Design method and structure of laser radar waveguide grating device

Abstract

The invention relates to a waveguide grating structure of an optical phased array for realizing large-deflection-angle light beam steering in the vertical direction based on mode conversion and a design method thereof, the waveguide grating structure comprises a substrate, a grating core layer located on the substrate and a covering layer located on the grating core layer, and is characterized in that the grating core layer supports n light transmission modes, n is a positive integer greater than or equal to 3, different optical transmission modes correspond to different grating diffraction angles, and the grating diffraction angles of adjacent optical transmission modes continuously change; under the condition that the wavelength of incident light ranges from 1.5 micrometers to 1.6 micrometers, the deflection angle of the grating diffraction angle of emergent light in the vertical direction is at least 30 degrees, the optical phased array enlarges the light beam steering range by superposing the light beam diffraction angles of a plurality of TE modes or a plurality of TM modes or the light beam diffraction angles of the TE modes and the TM modes, the light beam steering range is greatly enlarged while the light beam steering continuity is kept, and the light beam steering efficiency is improved. The problem that the steering range of light beams in the vertical direction of an integrated laser radar adopting a waveguide grating optical phased array at present is small is solved.

Description

Technical Field

[0001] The present invention relates to the field of optical communication and radar detection technology, and in particular to a design method and structure of a laser radar waveguide grating device. Background Art

[0002] In recent years, the rapid development of commercial fields such as unmanned driving and optical communications has given rise to the demand for high-precision, miniaturized, and low-cost 3D smart sensors. One of the principles behind this is beam steering scanning technology. Beam steering scanning technology is a technology that generates a laser beam with a narrow spot and a small divergence angle within the visible light or infrared light band, and can achieve rapid switching of the laser beam within a certain range. Laser beams with low divergence angles and high-speed steering can transmit information, measure speed and distance, etc., so they are very important in many application fields.

[0003] There are many technical solutions to achieve beam steering, but many current solutions often fail to fully take into account the above requirements. In a mechanical optical scanning system, a lens group is used for shaping, and a mechanical structure drives the lens group to rotate to achieve beam steering. However, such systems are often bulky, easy to wear, have a short life, and are expensive. They are easily affected by vibration in vehicle-mounted systems. A micro-electromechanical system integrates a mechanical structure on a chip and uses electric fields and other methods to control the movement of the micro-mechanical structure. The beam steering system based on a microcomputer system integrates an electrically deflectable micro-mirror. Changing the angle of the micro-mirror can change the angle of the laser hitting the micro-mirror. This technology greatly reduces the size, but is still susceptible to vibration and limitations such as the aperture and angle of the micro-mirror. Liquid crystal spatial light phase modulators can achieve beam steering without mechanical structures, but their phase modulation rate is often limited to milliseconds, which is obviously insufficient compared to the microsecond to nanosecond rate required for real-time imaging systems.

[0004] Waveguide grating optical phased array is a kind of light beam that uses interference between light emitting arrays to achieve angular deflection, and controls the phase of the array to achieve horizontal beam steering, and controls the wavelength to achieve vertical beam steering. Related theories have been proposed at the end of the last century. However, unlike the microwaves used in traditional phased arrays, the wavelength of light is only sub-micron, which makes it difficult to achieve arrays of this order of magnitude and their phase modulation functions. Traditional two-dimensional waveguide gratings only use single-mode light sources, and achieve vertical beam steering by tuning the wavelength of the light source. The tunable wavelength range of the laser transmitter is limited, usually 100nm, which limits the vertical beam steering range of the waveguide grating. Song Junfeng's team at Jilin University increased the vertical beam steering angle by manufacturing and integrating waveguide grating phased arrays of different periods. Although the wavelength tuning efficiency is improved to a certain extent, the vertical beam steering angle is not significantly increased. Summary of the invention

[0005] The primary purpose of the present invention is to provide an optical phased array that increases the beam steering range in the vertical direction, that is, the longitudinal field of view or the elevation angle range. Based on this purpose, the present invention at least provides the following solutions:

[0006] On one hand, the present invention provides an optical phased array waveguide grating device for realizing light beam steering with a large deflection angle in a vertical direction based on mode conversion, comprising a substrate, a grating core layer located on the substrate, and a cover layer located on the grating core layer, wherein the grating core layer supports n light transmission modes, where n is a positive integer greater than or equal to 3, and different light transmission modes correspond to different grating diffraction angles, and the grating diffraction angles of adjacent light transmission modes change continuously;

[0007] Under the condition that the wavelength of the incident light is 1.5 μm to 1.6 μm, the deflection angle of the grating diffraction angle of the outgoing light in the vertical direction is at least 30°.

