Patent ID: 12216208

DETAILED DESCRIPTION

The present disclosure describes examples of frequency-modulated continuous-wave (FMCW) LIDAR apparatus, and example methods therein, that incorporate free-space optical components (free-space optics) coupled to an optical source, which may be a coherent or non-coherent optical source and which may be a single-beam or multi-beam optical source, implemented in a photonic integrated circuit (PIC) or with discrete components, for example. The free-space optics may include, without limitation, polarizing beam splitters, lens systems, polarization wave plates, wavelength demultiplexers, reflectors and free-space photodetectors.

The free-space optics deliver an optical beam to the target environment, and generate and mix the local oscillator signal with the target return signal on the photodetector. The free-space optics design eliminates the challenging task of integrating the aforementioned components into a photonics chip.

The free-space design also increases the collection efficiency of the target return signal and produces a higher signal-to-noise ratio (SNR) than conventional integrated designs through the use of large aperture optics and photodetectors. In general, the efficiency of combining the target return signal with the LO signal is based on the spatial overlap between the LO signal and the target return signal on the photodetector. Examples in the present disclosure address the deficiencies of a conventional integrated LIDAR system by combining the LO signal and the target return signal in free space and providing the combined signal to a large aperture photodetector. In the free space optics, the target signal interferes with the LO signal to form the combined signal. The free-space design provides a large active surface area for mixing the signals compared with conventional integrated on-chip LIDAR designs. In addition to relaxing the alignment requirements, the large active surface area compensates for the time-dependent deleterious effects of lag angle and beam aberrations typically seen in fast scanning LiDAR systems.

FIG.1illustrates a LIDAR system100according to example implementations of the present disclosure. The LIDAR system100includes one or more of each of a number of components, but may include fewer or additional components than shown inFIG.1. The LIDAR system100may be implemented in any sensing market, such as, but not limited to, transportation, manufacturing, metrology, medical, and security systems. For example, in the automotive industry, the described beam delivery system becomes the front-end of frequency modulated continuous-wave (FMCW) devices that can assist with spatial awareness for automated driver assist systems, or self-driving vehicles. As shown, the LIDAR system100includes optical circuits101which may be implemented on a photonics chip. The optical circuits101may include a combination of active optical components and passive optical components. Active optical components may generate, amplify, or detect optical signals and the like. In some examples, the active optical components may generate, amplify or detect optical beams at different wavelengths. Passive optical components may filter, attenuate, guide, reflect or alter the polarization of optical beams and the like. In some examples, passive optical components such as wavelength demultiplexers may separate optical beams of different wavelengths.

Free space optics115may include off-chip passive optical components such as lens systems to collimate and expand optical beams, polarizing beam splitters, polarization filters, polarization wave plates such as quarter-wave plates and half-wave plates to carry optical signals, and route and manipulate optical signals to appropriate input and output ports of the active optical circuits.

Optical scanner102may include one or more scanning mirrors that are rotatable along respective orthogonal axes to steer optical signals to scan a target environment according to a scanning pattern. For example, the scanning mirrors may be rotatable by one or more galvanometers. The optical scanner102may also collect light incident upon any objects in the environment into a return optical beam (target return signal) that is returned to the free-space optics115. In addition to the mirrors and galvanometers, the optical scanning system may include components such as quarter-wave plates and half-wave plates, lenses, and anti-reflective coated windows or the like.

To control and support the optical circuits101and the optical scanner102, the LIDAR system100may include a LIDAR control system110. The LIDAR control system110may include a processing device for the LIDAR system100. In some examples, the processing device may be one or more general-purpose processing devices such as a microprocessor, central processing unit, or the like. More particularly, the processing device may be a complex instruction set computing (CISC) microprocessor, reduced instruction set computer (RISC) microprocessor, very long instruction word (VLIW) microprocessor, or processor implementing other instruction sets, or processors implementing a combination of instruction sets. The processing device may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like.

In some examples, the LIDAR control system110may include a signal processing unit112such as a digital signal processor. The LIDAR control system110may be configured to output digital control signals to control optical drivers103. In some examples, the digital control signals may be converted to analog signals through signal conversion unit106. For example, the signal conversion unit106may include a digital-to-analog converter. The optical drivers103may then provide drive signals to active components of optical circuits101to drive optical sources such as lasers and amplifiers. In some embodiments, several optical drivers103and signal conversion units106may be provided to drive multiple optical sources.

