TECHNICAL FIELD

The present disclosure relates generally to the field of light detection and ranging (LiDAR) systems and technology and more specifically, to a multi-beam transmitter stage, a continuous wave laser, and a two-dimensional detector array for frequency-modulated continuous wave (FMCW) LiDAR chips and systems.

BACKGROUND

In recent years, LiDAR technology has gained huge popularity in various applications such as navigation, robotics, remote sensing, and advanced driving assistance systems (ADAS). This popularity is mainly due to the improvements in the performance of the LiDAR systems, such as in terms of range detection, accuracy, power consumption, as well as physical features, such as form factor and weight. The conventional LiDAR systems are mainly based on time-of-flight (ToF) engines operating at a certain wavelength (typically at a wavelength of 905 nanometres). Moreover, the choice of the wavelength is mainly driven by the availability of low-cost off-the-shelf components, such as a vertical cavity surfaceemitting laser (VCSEL) at a transmitter (TX) stage, and a single-photon avalanche diode (SPAD) at a receiver (RX) stage. However, performance of the conventional LiDAR system is still limited, especially in terms of range, because the maximum optical power should comply with eye-safety regulations (i.e., 905 nm wavelength range is not 100% safe for human eyes). Moreover, time-of-flight based engines of the conventional LiDAR system require high pulsed power, are sensitive to ambient light, have limited range detection and other limitations, for example, limited or no capability of simultaneous target range and velocity detection.

Currently, certain attempts have been made to improve the performance of the conventional LiDAR system, such as via coherent silicon photonic frequency-modulated continuous wave (FMCW) LiDAR. In certain scenarios, a total switching time of the transmitter (Tx) stage of the conventional coherent silicon photonic FMCW LiDAR is limited by the inherent physics on the optical components used for switching functionalities, such as conventional thermooptic phase shifters in silicon photonics technology (e.g., on-off switching time < 20 microseconds (pts)). Moreover, other alternative technologies such as based on micro optoelectronic mechanical system (MOEMS) can offer fast switching functionalities (e.g., on- off switching time < 1 ps) but suffer from limited pitch between adjacent emitters and show a significant loss when scaling to a high number of emitters. Thus, the conventional transmitter stage is not suitable for meeting a data rate specification for example equal or greater than 2 millions of points per second. Moreover, the transmitter stage of the conventional FMCW LiDAR systems typically does not provide optimal power efficiency, hence they require advanced amplification stages integrated on chip. This is also beneficial to simplify and reduce the cost of assembly and packaging. In addition, the receiver (Rx) chip stage of the conventional FMCW LiDAR systems does not allow optimal pixel density and resolution in large numerical aperture (NA) and typically requires use of complex optics. Thus, the conventional FMCW LiDAR systems do not meet all minimum requirements that are required for automotive-grade qualification, and mainly fail while addressing a horizontal and vertical field of view (FoV), point rate, and the desired data rate as well. Thus, there exists a technical problem of how to meet specifications of horizontal and vertical FoV and resolutions with desired frame rates and desired data rates for advanced driving assistance systems applications.

Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks associated with the conventional FMCW LiDAR systems.

SUMMARY

The present disclosure provides a multi-beam transmitter stage for a LiDAR system, a continuous wave laser, and a two-dimensional detector array for the LiDAR system. The present disclosure provides a solution to the existing problem of how to meet specifications of horizontal and vertical FoV and resolutions with desired frame rates and desired data rates for advanced driving assistance systems applications. An objective of the present disclosure is to provide a solution that overcomes at least partially the problems encountered in the prior art and provides an improved multi -beam transmitter stage, improved continuous wave laser, and an improved two-dimensional detector array for a LiDAR system, for example, multi-beam frequency-modulated continuous wave (FMCW) laser for LiDAR chips and systems. One or more objectives of the present disclosure is achieved by the solutions provided in the enclosed independent claims. Advantageous implementations of the present disclosure are further defined in the dependent claims.

In one aspect, the present disclosure provides a multi-beam transmitter stage for a light detection and ranging (LiDAR) system, comprising a continuous wave laser configured to output a laser beam, an emitter array comprises a one-dimensional optical switching matrix (OSM) comprising a plurality of elements extending along a first axis. The OSM is configured to direct the laser beam to each of the elements sequentially in turn. The emitter array further comprises a plurality of one-dimensional columns of emitters, each column extending along a second axis perpendicular to the first axis, wherein each column is arranged to receive the laser beam from a corresponding element of the OSM and each emitter is configured to output the laser beam as an output beam propagating along a third axis that is perpendicular to both the first axis and the second axis. The multi -beam transmitter stage further comprises a lens configured to receive the output beam from each emitter in each column of the emitter array and to translate a first axis position of each output beam into a first axis propagation angle of the beam.

The multi-beam transmitter stage is used for the LiDAR system, such as for the frequency- modulated continuous wave (FMCW) LiDAR system. The emitter array of the multi-beam transmitter stage sequentially routes the laser beam from the one-dimensional optical switching matrix to the plurality of one-dimensional columns of emitters. Therefore, the multi-beam transmitter stage offers an efficient multi-beam generation approach with two mirrored switching modules. In this way, the number of one-dimensional optical switching matrices needed to meet the advanced driving assistance systems (ADAS) application can be reduced significantly. In addition, each Nth element from the plurality of elements in each optical switching matrix has a plurality of (e.g., four) one-dimensional columns of emitters (or four grating couplers emitters), e.g., resulting in a total number of eight emitters (or grating couplers per column). Beneficially as compared to the conventional approach, the laser beam from the plurality of elements of the one-dimensional optical switching matrix is routed to the plurality of one-dimensional columns of emitters (e.g., via a splitter tree). In addition, each emitter from the one-dimensional columns of emitters is activated simultaneously at time instants to to tN and simultaneously generates multiple beams (or HMB). As a result, the multi-beam transmitter stage can be properly designed and suitably scaled in order to meet the specifications of the horizontal FoV, the vertical FoV, and resolutions with desired frame rates and desired data rates for advanced driving assistance systems applications.

In an implementation form, the continuous wave laser is a frequency modulated continuous wave (FMCW) laser configured to generate frequency chirps.

As the continuous wave laser is a frequency modulated continuous wave laser, thus the laser beam is composed of a chirped signal (or a chirped optical signal).

In a further implementation form, the multi-beam transmitter stage further comprising an in- phase/quadrature (IQ) modulator coupled to the continuous wave laser and configured to perform frequency chirps.

The in-phase/quadrature modulator is configured to modulate the laser beam (i.e., via indirect modulation), and to perform frequency chirps.

In a further implementation form, the continuous wave laser is a wavelength-tunable laser.

In this implementation, beneficially, each emitted laser beam can be controlled by wavelength tuning.

In a further implementation form, the laser beam has a wavelength in a range of 1500 nm to 1600 nm.

As the laser beam has the wavelength range of 1500 nm to 1600 nm (or in C-band), thus the laser beam is about forty times safer to eyes than the conventional laser beam at 905 nm. Moreover, the laser beam is also compatible with coherent silicon photonic chip-based hardware.

In a further implementation form, the multi-beam transmitter stage further comprising a binary splitter configured to split the laser beam into two branches, wherein the transmitter stage comprises at least one emitter array for each branch.

The binary splitter is beneficial to split the laser beam into two branches, and to offer an efficient multi-beam generation approach with two mirrored switching modules.

In a further implementation form, each of the two branches comprising at least one booster semiconductor optical amplifier. Each semiconductor optical amplifier is configured to amplify the laser beam received through the corresponding branch, and then pass the amplified laser beam to the corresponding one-dimensional optical switching matrix (OSM).

In a further implementation form, the OSMs of the two branches are synchronised.

As the OSMs of the two branches are synchronised, thus the OSMs can operate in parallel.

In a further implementation form, the OSM comprises an active optical routing network including a plurality of cascaded interferometric components.

