Row-column scanning type silicon-based focal plane array transmitting device

Abstract

The row-column scanning type silicon-based focal plane array transmitting device comprises an input grating coupler, an output grating coupler, an optical switch network, a plurality of power dividers, a plurality of main waveguides and an off-chip lens, the input grating coupler is used for coupling light generated by the light source to the optical switch network, the optical switch network comprises a plurality of optical switch stages, each optical switch stage comprises one or more optical switches, and the optical switches in the optical switch network are distributed and connected in a tree shape; the input light is transmitted to the corresponding main waveguides by controlling the light output ports of the optical switches to be conducted or not conducted, the main waveguides transmit the light to the power dividers, the power dividers are connected with the output grating coupler, the output optical coupler radiates the light to a free space, and scanning of the light in the arrangement direction of the power dividers is achieved. The off-chip lens refracts the light entering the free space, so that the light deflects, and scanning of the light in the direction perpendicular to the arrangement direction of the power dividers is achieved.

Description

Technical Field

[0001] The invention belongs to the field of optical radar and optical waveguide integrated devices, and in particular relates to a row-column scanning silicon-based focal plane array transmitting device. Background Art

[0002] With the rapid development of intelligent unmanned systems, LiDAR has been widely used as a key sensor in the fields of autonomous driving, robot navigation and high-precision mapping. At present, mechanical LiDAR and LiDAR based on micro-electromechanical systems (MEMS) with relatively mature technology have achieved remarkable results in practical applications, but they have problems such as poor reliability, large size and limited life. To overcome these problems, photon integrated all-solid-state LiDAR technology came into being. It realizes beam control without mechanical moving parts through integrated optical technology, and has the advantages of high reliability, low power consumption and easy miniaturization. At present, the research on photon integrated LiDAR mainly focuses on two technical routes: optical phased array (OPA) and focal plane switch array (FPSA). Among them, the research on OPA was carried out earlier, and the light wave phase control was used to realize beam control and scanning. Its basic principle is to change the propagation direction of the light beam by adjusting the phase distribution of each optical unit in the array and using the interference effect. However, OPA technology faces many challenges in practical applications, such as low optical transmittance, serious sidelobe effect, high control complexity and limited dynamic range. In contrast, FPSA provides a simplified beam control method that works similarly to a camera, using lenses to establish a precise correspondence between the output beam direction and the position of the array antenna unit. In the FPSA system, each output waveguide of the optical switch network is individually connected to and controls an antenna unit, and its phase shifter only needs two states, "conducting" and "off", to achieve beam control. By switching different transmitting units in the array, FPSA can achieve directional scanning of the beam without mechanical movement, and avoid sidelobe effects, improving the far-field beam quality and system signal-to-noise ratio.

[0003] Although FPSA has shown significant advantages in regulation efficiency and control complexity, it still faces certain challenges when expanding the array. As the array scale increases, the number of output waveguides and optical switches increases exponentially, which will significantly increase the complexity of optical path design. In addition, the need for independent control also significantly increases the circuit drive power consumption and manufacturing difficulty, thereby limiting the scalability and system integration of the array. Summary of the invention

[0004] In order to solve the problem of complex optical path design of focal plane switch array in the prior art, a row-column scanning silicon-based focal plane array transmitting device is proposed;

[0005] A row-column scanning silicon-based focal plane array transmitting device comprises: an input grating coupler, an optical switch network, an off-chip lens, a plurality of power dividers, a plurality of main waveguides and a plurality of output grating couplers;

[0006] The input grating coupler is used to receive light emitted by the light source and input the light into the optical switch network;

[0007] The optical switch network includes a plurality of optical switch stages connected in sequence, each optical switch stage includes one or more optical switches, and the output of each optical switch of the last optical switch stage is simultaneously connected to two main waveguides; the optical switch network is used to transmit the input light to the corresponding main waveguide through an optical switch in each optical switch stage; each main waveguide is simultaneously connected to N power dividers arranged in sequence, and each main waveguide transmits light to the connected power divider; each power divider is connected to an output grating coupler, each power divider transmits light to the connected output grating coupler, and each output grating coupler emits light into free space;

[0008] The off-chip lens is used to refract the light incident into free space and deflect the light.

