Wavelength selection in lidar systems

Abstract

To provide a LIDAR system that has improved safety for skin and eyes.SOLUTION: A Frequency Modulated Continuous Wave (FMCW) LIDAR system has a LIDAR chip configured to output a LIDAR output signal with a wavelength between 1290 nm and 1310 nm. The LIDAR chip is also configured to receive a LIDAR input signal from off of the LIDAR chip. The LIDAR input signal includes light from the LIDAR output signal after reflection of the LIDAR output signal by an object located off the LIDAR chip. The LIDAR chip is configured to generate a composite signal that includes light from a comparative light signal and light from a reference signal. The comparative signal includes light from the LIDAR output signal but the reference signal does not include light from the LIDAR output signal.SELECTED DRAWING: Figure 1A

Description

Related Applications

[0001] This application is a continuation of U.S. Patent Application Serial No. 62 / 849,747, filed May 17, 2019, entitled “Wavelength Selection in LIDAR Systems.”

[0002] The present invention relates to optical devices, and in particular to LIDAR systems.

[0003] There is an increasing commercial demand for 3D sensing systems that can be economically deployed in applications such as ADAS (Advanced Driver Assistance Systems) and AR (Augmented Reality). LIDAR (Light Detection and Ranging) systems are one example of a technology that can be used to construct these 3D images. LIDAR systems construct these images by illuminating a scene with light and measuring the optical signal that returns from the illuminated scene to the LIDAR system. However, in LIDAR systems, lasers are often used as the optical signal source, and safety to skin and eyes is one of the challenges that expands the available applications of LIDAR. Therefore, there is a need for LIDAR systems with improved safety. Overview

[0004] A frequency modulated continuous wave (FMCW) LIDAR system includes a LIDAR chip configured to output a LIDAR output signal. The LIDAR chip is also configured to receive a LIDAR input signal from outside the LIDAR chip. The LIDAR input signal includes light from the LIDAR output signal after it is reflected by an object away from the LIDAR chip. The LIDAR chip is configured to generate a composite signal including light from a comparison optical signal and light from a reference signal. The comparison signal includes light from the LIDAR output signal, but the reference signal does not include light from the LIDAR output signal. The LIDAR output signal has a wavelength between 1290 and 1310 nm.

[0005] Another LIDAR system is configured to output a plurality of LIDAR output signals each simultaneously directed to a sample area within a field of view, the sample area being one of a plurality of sample areas included in the field of view. The LIDAR output signals each carry a channel at a different wavelength, the wavelengths of the different channels being non-periodically spaced across the wavelength spectrum. The LIDAR system is configured to simultaneously receive a plurality of LIDAR input signals each reflected by an object located outside the LIDAR system and within the sample area, the LIDAR input signals each including light from a different one of the LIDAR output signals.

[0006] Another LIDAR system is configured to output a plurality of LIDAR output signals each simultaneously directed to a sample area in a field of view, the sample area being one of a plurality of sample areas included in the field of view. The LIDAR output signals each carry channels at different wavelengths. The difference in wavelengths of the channels included in at least one channel pair is greater than 20 nm. The channels of each channel pair have wavelengths that are adjacently located to one another on the wavelength spectrum in that no other channel has a wavelength between the two channels included in each pair. The LIDAR system is configured to simultaneously receive a plurality of LIDAR input signals each reflected by an object located outside the LIDAR system and within the sample area. The LIDAR input signals each include light from a different one of the LIDAR output signals.

[0007] A method of generating and / or operating a LIDAR system includes identifying materials that may be included in an object that reflect a LIDAR output signal from the LIDAR system back to the LIDAR system, and configuring a plurality of LIDAR output signals to have wavelengths that have a higher reflectivity for one of the identified materials than any of the other LIDAR output signals. [Brief description of the drawings]

[0008] [Figure 1A] FIG. 1 is a schematic diagram of a LIDAR system.

[0009] [Figure 1B] FIG. 2 is a schematic diagram of another embodiment of a LIDAR system.

[0010] [Figure 2A] 1 shows a light source including multiple laser light sources.

[0011] [Figure 2B] 1 shows the frequency of the LIDAR output signals carrying different channels as a function of time.

[0012] [Figure 3A] 1A illustrates an example of a processing unit suitable for use with the LIDAR system of FIG. 1A and / or FIG. 1B.

[0013] [Figure 3B] 3B shows a schematic diagram of electronics suitable for use with a processing unit constructed according to FIG. 3A.

[0014] [Figure 3C] 1 is a graph of amplitude versus frequency, with the solid line on the graph showing the result of the complex Fourier transform.

[0015] [Figure 4A] A waveguide facet is shown serving as an output element.

[0016] [Figure 4B] 4B illustrates the LIDAR chip of FIG. 4A used with an off-chip scanning mechanism.

[0017] [Figure 4C] 4B illustrates the LIDAR chip of FIG. 4A used with another embodiment of an off-chip scanning mechanism.

[0018] [Diagram 5]1 illustrates an example of an output element that optionally includes beam steering capabilities. explanation

[0019] There are four main factors that influence the operating wavelength selected for the output optical signal from a LIDAR system. One of these factors includes eye and skin safety, which is exposed to the light from the LIDAR system. Another factor is the solar background activity at the selected wavelength. High levels of solar background activity at the operating wavelength can interfere with the operation of the LIDAR system. Another factor is the atmospheric transmittance of light at the selected wavelength. A low level of atmospheric transmittance reduces the amount of light that returns to the LIDAR system after being reflected from an object. Thus, a low level of transmittance reduces the performance of the LIDAR system and increases the power level required to operate successfully. The fourth factor is the optical reflectance of the target object. Increasing the amount of light reflected increases the amount of light returned to the LIDAR system, thereby improving the performance of the LIDAR system.

[0020] The inventors have surprisingly found that all four factors can be met using an FMCW LIDAR system that outputs optical signals over a narrow range of wavelengths. With regard to safety to eyes and skin, the inventors have found that a LIDAR output signal with wavelengths of 1290-1310 nm is 300-400 mW / cm 2 The authors found that the maximum permissible exposure (MPE) at these wavelengths is 100–200 mW / cm2 (according to the international standard IEC 60825-1, 2014). In contrast, wavelengths used for eye and skin safety are typically in the 1350–15500 nm range. However, the MPE at these wavelengths is typically in the 100–200 mW / cm2 range. 2Therefore, the LIDAR output signal with wavelengths of 1290-1310 nm is substantially safer for eyes and skin than conventional systems. Furthermore, the use of FMCW LIDAR systems effectively eliminates the effect of solar background activity on the performance of the LIDAR system. Also, the inventors have found that the wavelengths of 1290-1310 nm fall within one of the atmospheric transmittance windows in the 1280-1310 nm range. In contrast, the wavelengths of 1350-1390 nm are mostly outside the atmospheric transmittance window. Finally, in many applications such as face recognition and autonomous vehicles, one of the targets is the skin. Since the skin reflectance peaks have been found to be at 1090 nm and 1270 nm, the wavelength range of 1290 nm-1310 nm takes advantage of one of these skin reflectance peaks. Thus, the output signal of an FMCW LIDAR system with wavelengths in the 1290-1310 nm range can satisfy all four factors for selecting the operating wavelength.

