Spectroscopic analysis system with beat component

Abstract

An optical ranging and detection system enables a reconfigurable very wide field of view, high sampling of spatial points per second, and high optical power handling by effectively combining different wavelength, time and frequency encoding, and spatial selectivity using an architecture. A transmitter is capable of generating multiple narrow beams, encoding different beams, and transmitting in different spatial directions. A receiver can distinguish and extract range and reflectivity information of the reflected beams. Three-dimensional imaging of an environment is achieved by scanning the field of view of the transmitter. Control and signal processing electronics fabricated in a chip are packaged together with a chip containing photonic components of the ranging system. The optical ranging and detection system generates terahertz beams in addition to optical beams, and the combined two beams allow reconfigurable spectral analysis.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to LiDAR (light detection and ranging) or three- dimensional imaging and spectral analysis systems. BRIEF DESCRIPTION OF DRAWINGS

[0002] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more implementations of the present disclosure and together with the description, explain the principles and implementations of the present disclosure.

[0003] Figure 1 An exemplary transmitter according to the present disclosure is illustrated.

[0004] Figure 2 An exemplary encoding scheme is illustrated.

[0005] Figure 3 An exemplary 2D scanner is illustrated.

[0006] Figure 4 Some techniques to increase power handling of a LiDAR system are illustrated.

[0007] Figure 5 An exemplary cluster architecture for a scanner is illustrated.

[0008] Figure 6 An exemplary raster geometry for a transmitter is illustrated.

[0009] Figure 7 A top view of an exemplary transmitter is illustrated.

[0010] Figure 8 An exemplary raster beam transmitter is illustrated.

[0011] Figure 9 An exemplary layout of a 2D scanner to increase field of view of a LiDAR system is illustrated.

[0012] Figure 10 An exemplary layout of different transmitters is illustrated.

[0013] Figures 11-12 An exemplary receiver architecture is illustrated.

[0014] Figure 13 An exemplary receiver signaling flow diagram is illustrated.

[0015] Figure 14 An exemplary method of generating multiple beams from a transmitter for a multi-receiver architecture is illustrated.

[0016] Figure 15 An exemplary package for a LiDAR system is illustrated.

[0017] Figure 16Other embodiments of LiDAR configurations are illustrated.

[0018] Figure 17 A multi-receiver architecture is illustrated.

[0019] Figure 18 An exemplary arrayed waveguide grating is illustrated.

[0020] Figure 19 A time-varying frequency modulation signal for coherent detection is illustrated.

[0021] Figure 20 An exemplary optoelectronic-terahertz spectroscopy system is illustrated in which a transmitter emits both optical radiation generated as a beat note of two wavelengths sufficiently close using a nonlinear material and terahertz radiation.

[0022] Figure 21 An exemplary spectroscopy system operating at multiple wavelengths, each wavelength being individually locked and encoded, is illustrated. SUMMARY

[0023] In a first aspect of the disclosure, an apparatus is described, the apparatus comprising an imaging and spectroscopy system.

[0024] In a second aspect of the disclosure, a method is described, the method comprising a reconfigurable spectroscopy system operating in optical and terahertz regimes.

[0025] In a third aspect of the disclosure, a system is described, the system comprising the apparatus of the first aspect of the disclosure and the method of the second aspect of the disclosure. DETAILED DESCRIPTION

[0026] The present disclosure describes an optical terahertz spectroscopy system. In particular, the systems disclosed herein can advantageously scan a sample across its surface by emitting a beam of electromagnetic radiation across multiple wavelengths at a particular point or region of the sample and scanning the beam at different points or regions of the sample. In some embodiments, each region of the sample is scanned across an entire range of wavelengths. In other words, in some embodiments, the beam remains aimed at the same region of the sample while the wavelength is changed; subsequently, the beam is moved to a different location and the wavelength is changed again. In some embodiments, the area scanned for each point or region of the scan corresponds to the lateral size of the beam. In some embodiments, the electromagnetic radiation of the beam is in the optical wavelength range, the terahertz wavelength range, or both. The terahertz system can be combined with a LiDAR system to perform optical and terahertz spectroscopy. Hereinafter, the LiDAR system is described first, followed by the terahertz system. The two systems are combined to form the reconfigurable spectroscopy system of the present disclosure.

[0027] The present disclosure describes scalable LiDAR (light detection and ranging) systems that include an optical phased array architecture. The systems can include one or more lasers, a switch or multiplexer (MUX) to select the lasers, a splitter to split the lasers into multiple waveguides, one or more encoders to encode the laser signals, and one or more scanners that emit beams in different directions and adaptively shape the beams, and associated control circuitry to operate the photonic components.

[0028] LiDAR systems can be used in a variety of applications, such as unmanned vehicles, assisted driving vehicles, mapping, sensors, cameras, drones and aircraft in civilian and military applications, as well as consumer devices such as smartphones or tablets. The systems can be modified according to the particular application in terms of resolution, power usage requirements, spatial detection requirements, and other parameters. For example, in unmanned vehicles, the LiDAR system can provide a three-dimensional map and image the environment around the vehicle in real time, allowing the driving system to safely guide and control the vehicle. For example, an unmanned car can detect other cars, obstacles, pedestrians, and other traffic, allowing safe operation of the car. In some embodiments, consumer devices can use LiDAR to provide a three-dimensional (3D) map of the environment up to several meters distance (e.g., less than 10 meters or less than 20 meters). Three-dimensional imaging devices such as smartphones or tablets typically require a more limited range than vehicles. These consumer devices typically use less power and include a smaller number of components than vehicle LiDARs. For example, an imaging device for a vehicle can consume tens of watts, while an imaging device for a consumer electronic such as a smartphone can emit optical power in the milliwatt range. An imaging device for a consumer electronic can map the environment around the device and produce 3D images. These images can be used, for example, for video games, virtual reality, and facial recognition, for example, to enhance the security of the device.

[0029] LiDAR systems of the present disclosure can include a transmitter, a receiver, or both a transmitter and a receiver. The systems can modulate several parameters, such as laser wavelength, spatial coordinates such as emission or reception angle, and in the time domain by laser signal shape and duration. In some embodiments, the transmitter can include an array of scanners oriented in different directions to provide spatial selectivity of the emitted laser beams; the associated receiver can be broadband with a wide field of view to collect all signals. The received signals can then be identified by decoding the different parameters used to encode the signals. Decoding at the receiver allows determination of ranging information.

[0030] In other embodiments, the transmitter can be a wideband with a wide field of view, while the receiver includes an optical phased array to allow complex detection of ranging information. In other embodiments, both the transmitter and the receiver can include encoding and manipulation of several of the parameters listed above. As known to those skilled in the art, a phased array includes several radiating elements, each of which is operated with a different phase and / or amplitude. The beam can be formed as a result of changing the relative phase and / or amplitude of the signal emitted from each radiating element; and / or by providing constructive or destructive interference to direct the beam in a desired direction. Additionally, independently changing the amplitude of each emitter can change the beam shape in the far field, for example increasing the directivity of the beam or generating multiple beams in different directions. For example, a beam can include a main lobe and several side lobes at lower intensity. In some embodiments, the beam can be shaped so as to have two or more main lobes of similar intensity. In this case, the main lobes will have the same wavelength, and can be distinguished at the receiver, for example by including at least two receivers, which will receive different signals of the environmental reflections from the two main lobes, with spatial selectivity. Alternatively, in other embodiments, two beams can be shaped simultaneously, each at a different wavelength. In this case, for example, the receiver can distinguish the reflections from each beam due to the different wavelengths of the reflections from each beam. Such methods can also be combined in more complex configurations, if advantageous for a particular application.

[0031] In some embodiments, the optical phased arrays operate at wavelengths between 1500 nm and 1600 nm, although any wavelength can be used. For example, a wavelength of 1550 nm is advantageous because it is safe for the human eye. Since LiDAR systems for autonomous vehicles can operate with human traffic, it can be comparably important to have the LiDAR system operate effectively at a wavelength that is safe for humans. For example, some existing systems operate at a wavelength of 904 nm. A wavelength of 1550 nm allows for about a 40x increase in power compared to 904 nm, while remaining eye-safe, as well as about a 2x increase in ranging distance for the same amount of eye-safe power allowed. Additionally, using a wavelength of 1550 nm allows for leveraging the large amount of technical research and expertise developed in the field of fiber-optic communications. In some embodiments, the LiDAR systems disclosed in the present disclosure are wavelength agnostic in the sense that they do not need to operate at a particular wavelength but can work at multiple wavelengths depending on the materials chosen for fabrication. In other words, the systems described herein can be limited to the supported wavelength range of the material used to fabricate the relevant chip, such as Si or SiN. As known to those skilled in the art, for example, silicon-on-insulator (SOI) supports a particular wavelength range (from ~1200 nm to 3000 nm and above). Thus, if a LiDAR system is fabricated in SOI, it can support working in the wavelength range of that material. However, the LiDAR systems and methods described herein do not rely on a particular wavelength to function. Rather, the operating wavelength is chosen depending on the material used for fabrication. Smaller wavelengths require tighter specifications for the fabrication process because the operation of the optical phased array is optimal when the pitch of the emitters is about half of the operating wavelength.