The active optical routing network that includes the plurality of cascaded interferometric components is used to route the laser beam (or signal) to the specific area of the emitter array.

In a further implementation form, the continuous wave laser is configured to sweep a wavelength of the laser beam across a predetermined wavelength range; wherein each column of emitters is provided by grating couplers extending along the second axis, and an emission position of each emitter is dependent on a wavelength of the laser beam; and wherein the lens is further configured to translate a second axis position of each beam into a second axis propagation angle of the beam.

In this implementation, beneficially, multi beams do not interfere with one beam forming, instead, each focusing grating couplers generates an independent beam.

In a further implementation form, each column of emitters comprises a binary splitter tree.

The binary splitter tree feeds the plurality of emitters in a one-dimensional column.

In a further implementation form, the multi-beam transmitter stage further comprising an optical tap coupled to the continuous wave laser and configured to provide a local oscillator signal for a receiver stage of the LiDAR system.

The optical tap is configured to provide the local oscillator signal (i. e. , LO) for a receiver stage of the LiDAR system.

In another aspect, the present disclosure provides a continuous wave laser, comprising a plurality of active semiconductor components bonded to a silicon photonics layer. The continuous wave laser is a frequency modulated continuous wave laser that is configured to output the frequency chirped laser beam.

In yet another aspect, the present disclosure provides a two-dimensional detector array for a frequency modulated continuous wave (FMCW) LiDAR system, comprising a plurality of coherent detector pixel units, each comprising a semiconductor layer bonded to a silicon photonics layer with one or more integrated photodetectors.

The two-dimensional detector array is based on a dedicated receiver chip that includes the plurality of coherent (or heterodyne coherent) detector pixel units, such as the coherent detector pixel unit, which are manufactured by three-dimensional wafer bonding technique (e.g., electronics-photonics integration). Beneficially, as compared to the conventional detector array, a readout capacity and pixel density of the two-dimensional detector array are increased (e.g., by a factor 2). Moreover, the two-dimensional detector array enables a simplification of system assembly by including a transverse electric (TE) & transverse magnetic (TM) polarization-dependent grating coupler receivers, due to which polarization control devices are not required at the two-dimensional detector array (or RX stage).

In yet another aspect, the present disclosure provides a LiDAR system, comprising the multibeam transmitter stage, wherein the multi-beam transmitter stage comprises the continuous wave laser, and the detector array.

The LiDAR system archives all the advantages and technical effects of the multi-beam transmitter stage, the continuous wave laser, and the two-dimensional detector array.

It is to be appreciated that all the aforementioned implementation forms can be combined.

It has to be noted that all devices, elements, circuitry, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof. It will be appreciated that features of the present disclosure are susceptible to being combined in various combinations without departing from the scope of the present disclosure as defined by the appended claims.

Additional aspects, advantages, features and objects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative implementations construed in conjunction with the appended claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers.

Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:

FIG. 1 is an illustration of a multi-beam transmitter stage for a light detection and ranging (LiDAR) system, in accordance with an embodiment of the present disclosure;

FIG. 2 is an illustration of a multi-beam transmitter stage for a light detection and ranging (LiDAR) system, in accordance with another embodiment of the present disclosure;

FIG. 3 is an illustration of an extension of a multi-beam transmitter stage for a light detection and ranging (LiDAR) system, in accordance with an embodiment of the present disclosure;

FIG. 4A is a schematic illustration of die-to-wafer (D2W) bonding for a continuous wave laser, in accordance with an embodiment of the present disclosure;

FIG. 4B is a cross-sectional view of an active component for lasing and amplification functionalities on chip, in accordance with an embodiment of the present disclosure; FIG. 5 is a schematic illustration of a frequency modulated continuous wave (FMCW) a light detection and ranging (LiDAR) system, in accordance with an embodiment of the present disclosure; and

FIG. 6 is a block diagram of a light detection and ranging (LiDAR) system, in accordance with an embodiment of the present disclosure.

In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the nonunderlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.

DETAILED DESCRIPTION OF EMBODIMENTS

The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.

FIG. 1 is an illustration of a multi-beam transmitter stage for a light detection and ranging (LiDAR) system, in accordance with an embodiment of the present disclosure. With reference to FIG. 1 there is shown an illustration of a multi-beam transmitter stage 100 for a light detection and ranging (LiDAR) system. The multi-beam transmitter stage 100 includes a continuous wave laser 102, an emitter array 104, a one-dimensional optical switching matrix (OSM) 106A, a plurality of elements 108A-108N, N one-dimensional columns of emitters (i.e. a plurality of one-dimensional columns of emitters) 110A-110N, N being two or more, and a lens 112. In the drawing, the lens 112 is shown to the right of the emitter array 104 but this graphic representation is schematic. In reality, the lens 112 is located above (or below) the emitter array 104, i.e. it is displaced relative to the emitter array 104 along an out-of-plane direction z, the direction z being perpendicular to the plane defined by emitter array 104. There is further shown another one-dimensional optical switching matrix (OSM) 106B, an in-phase/ quadrature (IQ) modulator 114, an optical tap 116, a binary splitter 118, a first branch 120A, a second branch 120B, a booster semiconductor optical amplifier (SOA) 122A, and another booster semiconductor optical amplifier (SOA) 122B. The multi-beam transmitter stage 100 is used in light detection and ranging (LiDAR) system. The multi-beam transmitter stage 100 includes a new transmitter chip architecture to enable multi-beam generation and parallelization of multi-beam frequency-modulated continuous wave (FMCW) laser and next-generation LiDAR systems. The multi-beam transmitter stage 100 may also be referred to as a main unit, or a transmitter stage of the LiDAR system.

The continuous wave laser 102 is configured to output a laser beam. In some implementations, the continuous wave laser 102 may be a frequency modulated continuous wave (FMCW) laser that is configured to output a frequency chirped laser beam and the in- phase/quadrature (IQ) modulator 114 may be omitted.

The emitter array 104 includes the one-dimensional optical switching matrix (OSM) 106A. The one-dimensional optical switching matrix (OSM) 106A further includes the plurality of elements 108A-108N that are extending along a first axis. The one-dimensional OSM 106A is configured to direct the laser beam sequentially in turn to each of the elements. There is further shown the other one-dimensional optical switching matrix (OSM) 106B that is similar to the one-dimensional optical switching matrix (OSM) 106A. The emitter array 104 further includes the plurality of one-dimensional columns of emitters 110A-110N extending along a second axis that is perpendicular to the first axis. In an example, the plurality of onedimensional columns of emitters 110A-110N may be focusing grating couplers (GC). In some implementations, because the GCs are fed by a binary splitter tree, as described in more detail below, the number of focusing GC is a power of 2, for example, 4 grating couplers = 2 ² .

The lens 112 is a transmissive optical device with a specific focal length that focuses or disperses a light beam by means of refraction. In an example, the lens 112 consists of a single piece of transparent material.

The in-phase/quadrature (IQ) modulator 114 includes suitable logic, circuitry, interfaces and/or code that is configured to modulate the laser signal of the continuous wave laser 102.

The optical tap 116 is based on a photonic waveguide-based directional coupler that is cascaded to the continuous wave laser 102 or to the combination of the continuous wave laser 102 and the in-phase/quadrature (IQ) modulator 114.

The binary splitter 118 is configured to split the laser beam of continuous wave laser 102. In some implementations, the binary splitter 118 may be based on a photonics waveguide-based component. In an example, the binary splitter 118 is referred to as a beam splitter that feeds the plurality of one-dimensional columns of emitters 110A-110N to generate multi beams (e.g., HMB). The output of the binary splitter 118 is passed to the emitter array 104 through the first branch 120A, similarly, the output of the binary splitter 118 is also passed to another emitter array (arranged downward) through the second branch 120B.