The LIDAR control system110may also be configured to output digital control signals for the optical scanner102. A motion control system105may control the galvanometers of the optical scanner102based on control signals received from the LIDAR control system110. For example, a digital-to-analog converter may convert coordinate routing information from the LIDAR control system110to signals interpretable by the galvanometers in the optical scanner102. In some examples, a motion control system105may also return information to the LIDAR control system110about the position or operation of components of the optical scanner102. For example, an analog-to-digital converter may in turn convert information about the galvanometers' position to a signal interpretable by the LIDAR control system110.

The LIDAR control system110may be further configured to analyze incoming digital signals. In this regard, the LIDAR system100may include optical receivers104, such as free-space photodetectors, to measure one or more beams received by free-space optics115. For example, a free-space photodetector may measure the amplitude of a reference beam (e.g., a local oscillator signal) from the free-space optics115, and an analog-to-digital converter may convert signals from the optical receivers104to signals interpretable by the LIDAR control system110. The optical receivers104may also measure the optical signal (e.g., a target return signal) that carries information about the range and velocity of a target in the form of a beat frequency between the local oscillator signal and the target return signal. The optical receivers104may include a high-speed analog-to-digital converter to convert signals received by the optical receivers to signals interpretable by the LIDAR control system110.

In some examples, the LIDAR system100may additionally include one or more imaging devices108configured to capture images of the target environment, a global positioning system109configured to provide a geographic location of the system100, or other sensor inputs. The LIDAR system100may also include an image processing system114. The image processing system114may be configured to receive the images and geographic location, and send the images and location or information related thereto to the LIDAR control system110or other systems connected to the LIDAR system100.

In some examples, the LIDAR system100may be configured to use nondegenerate optical sources to simultaneously measure range and velocity across two dimensions, providing for real-time, long range measurements of range, velocity, azimuth, and elevation of the surrounding environment. In some examples, the system may direct multiple modulated optical beams to the same target environment.

In some examples, the scanning process begins with the optical drivers103and LIDAR control system110. The LIDAR control system110instructs the optical drivers103to independently modulate one or more optical beams, and these modulated signals propagate through the on-chip optical circuits, to and through the free-space optics115. The free-space optics115direct the optical beams at the optical scanning system102that scans the target environment over a preprogrammed pattern defined by the motion control subsystem105.

Optical signals reflected back from the target environment (the target return signals) pass through the passive free-space optics115to the free-space optical receivers104. Each return signal is time-shifted in proportion to the target range, producing a constant, range-related beat frequency when mixed with the frequency modulated reference signal (local oscillator signal), which is detected on the free-space optical receivers104. Any relative velocity component of an illuminated target (relative to the LIDAR system100) produces an additional Doppler frequency shift, proportional to the relative target velocity, that can be distinguished from the range-related frequency offset by a signal processing unit112described below. The configurations of the free-space optics115for polarizing and directing beams to the optical receivers104are described in detail below.

The analog signals from the optical receivers104are converted to digital signals using ADCs. The digital signals are then sent to the LIDAR control system110. A signal processing unit112may then receive the digital signals and interpret them. In some examples, the signal processing unit112also receives position data from the motion control system105and galvanometer (not shown) as well as image data from the image processing system114. The signal processing unit112can then generate a 3D point cloud with information about range and velocity of points in the environment as the optical scanner102scans additional points. The signal processing unit112can also overlay a 3D point cloud data with the image data to determine velocity and distance of objects in the surrounding area. The system also processes the satellite-based navigation location data to provide a precise global location.

FIG.2is a block diagram illustrating an example single-beam LIDAR apparatus200in a first configuration. The configuration illustrated inFIG.2includes a photonics chip201, including an FMCW LIDAR photonic integrated circuit (PIC)202, and free-space optics. In one example, the optical circuits101, described in respect toFIG.1, may be implemented on photonic chip201. The PIC202is configured to generate and emit an optical beam203, which may be multi-spectral (i.e., containing more than one wavelength). The PIC202is optically coupled to a polarizing beam-splitter (PBS)204. The PBS204transmits a p-polarization of the optical beam203in a first direction toward a target205in the target environment. The p-polarization of the optical beam203is the polarization of the beam that is parallel to the plane of incidence of the optical beam203in the PBS204. The PBS204is designed to have a finite polarization extinction ratio, such that a detectable p-polarized portion206of the optical beam203is leaked by the PBS204in a second direction toward a photodetector207. In one example, without limitation, the PBS204may have a polarization extinction ratio on the order of 1:1000. The leaked portion206of the optical beam203may be used as a local oscillator (LO) signal to mix with a target return signal as described in greater detail below.