[0009] Beneficial Effects

[0010] The row-column scanning silicon-based focal plane array transmitting device of the present application uses a fiber optic as a light source, and an input grating coupler couples the light generated by the light source to an optical switch network. The optical switch network includes multiple optical switch levels, each optical switch level includes one or more optical switches, and multiple optical switches in the optical switch network are connected in a tree-like distribution. The optical switch network is used to transmit the input light to the corresponding main waveguide through an optical switch in each optical switch level. The main waveguide transmits the light to multiple power dividers. The power dividers are connected to the output grating coupler, and the output optical coupler radiates the light to the free space to achieve the scanning of the light in the arrangement direction of the multiple power dividers; the off-chip lens refracts the light injected into the free space to deflect the light, so as to achieve the scanning of the light in the direction perpendicular to the arrangement direction of the multiple power dividers. The device can control the number of switches in the optical switch network according to actual needs, and the optical path design is simple and the integration is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic structural diagram of a row-column scanning silicon-based focal plane array transmitting device according to a specific embodiment of the present application;

[0012] Figure 2 This is a schematic diagram of the optical switch structure of a specific embodiment of the present application;

[0013] Figure 3 This is a graph showing the spectral response test results of a single optical switch according to a specific embodiment of the present application;

[0014] Figure 4The transmission efficiency and total transmission efficiency of the two ports of the optical switch under each power allocation ratio in the specific implementation mode of the present application;

[0015] Figure 5 This is a measured far-field distribution diagram of a specific implementation method of this application. DETAILED DESCRIPTION

[0016] The following will be combined with the attached embodiment of the present invention Figure 1 To Attachment Figure 5 , illustrate this implementation mode, and clearly and completely describe the technical solutions in the embodiments of the present invention:

[0017] A row-column scanning silicon-based focal plane array transmitting device comprises an input grating coupler, an optical switch network, an off-chip lens, a plurality of power dividers, a plurality of main waveguides and a plurality of output grating couplers;

[0018] The input grating coupler is used to receive light emitted by the light source and input the light into the optical switch network;

[0019] The optical switch network includes a plurality of optical switch stages connected in sequence, each optical switch stage includes one or more optical switches, and the output of each optical switch of the last optical switch stage is simultaneously connected to two main waveguides; the optical switch network is used to transmit the input light to the corresponding main waveguide through an optical switch in each optical switch stage; each main waveguide is simultaneously connected to a plurality of power dividers arranged in sequence, and each main waveguide transmits light to the connected power divider; each power divider is connected to an output grating coupler, each power divider transmits light to the connected output grating coupler, and each output grating coupler emits light into free space;

[0020] The off-chip lens is used to refract the light incident into free space and deflect the light.

[0021] Specifically, Figure 1 As shown, the light source is injected into the input grating coupler and coupled to the waveguide space; the light entering the waveguide space first selects a path through the optical switch network, and the connection mode of the optical switches adopts a tree-like distribution; the control ends of all optical switches are independent of each other, and the light enters the optical switch network and passes through different optical switches in each optical switch level, and the transmission paths are different. The selection between different paths can realize scanning in the y direction; after the path selection is completed, the light entering the main waveguide passes through N different arbitrary splitting ratio power dividers, and is output to the transmission port with the same energy through the output grating coupler to radiate to the free space; finally, the light radiated to the free space is deflected at different angles after passing through the off-chip lens to realize scanning in the x direction.

[0022] Furthermore, the optical switch network includes n optical switch stages connected in sequence, and the i-th optical switch stage includes 2 i-1optical switches, the output of the mth optical switch of the jth optical switch level is simultaneously connected to the inputs of the 2m-1th optical switch and the 2mth optical switch of the j+1th optical switch level, and each optical switch output of the nth optical switch level is simultaneously connected to two main waveguides; the optical switch is used to transmit the received light to the two optical switches or two main waveguides of the next level; m and n are both integers; i∈[1,2,3,···,n], j∈[1,2,3,···,n-1].

[0023] Furthermore, each main waveguide is simultaneously connected to a plurality of power dividers arranged in sequence, including: the light splitting ratio of the kth power divider among the N power dividers connected to the same main waveguide is

[0024] Specifically, the power divider is designed and optimized according to different splitting ratios, and its input end is connected to the main waveguide corresponding to the output port of the optical switch of the last stage. The output end is connected to the output grating coupler. For N power dividers connected to the same main waveguide, the splitting ratios of the power divider from the side close to the main waveguide to the side far from the main waveguide are 1 / N, 1 / (N-1), 1 / (N-2)...1 respectively. In this way, the simultaneous emission of N grating couplers can be achieved, and the emission energy is the same. Combined with the space division multiplexing technology, scanning in the x direction can be achieved.