[0008] Furthermore, the grating core layer has a striped grating structure.

[0009] Furthermore, the grating structure is a plurality of straight stripes arranged in parallel with equal spacing.

[0010] Furthermore, the grating core layer is selected from at least one of Si, Si3N4, GaAs and InP.

[0011] Furthermore, the covering layer is selected from at least one or more of air, SiO2 and polymer.

[0012] Furthermore, the substrate is selected from at least one or more of Si3N4, SiO2, Si and polymer.

[0013] On one hand, the present invention provides a method for designing a waveguide grating device of an optical phased array for realizing beam steering with a large deflection angle in a vertical direction based on mode conversion, comprising the following steps:

[0014] Step S1, selecting the wavelength range of the incident light and the material of the grating structure;

[0015] Step S2, determining a thickness range of the grating core layer to support n light transmission modes, where n is a positive integer greater than or equal to 3;

[0016] Step S3, calculating the effective refractive index under different light transmission modes according to the thickness of the grating core layer;

[0017] Step S4: Select appropriate duty cycle, grating period and etching depth to calculate the effective refractive index n of the grating core layer not etched in each light transmission mode. eff1 and the effective refractive index n at the etched eff2 ;

[0018] Step S5: Calculate the average effective refractive index in each light transmission mode

[0019] Step S6, calculating the diffraction angle θ of the light beam with different average effective refractive indices;

[0020] Step S7, selecting m appropriate light transmission modes from the n light transmission modes according to the variation relationship between the light beam diffraction angle and the wavelength of the incident light, so that the light diffraction angle of the incident light along the vertical direction is continuous;

[0021] Step S8, defining a quality factor function fom, the larger the fom is, the larger the deflection angle of the grating diffraction angle of the outgoing light in the vertical direction is.

[0022]

[0023] in represents the non-overlapping part of the diffraction angle θ of the light beam within the tunable wavelength range of the i-th mode light source, and φ represents the overlapping part of the diffraction angle θ of the light beam within the tunable wavelength range of all mode light sources;

[0024] Step S9, adjusting the thickness, grating period, etching depth and duty cycle of the waveguide grating core layer through the optimization algorithm to obtain a new thickness, grating period, etching depth and duty cycle of the grating core layer, and calculating the corresponding fom according to the electromagnetic field numerical simulation method, repeating this step until a suitable fom is obtained, so that the deflection angle of the grating diffraction angle of the outgoing light in the vertical direction is at least 30°.

[0025] Furthermore, the preferred algorithm is selected from one of a direct range search method, a genetic algorithm, a simulated annealing algorithm, and a particle swarm algorithm.

[0026] Furthermore, the electromagnetic field numerical simulation method includes one of a time-domain finite difference method, a finite element method, and a beam propagation method.

[0027] One aspect of the present invention provides a laser radar, which includes the above-mentioned optical phased array.

[0028] In a specific embodiment, the S8 comprises the following steps:

[0029] S9.1. Under the requirements of S8, determine the upper and lower limits of the waveguide grating core thickness, grating period, etching depth and duty cycle. Randomly select n1, n2, and n3 values ​​for each parameter within the upper and lower limits, and arrange and combine them as the initial value n1*n2*n3*n4 four-dimensional matrix, and calculate the corresponding fom. The obtained fom forms a one-dimensional matrix FOM and is recorded as 0-generation FOM (0,a). a is the ath value in the FOM one-dimensional matrix.

[0030] S9.2. Select specific values ​​of the waveguide grating core thickness, grating period, etching depth and duty cycle within the above upper and lower limits, and calculate the corresponding FOM matrix, recorded as the i-th generation, i.e., FOM (i,a) . Compare the FOM matrix with the i-1th generation FOM matrix. If the FOM (i,a) ≥FOM (i-1,a) , then save FOM (i,a) And the corresponding waveguide grating core thickness, grating period, etching depth and duty cycle. (i,a) <FOM (i-1,a) , then save FOM (i-1,a) And the corresponding waveguide grating core thickness, grating period, etching depth and duty cycle.

