An optical phased array chip of large critical dimension weakly coupled non-uniform grating antenna

Abstract

The application discloses an optical phased array chip of a large key size weakly coupled non-uniform grating antenna, and relates to the technical fields of integrated optoelectronic devices and solid-state laser radars. The chip is integrated on a silicon nitride platform, and comprises an input coupler, an optical power splitting network connected with the input coupler, and a gap-modulated weakly coupled grating antenna array connected with the optical power splitting network. The gap-modulated weakly coupled grating antenna array is composed of a plurality of weakly coupled grating antennas, each of which is arranged at a non-uniform interval in a transverse direction, and the non-uniform interval is obtained through genetic algorithm optimization. After optimization, the grating lobe suppression of the array in a ±90° transverse scanning range is below-13 dB. The application is suitable for the fields of autonomous driving solid-state laser radars, free space optical communication and the like.

Description

Technical Field

[0001] This invention relates to the fields of integrated optoelectronic devices and solid-state lidar technology, and in particular to an optical phased array chip for a large-critical-size weakly coupled non-uniform grating antenna. Background Technology

[0002] Optical phased arrays (OPAs) are the core beam scanning devices for solid-state lidar and free-space optical communication. High-performance OPAs must simultaneously meet three key performance indicators: narrow longitudinal divergence angle (corresponding to a large effective aperture), wide lateral scanning field of view, and effective grating lobe suppression. However, these three objectives have long been contradictory in practical designs: The contradiction between longitudinal divergence angle and manufacturing process: To obtain a narrow divergence angle, a long effective radiation length (Leff) is required. Traditional uniform grating antennas have a short Leff due to the rapid attenuation of guided wave power. They usually need to be extended by shallow etching or chirped gratings with a critical size of less than 100 nm, but this will greatly increase the manufacturing difficulty and cost, and is difficult to be compatible with low-cost processes such as deep ultraviolet (DUV) lithography.

[0003] The contradiction between lateral scanning range and grating lobe suppression: According to array antenna theory, to suppress grating lobes, the element spacing of a uniform array must satisfy d < λ / (1 + sin To achieve a wide field of view (e.g., ±50°), the spacing needs to be less than half a wavelength (approximately 775nm @ 1550 nm). Such a small spacing will cause strong optical crosstalk between adjacent waveguides and requires extremely high photolithography precision. Conversely, if a larger spacing (e.g., 6 μm) is used, although it is easier to manufacture, it will produce strong grating lobes, limiting the grating-free field of view to an extremely narrow range (<15°).

[0004] Limitations of existing technology: Gelin Tang et al. proposed a gap-modulated weakly coupled grating antenna. By inserting a narrow waveguide between the main waveguide and the grating teeth and adjusting the coupling gap, they extended the effective radiation length to 1.5 mm while maintaining all critical dimensions ≥200 nm, achieving a longitudinal divergence angle of 0.05°, perfectly compatible with 248 nm DUV lithography. However, this design uses a 32-channel uniform array with a spacing of 6 μm, resulting in grating lobes located at ±14.2° and a lateral scanning range of only about 14.8°, far from meeting the requirements of applications such as autonomous driving.

[0005] Yige Du successfully suppressed grating lobes and extended the lateral scanning range using a non-uniform array optimized by a genetic algorithm. However, the antenna element in this work is a conventional waveguide without a weakly coupled structure, resulting in a wide longitudinal divergence angle (short effective aperture), small critical dimensions, and poor fabrication compatibility.

[0006] In summary, there is currently no solution in the technology that combines a "weakly coupled grating antenna with a large critical size and long effective aperture" with a "non-uniform wide field of view array". Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing an optical phased array chip for a large-critical-size, weakly coupled, non-uniform grating antenna. This chip overcomes the bottleneck of the traditional optical phased array where "aperture-field of view-process" cannot be simultaneously achieved, while simultaneously realizing a narrow longitudinal divergence angle, ±90° wide field of view with grating-lobe-free scanning, and full compatibility with 248nm DUV lithography.

[0008] To achieve the above objectives, the present invention provides the following solution: An optical phased array chip for a large-critical-size, weakly coupled, non-uniform grating antenna, characterized in that it is integrated on a silicon nitride platform and includes: An input coupler for coupling external laser light into an on-chip single-mode waveguide; An optical power beam splitter connected to the input coupler, the optical power beam splitter being used to uniformly distribute the input light to multiple parallel waveguides; And a gap-modulated weakly coupled grating antenna array connected to the optical power beam splitter network; The gap-modulated weakly coupled grating antenna array is composed of multiple weakly coupled grating antennas, each of which is arranged with a non-uniform spacing along the lateral direction. The non-uniform spacing is optimized by a genetic algorithm, and after optimization, the grating lobes of the array are suppressed to below -13dB within the ±90° lateral scanning range.

