced detector 226. Specifically, the first and second optical sensors 223 and 224 are connected in series. The electronic circuitry also connects the first and second auxiliary optical sensors 218 and 220 in series. The first and second balanced detectors communicate with a first data line 228 carrying the output from the first balanced detector as a first data signal. The second and second balanced detectors communicate with a second data line 232 carrying 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 a first waveform and a second waveform, and the second data signal is a composite of the first and second waveforms. A portion of the first waveform in the first data signal is out of phase with a portion of the first waveform in the first data signal, while a portion of the 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 has a portion of the reference signal that is out of phase with a different portion of the reference signal included in the first data signal. Additionally, the second data signal has a portion of the comparison signal that is in phase with a different portion of the comparison signal included in the first data signal. The first and second data signals beat as a result of the beat between the comparison signal and the reference signal, i.e., the beat in the first composite signal and the beat in the second composite signal.

[0079] The electronic circuitry 32 includes a transform mechanism 238 configured to perform a mathematical transformation of the first and second data signals. For example, the mathematical transformation can be a complex Fourier transform with the first and second data signals as inputs. Because the first data signal is the in-phase component and the second data signal is its quadrature component, the first and second data signals together act as a complex data signal, with the first data signal being the real component of the input and the second data signal being the imaginary component of the input.

[0080] The conversion mechanism 238 includes a first analog-to-digital converter (ADC) 264 that receives the first data signal from the first data line 228. The first analog-to-digital converter (ADC) converts the first data signal from analog to digital format and outputs a first digital data signal. The conversion mechanism 238 includes a second analog-to-digital converter (ADC) 266 that receives the second data signal from the second data line 232. The second analog-to-digital converter (ADC) 226 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 act as a complex signal, with the first digital data signal acting as the real component of the complex signal and the second digital data signal acting as the imaginary component of the complex data signal.

[0081] The conversion mechanism 238 includes a conversion component 268 that receives a complex data signal. For example, the conversion component 268 receives as an input a first digital data signal from a first analog-to-digital converter (ADC) 264 and a second digital data signal from a second analog-to-digital converter (ADC) 266. The conversion component 268 can be configured to perform a mathematical transform on the complex 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 frequency shift 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 electronic circuitry utilizes one or more frequency peaks output from the conversion component 268 for further processing to generate LIDAR data (e.g., the distance and / or radial velocity between the reflecting object and the LIDAR tip or LIDAR system). The transformation component 268 can use firmware, hardware, or software, or a combination thereof, to perform the attributed functions.

[0082] 5C shows an example of the relationship between frequency, time, period, and data period of the system output signal. The base frequency (f0) of the system output signal can be the frequency of the system output signal at the start of a period.

[0083] FIG. 5C shows frequency versus time for a sequence of two periods, labeled Period j and Period j+1. In some examples, the frequency versus time pattern is repeated in each period as shown in FIG. 5C. The periods shown do not have rearrangement periods and / or the rearrangement periods are not spaced between periods. As a result, FIG. 5C shows the results of a continuous scan.

[0084] Each period of the multiple periods has K data periods, each associated with a period index k and labeled DPk. In the example of FIG. 5C, each period has two data periods labeled DPk, with k=1 and k=2. In some cases, as shown in FIG. 5C, the frequency versus time pattern is the same for corresponding data periods in different periods. Corresponding data periods are data periods with the same period index. As a result, each of the data periods DP1 can be considered a corresponding data period, and the associated frequency versus time pattern is the same in FIG. 5C. At the end of a period, the electronic circuitry returns the frequency to the same frequency level that started the previous period.

[0085] During data period DP1 and data period DP2, the electronic circuitry operates the light source so that the frequency of the system output signal changes at a linear rate of change α, where the direction of the frequency change during data period DP1 is opposite to the direction of the frequency change during data period DP2.

[0086] The frequencies output from the complex Fourier transform represent the beat frequencies of the complex signal, with each comparison signal beating relative to a reference signal. Beat frequencies (fLDP) from two or more different data periods can be combined to generate LIDAR data. For example, the beat frequency determined from DP1 in FIG. 5C can be combined with the beat frequency determined from DP22 in FIG. 5C to determine LIDAR data. As an example, during a data period, such as data period DP1 in FIG. 5C, where the electronic circuitry increases the frequency of the outgoing LIDAR signal during the data period, the following equation applies: fub=-fd+ατ, where fub is the frequency provided by the transformation component 268 (here, fLDP determined from DP1), and fd represents the Doppler shift (fd=2νfc / c), where fc represents the optical frequency (f0), c represents the speed of light, ν represents the radial velocity between the reflecting object and the LIDAR system, and v 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. During a data period, such as data period DP2 of cycle j in FIG. 5C, when the electronic circuitry decreases the frequency of the outgoing LIDAR signal during the data period, the following equation is applied: fdb=-fd-ατ, where fdb is the frequency provided by the transformation component 268 (here, f.LDP determined from DP2). In these two equations, fd and τ are unknowns. The electronic circuitry solves these two equations for the two unknowns fd and τ, and the radial velocity for the sample volume can be determined from the Doppler shift (ν=c×fd / (2fc)) and / or the separation distance for the sample volume can be determined from c×fd / 2.