[0031] S9.3. Comparison of the obtained FOM (i) , FOM (i-1) After the matrix result, select the optimal FOM (i,a) , a new waveguide grating core thickness, grating period, etching depth and duty cycle are constructed through the optimization algorithm, and the corresponding FOM matrix is ​​calculated.

[0032] S9.4. Repeat steps S9.2-S9.3 until the fom of the waveguide grating designed to achieve light beam steering in a large vertical direction based on mode conversion meets the design requirements.

[0033] Compared with the prior art, the present invention has at least the following beneficial effects:

[0034] The present invention provides a waveguide grating device of an optical phased array for realizing beam steering with a large deflection angle in a vertical direction based on mode conversion. The grating core layer thereof supports n light transmission modes, where n is a positive integer greater than or equal to 3. Different light transmission modes correspond to different grating diffraction angles, and the grating diffraction angles of adjacent light transmission modes change continuously. Under the condition that the wavelength of incident light is 1.5 μm to 1.6 μm, the deflection angle of the grating diffraction angle of the emergent light in the vertical direction is at least 30°, which fundamentally breaks through the tuning wavelength range under a single mode light source to realize beam steering, maintains the continuity of beam steering, and greatly improves the overall beam steering angle range, thereby improving the problem of small beam steering range of the optical phased array in a laser radar.

[0035] The design method provided by the present invention selects a suitable light transmission mode by calculating the average effective refractive index and establishing a waveguide grating structure, as well as the corresponding relationship between the average effective refractive index and the beam diffraction angle, and then optimizes the four variables of the waveguide grating core thickness, grating period, etching depth and duty cycle through an optimization algorithm to improve the overall beam steering angle range. If the process conditions permit, this method can achieve the superposition of multiple or more mode beam steering ranges, greatly improving the beam steering range. Moreover, the waveguide grating of the present invention only needs to be manufactured using one etching process, and no additional steps are required, so the process preparation is simple and feasible.

[0036] In the design method of the present invention, the use of the electromagnetic field numerical simulation method improves the accuracy of calculating the diffraction angle of the light beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the structure of the waveguide grating device of the present invention;

[0038] Figure 2 It is a schematic diagram of the principle of the waveguide grating device of the present invention;

[0039] Figure 3 A graph showing the relationship between the grating core layer thickness and the effective refractive index when the incident light wavelength is 1550 nm (1.55 μm) for TE0, TE1, TE2, TM0 and TM1 light transmission mode light sources in a specific embodiment of the present invention;

[0040] Figure 4 This is a graph showing the relationship between wavelength and effective refractive index for TE0, TE1, TE2, TM0 and TM1 light transmission mode light sources when the grating core layer thickness is 1200nm in a specific embodiment of the present invention. ;

[0041] Figure 5 A graph showing the relationship between etching depth and average effective refractive index for TE0, TE1, TE2, TM0 and TM1 light transmission mode light sources in a specific embodiment of the present invention when the grating core thickness is 1200nm, the grating period is 500nm, the duty cycle is 0.5, and the incident light wavelength is 1550nm (1.55μm);

[0042] Figure 6 An example of a curve showing the relationship between the duty cycle and the average effective refractive index for the TE0, TE1, TE2, TM0 and TM1 light transmission mode light sources in a specific embodiment of the present invention when the grating core thickness is 1200nm, the grating period is 500nm, the etching depth is 10nm, and the incident light wavelength is 1550nm (1.55μm);

[0043] Figure 7The graph is a relationship curve between the average effective refractive index and the diffraction angle of the light beam when the wavelength of the incident light is 1500nm (1.5μm) and 1600nm (1.6μm) in a specific embodiment of the present invention;

[0044] Figure 8 A graph showing the relationship between the wavelength of incident light and the diffraction angle of the light beam on a waveguide grating designed with a target parameter combination in a specific embodiment of the present invention; DETAILED DESCRIPTION

[0045] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0046] The present invention provides a laser radar waveguide grating device design method, comprising:

[0047] S1: Determine the wavelength range of the incident light and the grating structure material, including:

[0048] Determine the wavelength range of the incident light to be 1.5μm to 1.6μm. Determine the grating material, see Figure 1 As shown, Figure 1 The schematic diagram of the principle of the waveguide grating device of the present invention is a substrate, a grating core layer and a cover layer stacked in sequence: wherein the first substrate and the first cover layer are the substrate and the cover layer closest to the grating core layer, the second substrate and the second cover layer are the substrate and the cover layer next to the grating core layer, and so on, and are not limited to a single substrate and a cover layer. The grating core layer is made of Si; the first substrate and the first cover layer are both made of SiO2; the second substrate and the second cover layer are respectively made of Si and air; the refractive index of the grating core layer is greater than the refractive index of the first substrate, and the refractive index of the grating core layer is greater than the refractive index of the first cover layer.