In one example, the free-space optics may include a lens system208to magnify the optical beam203. The lens system208may be any suitable lens system such as a Galilean or a Keplerian lens system, for example.

In one example, the free-space optics may include a polarization wave plate (PWP)209, which may be a quarter-wave plate or half-wave plate, to convert the optical beam203from the first linear polarization (p-polarization) to a first circular polarization. In the example configuration ofFIG.2, the first circular polarization is shown as a right-hand (RH) or clockwise (CW) circular polarization. The circularly polarized optical beam203is then directed to the target environment by optical scanners210. In the example illustrated inFIG.2, the optical beam203illuminates the target205, which reflects the optical beam as a target return signal211. The principle component of the target return signal211will be a circularly polarized signal (second circular polarization) with the opposite polarization sense of the circularly polarized optical beam203. In the example ofFIG.2, the target return signal will have a left-hand (LH) or counter-clockwise (CCW) circular polarization.

The target return signal211is de-scanned by the optical scanner210and transmitted through the PWP209, where the polarization of the target return signal211is converted from the second circular polarization to an s-polarized signal (second linear polarization), perpendicular to the p-polarization (first linear polarization) of the original optical beam203. The s-polarized target return signal211then passes through the lens system208and is reflected by the PBS204in a third direction to a second PWP212, which may be a quarter-wave plate or half-wave plate, to convert the target return signal211from the second linear polarization (s-polarization) to the first circular polarization (RH or CW circular polarization in the example ofFIG.2). The circularly polarized target return signal211is then reflected by retro-reflector213back through the second PWP212. The retro-reflector211reverses the polarization sense of the target return signal211from the first circular polarization (RH or CW in the example ofFIG.2) to the second circular polarization (LH or CCW in the example ofFIG.2), and the second PWP212converts the target return signal211from the second circular polarization to the first linear polarization (p-polarization in the example ofFIG.2).

The p-polarized target return signal211passes through PBS204to co-propagate with the LO signal206(leakage signal), where the p-polarized target return signal211and the p-polarized LO signal206pass through a linear polarizer214. The linear polarizer passes the p-polarized light and rejects any signal that is not p-polarized, which prevents light of different polarizations from elevating the noise floor of the detection system.

For multiple wavelength beams, wavelength demultiplexers may be used to separate different wavelengths and direct them to dedicated detectors.FIG.2illustrates an example of a two-wavelength configuration, where a wavelength demultiplexer (DEMUX)215separates the first wavelength, λ1, from the second wavelength, λ2. The DEMUX215may be for example, and without limitation, a dichroic mirror, a Bragg grating or any other suitable wavelength demultiplexer. The separate wavelengths may then be focused by respective lens systems216and217onto respective photodetectors207and218, where the interference between the LO signal206and the target return signal211generates target information as described above. The use of large aperture free-space optics and free-space photodetectors ensures that any beam decentering caused by insufficient de-scan does not degrade the SNR of the target return signal211.

FIG.3is a block diagram illustrating an example multi-beam LIDAR apparatus in a first configuration. LIDAR apparatus300is similar in almost all respects to LIDAR apparatus200, except that the photonics chip301and the FMCW LIDAR PIC302are configured to emit multiple beams, where each beam may be multi-spectral. In one example, the optical circuits101, described in respect toFIG.1, may be implemented on photonics chip301. As illustrated inFIG.3, the example LIDAR apparatus300also includes a lens array318to collimate the multiple beams into a collimated optical beam303, which is directed to the PBS204. The PBS204transmits a p-polarization of the optical beam303in a first direction toward the target205in the target environment. As described above, due to the finite extinction ratio of the PBS204, a detectable p-polarized portion306of the optical beam303is leaked by the PBS204in a second direction toward photodetector207. The leaked portion306of the optical beam303may be used as a local oscillator (LO) signal to mix with a target return signal. The p-polarized optical beam303is then magnified by the lens system208.