[0021] In some examples, the LIDAR system is configured to generate a plurality of LIDAR output signals that are scanned across a series of sample areas in a field of view. Different LIDAR output signals, each carrying a different channel, simultaneously illuminate each sample area during the scan. The LIDAR system can generate LIDAR data results (distance and / or line of sight velocity between the light source of the LIDAR output signal and the reflecting object) for each LIDAR output signal. As a result, the LIDAR can generate a plurality of LIDAR data results for each sample area. The wavelengths of the different channels carried by the LIDAR output signals can be selected to be effective for particular materials that may be present in the field of view. As noted above, channels in the wavelength range 1290-1310 nm are effective and safe for use with skin. However, for some targets, channels in that wavelength range are not as reflective as channels at other wavelengths. As an example, the reflectivity of metals such as dull aluminum and zinc is approximately 22% higher for wavelengths in the 1540-1560 nm range than for wavelengths in the 1290-1310 nm range. As a result, LIDAR output signals carrying channels with wavelengths in the 1540-1560 nm range can provide more reliable LIDAR data results than wavelengths in the 1290-1310 nm range when metals are in the field of view. Thus, LIDAR output signals carrying channels with wavelengths in the 1290-1310 nm range, and LIDAR systems producing LIDAR output signals carrying channels with wavelengths in the 1290-1310 nm range, can efficiently generate LIDAR data for both skin and metals in the field of view. Thus, by using LIDAR output signals with different wavelengths, the range of materials for which LIDAR data can be reliably generated is expanded.

[0022] 1A is a top view of a LIDAR chip that includes a frequency modulated continuous wave (FMCW) LIDAR system, in which light from a LIDAR input signal reflected by an object distant from the LIDAR chip is received by the LIDAR chip and combined with light from a reference light signal that is not reflected by the object to generate a composite signal from which LIDAR data is generated. If there is a frequency difference between the reference light signal and the LIDAR input signal, the composite signal can be a pulsating signal. The frequency difference can be due to relative movement between the object and the LIDAR chip (i.e., Doppler effect) and / or the use of a LIDAR output signal and a reference signal with a frequency that changes over time.

[0023] The system includes a light source (10), such as a laser, that outputs an outgoing LIDAR signal. The outgoing LIDAR signal carries one or more different channels, each at a different wavelength. In one example, the outgoing LIDAR signal carries one channel. In one example, the outgoing LIDAR signal carries one channel having a wavelength between 1290 and 1310 nm. In one example, the outgoing LIDAR signal carries multiple channels, each at a different wavelength.

[0024] The LIDAR system also includes a utility waveguide (12) that receives an outgoing LIDAR signal from the light source (10). Amplifiers (16) are optionally disposed along the utility waveguide (12). Because the power of the outgoing LIDAR signal is distributed among multiple channels, it is desirable for the amplifiers (16) to provide a desired level of power to each channel in the utility waveguide (12). Suitable amplifiers include, but are not limited to, semiconductor optical amplifiers (SOAs).

[0025] The utility waveguide (12) carries the outgoing LIDAR signal to a signal directing element (18) that can direct the outgoing LIDAR signal to a LIDAR branch (20) and / or a data branch (22). The LIDAR branch outputs a LIDAR output signal and receives a LIDAR input signal. The data branch processes the LIDAR input signal to generate LIDAR data (distance and / or radial velocity between the light source and a reflecting object of the LIDAR output signal).

[0026] The LIDAR branch includes a LIDAR signal waveguide (24) that receives at least a portion of the outgoing LIDAR signal from the signal directing element (18). The LIDAR signal waveguide (24) carries at least a portion of the outgoing LIDAR signal to an output element (26) where the outgoing LIDAR signal exits the LIDAR chip. If the outgoing LIDAR signal includes multiple different channels at different wavelengths, the output element (26) can be configured such that each different channel is incident on the same sample area in the field of view. For example, the output element (26) can be configured such that each different channel travels in the same or substantially the same direction from the LIDAR chip.

[0027] After exiting the output element (26), the different channels each function as a LIDAR output signal of a different wavelength (channel). The LIDAR output signals may be reflected by reflective objects (not shown) located outside the LIDAR system. Each reflected LIDAR output signal returns to the output element (26) as a LIDAR input signal. The output element (26) receives the LIDAR input signals and outputs the result onto the LIDAR signal waveguide (24) as an incident LIDAR signal.

[0028] In some examples, the output elements (26) also include beam steering functionality. In these examples, the output elements (26) can be in electrical communication with electronics (not shown) that can operate the output elements (26) to steer the LIDAR output signals from one of the sample areas in the field of view to another sample area in the field of view. The output elements (26) and / or electronics can be configured such that different LIDAR output signals are steered simultaneously.

[0029] Although the output element 26 is shown as a single element, the output element 26 may include multiple optical and / or electrical elements. Suitable output elements 26 include, but are not limited to, optical phased arrays (OPAs), transmission gratings, reflective gratings, and diffractive optical elements (DOEs). Suitable output elements 26 with beam steering capabilities include, but are not limited to, optical phased arrays (OPAs) with active phase control elements on arrayed waveguides.

[0030] The LIDAR signal waveguide (24) carries the incident LIDAR signal to the signal directing element (18), which directs the incident LIDAR signal to the utility waveguide (12) and / or to a comparison signal waveguide (28). The portion of the incident LIDAR signal directed to the comparison signal waveguide (28) serves as a comparison incident LIDAR signal.

[0031] The comparison signal waveguide (28) carries the comparison incident LIDAR signal to a comparison splitter (30). If the comparison optical signal includes multiple channels, the comparison splitter (30) splits the comparison incident LIDAR signal into different comparison signals, each carrying a different channel. The comparison splitter (30) outputs the comparison signals to different comparison waveguides (32). The comparison waveguides (32) each carry one of the comparison signals to a different processing element (34). Thus, the different processing elements (34) each receive a comparison signal carrying a different channel.

[0032] The signal directing element (18) is configured, when it directs at least a portion of the incoming LIDAR signal to the comparison waveguide (32), to also direct at least a portion of the outgoing LIDAR signal to the reference signal waveguide (36), the portion of the outgoing LIDAR signal received by the reference signal waveguide (36) serving as a reference optical signal.

[0033] The reference signal waveguide (36) carries the reference optical signal to a reference splitter (38). When the reference optical signal carries multiple channels, the reference splitter (38) splits the reference optical signal into different reference signals, each carrying a different one of the channels. The reference splitter (38) outputs the reference signals on different reference waveguides (40). The reference waveguides (40) each carry one of the reference signals to a different one of the processing elements (34). Thus, the different processing elements (34) each receive a reference signal carrying a different one of the channels.

[0034] The comparison waveguide 32 and the reference waveguide 40 are configured such that the comparison signal and the corresponding reference signal are received at the same processing element 34. For example, the comparison waveguide 32 and the reference waveguide 40 are configured such that the comparison signal and the corresponding reference signal of the same wavelength are received at the same processing element 34. Thus, the different processing elements 34 each receive the comparison signal and the reference signal carrying the same channel.

[0035] As described in more detail below, the processing elements (34) each combine the comparison signal with a corresponding reference signal to form a composite signal carrying LIDAR data for a sample area on the field of view, which can then be processed to extract LIDAR data for the sample area.

[0036] The signal directing element (18) can be an optical coupler. When the signal directing element (18) is an optical coupler, it directs a first portion of the outgoing LIDAR signal to the LIDAR signal waveguide (24), directs a second portion of the outgoing LIDAR signal to the reference signal waveguide (36), and directs a first portion of the incident LIDAR signal to the utility waveguide (12), and directs a second portion of the incident LIDAR signal to the comparison signal waveguide (28). Thus, the second portion of the incident LIDAR signal can function as a comparison input LIDAR signal, and the second portion of the outgoing LIDAR signal can function as a reference optical signal.

[0037] The signal directing element (18) can be an optical switch, such as a crossover switch. A suitable crossover switch can operate in a crossover mode or a pass mode. In the pass mode, the outgoing LIDAR signal is directed to the LIDAR signal waveguide (24) and the incoming LIDAR signal is directed to the utility waveguide (12). In the crossover mode, the outgoing LIDAR signal is directed to the reference signal waveguide (36) and the incoming LIDAR signal is directed to the comparison signal waveguide (28). Thus, the incoming LIDAR signal, or a portion thereof, can function as the comparison optical signal and the outgoing LIDAR signal, or a portion thereof, can function as the reference optical signal.