[0087] In some examples, more than one object is present in the sample region. The different objects need not be physically separate objects and can be different surfaces of the same object. When more than one object is present in the sample region, the transform may output more than one frequency, with each frequency associated with a different object. Frequencies arising from the same object in different data periods of the same cycle may be considered corresponding frequency pairs. LIDAR data may be generated for each corresponding frequency pair output by the transform. As a result, different LIDAR data may be generated for each object in the sample region.

[0088] 5A-5B show an optical combining component that combines a portion of the reference signal with a portion of the comparison signal, the processing component can include a single optical combining component 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 can be combined to form a composite signal. The combined portion of the reference signal can be the entire reference signal or a portion of the reference signal, and the combined portion of the comparison signal can be the entire comparison signal or a portion of the comparison signal.

[0089] As an example of a processing component that combines the reference signal and the comparison signal to form a composite signal, Figures 5D-5E show the processing component of Figures 5A-5B modified to include a single optically coupled component. Comparison waveguide 196 carries the comparison signal directly to first optically coupled component 211, and reference waveguide 198 carries the reference signal directly to first optically coupled component 211.

[0090] The first optical coupling component 211 couples the first portion of the comparison signal and the first portion of the reference signal into a first composite signal. Due to the frequency difference between the first portion of the comparison signal and the first portion of the reference signal, the first composite signal oscillates between the first portion of the comparison signal and the first portion of the reference signal. The first optical coupling component 211 also splits the first composite signal into a first detection waveguide 221 and a second detection waveguide 222. The first detection waveguide 221 carries the 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 detection waveguide 222 carries the 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.

[0091] Figure 5E provides a schematic of the relationship between the electronic circuitry, first optical sensor 223, and second optical sensor 224. Although symbols for photodiodes are 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 Figure 5E are included on the LIDAR chip. In some cases, the components shown in the schematic diagram of Figure 5E are distributed between the LIDAR chip and electronic circuitry located off the LIDAR chip.

[0092] The electronic circuitry connects the first photosensor 223 and the second photosensor 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. The first data signal is an electrical representation of the first composite signal.

[0093] The electronics 32 includes a transform mechanism 238 configured to perform a mathematical transform on the first data signal. The mathematical transform can be a real Fourier transform with the first data signal as an input. The electronics can extract the LIDAR data using frequencies output from such a transform.

[0094] 5A-5E can be replaced with a single optical sensor. As a result, the processing component can have one or more optical sensors that each receive at least a portion of the composite signal, where the received portion of the composite signal can be the entire composite signal or a portion of the composite signal.

[0095] As discussed in connection with Figure 5C, the electronic circuitry 32 adjusts the frequency of the system output signal. One way to generate this frequency chirp is to modulate the current applied to the light source by the electronic circuitry. In semiconductor lasers, which can be used as light sources in LIDAR systems, current modulation results in frequency modulation via strong nonlinear carrier / photon coupling.

[0096] 6A and 6B illustrate an example of a control component suitable for use as all or part of the control component 30 disclosed in connection with FIGS. 1A through 1C and 4. The control component 30 includes a Mach-Zehnder interferometer configured to generate an optical signal having an in-phase component and a quadrature component using light from a tap signal. The Mach-Zehnder interferometer receives the tap signal through a control waveguide 28. The control waveguide directs the tap signal to a splitter 270, which splits the tap signal into a delay signal and a forward signal. A delay waveguide 272 carries the delay signal to a first splitter 274. A forward waveguide 276 carries the forward signal to a second splitter 278. The delay waveguide 272 can include a delay section 279 that can be used to increase the length of the delay waveguide beyond the length of the forward waveguide 276. For example, the delay section 279 shown in FIG. 6A can correspond to a helical arrangement of the delay waveguide 272. Suitable splitters for use as splitter 270, first splitter 274, and second splitter 278 include, but are not limited to, directional couplers, optical couplers, y-couplers, tapered couplers, and multi-mode interference (MMI) devices.