The booster semiconductor optical amplifiers (SOA) 122A and 122B include suitable logic, circuitry, interfaces and/or code that is configured to amplify the laser beam. The booster semiconductor optical amplifiers 122A and 122B may also be referred to as optical amplifiers.

In operation, the continuous wave laser 102 is configured to output the laser beam. The continuous wave laser 102 includes a plurality of active semiconductor components that are bonded to a silicon photonics layer. In an example, the silicon photonics layer of the continuous wave laser 102 includes at least one external cavity. Moreover, the active semiconductor components of the continuous wave laser 102 include III-V active components including at least one reflective semiconductor optical amplifier (RSOA), and at least one booster semiconductor optical amplifier (SOA), such as the booster semiconductor optical amplifiers 122A, and 122B. In an implementation, each of the active semiconductor components of the continuous wave laser 102 is formed from a semiconductor die (e.g., an indium phosphide die) including a semiconductor substrate and each of the semiconductor dies are bonded to the silicon photonics layer in parallel before removal of the semiconductor substrates. In an example, the laser beam of the continuous waver laser 102 includes a range of wavelength range (AX). In another example, the laser beam is a continuous wave laser beam that includes a wavelength (Xo).

In accordance with an embodiment, the continuous wave laser 102 is a frequency modulated continuous wave (FMCW) laser configured to generate frequency chirps. Therefore, the laser beam is a chirped signal (or a chirped optical signal). In other words, the laser beam is an FMCW chirped signal with an FMCW carrier wavelength (Xo) (or an FMCW carrier wavelength range (AX)). In an implementation, the continuous wave laser 102 is an external cavity laser (ECTL) that is configured to modulate a continuous wave (CW) signal via direct modulation, and to generate the frequency chirps. Alternatively, in some implementations the continuous wave laser 102 may be a distributed Bragg reflector, DBR, laser. In accordance with an embodiment, the continuous wave laser 102 is a frequency modulated continuous wave (FMCW) laser configured to output a frequency chirped laser beam. In an example, an in-phase/quadrature modulator is coupled to the continuous wave laser 102 to modulate the laser beam (e.g., via indirect modulation), and to perform frequency chirps. As a result, the continuous wave laser 102 is the frequency modulated continuous wave laser that is configured to output the frequency chirped laser beam.

In accordance with an embodiment, the multi-beam transmitter stage 100 further includes the in-phase/quadrature (IQ) modulator 114 coupled to the continuous wave laser 102 and configured to perform frequency chirps. The in-phase/quadrature modulator 114 is configured to modulate the laser beam (i.e., via indirect modulation), and to perform frequency chirps. In an implementation, the in-phase/quadrature modulator 114 and the continuous wave laser 102 are also coupled to the optical tap 116, which is configured to generate a local oscillator (LO) signal that is a fraction of the FMCW chirped signal.

In accordance with an embodiment, the continuous wave laser 102 is a wavelength-tunable laser. Therefore, each emitted laser beam of the continuous wave laser 102 can be controlled by wavelength tuning.

In accordance with an embodiment, the laser beam has a wavelength in a range of 1500 nm to 1600 nm. The laser beam with the wavelength range of 1500 nm to 1600 nm (or in C- band) is about forty times eye-safer than the conventional laser beam at the wavelength of 905 nm. Moreover, the laser beam is also compatible with coherent silicon photonic chipbased hardware. The laser beam for FMCW LiDAR application, can offer significantly improved performance, extending the applicability range even longer than 300 metres (m).

In accordance with an embodiment, the multi-beam transmitter stage 100 further includes the optical tap 116 coupled to the continuous wave laser 102 and configured to provide a local oscillator signal for a receiver stage of the LiDAR system. Firstly, the laser beam of the continuous wave laser 102 is passed through the optical tap 116 that is coupled to the continuous wave laser 102. In an example, the optical tap 116 is coupled to the combination of the continuous wave laser 102 and the in-phase/quadrature (IQ) modulator 114. The optical tap is configured to provide the local oscillator signal for a receiver stage (e.g., a two- dimensional detector array) of the LiDAR system. In accordance with an embodiment, the multi-beam transmitter stage 100 further comprising the binary splitter 118 configured to split the laser beam into two branches, and the multibeam transmitter stage 100 comprises at least one emitter array for each branch. Firstly, the laser beam from the optical tap 116 is passed through the binary splitter 118 that is configured to split the laser beam into two branches, such as the first branch 120A, and the second branch 120B. Therefore, the multi-beam transmitter stage 100 offers an efficient multi-beam generation approach with two mirrored switching modules. Moreover, the laser beam is further passed to at least one emitter array for each branch, such as to the emitter array 104 through the first branch 120A, and to another emitter array (not marked in FIG.1) through the second branch 120B. In an example, the binary splitter 118 is a three decibels (dB) binary splitter that generates two co-propagating frequency chirped optical signals.

In accordance with an embodiment, each of the two branches comprises at least one booster semiconductor optical amplifier. In an implementation, the binary splitter 118 is configured to split the laser beam into two branches, such as the first branch 120A, and the second branch 120B. Moreover, each of the two branches includes at least one booster semiconductor optical amplifier, such as the booster semiconductor optical amplifier (SOA) 122A, and the other booster semiconductor optical amplifier (SOA) 122B. Each semiconductor optical amplifier is configured to amplify the laser beam received through the corresponding branch, and then pass the amplified laser beam to the corresponding onedimensional optical switching matrix (OSM). For example, the booster semiconductor optical amplifier 122A is configured to amplify the laser beam received through the first branch 120A, and then pass the amplified laser beam to the one-dimensional optical switching matrix (OSM) 106A. In an implementation, there are at least two optical switching matrices (1XN), such as the one-dimensional optical switching matrix 106A, and the other one-dimensional optical switching matrix 106B. The one-dimensional two optical switching matrices are configured to receive the laser beam as an input from the binary splitter 118 through the booster semiconductor optical amplifiers (SOA) 122A, and 122B.

The emitter array 104 includes the one-dimensional optical switching matrix (OSM) 106A that includes the plurality of elements 108A-108N extending along a first axis. The onedimensional optical switching matrix 106A is configured to direct the laser beam to each of the elements sequentially in turn. Firstly, the plurality of elements 108A-108N that extends along the first axis are equally separated by a certain distance or pitch (i.e., p _x as shown in FIG.l), are synchronized optically and are activated sequentially in turn by the onedimensional optical switching matrix 106A. As a result, the laser beam is directed towards each element of the plurality of elements 108A-108N. For example, initially, the onedimensional optical switching matrix 106A is configured to direct the laser beam to the element 108A, and then to the element 108B, and finally, direct the laser beam to the element 108N. As a result, the one-dimensional optical switching matrix (OSM) 106A has at least N output laser beams (or output channels), corresponding to the plurality of elements 108A- 108N that are required to perform the lens assisted beam steering (LABS) in one dimensional (ID).

In accordance with an embodiment, the optical switching matrices (OSMs) of the two branches are synchronised. For example, the one-dimensional optical switching matrix 106A of the first branch 120A, and the other one-dimensional optical switching matrix (OSM) 106B of the second branch 120B are synchronised simultaneously, so as to operate them in parallel.

In accordance with an embodiment, the one-dimensional optical switching matrix (OSM) 106A comprises an active optical routing network including a plurality of cascaded interferometric components. The active optical routing network that includes the plurality of cascaded interferometric components that are used to rout the laser beam (or signal) to a specific area of the emitter array 104. For example, to rout the laser beam towards the plurality of one-dimensional columns of emitters 110A-110N that extends along the second axis that is perpendicular to the first axis.