[0038] An optical switch, such as a crossover switch, can be controlled by electronics. For example, electronics can control the operation of the switch so that the switch is in cross mode or pass mode. When a LIDAR output signal is transmitted from a LIDAR system, the electronics operates the switch so that the switch is in pass mode. When a LIDAR input signal is received by a LIDAR system, the electronics operates the switch so that the switch is in cross mode. The use of a switch can reduce the level of optical loss when using an optical coupler as the signal directing element (18).

[0039] In the above description of the operation of the signal directing element 18, the comparison optical signal and the reference optical signal are simultaneously directed to the data branch so that the processing element 34 can combine each comparison signal with a corresponding reference signal.

[0040] In some examples, optical amplifiers (42) are optionally disposed along the LIDAR signal waveguide (24) and configured to amplify the outgoing LIDAR signal and / or the incoming LIDAR signal, thus reducing the effects of optical loss in the signal directing element (18).

[0041] FIG. 1B shows the LIDAR system of FIG. 1A modified to include an optical circulator as the signal directing element (18). The optical circulator is configured such that the outgoing LIDAR signal is directed to the LIDAR signal waveguide (24) and the incident LIDAR signal is directed to the comparison signal waveguide (28). The comparison signal waveguide (28) conveys the comparison incident LIDAR signal to the comparison splitter (30). Also, a tap element (44) is disposed along the utility waveguide (12). The tap element (44) is configured to tap off a first portion of the outgoing LIDAR signal such that the first portion of the outgoing LIDAR signal is received on the reference signal waveguide (36). The first portion of the outgoing LIDAR signal received by the reference signal waveguide (36) serves as a reference optical signal. The reference signal waveguide (36) conveys the reference optical signal to the reference splitter (38). Thus, the electronics can operate the LIDAR system of Figure 1B as disclosed in Figure 1A. Suitable optical circulators include, but are not limited to, fiber optic circulators and integrated optical circulators based on Faraday rotators. Although the signal directing element (18) of Figure 1B is disclosed as an optical circulator, it can be an optical coupler or an optical switch.

[0042] FIG. 2A shows an example of a light source (10) that includes multiple laser light sources (84). In some examples, each laser light source (84) outputs one or more channels on a light source waveguide (86). The light source waveguide (86) conveys the channels to a laser combiner (88) that combines the channels to form an optical signal that is received on a channel or utility waveguide (12). Suitable laser combiners (88) include, but are not limited to, an arrayed waveguide grating (AWG) combiner, an echelle grating combiner, and a star coupler. The electronics operate the laser light sources (84) such that the laser light sources (84) can output each channel simultaneously. The electronics operate the laser light sources (84) such that the laser light sources (84) can output each channel simultaneously.

[0043] In some examples, each laser source (84) outputs one channel on the source waveguide (86). The total number of laser sources (84) included in the light source (10) may be greater than or equal to the number of LIDAR output signals simultaneously directed to the sample area. In some examples, the total number of laser sources (84) included in the light source (10) is equal to the number of LIDAR output signals simultaneously directed to the sample area. As a result, each laser source (84) can be a different source of one of the LIDAR output signals simultaneously directed to the sample area.

[0044] The electronics can independently operate the laser sources (84). For example, the electronics can operate the laser sources (84) to provide a particular LIDAR output signal with a particular frequency versus time waveform. The electronics can independently operate the laser sources (84), and each laser source (84) can be a different source of the LIDAR output signal, so that the electronics can operate the laser sources (84) such that different LIDAR output signals have different frequency versus time waveforms.

[0045] Modulators (14) may optionally be positioned along one or more of the light source waveguides (86). Each of the modulators (14) may be configured to modulate the power of one channel, thereby modulating the amplitude of the resulting LIDAR output signal. Electronics may operate the modulators (14). Thus, the electronics may modulate the power of the LIDAR output signal. Suitable modulators (14) include, but are not limited to, PIN diode carrier injection devices, Mach-Zehnder modulators, and electroabsorption modulators. Suitable modulators, when constructed on a silicon-on-insulator platform, are disclosed in U.S. Patent Application Serial No. 617,810, filed September 21, 1993, entitled “Integrated Silicon PIN Diode Electro-Optic Waveguide.”

[0046] Amplifiers (16) may optionally be disposed along one or more of the light source waveguides (86). The modulators (16) may each be configured to modulate the intensity of one of the channels, thereby modulating the power of the resulting LIDAR output signal. Electronics may operate the modulators (16). Thus, the electronics may amplify the power of one or more of the LIDAR output signals. Suitable amplifiers (16) include, but are not limited to, optical fiber amplifiers, such as an erbium-doped optical fiber amplifier (EDFA) or a praseodymium-doped optical fiber amplifier (PDF), and a semiconductor optical amplifier (SOA).

[0047] The electronics can operate the modulators (14) and / or the laser light sources (84) to provide different LIDAR output signals with different waveforms. For example, the electronics can operate one or more laser light sources (84) to generate LIDAR output signals each having a frequency that is not a function of time, such as a continuous wave. Additionally or alternatively, the electronics can operate one or more laser light sources (84) and associated modulators (14) to generate one or more LIDAR output signals, each having a chirped amplitude. Additionally or alternatively, the electronics can operate one or more laser light sources (84) and associated modulators (14) to generate one or more LIDAR output signals with a frequency that varies with time. In one example, the electronics can operate one or more laser light sources (84) and / or associated modulators (14) to generate at least one LIDAR output signal having an electric field that is a function of a sine wave having a frequency that is a function of time. In another example, each light source waveguide (86) eliminates a modulator (14), and the electronics operate one or more laser light sources (84) and / or associated modulators (14) to generate at least one LIDAR output signal having an electric field that is a function of a sine wave having a frequency that is a function of time.

[0048] During operation of the LIDAR system, the generation of LIDAR data is divided into a series of periods in which LIDAR data is generated. In some examples, one of the periods corresponds to a different sample area in the field of view. Thus, the different periods can generate LIDAR data for different areas in the field of view. The periods can be performed such that the duration of each period can be divided into different periods. For example, the duration of one period can include one or more data periods during which the LIDAR input signal is generated and received by the LIDAR chip, and one or more relocation periods during which the LIDAR output signal is moved from one sample area to another sample area. In a continuous scan mode, the period does not include a relocation period, and the LIDAR output signal is moved continuously. In one example, the period includes multiple data periods, and the multiple LIDAR output signals each carry a different channel, and the LIDAR output signals are simultaneously directed to the same sample area in the field of view. In one example, at least one of the LIDAR output signals is a sinusoidal function having a frequency that varies as a function of time. In one example, each LIDAR output signal is a function of a sine wave having a frequency that varies as a function of time.

[0049] FIG. 2B shows an example of a schematic diagram for conditioning the LIDAR output signal. The frequency is several cycles. j ~period j+2 The frequency of the periodic periods, denoted by k, is shown. Each period is associated with a periodic index k, and the DP k In the example of FIG. 2B, each period includes k data periods labeled k = 1 and k = 1 DPs. k Each of the illustrated periods is associated with a period index m, and the SR m ~SR m+2 Each period corresponds to one of M different sample areas labeled . Thus, in the illustrated example, the LIDA data generated in each period is for a different sample area, although other configurations are possible. Since there is no repositioning period illustrated, the LIDAR system is operated with or without continuous scanning.