[0097] The first splitter 274 splits the delayed signal into a first portion of the delayed signal and a second portion of the delayed signal. A first delay waveguide 280 carries the first portion of the delayed signal to a first optical combining component 282. A second delay waveguide 284 carries the second portion of the delayed signal to a second optical combining component 286.

[0098] The second splitter 278 splits the forward signal into a first portion of the forward signal and a second portion of the forward signal. The first forward waveguide 290 carries the first portion of the forward signal to the first optical combining component 282. The second forward waveguide 292 carries the second portion of the forward signal to the second optical combining component 286.

[0099] The second optical combining component 286 combines the second portion of the early signal and the second portion of the delayed signal into a second beat signal. As described above, the length of the delayed waveguide is longer than the length of the early waveguide 276. As a result, the second portion of the delayed signal is delayed in phase relative to the second portion of the early signal. Because the electronic circuitry can tune the frequency of the outgoing LIDAR signal, the delay results in the second portion of the delayed signal having a different frequency than the second portion of the early signal. Due to the difference in frequency between the second portion of the early signal and the second portion of the delayed signal, the second beat signal beats between the second portion of the early signal and the second portion of the delayed signal.

[0100] The second optical coupling component 286 also splits the second beat signal to a first auxiliary detector waveguide 294 and a second auxiliary detector waveguide 296. The first auxiliary detector waveguide 294 carries a first portion of the second beat signal to a first auxiliary optical sensor 298. The first auxiliary optical sensor 298 converts the first portion of the second beat signal into a first auxiliary electrical signal. The second auxiliary detector waveguide 296 carries a second portion of the second beat signal to a second auxiliary optical sensor 300. The second auxiliary optical sensor 300 converts the second portion of the second beat signal into a second auxiliary electrical signal. Examples of suitable optical sensors include germanium photodiodes (PDs) and avalanche photodiodes (APDs).

[0101] In some cases, the second optical coupling component 286 splits the second beat signal such that the lead signal portion in the first portion of the second beat signal (i.e., part of the second portion of the lead signal) is 180° out of phase with the lead signal portion in the second portion of the second beat signal (i.e., part of the second portion of the lead signal), while the lag signal portion in the second portion of the second beat signal (i.e., part of the second portion of the lag signal) is not out of phase with the lag signal portion in the first portion of the second beat signal (i.e., part of the second portion of the lag signal).

[0102] The first optical combining component 282 combines the first portion of the early signal with the first portion of the delayed signal to form a first beat signal. The delay section 279 delays the first portion of the delayed signal relative to the first portion of the early signal. As a result, the first portion of the delayed signal is delayed relative to the first portion of the early signal. The delay results in the first portion of the delayed signal having a different frequency than the first portion of the early signal. Due to the difference in frequency between the first portion of the early signal and the first portion of the delayed signal, the first beat signal beats between the second portion of the early signal and the second portion of the delayed signal.

[0103] The first optical coupling component 282 also splits the first beat signal into a first detector waveguide 302 and a second detector waveguide 304. The first detector waveguide 302 carries a first portion of the first beat signal to a first optical sensor 306, which converts it into a first electrical signal. The second detector waveguide 304 carries a second portion of the second beat signal to a second optical sensor 308, which converts it into a second electrical signal. Examples of suitable optical sensors include germanium photodiodes (PDs) and avalanche photodiodes (APDs).

[0104] In some cases, the first optical coupling component 282 splits the first beat signal such that the lead signal portion in the first portion of the beat signal (i.e., part of the first portion of the lead signal) is 180° out of phase with the lead signal portion in the second portion of the beat signal (i.e., part of the first portion of the lead signal), while the lag signal portion in the first portion of the beat signal (i.e., part of the first portion of the lag signal) is not out of phase with the lag signal portion in the second portion of the beat signal (i.e., part of the first portion of the lag signal).

[0105] The second optical coupling component 286 splits the second beat signal such that the lead signal portion of the first portion of the second beat signal is 180° out of phase with the lead signal portion of the second portion of the second beat signal, and the first optical coupling component 282 also splits the beat signal such that the lead signal portion of the first portion of the beat signal is 180° out of phase with the lead signal portion of the second portion of the beat signal.