[0049] S2: Determine the grating core thickness and supported light transmission mode, including:

[0050] First, the target thickness of the grating core layer is determined. The target thickness belongs to the target thickness interval, that is, the target thickness is within the target thickness interval. The target thickness interval can support n light transmission modes, where n is an integer greater than or equal to 3. That is, the light transmission mode supported by the waveguide grating is determined by the target thickness interval.

[0051] Because different light transmission modes correspond to different light beam diffraction angles, and the light beam diffraction angles of adjacent light transmission modes change continuously, and under the condition that the wavelength of the incident light is 1.5μm~1.6μm, the deflection angle of the light beam diffraction angle of the outgoing light in the vertical direction is at least 30°, therefore, in the present invention, selecting a suitable grating core layer thickness as the target thickness can fundamentally break through the tuning wavelength range under a single mode light source to achieve light beam steering, while maintaining the continuity of the light beam steering, it can also greatly improve the overall vertical direction light beam steering angle range.

[0052] See also Figure 2 As shown, Figure 2 This is a schematic diagram of the principle of the waveguide grating device. The light source in the light transmission mode is transmitted from left to right in the grating core layer and diffracted upward at the grating etched part. Different light sources with different modes and different light source wavelengths have different beam diffraction angles θ and beam steering ranges Φ. That is, the i-th light transmission mode short wavelength model-i-λ1 in the figure corresponds to a beam diffraction angle θ model-i-λ1 , the long wavelength model-i-λ2 of the i-th light transmission mode corresponds to the beam diffraction angle θ model-i-λ2 ,θ model-i-λ1 With θ model-i-λ2 The angle Φ corresponds to the beam steering range Φ.

[0053] S3: Determine the relationship between the grating core thickness and the effective refractive index of the supported light transmission mode, including:

[0054] Each target thickness corresponds to an effective refractive index of a supported light transmission mode. Therefore, according to different target thicknesses of the grating core layer, the effective refractive indices of n light transmission modes supported by the grating core layer at this target thickness are determined by the electromagnetic field numerical simulation method.

[0055] See also Figure 2 As shown in the figure, H is the thickness of the grating core layer, W is the width of the unetched part, T is the grating period, and E is the depth of the etched part. The thickness of the grating core layer, the width of the unetched part, the duty cycle and the depth of the etched part are structural parameters of the waveguide grating, and the duty cycle cannot be directly obtained. It needs to be calculated based on the width of the unetched part and the grating period. The calculation formula is dc=W / T, where dc is the duty cycle, W is the width of the unetched part, and T is the grating period. Therefore, when designing a waveguide grating, it is necessary to determine the target grating period, target unetched width and target etched depth of the grating core layer, and then calculate the target duty cycle based on the target grating period and target unetched width according to the calculation formula of the duty cycle.

[0056] See also Figure 3 As shown, Figure 3The graph shows the relationship between the grating core layer thickness and the effective refractive index of the TE0, TE1, TE2, TM0 and TM1 optical transmission mode light sources of the present invention when the incident light wavelength is 1550nm (1.55μm).

[0057] See also Figure 4 As shown, Figure 4 The relationship curve between the wavelength and the effective refractive index of the TE0, TE1, TE2, TM0 and TM1 light transmission mode light sources of the present invention is shown when the grating core layer thickness is 1200nm.

[0058] According to the thickness of the grating core layer, multiple light transmission modes that the grating core layer can accommodate in the vertical direction can be determined. In the present invention, 1150nm~1200nm is selected as the target thickness range. Within the target thickness range, light transmission modes such as TE0, TE1, TE2, TM0 and TM1 can be supported, and there are 3 or more light transmission modes with an effective refractive index difference of no more than 0.25, so as to meet the continuity of the light beam diffraction angle of different light transmission modes supported within the wavelength range of the incident light.

