A line and column scanning silicon-based focal plane array emitting device

Abstract

The present application discloses a line scanning silicon-based focal plane array transmitting device, which 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 couples light generated by a light source to the optical switch network; the optical switch network comprises a plurality of optical switch stages, each of which comprises one or more optical switches; the plurality of optical switches in the optical switch network are connected in a tree shape; the input light is transmitted to the corresponding main waveguide by controlling the conduction or non-conduction of the optical switch light output port; the main waveguide transmits the light to the plurality of power dividers; the power dividers are connected with the output grating coupler; the output grating coupler radiates the light to the free space, thereby realizing the scanning of the light in the arrangement direction of the plurality of power dividers; and the off-chip lens refracts the light entering the free space, thereby deflecting the light and realizing the scanning of the light in the direction perpendicular to the arrangement direction of the plurality of power dividers.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of optical radar and optical waveguide integrated devices, and particularly relates to a row-column scanning type silicon-based focal plane array transmitting device. BACKGROUND

[0002] With the rapid development of intelligent unmanned systems, laser radar as a key sensor has been widely used in automatic driving, robot navigation and high-precision mapping fields. At present, the mechanical optical radar and the optical radar based on micro-electro-mechanical system (MEMS) have achieved remarkable results in practical applications, but there are problems such as poor reliability, large volume and limited service life. In order to overcome these problems, photonic integrated all-solid-state LiDAR technology has emerged, which 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 of photonic integrated optical radar mainly focuses on two technical routes: optical phased array (OPA) and focal plane switch array (FPSA). The research of OPA is carried out earlier, which realizes beam control and scanning by adjusting the phase distribution of each optical unit in the array and changing the direction of light propagation by interference effect. However, OPA technology faces many challenges in practical application, such as low optical transmittance, serious sidelobe effect, high control complexity and limited dynamic range. In contrast, FPSA provides a simplified method of beam control, whose working principle is similar to that of a camera, which uses a lens to establish an accurate correspondence between the output beam direction and the array antenna element position. In the FPSA system, each output waveguide of the optical switch network is connected and controlled by a single antenna element, and the phase shifter only needs to be "on" and "off" to realize beam control. By switching different transmitting units in the array, FPSA can realize directional scanning of the light beam without mechanical movement, and avoid sidelobe effect, which improves the far-field beam quality and system signal-to-noise ratio.

[0003] Although FPSA has shown significant advantages in control efficiency and control complexity, it still faces certain challenges when the array is expanded. With the expansion of the array size, the number of output waveguides and optical switches increases exponentially, which significantly increases the complexity of optical path design. In addition, the need for independent control also significantly increases the power consumption and manufacturing difficulty of the circuit driving, thereby limiting the scalability and system integration of the array. SUMMARY

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

[0005] A line-by-line scanning silicon-based focal plane array emitting device, comprising: 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 for receiving light emitted by a light source and inputting the light into the optical switch network.

[0007] The optical switch network comprises a plurality of optical switch stages connected in sequence, each optical switch stage comprises one or more optical switches, and the output of each optical switch of the last optical switch stage is connected to two main waveguides at the same time; the optical switch network is used for transmitting the input light through one optical switch of each optical switch stage to the corresponding main waveguide; each main waveguide is connected to N power dividers arranged in sequence at the same time, and each main waveguide transmits light to the connected power divider; each power divider is connected to an output grating coupler, and 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 for refracting the light emitted into the free space to deflect the light.

[0009] Advantages

[0010] The line-by-line scanning silicon-based focal plane array emitting device of the present application uses a fiber optical device as a light source, an input grating coupler couples light generated by the light source to an optical switch network, the optical switch network comprises a plurality of optical switch stages, each optical switch stage comprises one or more optical switches, the plurality of optical switches in the optical switch network are distributed and connected in a tree shape, the optical switch network is used for transmitting the input light through one optical switch of each optical switch stage to the corresponding main waveguide, the main waveguide transmits light to a plurality of power dividers, the power dividers are connected to output grating couplers, the output grating couplers radiate light to free space, and the light is scanned in the arrangement direction of the plurality of power dividers; the off-chip lens refracts the light emitted into the free space to deflect the light, and the light is scanned in the direction perpendicular to the arrangement direction of the plurality of power dividers. The device can control the number of optical switches in the optical switch network according to actual needs, the optical path design is simple, and the integration degree is high. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 It is a structure schematic diagram of the line-by-line scanning silicon-based focal plane array emitting device of the embodiment of the present application.