[0032] Generally, existing LiDAR systems include two different modes of operation. In some systems, a flash LiDAR approach is used, in which the transmitter fills the environment and the receiver is spatially selective. These systems can incur resolution loss due to multiple reflections, possible interference between reflections, and resolution limitations due to the physical size of the receiver. In other systems, the transmitter is spatially selective, and the receiver is broadband with a wide field of view to maximize the received signal. Conventionally, rotating mirrors or liquid crystals have been used to direct the beam and create spatial selectivity.

[0033] In the present disclosure, a phased array system is used to provide spatial selectivity over a very wide field of view that is scalable, and to maximize the throughput of the number of points that the imaging system can measure per second. Wavelength tuning is used to direct the beams in one direction. Under current laser technology, it can be difficult to have wide tunability in a single laser, so multiple lasers can be used to allow different wavelengths to be used. The wavelength parameter can thus be controlled along with other parameters. A switch can be used to switch between lasers with different wavelengths in order to select one or more wavelengths to be transmitted at any one time. For example, the system can turn on one laser and turn off the remaining lasers, allowing the beam from that laser to enter the waveguide towards the phased array scanner. After a specified amount of time, the switch can turn off the beam and start another one. In some embodiments, more than one laser can be on, with the beams pointing in different directions, thus allowing different wavelengths or bands of wavelengths to be emitted simultaneously. A splitter can be used to split the on lasers beams to several encoders, allowing tuning to be done using sub-bands. For example, the wavelengths used can vary by 50-100 nm.

[0034] In some embodiments, different wavelengths are used for different beams that are emitted in different spatial directions. In these embodiments, the radiation direction of the emitters can be tuned by wavelength; this capability can be designed into the system. For example, a change of 20° in spatial direction can correspond to a change of 100 nm in wavelength. In some embodiments, a "scanner" or "optical scanner" can be defined as a device that generates one or more optical beams and is capable of adaptively scanning and / or beamforming.

[0035] In some embodiments, each encoder is connected to a scanner, such as a 2D scanner, that can direct the beam into different directions. In some embodiments, the 2D scanners are fabricated on a monolithic chip. Each 2D scanner can direct the beam in a particular direction in space for a given setting and / or wavelength, and direct the beam by a particular amount by changing its setting and / or wavelength. Thus, each scanner can direct the beam in a particular 0 and direction. As understood by one skilled in the art, 0 and are spherical coordinate angles. For example, 0 can be defined as the angle between the emitted beam and an axis that is perpendicular to the plane of the photonic chip on which the scanner is fabricated, while may be defined as the angle between the emitted beam and an axis that is perpendicular to the axis that is perpendicular to the plane of the photonic chip, e.g., the longitudinal axis of the chip. Different reference frames can be used by simple coordinate transformations. Different LiDAR systems can cover different angles in space. Multiple systems can be used together to cover a larger set of angles. For example, if a system can cover 120° horizontally, three such systems can cover 360°. Two emission angles 0 and The emission space is represented by parameters. In some implementations, a 1D scanner can be used instead of a 2D scanner to guide the beam in one direction (e.g., Furthermore, multiple 1D scanners can be used to orient the beam in another direction (e.g., θ) to cover a specific angular range. Examples of transmitters that can be used in 1D scanners are etched endface Si waveguides, grating couplers, or plasma radiators.

[0036] In some implementations, the θ angle of the transmitted beam can be controlled by engineering the transmitter (e.g., a grating) in the phased array, and the angle can be swept by changing the wavelength input to the phased array. The orientation of the phased array can be used to control the position of the transmitted beam. The scanning arc of LiDAR can be swept at an angle, and this angle can be controlled (e.g., by CMOS electronic circuitry) by controlling the phase or amplitude of the transmitter. Different phased arrays can also be arranged with different orientations relative to each other. Through engineering design and electronic control, the scanning arc of LiDAR is therefore configurable in design and customizable in use.

[0037] Encoding advantageously increases the capacity of a LiDAR system (the number of points processed per second in space) because instead of transmitting a single laser pulse, multiple pulses can be emitted within a short period, each with a different code. This code can be designed to enable the receiver to reconstruct and decode the received laser pulses.

[0038] Different applications of LiDAR systems may have different requirements within the coverage angle. These requirements can be met in different ways. In some implementations, a 1D scanner can be used to generate multiple beams in the horizontal plane. In other implementations, a 2D scanner can be used by changing θ and The use of multiple beams allows for coverage in both the horizontal and vertical directions. In some embodiments, the receiver may use multiple orthogonal receivers to detect multiple beams emitted by multiple scanners. Therefore, in some embodiments, a phased array may be implemented only at the transmitter, only at the receiver, or at both the transmitter and receiver.

[0039] In optical phased arrays, multiple emitters are typically placed close together with uniform or non-uniform spacing. By independently changing the phase and amplitude of each emitter, the generated far-field beam can be steered and its shape can be arbitrarily electronically formed without physically moving any parts. The tuning mechanism of optical phase or amplitude can be performed, for example, by using photoelectric effect (such as carrier injection / depletion within a Si PIN diode), thermo-optic effect, and electrical absorption effect (e.g., Franz-Keldysh effect) within materials such as SiGe or Ge. The electrical signals for tuning can be provided, for example, by complementary metal-oxide-semiconductor (CMOS) circuitry. The optical phased arrays in this disclosure can thus achieve beam steering, beam shaping, and spatial selectivity by electronic control rather than mechanically moving emitters. In a phased array, the inter-antenna spacing is expected to be sub-wavelength to allow a wide steering range, otherwise the same image (grating lobes) is produced in the far field, resulting in reduced power efficiency while limiting the range of steerable beams. The distance between emitters can be controlled during fabrication. Reducing the spacing between emitters can reduce the radiative efficiency of the array, or cause power leakage from one emitter to a neighboring emitter. For example, Si waveguides with sub-micron thickness placed on the same substrate with a center-to-center spacing of less than 1.5-2 pm can cause power leakage between neighboring emitters. Due to these current technology constraints, the steering range can be limited to around 50°. In this disclosure, the steering range can be higher than 50° because thicker Si can be used to fabricate the emitters, and the highly confined optical mode within the waveguide allows shrinking the emitter pitch without causing power leakage to neighboring emitters.

[0040] In some embodiments, the photonic components are all fabricated monolithically in a single chip, while the control circuitry (e.g., CMOS circuitry) is fabricated in a separate chip. The spacing between the chips allows for separate independent optimization of the photonics on custom silicon photonic processes (e.g., Si) and the electronic circuitry in the CMOS chip. Fabricating the two parts monolithically in a single chip is possible, but can cause impairment to performance, which can limit the overall performance of the LiDAR system. For example, the monolithic process does not support thick (micron-level) Si waveguides, while micron-sized waveguides can guide and radiate high optical power (e.g., at the watt level required for about 200 meters of ranging in self-driving car applications). In the future, as CMOS and photonic fabrication technologies become more advanced, the entire system can be fabricated monolithically.

[0041] In some embodiments, different components are fabricated on Si chips with different thicknesses. For example, the thickness can be larger at the laser input and switch side and taper or step down towards the splitter, encoder, and scanner. For example, a thickness of 3 microns or more can be used to vertically confine the optical mode in the waveguide in the early stages of the system (e.g., on the laser input side) to increase the optical power handling of the system. In some embodiments, the number of emitters within the scanner can be in the hundreds or thousands. Thus, the input optical power is one or several orders of magnitude higher than the power per emitter. The thickness of the Si on the scanner side is typically a few microns. The micron-level thickness allows for stronger vertical confinement. In other words, most of the optical power is confined in the middle of the waveguide and the amount of power that leaks into the cladding (typically Si02) is much smaller than in the case of sub-micron Si waveguide thickness. The thickness gradient helps to reduce the emitter pitch without causing performance degradation, while allowing for an increase in the steering range. Another advantage of using micron-level waveguides is the low sensitivity of the optical phase of the emitted beams to: fabrication process tolerances, waveguide sidewall roughness, width tolerances, and thickness variations from one point to another in the waveguide photonic circuit. The size of the photonic circuit is typically in the order of millimeters, so it is advantageous to keep unwanted optical phase variations as low as possible. The refractive index of Si varies in the order of 10 -4 for variations in the fabrication process in sub-micron silicon photonics, which can be two orders of magnitude lower (e.g., 10 -6 ) in micron-level fabrication processes. For a wavelength equal to 1.55 pm, a sub-wavelength level pitch (e.g., below 1 micron (e.g., 0.7 to 0.8 microns)) between emitters allows for a wide steering range (e.g., over 140°), which is significantly larger than the state-of-the-art value of 50°.