The emitter array 104 further comprises a plurality of one-dimensional columns of emitters 110A-110N extending along a second axis perpendicular to the first axis. Each column is arranged to receive the laser beam from a corresponding element of the one-dimensional optical switching matrix (OSM) 106A, and each emitter is configured to output the laser beam as an output beam. The plurality of elements 108A-108N that are extending along the first axis is arranged to provide the laser beam to each one-dimensional column of the emitter from the plurality of one-dimensional columns of emitters 110A-110N that are extending along the second axis. For example, the element 108A is configured to provide the laser beam to the one-dimensional columns of emitter 110A, and similarly for subsequent onedimensional columns of emitters from the plurality of one-dimensional columns of emitters 110A-110N. In an example, the plurality of elements 108A-108N are integrated waveguides for routing the optical signal from the OSM to the plurality of columns of emitters 110A- 110N, respectively. In an example, the plurality of one-dimensional columns of emitters 110A-110N are focusing grating couplers (GC). Moreover, the plurality of one-dimensional columns of emitters 110A-110N are activated sequentially at time instants to to tN so as to generate UMB multi beams simultaneously at each instant, wherein UMB is the number of GCs per column. In this case, four emitters are shown for each one-dimensional column by way for example, but it can be any number of emitters, with the power of 2, e.g., UMB = 2°, 2 ¹ , 2 ² , etc. . without limiting the scope of the disclsoure.

In an implementation, there exists two optical switching matrices, such as the onedimensional optical switching matrix 106A, and the other one-dimensional optical switching matrix 106B that also includes a number of elements (not shown in FIG. 1). There also exists another column of emitters that are mirrored along with the one-dimensional columns of emitters 110A-110N, and towards the second axis (i.e., py as shown in FIG.l). As a result, the one-dimensional optical switching matrix 106A, the other one-dimensional optical switching matrix 106B, the one-dimensional columns of emitters 110A-110N, and the other columns of emitters collectively constitute or the multi-beam transmitter stage 100 (or a main unit) with NxM emitters in both axes.

The multi-beam transmitter stage 100 further includes a lens 112 configured to receive each output beam from the emitter array 104 and translate a first axis position of each output beam into a first axis propagation angle of the beam. The lens 112 is configured to receive the output beam from the emitter array 104, such as from the plurality of one-dimensional columns of emitters 110A-110N. Thereafter, the lens 112 is configured to translate the first axis position of each output beam into the first axis propagation angle of the beam. For example, the lens 112 is configured to translate the first axis position of the output beam of the one-dimensional column of emitter 110A into the first axis propagation angle of the beam. Therefore, the multi-beam transmitter stage 100 includes a combination of lens- assisted beam steering (LABS) with multi-beam generation for one dimensional (ID) or two-dimensional (2D) beam steering, depending on the configuration of the multi-beam transmitter stage 100, such as quasi-solid state system configuration or solid-state system configuration. In an example, if the configuration of the multi-beam transmitter stage 100 is based on the quasi-solid-state system, then the two-dimensional (2D) beam steering is implemented by one dimensional lens-assisted beam steering (LABS) and one-dimensional steering by an external mirror. In another example, if the configuration of the multi-beam transmitter stage 100 is based on the solid-state system, then the two-dimensional (2D) beam steering is implemented using one dimensional steering by the LABS and one-dimensional steering by wavelength (X)-sweeping.

In an implementation, the multi-beam transmitter stage 100 is the quasi-solid-state system, and multi-beam transmitter stage 100 operates at a fixed wavelength (Xo) and generates M number of multiple beams due to the presence of the plurality of one-dimensional columns of emitters 110A-110N. Specifically, M = UMB in the case of one emitter array 104 in the multi-beam transmitter stage 100, while M = 2 X UMB in the case of a multi-beam transmitter stage 100 with two mirrored emitter arrays synchronized to operate in parallel as shown in FIG. 1. Moreover, the optical steering in one dimension is based on the lens-assisted beam steering (LABS) principle. In addition, the plurality of elements 108A-108N that are extending along the first axis (or N columns), and each of the plurality of one-dimensional columns of emitters 110A-110N, such as M number of multi beams are activated sequentially and the steering is performed in combination with the lens 112 (or at least one external lens) that is designed with a specific focal length. Further, along the second axis (or another dimension), the M number of multi beams are steered by an external onedimensional scanning mirror or array of mirrors (e.g., based on MEMS technology). The resonant frequency, diameter, and the number of MEMS mirrors can be designed as a function of the LiDAR system specification.

In another implementation, the multi-beam transmitter stage 100 is the solid-state system. The multi-beam transmitter stage 100 operates in a wavelength range (AX) and generates M number of multiple beams. The optical steering in one dimension is based on the LABS principle. In addition, the plurality of elements 108A-108N that are extending along the first axis (or N columns), and each of the plurality of one-dimensional columns of emitters 110A- 110N, such as M number of multi beams are activated sequentially and the steering is performed in combination with at the lens 112 (i.e., least one external lens). In an example, the lens 112 is a cylindrical lens that is designed with a specific focal length. Further, along the second axis (or another dimension), the M number of multi beams are steered by tuning the wavelength of the continuous wave laser 102 (or laser source) within a specific wavelength range (AX) and via the principle of the grating coupler wavelength steering efficiency (WSE). In an example, the selection of the wavelength range (AX) is determined as a function of the grating coupler wavelength steering efficiency, pitch of the column grating couplers py and the LiDAR system specifications (e.g., field of view, resolution).

In accordance with an embodiment, each emitter in each column of emitters comprises a focusing grating coupler, and the multi-beam transmitter stage 100 further comprises one or more mirrors arranged to collectively adjust a second axis propagation angle of the output beams. In an implementation, the one-dimensional column of emitter 110A includes four grating couplers (i.e., at top), and another one-dimensional column of emitter also includes four grating couplers (i.e., at the bottom side). As a result, there exists a total of eight grating couplers in each one-dimensional column of the multi-beam transmitter stage 100, as shown in FIG. 1. Moreover, one or more mirrors are also arranged to collectively adjust the second axis propagation angle of the output beams. In an example, one or more mirrors are based on micro-electro-mechanical systems (MEMS) technology, and the diameter of one or more mirrors ranges from 0.55 to 12 millimetres (mm).

In an implementation, an emitter beam size of the one-dimensional columns of emitters 110A-110N is ‘w’ , with a pitch of py in the second axis (i.e., y-axis), which ensures spatial multiplexing and no interference among emitted parallel multi beams (i.e., pitch » X/2). Moreover, if a field of view (FoV) along the second axis is F, each multi beam from the column emitter array of the multi-beam transmitter stage 100 can cover a sub-FoV of F/UMB. In addition, the scanning mirror or equivalent array of scanning mirrors can steer an equivalent FoV of F/UMB instead of F and meet the requirement of the angular resolution (e.g., < O.ldeg). The total length of the array of one-dimensional column of emitters, Ldev.Y, depends on the pitch py, number of multi beams IIMB, and total field of view F along the Y- axis.

In accordance with an embodiment, the continuous wave laser 102 is configured to sweep a wavelength of the laser beam across a predetermined wavelength range. Each column of emitters is provided by grating couplers extending along the second axis, an emission position of each emitter is dependent on a wavelength of the laser beam, and the lens is further configured to translate a second axis position of each beam into a second axis propagation angle of the beam. Firstly, steering along the second axis (i.e., Y-axis) is performed by sweeping the wavelength of the laser beam across the predetermined wavelength range, such as within a wavelength range of AX. In an example, the continuous wave laser 102 is configured to sweep the wavelength of the laser beam without any external one-dimensional mirror. In addition, each column of emitters from the plurality of onedimensional columns of emitters 110A-110N is provided by the focusing grating couplers that extends along the second axis. In example, the design of grating couplers, and spacing among them (i.e., p _y or Y-pitch) can be tailored depending on specifications of the LiDAR system. Moreover, as the emission position of each emitter is dependent on the wavelength of the laser beam, therefore, wavelength dependency principle (i.e., wavelength steering efficiency (WSE)) of the focusing grating couplers is useful. Due to which, the output angle of each emitted multi-beam from the emitter array 104 can be controlled by wavelength tuning. Thereafter, the lens 112 is configured to translate the second axis position of each multi beam into the second axis propagation angle of the beam. Thus, it is worth emphasising that the multi beams do not interfere with one beamforming, instead, each focusing grating couplers generates an independent beam.