[0012] Figure 2 It is a structure schematic diagram of the optical switch of the embodiment of the present application.

[0013] Figure 3 It is a spectral response test result diagram of a single optical switch of the 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 embodiment of this application;

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

[0016] The following is a combination of the embodiments of the present invention Figure 1 To the attached Figure 5 , illustrate this embodiment, 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 input from the light source and input the light into the optical switch network;

[0019] The optical switching network includes multiple optical switch stages connected in sequence, each optical switch stage including 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 input light to the corresponding main waveguide through an optical switch in each optical switch stage. Each main waveguide is simultaneously connected to multiple power splitters arranged in sequence, and each main waveguide transmits light to the connected power splitter. Each power splitter is connected to an output grating coupler, and each power splitter transmits light to the connected output grating coupler. Each output grating coupler emits light into free space.

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

[0021] Specifically, if Figure 1 As shown, the light source is injected into the input grating coupler and coupled into the waveguide space. The light entering the waveguide space first selects a path through the optical switch network, and the optical switches are connected in a tree-like manner. The control ends of all optical switches are independent of each other. After entering the optical switch network, the light passes through different optical switches in each optical switch level, and the transmission path is different. The selection between different paths can achieve 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 into free space. Finally, the light radiated into free space is deflected by different angles after passing through the off-chip lens to achieve scanning in the x direction.

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

[0023] Further, each main waveguide is connected to a plurality of power dividers arranged in sequence, comprising: the light splitting ratio of the kth power divider connected to the same main waveguide is

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

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

[0026] One end of the input multimode interferometer is connected to the input grating coupler or the output of the upper stage of the optical switch, and the other end of the input multimode interferometer is connected to one end of the No. 1 curved connection waveguide and one end of the No. 2 curved connection waveguide at the same time, and the input multimode interferometer is used for transmitting the light output by the input grating coupler or the upper stage of the 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 connection waveguide and the other end of the No. 2 curved connection waveguide are respectively connected to one end of the No. 1 phase shifter and one end of the No. 2 phase shifter, and the No. 1 curved connection waveguide is used for transmitting the received light to the No. 1 phase shifter, and the No. 2 curved connection waveguide is used for transmitting the received light to the No. 2 phase shifter;

[0028] 1st phase shifter is provided with a 1st TiN heater, a 2nd phase shifter is provided with a 2nd TiN heater, and the other ends of the 1st phase shifter and the 2nd phase shifter are connected with the other ends of the 3rd curved connecting waveguide and the 4th curved connecting waveguide respectively; the 1st TiN heater and the 2nd TiN heater are used to change the phase difference of the 1st phase shifter and the 2nd phase shifter by changing the temperature, and control the 1st phase shifter to transmit light to the 3rd curved connecting waveguide or the 2nd phase shifter to transmit light to the 4th curved connecting waveguide according to the phase difference;

[0029] The other ends of the 3rd curved connecting waveguide and the 4th curved connecting waveguide are connected with one end of the output multimode interferometer, and the 3rd curved connecting waveguide and the 4th curved connecting waveguide are used to transmit the received light to the output multimode interferometer; the other end of the output multimode interferometer comprises a 1st port and a 2nd port, and the 1st port and the 2nd port are connected with two optical switches or two main waveguides of the next stage respectively; the output multimode interferometer is used to transmit the received light to one optical switch of the next stage through the 1st port, or transmit the received light to one optical switch of the next stage through the 2nd port; the output multimode interferometer is also used to transmit the received light to the main waveguide through the 1st port, or transmit the received light to the main waveguide through the 2nd port.

[0030] Specifically, the input multimode interferometer needs 1x2 working ports, and the output multimode interferometer needs 2x2 working ports.

[0031] Further, the 1st phase shifter and the 2nd phase shifter are multimode waveguides with a width of 2 microns and a length of 50 microns.

[0032] Specifically, as shown in Figure 2 is a single 1x2 Mach-Zehnder optical switch design, where the length, width and output / input spacing of the multimode interference region have been optimized through theoretical calculation and genetic algorithm. In order to further improve the coupling efficiency and reduce the phase error, the width of the input and output port 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 choose to use a multimode waveguide with a width of 2 microns and a length of 50 microns, and a TiN heater is covered on it for thermal tuning of the optical switch.