[0106] The first delay waveguide 280, the second delay waveguide 284, the first lead waveguide 290, and the second lead waveguide 292 can be configured so that the first beat signal and the second beat signal collectively act as the in-phase and quadrature components of the optical process variable signal, where the first beat signal is the in-phase component of the optical process variable signal and the second beat signal is the quadrature component of the optical process variable signal, or the second beat signal is the in-phase component of the optical process variable signal and the first beat signal is the in-phase component of the optical process variable signal. For example, the first delay waveguide 280 and the second delay waveguide 284 can be configured to provide a phase shift between the first portion of the delay signal and the second portion of the delay signal, while the first lead waveguide 290 and the second lead waveguide 292 can be configured so that the first portion of the lead signal and the second portion of the lead signal are in phase. As an example, the first delay waveguide 280 and the second delay waveguide 284 can be configured to provide a 90° phase shift between the first portion of the delayed signal and the second portion of the delayed signal. Thus, one portion of the delayed signal can be a sine function and the other portion of the delayed signal can be a cosine function operating with the same argument as the sine function. In one example, the first delay waveguide 280 and the second delay waveguide 284 can be configured so that the first portion of the delayed signal is a cosine function and the second portion of the delayed signal is a sine function. In this example, the delayed signal portion of the second beat signal is out of phase with the delayed signal portion of the first beat signal, but the lead signal portion of the first beat signal is not out of phase with the lead signal portion of the second beat signal.

[0107] In another example, first delay waveguide 280 and second delay waveguide 284 are configured so that the first portion of the delayed signal and the second portion of the delayed signal are in phase, while first forward waveguide 290 and second forward waveguide 292 are configured to provide a phase shift between the first portion of the forward signal and the second portion of the forward signal. As an example, first forward waveguide 290 and second forward waveguide 292 can be configured to provide a 90° phase shift between the first portion of the forward signal and the second portion of the forward signal. Thus, one portion of the forward signal can be a sine function and the other portion of the forward signal can be a cosine function operating on the same argument as the sine function. In one example, first forward waveguide 290 and second forward waveguide 292 are configured so that the first portion of the forward signal is a cosine function and the second portion of the forward signal is a sine function operating on the same argument as the cosine function. In this example, the lead signal portion of the second beat signal is out of phase with respect to the lead signal portion of the first beat signal, but the lag signal portion of the first beat signal is not out of phase with respect to the lag signal portion of the second beat signal.

[0108] The first optical sensor 306 and the second optical sensor 308 can be connected as a balanced detector, and the first auxiliary optical sensor 298 and the second auxiliary optical sensor 300 can also be connected as a balanced detector. For example, FIG. 6B provides a schematic of the relationship between the electronic circuitry, the first optical sensor 306, the second optical sensor 308, the first auxiliary optical sensor 298, and the second auxiliary optical sensor 300. Although symbols for photodiodes are used to represent the first optical sensor 306, the second optical sensor 308, the first auxiliary optical sensor 298, and the second auxiliary optical sensor 300, one or more of these sensors can 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 examples, the components shown in the schematic diagram of FIG. 6B are distributed between the LIDAR chip and electronic circuitry located remotely from the LIDAR chip.

[0109] The electronic circuitry connects the first and second photosensors 306 and 308 as a first balanced detector 3312 and the first and second auxiliary photosensors 298 and 300 as a second balanced detector 314. Specifically, the first and second photosensors 306 and 308 are connected in series. Additionally, the first and second auxiliary photosensors 298 and 300 are connected in series. The series connection in the first balanced detector communicates with a first data line 316 that carries the output from the first balanced detector as a first process variable signal. The series connection in the second balanced detector communicates with a second data line 318 that carries the output from the second balanced detector as a first process variable signal.

[0110] The first process variable signal is an electrical representation of the first beat signal, and the second process variable signal is an electrical representation of the second beat signal. Thus, the first process variable signal is beating and the second process variable signal is beating. Additionally, the first process variable signal and the second process variable signal can each carry a different component selected from the group consisting of an in-phase component of the process variable signal and a quadrature component of the process variable signal. For example, the first process variable signal can include contributions from a first waveform and a second waveform, and the second process variable signal can include contributions from the first waveform and the second waveform. A portion of the first waveform of the first process variable signal is out of phase with a portion of the first waveform of the second process variable signal, while a portion of the second waveform of the first process variable signal is in phase with a portion of the second waveform of the second process variable signal. For example, the second process variable signal can include a lagging signal portion that is out of phase with a different portion of the lagging signal included in the first process variable signal. Additionally, the second process variable signal may include a portion of the lead signal that is in phase with a different portion of the lead signal included in the first process variable signal. The first and second process variable signals are beating as a result of the beat between the lead and lag signals, i.e., the beat in the first and second beat signals, respectively.