[0042] Different LiDAR systems as described herein can have different numbers of scanners or antennas, depending on the application. Different scanning speeds can also be implemented. An example scanning speed can be 10 6 points per second. For example, an autonomous vehicle can require a high scanning speed, while other applications can require a high resolution, but can be able to tolerate a lower scanning speed. The LiDAR system can also be configured to automatically or manually switch to a low power operation state, in which some scanners are turned off or the laser power is controlled. For example, the system can normally operate with multiple (M) scanners, but in specific situations, a portion of the scanners can be turned off or even simply operate with only one scanner. The system can then turn on additional scanners when needed.

[0043] Different applications can have different requirements for a phased array. The beams generated by a phased array often include side lobes and a main lobe. For some applications, such as self-driving cars, a peak-to-peak ratio of the main lobe to the side lobes of 40 dB to 50 dB can be required. This requirement can arise from reflections from bright surfaces, such as traffic signs. In these cases, the reflections can cause saturation of the main lobe signal compared to the side lobe peak power. On the other hand, dark objects have much lower reflectivity compared to bright objects. The variation in reflectivity of objects that are typically present in a driving environment can require that the receiver be able to handle a dynamic range of around 100 dB. This requirement can be met by a combination of efficient beamforming at the receiver and a high dynamic range.

[0044] The optical phased arrays of the present disclosure allow independent control of the phase and amplitude of each emitter inside each scanner, thus allowing beamforming. Independent control of the phase shift and amplitude of the optical field at each element enables the creation of an arbitrary radiation pattern. The wavelength band of the electromagnetic waves used (e.g., 1500 nm to 1600 nm) allows implementation of small size of each unit element and reduces unwanted grating lobes in the far field radiation pattern. As known to those skilled in the art, the phased arrays described in the present disclosure can be implemented using a radiation element comprising a grating coupler, an etched end waveguide, or a mirror-tipped end waveguide. The optical phased arrays, when implemented in a transmitter system, can radiate light with a desired pattern. The optical phased arrays, when implemented as a receiver system, can also receive light incident to the array in a desired direction.

[0045] The 3D imaging systems of the present disclosure can differ in their specifications depending on their applications. For example, for autonomous vehicles, the imaging system can have a range of hundreds of meters, a power consumption of tens of watts, a peak power of the radiation can be tens of watts, the size of the system can be about 10 x 10 cm 2 , the angular resolution can be less than 0.1°, the horizontal or vertical field of view (FOV) can be 100° x 20°. For example, for consumer electronics, the range can be limited to less than 5 meters, the power consumption can be less than 2 W, the peak power of the radiation can be less than 10 mW, the size of the system can have high constraints, for example, less than 1 cm 2 (e.g., a single stage laser can be sufficient), the angular resolution can be less than 0.2°, the horizontal or vertical field of view can be 80° x 80° or more, for example, 100° x 100°. In some embodiments, the FOV of a consumer device is square.

[0046] Figure 1 An exemplary transmitter according to embodiments of the present disclosure is illustrated. A certain number of lasers (110) with tunable wavelengths are driven by an electronic circuit (e.g., a CMOS chip (105)) from 1 to K. The wavelength range of each laser is indicated as λ1-λ2up to λm -λ n The laser is followed by a Kxl optical switch, which can be based on a cascaded MZI interferometer (115) with active phase tuners, also controlled by an electronic circuit (e.g., a CMOS chip) (125), for example. The laser beam then enters a lxm splitter (120), where m is the number of scanners. Each scanner (150) includes a phased array architecture. All optical components (e.g., excluding the electronic circuit) can be fabricated on a single die with or without the laser, while the rest of the circuit can be fabricated separately and then bonded or attached to the optical component die. The light can be guided using waveguides made of Si, for example. In some embodiments, the Si waveguides have a thickness gradient that decreases towards the output direction (i.e., the direction of the scanners). From a fabrication standpoint, the thickness gradient is possible and important because the earlier stages of the system (i.e., before the splitter) can require high optical power, while each emitter within each scanner radiates a fraction of the total input power and thus does not require high optical power handling. On the other hand, using smaller waveguides on the scanner side of the system reduces the effective power consumption required to tune each scanner and also enables the design of emitters with higher radiance efficiency. Thus, in some embodiments, the waveguides have a thickness gradient, with a thicker thickness before the splitter and a lower thickness after the splitter. In other embodiments, alternatively, the thickness of the Si can be increased if the particular application requires. In some embodiments, the thickness reduction can be used to transition between high power and low power elements, as waveguides with reduced thickness can transport lower power. In some embodiments, the Si thickness, while different, is maintained at 1 micron or higher. For example, a phase error of a waveguide that is at least 3 microns thick is 2 orders of magnitude lower than a phase error of a waveguide with a sub-micron thickness. Certain applications can benefit from sub-micron or higher than micron thickness. In some embodiments, by keeping the thickness at one micron or higher, it can be advantageous to simplify the fabrication and integration of a large number of components in a single chip, and lead to high yield and better performance.

[0047] The m encoders (135, 140) can then encode the laser signals to enable spatial selectivity. For example, the signals can be encoded in the time or frequency domain to support time-of-flight or frequency modulated continuous wave imaging architectures. The laser optical path then continues through the encoders into the scanners. In some embodiments, the encoders are implemented as phase shifters, which are controlled by the electronic circuit (e.g., CMOS chip) (125). In some embodiments, the encoders are implemented as amplitude modulators, which are controlled by the electronic circuit (e.g., CMOS chip) (125). In some embodiments, the encoders are implemented as a combination of phase shifters and amplitude modulators, which are controlled by the electronic circuit (e.g., CMOS chip) (125). Figure 1In the example of FIG. 1, the scanners are 2D scanners (150, 155) that can each encode in different spatial directions determined by two parameters. For a given wavelength and settings of amplitude and / or phase of the active components within each scanner, each 2D scanner is fabricated on the same chip to emit in a fixed direction. The output beam generated by each scanner can be directed in different directions by tuning the phase and / or amplitude of the emitters within each scanner and the wavelength. In Figure 1 In the example of FIG. 1, the two parameters controlled by the 2D scanners are the angle Θ and (145). Figure 1 The system of FIG. 1 can also vary other parameters as discussed above, such as the wavelength, the wavelength band for each laser, what lasers are turned on or off at any given time, and different signal patterns encoded for each 2D scanner. By controlling different parameters, the operational capabilities of the LiDAR system are greatly enhanced. In Figure 1 In FIG. 1, the modulated beams (160) of three example scanners are illustrated, but any number of scanners can be incorporated in the array. In some embodiments, the switches, splitters, encoders, and 2D scanners are all fabricated monolithically in one Si chip, while the CMOS circuit (125) is fabricated on a different chip, and the two chips are packaged together. The CMOS circuit (125) also controls the encoders (135, 140), the switches (115), and can also control the 2D scanners (155). The CMOS circuit can also synchronize with the receivers (130) using electronic control signals to enhance signal collection.

[0048] The lasers (110) can include multiple tunable lasers. Some parameters of the LiDAR system include the wavelength of the beam, the time domain, the encoding, and the spatial orientation. Controlling different parameters allows the LiDAR system to minimize interference from other LiDAR systems (unwanted interference). For example, as expected in certain applications such as self-driving cars, the encoding can reduce interference during operation in the case that other LiDAR systems are operating simultaneously in the same environment.

[0049] In some embodiments, a fixed wavelength and one scanner can be used to direct the beam in one direction by controlling In these embodiments, multiple ID scanners fabricated in different chips can be used to direct the beam by controlling Θ; these ID scanners are designed to be oriented at different Θ within the same package.

[0050] In some embodiments, an optical multiplexer (MUX) can be used instead of the Kxl optical switch (115). As understood by one skilled in the art, an optical switch operates as an active component that consumes power, while an optical multiplexer operates as a passive component that does not consume power. On the other hand, the use of an active switch gives the flexibility to select different wavelengths when needed to adaptively control the number of samples per second. For example, an active switch can rapidly switch between the beams of different lasers at different wavelengths, thus illuminating the same point using multiple wavelengths.