[0050] In the example of FIG. 2B, the LIDAR output signals are each λ i The LIDAR output signal λ carries channels labeled λ, where i is an integer channel index starting from 0. The electric field of each channel is a sinusoidal function with frequencies as shown in FIG. 2B. 0 and λ 1 Each of the λ has an electric field that is a sinusoidal function with a frequency that varies with time. 0 and λ 1 The frequency changes are in opposite directions, but at the same rate. As a result, Figure 2B shows a sample area simultaneously illuminated by at least one LIDAR output signal of increasing frequency and at least one LIDAR output signal of decreasing frequency, where the rates of change of frequency are the same.

[0051] In one example, the electric field of the LIDAR output signal for each channel shown in FIG. 2B may be a function of a sine wave having a frequency represented by the following equation: f=f i +0.5×α i ×DP×[(-1) j +1]+(-1) (j-1) {t-[(j-1)(DP)}α i , and (Equation 2) f = f i +0.5×α i ×DP×[(-1) (j+1) +1]-(-1) (j-1) {t-[(j-1)](DP)}α i Here, α i represents the rate of change of frequency of channel i during the data period, and f i represents the lowest frequency (fundamental frequency) of channel i during one period. The variable t represents time and is calculated at the beginning of each new period and / or each DP k At the beginning of the time t, t is 0. 0 = α 1 In some examples, f i The value of is selected such that there is no overlap in the frequencies of the various LIDAR output signals, as shown in FIG. 2B. In one example, the electric field of the LIDAR output signal is expressed by the formula: N×cos(2π×i×t+E×t2 ), where N and E are constants, and E may or may not be zero (N≠0). In some examples, f is a frequency provided by Equation 1 or Equation 2.

[0052] In FIG. 2B, λ 0 The channel labeled λ has an electric field that is a sinusoidal function with a frequency expressed in Equation 1, 1 The channel labeled as has an electric field that is a function of a sine wave having a frequency represented by Equation 2. Although FIG. 2B shows one channel having a frequency according to either Equation 1 or Equation 2, the LIDAR system may generate one or more LIDAR output signals having an electric field that is a function of a sine wave having a frequency represented by an equation selected from the group consisting of Equation 1 and Equation 2. Additionally or alternatively, the one or more LIDAR output signals generated by the LIDAR system may exclude any LIDAR output signals having an electric field that is a function of a sine wave having a frequency represented by an equation selected from the group consisting of Equation 1 and Equation 2. Thus, the one or more LIDAR output signals generated by the LIDAR system may only be LIDAR output signals having an electric field that is a function of a sine wave having a frequency represented by an equation selected from the group consisting of Equation 1 and Equation 2.

[0053] An example LIDAR system includes a light source configured according to Figure 2A and configured to generate two LIDAR output signals, one of which is channel λ of Figure 2B. 0 and another of the LIDAR output signals carries a frequency vs. time channel according to the channel λ of FIG. 1The LIDAR system may include a number of processing elements (34) that correspond to the number of LIDAR output signals, each carrying a different channel. Thus, the LIDAR system may be constructed with two processing elements (34) according to Fig. 1A. Although Fig. 2B shows frequency versus time waveforms for two different channels, the LIDAR system may be configured to output two or more LIDAR output signals, each carrying a different channel.

[0054] The laser light source (84) used with the light source (10) constructed according to FIG. 2A can be selected to be efficient for the wavelength of the channel output by the laser light source (84). For example, a laser light source having a gain medium including or consisting of quantum dots efficiently outputs light with wavelengths of 1290-1310 nm, and a laser light source having a gain medium including or consisting of quantum wells efficiently outputs light with wavelengths of 1480-1550 nm. Thus, the light source (10) can include multiple laser light sources, where the different laser light sources have different gain media. In some examples, the laser system includes one, two or more, or two laser light sources selected from the group consisting of a laser light source having a gain medium including or consisting of quantum dots, and a laser light source having a gain medium including or consisting of quantum wells. In one example, the laser system includes a light source (10) including one or more laser light sources, at least some of which have a gain medium including or consisting of quantum dots and are constructed to output channels having wavelengths of 1290-1310 nm. Suitable laser constructions include, but are not limited to, external cavity lasers, distributed feedback lasers (DFB), and Fabry-Perot (FP) lasers. External cavity lasers are advantageous in this embodiment due to their typically narrow linewidth, which can reduce noise in the detected signal.

[0055] Although FIG. 2A shows each light source (84), optional modulator (14), and optional amplifier (16) integrated and / or located on the LIDAR chip, one or more components selected from the group consisting of light source (84), optional modulator (14), and optional amplifier (16) may be external to the LIDAR chip and connected to the LIDAR chip and / or other components, for example, by a waveguide such as an optical fiber.

[0056] 3A-3B show an example of a processing element (34) for application in the LIDAR system of FIGS. 1A and 1B. The processing unit includes a first splitter (102) for splitting a reference signal carried in a reference waveguide (40) into a first reference waveguide (110) and a second reference waveguide (108). The first reference waveguide (110) carries a first portion of the reference signal to an optical coupling element (111). The second reference waveguide (108) carries a second portion of the reference signal to a second optical coupling element (112).

[0057] The processing unit includes a second splitter (100) that splits the comparison signal carried to the comparison waveguide (32) into a first comparison waveguide (104) and a second comparison waveguide (106). The first comparison waveguide (104) carries a first portion of the comparison signal to an optical combining element (111). The second comparison waveguide (108) carries a second portion of the comparison signal to a second optical combining element (112).

[0058] A second optical combining element (112) combines the second portion of the comparison signal and the second portion of the reference signal into a second composite signal, the second composite signal pulsating between the second portion of the comparison signal and the second portion of the reference signal due to a frequency difference between the second portion of the comparison signal and the second portion of the reference signal.

[0059] The second optical combining element (112) also splits the resulting second composite signal onto a first auxiliary detector waveguide (114) and a second auxiliary detector waveguide (116). The first auxiliary detector waveguide (114) conveys a first portion of the second composite signal to a first auxiliary optical sensor (118) that converts the first portion of the second composite signal into a first auxiliary electrical signal. The second auxiliary detector waveguide (116) conveys a second portion of the second composite signal to a second auxiliary optical sensor (120) that 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).

[0060] In some examples, the second optical combining element (112) splits the second composite signal such that a portion of the comparison signal included in the first portion of the second composite signal (i.e., a portion of the second portion of the comparison signal) is phase shifted by 180 degrees relative to a 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), but a 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) is not phase shifted relative to a 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). Alternatively, the second optical combining element (112) splits the second composite signal such that the portion of the reference signal in the first portion of the second composite signal (i.e., the portion of the second portion of the reference signal) is phase-shifted by 180 degrees with respect to the portion of the reference signal in the second portion of the second composite signal (i.e., the 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., the portion of the two portions of the comparison signal) is not phase-shifted with respect to the portion of the comparison signal in the second portion of the second composite signal (i.e., the portion of the second portion of the comparison signal). Examples of suitable optical sensors include germanium photodiodes (PDs) and avalanche photodiodes (APDs).

[0061] A first optical combining element (111) combines the first portion of the comparison signal and the first portion of the reference signal into a first composite signal, the first composite signal pulsating between the first portion of the comparison signal and the first portion of the reference signal due to a frequency difference between the first portion of the comparison signal and the first portion of the reference signal.

[0062] The optical combining element (111) also splits the first composite signal onto a first detector waveguide (121) and a second detector waveguide (122). The first detector waveguide (121) conveys a first portion of the first composite signal to a first optical sensor (123) that converts a first portion of a second composite signal into a first electrical signal. The second detector waveguide (122) conveys a second portion of the second composite signal to a second auxiliary optical sensor (124) that 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).