[0025] Further, each optical switch includes an input multimode interferometer, a bent connecting waveguide No. 1, a bent connecting waveguide No. 2, a phase shifter No. 1, a phase shifter No. 2, a bent connecting waveguide No. 3, a bent connecting waveguide No. 4, a TiN heater No. 1, a TiN heater No. 2, and an output multimode interferometer;

[0026] One end of the input multimode interferometer is connected to the output of the input grating coupler or the previous optical switch, and the other end of the input multimode interferometer is simultaneously connected to one end of the No. 1 curved connection waveguide and one end of the No. 2 curved connection waveguide. The input multimode interferometer is used to transmit the light output by the input grating coupler or the previous optical switch to the No. 1 curved connection waveguide and the No. 2 curved connection waveguide;

[0027] The other end of the No. 1 curved connecting waveguide and the other end of the No. 2 curved connecting waveguide are connected to one end of the No. 1 phase shifter and one end of the No. 2 phase shifter respectively. The No. 1 curved connecting waveguide is used to transmit the received light to the No. 1 phase shifter, and the No. 2 curved connecting waveguide is used to transmit the received light to the No. 2 phase shifter;

[0028] A TiN heater No. 1 is arranged above phase shifter No. 1, and a TiN heater No. 2 is arranged above phase shifter No. 2. The other end of phase shifter No. 1 and the other end of phase shifter No. 2 are connected to one end of curved connecting waveguide No. 3 and one end of curved connecting waveguide No. 4 respectively; TiN heater No. 1 and TiN heater No. 2 are used to change the phase difference between phase shifter No. 1 and phase shifter No. 2 by changing the temperature, and control phase shifter No. 1 to transmit light to curved connecting waveguide No. 3 or phase shifter No. 2 to transmit light to curved connecting waveguide No. 4 according to the phase difference;

[0029] The other end of the No. 3 curved connecting waveguide and the other end of the No. 4 curved connecting waveguide are simultaneously connected to one end of the output multimode interferometer. The No. 3 curved connecting waveguide and the No. 4 curved connecting waveguide are used to transmit the received light to the output multimode interferometer. The other end of the output multimode interferometer includes port No. 1 and port No. 2. Port No. 1 and port No. 2 are respectively connected to two optical switches or two main waveguides of the next stage. The output multimode interferometer is used to transmit the received light to an optical switch of the next stage through port No. 1, or to an optical switch of the next stage through port No. 2; the output multimode interferometer is also used to transmit the received light to the main waveguide through port No. 1 or to the main waveguide through port No. 2.

[0030] Specifically, the input multimode interferometer requires 1×2 working ports, and the output multimode interferometer requires 2×2 working ports.

[0031] Furthermore, phase shifter No. 1 and phase shifter No. 2 are multimode waveguides with a width of 2 microns and a length of 50 microns.

[0032] Specifically, Figure 2 The figure shows a single 1×2 Mach-Zehnder optical switch design, in which the length, width and output / input spacing of the multimode interference zone have been obtained through theoretical calculation and genetic algorithm optimization. In order to further improve the coupling efficiency and reduce the phase error, the width of the input and output port parts is optimized by genetic algorithm, and the quarter circle with a radius of 8 microns is optimized by topology optimization. For the phase shifter, we chose to use a multimode waveguide with a width of 2 microns and a length of 50 microns, which is covered with a TiN heater for thermal tuning of the optical switch.

[0033] like Figure 3 The figure shows the transmission efficiency and total transmission efficiency of the two ports of the power splitter at each power distribution ratio. The power splitters at all splitting ratios are designed by topology optimization. The design structure robustness and total transmission efficiency are better than those based on traditional directional couplers and multimode interferometers. The splitting ratio of each device meets the target design requirements, and the overall transmission efficiency reaches more than 98%.