[0051] Figure 2 An example encoding scheme for some of the encoders of Figure 1 is illustrated. For example, three different encoding schemes for three different scanners (205, 210, 215) are illustrated. The light intensity is plotted on the y-axis versus time on the x-axis. In some embodiments, a digital code with high and low states can be used. The code can be pseudo-random to create orthogonality between the codes and minimize interference at the receiver. Each scanner can operate using a code with a different pulse scheme. For example, the number, sequence, and duration of the pulses can be modulated. In the example of Figure 2 , each pulse has a small rise and fall, with a shape similar to a square wave. In some embodiments, the code used is digital, where each binary digit is a square wave pulse of equal duration, for example, each 1 is a square pulse of equal duration and amplitude. In example (205), the 4-bit code word [1 0 0 1] is implemented by a time-domain waveform and includes four pulses with high, low, low, and high values, each with a duration T b . In example (210), the 4-bit code word is [1 1 0 1] and in example (215) it is [0 1 0 0]. The code words can repeat with a period of T. One skilled in the art will appreciate that different digital encoding schemes can be applied. Once the encoded signal is transmitted, the distance to the object can be determined by measuring the time it takes for a pulse to be detected at the receiver (the time between transmission at the transmitter and reception at the receiver after reflection from the environment).

[0052] Figure 3 An example 2D scanner is illustrated. In some embodiments, the system of Figure 1 may include multiple scanners (150). In some embodiments, each scanner (150) can include the components of Figure 3 . In some embodiments, the spacing between the emitters is uniform, however, in other embodiments, non-uniform spacing can make the far-field beam appear more focused. In these embodiments, non-uniform spacing between the emitters narrows the beam width and increases the beam directivity.

[0053] The angular range covered in the disclosed architecture is reconfigurable and can typically cover more than 120° horizontally and more than 80° vertically by design. For applications requiring very wide angular range, such as 360° horizontal range in self-driving cars, multiple LiDAR systems can be used.

[0054] Figure 3 An exemplary scanner is illustrated. Multiple scanners can be used in a single system. Thus, each scanner can include a power splitter to split the optical mode across multiple emitters. The split ratio at the power splitter can be non-uniform to save power consumption and perform passive beamforming. In Figure 3 In some embodiments, the waveguide (305) has a thickness that allows for high optical power handling. For example, the size of the cross-section can be designed accordingly and / or a PIN junction can be used to sweep free carriers released due to high optical power to keep the propagation loss as low as possible, thus increasing the optical power handling. As known to those skilled in the art, a PIN junction includes an intrinsic layer or an undoped layer sandwiched between a p-doped region and an n-doped region. In some embodiments, tens of W can be passed through the waveguide. For example, ranging at distances greater than 200 m can require 60-80 W, which can be acceptable for a car, and other vehicles such as helicopters or drones can require longer ranges. In some embodiments, a thickness of 3 microns or higher can be used, such as 10-20 microns. For example, a 3 micron Si thickness of the waveguide can be sufficient for a peak power of 30-50 W of radiation, while km ranging can require a higher thickness.

[0055] The splitter (310) distributes the laser optical power to different channels, through an amplitude modulator (315), a phase modulator (320) in succession, and to an emitter (325). The amplitude modulator and the phase modulator can include a PIN junction, a ring resonator, a thermo-optic device, a Franz-Keldysh based electro-absorption modulator, or a quantum confined Stark effect (QCSE), among others. The emitter fabrication parameters can include a separate length L e , width W eThe spacing between the emitters and the receiver. The spacing can be uniform or vary between emitters. In some embodiments, for calibration purposes, a calibration photodiode can be connected across each emitter. In some embodiments, each emitter has residual power at its end as designed, which can be fed to an on-chip or off-chip photodetector. The photodetector can be made of, for example, Ge and integrated in the same fabrication process, or a heterogenously integrated III-V semiconductor. In some embodiments, 1-5% of the input power to the emitters is left at the end of the emitters to be detected by a photodiode to calibrate the amplitude response of each emitter and the losses in the transmission from the laser to each emitter. Thus, in some embodiments, the system can continuously monitor and calibrate the amplitude response of each emitter.

[0056] In some embodiments, the signals output by the LiDAR system can have side lobes, which can create a blur in the 3D imaging in the case where one of the objects in the system’s environment has a reflected signal with an amplitude that drops within the same range as one of the side lobes. One way to address this issue is to increase the peak-to-peak ratio of the main lobe peak and the side lobe peak by doing beamforming. Beamforming can be performed using the amplitude controller of the phased array, such as the AM module (520) in Figure 5 For example, by implementing a Gaussian amplitude distribution, it is possible to achieve a 20-25 dB increase in the peak-to-peak ratio of the main lobe peak and the side lobe peak compared to a uniform amplitude distribution. Under a Gaussian distribution, some emitters will receive a lower amplitude than other emitters, with the amplitude variation determined by the Gauss function. For example, the central emitters will receive a higher amplitude than the non-central emitters. By controlling the amplitude distribution of the light transmitted through each emitter (e.g., uniform, Gaussian, etc.), it is possible to control the spot size of the light emitted by the LiDAR system.

[0057] The amplitude modulators and phase modulators, and the emitters, can be collectively referred to as a phased array. The Si thickness can gradually decrease from the splitter to the emitters in a vertical taper. For example, if the Si thickness is 3 microns at the splitter side, the emitters can have a Si thickness of about 1 micron, with the spacing d also being about 1 micron. Since the laser power is split between the emitters, the waveguides through the emitters can have a reduced thickness, as high power handling is not needed in the termination elements. In some embodiments, the spacing between the emitters and / or the width of each emitter is selected to have a sub-wavelength value. Since multiple beams can confuse the reception at the receiver, the phased array can apply beamforming, as known to those skilled in the art. In some embodiments, 100 emitters or more can be fabricated for each phased array to produce a fine angular resolution up to the 0.1° level.

[0058] In some applications, a 10% reflectivity of an object in the environment at a distance of 200m is considered acceptable, and a LiDAR system can be configured to allow the detection of reflected signals with a 10% reflectivity at 200m.

[0059] Figure 4 Some techniques for increasing power processing in LiDAR systems are illustrated. Cross-sections in the yz plane (405) and yx plane (410) are shown. An optical mode (415) in the PIN diode (410) is also illustrated. Power processing can be increased by increasing the silicon waveguide thickness and / or using a PIN diode across the waveguide to sweep free carriers. In some implementations, Figure 4 h a (430) The size is in the range of 2μm to 10μm, while h b (435) can range from 0.5 μm to 2 μm. Figure 4 In the diagram, section (420) represents the input waveguide after the splitter, where the power level is at least an order of magnitude smaller than the input power, while section (425) represents even lower-power photonic circuitry, such as a transmitter and associated amplitude and phase controllers. In some embodiments, the diode may include n++ regions (440) and p++ regions (445), where there is no doping requirement for the central region or sidewalls of the waveguide (450), which can be retained intrinsically. This embodiment may have better power efficiency because the n and p regions do not need to extend onto the central region (450). Figure 3 The modulator (320) directs the beam in the desired direction. In some implementations, Figure 1 Use a modulator instead Figure 1 The encoder changes the operation to a continuous wave mode instead of a pulsed mode. In some implementations, the amplitude can remain constant and the frequency modulated only over time. For example, linear frequency modulation can be performed, and the lasers are turned on one at a time. In some implementations, a single modulator can be used, and this single modulator is shared by all lasers. In other implementations, the number of modulators used instead of the encoder can be equal to the number of scanners or optical phased arrays. If multiple modulators are used, each modulator can modulate a different beam in a different way, which can be advantageous. However, the trade-off is the need for a higher number of components, thus increasing power consumption.

[0060] Figure 5 An exemplary cluster architecture for the scanner is illustrated. Figure 5 In this context, each subarray (505, 510, 515) is composed of (for example) Figure 3The scanner described in the middle constitutes. The amplitude (520) and phase (525) modulators can adjust and control the relative mismatch between the sub-arrays. Different spacings d can separate different sub-arrays. The number and spacing of the emitters can be different between sub-arrays to optimize the beam width and shape of the far field pattern.

[0061] The emitters of the scanner described above can be fabricated in different ways. For example, grating couplers can be used. As known to those skilled in the art, grating couplers typically include a grating located above or below a waveguide. Depending on the resonance between the waveguide and the grating, a particular optical mode can be coupled between the two structures. In other embodiments, other types of emitters can be used, such as etched facet Si waveguides, metal mirrors, etc. In some embodiments, the emitters used in this disclosure have a wavelength dependent dispersion, resulting in directing the beam in one direction, widening the far field beam width in a first direction, and narrowing the beam width in a second direction perpendicular to the first direction.