[0033] As shown in Figure 3 is the transmission efficiency of the two ports of the power divider under each power distribution ratio and the total transmission efficiency. The power divider under all splitting ratios is designed by topology optimization, and the design structure robustness and total transmission efficiency are better than that of the power divider based on traditional directional coupler and multimode interferometer design. The splitting ratio of each device has reached the target design requirement, and the overall transmission efficiency has reached more than 98%.

[0034] As shown in Figure 4The spectral response test result of a single 1x2 Mach-Zehnder optical switch is shown, the test result shows that the insertion loss of the single optical switch in the "on" state is only 0.1 dB when the center wavelength is 1550 nm, which proves its high transmission performance; the insertion loss in the "off" state reaches-30 dB, which shows that its extinction ratio reaches 30.1 dB, which also proves its excellent switching ability.

[0035] Further, a row-column scanning type silicon-based focal plane array emission device is manufactured based on a silicon-on-insulator platform; the silicon-on-insulator platform comprises, from top to bottom, a silicon substrate layer, a silicon dioxide buffer layer, a silicon waveguide layer and a silicon dioxide cladding layer; the silicon substrate layer has a thickness of 2 mm, the silicon dioxide buffer layer has a thickness of 2 microns, the silicon waveguide layer has a thickness of 220 nanometers, and the silicon dioxide cladding layer has a thickness of 2 microns.

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

[0037] Specifically, the input grating coupler is used for coupling of fiber mode to waveguide mode, and mainly optimizes the coupling efficiency. The output grating coupler is used for coupling of waveguide mode and free space mode, and in addition to optimizing the coupling efficiency, the matching degree of the outgoing light field and the standard Gaussian beam mode field also needs to be optimized. Such optimization can ensure the far-field quality of the outgoing grating coupler, so that it can be directly combined with an off-chip lens to realize deflection at a certain angle. Specific embodiments:

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

[0040] Although the present application is described herein with reference to particular embodiments, it is to be understood that these examples are merely illustrative of principles and applications of the present application. It should therefore be understood that numerous modifications can be made to the illustrative embodiments and that other arrangements can be devised without departing from the spirit and scope of the present application as defined by the appended claims. It should be understood that the features described in connection with one embodiment can be used in conjunction with other embodiments described herein. It should be understood that the features described in connection with one embodiment can be used in conjunction with other embodiments described herein.

Claims

1. A row-column scanning silicon-based focal plane array transmitting device, characterized by: The 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; The input grating coupler is used to receive light input from the light source and input the light into the optical switch network; The optical switching network includes multiple optical switch stages connected in sequence, each optical switch stage including 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 input light to the corresponding main waveguide through an optical switch in each optical switch stage. Each main waveguide is simultaneously connected to multiple power splitters arranged in sequence, and each main waveguide transmits light to the connected power splitter. Each power splitter is connected to an output grating coupler, and each power splitter transmits light to the connected output grating coupler. Each output grating coupler emits light into free space. The off-chip lens is used to refract the light entering the free space and deflect the light; The optical switching 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 in the jth optical switch level is simultaneously connected to the inputs of the 2m-1th optical switch and the 2mth optical switch in the j+1th optical switch level, and the output of each optical switch in 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].

2. The row-column scanning silicon-based focal plane array transmitting device according to claim 1, characterized in that: Each main waveguide is connected to a plurality of power splitters arranged in sequence at the same time, including: the splitting ratio of the kth power splitter among the N power splitters connected to the same main waveguide is N is an integer.

3. 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 connected to one end of the curved connection waveguide No. 1 and one end of the curved connection waveguide No.

2. The input multimode interferometer is used to transmit the light output by the input grating coupler or the previous optical switch to the curved connection waveguide No. 1 and the curved connection waveguide No. 2; 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 provided above phase shifter No. 1, and a TiN heater No. 2 is provided above phase shifter No.

2. The other ends of phase shifter No. 1 and 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 transmit it 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.

4. The row-column scanning silicon-based focal plane array transmitting device according to claim 3, 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.

5. 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-on-insulator platform; the silicon-on-insulator platform consists of a silicon base layer, a silicon dioxide buffer layer, a silicon waveguide layer, and a silicon dioxide cladding layer from top to bottom; the silicon base layer is 2 mm thick, the silicon dioxide buffer layer is 2 microns thick, the silicon waveguide layer is 220 nanometers thick, and the silicon dioxide cladding is 2 microns thick.

6. 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.

7. 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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