[0059] S4: Determine the appropriate grating period, duty cycle and etching depth target range:

[0060] After determining the target range of the grating core thickness, 450nm to 550nm is selected as the target grating period interval; 0.4 to 0.6 is selected as the target duty cycle interval; and 10nm to 20nm is selected as the target etching depth interval. This is to ensure that the effective refractive index difference of 3 or more of the optical transmission modes TE0, TE1, TE2, TM0 and TM1 is not greater than 0.25.

[0061] Afterwards, the effective refractive index of the unetched portion of the grating core layer is determined according to the target grating period, the target duty cycle and the target etching depth.

[0062] Next, the effective refractive index of the grating core layer at the etching location is determined according to the target grating period, the target duty cycle and the target etching depth.

[0063] S5: Determine the average effective refractive index for each light transmission mode

[0064] According to the target duty cycle, the effective refractive index of the grating core layer where it is not etched, and the effective refractive index of the grating core layer where it is etched, the average effective refractive index corresponding to the light transmission mode is determined. The calculation formula is as follows:

[0065] dc=W / T

[0066]

[0067] Where, dc is the duty cycle, W is the width of the unetched portion, T is the grating period, is the average effective refractive index, n eff1 is the effective refractive index of the grating core layer that has not been etched, n eff2 is the effective refractive index at the etched portion of the grating core layer.

[0068] See also Figure 5 As shown, Figure 5 This is a graph showing the relationship between the etching depth and the average effective refractive index when the grating core thickness is 1200nm, the grating period is 500nm, the duty cycle is 0.5, and the light source of TE0, TE1, TE2, TM0 and TM1 optical transmission modes is at an incident light wavelength of 1550nm (1.55μm).

[0069] See also Figure 6 As shown, Figure 6 The graph shows the relationship between the duty cycle and the average effective refractive index when the grating core thickness of the present invention is 1200nm, the grating period is 500nm, the etching depth is 10nm, and the incident light wavelength is 1550nm (1.55μm) for the TE0, TE1, TE2, TM0 and TM1 optical transmission mode light sources.

[0070] Figure 3-6 It is shown that the light transmission mode, wavelength, grating core thickness, grating period, etching depth and duty cycle jointly determine the average effective refractive index. Among them, the light transmission mode, wavelength and grating core thickness play a leading role.

[0071] S6: Calculate the diffraction angle θ of the light beam with different average effective refractive index;

[0072] The diffraction angle of the light beam under different incident light wavelengths and different average effective refractive indices is calculated by electromagnetic field numerical simulation method.

[0073] See also Figure 7 As shown, Figure 7 The graph of the relationship between the average effective refractive index and the diffraction angle of the light beam when the wavelength of the incident light is 1500nm (1.5μm) and 1600nm (1.6μm) is shown.

[0074] S7: Determine 3 suitable light transmission modes, including:

[0075] Determine the target light transmission mode; the diffraction angles of the beams of the outgoing light of multiple target light transmission modes within the wavelength range of the incident light are continuous in the vertical direction, that is, the diffraction angles of the beams of the outgoing light of different light transmission modes in the vertical direction have overlapping parts, and the overlapping parts are minimal.

[0076] Figure 3-7The light transmission mode, wavelength, grating core thickness, grating period, etching depth and duty cycle determine the beam diffraction angle. To meet the target incident light wavelength range of 1.5μm to 1.6μm, the corresponding beam steering angle range is θ model-1-1500nm ~θ model-1-1600nm (1st light source mode beam steering range ),θ model-2-1500nm ~θ model-2-1600nm (Second light source mode beam steering range ),θ model-3-1500nm ~θ model-3-1600nm (Beam steering range of the third light source mode ) has overlapping range, θ model-1-1600nm <θ model-2-1500nm ,θ model-2-1600nm <θ model-3-1500nm or θ model-1-1500nm >θ model-2-1600nm ,θ model-2-1500nm >θ model-3-1600nm . And the overlap is minimal, The overlapping portion is the smallest, so the optical transmission modes TE0, TM1, and TE2 are determined as the target optical transmission modes.