[0034] like Figure 4The figure shows the spectral response test results of a single 1×2 Mach-Zehnder optical switch. The test results show that when the central wavelength is 1550nm, the insertion loss of a single optical switch in the "on" state is only 0.1dB, which proves its efficient transmission performance; the insertion loss in the "off" state reaches -30dB, indicating that its extinction ratio reaches 30.1dB, which also proves its excellent switching capability.

[0035] Furthermore, a row-column scanning silicon-based focal plane array transmitting device is manufactured based on a silicon platform on an insulator; the silicon platform on an insulator comprises, from top to bottom, a silicon base layer, a silicon dioxide buffer layer, a silicon waveguide layer and a silicon dioxide cladding layer; the silicon base layer is 2 mm thick, the silicon dioxide buffer layer is 2 μm thick, the silicon waveguide layer is 220 nm thick, and the silicon dioxide cladding layer is 2 μm thick.

[0036] Furthermore, the input grating coupler and the output grating coupler are grating couplers with optimized coupling efficiency.

[0037] Specifically, the input grating coupler is used to couple the fiber mode to the waveguide mode, and its coupling efficiency is mainly optimized. The output grating coupler is used to couple the waveguide mode to the free space mode. In addition to optimizing the coupling efficiency, it is also necessary to optimize the mode field matching degree between the output light field and the standard Gaussian beam. Such optimization can ensure the far-field quality of the output grating coupler, so that it can be directly combined with an off-chip lens to achieve a certain angle of deflection. Specific embodiment:

[0039] like Figure 1As shown, a row-column scanning silicon-based focal plane array transmitting device is shown, in which an incident grating coupler receives incident light from a fiber light source and couples it into an optical switch network. The optical switch network includes three optical switch stages connected in sequence, wherein the first optical switch stage includes one optical switch, the second optical switch stage includes two optical switches, and the third optical switch stage includes four optical switches. The four optical switches of the third optical switch stage are respectively connected to two main waveguides, each main waveguide is respectively connected to six power dividers, and each power divider is connected to an output grating coupler; the optical switch of the first optical switch stage receives light coupled by the incident grating coupler, and the optical switch of the first optical switch stage transmits the light to the first optical switch of the second optical switch stage; The first optical switch transmits light to the first optical switch of the third optical switch level. The first optical switch of the third optical switch level transmits light to a main optical waveguide connected to it. The main optical waveguide transmits light to six power dividers connected to it. The splitting ratios of the six power dividers are 1 / 6, 1 / 5, 1 / 4, 1 / 3, 1 / 2 and 1 respectively. The mode field light transmitted by the power divider is radiated to the free space through the output grating coupler array to realize scanning in the y direction. By controlling the conduction or non-conduction of the optical output port of the optical switch, the optical switch network transmits light to different main waveguides to realize scanning in the x direction. The radiated optical signal is collimated by an off-chip aspheric lens and deflected at different angles to form a two-dimensional beam scan. Figure 5 As shown, each main waveguide is connected to four power dividers respectively, and the measured far-field distribution diagram of the row-column scanning silicon-based focal plane array transmitting device at four times t1, t2, t3 and t4 respectively.

[0040] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A row-column scanning silicon-based focal plane array transmitting device, characterized in that: It includes an input grating coupler, an optical switch network, an off-chip lens, a plurality of power dividers, a plurality of main waveguides and a plurality of output grating couplers; The input grating coupler is used to receive light emitted by the light source and input the light into the optical switch network; The optical switch network includes a plurality of optical switch stages connected in sequence, each optical switch stage includes one or more optical switches, and the output of each optical switch of the last optical switch stage is simultaneously connected to two main waveguides; the optical switch network is used to transmit the input light to the corresponding main waveguide through an optical switch in each optical switch stage; each main waveguide is simultaneously connected to a plurality of power dividers arranged in sequence, and each main waveguide transmits light to the connected power divider; each power divider is connected to an output grating coupler, each power divider transmits light to the connected output grating coupler, and each output grating coupler emits light into free space; The off-chip lens is used to refract the light incident into free space and deflect the light.

2. A row-column scanning silicon-based focal plane array transmitting device according to claim 1, characterized in that: The optical switch network includes n optical switch stages connected in sequence, and the i-th optical switch stage includes 2 i-1 optical switches, the output of the mth optical switch of the jth optical switch level is simultaneously connected to the inputs of the 2m-1th optical switch and the 2mth optical switch of the j+1th optical switch level, and each optical switch output of the nth optical switch level is simultaneously connected to two main waveguides; the optical switch is used to transmit the received light to the two optical switches or two main waveguides of the next level; m and n are both integers; i∈[1,2,3,···,n], j∈[1,2,3,···,n-1].