In accordance with an embodiment, each column of emitters comprises a binary splitter tree. The binary splitter tree may be implemented by a waveguide-based passive component, for example, made of cascaded Y-junctions or 3dB splitters. The binary splitter tree feeds the plurality of one-dimensional columns of emitters 110A-110N to generate the multi beams (UMB).

In accordance with an embodiment, the multi-beam transmitter stage 100 is formed on a silicon-nitride/silicon-on-insulator (SiNSOI) platform. In an implementation, the multibeam transmitter stage 100 is based on the SiNSOI platform with integrated components possibly based on silicon nitride (SiN) or silicon-on-insulator (SOI) photonic waveguides. The SiNSOI platform includes the continuous wave laser 102 (or an external cavity laser (ECTL)), in-phase/quadrature (IQ) modulator 114, the optical tap 116, the binary splitter 118 (e.g., a 3dB splitter), and the one-dimensional optical switching matrix (OSM) 106A (e.g., Mach-Zehnder interferometer (MZI)-based optical switching matrix). The SiNSOI platform further includes directional couplers (or Y-junctions) constituting the binary splitter 118, the binary splitter tree for the M grating coupler emitters in each of the plurality of columns 110A-110N, and the waveguides for optical signal routing.

The multi-beam transmitter stage 100 is used for the LiDAR system, such as for the FMCW LiDAR system. The emitter array 104 of the multi-beam transmitter stage 100 splits the laser beam from the one-dimensional optical switching matrix 106A to the plurality of onedimensional columns of emitters 110A-110N. Therefore, the multi-beam transmitter stage 100 offers an efficient multi-beam generation approach with two mirrored emitter arrays where the switching modules are synchronized to operate in parallel. In this way, the total number of emitter arrays with active optical switching matrices needed for system parallelization in order to meet the advanced driving assistance systems (ADAS) application requirements, can be reduced significantly. In an example, each N ^lh element from the plurality of elements 108A-108N in each optical switching matrix activates each of the N one-dimensional columns of four emitters (or four grating couplers emitters) sequentially, so results in a total number of eight emitters (or grating couplers activated simultaneously in the mirrored architecture in FIG. 1, to generate M = 2 X UMB = 8 multi beams). In another example, each N ^th one-dimensional column from the plurality of one-dimensional columns 110A-110N in each optical switching matrix can have one, two, four (or eight) number of emitters, up to UMB. Beneficially as compared to the conventional approach, the laser beam from the plurality of elements 108A-108N of the one-dimensional optical switching matrix 106A is routed efficiently to the plurality of one-dimensional columns of emitters 110A- 110N (e.g., via a splitter tree). In addition, each emitter from the one-dimensional columns of emitters 110A-110N is activated simultaneously at time instants to to tN and generates simultaneously the multi beams (or UMB multi beams). Increasing the number of grating couplers in the one-dimensional column of emitters 110A-110N to generate M = IIMB multi beams determines an increase of the total optical power budget required by the emitter array 104. To this purpose, integration of active components (e.g., booster SOAs) on chip for laser beam amplification and design of multi-beam transmitter stage with two mirrored emitter arrays where the OSMs are synchronized to operate in parallel, allows optimal management of the optical power benefitting from a reduced number of grating couplers needed in the one-dimensional columns of emitters. Due to which, the multi-beam transmitter stage 100 can meet the specifications of the horizontal FoV, the vertical FoV, and resolutions with desired frame rates and desired data rates for advanced driving assistance systems applications.

In an implementation of the transmitter stage 100, wavelength tunability is applied to multi beams along the second axis, such as for thirty-two total number of multi-beams (16 emitters/column driven by OSM 106A plus mirrored 16 emitters/column driven by OSM 106B). With a field of view F along the one dimension, for example with the vertical VoF = 20°, the equivalent field of view of each multi beam is F/UMB = 0.625°, and the number of points in the equivalent field of view is 7 to meet the requirement of a vertical angular resolution of, for example, 0.1°. If the grating coupler emitters have a wavelength steering efficiency of 0.2deg/nm, the wavelength tenability range is 3.125 nm with an estimated pitch (i.e., Py) of around 75 pm along the said vertical one dimension. Therefore, the higher the number of multi beams the smaller the equivalent field of view, and the shorter the wavelength tenability range (AX), and the more relaxed the wavelength steering efficiency specifications of the grating couplers. Moreover, for 512 number of elements (or emitters) along the first axis, the total elements (or emitter in each emitter array) is 512 X 32 = 16384.

Further, a total 2D steering time of 512 X (62.5 ps + 10 ps) = 0.037s is estimated with 62.5 ps the tuning time required by the laser to sweep 3.125 nm and 10 ps half the on-off switching time for the OSM to activate 1 column array in the other one-dimension. \In comparison, the total estimated 2D steering time in an equivalent single beam transmitter stage where wavelength tunability is applied to a total number of emitters of 512 X 1 = 512 activated by a ID OSM is 512 X (2 ms + 10 ps) = 1.03 s, with 2 ms the tuning time required for the laser to sweep 100 nm and cover a total VFoV of 20° with a wavelength steering efficiency of 0.2 nm/deg for the grating emitter, and 10 ps half the on-off switching time for the OSM to activate the each emitter sequentially.

FIG. 2 is an illustration of a multi-beam transmitter stage for a light detection and ranging (LiDAR) system, in accordance with another embodiment of the present disclosure. FIG. 2 is described in conjunction with elements from FIG.l. With reference to FIG.2, there is shown an illustration of a multi-beam transmitter stage 200 for a light detection and ranging (LiDAR) system. The multi-beam transmitter stage 200 includes a first continuous wave laser 202A, a first emitter array 204A, a one or more additional continuous wave lasers 202B, a second emitter array 204B. There is further shown a first one-dimensional optical switching matrix (OSM) 206A, a second one-dimensional optical switching matrix (OSM) 206B, a third one-dimensional optical switching matrix (OSM) 206C, and a fourth onedimensional optical switching matrix (OSM) 206D that are synchronized to operate in parallel. There is further shown a first optical tap 208A, a second optical tap 208B, a first binary splitter 210A, and a second binary splitter 210B. There is further shown a first booster semiconductor optical amplifier (SOA) 212A, a second booster semiconductor optical amplifier (SOA) 212B, a third booster semiconductor optical amplifier (SOA) 212C, and a fourth booster semiconductor optical amplifier (SOA) 212D.

In accordance with an embodiment, the continuous wave laser 102 is the first continuous wave laser 202A, and the laser beam is a first laser beam. The multi-beam transmitter stage 200 further comprises the one or more additional continuous wave lasers 202B configured to output a second laser beam with a wavelength different from a wavelength of the first laser beam. In an implementation, the multi-beam transmitter stage 200 includes the first continuous wave laser 202A, the one or more additional continuous wave lasers 202B, as shown in FIG. 2, which are similar to the continuous wave laser 102 of the FIG. 1, and are also configured to operate in a similar way. For example, the first continuous wave laser 202A is configured to output the first laser beam with a desired wavelength (i.e., X _o ), and the one or more additional continuous wave lasers 202B are also configured to output the second laser beam with a wavelength (i.e., Xi), which is different from the wavelength of the first laser beam. The first laser beam is further passed to the first emitter array 204A through the first booster semiconductor optical amplifier (SOA) 212A, and to another emitter array through the second booster semiconductor optical amplifier (SOA) 212B. After that, the first emitter array 204A is configured to receive the first laser beam to generate the first beams (or multi-beams) in a similar way of the multi-beam transmitter stage 100. The multi-beam transmitter stage 200 further includes at least one second emitter array 204B configured to receive one or more of the additional laser beams and generate a plurality of second beams. In addition, the lens 112 or array of lenses is further configured to receive each of the plurality of second beams and direct the second beams to illuminate an area adjacent on the first axis to the beams from the first laser beam. At least one second emitter array 204B firstly receives the one or more of the additional laser beams and then generate the plurality of second beams. Thereafter, each of the plurality of second beams are received by the lens 112 or array of lenses, which is configured to direct the second beams to illuminate an area (e.g., a frame), which is adjacent on the first axis to the beams from the first laser beam. As a result, the illuminated area or frame is also segmented by the wavelengths.