[0063] In some examples, the optical combining element (111) splits the first composite signal such that a portion of the comparison signal in the first portion of the composite signal (i.e., a portion of the first portion of the comparison signal) is phase shifted by 180 degrees with respect to a portion of the comparison signal in the second portion of the composite signal (i.e., a portion of the first portion of the comparison signal), but a portion of the reference signal in the first portion of the composite signal (i.e., a portion of the first portion of the reference signal) is not phase shifted with respect to a portion of the reference signal in the second portion of the composite signal (i.e., a portion of the first portion of the reference signal). Alternatively, the optical combining element (111) splits the composite signal such that a portion of the reference signal in the first portion of the composite signal (i.e., a portion of the first portion of the reference signal) is phase shifted by 180 degrees with respect to a portion of the reference signal in the second portion of the composite signal (i.e., a portion of the first portion of the reference signal), but a portion of the comparison signal in the first portion of the composite signal (i.e., a portion of the first portion of the comparison signal) is not phase shifted with respect to a portion of the comparison signal in the second portion of the composite signal (i.e., a portion of the first portion of the comparison signal).

[0064] If the second optical combining element (112) splits the second composite signal such that a portion of the comparison signal in the first portion of the second composite signal is phase shifted by 180° relative to a portion of the comparison signal in the second portion of the second composite signal, the optical combining element (111) also splits the composite signal, such that a portion of the comparison signal in the first portion of the composite signal is phase shifted by 180° relative to a portion of the comparison signal in the second portion of the second composite signal. If the second optical combining element (112) splits the second composite signal such that a portion of the reference signal in the first portion of the second composite signal is phase shifted by 180° relative to a portion of the reference signal in the second portion of the second composite signal, the optical combining element (111) also splits the composite signal, such that a portion of the reference signal in the first portion of the composite signal is phase shifted by 180° relative to a portion of the reference signal in the second portion of the second composite signal.

[0065] The first reference waveguide (110) and the second reference waveguide (108) are constructed to provide a phase shift between the first portion of the reference signal and the second portion of the reference signal. For example, the first reference waveguide (110) and the second reference waveguide (108) can be constructed to provide a 90 degree phase shift between the first portion of the reference signal and the second portion of the reference signal. As an example, one reference signal portion can be an in-phase component and the other can be a quadrature component. Thus, one of the reference signal portions can be a sine function and the other reference signal portion can be a cosine function. In one example, the first reference waveguide (110) and the second reference waveguide (108) are constructed such that the first reference signal portion is a cosine function and the second reference signal portion is a sine function. Thus, the portion of the reference signal in the second composite signal is phase shifted with respect to the portion of the reference signal in the first composite signal, but the portion of the comparison signal in the first composite signal is not phase shifted with respect to the portion of the comparison signal in the second composite signal.

[0066] The first light sensor (123) and the second light sensor (124) can be connected as a balanced detector, and the first auxiliary light sensor (118) and the second auxiliary light sensor (120) can also be connected as a balanced detector. For example, FIG. 3B provides a schematic of the relationship between the electronics, the first light sensor (123), the second light sensor (124), the first auxiliary light sensor (118), and the second auxiliary light sensor (120). Symbols for photodiodes are used to represent the first light sensor (123), the second light sensor (124), the first auxiliary light sensor (118), and the second auxiliary light sensor (120), although one or more of these sensors can have other configurations. In some examples, all of the elements shown in the schematic diagram of FIG. 3B are included on the LIDAR chip. In some examples, the elements shown in the schematic diagram of FIG. 3B are distributed between the LIDAR chip and electronics located away from the LIDAR chip.

[0067] The electronics connects the first optical sensor (123) and the second optical sensor (124) to form a first balanced detector (125) and connects the first auxiliary optical sensor (118) and the second auxiliary optical sensor (120) to form a second balanced detector (126). Specifically, the first optical sensor (123) and the second optical sensor (124) are connected in series. Additionally, the first auxiliary optical sensor (118) and the second auxiliary optical sensor (120) are connected in series. The series connection in the first balanced detector communicates with a first data line (128) that carries the output from the first balanced detector as a first data signal. The series connection in the second balanced detector communicates with a second data line (132) that carries the output from the second balanced detector as a second data signal. The first data signal is an electrical representation of the first composite signal, and the second data signal is an electrical representation of the second composite signal. 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 phase shifted relative to 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 includes a portion of a reference signal that is phase shifted relative to a different portion of the reference signal included in the first data signal. Also, the second data signal includes a portion of a comparison signal that is in phase with a different portion of a comparison signal included in the first data signal. As a result of the pulsation between the comparison signal and the reference signal, i.e. the pulsation in the first composite signal and the second composite signal, the first data signal and the second data signal are pulsating.

[0068] The electronics (62) includes a transform mechanism (138) configured to perform a mathematical transformation on the first data signal and the second data signal. For example, the mathematical transformation may be a complex Fourier transform with the first data signal and the second data signal as inputs. The first data signal is an in-phase component and the second data signal is a quadrature component, so that the first data signal and the second data signal together function as a complex data signal, where the first data signal is the real component of the input and the second data signal is the imaginary component of the input.

[0069] The conversion mechanism (138) includes a first analog-to-digital converter (ADC) (164) that receives the first data signal from the first data line (128). The first analog-to-digital converter (ADC) (164) converts the first data signal from analog to digital form to output a first digital data signal. The conversion mechanism (138) includes a second analog-to-digital converter (ADC) (166) that receives the second data signal from the second data line (132). The second analog-to-digital converter (ADC) (166) converts the second data signal from analog to digital form to output a second digital data signal. The first digital data signal is a digital representation of the first data signal and the second digital data signal is a digital representation of the second data signal. Thus, the first digital data signal and the second digital data signal together function as a composite signal, where the first digital data signal functions as a real component of the composite signal and the second digital data signal functions as an imaginary component of the composite data signal.

[0070] The conversion mechanism (138) includes a conversion element (168) that receives the composite data signal. For example, the conversion element (168) receives as an input a first digital data signal from a first analog-to-digital converter (ADC) (164) and also receives as an input a second digital data signal from a first analog-to-digital converter (ADC) (166). The conversion element (168) can be configured to perform a mathematical transformation on the composite signal to convert it from the time domain to the frequency domain. The mathematical transformation can be a complex transformation, such as a complex Fast Fourier Transform (FFT). A complex transformation, such as a complex Fast Fourier Transform (FFT), provides an explicit answer to the frequency shift of the LIDAR input signal relative to the LIDAR output signal due to the line of sight velocity between the reflecting object and the LIDAR tip. The conversion element (168) can perform the ascribed functions using firmware, hardware, software, or a combination thereof.

[0071] The solid line in FIG. 3C shows an example of the output of the transformation mechanism when the complex Fourier transform converts the input from the time domain to the frequency domain. The solid line shows one single frequency peak. The frequency associated with the peak is used by the electronics since the frequency shift of the LIDAR input signal relative to the LIDAR output signal is caused by the radial velocity and / or distance between the reflecting object and the LIDAR tip. When the LIDAR output signal is λ 2 in FIG. 2B , 2 If the LIDAR input signal has a frequency that does not change with time as shown in FIG. 1, the frequency shift of the LIDAR input signal relative to the LIDAR output signal is due to the radial velocity between the reflecting object and the LIDAR chip, not the distance between the reflecting object and the LIDAR chip. The electronics use the frequency output from the transducer element (168) to generate LIDAR data (distance and / or radial velocity between the reflecting object and the LIDAR chip or LIDAR system) for further processing.

