OPA receiving antenna chip

Abstract

The invention discloses an OPA receiving antenna chip, belongs to the technical field of optical phased array antennas, and solves the problem of how to improve the low receiving efficiency of a silicon-based optical phased array antenna in the prior art. The grating waveguide array layer generates periodic refractive index disturbance on the slab waveguide, and when incident light received by the chip passes through the slab waveguide, first-order diffraction light of the incident light is transmitted along the slab waveguide, then is transmitted into the superlattice waveguide through the conical waveguide and is finally output by the superlattice waveguide. According to the invention, the transmission structure is received through the flat grating, the chip can efficiently receive incident light and transmit the incident light to the superlattice waveguide for output, the duty ratio of 100% is realized, and the optical coupling efficiency and the receiving optical power are remarkably improved; the structure of the superlattice waveguide and the adiabatic tapered waveguide effectively reduces transmission loss and light field crosstalk.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical phased array antennas and relates to an OPA receiving antenna chip. Background Art

[0002] At present, the phased array antenna in the optical phased array (OPA) is difficult to achieve integrated transmission and reception. It is only used to transmit light beams, and the echo signals are mostly received by spatial optical paths and detector arrays. This does not conform to the current trend of device integration and miniaturization, and hinders the development of vehicle-mounted and airborne lidar systems towards lightweight, low power consumption and low cost. Therefore, research on OPA receiving antennas is of great significance to reducing the size, power consumption and cost of lidar systems.

[0003] The main reasons why OPA antennas currently struggle to achieve reception are high reception losses and small apertures: 1) Phased array antennas have high coupling strength. If the antenna is long, light passing from free space through the phased array antenna is coupled into the waveguide and then radiated back into free space, resulting in power loss; 2) Phased array antennas have a low duty cycle. Phased array antennas consist of periodically arranged antenna elements with a specific duty cycle, and each element can only cover a certain receiving area. When receiving parallel light from a distance, some light falls on the blank area and cannot be coupled into the optical waveguide, resulting in optical power loss.

[0004] As demand for all-solid-state LiDAR continues to grow in autonomous driving, traditional mechanical LiDARs, with their large size, heavy weight, and high power consumption, are no longer suitable for current applications. Optical phased array (OPA) technology, a new approach to implementing all-solid-state LiDAR, has gradually attracted attention. OPA, an electronically scanned beam-steering technology, offers non-mechanical deflection capabilities, a wide field of view, low power consumption, and lightweight performance, effectively meeting the application requirements of all-solid-state LiDARs.

[0005] At present, the phased array antenna in the optical phased array (OPA) is difficult to achieve integrated transmission and reception. It is only used to transmit light beams, and the echo signals are mostly received by spatial optical paths and detector arrays. This does not conform to the current trend of device integration and miniaturization, and hinders the development of vehicle-mounted and airborne lidar systems towards lightweight, low power consumption and low cost. Therefore, research on OPA receiving antennas is of great significance to reducing the size, power consumption and cost of lidar systems.

[0006] There are many ways to implement OPAs, but silicon-based waveguide OPAs have attracted researchers' attention due to their fast response, wide scanning angle, and high integration density. The development of silicon-on-insulator (SOI) technology, which is compatible with complementary metal-oxide semiconductor (CMOS) process lines, has provided a solid foundation for large-scale silicon photonic integration. Consequently, silicon-based OPA chips have become a research hotspot in the lidar field in recent years.

[0007] Currently, silicon-based OPAs typically use grating couplers or waveguide gratings as the unit structure of array antennas. Grating couplers have high optical coupling efficiency, but the structure is large, and the antenna array has a low duty cycle, resulting in high overall reception loss. Phased array antennas based on waveguide gratings typically use single-mode waveguides, which have a small receiving area and low coupling efficiency. To prevent crosstalk between waveguides, the antennas are spaced far apart, resulting in a low duty cycle.