3. The row-column scanning silicon-based focal plane array transmitting device according to claim 2, characterized in that: Each main waveguide is simultaneously connected to a plurality of power dividers arranged in sequence, including: the splitting ratio of the kth power divider among the N power dividers connected to the same main waveguide is N is an integer.

4. The row-column scanning silicon-based focal plane array transmitting device according to claim 1, characterized in that: Each optical switch includes an input multimode interferometer, a bent connecting waveguide No. 1, a bent connecting waveguide No. 2, a phase shifter No. 1, a phase shifter No. 2, a bent connecting waveguide No. 3, a bent connecting waveguide No. 4, a TiN heater No. 1, a TiN heater No. 2, and an output multimode interferometer; One end of the input multimode interferometer is connected to the output of the input grating coupler or the previous optical switch, and the other end of the input multimode interferometer is simultaneously connected to one end of the No. 1 curved connection waveguide and one end of the No. 2 curved connection waveguide. The input multimode interferometer is used to transmit the light output by the input grating coupler or the previous optical switch to the No. 1 curved connection waveguide and the No. 2 curved connection waveguide; The other end of the No. 1 curved connecting waveguide and the other end of the No. 2 curved connecting waveguide are connected to one end of the No. 1 phase shifter and one end of the No. 2 phase shifter respectively. The No. 1 curved connecting waveguide is used to transmit the received light to the No. 1 phase shifter, and the No. 2 curved connecting waveguide is used to transmit the received light to the No. 2 phase shifter; A TiN heater No. 1 is arranged above phase shifter No. 1, and a TiN heater No. 2 is arranged above phase shifter No.

2. The other end of phase shifter No. 1 and the other end of phase shifter No. 2 are connected to one end of curved connecting waveguide No. 3 and one end of curved connecting waveguide No. 4 respectively; TiN heater No. 1 and TiN heater No. 2 are used to change the phase difference between phase shifter No. 1 and phase shifter No. 2 by changing the temperature, and control phase shifter No. 1 to transmit light to curved connecting waveguide No. 3 or phase shifter No. 2 to transmit light to curved connecting waveguide No. 4 according to the phase difference; The other end of the No. 3 curved connecting waveguide and the other end of the No. 4 curved connecting waveguide are simultaneously connected to one end of the output multimode interferometer. The No. 3 curved connecting waveguide and the No. 4 curved connecting waveguide are used to transmit the received light to the output multimode interferometer. The other end of the output multimode interferometer includes port No. 1 and port No.

2. Port No. 1 and port No. 2 are respectively connected to two optical switches or two main waveguides of the next stage. The output multimode interferometer is used to transmit the received light to an optical switch of the next stage through port No. 1, or to an optical switch of the next stage through port No. 2; the output multimode interferometer is also used to transmit the received light to the main waveguide through port No. 1 or to the main waveguide through port No.

2.

5. The row-column scanning silicon-based focal plane array transmitting device according to claim 4, characterized in that: Phase shifter No. 1 and phase shifter No. 2 are multimode waveguides with a width of 2 microns and a length of 50 microns.

6. The row-column scanning silicon-based focal plane array transmitting device according to claim 1, characterized in that: The device is manufactured based on a silicon platform on an insulator; the silicon platform on an insulator comprises, from top to bottom, a silicon base layer, a silicon dioxide buffer layer, a silicon waveguide layer and a silicon dioxide cladding layer; the thickness of the silicon base layer is 2 mm, the thickness of the silicon dioxide buffer layer is 2 microns, the thickness of the silicon waveguide layer is 220 nanometers, and the thickness of the silicon dioxide cladding layer is 2 microns.

7. The row-column scanning silicon-based focal plane array transmitting device according to claim 1, characterized in that: The input grating coupler and the output grating coupler are grating couplers with optimized coupling efficiency.

8. The row-column scanning silicon-based focal plane array transmitting device according to claim 1, characterized in that: The light source is a fiber laser, which is used to generate light and inject the light into the input grating coupler.

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