[0072] FIG. 3C also includes another peak, shown in dashed lines. Conventional methods for resolving the frequency of a LIDAR input signal used a real Fourier transform rather than the complex Fourier transform technique described above. These conventional methods output both the dashed and solid peaks. Thus, the conventional methods output multiple different frequencies, both associated with a single object in the sample volume, in that each of the associated frequencies would not be present if the object were removed from the sample volume. As described above, identifying the correct peak can be difficult when using LIDAR applications. The frequency resolving techniques described above produce a single frequency solution, so the inventors have solved the problem of ambiguity in frequency decomposition.

[0073] The electronics generate LIDAR data using a single frequency, represented by the solid line in Figure 3C. For example, the following equation is DP 1 The LIDAR output signal λ in FIG. 2B during the data period labeled 0 is applied during the data period such that the frequency of the LIDAR output increases during the data period, such that ub = -f d+ ατ 0 where f ub is the frequency given by the conversion element, and f d is the Doppler shift (f d = 2νf c / c), where f c is the frequency of the LIDAR output signal at the beginning of the data period (i.e., t=0), ν is the line-of-sight velocity between the reflecting object and the LIDAR tip, where the direction from the reflecting object to the tip is assumed to be the positive direction, c is the speed of light, α represents the rate at which the frequency of the outgoing LIDAR signal increases or decreases during the period, and τ 0 is the round trip delay of a stationary reflecting object (the time between the LIDAR output signal leaving the LIDAR chip and the associated LIDAR input signal returning to the LIDAR chip). The following equation is 2 The LIDAR output signal λ in FIG. 2B during the data period labeled 1 is applied during the data period in which the electronics reduce the frequency of the LIDAR output signal during the data period so that db = -f d - ατ 0 where f db is the frequency provided by the conversion mechanism. In these two equations, f d and τ 0 are unknowns. These two equations are expressed in terms of two unknowns, f d and τ 0 Solved for f db and f ub The values ​​of f come from the same channel, and therefore the same processing unit (denoted as (34) in Figures 1A and 1B), but occur during different data periods in the same period. Since the period is related to the sample area in the field of view, the answer is d and τ 0 The radial velocity for the sample region is then calculated using the Doppler shift (ν = c × f d / (2f c )) and the separation distance for the sample area can be measured by c×τ 0 / 2. As a result, LIDAR data for a sample area is measured for a single LIDAR output signal (channel) that illuminates the sample area.

[0074] As described above, the LIDAR system can output two or more LIDAR output signals, each carrying a different channel. For example, the LIDAR system can output three LIDAR output signals having a frequency versus time waveform according to FIG. 2B. The LIDAR output signals can be simultaneously directed to the same sample area in the field of view. Also, the LIDAR output signals can be sequentially scanned over a series of sample areas such that each LIDAR output signal is simultaneously directed to each sample area in the frequency. In some examples, the frequency includes all sample areas in the field of view.

[0075] The LIDAR system can generate LIDAR data results for each channel simultaneously illuminating the sample area, so that the LIDAR system can generate multiple LIDAR data results for each sample area. The wavelengths of the different channels can be selected to be effective for particular materials that may be present within the field of view. As noted above, channels having wavelengths in the 1290-1310 nm range are effective for use on skin. However, other wavelengths are more effective on many metals due to increased reflectance. For example, channels having wavelengths in the 1540-1560 nm range have higher reflectance for many metals. As an example, the reflectance of metals such as dull aluminum and zinc is about 22% higher for wavelengths in the 1540-1560 nm range than for wavelengths in the 1290-1310 nm range. In contrast, the reflectance of skin for wavelengths in the 1290-1310 nm range is more than three times that of wavelengths in the 1540-1560 nm range. As a result, a LIDAR system that generates LIDAR output signals such that at least one LIDAR output signal has a wavelength in the 1540-1560 nm range and at least one LIDAR output signal has a wavelength in the 1290-1310 nm range is effective for both metal objects and skin. The wavelengths selected may be specific to the application of the LIDAR system. For example, the 1290-1310 nm and 1540-1560 nm wavelength ranges are suitable for use in autonomous vehicles, since skin and metal are materials that may be in the path of the vehicle.

[0076] LIDAR output signals carrying channels in the wavelength range 1540-1560 nm have other advantages over LIDAR output signals carrying channels in the wavelength range 1290-1310 nm. For example, amplifiers for light in the wavelength range 1540-1560 nm are more readily available than amplifiers for light in the wavelength range 1290-1310 nm. As a result, LIDAR output signals carrying wavelength range 1540-1560 nm can have higher intensity than LIDAR output signals in the wavelength range 1290-1310 nm. Also, wavelengths in the 1540-1560 nm range can have higher atmospheric transmittance than wavelengths in the 1290-1310 nm range. The enhanced power level and atmospheric transmittance can compensate for the low reflectance of certain materials.

[0077] Wavelengths in the 1290-1310 nm range are also effective for use in generating LIDAR data for wet and dry textiles including polyester and wet wood (e.g., oak, snow, conifers, deciduous trees, and grasses). Additionally, wavelengths in the 1540-1560 nm and 1290-1310 nm ranges are effective for generating LIDAR data for dry wood such as oak, wet and dry concrete, asphalt, soil, plastics such as PVC, and clouds. As a result, if a LIDAR system generates LIDAR output signals such that at least one LIDAR output signal has a wavelength in the 1540-1560 nm range and at least one LIDAR output signal has a wavelength in the 1290-1310 nm range, the LIDAR system is effective for a wide range of materials and is therefore suitable for a wide range of applications.

[0078] In some examples, a method of generating and / or operating a LIDAR system includes identifying materials that may be included in one or more objects that may reflect LIDAR output signals from the LIDAR system back to the LIDAR system. The method also includes configuring at least a portion of the LIDAR output signals to have wavelengths that have a higher reflectivity for one of the identified materials than any of the other LIDAR output signals. In some examples, the number of LIDAR output signals included in the portion of the LIDAR output signals is equal to the total number of LIDAR output signals output from the LIDAR system.

[0079] Other examples of wavelength ranges useful for particular materials include, but are not limited to, wavelengths in the 850-905 nm range useful for trees and wavelengths in the 2000-2500 nm range useful for penetrating the atmosphere during poor visibility conditions including rain and fog.Thus, the LIDAR system may generate at least one, two, three, or four LIDAR output signals each having a wavelength within a different one of the ranges in the group consisting of 1290-1310 nm, 1540-1560 nm, 850-905 nm, and 1290-1310 nm.

[0080] For wavelength selection, wavelengths of different channels are generally spaced irregularly on the wavelength spectrum, rather than periodically on the wavelength spectrum, since wavelength selection involves selecting wavelengths that are effective for a particular material. Additionally or alternatively, channels can be considered as pairs, with the channels of each pair being adjacent to each other on the wavelength spectrum, and the other channel not having a wavelength between the two channels included in the pair. In this configuration, a single channel can be included in two or more pairs of channels that are adjacent to each other on the wavelength spectrum. The selection of wavelengths based on materials can increase the spacing between channels in a channel pair. For example, the LIDAR system can generate a LIDAR output signal such that at least one, two, or three channel pairs have wavelengths that are 10 nm, 20 nm, or 30 nm or more apart.

[0081] In some embodiments, the LIDAR system may be configured to direct multiple LIDAR output signals (e.g., two or more LIDAR output signals), each corresponding to a different wavelength range, to scan the same sample area. The LIDAR system may then receive multiple reflected LIDAR input signals, each corresponding to a different wavelength range, which may be combined with a locally generated reference signal to generate multiple LIDAR data signals, as described above in FIGS. 1A-3C.

[0082] In some examples, the system may simultaneously scan the same sample area with multiple LIDAR output signals. The LIDAR system may be configured to combine multiple LIDAR data signals to generate combined data related to the distance and / or velocity of objects within the scanned sample area. In these examples, the system software may process the results of the combined LIDAR data to maximize the amount of information about the sample area obtained. The combined data may depend on the reflectivity of the object for each different wavelength range incident on the object. In some examples, objects comprising different materials may produce different signal-to-noise ratios associated with the LIDAR input signals that correspond to different LIDAR output signals.