[0008] Grating couplers in two-dimensional grating antenna arrays offer the advantages of high coupling efficiency and compact size, but their scale or aperture is difficult to increase and their duty cycle is low. Waveguide gratings in one-dimensional grating antennas reduce the number of two-dimensional antennas by increasing the longitudinal propagation length, but the lateral layout still uses discrete antenna structures. To prevent crosstalk between antennas, a large spacing is required between adjacent antennas. Furthermore, waveguide gratings typically use narrow single-mode waveguides, resulting in a low duty cycle for the antenna array, which in turn affects reception efficiency. Summary of the Invention

[0009] The technical solution of the present invention is used to solve the problem of how to improve the low receiving efficiency of silicon-based optical phased array antennas in the prior art.

[0010] The present invention solves the above technical problems through the following technical solutions: The present invention provides an OPA receiving antenna chip, comprising: a substrate layer, an intermediate cladding layer and an upper cladding layer stacked in sequence from bottom to top; the intermediate cladding layer sequentially comprises a buried layer, a grating waveguide array layer, an adjustment layer and a waveguide transmission layer, wherein the grating waveguide array layer is composed of a plurality of strip waveguides arranged in an array along the x-axis direction, and the waveguide transmission layer comprises a slab waveguide, a tapered waveguide and a superlattice waveguide; the slab waveguide is connected to a plurality of tapered waveguides, and the tapered waveguides are connected to the superlattice waveguide; the grating waveguide array layer and the waveguide transmission layer constitute a slab grating receiving and transmission structure, and the incident light received by the chip passes through the slab waveguide, and the grating waveguide array layer generates periodic refractive index disturbances on the slab waveguide. When the incident light received by the chip passes through the slab waveguide, its first-order diffracted light is transmitted along the slab waveguide, then transmitted into the superlattice waveguide through the tapered waveguide, and finally output by the superlattice waveguide.

[0011] Furthermore, the sum of the widths of the bases of the plurality of tapered waveguides is equal to the width of the slab waveguide.

[0012] Furthermore, adjacent superlattice waveguides have different widths.

[0013] Furthermore, the substrate layer is used to support the chip, and the material of the substrate layer is silicon.

[0014] Furthermore, the upper cladding layer is used to protect the waveguide transmission layer, and the material of the upper cladding layer is silicon dioxide.

[0015] Furthermore, the buried layer serves to separate the substrate layer from the grating waveguide array layer.

[0016] Furthermore, the thickness of the adjustment layer is adjustable, and its function is to adjust the distance between the grating waveguide array layer and the waveguide transmission layer.

[0017] Preferably, the material of the buried layer and the adjustment layer is silicon dioxide.

[0018] Preferably, the material of the grating waveguide array layer is silicon nitride.

[0019] Preferably, the material of the waveguide transmission layer is silicon.