[0062] Figure 6 A side view of an exemplary grating geometry of an emitter is illustrated. The light of the laser is in the plane of the figure (from left to right) (625). Several geometric and material parameters can be specified, such as hi for the material thickness (630), h2 for the thickness that shapes the grating (655) beam, and h3 for the material thickness at the final end of the emitter (650). In Figure 6 In the middle, the refractive indices of different parts of the structure are indicated as n1 (620), n2 (610), and n3 (605). In some embodiments, (610) and (605) are made of Si or SiN, while the cladding (620) and the cavity (615) are made of Si02. The cavity (615) can minimize back reflection and improve the upward radiation efficiency. The height and length of the cavity (615) are indicated as e (635) and (640). Other geometric parameters include the spacing between the teeth (the beams that make up the grating), gi (665), the period of the grating Λ1 (660), and the grating L e1 total length (645).

[0063] As designed, the grating geometry can be tuned for each 2D scanner so that for a given wavelength, the scanner radiates at different radiation angles Θ. The emitter geometry and design can be tuned to optimize the upward radiation efficiency at different Θ. In Figure 6 In the middle, exemplary directions of the radiated light are shown (680).

[0064] Figure 7 A top view of an emitter is illustrated. For example, Figure 7 represents Figure 6 a top view of a portion of (700). The light of the laser (705) enters as Figure 6structure in FIG. 7B. Figure 6 Parameters (715, 710, 720) are defined in FIG. 7C. Figure 7 The width W of the grating is shown in FIG. 7D. e (725). The grating width can be designed to be typically a sub-wavelength size to shrink the antenna pitch size in the optical phased array. For example, the width of the grating can be sub-micron, e.g., a 0.5 pm width will generate a far field beam width of about 150°. In Figure 7 In FIG. 7E, the exemplary radiation direction is out of the paper.

[0065] Figure 8 An exemplary beam emitted by the grating is illustrated. In Figure 8 In FIG. 7F, the light from the laser is directed into the grating in direction (805). As in previous figures, only a portion of the grating (810) is shown, as the grating can include a significantly larger number of beams than shown in the figures of this application, as understood by one skilled in the art. In some embodiments, different emitters can have different radiation angles by design. An exemplary far field radiation beam (815) is shown emitted at angle θι (825). The beam size can be described as angle a (820), and the beam can be designed to be narrow, depending on the particular emitter design. In some embodiments, for an emitter with length L e1 (720) of a few hundred microns, a is typically less than 0.1°, as this can be required for some applications such as self-driving cars. This beam size has a weak wavelength dependence. For example, the beam width can vary by about 6% for a 100 nm wavelength change relative to 1500 nm to 1600 nm. The beam width of the far field beam of the phased array in the angular direction along the emitter array is approximately inversely proportional to the number of antennas, as known to one skilled in the art. In some embodiments, hundreds of antennas can be required to achieve a resolution of 0.1°, e.g., at least 100 antennas can be required. Similar to a, there is also a weak wavelength dependence on the beam width size along the phased array. For a 100 nm wavelength change relative to 1500 nm to 1600 nm, the beam width can vary by about 6%.

[0066] The tolerance in the absolute beam angle direction in θ varies with the error in the wavelength as well as the process tolerance on the emitter fabrication. For typical device parameters, the tolerance is about 0.1% of the beam size (hence negligible). In In the direction (phased array), it varies with phase as well as amplitude settings and process tolerances. Analysis shows it to be about 1% of the beam size. A look-up table of phase and amplitude settings can be used to calibrate this tolerance. The characteristics of the beam distribution at different points within the field of view can be calibrated and set based on the application to account for unwanted variations due to process variations, wavelength drift, etc. to meet the required performance parameters of the LiDAR system, such as angular resolution. In other words, continuous calibration allows detection and adjustment of unwanted variations in the emission.

[0067] Figure 9 An exemplary layout of a 2D scanner to increase the field of view of a LiDAR system is illustrated. In this example, four lasers are coupled into four Si waveguides (905, 910, 915, 920) and operate at four different wavelength bands. The waveguides connect the lasers to two 2x1 switches. Each 2x1 switch includes a 2x2 power splitter (925), such as a multimode interferometer, followed by two balanced waveguides, one or both of which have an electro-optic phase modulator, such as a PIN diode or a thermo-optic device, to switch into one of the inputs to the output waveguide. In some embodiments, depending on the voltage across each phase modulator, only one input is simultaneously connected to the output. The 2x1 switch can thus include a 2x2 splitter, a phase modulator, and a 2x1 splitter. In some embodiments, different voltage settings can be used to transmit a portion of both inputs to the output depending on the relative phase difference between the arms of the switch. Several waveguides (935) are illustrated, as understood by one skilled in the art. In some embodiments, the thickness of the Si is tapered down structurally, decreasing from the lasers and switches towards the emitters. In some embodiments, the thickness is kept no lower than one micron to keep the phase errors between the waveguides under control and to enable increasing the number of components in the chiplet, improving performance parameters such as the angular resolution of the LiDAR system.

[0068] In Figure 9 Several switches and splitters are illustrated in FIG. 1, as understood by one skilled in the art. For example, a 1x3 splitter (940) distributes optical power across three waveguides, typically uniformly designed, each with its own encoder (945). The encoders and switches connections (950) are, for example, to CMOS control circuitry on a different chip packaged together with the photonic chip. In some embodiments, electro-optic amplitude modulators can be used as encoders (945), for example, PIN diodes. The waveguides then connect each encoder to its own optical phased array, for example, (950). Each optical phased array can include a 1xN splitter (955), where N is, for example, determined according to the desired beam width and can equal 100-200.

[0069] In some embodiments, tapering is performed only downstream (to the right) of the segment (960) for each optical path in the phased array. In other words, in some embodiments, the thickness of the Si material is the same in the system, or the thickness can taper down from the laser to the emitter, or the thickness can taper down in the terminal portion of the phased array, which includes the segment (960) and the segments downstream of the vertical tape segment (960). The emitters (965) can be customized to emit at a specific radiation angle Θ and Figure 9 at a given wavelength and phased array setting specified for each emitter in the phased array. For example, each emitter in a phased array can emit at the same Θ, where different phased arrays emit at different Θ, or emitters in the same phased array can also emit at different Θ. For example, one phased array can emit at Θ1at a fixed wavelength, while another phased array in the system can emit at Θ2at the fixed wavelength, and a third phased array can emit at Θ3at the fixed wavelength. Additionally, each phased array can be placed on the chip layout at different orientations to change the radiation angle Θ For example, each of the phased arrays in Figure 9 may radiate at different angles, or some arrays can emit at the same but different Θ angles. For example, the angle is greater than zero. Thus, it is possible to vary the radiation angle Θ and of each scanner as a function of wavelength to increase the angular coverage, i.e., the field of view, of the LiDAR system.

[0070] In the example of Figure 9 four lasers and three optical phased arrays are used. However, a different number of lasers or phased arrays can be used. The encoders, which in some embodiments are fast amplitude modulators, can be used with a time response on the order of nanoseconds.

[0071] Figure 10 An example layout of different emitter types is illustrated similarly but from a different perspective than Figure 9 In Figure 10 several elements of the photonic circuit are not shown but can be present in (1005). Three example beams (1010, 1015, 1020) are illustrated. Each beam is radiated from a 2D scanner at a specific wavelength as described above with reference to Figure 9 and at Θ and .

[0072] Figure 11An exemplary receiver architecture is illustrated. For example, signal processing can include a digital signal processing unit (1105), which can be synchronized with the circuitry at the transmitter; an n-bit analog-to-digital converter (ADC, 1110); a plurality of decoders (1120); a clock (1130); and an analog receiver (1125). Light reflected from the environment after being emitted by the transmitter is received, for example, by an optical receiver with a wide field of view, as illustrated in (1145), to maximize the captured power (1140). The receiver can include a single photodiode, such as an avalanche photodiode (APD), with a large aperture; or a detector array to increase the received signal-to-noise ratio (SNR); or a phased array. In some embodiments, a tunable optical filter (1135) can be used to suppress noise and increase the received SNR. The processed range and reflectivity data (1115) is sent to the processing unit (1105).