[0083] For example, when scanning a sample area including a user and a vehicle with a LIDAR, the LIDAR wavelengths in the 1250-1300 nm range may receive higher LIDAR return signal power levels when directed at a sample area associated with the user's skin than other LIDAR wavelengths (e.g., 1540-1560 nm). Conversely, the LIDAR wavelengths of about 1540-1560 nm may be more strongly reflected by the vehicle's metal body than the 1250-1300 nm LIDAR wavelengths. The LIDAR system may then receive higher levels of LIDAR return signal power associated with the wavelengths of about 1540-1560 nm when scanning the vehicle, resulting in higher signal power LIDAR data.

[0084] A LIDAR return signal with a higher power level may result in improved system performance (e.g., accuracy, precision, scan speed and / or range) due to a higher signal-to-noise ratio. Thus, the combined LIDAR data generated based on a combination of LIDAR data generated at different wavelengths may be able to simultaneously and accurately detect various objects made of different materials. This may allow the LIDAR system to increase the scan speed by decreasing the chirp period in some embodiments. In other examples, the improved signal-to-noise ratio in the LIDAR input signal may allow the LIDAR system to operate at a lower laser power level, avoiding the need to operate at a higher laser power level for materials that are otherwise difficult to detect. This increases the probability of detecting a wide range of different materials and / or reduces the probability of false positives.

[0085] As described above, the LIDAR system may generate one or more LIDAR data results for a sample area when directing one or more LIDAR output signals to the sample area. In these examples, the electronics may process the combined LIDAR data results to maximize the amount of information about the sample area obtained. In one example, the reflectance characteristics of the sample area may be so low in all but a single channel that the LIDAR data results are not measurable for all but the single channel. In that case, the LIDAR data from the channel with the measurable reflectance is treated as the final LIDAR data for the sample area.

[0086] In another example, the measured reflectance for each channel may vary in a pattern indicative of materials within the sample region. For example, a ratio of intensities of one or more different LIDAR input signals may indicate which materials are within the sample region. LIDAR data generated from LIDAR output signals favorable to the identified materials may be processed as the final LIDAR data for the sample region. In another example, the sample region may consist of an object of interest (e.g., a polar bear in snow as seen from above) surrounded by background material. In this case, it may be advantageous to compare the reflectance of the sample region including the polar bear and its surrounding snow using a channel where there is a large difference in reflectance between the bear and its surroundings. This may increase the contrast between the bear and its surroundings. For example, at 1500 nm, the reflectance of a bear's fur ranges from 20-60%, while the reflectance of snow is less than 5%. Thus, contrast is increased, aiding in object recognition.

[0087] Additionally or alternatively, other methods of combining the different LIDAR data results can be used. For example, the different LIDAR data results for the sample area can be averaged to find a final LIDAR data result, and the median can be used as the final LIDAR data result. Also, a weighted average of the LIDAR data results can be used as the final LIDAR data result. In one example, the weighted average is weighted by the strength of the different LIDAR input signals.

[0088] Although the composite data signal has been described above as having an in-phase component and a quadrature component that includes the out-of-phase portion of the reference signal, an unambiguous LIDAR data solution may be achieved by generating other composite data signals. For example, an unambiguous LIDAR data solution may be achieved using a composite data signal in which the in-phase and quadrature components include the out-of-phase portion of the comparison signal. For example, the first comparison waveguide (104) and the second comparison waveguide (106) may be constructed to provide a 90 degree phase shift between the first portion of the comparison signal and the second portion of the comparison signal, and the first reference waveguide (110) and the second reference waveguide are constructed such that the first portion of the reference signal and the second portion of the reference signal are in phase within the composite signal. Thus, the portion of the comparison signal in the first composite signal is phase shifted relative to the portion of the comparison signal in the second composite signal, but the portion of the reference signal in the first composite signal is not phase shifted relative to the portion of the reference signal in the second composite signal.

[0089] A suitable output element (26) for use in the LIDAR systems of Figures 1A-3C may be a waveguide facet. For example, Figure 4A shows a top view of a portion of a LIDAR chip including a LIDAR signal waveguide (24) terminating in a facet (300) through which a LIDAR output signal exits the LIDAR chip and / or through which a LIDAR input signal enters the LIDAR chip.

[0090] In some examples, it may be desirable to scan the LIDAR output signal to multiple different sample areas within the field of view, so that LIDAR data relating to the different sample areas may be generated. When the LIDAR signal waveguide (24) terminates at the facet (300), various scanning mechanisms may be used to scan the LIDAR output signal. For example, the LIDAR output signal may be received by one or more reflectors and / or one or more collimation devices. The one or more reflectors may be configured to redirect and / or steer the LIDAR output signal to provide a scan of the LIDAR output signal. Suitable reflectors include, but are not limited to, mirrors, such as mechanically driven mirrors and microelectromechanical system (MEMS) mirrors. The one or more collimation devices may provide collimation of the LIDAR output signal, thereby increasing the portion of the LIDAR input signal that is incident on the LIDAR signal waveguide (24). Suitable collimation devices include, but are not limited to, discrete lenses and compound lenses.

[0091] FIG. 4B shows a portion of the LIDAR chip shown in FIG. 4A used with a reflector (302) and a collimation device (304). For example, a lens serves as a collimation device to receive the LIDAR output signal and provide collimation of the LIDAR output signal. A mirror serves as a reflector (302) to receive the collimated LIDAR output signal and reflect the collimated LIDAR output signal in a desired direction. As shown by arrow A, electronics can move the mirror to steer and / or scan the collimated LIDAR output signal. The mirror can move in two or three dimensions. Suitable mirrors include, but are not limited to, mechanically driven mirrors and microelectromechanical system (MEMS) mirrors.

[0092] FIG. 4C shows a portion of the LIDAR chip shown in FIG. 4A used with a reflector (302) and a collimation device (304). For example, a mirror serves as a reflector (302) that receives the LIDAR output signal and reflects the LIDAR output signal in a desired direction. As shown by arrow A, electronics can move the mirror to steer and / or scan the LIDAR output signal. A lens serves as a collimation device (304) that receives the LIDAR output signal from the mirror and provides collimation of the LIDAR output signal. The lens can be configured to move with the movement of the mirror, such that the lens continues to receive the LIDAR output signal at different positions of the mirror. Alternatively, the movement of the mirror can be sufficiently limited so that the lens continues to receive the LIDAR output signal at different positions of the mirror. The mirror can move in two or three dimensions. Suitable mirrors include, but are not limited to, mechanically driven mirrors and microelectromechanical system (MEMS) mirrors.

[0093] 5 shows an example of a suitable output element (26), which may optionally include beam steering capabilities. The output element (26) includes a splitter (384) that receives the outgoing optical signal from the LIDAR signal waveguide (24). The splitter (384) splits the outgoing optical signal into multiple output signals that are each carried on a steering waveguide (386). Each steering waveguide terminates in a facet (388). The facets are positioned such that the output signals exiting the LIDAR chip through the facets (388) combine to form the LIDAR output signal.

[0094] The splitter (384) and steering waveguides (386) can be constructed such that there is no phase difference between the output signals at the facets of adjacent steering waveguides. For example, the splitter can be constructed such that each output signal is in phase upon exiting the splitter and each steering waveguide has the same length. Due to the lack of phase difference between the output signals, each channel in the outgoing LIDAR signal travels away from the output element (26) in the same direction (θ). Suitable numbers (M) of steering waveguides (386) include, but are not limited to, greater than 10 or 500 and / or less than 1000 or 2000. Suitable splitters include, but are not limited to, star couplers, cascaded Y-junctions, and cascaded 1×2 MMI couplers.