[0020] The beneficial effects of the present invention are as follows: The present invention uses a flat grating receiving and transmission structure. The chip can efficiently receive incident light and transmit it to the superlattice waveguide output, achieving a 100% duty cycle and significantly improving the optical coupling efficiency and received light power. The use of silicon nitride gratings has a low refractive index and is easy to process, which solves the process limitations of traditional silicon gratings and supports larger longitudinal lengths. The superlattice waveguide and adiabatic tapered waveguide structure effectively reduce transmission loss and light field crosstalk. The chip has a compact structure, which meets the requirements of lightweight and low power consumption for vehicle-mounted and airborne lidars. It is compatible with CMOS technology, suitable for large-scale production, and reduces costs. The receiving part and the transmitting part are designed separately, and the performance can be independently optimized to improve overall efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 1. This is a perspective view of the three-dimensional structure of the OPA receiving antenna chip according to an embodiment of the present invention; Figure 2 is a perspective view of the xoz plane front view of the OPA receiving antenna chip according to an embodiment of the present invention; Figure 3 is a yoz plane side perspective view of the OPA receiving antenna chip according to an embodiment of the present invention; Figure 4 1 is a perspective view of an OPA receiving antenna chip in an xoy plane according to an embodiment of the present invention; Figure 5 This is a front view of the three-dimensional structure of the grating waveguide array layer and waveguide transmission layer of the OPA receiving antenna chip according to an embodiment of the present invention; Figure 6 2. FIG. 1 is an Xoy plane top view of the grating waveguide array layer and the waveguide transmission layer of the OPA receiving antenna chip according to an embodiment of the present invention; Figure 7 2. A yoz-plane side view of the grating waveguide array layer and the waveguide transmission layer of the OPA receiving antenna chip according to an embodiment of the present invention; Figure 8 2. FIG. 2 is a front view of the grating waveguide array layer and the waveguide transmission layer of the OPA receiving antenna chip according to an embodiment of the present invention in the xoz plane; Figure 9 1. This is a dimension design diagram of the grating waveguide array layer and waveguide transmission layer of the OPA receiving antenna chip according to an embodiment of the present invention; Figure 10 Schematic diagram of incident light transmission of the grating waveguide array layer and waveguide transmission layer of the OPA receiving antenna chip according to an embodiment of the present invention; Figure 11 4 is a curve diagram of the simulation results of the receiving efficiency of the OPA receiving antenna chip according to an embodiment of the present invention; Figure 12 This is the structure diagram of the traditional silicon planar grating antenna. DETAILED DESCRIPTION

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0023] The technical solution of the present invention is further described below with reference to the accompanying drawings and specific embodiments: Example 1 exist Figures 1 to 3 、 Figure 5 、 Figure 7 and Figure 8 In the figure, the incident direction of light is the negative direction of the z-axis.

[0024] like Figures 1 to 4 As shown, the OPA receiving antenna chip of an embodiment of the present invention includes: a substrate layer 10, an intermediate cladding layer 11 and an upper cladding layer 12, and the substrate layer 10, the intermediate cladding layer 11 and the upper cladding layer 12 are stacked in sequence from bottom to top along the positive direction of the z-axis.

[0025] like Figure 2 and Figure 3 As shown, the intermediate cladding 11 includes: a buried layer 110, a grating waveguide array layer 111, an adjustment layer 112 and a waveguide transmission layer 113, and the buried layer 110, the grating waveguide array layer 111, the adjustment layer 112 and the waveguide transmission layer 113 are stacked in sequence from bottom to top along the positive direction of the z-axis.

[0026] The substrate layer 10 serves as the bottom layer of the OPA receiving antenna chip and plays a supporting role. The material of the substrate layer 10 is silicon. The buried layer 110 serves to separate the substrate layer 10 from the grating waveguide array layer 111. The thickness of the adjustment layer 112 is adjustable, and its function is to adjust the distance between the grating waveguide array layer 111 and the waveguide transmission layer 113. The materials of the buried layer 110 and the adjustment layer 112 are uniform silicon dioxide, the material of the grating waveguide array layer 111 is silicon nitride, and the material of the waveguide transmission layer 113 is silicon. The upper cladding layer 12 is located on the top layer of the chip and is used to protect the waveguide transmission layer 113. The material of the upper cladding layer 12 is silicon dioxide.

[0027] like Figures 5 to 8As shown, the grating waveguide array layer 111 includes multiple strip waveguides 1111, and the waveguide transmission layer 113 includes: a slab waveguide 1131, a tapered waveguide 1132 and a superlattice waveguide 1133. The multiple strip waveguides 1111 are arranged in an array along the x-axis direction. One end of the slab waveguide 1131 is connected to multiple tapered waveguides 1132, and one end of the tapered waveguide 1132 is connected to a superlattice waveguide 1133. The sum of the bottom widths of the multiple tapered waveguides 1132 is equal to the width of the slab waveguide 1131, and the length of the strip waveguide 1111 is equal to the width of the slab waveguide 1131. The length direction of the strip waveguide 1111 is the y-axis direction, the length direction of the slab waveguide 1131 is the x-axis direction, and the width direction of the slab waveguide 1131 is the y-axis direction.