[0111] The process variable signal is received by the process variable identification component 320. The process variable identification component 320 uses the process variable signal to output an indicator signal that indicates, functions as, and / or can be used to determine the frequency (fTS) of the tap signal. In some cases, the indicator signal is an analog signal having one or more characteristics associated with the frequency (fTS) of the tap signal. In some cases, the indicator signal is a digital signal that quantifies, is related to, or can be used to quantify the frequency (fTS) of the tap signal. Because the system output signal and the tap signal represent portions of the outgoing LIDAR signal, the frequency (fTS) of the tap signal can represent a frequency value for the outgoing LIDAR signal and / or for the system output signal.

[0112] The indicator signal can be received by the light control component 322. The light control component 322 can control the light source in response to the indicator signal. For example, the light source can be controlled in a control architecture in which the frequency of the tap signal (fTS) serves as the controlled process variable. When the process variable is the frequency of the tap signal, the desired frequency of the LIDAR output signal serves as the reference variable. Because the frequency of the LIDAR output signal is modulated, the desired frequency of the LIDAR output signal, represented by the tap signal, varies as a function of time. For triangular modulation, FIG. 5C can represent an example of a desired waveform. As can be seen from FIG. 5C, the frequency of the tap signal is a linear function of time. Thus, the control mechanism can control the light source such that the frequency of the tap signal substantially maintains the desired waveform. Suitable control mechanisms include, but are not limited to, control architectures using feedback control and / or feedforward control. Thus, the control mechanism can be a feedback control loop.

[0113] The optical control component 322 can control the tap signal, and thus the outgoing LIDAR signal and / or the system output signal, in response to the value of the error signal determined from the value of the controlled process variable at a particular point in time and the value of the reference variable at the same time. For example, the optical control component 322 can control the characteristics of the tap signal to decrease the value of the error signal. As an example, the optical control component 322 can control the characteristics of the tap signal to move the value of the controlled process variable toward the value of the reference variable. In some cases, the control mechanism is a control loop, such as a feedback control loop. When the control mechanism is a feedback control loop, the error signal for the control mechanism can be equal to the difference between the value of the controlled process variable and the value of the reference variable at a particular point in time.

[0114] If the process variable is the frequency of the tap signal, the optical control component 322 can send an optical control signal that adjusts the frequency of the tap signal. For example, the optical control component 322 can adjust the frequency of the tap signal by sending an optical control signal that varies the level of current through the optical source. Other optical control signals are possible. For example, if the optical source is an electrostatic MEMS tunable laser, the optical control component 322 can adjust the frequency of the tap signal by sending an optical control signal that varies the level of voltage that moves a MEMS facet of the MEMS tunable laser.

[0115] In some examples, the optical control component 322 and / or the process variable identification component 320 actually quantify the tap signal (fTS). However, this quantification is not necessary. For example, if the indicator signal is an analog signal having characteristics related to the tap signal (fTS), the optical control signal can be derived directly from the indicator signal without actually quantifying the frequency of the tap signal (fTS). For example, the control signal can be a one-to-one function of the indicator signal and / or a conversion signal, as described below. As an example, the control signal can be a one-to-one function of the instantaneous frequency.

[0116] Figure 6C shows the amplitude of the optical process variable signal and / or the in-phase and quadrature components of the process variable signal on the same time axis as the frequency of the system output signal. For example, Figure 6C can compare the frequency of the system output signal during the first two data periods shown in Figure 5C compared to the changes in the in-phase and quadrature components of the optical process variable signal and / or the process variable signal. Although Figure 6C shows the optical process variable signal and / or the process variable signal having only one period per data period, the optical process variable signal and / or the process variable signal may have more than one period per data period.

[0117] Various process variable identification components 320 can be used to determine the value of the process variable indicator. Figure 6D shows an example of a process variable identification component 320 suitable for use when the process variable is the frequency of the tap signal, the emitted LIDAR signal, and / or the system output signal. The illustrated process variable identification component 320 includes a local oscillator 324 that outputs a local signal having a first local signal and a second local signal. The first local signal and the second local signal each carry a different component selected from the group consisting of an in-phase component of the local signal and a quadrature component of the local signal.

[0118] The process variable identification component 320 also includes a first multiplier 326 that receives the first process variable signal and the first local signal. The first multiplier 326 multiplies the first process variable signal and the first local signal. If the first process variable signal carries the in-phase component of the process variable signal, the first local signal carries the quadrature component of the local signal. If the first process variable signal carries the quadrature component of the process variable signal, the first local signal carries the in-phase component of the local signal. The first multiplier 326 outputs the first multiplied signal.

[0119] The process variable identification component 320 also includes a second multiplier 328 that receives the second process variable signal and the second local signal. The second multiplier 328 multiplies the second processed variable signal and the second local signal. When the second process variable signal carries the in-phase component of the process variable signal, the second local signal carries the quadrature component of the local signal. When the second process variable signal carries the quadrature component of the process variable signal, the second local signal carries the in-phase component of the local signal. The second multiplier 326 outputs the second multiplied signal.