[0077] S8: define the target quality factor function fom;

[0078] The larger the quality factor fom is, the larger the deflection angle of the beam diffraction angle of the outgoing light in the vertical direction is. Its expression is as follows:

[0079]

[0080] in, Represents the non-overlapping part of the diffraction angle θ of the light beam within the tunable wavelength range of the TE0 optical transmission mode light source, Represents the non-overlapping portion of the diffraction angle θ of the beam within the tunable wavelength range of the TM1 optical transmission mode light source, represents the non-overlapping part of the diffraction angle θ of the light beam within the tunable wavelength range of the light source in the TE2 optical transmission mode, and φ represents the overlapping part of the diffraction angle θ of the light beam within the tunable wavelength range of the optical transmission modes TE0, TM1 and TE2.

[0081] S9: determining a target quality factor and a corresponding target parameter combination, wherein the target quality factor indicates that the deflection angle of the beam diffraction angle of the outgoing light in the vertical direction is greater than a preset angle, and optimizing the design of the grating device using a genetic algorithm according to the target parameter combination, including:

[0082] S9.1: Determine the grating core thickness range, grating period range, etching depth range and duty cycle range. In the present invention, the grating core thickness H range is selected to be 1150nm~1200nm; the grating period T range is 450nm~550nm; the etching depth E range is 10nm~20nm; and the duty cycle D range is 0.4~0.6.

[0083] According to the genetic algorithm logic, 50 H, T, E, and D are selected in the selected interval (the number of selections is not limited here and can be changed according to actual needs), and their values ​​are respectively used to form 4 matrices, the grating core thickness matrix H = [h1; h2; ...; h i ;…;h 50 ], grating period matrix T = [t1; t2; ...; t i ;…;t 50 ], etching depth matrix E = [e1; e2; ...; e i ;…;e 50 ], duty cycle matrix D = [d1; d2; ...; d i ;…;d 50 ], and 1150nm≤h i ≤1200nm, 450nm≤t i ≤550nm, 10nm≤e i ≤20nm, 0.4≤d i ≤0.6.

[0084] The parameter matrix a formed by combining these four parameters is: a(1) = [h1; t1; e1; d1]; ...; a(i) = [h i ;t i ;e i ;d i ]; ...a(50) = [h 50 ;t 50 ;e 50 ;d 50 ], these 50 parameter matrices constitute a parameter combination matrix, the parameter combination matrix is ​​denoted as A(m) = [a(m,1); a(m,2); …; a(m,i); …; a(m,50)], and the quality factor fom corresponding to each parameter combination is calculated by the electromagnetic field numerical simulation method, and the quality factor fom corresponding to each parameter combination constitutes a quality factor matrix, which is FOM(m) = [fom(m,1); fom(m,2); …; fom(m,i); …; fom(m,50)], where m represents the number of iterations, and i represents the number of groups of parameter combinations in each generation.

[0085] S9.2: The quality factor matrix obtained in the first generation is FOM(1) = [fom(1,1); fom(1,2); …; fom(1,i); …; fom(1,50)], and the quality factor fom with the largest value in the quality factor matrix FOM(1) is determined as the optimal quality factor fom(max) of the first generation; the quality factor matrix obtained in the second generation is FOM(2) = [fom(2,1); fom(2,2); …; fom(2,i); …; fom(2,50)].

[0086] The optimal quality factor fom(max) in the quality factor matrix FOM(1) obtained in the first generation is compared with each quality factor in the quality factor matrix FOM(2) obtained in the second generation, and the largest fom value is retained; for example, if the quality factors in FOM(2) are all smaller than the optimal quality factor fom(max), the optimal quality factor fom(max) is retained, and the quality factors in FOM(2) that do not meet the conditions are deleted; if there is a quality factor in FOM(2) that is greater than the optimal quality factor fom(max), the quality factor with the largest value in FOM(2) is retained, and the optimal quality factor fom(max) is updated to the quality factor with the largest value in FOM(2), and the remaining quality factors that do not meet the conditions are deleted.

[0087] S9.3: Based on the retained optimal quality factor fom(max), the parameter combination matrix A(m+1) = [a(m+1,1); a(m+1,2); …; a(m+1,i); …; a(m+1,50)] of the m+1th generation is created through a genetic algorithm, and the quality factor matrix FOM(m+1) = [fom(m+1,1); fom(m+1,2); …; fom(m+1,i); …; fom(m+1,50)] of the m+1th generation is calculated through the electromagnetic field numerical simulation method.