[0009] Furthermore, the weakly coupled grating antenna includes a main waveguide, side waveguides, and grating teeth; the side waveguides are disposed on both sides of the main waveguide, the grating teeth are arranged at equal intervals on the outer side of the side waveguides, and a coupling gap is provided between the two side waveguides.

[0010] Furthermore, the main waveguide width is 1000nm, the side waveguide width is 200nm, the grating tooth height is 900nm, the coupling gap is 500nm, the grating teeth are evenly spaced at 900nm, and the duty cycle is 0.5.

[0011] Furthermore, the input coupler has an inverted conical structure.

[0012] Furthermore, the optical power beam splitter network adopts a 1×N cascaded multimode interferometer structure, where N is a positive integer.

[0013] Furthermore, N is 128.

[0014] Furthermore, the optimization parameters of the genetic algorithm are as follows: the design variable is the spacing between adjacent array elements, the constraint range of the spacing between adjacent array elements is a minimum spacing of 3μm and a maximum spacing of 11μm, the fitness function is to maximize the edge mode suppression ratio within the lateral scan range of -90° to 90°, the population size is 300, the maximum number of generations is 500, the crossover probability is 0.9, the mutation probability is 0.05, and an elite retention strategy is adopted.

[0015] Furthermore, the optical phased array chip operates at a wavelength of 1550nm.

[0016] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects: This invention is the first to combine a gap-modulated weakly coupled grating antenna with a non-uniform array optimized by a genetic algorithm, achieving the combined advantages of a narrow longitudinal divergence angle (approximately 0.05°), a large critical size (≥200nm), and a ±90° wide field of view with grating lobe-free scanning, filling a gap in existing technologies.

[0017] This invention achieves a gate lobe suppression ratio of 13dB within a ±90° lateral scanning range under a minimum spacing of 3μm (far greater than half a wavelength of approximately 775nm) through genetic algorithm optimization. This is more than 6 times higher than the 14.8° scanning range of existing uniform weakly coupled arrays. At the same time, it significantly improves the process tolerance and completely avoids the waveguide crosstalk and lithography accuracy problems caused by submicron spacing.

[0018] All key dimensions of this invention are ≥200nm, fully compatible with 248nm deep ultraviolet (DUV) lithography mass production process, eliminating the need for 130nm lithography or electron beam lithography, significantly reducing manufacturing costs, and making it suitable for large-scale industrial applications.

[0019] The total width of the array in this invention is only about 1000μm, which can be easily expanded to 256 or 512 channels, while the total width of the array can still be controlled within 2mm, thereby further improving the angular resolution of the beam and meeting the application requirements of higher precision. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 is a schematic diagram of the structure of the optical phased array chip of the present invention, wherein (a) is a schematic diagram of the overall antenna array, (b) is a top view of a single weakly coupled grating antenna, and (c) is a side view of a single weakly coupled grating antenna. Figure 2 is a schematic diagram of the optimized spacing distribution of the 128-channel non-uniform array of the present invention; Figure 3 shows the far-field radiation pattern of the optical phased array chip of the present invention, which shows that there are no grating lobes within a range of ±90° and the side mode suppression ratio (SMSR) is 13dB. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] This embodiment provides an optical phased array chip for a large critical-size weakly coupled non-uniform grating antenna, operating at a wavelength around 1550 nm, integrated on a silicon nitride (SiN) material platform. As shown in Figure 1(a), the chip includes an input coupler, an optical power beam splitter network, and a gap-modulated weakly coupled grating antenna array connected in sequence.

[0025] The input coupler adopts an inverted conical structure to couple the laser (operating wavelength around 1550 nm) in the external optical fiber into the on-chip single-mode waveguide.

[0026] The optical power beam splitter network uses a 1×128 cascaded multimode interferometer (MMI) structure to achieve 128 uniform distributions of the input light.

[0027] The gap-modulated weakly coupled grating antenna array 3 consists of 128 structurally identical weakly coupled grating antennas, all arranged at non-uniform intervals along the transverse (y-axis). The structure of a single weakly coupled grating antenna is shown in Figures 1(b) and (c), and its design parameters are shown in Table 1: main waveguide width W3 = 1000 nm, side waveguide width W1 = 200 nm, grating tooth height W2 = 900 nm, coupling gap between the side waveguide and the main waveguide = 500 nm, grating period pitch = 900 nm, duty cycle dc = 0.5, waveguide core thickness H1 = 400 nm, and cladding thickness H2 = 400 nm.