[0028] like Figure 9 As shown, the width of the slab waveguide 1131 is 7.5 μm, the length of the slab waveguide 1131 is 200 μm, the width of the slab waveguide 1131 is 7.5 μm, and the slab waveguide 1131 covers the entire grating waveguide array layer 111; the length L1 of the five tapered waveguides 1132 is 21 μm, the bottom width w6 of the tapered waveguide 1132 is 1.5 μm, and the sum of the bottom widths of the five tapered waveguides 1132 is equal to the total width of the slab waveguide 1131. The widths of the five superlattice waveguides 1133 are equal, and the width ratios of the five superlattice waveguides 1133 are w1, w2, w3, w4, and w5, which are 410nm, 430nm, 450nm, 470nm, and 490nm respectively. The widths of adjacent superlattice waveguides 1133 are different, so that the effective refractive index of each superlattice waveguide 1133 is different, which can avoid light field crosstalk; the width a of the strip waveguide 1111 is 420nm, and the period d is 600nm.

[0029] The working principle of the OPA receiving antenna chip in the embodiment of the present invention is as follows: like Figure 10 As shown, the grating waveguide array layer 111 and the waveguide transmission layer 113 constitute a planar grating receiving and transmission structure. The incident light received by the chip passes through the planar waveguide 1131. The grating waveguide array layer 111 generates periodic refractive index perturbations on the planar waveguide 1131. According to the principle of light diffraction, this will cause the first-order diffracted light of the incident light received by the chip to be transmitted along the planar waveguide 1131 when passing through the planar waveguide 1131 (as shown by the red arrow in the figure), and then be transmitted into the superlattice waveguide 1133 through the tapered waveguide 1132, and finally be output by the superlattice waveguide 1133.

[0030] In the embodiment of the present invention, since the sum of the bottom widths of the plurality of tapered waveguides 1132 is equal to the width of the slab waveguide 1131 , all light transmitted in the slab waveguide 1131 is output through the tapered waveguide 1132 , thereby improving light utilization.

[0031] The OPA receiving antenna chip of the present invention realizes efficient reception of the antenna, such as Figure 11 As shown in the figure, the receiving efficiency is 25% obtained by FDTD optical simulation software.

[0032] Usually, an optical phased array receiving antenna is an antenna array composed of multiple discrete grating waveguides. The grating waveguide couples the light in space into the waveguide and then transmits it separately in the horizontal direction. Since each grating waveguide is a separate path, in order to avoid optical crosstalk between the gratings, the adjacent waveguides need to be separated by a distance, thus forming a non-100% duty cycle in the Y direction. Part of the light irradiated on the antenna surface passes through the blank area between the grating waveguides and cannot enter the waveguide. The advantage of the flat grating is that the lateral length of the grating covers the length of the flat waveguide, the duty cycle is 100%, and the area in contact with the light is greatly increased compared to the traditional waveguide grating, thereby increasing the total amount of light entering; silicon nitride gratings are large in size and easy to process. At the same time, the refractive index of the material is low, about 2, and the refractive index disturbance of the introduced silicon flat waveguide is small. These two points make it possible to make a larger array of gratings, that is, the longitudinal length can reach 200μm. Figure 12 As shown, for a traditional silicon slab grating, the silicon is divided into two layers: the silicon grating and the silicon slab waveguide layer. The total thickness h2 is 220nm. The grating structure is formed by etching, and the standard etching depth h1 is 150nm. Simulations using this structure yield receiving efficiencies of 6%, 3.2%, 2.2%, and 1.7% at lengths of 20, 40, 60, and 80μm, respectively. The receiving efficiency decreases with increasing length. For a length of 80μm, simulations were performed for h1 values ​​of 120nm, 100nm, 80nm, 60nm, 40nm, and 20nm, yielding receiving efficiencies of 2%, 2.7%, 4%, 7%, 13%, and 14.6%, respectively. It can be seen that as the etching depth decreases, the receiving efficiency at this length gradually increases. The reason for this is that the refractive index variation introduced by the grating gradually decreases, reaching 0.66, 0.5, 0.37, 0.25, 0.15, and 0.07, respectively. Therefore, the smaller the refractive index variation, the longer the grating length that can be achieved. However, for silicon waveguides, the etching depth is very small, making it difficult to achieve in terms of process. The grating-based structure proposed in this invention solves this problem. The low refractive index of silicon nitride allows for a larger grating height of 300nm, while the refractive index difference is small, at 0.02, allowing for longer lengths of up to 200μm.