[0120] The process variable identification component 320 includes a summing unit 330 that receives the first multiplied signal and the second multiplied signal, sums the first multiplied signal and the second multiplied signal, and outputs a control signal.

[0121] The control signal is received by the process variable evaluator 334. The process variable evaluator 334 uses the control signal to output an indicator signal having one or more characteristics related to the frequency (fTS) of the tap signal. For example, the process variable evaluator 334 can be a time-to-digital converter (TDC) that outputs an indicator signal having a voltage related to the frequency (fTS) of the tap signal. In some cases, the time-to-digital converter (TDC) outputs an indicator signal having a voltage proportional to the frequency (fTS) of the tap signal. The indicator signal can be received by the light control component 322 for use in controlling the frequency of the light source.

[0122] Another example of a suitable process variable evaluator 332 is a frequency counter that outputs an indicator signal indicative of the time between reference line crossings (dn) of the control signal. The frequency (fTS) determined for the tap signal can be related to the time between reference line crossings (dn) by equation 1: fTS = fLO-1 / (2 x dn), where fLO represents the local oscillator frequency. The process variable evaluator 334 can output an indicator signal carrying data indicative of the value of the frequency (fTS) determined for the tap signal. The indicator signal can be received by the light control component 322 for use in controlling the frequency of the light source.

[0123] The local signal is selected so that the frequency of the control signal is higher than the frequency of the process signal. Increasing the frequency of the control signal increases the frequency at which the process variable can be accurately sampled. This increase in sampling frequency provides more accurate control of the process variable by the control mechanism. As a result, increasing the frequency of the control signal enhances control of the process variable by the control mechanism. Suitable sampling frequencies include, but are not limited to, sampling frequencies greater than 100 times the modulation frequency, where the modulation frequency is 1 / (period duration). In some cases, all or part of the data period in each period has a sampling frequency greater than 30 or 100 times the duration of the data period. In some cases, the local signal is selected so that the frequency of the control signal is greater than 100 times but less than 10,000 times the frequency of the process variable signal.

[0124] 6E shows another example of a process variable identification component 320 suitable for use when the process variable is the frequency of a tap signal, an emitted LIDAR signal, and / or a system output signal. The process variable identification component 320 includes an analog-to-digital converter (ADC) 340 that receives the control signal from the summing component 330. The analog-to-digital converter (ADC) 340 converts the first process variable signal from analog to digital form and outputs a digital data signal. The digital data signal is a digital representation of the control signal.

[0125] The process variable identification component 320 includes a transformation component 342 that receives the digital data signal. The transformation component 342 performs a mathematical transform on the digital data signal. The transformation component 342 selects the mathematical transform such that the transformation component 342 outputs a transformed signal that is related to, has, or is indicative of, the frequency of the LIDAR output signal. A suitable first mathematical transform includes, but is not limited to, a Hilbert transform. The Hilbert transform outputs a transformed signal that is indicative of the instantaneous phase and, consequently, the frequency of the control signal.

[0126] The converted signal is received by the frequency estimator 344. The frequency estimator can be configured to output an indicator signal having and / or indicative of the frequency of the LIDAR output signal. For example, the frequency estimator can convert the instantaneous frequency to the frequency of the tap signal (fTS) by: fTS = (f inst - fLO) × (T / τ), where fLO is the local oscillator frequency, f inst is the instantaneous frequency extracted from the Hilbert transform, T is the duration of a data period in a triangular modulation scheme, and τ is the delay due to the difference in length between the lag waveguide 272 and the lead waveguide 276. Thus, the indicator signal can be a digital signal that quantifies the frequency of the tap signal (fTS). The indicator signal can be received by the light control component 322 for use in frequency control of the light source.

[0127] Although the indicator signal is described in relation to a signal carrying data related to the frequency of the tap signal, the indicator signal can carry data indirectly related to the frequency of the tap signal. For example, the indicator signal can carry data that can be used to determine the frequency of the tap signal. As an example, the frequency of the tap signal (fTS) can be determined from the rate of phase change of the tap signal. Thus, the indicator signal can carry data indicative of the rate of phase change of the tap signal.