[0073] Figure 12 An exemplary receiver architecture is illustrated, with an avalanche photodiode (APD) array in the front end to increase gain. In this embodiment, the gain of each photodiode can be adjusted by controlling the bias voltage to maximize the received SNR. Received light is illustrated (1220). The receiver includes an array of avalanche photodiodes (1215) and an analog receiver (1205), which includes, for example, a transimpedance amplifier (TIA) with adjustable gain. A transimpedance amplifier is a current-to-voltage converter, typically implemented with an operational amplifier. Similar blocks (1130) as described in FIG. 11 can be used to process the received electrical signal. Figure 11

[0074] Figure 13 An exemplary receiver signaling flow diagram is illustrated, which includes a plurality of steps, for example: filtering the received light by wavelength to improve SNR (1305); converting to an electrical signal using a photodetector (1310); decoding the signal to determine which scanner the signal originated from (1315); measuring the delay and reflectivity of the signal (1320); digitizing the measured data (1325); and processing the digital signal (1330).

[0075] Figure 14 A way to increase the field of view by generating multiple beams at the transmitter and using a multi-receiver architecture is illustrated. For example, a phased array transmitter (1405) with an architecture similar to that of FIG. 14 can emit multiple beams, for example, two beams (1420) and (1425), simultaneously in different directions. Two receivers (1410, 1415) are illustrated. The multiple receivers can be positioned orthogonally with respect to each other to produce spatial selectivity to the reception path, increasing the effective field of view. For example, as illustrated in FIG. 14, the first receiver (1410) can receive the first beam (1420) and the second receiver (1415) can receive the second beam (1425). Figure 1 Figures 11-12 ​​The receiver architecture is implemented in some embodiments. In some embodiments, each beam (1420, 1425) has a different wavelength. If the same wavelength is used, the beams can be oriented in different directions. Alternatively, a single receiver can also be used, for example with a bandpass filter. In some embodiments, each beam from the same scanner can have a different code instead of sharing the same code. In some embodiments, the receiver can include a number of devices similar to the scanners (150, 155) in Figure 1 In these embodiments, the scanners can also receive power due to reciprocity. By using multiple beams and multiple receivers, the field of view of the LiDAR system can be increased, thus also increasing the number of scan points per second. For example, due to the use of two simultaneous beams, the number of scan points per second is doubled in the example of Figure 14

[0076] In some embodiments, the operating wavelength of the LiDAR scanners described herein is between 1 and 10 microns. The optical three-dimensional imaging systems disclosed herein can provide very fast scanning (number of sample points per second) by mixing wavelength, time and frequency encoding and spatial selectivity, for example, more than 10 6 points per second. Using CMOS-compatible silicon processing can provide much cheaper manufacturing compared to existing systems. The presently disclosed LiDAR system can handle large optical power, enabling ranging at long distances (hundreds of meters or a kilometer). Other advantages of the LiDAR systems described herein are: fast tuning of the optical beam scanner using carrier injection modulators; on-chip calibration scheme for the beam scanner using photodetectors; high sampling rate for imaging; combination of wavelength, time and frequency encoding to increase throughput; all-semiconductor-based optical imaging system (cheap and highly manufacturable solution); increasing the field of view by sending multiple beams from the transmitter and using multiple receivers to spatially scan orthogonal areas; the transmitter design of the 2D scanner can be different to optimize the radiative efficiency.

[0077] Figure 15 An exemplary packaging of a LiDAR system is illustrated. For example, the system includes: receiver electronics, for example, an integrated CMOS chip (1505); a lens (1535) to maximize the power received by the receiver; a carrier board, for example, a printed circuit board (1525), to supply the electronic chip, decoupling capacitors, and provide a synchronized clock and circuitry; electrical connections from the CMOS chip to the photonic chip, for example, wire-bonding or bonding to the photonic chip through the use of through-silicon vias (TSVs) connections (1515); a lens (1520) to adjust the transmitter beam width; transmitter electronics, for example, an integrated CMOS chip (1510); a photonic transmitter (1530) and a photonic receiver (1540).​

[0078] Figure 16 Other embodiments of LiDAR configurations are illustrated. For example, the transmitter (1605) can flash in an omnidirectional manner in a single- or multi-wavelength configuration, rather than using spatially directed beams. The transmitted light (1615) is reflected by an object (1620) and received (1620) by a receiver (1610) based on an optical phased array with spatial reflectivity. In other words, the receiver determines which light comes from which direction. In this embodiment, spatial selectivity can be produced at the receiver using an optical phased array when the transmitter transmits light in all directions at least within the field of view of the receiver. In other embodiments, both the receiver and the transmitter can have spatial selectivity using the optical phased array architecture illustrated in Figure 1

[0079] In some embodiments, the transmitter can include multiple scanners, each manufactured with a different geometric orientation. In this way, each scanner covers a certain range of angles at a particular wavelength or range of wavelengths. By changing the laser wavelength, it is also possible to change the angle covered by the scanner, thus allowing tuning of the spatial direction and overall coverage of the LiDAR system. In some embodiments, the emitters in each 2D scanner will be encoded in the same way as compared to the adjacent 2D scanner, but will have different codes.

[0080] Figure 17 An example is illustrated regarding how the field of view can be increased by generating multiple beams and using multiple receivers. In some embodiments, multiple beams can be emitted by using two different wavelengths in the same scanner (e.g., by two lasers operating at different wavelengths). In other embodiments, multiple beams can be emitted by using two scanners, each emitting at a different wavelength (e.g., by two lasers operating at different wavelengths). In other embodiments, two simultaneous beams can be emitted in two different directions using a single wavelength by controlling the phased array and shaping its beam to have two main lobes instead of a single main lobe.

[0081] In Figure 17 ​In the example of FIG. 17, a transmitter (1720) emits two beams (1760, 1765) at two different angles. The emitted beams are reflected by two objects (1735, 1740) located at different distances (1750, 1755) from the transmitter. Each of the two beams has a scan range (1745, 1750), which can be scanned over by controlling the amplitude and phase of the emitters in the optical phased array in the transmitter. The light (1730) reflected by object (1735) and the light (1725) reflected by object (1740) are received by two receivers (1715, 1710) oriented in different directions. For example, the angle between the longitudinal axes of the receivers can be referred to as β (1705). The orientation angle (1705) of the receiver chips is optimized to maximize the SNR received at each receiver from the designated scan region.

[0082] In some embodiments, one or more optical multiplexers that can be implemented with an arrayed waveguide grating can be used in place of the switch (115) of FIG. 1. Figure 1 Figure 18 An example arrayed waveguide grating (AWG) that can be used to multiplex multiple wavelengths is illustrated. An arrayed waveguide grating is based on wavelength-dependent constructive interference of delayed optical signals. The effect will create constructive interference of different wavelengths at specific locations, thus multiplexing (demultiplexing) different wavelengths at different locations. Different wavelengths (1815) from multiple lasers are input to the AWG and enter a free-space propagation region (1813), followed by a grating waveguide (1810). In some embodiments, the grating is composed of a large number of waveguides with constant length increments (ΔL). Light of each wavelength that is coupled to the grating waveguide (1810) experiences a wavelength-dependent change in phase due to the constant length increments in the grating waveguide. Light diffracted from each waveguide of the grating (1810) into a second free-space propagation (1807) constructively interferes (1817) and is refocused at an output waveguide (1805). The AWG can act as a MUX with negligible crosstalk between channels. Thus, the K x 1 switch (115) of FIG. 1 can be replaced with an AWG, where K wavelengths (λ1, λ Figure 1 k ) are input to the AWG and output as a single wavelength. The K x 1 switch is no longer actively controlled to select which laser is coupled through the rest of the LiDAR system, so the light from a single laser can be passively transmitted to the rest of the LiDAR system using the MUX. The lasers can be, for example, current-controlled to select which laser is transmitting its wavelength through the MUX. Figure 18 The AWG of FIG. 1 can also be used as a demultiplexer if used in the opposite orientation.

[0083] ​​In some embodiments, a power of about 1% to 2% can be used after the MUX to insert a wavelength locker to stabilize the laser and precisely control the wavelength of the laser. Otherwise, the wavelength of the laser can not be precise. In some embodiments, the wavelength locker can relax the calibration requirements.

[0084] In some embodiments, referring to the encoder (135) of Figure 1 , it is possible to add phase and amplitude modulation (PM and AM) to enable continuous wave (CW) operation. Pulsed operation requires higher peak power, so in some embodiments, CW operation can be advantageous. In some embodiments, the frequency of the signal transmitted by the LiDAR system onto the surrounding objects can be shifted over time, e.g., after a triangular wave modulation, as illustrated in Figure 19 . Figure 19 The frequency of the signal in the y-axis as a function of time in the x-axis is illustrated. The signal emitted by the LiDAR system is illustrated as (1905), while the reflected signal is illustrated as (1910). The light reflected from the object is shifted by an amount τ (1915). In some embodiments, the light at the first emitted frequency and the light at the second reflected frequency can be mixed to obtain a beat (the difference between the two frequencies). For example, two sinusoidal signals can be used to obtain a beat. The difference between the two frequencies (1905, 1910) will be proportional to τ.