[0095] In some examples, phase tuners (390) are optionally disposed along at least a portion of the steering waveguides. Although phase tuners are shown disposed along the first and last steering waveguides, one or both of these phase tuners are optional. For example, the output element (26) need not include a phase tuner on steering waveguide k=1.

[0096] The electronics can be configured to operate the phase tuner (390) to generate a phase difference between the output signals at the facets of adjacent steering waveguides (386). The electronics can operate the phase tuner (390) such that the phase difference is constant, such that it increases linearly across the steering waveguides. For example, the electronics can operate the phase tuner such that the tuner-induced phase for steering waveguide number k is (k-1)β, where k is an integer from 1 to M and represents a number associated with the steering waveguides when the steering waveguides are numbered sequentially as shown in FIG. 5, and β is the tuner-induced phase difference between adjacent steering waveguides. Thus, the phase for steering waveguide number k is f 0+(k-1)f+(k-1)β. Although Figure 5 shows a chip with only four steering waveguides for simplicity of illustration, the chip can include many more steering waveguides. For example, the chip can include more than 4, 100, or 1000 and / or less than 10,000 steering waveguides.

[0097] The electronics can be configured to operate the phase tuner (390) to adjust the value of the phase difference β. Adjusting the value of the phase difference β changes the direction (θ) that the LIDAR output signal moves away from the chip. Thus, the electronics can scan the LIDAR output signal by varying the phase difference α. The range of angles over which the LIDAR output signal can be scanned is Φ R and in some examples, Φ v From -Φ v and when β=0, Φ=0° when measured in the direction of the LIDAR output signal.

[0098] In addition to or instead of producing a phase difference, the phase tuner (390) can be operated to collimate or focus the LIDAR output signal. For example, the phase tuner (390) can be operated to induce a constant phase difference β between successive waveguides, such that the induced phase of waveguide k is φ k = (k-1)β, where β is a constant for a collimated beam. For a focused beam, a suitable nonlinear phase dependence can be induced.

[0099] Further details regarding the construction and operation of an output element (26) constructed in accordance with FIG. 5 are described in U.S. Provisional Patent Application Serial No. 62 / 680,787, filed June 5, 2018, which is incorporated herein in its entirety.

[0100] As the different LIDAR output signals move away from the output element (26), they may spread to some extent in the outgoing LIDAR signal. Because the LIDAR output signals are directed to the same sample area, the spot size of each LIDAR output signal may be spread enough to overlap with at least one of the other LIDAR output signals by more than an overlap threshold percentage at the maximum distance for which the LIDAR system is configured to provide LIDAR data. Preferred overlap thresholds are greater than 5%, 25%, or 50% of the spot size. As noted above, the maximum distance is commonly set in the specifications of the application to which the LIDAR system is applied. An example of a situation in which there may be some spread of the different LIDAR output signals in the outgoing LIDAR signal as they move away from the output element (26) is when the path length difference between the steering waveguides (386) is non-zero.

[0101] Other embodiments, combinations, and modifications of the present invention will occur readily to those of ordinary skill in the art in view of these teachings. Accordingly, the present invention is to be 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. 1. A frequency modulated continuous wave (FMCW) LIDAR system including a LIDAR chip configured to output a LIDAR output signal having a wavelength between 1290 and 1310 nm, the LIDAR chip is configured to receive a LIDAR input signal from outside the LIDAR chip; the LIDAR input signal includes light from the LIDAR output signal after reflection of the LIDAR output signal by an object remote from the LIDAR chip; the LIDAR chip is configured to generate a composite signal including light from a comparison optical signal and light from a reference signal; the comparison signal includes light from the LIDAR output signal; and the reference signal does not include light from the LIDAR output signal; Frequency Modulated Continuous Wave (FMCW) LIDAR system.

2. The system of claim 1 , wherein the LIDAR output signal comprises light from an starting LIDAR signal and the reference signal comprises light from the starting LIDAR signal.

3. The system of claim 1 , wherein the LIDAR input signal is a function of radial velocity and / or distance between the object and the LIDAR tip.

4. The system of claim 3 , wherein the reference signal is not a function of radial velocity and / or distance between the object and the LIDAR tip.

5. The system of claim 1 , wherein the reference signal does not exit the LIDAR chip before being included in the composite signal.

6. The system of claim 1 , wherein the LIDAR chip includes a waveguide that guides both the LIDAR output signal and the LIDAR input signal.

7. The system of claim 1 , wherein the composite signal includes a comparison signal that is pulsating relative to the reference signal.

8. 10. The system of claim 1, wherein the LIDAR chip includes one or more waveguides configured to guide light through silicon.

9. 1. A LIDAR system comprising: a LIDAR system configured to output a plurality of LIDAR output signals each simultaneously directed to a sample area within a field of view, the sample area being one of a plurality of sample areas included in the field of view; the LIDAR output signals each carry one channel at a different wavelength; the wavelengths of the different channels are non-periodically spaced across a wavelength spectrum; and the LIDAR system is configured to simultaneously receive a plurality of LIDAR input signals each reflected by an object located outside the LIDAR system and within the sample volume, the LIDAR input signals each including light from a different one of the LIDAR output signals; LIDAR system.

10. 10. The system of claim 9, wherein at least one pair of adjacent channels in the wavelength spectrum have wavelengths that are more than 10 nm apart.

11. The system of claim 10 , wherein at least two pairs of adjacent channels in the wavelength spectrum have wavelengths that are more than 30 nm apart.

12. 10. The system of claim 9, wherein the LIDAR system outputs at least three LIDAR output signals each simultaneously directed at a sample region within the field of view and each carrying a channel at a different wavelength.

13. 10. The system of claim 9, wherein at least one of the LIDAR output signals comprises light from a laser source having a gain medium including quantum dots.

14. The system of claim 13 , wherein at least one of the LIDAR output signals carries one channel having a wavelength in the 1290-1310 nm range.

15. 10. The system of claim 9, further comprising electronics for performing a mathematical transformation on the electrical signal that is a function of radial velocity and / or distance between the LIDAR system and the object, A system wherein the transform outputs only one frequency solution associated with an object in the sample volume, and if the object is removed from the sample volume, no frequency solutions associated with the object are output by the mathematical transform.

16. 16. The system of claim 15, wherein the mathematical transformation is one of a plurality of mathematical transformations that the electronics are configured to perform, each transformation being performed on electrical signals that are a function of line-of-sight separation and / or distance between the LIDAR systems, and different transformations being performed on electrical signals carrying different channels.

17. 1. A LIDAR system comprising: a LIDAR system configured to output a plurality of LIDAR output signals each simultaneously directed to a sample area within a field of view, the sample area being one of a plurality of sample areas included in the field of view; the LIDAR output signals each carry one channel at a different wavelength; The wavelengths of the different channels are such that a difference between the wavelengths of the channels in at least one channel pair is greater than 10 nm, and the channels in each channel pair have wavelengths that are located adjacent to one another on the wavelength spectrum; and 1. A LIDAR system configured to simultaneously receive a plurality of LIDAR input signals each reflected by an object located outside the LIDAR system and within the sample region, the LIDAR input signals each including light from a different one of the LIDAR output signals.

18. 20. The system of claim 17, wherein the LIDAR system outputs at least three LIDAR output signals each simultaneously directed at a sample region within a field of view, each carrying a channel at a different wavelength.

19. 20. The system of claim 17, wherein at least one channel has a wavelength in the range of 1290 to 1310 nm.

20. 20. The system of claim 19, wherein at least one channel has a wavelength in the range of 1540 to 1560 nm.

Images