[0128] By combining information from the in-phase and quadrature components at any given time, the process variable identification component 320 increases the sensitivity of the indicator signal to the frequency of the tap signal, thereby reducing the amount of delay that needs to be generated by the delay waveguide 272. Conventional systems attempt to increase this sensitivity by increasing the length of the delay waveguide 272. Because the process variable identification component 3203 increases the sensitivity of the indicator signal, the length of the delay waveguide 272 can exceed the length of the lead waveguide 276 by a lower amount than can be achieved in conventional systems. For example, the time delay in the delay waveguide 272 can exceed the time delay of the lead waveguide 276 by an amount equal to or greater than 50 ps and equal to or less than 100 ns. In one example, the length of the delay waveguide 272 exceeds the length of the lead waveguide 276 by an amount less than 1000 cm, less than 500 cm, or less than 100 cm and greater than 0.0 cm or 0.4 cm. In one example, the delay waveguide 272 and the forward waveguide 276 guide light through silicon, and the length of the delay waveguide 272 is less than 1000 cm and exceeds the length of the forward waveguide 276 by an amount greater than 0.0 cm or 0.4 cm.

[0129] Suitable platforms for LIDAR chips include, but are not limited to, silica, indium phosphide, and silicon-on-insulator wafers. FIG. 6 shows a cross section of a portion of a chip constructed from a silicon-on-insulator wafer. A silicon-on-insulator (SOI) wafer has a buried layer 310 between a substrate 312 and an optically transmissive medium 314. In a silicon-on-insulator wafer, the buried layer 310 is silica, while the substrate 312 and optically transmissive medium 314 are silicon. The substrate 31 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 in the LIDAR chips of FIGS. 1A-1C can be disposed on or above the top and / or side surfaces of the substrate 312.

[0130] 7 is a cross-sectional view of a portion of a LIDAR chip including a waveguide structure suitable for use in a LIDAR chip constructed from a silicon-on-insulator wafer. A ridge 316 of optical transmission medium extends away from a slab region 318 of optical transmission medium. The optical signal is confined between the apex of the ridge 316 and a buried oxide layer 310.

[0131] FIG. 7 labels the dimensions of a ridge waveguide. For example, the ridge has a width, labeled w, and a height, labeled h. The thickness of the slab region is labeled T. In 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 slab region thickness is greater than 0.5 μm and less than 3 μm. These dimensions 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 will be single-mode. However, in some cases, these dimensions apply to straight or substantially straight sections of the waveguide. Additionally or alternatively, the curved portion of the waveguide can have a reduced slab thickness to reduce optical loss in the curved portion of the waveguide. For example, the curved portion of the waveguide can have a ridge extending away from the slab region that is greater than 0.0 μm and less than 0.5 μm thick. While the above dimensions generally provide straight or substantially straight portions of the waveguide with a single-mode structure, they can result in tapered and / or curved portions that are multimode. Coupling between multimode geometries and single-mode geometries can be achieved using tapers that do not substantially excite higher-order modes. Thus, the waveguide can be configured such that signals carried in the waveguide are carried in single mode even when carried in a waveguide portion with multimode dimensions. The waveguide structure disclosed in connection with FIG. 6 is suitable for all or a portion of the waveguides of a LIDAR chip constructed according to FIGS. 1A-1C.

[0132] The optical sensor connected to the waveguide in 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, InGaAs PIN photodiodes manufactured by Hamamatsu, located in Hamamatsu, Japan, or InGaAs APDs (avalanche photodiodes) manufactured by Hamamatsu, located in Hamamatsu, Japan. These optical sensors can be centrally located on the LIDAR chip. Alternatively, all or a portion of the waveguide terminating in the optical sensor can terminate in a facet located at the edge of the chip, and the optical sensor can be attached to the edge of the chip beyond the facet so that the optical sensor receives light passing through the facet. The use of an optical sensor that is a component separate from the chip is suitable for all or a portion of the optical sensors selected from the group consisting of first auxiliary optical sensor 218, second auxiliary optical sensor 220, first optical sensor 223, and second optical sensor 224.

[0133] As an alternative to a light sensor that is a separate component, all or part of the light sensor can be integrated into the chip. For example, examples of light sensors coupled to ridge waveguides of chips constructed from silicon-on-insulator wafers can be found in Optical 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, all of which are incorporated herein in their entireties. The use of a light sensor integrated into the chip is suitable for all or part of the light sensors selected from the group consisting of auxiliary light sensor 218, second auxiliary light sensor 220, first light sensor 223, and second light sensor 224.