The optical beam303is then converted by the PWP209from the first linear polarization (p-polarization) to a first circular polarization. In the example configuration ofFIG.3, the first circular polarization is shown as a right-hand (RH) or clockwise (CW) circular polarization. The circularly polarized optical beam303is then directed to the target environment by optical scanners210. In the example illustrated inFIG.3, the optical beam303illuminates the target205, which reflects the optical beam as a target return signal311. The principle component of the target return signal311will be a circularly polarized signal (second circular polarization) with the opposite polarization sense of the circularly polarized optical beam303. In the example ofFIG.3, the target return signal will have a left-hand (LH) or counter-clockwise (CCW) circular polarization.

The target return signal311is de-scanned by the optical scanner210and transmitted through the PWP209, where the polarization of the target return signal311is converted from the second circular polarization to an s-polarized signal (second linear polarization), perpendicular to the p-polarization (first linear polarization) of the original optical beam303. The s-polarized target return signal311then passes through the lens system208and is reflected by the PBS204in a third direction to a second PWP212, to convert the target return signal311from the second linear polarization (s-polarization) to the first circular polarization (RH or CW circular polarization in the example ofFIG.3). The circularly polarized target return signal311is then reflected by retro-reflector213, back through the second PWP212. The retro-reflector211reverses the polarization sense of the target return signal311from the first circular polarization (RH or CW in the example ofFIG.3) to the second circular polarization (LH or CCW in the example ofFIG.3), and the second PWP212converts the target return signal311from the second circular polarization to the first linear polarization (p-polarization in the example ofFIG.3).

The p-polarized target return signal311passes through PBS204to co-propagate with the LO signal306(leakage signal), where the p-polarized target return signal311and the p-polarized LO signal306pass through linear polarizer214. The linear polarizer passes the p-polarized light and rejects any signal that is not p-polarized, which prevents light of different polarizations from elevating the noise floor of the detection system.

For multiple wavelength beams, wavelength demultiplexers may be used to separate different wavelengths and direct them to dedicated detectors.FIG.3illustrates an example of a two wavelength configuration, where a wavelength demultiplexer215separates the first wavelength, λ1, from the second wavelength, λ2. In the multi-beam system illustrated byFIG.3, although not shown, multiple wavelength demultiplexers may be used to spatially separate the multiple beams. The separate wavelengths may then be focused by respective lens systems216and217onto respective photodetectors207and218, where the interference between the LO signal306and the target return signal311generates target information as described above. The use of large aperture free-space optics and free-space photodetectors insures that any beam decentering caused by insufficient de-scan does not degrade the SNR of the target return signal311.

FIG.4is a block diagram illustrating an example single-beam LIDAR apparatus in a second configuration. The configuration illustrated inFIG.4is similar in many respects to the single-beam LIDAR apparatus illustrated inFIG.2, except that the scan port of the PBS204and the detection port of the PBS204are reversed.

InFIG.4, the LIDAR apparatus400includes a photonics chip201including an FMCW LIDAR photonic integrated circuit (PIC)202configured to generate and emit an optical beam403, which may be multi-spectral. In one example, the optical circuits101, described in respect toFIG.1, may be implemented on photonics chip201. The PIC202is optically coupled to the polarizing beam-splitter (PBS)204. The PBS204reflects an s-polarization of the optical beam403in a first direction toward a target205in the target environment. The s-polarization of the optical beam403is the polarization of the beam that is perpendicular to the plane of incidence of the optical beam403in the PBS204. The PBS204has a finite polarization extinction ratio, such that a detectable s-polarized portion406of the optical beam403is leaked by the PBS204in a second direction toward photodetector207. The leaked portion406of the optical beam403may be used as a local oscillator (LO) signal to mix with a target return signal. In one example, the free-space optics may include a lens system208to magnify the optical beam403.

The free-space optics may include a polarization wave plate (PWP)209, to convert the optical beam403from the first linear polarization (s-polarization) to a first circular polarization. In the example configuration ofFIG.4, the first circular polarization is shown as a right-hand (RH) or clockwise (CW) circular polarization. The circularly polarized optical beam403is then directed to the target environment by optical scanners210. In the example illustrated inFIG.4, the optical beam403illuminates the target205, which reflects the optical beam as a target return signal411. The principle component of the target return signal411will be a circularly polarized signal (second circular polarization) with the opposite polarization sense of the circularly polarized optical beam403. In the example ofFIG.4, the target return signal will have a left-hand (LH) or counter-clockwise (CCW) circular polarization.