The first emitter array 204A includes the first one-dimensional OSM 206A, and the plurality of one-dimensional columns of emitters 110A-110N (of FIG.1), and the second emitter array 204B also includes the third one-dimensional OSM 206C, and a plurality of one-dimensional columns of emitters. As a result, there exist multiple output beams that are received by the lens 112 (of FIG.l). The lens 112 is further configured to direct the first beams and the second beams. In an example, the lens 112 is configured to direct the second beams to illuminate the area adjacent on the first axis to the beams from the first laser beam. Beneficially, each transmitter stage of the multi-beam transmitter stage 200 is configured to cover half of a total field of view in one dimension, for example the horizontal, (HFoV/2), and a total field of view in the other dimension, for example the vertical, (VFoV). In each transmitter stage, Ldev,x/2, is defined as the distance between the centers of the outermost emitters, where Ldev,x satisfies the equation HFoV = 2 tan ^-1 ( dev,x Beneficially, (p _e

\ Zy / first emitter array 204A and the second emitter array 204B in an implementation (FIG. 2) can cover HFoV/2 each, thus resulting in a limited length of the array of emitters in the one- dimension for each emitter array. In the possible implementation of FIG. 2 with external scanning components for beam steering in the one-dimension, this parallelization approach can significantly simplify the design of the mirror component or array of mirrors component in terms of reduced steering angles and lower operating frequencies.

In an implementation, the multi-beam transmitter stage 200 includes a Mach-Zehnder interferometer (MZI)-based binary splitter tree switching matrix (or an SOI MZI-based thermo-optic phase shifters) with an on-off switching time of around 20 microseconds (ps). Moreover, the multi-beam transmitter stage 200 includes two transmitter stages (or main units), such as a left transmitter stage and a right transmitter stage of FIG. 2 that are synchronized to operate in parallel. Beneficially, the first one-dimensional OSM 206A of the first emitter array 204A includes a total of 256 emitters, and similarly the third onedimensional OSM 206C of the second emitter array 204B also includes a total of 256 elements. A total number of 512 emitters along the one-dimension with a pitch of 13pm, a total array length of 6.7 mm, and using a lens with a focal length of 8 mm, can cover the HFoV of 45° with a resolution of 0.09°. Thus, for the one-dimensional mirror (or mirror array) beam steering in a second axis, there are eight multi-beams for the total VFoV, then each beam for an equivalent field of view of F/UMB with UMB = 8 (for example, with a total VFoV of 20° and 8 multi beams, the equivalent FoV is 2.5°). As a result, the higher the number of multi-beams, the smaller the equivalent FoV to be covered by a mirror, such as the one-dimensional mirror. Moreover, total elements (or emitter in each emitter array) is = 256 X 8 = 2048, because there are eight emitters in each one-dimensional column. Further, the total estimated 2D steering time is (145 ps + 10 ps) X 256 = 0.039 s, with 145 ps the bottom-up / up-bottom scanning time of a MEMS with a resonance frequency of > 3.5 kilohertz (kHz) and a resolution of 25 points/beam, while 10 ps is half the on-off switching time for the OSM to activate 1 column array in the other one-dimension. This total time in combination with the propose parallelization approach with at least two transmitter stages that are synchronized and are operating in parallel, can support a data rate equal or higher than two mega points per second (M pts/s), depending on FMCW LiDAR system specifications (e.g., vertical and horizontal angular resolution, point rate (fast axis), frame rate). In comparison, the total estimated 2D steering time in an equivalent single beam transmitter stage with a total number of emitters of 512 X 256 = 131072 activated sequentially to support the 2D steering in combination with a lens (no external mirror, neither wavelength tenability) is 1.31 s.

In an implementation, wavelength tunability (AXo, AXi ) is applied to steer multi beams along the second axis in the multi-beam transmitter stage 200.

FIG. 3 is an illustration of an extension of a multi-beam transmitter stage for a light detection and ranging (LiDAR) system, in accordance with an embodiment of the present disclosure. FIG. 3 is described in conjunction with elements from FIGs. 1, and 2. With reference to FIG. 3 there is shown an illustration of an extension of a multi-beam transmitter stage 300 for a light detection and ranging (LiDAR) system. The extension of the multi-beam transmitter stage 300 includes a plurality of continuous wave lasers 302A-302Z, a plurality of optical taps, 304A-304Z, a plurality of binary splitters 306A-306Z, a plurality of booster semiconductor optical amplifiers 308A1, 308A2, 308B1, 308B2,... ,3O8Z1, 308Z2, and a plurality of one-dimensional optical switching matrices 310A1, 310A2, 310B1, 310B2, ... , 310Z1, and 310Z2

In an implementation, the extension of the multi-beam transmitter stage 100 of FIG.1 is obtained through parallelization and via wavelength multiplexing technique as shown in FIG. 3. The principle of operation of the multi -beam transmitter stage 300 is the same as that of the multi-beam transmitter stage 100 of FIG.1. However, there is a small difference in the multi-beam transmitter stage 300 that a total field of view (FoV) in an arbitrary direction (e.g., in a second axis or Y-axis) is also segmented by wavelength. In the example, s _y refers to the plurality of optical switching matrices based on a binary splitter tree and also indicates the separation along the second axis due to the optical switching matrix component. This determines the scanning mirror to steer a FoV of greater than F/nMB (i.e., FoV > F/HMB), to avoid black zones between the adjacent transmitter stages from the multi-beam transmitter stages that are shown in FIG. 3. Further, the excess of FoV can be estimated by considering the effective length of Ldev.Y + s _y in a certain scanning angle. Moreover, depending on dimensions of the multi -beam transmitter stage 100 (i.e., the main unit) and system specification, multiple combinations of lens and mirror (e.g., up to Z combinations) can be used to support steering along the second axis and the first axis.

In an implementation, the multi-beam transmitter stage 300 includes Z multi-beam transmitter stages (e.g., the multi-beam transmitter stage of FIG. 1). Each multi-beam transmitter stage generates M multi beams at each sequential activation of the N ^th element of the OSM. In addition, for a total number of N elements of the OSM, the total number of emitters in the Z ¹¹¹ multi-beam transmitter stage (main unit) is MXN. The Z multi-beam transmitter stages are configured and synchronized to operate in parallel, therefore the number of multi -beams at each sequential activation of the N ^th element of the OSMs is equal to MXZ. Therefore, a total number of MXNXZ emitters of the multi -beam transmitter stage 300 are focusing grating couplers.

FIG. 4A is a schematic illustration of die-to-wafer (D2W) bonding for a continuous wave laser, in accordance with an embodiment of the present disclosure. FIG. 4A is described in conjunction with elements from FIGs. 1, 2, and 3. With reference to FIG. 4A there is shown a schematic illustration 400A of die-to-wafer (D2W) bonding for the continuous wave laser 102 (of FIG. 1). There is further shown a silicon photonics layer 402, semiconductor dies 404, and semiconductor layers 406.

The silicon photonics layer 402 is a semiconductor layer. Further, the semiconductor dies 404 may also be referred to as dies made of semiconductor material. In an example, the semiconductor dies 404 are based on indium phosphide (InP). Moreover, the semiconductor layers 406 are EPI-ready semiconductor layers.