[0134] The light source 4 connected to the utility waveguide 12 can be a laser chip separate from and attached to the LIDAR chip. For example, the light source 4 can be a laser chip attached to the chip using a flip-chip arrangement. Use of a flip-chip arrangement is preferred when the light source 4 is connected to a ridge waveguide of 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 acts as a reflector for an external cavity laser. In these examples, the light source 4 can include a gain element separate from the LIDAR chip and attached to the LIDAR chip in a flip-chip arrangement. Examples of suitable interfaces between silicon-on-insulator wafer gain elements and ridge waveguides can be found in U.S. Patent No. 9,700,278, issued July 11, 2017, and U.S. Patent No. 5,991,484, issued November 23, 1999, which are incorporated herein in their entireties. If light source 4 is a gain element or laser chip, electronic circuitry 32 can change the frequency of the emitted LIDAR signal by varying the level of current applied through the gain element or laser cavity.

[0135] Suitable electronic circuitry 32 may include, but is not limited to, an electronic controller comprising or configured with analog circuitry, digital circuitry, a processor, a microprocessor, a digital signal processor (DSP), a field programmable gate array (FPGA), a computer, a microcomputer, or any suitable combination for performing the above-described operation, control, and control functions. In some examples, the electronic controller has access to a memory containing instructions that are executed by the electronic controller during the performance of the operation, control, and monitoring functions. While the electronic circuitry is illustrated as a single component in a single location, the electronic circuitry may comprise multiple distinct components that are separate from one another and / or located in different locations. Additionally, as discussed above, all or a portion of the disclosed electronic circuitry may be included on a chip with the integrated electronic circuitry of the chip.

[0136] The LIDAR systems described above include multiple optical components, such as a LIDAR chip, a LIDAR adapter, a light source, a light sensor, a waveguide, and an amplifier. In some examples, 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 that exclude 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 examples, the LIDAR system includes one or more active optical components in addition to or in place of the optical components shown. Suitable active components include, but are not limited to, optical switches, phase tuners, attenuators, steerable mirrors, steerable lenses, tunable demultiplexers, and tunable multiplexers.

[0137] Other embodiments, combinations, and modifications of the present invention will be readily apparent to those skilled in the art in view of these teachings. Accordingly, the present invention is limited only by the scope of the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.

Claims

1. at least one optical component configured to output a system output signal that travels away from the LIDAR system and that can be reflected by an object located external to the LIDAR system, the LIDAR system configured such that the system output signal and the tap signal each include light from the outgoing LIDAR signal; and a control mechanism configured to control one or more process variables of the system output signal, the control mechanism generating an electrical process variable signal from a tap signal and using the electrical process variable signal to control the process variables, the electrical process variable signal having an in-phase component and a quadrature component; the control mechanism is configured to multiply the electrical process variable signal by a local signal including an in-phase component and a quadrature component; Including, the control mechanism is configured to multiply the electrical process variable signal with the local signal such that an in-phase component of the electrical process variable signal is multiplied with a quadrature component of the local signal, and such that the quadrature component of the electrical process variable signal is multiplied with an in-phase component of the local signal; the control mechanism includes a first multiplier configured to multiply an in-phase component of the electrical process variable signal with a quadrature component of the local signal to generate a first multiplied signal; The control mechanism includes a first multiplier section including a second multiplier section configured to multiply a quadrature component of the electrical process variable signal with an in-phase component of the local signal to generate a second multiplied signal; A LIDAR system including a summing unit configured to sum the first multiplied signal and the second multiplied signal to generate a control signal.

2. the control mechanism is a control loop; 2. The LIDAR system according to claim 1.

3. the control loop is a feedback control loop; 3. The LIDAR system according to claim 2.

4. 10. The LIDAR system of claim 1, wherein the control mechanism uses the electrical process variable signal to determine a value of a process variable in the system output signal.

5. The control mechanism a control component having a Mach-Zehnder interferometer; 5. The LIDAR system according to claim 4.

6. The Mach-Zehnder interferometer is included in a LIDAR chip.

6. A LIDAR system according to claim 5.

7. The LIDAR chip comprises: Built on a silicon-on-insulator platform, 7. A LIDAR system according to claim 6.

8. The process variable is is the frequency of the system output signal; 2. The LIDAR system according to claim 1.

9. the frequency of the system output signal is varied in a repetition period, and values ​​of the frequency of the system output signal are determined at a frequency greater than 100 times the duration of the repetition period.

9. A LIDAR system according to claim 8.

10. the frequency of the system output signal varies at a non-zero rate over the duration of a data period of the system output signal, and determining a value of the frequency of the system output signal by greater than 100 times during the duration of the data period; 2. The LIDAR system according to claim 1.

11. The process variable is is the phase of the system output signal; 2. The LIDAR system according to claim 1.

12. 10. The LIDAR system of claim 1, wherein the control mechanism includes a time-to-digital converter (TDC) configured to receive the control signal and output an indicator signal having a voltage related to a frequency of the tap signal.

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