The target return signal411is de-scanned by the optical scanner210and transmitted through the PWP209, where the polarization of the target return signal411is converted from the second circular polarization to a p-polarized signal (second linear polarization), perpendicular to the s-polarization (first linear polarization) of the original optical beam403. The p-polarized target return signal411then passes through the lens system208and is passed by the PBS204in a third direction to the second PWP212, to convert the target return signal411from the second linear polarization (p-polarization) to the second circular polarization (LH or CCW circular polarization in the example ofFIG.4). The circularly polarized target return signal411is then reflected by retro-reflector213back through the second PWP212. The retro-reflector211reverses the polarization sense of the target return signal411from the second circular polarization (LH or CCW in the example ofFIG.4) to the first circular polarization (RH or CW in the example ofFIG.4), and the second PWP212converts the target return signal411from the first circular polarization to the first linear polarization (s-polarization in the example ofFIG.4).

The s-polarized target return signal411passes through PBS204to co-propagate with the LO signal406(leakage signal), where the s-polarized target return signal411and the s-polarized LO signal406pass through a linear polarizer414. The linear polarizer414passes the s-polarized light and rejects any signal that is not s-polarized, which prevents light of different polarizations from elevating the noise floor of the detection system.

For multiple wavelength beams, wavelength demultiplexers may be used to separate different wavelengths and direct them to dedicated detectors.FIG.4illustrates an example of a two-wavelength configuration, where a where a wavelength demultiplexer (DEMUX)215separates the first wavelength, λ1, from the second wavelength, λ2. The DEMUX215may be for example, and without limitation, a dichroic mirror, a Bragg grating or any other suitable wavelength demultiplexer. The separate wavelengths may then be focused by respective lens systems216and217onto respective photodetectors207and218, where the interference between the LO signal406and the target return signal411generates target information as described above. The use of large aperture free-space optics and free-space photodetectors insures that any beam decentering caused by insufficient de-scan does not degrade the SNR of the target return signal411.

FIG.5is a block diagram illustrating an example multi-beam LIDAR apparatus in a second configuration. LIDAR apparatus500is similar in almost all respects to LIDAR apparatus400, except that the photonics chip501and the FMCW LIDAR PIC502are configured to emit multiple beams, where each beam may be multi-spectral. In one example, the optical circuits101, described in respect toFIG.1, may be implemented on photonics chip501. As illustrated inFIG.5, the example LIDAR apparatus500includes a lens array518to collimate the multiple beams into a collimated optical beam503, which is directed to the PBS204. The PBS204reflects an s-polarization of the optical beam503in a first direction toward a target205in the target environment. The s-polarization of the optical beam503is the polarization of the beam that is perpendicular to the plane of incidence of the optical beam503in the PBS204. The PBS204has a finite polarization extinction ratio, such that an s-polarized portion506of the optical beam503is leaked by the PBS204in a second direction toward photodetector207. The leaked portion506of the optical beam503may be used as a local oscillator (LO) signal to mix with a target return signal. The free-space optics may include a lens system208to magnify the optical beam503.

The free-space optics may include a polarization wave plate (PWP)209, to convert the optical beam503from the first linear polarization (s-polarization) to a first circular polarization. In the example configuration ofFIG.5, the first circular polarization is shown as a right-hand (RH) or clockwise (CW) circular polarization. The circularly polarized optical beam503is then directed to the target environment by optical scanners210. In the example illustrated inFIG.5, the optical beam503illuminates the target205, which reflects the optical beam as a target return signal511. The principle component of the target return signal511will be a circularly polarized signal (second circular polarization) with the opposite polarization sense of the circularly polarized optical beam503. In the example ofFIG.5, the target return signal will have a left-hand (LH) or counter-clockwise (CCW) circular polarization.

The target return signal511is de-scanned by the optical scanner210and transmitted through the PWP209, where the polarization of the target return signal511is converted from the second circular polarization to a p-polarized signal (second linear polarization), perpendicular to the s-polarization (first linear polarization) of the original optical beam503. The p-polarized target return signal511then passes through the lens system208and is passed by the PBS204in a third direction to the second PWP212, to convert the target return signal511from the second linear polarization (p-polarization) to the second circular polarization (LH or CCW circular polarization in the example ofFIG.4). The circularly polarized target return signal511is then reflected by retro-reflector213back through the second PWP212. The retro-reflector211reverses the polarization sense of the target return signal511from the second circular polarization (LH or CCW in the example ofFIG.5) to the first circular polarization (RH or CW in the example ofFIG.5), and the second PWP212converts the target return signal511from the first circular polarization to the first linear polarization (s-polarization in the example ofFIG.5).