[0085] In some embodiments, the LiDAR system can perform adaptive tracking. For example, the system can lock onto and track a visible object. For example, the object can have a specific reflection that can enable it to be easily identified. The system can also lock onto a moving object, e.g., follow a child moving within a visible frame or track the rise and fall of a breathing chest to track the health of a human.

[0086] In some embodiments, the light emitted by the system can also have a penetration depth of a few mm or less than a mm. This will enable health monitoring, e.g., capturing heartbeats as well as breathing.

[0087] In some embodiments, the wavelength range of each laser can be, e.g., 1500 nm to 1520 nm, 1520 nm to 1540 nm, etc., in increments of 20 nm up to 1580 nm to 1600 nm. In some embodiments, the scanner can be 2D or ID. In some embodiments, the ID scanner controls the angle Θ at which light is emitted at a specific wavelength by the optical phased array of the scanner by controlling the phase of the light emitted by the emitters of the phased array. In other embodiments, the 2D optical phased array can control Θ and φ at a specific wavelength. Both angles of emission. The wavelength can be controlled by switching the light from one of the lasers of the system. If a ID scanner is used, it is possible to have sub-micron spacing between emitters. In this implementation, the wavelength can be used to sweep. In some implementations, if a 2D scanner is used, the two angles can be changed by controlling the phased array (by changing the phase and amplitude) instead of changing the wavelength. In some implementations, theta can be defined as Figure 10 the angle theta in Figures 9-10 along a plane perpendicular to the horizontal plane of the device (e.g. can be defined in a plane perpendicular to theta and includes the longitudinal axis of the scanner (such as the rightward direction in Figure 8 ).

[0088] In some implementations, the angular width of the main lobe of the emitted beam can be defined as the width value at which the intensity drops 3dB from the peak of the far field pattern. The present disclosure describes a system with a reconfigurable field of view. The field of view can be customized according to the specific application. The scanning can be performed by selecting the wavelength, since the emitters of the phased array will emit at different angles according to the input wavelength. The scanning resolution and rate can be increased in specific regions of the field of view, increasing the flexibility of the system, since more resources can be applied to scan specific regions. In some implementations, multiple input wavelengths can be applied simultaneously as input to one or more phased arrays in the system. In some implementations, different lasers operating in different wavelength ranges are present in the system, and a switch allows controlling the emission angle theta by changing the input wavelength (selecting the laser). In some implementations, can be controlled by the electronic input of the optical phased array. In some implementations, a calibration diode is included to allow on-chip calibration by detecting a portion (e.g., 1-5%) of the emitted light. This portion of light is captured by the diode. As known to those skilled in the art, calibrating current LiDAR ranging systems is a difficult task. On-chip calibration integrated in the system can be advantageous. In some implementations, the photonic chip can be fabricated with Si or other materials such as III-V semiconductors. In some implementations, the control circuitry for digital processing can be based on CMOS or other processes such as BiCMOS (a combination of bipolar and CMOS technologies) or field-programmable gate arrays (FPGA) or others.

[0089] In some implementations, a grating coupler can be used as an emitter. The system can also compute the distance and reflectivity, velocity, and Doppler shift of objects in the environment. In some implementations, it is possible to control the number of emitters that are transmitting to change the pitch. For example, half of the emitters can be turned off to change the pitch, since the pitch is determined by the distance between the active emitters. Thus, the LiDAR system described herein is reconfigurable.

[0090] In some implementations, it is possible to change the thickness of the optical transmission material. For example, if Si is used, its thickness in the waveguides and other optical components can be changed. As the optical signal moves towards the emitters, the power at the laser side is gradually split between multiple channels. For example, the light of one laser is eventually split between a large number of emitters. Thus, the thickness required to safely carry that power at the laser side is larger and can be gradually reduced towards the emitter side. For example, Si can have a thickness of 3 microns at the laser side and gradually reduce to 1 micron at the emitter side, as the light is split between a larger number of components. Similar features can be implemented at the receiver side.

[0091] In some implementations, the transmitters enable spatial selectivity, as the optical phased arrays can spatially direct the average beam. The receivers can also have spatial selectivity to determine from which location the beam is reflected, for example, to enable line-of-sight applications. In some implementations, a large number of transmitters can be used, while the receivers have spatial selectivity. In some implementations, both the receivers and the transmitters can have spatial selectivity. The LiDAR systems described herein can operate at different wavelengths, including the visible range.

[0092] In some implementations, the transmitters can emit optical radiation. A portion of the optical radiation can be transmitted through a nonlinear material as two different wavelengths, creating beats of the two wavelengths and obtaining frequencies in the terahertz range (e.g., several terahertz). The values of the two different wavelengths are close to each other in order to generate the beats. In some implementations, the frequencies can be in the sub-terahertz range). As known to those skilled in the art, a beat is an interference pattern between two waves of slightly different frequencies, which is perceived as a periodic change in intensity, at a rate equal to the difference of the two frequencies. For example, if two sinusoidal waves are at 193 terahertz and 194 terahertz, a sinusoidal wave at a frequency equal to the difference of the two original waves (e.g., 1 terahertz in this example) can be obtained. For example, wavelengths of 1550 nm and 1558 nm can be used, which have a difference of 8 nm, which enables a beat of 1 terahertz. As another example, a difference of 0.8 nm would give a frequency of 100 GHz. Thus, in some implementations, in order to generate beams in the terahertz range, the difference between the wavelengths is 8 nm or more.

[0093] In some implementations, the system can include components to generate terahertz beams and the LiDAR systems described above in this disclosure to emit optical beams. Thus, the systems of this disclosure can emit both terahertz beams and optical beams.

[0094] After the optical and terahertz beams are transmitted and / or reflected by an object, optical and terahertz radiation can be collected at optical and terahertz receivers. The signals can then be processed using adaptive post-processing. In some embodiments, the optical system is a LiDAR system described in this disclosure. The LiDAR system is enhanced by also including components for terahertz beam operation. The optical and terahertz radiation are used together for spectroscopy applications. For example, the optical LiDAR can perform 3D imaging enhanced by terahertz spectroscopy.

[0095] Multiple tunable lasers can be used, each operating in a different sub-band wavelength range. Subsequent stages of the system can include multiple wavelength lockers. The wavelength lockers enable cancellation of phase noise in the laser output, and can be implemented in different ways. For example, a feedforward or feedback approach can be used. The lasers and wavelength lockers can be controlled by associated circuitry, such as CMOS circuitry on the same chip or different chips.

[0096] In a stage after the wavelength lockers, encoders can implement encoding of the amplitude and / or phase of the optical signal. In some embodiments, each wavelength locker transmits a signal at a different wavelength. The wavelengths entering the encoders will be clean due to the removal of phase noise. Each wavelength can therefore be encoded by multiple encoders. For example, a digital code can be used, in which each wavelength has an associated square wave pulse. In some embodiments, the wavelength locker outputs an optical signal centered at a respective wavelength, with a narrow wavelength band centered at the respective wavelength. In some embodiments, the encoders as a whole can provide a series of consecutive square waves, each centered at a respective wavelength. In some embodiments, the encoders can be replaced by amplitude and phase modulators as described in this disclosure.

[0097] In a stage after the encoders, a broadband combiner can enable combining of different wavelengths into a single optical signal. This optical signal includes multiple clean wavelengths, which can be emitted as a beam onto an object. For example, the beam can include multiple wavelengths emitted simultaneously, or multiple wavelengths emitted consecutively in time, each wavelength or narrower range of wavelengths being emitted consecutively in time. The multiple wavelengths can be directed as a beam toward a particular point of a sample, with the beam being scanned across the surface of the sample. Alternatively, the beam can be wide enough to cover the entire surface of the sample, in which case scanning is not necessary. In some embodiments, only a portion of the sample of interest can be illuminated.

[0098] At the receiver, the light transmitted or reflected by the sample is collected, the wavelengths can be separated, and each wavelength can be sent to a sub-band detector. In a subsequent stage, the different sub-band detectors can input their signals to a decoder and spectral data processing module, followed by a digital signal processing module, for example, to implement adaptive learning.