In an implementation, the die-to-wafer (D2W) bonding represents that each of the semiconductor dies 404 is bonded in parallel to the silicon photonics layer 402 before removal of a semiconductor substrate. As shown in FIG. 4A, initially, each of the semiconductor dies, such as the semiconductor dies 404 that includes the semiconductor substrate is bonded to the silicon photonics layer 402 before removal of the semiconductor substrate. Moreover, after removal of the semiconductor substrate, there exist only the semiconductor layers 406 (or epitaxial-ready layers) on the silicon photonics layer 402 (i.e., on the device wafer).

In accordance with an embodiment, the semiconductor dies 404 are bonded to the silicon photonics layer 402 in parallel, then partially removed so that only EPI-ready semiconductor layers 406 remain on the silicon photonic layer (or a wafer). Therefore, the semiconductor layers 406 are patterned and processed to generate the active semiconductor components. Each of the active semiconductor components are formed after removal of a semiconductor substrate from the semiconductor die 404, and each of the semiconductor dies 404 are bonded to the silicon photonics layer 402 in parallel before removal of the semiconductor substrates.

In accordance with an embodiment, each semiconductor die is an indium phosphide die. Due to the presence of indium phosphide die, the semiconductor dies 404 can be used to produce efficient lasers, amplifiers and modulators in the wavelength range for the continuous wave laser 102 (of FIG. 1).

There exists a heterogeneous integration of die-to-wafer (D2W) bonding, such as bonding of the semiconductor die 404 over the silicon photonics layer 402. In an example, plasma activation and bonding process are used to bond the semiconductor die 404 that are transferred in parallel to the silicon photonics layer 402 (or wafer) as shown in the FIG. 4A.

FIG. 4B is a cross-sectional view of an active component for lasing and amplification functionalities on chip, in accordance with an embodiment of the present disclosure. FIG. 4B is described in conjunction with elements from FIGs. 1, 2, 3 and 4A. With reference to FIG. 4B there is shown a cross-sectional view of an active component 400B that includes the silicon photonics layer 402, silicon photonic waveguides 408, a doped semiconductor layer 410, and a semiconductor active layer stack (or a semiconductor active component) 412. The doped semiconductor layer 410 and the semiconductor active layer stack 412 result from the processing and patterning of the EPI-ready semiconductor layers 406, for each semiconductor active component.

The active component 400B is used for lasing and amplification functionalities on chip, such as used in the continuous wave laser 102 (of FIG. 1). In an example, the active component 400B corresponds to a semiconductor optical amplifier (SOA), a reflective semiconductor optical amplifier (RSOA), and the like.

The silicon photonics layer 402 is a semiconductor layer underneath the doped semiconductor layer 410 and the semiconductor active layer stack 412. The silicon photonic waveguides embedded 408 represents a silicon photonic waveguide layer. In an example, the silicon photonic waveguides 408 is used for coupling light from the silicon photonics layer 402 to the semiconductor active layer stack 412 (or the active semiconductor component) and vice-versa.

The active component 400B, comprises the plurality of active semiconductor components, such as the semiconductor active layer stack 412 and the doped semiconductor layer 410 on the silicon photonics layer 402. In an example, the active component 400B is configured to produce laser beams through the plurality of active semiconductor components that are bonded directly on the silicon photonics layer 402.

In accordance with an embodiment, the silicon photonics layer 402 includes at least one external cavity based on silicon photonics waveguides, and the plurality of active semiconductor components on the plurality of semiconductor substrates are III-V active components including at least one reflective semiconductor optical amplifier (RSOA), and at least one booster semiconductor optical amplifier (SOA). Due to the presence of at least one external cavity, and the III-V active components of the active semiconductor components, there exists an evanescent coupling (or adiabatic taper) through a properly designed and manufactured silicon photonics waveguide 408 with a coupling loss of less than one decibel (i.e., < IdB). In addition, at least one reflective semiconductor optical amplifier (RSOA), and at least one booster semiconductor optical amplifier (SOA) is configured to amplify the laser beam signal of the continuous wave laser 102 of FIG. 1.

In accordance with an embodiment, the active layer stack 412 and the doped semiconductor layer 410 constitutes a distributed Bragg reflector (DBR) laser evanescently coupled to the silicon photonic layer through a properly designed and manufactured silicon photonic waveguide 408. In addition, at least one booster semiconductor optical amplifier (SOA) is configured to amplify the laser beam signal of the continuous wave laser 102 of FIG. 1.

FIG. 5 is a schematic illustration of a frequency modulated continuous wave (FMCW) light detection and ranging (LiDAR) system, in accordance with an embodiment of the present disclosure. FIG. 5 is described in conjunction with elements fromFIGs. 1, 2, 3, 4A, 4B. With reference to FIG. 5, there is shown a schematic illustration of a frequency modulated continuous wave (FMCW) LiDAR system 500. There is further shown a two-dimensional detector array 502, a coherent detector pixel unit 504 that includes a semiconductor layer 506, a silicon photonics layer 508, and one or more integrated photodetectors 510. There is further shown a receiver optics 512, a frame 514 and the multi-beam transmitter stage 100.

The FMCW LiDAR system 500 is used in remote sensing for the measurement of an almost precise distance and velocity of an object on the earth’s surface. The FMCW LiDAR system 500 includes the multi-beam transmitter stage 100, and the two-dimensional detector array 502. The two-dimensional detector array 502 acts as a detector (or a receiver stage) for the FMCW LiDAR system 500.

The coherent detector pixel unit 504 includes the semiconductor layer 506, the silicon photonics layer 508, and one or more integrated photodetectors 510. The semiconductor layer 506, and the silicon photonics layer 508 are layers of semiconductor material, and each integrated photodetector from one or more integrated photodetectors 510 corresponds to photosensors that are sensitive to the laser beam. The receiver optics 512 is an optical element, and the frame 514 corresponds to an area that is illuminated and therefore imaged by the FMCW LiDAR system 500.

The two-dimensional detector array 502 for a frequency modulated continuous wave (FMCW) LiDAR system, comprises a plurality of coherent detector pixel units, each comprising the silicon photonics layer 508 with one or more integrated photodetectors 510 bonded to the semiconductor layer 506. The two-dimensional detector array 502 is realized via a three-dimensional (3D) wafer bonding technique. The two-dimensional detector array 502 includes the plurality of coherent detector pixel units, such as the coherent detector pixel unit 504. Firstly, the coherent detector pixel unit 504 includes the semiconductor layer 506 that acts as a substrate for the coherent detector pixel unit 504 (or coherent heterodyne pixel). Thereafter, the silicon photonics layer 508 is bonded on the semiconductor layer 506. The coherent detector pixel unit 504 further includes one or more integrated photodetectors 510 that are arranged over the silicon photonics layer 508. In an example, there are four integrated photodetectors that are arranged over the silicon photonics layer 508. One or more integrated photodetectors 510 are beneficial to detect a laser beam received from the multibeam transmitter stage 100. In an example, one or more integrated photodetectors 510 are germanium-balanced photodetectors that are monohthically integrated on the silicon photonics layer 508. The plurality of coherent detector pixel units is beneficial for improvement in pixel density with the same footprint (electronics best placed ‘behind’). In an example, pixel density can be improved at least two times as compared to the conventional approach, for example the monolithic integration approach. In addition, the plurality of coherent detector pixel units can exhibit parasitic capacitance of the order of a few femtofarad (fF), for example ~3fF, due to the tight integration of the silicon photonics layer 508 with the CMOS digital layer, hence the semiconductor layer 506.