[0033] The OPA receiving antenna chip of the present invention improves the duty cycle of the grating antenna, greatly improving the receiving efficiency; at the same time, the weak coupling strength and large structural size of the silicon nitride grating increase the longitudinal length of the antenna, greatly improving the received optical power; the antenna is divided into two parts, the receiving part and the transmitting part, which are designed separately to improve the efficiency of each part; the superlattice waveguide and the adiabatic tapered waveguide are used to improve and reduce optical power crosstalk and reduce transmission loss.

[0034] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. An OPA receiving antenna chip, characterized in that: include: A substrate layer (10), an intermediate cladding layer (11), and an upper cladding layer (12) are stacked sequentially from bottom to top; the intermediate cladding layer (111) sequentially comprises a buried layer (110), a grating waveguide array layer (111), an adjustment layer (112), and a waveguide transmission layer (113), wherein the grating waveguide array layer (111) is arrayed along the x-axis direction by a plurality of strip waveguides (1111); the waveguide transmission layer (113) comprises a planar waveguide (1131), a tapered waveguide (1132), and a superlattice waveguide (1133); the planar waveguide (1131) is connected to a plurality of tapered waveguides (1132); the tapered waveguide ( 1132) is connected to the superlattice waveguide (1133); the grating waveguide array layer (111) and the waveguide transmission layer (113) constitute a flat grating receiving and transmission structure, the incident light received by the chip passes through the flat waveguide (1131), and the grating waveguide array layer (111) generates a periodic refractive index disturbance on the flat waveguide (1131). When the incident light received by the chip passes through the flat waveguide (1131), its first-order diffraction light is transmitted along the flat waveguide (1131), and then transmitted into the superlattice waveguide (1133) through the tapered waveguide (1132), and finally output by the superlattice waveguide (1133).

2. The OPA receiving antenna chip according to claim 1, characterized in that: The sum of the bottom widths of the plurality of tapered waveguides (1132) is equal to the width of the flat waveguide (1131).

3. The OPA receiving antenna chip according to claim 1, characterized in that: Adjacent superlattice waveguides (1133) have different widths.

4. The OPA receiving antenna chip according to claim 1, characterized in that: The substrate layer (10) is used to support the chip, and the material of the substrate layer (10) is silicon.

5. The OPA receiving antenna chip according to claim 1, characterized in that: The upper cladding layer (12) is used to protect the waveguide transmission layer (113), and the material of the upper cladding layer (12) is silicon dioxide.

6. The OPA receiving antenna chip according to claim 1, characterized in that: The buried layer (110) serves to separate the substrate layer (10) from the grating waveguide array layer (111).

7. The OPA receiving antenna chip according to claim 1, characterized in that: The thickness of the adjustment layer (112) is adjustable, and its function is to adjust the distance between the grating waveguide array layer (111) and the waveguide transmission layer (113).

8. The OPA receiving antenna chip according to claim 1, characterized in that: The materials of the buried layer (110) and the regulating layer (112) are homogeneous silicon dioxide.

9. The OPA receiving antenna chip according to claim 1, characterized in that: The material of the grating waveguide array layer (111) is silicon nitride.

10. The OPA receiving antenna chip according to claim 1, characterized in that: The material of the waveguide transmission layer (113) is silicon.

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