The s-polarized target return signal511passes through PBS204to co-propagate with the LO signal506(leakage signal), where the s-polarized target return signal511and the s-polarized LO signal506pass through a linear polarizer514. The linear polarizer514passes the s-polarized light and rejects any signal that is not s-polarized, which prevents light of different polarizations from elevating the noise floor of the detection system.

For multiple wavelength beams, wavelength demultiplexers may be used to separate different wavelengths and direct them to dedicated detectors.FIG.5illustrates an example of a two-wavelength configuration, where a where a wavelength demultiplexer (DEMUX)215separates the first wavelength, λ1, from the second wavelength, λ2. The DEMUX215may be for example, and without limitation, a dichroic mirror, a Bragg grating or any other suitable wavelength demultiplexer. In the multi-beam system illustrated byFIG.5, although not shown, multiple wavelength demultiplexers may be used to spatially separate the multiple beams. The separate wavelengths may then be focused by respective lens systems216and217onto respective photodetectors207and218, where the interference between the LO signal506and the target return signal511generates target information as described above. The use of large aperture free-space optics and free-space photodetectors insures that any beam decentering caused by insufficient de-scan does not degrade the SNR of the target return signal511.

FIG.6is a block diagram illustrating an example single-beam LIDAR apparatus in a third configuration. The LIDAR apparatus600illustrated inFIG.6includes a photonics chip201, including an FMCW LIDAR photonic integrated circuit (PIC)202, and free-space optics. In one example, the optical circuits101, described in respect toFIG.1, may be implemented on photonics chip201. The PIC202is configured to generate and emit an optical beam603, which may be multi-spectral (i.e., containing more than one wavelength). The PIC202is optically coupled to a polarizing beam-splitter (PBS)204. The PBS204transmits a p-polarization of the optical beam603in a first direction toward a target205in the target environment. In one example, the free-space optics may include a lens system208to magnify the optical beam603.

In one example, the free-space optics includes a polarization wave plate (PWP)209, which may be a quarter-wave plate or half-wave plate, to convert the optical beam603from the first linear polarization (p-polarization) to a first circular polarization. In the example configuration ofFIG.6, the first circular polarization is shown as a right-hand (RH) or clockwise (CW) circular polarization. The circularly polarized optical beam603is then directed to the target environment by optical scanners210.

The PWP209is designed to partially reflect and change the polarization of the p-polarized optical beam603, such that a detectable s-polarized portion606of the optical beam603is reflected back through the lens system208to the PBS204, where it is reflected in a second direction toward PD207, and where it may be used as a local oscillator (LO) signal to mix with a target return signal as described below.

Continuing with the example illustrated inFIG.6, the circularly polarized optical beam603illuminates the target205, which reflects the optical beam as a target return signal611. The principle component of the target return signal611will be a circularly polarized signal (second circular polarization) with the opposite polarization sense of the circularly polarized optical beam603. In the example ofFIG.6, the target return signal will have a left-hand (LH) or counter-clockwise (CCW) circular polarization.

The target return signal611is de-scanned by the optical scanner210and transmitted through the PWP209, where the polarization of the target return signal611is converted from the second circular polarization to an s-polarized signal (second linear polarization), perpendicular to the p-polarization (first linear polarization) of the original optical beam603. The s-polarized target return signal611then passes through the lens system208and is reflected by the PBS204in the second direction to co-propagate with the LO signal606(reflected signal), where the s-polarized target return signal611and the s-polarized LO signal606pass through a linear polarizer614. The linear polarizer passes the s-polarized light and rejects any signal that is not s-polarized, which prevents light of different polarizations from elevating the noise floor of the detection system.

For multiple wavelength beams, wavelength demultiplexers may be used to separate different wavelengths and direct them to dedicated detectors.FIG.6illustrates an example of a two-wavelength configuration, where a where a wavelength demultiplexer (DEMUX)215separates the first wavelength, λ1, from the second wavelength, λ2. The DEMUX215may be for example, and without limitation, a dichroic mirror, a Bragg grating or any other suitable wavelength demultiplexer. The separate wavelengths may then be focused by respective lens systems216and217onto respective photodetectors207and218, where the interference between the LO signal606and the target return signal611generates target information as described above. The use of large aperture free-space optics and free-space photodetectors insures that any beam decentering caused by insufficient de-scan does not degrade the SNR of the target return signal611.