In accordance with an embodiment, the silicon photonics layer 508 is formed on a silicon substrate, inverted, and bonded to the semiconductor layer 506 with an intermediate bonding layer. Firstly, the silicon photonics layer 508 is formed on the silicon substrate, which is further inverted, such as the silicon photonics layer 508 acts as a bottom layer, and the silicon substrate is on the top surface. After that, the silicon photonics layer 508 and the semiconductor layer 506 are bonded through an intermediate bonding layer, for example an oxide bonding layer. As a result, semiconductor layer 506 is bonded to the silicon photonics layer 508, as shown in FIG. 5.

In accordance with an embodiment, the silicon substrate is removed after bonding with the semiconductor layer 506. The silicon substrate that is used to form the silicon photonics layer 508 is removed (e.g., via etching) to form the plurality of coherent detector pixel units on the silicon photonics layer 508.

In accordance with an embodiment, each coherent detector pixel unit comprises two grating couplers, a first grating coupler configured to detect transverse electric polarised light, and a second grating coupler configured to detect transverse magnetic polarised light. The first grating coupler and the second grating coupler are used to detect FMCW modulated transverse electric (TE) or transverse magnetic (TM) polarized light. In an example, the first grating coupler is used to detect the FMCW modulated transverse electric polarized light, while the second grating coupler is used to detect the FMCW modulated transverse magnetic polarized light to simplify the receiver optics 512.

In accordance with an embodiment, each pixel unit further comprises two directional couplers, each associated with two integrated photodetectors, also named as balanced photodetectors. In an example, the coherent detector pixel unit 504 includes two directional couplers and four integrated photodetectors. Moreover, each directional coupler is associated with two integrated photodetectors, such as a first directional coupler is associated with two integrated photodetectors, and a second directional coupler is also associated with another two integrated photodetectors. In an example, each directional coupler is a waveguide-based directional coupler, and each directional coupler includes one local oscillator signal (e.g., LO in the FIG. 5) and one focusing grating coupler coupled light as input signals.

In accordance with an embodiment, the semiconductor layer 506 is a complementary metal oxide semiconductor (CMOS) layer. The semiconductor layer 506 can be processed with different dedicated processes compared to the silicon photonics layer 508 which typically requires less advanced technology nodes. As the semiconductor layer 506 is the CMOS layer (e.g., CMOS nodes), thus the semiconductor layer 506 is beneficial for power consumption and efficient electronics, and to complement the SiNSOI platform for the silicon photonics layer 508 with a CMOS digital layer.

In accordance with an embodiment, the semiconductor layer 506 includes an amplifier, an analog-to-digital converter, and a CMOS driving circuitry. In an example, the semiconductor layer 506 is fabricated on a specific technology node (e.g., 28 nm, 40 nm, 90 nm). Moreover, the semiconductor layer 506 includes the amplifier, such as a trans-impedance amplifier (TIA) that is with the two-directional couplers that are associated with one or more integrated photodetectors (or germanium balanced photodetectors). The semiconductor layer 506 further includes the analog-to-digital converter to convert the amplified signal and the CMOS driving circuitry for further analog-to-digital functionalities with reduced power consumption. In an example, the semiconductor layer 506 also includes metal traces for radio-frequency (RF) output signal processing, analog-to-digital converters (ADCs), digital driver circuits, Current Mode Logic (CML) drivers.

In accordance with an embodiment, each of the pixel units is a heterodyne detector pixel unit configured to receive a local oscillator signal. In an implementation, the two-dimensional detector array 502 is based on a focal plane array of the heterodyne detector pixel unit (or a heterodyne coherent pixel) in combination with receiver optics 512, to receive the local oscillator signal. In an example, the heterodyne detector pixel unit is heterogeneously manufactured by a three-dimensional wafer bonding approach. In accordance with an embodiment, the local oscillator signal is provided by the multi-beam transmitter stage 100 of the FMCW LiDAR system 500. The local oscillator signal is coupled to two-dimensional detector array 502 by means of free-space optics. In an example, the local oscillator signal is received by the two-dimensional detector array 502 at a fixed wavelength Xo or, as an extension of the multi-beam transmitter stage 100. In another example, the two-dimensional detector array 502 receives a number of local oscillator signals at the fixed wavelengths (e.g., Xo, Xi,... , Xz). Alternatively, multiple receiver (RX) chips receive a number of local oscillator signals at the fixed wavelengths (Xo, Xi,... , X _z ), respectively. In yet another example, the two-dimensional detector array 502 receives at least one local oscillator signal in a wavelength range (e.g., AXo) or, as an extension of the multibeam transmitter stage 100. In another example, the two-dimensional detector array 502 receives a number of local oscillator signals at the wavelength ranges (e.g., AXo, AXi,... , AXz). Alternatively, multiple receiver (RX) chips receive a number of local oscillator signals at the wavelength ranges (AXo, AXi,... , AX _Z ), respectively.

In accordance with an embodiment, the two-dimensional detector array 502 further comprises a switching optical matrix configured to direct the local oscillator signal to one or more designated pixel units of the two-dimensional detector array 502. The switching optical matrix is configured to direct (or rout) the local oscillator signal to a specific area of the two- dimensional detector array 502, and a reflected signal from a target (e.g., the multi-beam transmitter stage 100) is expected to illuminate.

In accordance with an embodiment, the switching optical matrix is synchronised with the multi-beam transmitter stage 100 of the FMCW LiDAR system 500. In an implementation, an illuminated area on the two-dimensional detector array 502 depends on the activated emitter array (e.g., the emitter array 104) of the multi -beam transmitter stage 100. Thus, synchronization between the multi-beam transmitter stage 100, and the switching optical matrix (or the two-dimensional detector array 502) is required for proper operation of the FMCW LiDAR system 500. In an example, if the multi-beam transmitter stage 100 is based on quasi-solid state system configuration, then the two grating couplers of each coherent detector pixel unit, and the switching optical matrix operate at only FMCW carrier wavelength (e.g., X). In another example, if the multi-beam transmitter stage 100 is based on solid-state system configuration, then the two grating couplers of each coherent detector pixel unit, and the switching optical matrix operate within the FMCW carrier wavelength range (e.g., AX).

The two-dimensional detector array 502 is used for the frequency modulated continuous wave (FMCW) LiDAR system that enables, dedicated, and differentiated process via the silicon photonics (SiPh) layer 508, and the semiconductor layer 506 (i.e., CMOS wafers), respectively. The two-dimensional detector array 502 is based on a dedicated receiver chip that includes the plurality of coherent (or heterodyne coherent) detector pixel units, such as the coherent detector pixel unit 504 that are manufactured by the three-dimensional wafer bonding technique (e.g., electronics-photonics convergence). Beneficially, as compared to the conventional detector array, a readout capacity and pixel density of the two-dimensional detector array 502 is increased (e.g., by a factor 2). Moreover, the two-dimensional detector array 502 is based on a simplification of system assembly by including the TE & TM polarization-dependent grating coupler receivers, which results in the possible removal of polarization control devices at the two-dimensional detector array 502 (or RX stage).

FIG. 6 is a block diagram of a light detection and ranging (LiDAR) system, in accordance with an embodiment of the present disclosure. FIG. 6 is described in conjunction with elements from FIGs. 1, 2, 3, 4A, 4B, and 5. With reference to FIG. 6, there is shown a schematic illustration of a LiDAR system 602 that includes the multi-beam transmitter stage 100, and the two-dimensional detector array 502. There is further shown the continuous wave laser 102.

The LiDAR system 602 includes the multi-beam transmitter stage 100, and the multi-beam transmitter stage 100 includes the continuous wave laser 102. The LiDAR system 602 further includes the two-dimensional detector array 502. The LiDAR system 602 archives all the advantages and technical effects of the multi-beam transmitter stage 100, the continuous wave laser 102, and the two-dimensional detector array 502.

Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as "including", "comprising", "incorporating", "have", "is" used to describe and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or to exclude the incorporation of features from other embodiments. The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". It is appreciated that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination or as suitable in any other described embodiment of the disclosure.