[0088] S9.4: Repeat the above steps, repeatedly comparing the optimal quality factor of FOM(m) and FOM(m+1), until the deflection angle of the diffraction angle of the light beam in the vertical direction represented by the retained quality factor is greater than the preset angle, then the quality factor is determined as the target quality factor, and the parameter combination corresponding to the target quality factor is determined as the target parameter combination, where the preset angle is 30°.

[0089] See also Figure 8 As shown, Figure 8 A curve diagram showing the relationship between the wavelength of incident light and the diffraction angle of the light beam on the waveguide grating of the TE0, TM1 and TE2 optical transmission mode light sources of the present invention optimized by adopting the target parameter combination design.

[0090] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A waveguide grating device for use in an optical phased array that realizes beam steering with a large deflection angle in the vertical direction based on mode conversion, comprising a substrate, a grating core layer located on the substrate, and a covering layer located on the grating core layer, characterized in that: The grating core layer supports n light transmission modes, where n is a positive integer greater than or equal to 3, different light transmission modes correspond to different grating diffraction angles, and the grating diffraction angles of adjacent light transmission modes change continuously; Under the condition that the wavelength of the incident light is 1.5 μm to 1.6 μm, the deflection angle of the grating diffraction angle of the outgoing light in the vertical direction is at least 30°.

2. The waveguide grating device according to claim 1, characterized in that: The grating core layer has a striped grating structure.

3. The waveguide grating device according to claim 2, characterized in that: The grating structure is a plurality of parallel straight stripes with equal spacing.

4. The waveguide grating device according to any one of claims 1 to 3, characterized in that: The grating core layer is selected from at least one of Si, Si3N4, GaAs and InP.

5. The waveguide grating device according to claim 4, characterized in that: The covering layer is selected from at least one or more of air, SiO2 and polymer.

6. The waveguide grating device according to claim 5, characterized in that: The substrate is selected from at least one or more of Si3N4, SiO2, Si and polymer.

7. A design method for a waveguide grating device for an optical phased array that realizes beam steering with a large deflection angle in the vertical direction based on mode conversion, characterized in that: The steps include: Step S1, selecting the wavelength range of incident light; Step S2, determining a thickness range of the grating core layer to support n light transmission modes, where n is a positive integer greater than or equal to 3; Step S3, calculating the effective refractive index under different light transmission modes according to the thickness of the grating core layer; Step S4: Select appropriate duty cycle, grating period and etching depth to calculate the effective refractive index n of the grating core layer not etched in each light transmission mode. eff1 and the effective refractive index n at the etched area eff2 ; Step S5: Calculate the average effective refractive index in each light transmission mode Step S6, calculating the diffraction angle θ of the light beam with different average effective refractive indices; Step S7, selecting m appropriate light transmission modes from the n light transmission modes according to the variation relationship between the light beam diffraction angle and the wavelength of the incident light, so that the light diffraction angle of the incident light along the vertical direction is continuous, wherein m is less than or equal to n; Step S8, defining a quality factor function fom. The larger the fom is, the larger the deflection angle of the grating diffraction angle of the outgoing light in the vertical direction is. The expression is as follows: in represents the non-overlapping part of the diffraction angle θ of the light beam within the tunable wavelength range of the i-th mode light source, and φ represents the overlapping part of the diffraction angle θ of the light beam within the tunable wavelength range of all mode light sources; Step S9, adjusting the thickness, grating period, etching depth and duty cycle of the waveguide grating core layer through the optimization algorithm to obtain a new thickness, grating period, etching depth and duty cycle of the grating core layer, and calculating the corresponding fom according to the electromagnetic field numerical simulation method, repeating this step until a suitable fom is obtained, so that the deflection angle of the grating diffraction angle of the outgoing light in the vertical direction is at least 30°.

8. The design method according to claim 7, characterized in that: The preferred algorithm is selected from one of direct range search method, genetic algorithm, simulated annealing algorithm and particle swarm algorithm.

9. The design method according to claim 7 or 8, characterized in that: The electromagnetic field numerical simulation method includes one of a time-domain finite difference method, a finite element method, and a beam propagation method.

10. A laser radar, characterized in that: The optical phased array comprises the optical phased array described in any one of claims 1 to 6.

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