FIG.7is a block diagram illustrating an example multi-beam LIDAR apparatus in a third configuration. LIDAR apparatus700is similar in almost all respects to LIDAR apparatus600, except that the photonics chip701and the FMCW LIDAR PIC702are configured to emit multiple beams, where each beam may be multi-spectral. In one example, the optical circuits101, described in respect toFIG.1, may be implemented on photonics chip701. As illustrated inFIG.7, the example LIDAR apparatus700includes a lens array718to collimate the multiple beams into a collimated optical beam703, which is directed to the PBS204. The PBS204transmits a p-polarization of the optical beam703in a first direction toward a target205in the target environment. As described above, the free-space optics may include a lens system208to magnify the optical beam703.

In one example, the free-space optics include a polarization wave plate (PWP)209, which may be a quarter-wave plate or half-wave plate, to convert the optical beam703from the first linear polarization (p-polarization) to a first circular polarization. In the example configuration ofFIG.7, the first circular polarization is shown as a right-hand (RH) or clockwise (CW) circular polarization. The circularly polarized optical beam703is then directed to the target environment by optical scanners210.

The PWP209is designed to partially reflect and change the polarization of the p-polarized optical beam703, such that a detectable s-polarized portion706of the optical beam703is reflected back through the lens system208to the PBS204, where it is reflected in a second direction toward PD207, and where it may be used as a local oscillator (LO) signal to mix with a target return signal as described below.

Continuing with the example illustrated inFIG.7, the circularly polarized optical beam703illuminates the target205, which reflects the optical beam as a target return signal711. The principle component of the target return signal711will be a circularly polarized signal (second circular polarization) with the opposite polarization sense of the circularly polarized optical beam603. In the example ofFIG.7, the target return signal will have a left-hand (LH) or counter-clockwise (CCW) circular polarization.

The target return signal711is de-scanned by the optical scanner210and transmitted through the PWP209, where the polarization of the target return signal711is converted from the second circular polarization to an s-polarized signal (second linear polarization), perpendicular to the p-polarization (first linear polarization) of the original optical beam703. The s-polarized target return signal711then passes through the lens system208and is reflected by the PBS204in the second direction to co-propagate with the LO signal706(reflected signal), where the s-polarized target return signal711and the s-polarized LO signal706pass through a linear polarizer714. The linear polarizer passes the s-polarized light and rejects any signal that is not s-polarized, which prevents light of different polarizations from elevating the noise floor of the detection system.

For multiple wavelength beams, wavelength demultiplexers may be used to separate different wavelengths and direct them to dedicated detectors.FIG.6illustrates an example of a two-wavelength configuration, where a where a wavelength demultiplexer (DEMUX)215separates the first wavelength, λ1, from the second wavelength, λ2. The DEMUX215may be for example, and without limitation, a dichroic mirror, a Bragg grating or any other suitable wavelength demultiplexer. In the multi-beam system illustrated byFIG.7, although not shown, multiple wavelength demultiplexers may be used to spatially separate the multiple beams. The separate wavelengths may then be focused by respective lens systems216and217onto respective photodetectors207and218, where the interference between the LO signal706and the target return signal711generates target information as described above. The use of large aperture free-space optics and free-space photodetectors insures that any beam decentering caused by insufficient de-scan does not degrade the SNR of the target return signal711.

FIG.8is a flow diagram illustrating an example method800in a LIDAR apparatus, according to the present disclosure. Various portions of method800may be performed by LIDAR apparatus200,300,400and500, illustrated inFIGS.2,3,4and5, respectively and described in detail above.

With reference toFIG.8, method800illustrates example functions used by various embodiments. Although specific function blocks (“blocks”) are disclosed in method800, such blocks are examples. That is, embodiments are well suited to performing various other blocks or variations of the blocks recited in method800. It is appreciated that the blocks in method800may be performed in an order different than presented, and that not all of the blocks in method800may be performed.

At block802, an optical source of a LIDAR apparatus generates an optical beam having a first linear polarization. In various examples, the optical light source may be any of photonic ICs202,302and502as described with respect toFIGS.2-5. The optical sources may generate multiple beams, and each beam may have multiple wavelengths. In various examples the linear polarization may be p-polarization or s-polarization with respect to a PBS that receives the optical beam.