[0099] In embodiments in which the beam is scanned across the surface of the sample, the scanner can be implemented in different ways. In some embodiments, the scanner is implemented using an optical phased array. The optical phased array can, for example, direct the beam in a desired direction electronically. In some embodiments, the optical phased array can simultaneously emit two or more beams by modifying the number and intensity of the lobes emitted. For example, two beams can illuminate different regions of the sample, or even different samples. In some embodiments, the emitters of the optical phased array are configured to emit beams in the same spatial direction (i.e., the same emission angle) for different wavelengths.

[0100] The receiver is then configured to interpret the reflectivity data by wavelength, and is able to distinguish between signals originating from different objects. For example, if two beams are emitted, each at a different object, the receiver can distinguish between the signals reflected from each object due to the use of different encoded beams.

[0101] In some embodiments, 3D imaging of the sample is performed by an optical phased array system, and in addition, multiple wavelengths are illuminated at each point of the sample. The different wavelengths can be transmitted simultaneously on the same point of the sample or consecutively in time (e.g., with very short time intervals). In addition to measuring the reflected radiation as described hereinabove, the reflectivity of the sample can be measured by the optical wavelength and terahertz frequency, and the angle of reflection or reception. For example, the reflectivity can be measured by θ and φ as discussed herein with reference to the optical phased array.

[0102] By using a terahertz radiation with a LiDAR system, an optoelectronic-terahertz spectroscopy analysis system can be manufactured. The terahertz beam can be an additional beam used to illuminate the sample. The terahertz beam can be generated by creating beats as described hereinabove. The wavelengths used to create the beats can vary over time due to normal fluctuations in the lasers or other components of the system. These variations can adversely affect the beats, as one wavelength can drift away from the other, increasing or decreasing their difference. Thus, the beats can vary and exit the terahertz range. Therefore, a wavelength locker can be used to track and lock the two wavelengths used to generate the terahertz beats.

[0103] Figure 20 ​An exemplary photo-electronic-terahertz spectral analysis system is illustrated in which the transmitted combined wavelength is emitted through a nonlinear material as optical radiation and terahertz radiation generated by wavelength beating to beat the two wavelengths and generate a terahertz beam. Figure 20 A transmitter (2005) is illustrated that emits optical beams (2010) and terahertz beams (2015) generated through a nonlinear material (2020). Both beams illuminate an object (2025). Radiation reflected by the object is collected at optical receivers (2035) and terahertz receivers (2030) for adaptive post-processing (2040).

[0104] Figure 21 An exemplary spectral analysis system is illustrated that operates at multiple wavelengths, each individually locked and encoded. Multiple tunable lasers (2105) generate multiple wavelengths that are input to a wavelength locker (2110) and subsequently to an encoder (2115), a wideband combiner (2120), and a transmitter (2125). The above components are part of a transmitter (2130). Light (2141) reflected (2142) from an object (2140) is received at a receiver (2135) that separates the wavelengths (2145) for different sub-band detectors (2150) followed by decoding and other digital signal processing (2160).

[0105] In some embodiments including LiDAR-based spectral analysis systems and terahertz spectral analysis systems, the spectral beams are scannable, giving depth (spatial) information as a function of wavelength / frequency in addition to reflectivity (reflectance intensity). Other embodiments can include transmitted intensity and transmitted wavelengths for spectral analysis through a target object rather than reflecting off. In some embodiments, the nonlinear material is configured to produce beat waves from two wavelengths having a frequency between 1 terahertz and 100 terahertz.

[0106] As used herein, the range of 1 terahertz to 100 terahertz will be the “terahertz band” involving beat frequencies, and the range of 101 terahertz to 1000 terahertz will be the “optical band” involving optical and near-optical laser frequencies. In one embodiment, the laser frequencies will be in the “visible band” from 430 terahertz to 770 terahertz.

[0107] In some embodiments, the receiver is able to separate incoming signals in different wavelength bands. The receiver also includes a terahertz detector to receive the terahertz portion of the beat tone.

[0108] Several embodiments of the disclosure have been described. However, it will be understood that various modifications can be made without departing from the spirit and scope of the disclosure. Therefore, other embodiments are within the scope of the following claims.

[0109] The examples set forth above are provided as full disclosure for purposes of the patent to enable a person in the art to make and use the embodiments of the present disclosure and are not intended to limit the scope of what the inventors regard as their disclosure.

[0110] Modifications to the above-described modes for carrying out the methods and systems disclosed herein which are obvious to persons of skill in the art are intended to be within the scope of the following claims. All patents and publications mentioned in the specification are indicative of the levels of those skilled in the art to which the disclosure pertains. All references cited in the present disclosure are incorporated by reference as if each had been individually incorporated by reference in its entirety.

[0111] It will be understood that the present disclosure is not limited to a particular method or system, which of course can vary. It will also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in this specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term "plurality" includes two or more referents unless the content clearly dictates otherwise. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0112] The references shown in the following reference list in this application are incorporated by reference in their entirety herein.

[0113] REFERENCES

[0114] 1. H. Abediasl and H. Hashemi, "Monolithic optical phased-array transceiver in a standard SOI CMOS process," Optics Express, vol. 23, no. 5, pp. 6509-6519, Mar 2015.

[0115] 2. S. Chung, H. Abediasl and H. Hashemi, “A 1024-element scalable optical phased array in 180 nm SOI CMOS,” in IEEE International Solid-State Circuits Conference (ISSCC) Digest of Technical Papers (2017).

[0116] 3. C. V. Poulton et. al. “Optical Phased Array with Small Spot Size, High Steering Range and Grouped Cascaded Phase Shifters.” In Integrated Photonics Research, Silicon and Nanophotonics Optical Society of America 2016.

[0117] 4. US Patent No. 9,476,981 “Optical phased arrays”

Claims

1. A spectroscopic analysis apparatus, the apparatus comprising a transmitter and a receiver, the transmitter being configured to transmit an optical beam and a terahertz beam to a sample to perform spectroscopic analysis, and the transmitter comprising: Multiple tunable lasers, wherein the multiple tunable lasers generate multiple wavelengths; Multiple wavelength lockers are used to reduce wavelength noise from the multiple wavelengths, and each wavelength locker is configured to transmit a signal at a different wavelength. Multiple encoders, each encoder being configured to encode the light of a wavelength locker among the multiple wavelength lockers; At least one broadband combiner is used to combine the outputs of the plurality of encoders into the optical beam; A plurality of transmitters, the plurality of transmitters being connected to the at least one broadband combiner and configured to transmit the optical beam; as well as A nonlinear material is configured to generate beat waves from a portion of the optical beam, thereby generating the terahertz beam, the beat waves having two wavelengths and frequencies between 1 terahertz and 100 terahertz. The receiver is configured to receive light reflected from the sample, and the receiver includes an optical receiver and a terahertz receiver.

2. The apparatus of claim 1, wherein each of the plurality of transmitters comprises a grating coupler.

3. The apparatus of claim 1, wherein the plurality of encoders are configured to encode the amplitude of light, the phase of light, or both the amplitude and phase of light.

4. The apparatus of claim 1, wherein the plurality of tunable lasers operate in pulse mode.

5. The apparatus of claim 1, wherein the plurality of tunable lasers operate in a frequency-modulated continuous wave mode.

6. The apparatus of claim 1, wherein the apparatus comprises Si, and the thickness of Si gradually decreases from a first side of the apparatus comprising the plurality of tunable lasers to a second side of the apparatus comprising the plurality of emitters.

7. The apparatus of claim 6, wherein the thickness of Si at the first side is 3 micrometers and the thickness of Si at the second side is 1 micrometer.

8. A method for spectral analysis, the method comprising: Multiple wavelengths are generated by multiple tunable lasers; Noise from the multiple wavelengths is reduced by multiple wavelength lockers, each of which transmits a signal at a different wavelength; The multiple wavelengths are encoded by multiple encoders in a certain mode; Beat waves are generated from two of the plurality of wavelengths by a nonlinear material, the beat waves having a frequency between 1 terahertz and 100 terahertz. An optical phased array comprising multiple transmitters transmits the multiple wavelengths as optical beams onto the sample in a spatial direction to perform spectral analysis, wherein each transmitter is connected to a corresponding encoder among the multiple encoders via a corresponding waveguide. The beat wave is transmitted to the sample as a terahertz beam. as well as The light reflected from the sample is received by a receiver, which includes an optical receiver and a terahertz receiver.

9. The method of claim 8, wherein the mode includes the amplitude, phase, number, duration, and period of the square wave pulse.

10. The method of claim 8, further comprising: Multiple wavelengths reflected from the sample are received by a receiver; The receiver separates the plurality of wavelengths by wavelength bands, the wavelength bands including at least one terahertz band and one optical band; as well as The receiver detects the beat wave reflected by the sample in the terahertz band.

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