[0028] Table 1

[0029] All the aforementioned key dimensions are ≥200nm, fully compatible with the resolution requirements of 248nm DUV lithography, eliminating the need for higher precision lithography techniques. This gap-modulated weakly coupled structure significantly reduces the coupling coefficient between the waveguide and the radiation mode, allowing the light wave to radiate slowly along the waveguide axis. The effective radiation length Leff≈1.5mm and the longitudinal far-field divergence angle reach the diffraction limit of approximately 0.05°, achieving a large effective aperture and a narrow longitudinal divergence angle.

[0030] The lateral coordinates ym (m=1,2,...,128) of the 128 antenna elements were determined through optimization using a genetic algorithm (GA). The constraints for the spacing di (i=1,2,...,127) between adjacent elements were: minimum spacing dmin=3μm, maximum spacing dmax=11μm, and the total array width was approximately 1000μm. Choosing 3μm as the minimum spacing ensured that the crosstalk between adjacent waveguides was less than -30dB and was far greater than the resolution limit of 248nm DUV lithography, providing sufficient tolerance for the manufacturing process.

[0031] The specific optimization parameters of the genetic algorithm are set as follows: the design variable is the spacing di between 127 adjacent array elements; the fitness function is to maximize the side mode suppression ratio (SMSR) within the entire target lateral scan range (-90° to 90°); the population size is 300, the maximum number of generations is 500, the crossover probability is 0.9, the mutation probability is 0.05, and an elite retention strategy is adopted to ensure that the optimal solution is not lost.

[0032] The optimized 128-channel non-uniform array spacing distribution is shown in Figure 2. This distribution breaks the periodicity of the uniform array, allowing the far-field sidelobe energy to diffuse evenly throughout the entire angular domain, thus avoiding energy concentration and the formation of grid lobes.

[0033] Figure 3 shows the far-field radiation pattern of the optimized chip. It can be seen that within the ±90° lateral scanning range, all grating lobes are suppressed to below -13dB, and the side mode suppression ratio reaches 13dB, achieving full-field-of-view grating lobe-free scanning.

[0034] The optical phased array chip in this embodiment simultaneously meets the requirements of narrow longitudinal divergence angle (0.05°), ±90° wide field of view without grating lobe scanning, and large critical size (≥200nm), breaking through the performance bottleneck of traditional optical phased arrays.

[0035] Furthermore, this structure has good scalability. By increasing the number of cascaded MMIs, the number of channels can be expanded to 256 or 512, while the total array width can still be controlled within 2mm, thereby further improving the angular resolution of the beam and meeting the application requirements of higher precision solid-state lidar.

[0036] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0037] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An optical phased array chip for a large-critical-size, weakly coupled, non-uniform grating antenna, characterized in that, Integrated into the silicon nitride platform, including: Input coupler; Optical power beam splitter network connected to the input coupler; And a gap-modulated weakly coupled grating antenna array connected to the optical power beam splitter network; The gap-modulated weakly coupled grating antenna array is composed of multiple weakly coupled grating antennas, each of which is arranged with a non-uniform spacing along the lateral direction. The non-uniform spacing is optimized by a genetic algorithm, and after optimization, the grating lobes of the array are suppressed to below -13dB within the ±90° lateral scanning range.

2. The optical phased array chip according to claim 1, characterized in that, The weakly coupled grating antenna includes a main waveguide, side waveguides, and grating teeth; the side waveguides are disposed on both sides of the main waveguide, the grating teeth are arranged at equal intervals on the outer side of the side waveguides, and a coupling gap is provided between the two side waveguides.

3. The optical phased array chip according to claim 2, characterized in that, The main waveguide has a width of 1000nm, the side waveguide has a width of 200nm, the grating tooth height is 900nm, the coupling gap is 500nm, the grating teeth are evenly spaced at 900nm, and the duty cycle is 0.

5.

4. The optical phased array chip according to claim 1, characterized in that, The input coupler has an inverted conical structure.

5. The optical phased array chip according to claim 1, characterized in that, The optical power beam splitter network adopts a 1×N cascaded multimode interferometer structure, where N is a positive integer.

6. The optical phased array chip according to claim 5, characterized in that, The value of N is 128.

7. The optical phased array chip according to claim 1, characterized in that, The optimization parameters of the genetic algorithm are as follows: the design variable is the spacing between adjacent array elements, the constraint range of the spacing between adjacent array elements is a minimum spacing of 3μm and a maximum spacing of 11μm, the fitness function is to maximize the edge mode suppression ratio within the lateral scan range of -90° to 90°, the population size is 300, the maximum number of generations is 500, the crossover probability is 0.9, the mutation probability is 0.05, and an elite retention strategy is adopted.

8. The optical phased array chip according to claim 1, characterized in that, The optical phased array chip operates at a wavelength of 1550nm.

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