At block804, the optical beam is directed by a PBS in the direction of a target environment. In some examples, the optical beam may be p-polarized, and the PBS passes the optical beam toward the target environment, as illustrated and described with respect to LIDAR apparatus200and300inFIGS.2and3, respectively. In other examples, the optical beam may be s-polarized, and the PBS may reflect the optical beam toward the target environment, as illustrated and describes with respect to LIDAR apparatus400and500inFIGS.4and5, respectively.

At block806, a portion of the optical beam is leaked from the PBS in the direction of a photodetector (PD) as an LO signal. In some examples, the optical beam may be p-polarized, and the PBS reflects the leaked portion of the optical beam toward the PD, as illustrated and described with respect to LIDAR apparatus200and300inFIGS.2and3, respectively. In other examples, the optical beam may be s-polarized, and the PBS passes the leaked portion of the optical beam toward the PD, as illustrated and described with respect to LIDAR apparatus400and500inFIGS.4and5, respectively.

At block808, the LO signal and the target return signal are received at the PD with the same polarization. In some examples, the two signals may both be p-polarized as illustrated and described with respect to LIDAR apparatus200and300inFIGS.2and3, respectively. In other examples, both signals may be s-polarized as illustrated and described with respect to LIDAR apparatus400and500inFIGS.4and5, respectively.

At block810, the LO signal and the target return signal are mixed to generate target information. The mixing may occur at the PD or anywhere along the optical path where the two signals are co-propagating with the same polarization.

FIG.9is a flow diagram illustrating an example method900in a LIDAR apparatus, according to the present disclosure. Various portions of method900may be performed by LIDAR apparatus600and700, illustrated inFIGS.6and7, respectively, and described in detail above.

With reference toFIG.9, method900illustrates example functions used by various embodiments. Although specific function blocks (“blocks”) are disclosed in method800, such blocks are examples. That is, embodiments are well suited to performing various other blocks or variations of the blocks recited in method900. It is appreciated that the blocks in method900may be performed in an order different than presented, and that not all of the blocks in method800may be performed.

At block902, an optical source of a LIDAR apparatus generates an optical beam having a first linear polarization. In various examples, the optical light source may be either of photonic ICs202and702as described with respect toFIGS.6and7, respectively. The optical sources may generate multiple beams, and each beam may have multiple wavelengths. In various examples the linear polarization may be p-polarization or s-polarization with respect to a PBS that receives the optical beam.

At block904, the optical beam is directed by a PBS in the direction of a target environment. In the examples ofFIGS.6and7, the optical beam is p-polarized, and the PBS passes the optical beam toward the target environment. It will be appreciated, however, that the target port and the detection port of apparatus600and700may be interchanged, to provide for the use of s-polarization in the optical beam generated by PICs202or702, in which case an s-polarized optical beam would be reflected toward the target environment by the PBS.

At block906, a portion of the optical beam is reflected from a PWB to generate an LO signal with a second linear polarization. In the examples of LIDAR apparatus600and700inFIGS.6and7, the second polarization is illustrated as s-polarization. As illustrated inFIGS.6and7, the LO signal co-propagates with a target return signal of the same polarization all the way back to the PD.

At block908, the LO signal and the target return signal are received at the PD with the same polarization after co-propagating through apparatus600and700from the PWP to the PD, as illustrated inFIGS.6and7, respectively.

At block910, the LO signal and the target return signal are mixed to generate target information. The mixing may occur at the PD or anywhere along the optical path where the two signals are co-propagating with the same polarization.

The preceding description sets forth numerous specific details such as examples of specific systems, components, methods, and so forth, in order to provide a good understanding of the present disclosure. It will be apparent to one skilled in the art, however, that other examples may be practiced without these specific details. In other instances, well-known components or methods are not described in detail or are presented in simple block diagram form in order to avoid unnecessarily obscuring the present disclosure. Thus, the specific details set forth are merely non-limiting examples.

Although the operations of the methods herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operation may be performed, at least in part, concurrently with other operations. In other examples, instructions or sub-operations of distinct operations may be performed in an intermittent or alternating manner.

The above description of illustrated examples of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific examples are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the disclosure, as those skilled in the relevant art will recognize. The word “example” or is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “example” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word “example” is intended to present concepts in a concrete fashion. As used in this disclosure, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X includes A or B” is intended to mean any of the natural inclusive permutations. That is, if X includes A; X includes B; or X includes both A and B, then “X includes A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. Furthermore, the terms “first,” “second,” “third,” “fourth,” etc. as used herein are meant as labels to distinguish among different elements and may not necessarily have an ordinal meaning according to their numerical designation.