An on-chip light field wavefront measurement system and method based on grating coupler

Abstract

The present application belongs to the technical field of light field wavefront measurement, and discloses an on-chip light field wavefront measurement system and method based on a grating coupler. The system comprises a grating coupler array, an optical fiber array, an optical fiber and a photoelectric detector connected in sequence. The grating coupler array is arranged on a silicon photon chip and is used for coupling a wavefront to be measured into a waveguide and converting a wavefront angle into an optical intensity signal in the waveguide. The optical fiber array is used for transmitting the optical intensity signal coupled into the waveguide to the photoelectric detector. The photoelectric detector is used for receiving the optical intensity signal and performing photoelectric conversion processing on the optical intensity signal to obtain characteristic parameters of the wavefront to be measured. The present application converts the wavefront angle into the optical intensity signal in the waveguide through the grating coupler array, and reconstructs the wavefront to be measured according to the optical intensity signal received by the photoelectric detector. The measurement method and device are simple, have high spatial resolution and a large dynamic angle range.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical information measurement, and more particularly relates to an on-chip light field wavefront measurement system and method based on a grating coupler. BACKGROUND

[0002] Wavefront sensing has a wide range of applications in astronomical adaptive optics, micro-nano three-dimensional topography measurement, laser communication, biological quantitative phase microscopy, etc. Traditional wavefront phase sensing methods mainly include Shack-Hartmann wavefront sensor and digital holographic quantitative phase imaging.

[0003] Traditional phase measurement techniques usually employ complex optical devices, which are difficult to meet the needs of many practical applications. Quantitative phase measurement methods based on interference require a large number of complex optical elements and are very sensitive to environmental perturbations, limiting their application scenarios. Traditional Shack-Hartmann sensors based on microlens arrays, although relatively simple in device, have low imaging resolution and small dynamic range, and can only meet the needs of some wavefront measurement requirements with low resolution.

[0004] In recent years, silicon photonics chips have been widely used in optical communication, optical computing, optical sensing, etc. On-chip micro-nano optical devices can flexibly control optical polarization, phase and amplitude, making it possible to miniaturize and microminiaturize traditional optical measurement equipment. SUMMARY

[0005] In view of the defects and improvement needs of the prior art, the present application provides an on-chip light field wavefront measurement system and method based on a grating coupler, which converts the angle information of the wavefront to be measured into light intensity information in the waveguide using a grating coupler, and measures the light intensity signal in the waveguide through a fiber array and a photodetector to determine the angle information of the wavefront to be measured at each spatial position, thereby realizing a high-resolution, high-dynamic-range wavefront measurement system.

[0006] To achieve the above-mentioned purpose, according to a first aspect of the present application, the present application first provides an on-chip light field wavefront measurement system based on a grating coupler, comprising a grating coupler array, a fiber array, an optical fiber and a photodetector connected in sequence;

[0007] The grating coupler array is arranged on a silicon photonics chip and comprises a grating coupling unit array and a waveguide array in the same plane, the grating coupling unit array is used to receive a wavefront to be measured and couple the wavefront to be measured into the waveguide array, and convert the wavefront angle signal into a light intensity signal in the waveguide array;

[0008] The fiber array is used to couple the light intensity signal in the waveguide array into the optical fiber and transmit it to the photodetector through the optical fiber;

[0009] The photoelectric detector is used for photoelectric conversion processing of the light intensity signal to obtain a characteristic parameter of the wavefront to be measured.

[0010] Further, the grating coupler unit array comprises four grating couplers which are 90 degrees apart from each other in the same plane, and each of the grating couplers is provided with a waveguide at a distal end away from each other, and each of the grating couplers couples the wavefront to be measured into the waveguide, and the waveguide is used to form the waveguide array.

[0011] Further, the optical fiber array couples the light intensity signal in the waveguide into the optical fiber through an edge coupler or a vertical coupler.

[0012] Further, the photoelectric detector is a CMOS camera, a CCD camera or a multi-channel optical power meter.

[0013] According to another aspect of the present application, the present application also provides a measurement method for measuring a characteristic parameter of a wavefront to be measured by using the above measurement system, comprising:

[0014] S1: determining the light intensity signal in the waveguide array according to the light intensity signal in the optical fiber array received by the photoelectric detector;

[0015] S2: calculating the normalized coupling power ratio of the grating coupler array in the plane according to the light intensity signal in the waveguide array;

[0016] S3: calculating the wavefront angle of the wavefront to be measured corresponding to the current normalized coupling power ratio according to the response curve of the normalized coupling power ratio and the wavefront angle of the wavefront to be measured pre-calibrated;

[0017] S4: determining the wavefront distribution of the wavefront to be measured by integrating the wavefront angle measurement values at different positions by using a regional wavefront reconstruction algorithm according to the wavefront angle.

[0018] Further, in steps S2-S3, the plane is a plane composed of x and y directions, the grating coupler array comprises grating couplers distributed along +x, -x, +y and -y directions in the plane, the direction of the wavefront to be measured is z direction perpendicular to the plane, the normalized coupling power ratios of the grating couplers in the +x and -x directions are:

[0019]

[0020] the normalized coupling power ratios of the grating couplers in the +y and -y directions are:

[0021]

[0022] Among them, the normalized coupling power ratio R in the x-direction and y-direction is x and R y are respectively about the wavefront angle θ x and the wavefront angle θ y A monotonic function of

[0023] Where, the power in the waveguide P +x is about the wavefront angle θ x Gaussian distribution, the coupling peak angle is θ1, the wavefront angle θ x P is the angle between the wavefront to be measured and the x-direction projected into the xz plane; -x is the wavefront angle θ x The response curve of P +x Symmetric about the yz plane; P +y is about the wavefront angle θ y Gaussian distribution, where θ y P is the angle between the wavefront to be measured and the y direction projected into the yz plane; -y is the wavefront angle θ y The response curve of P +y Symmetric about the xz plane.

[0024] Furthermore, the grating coupler structure distributed along the +x direction is obtained according to the following method: constructing the objective function of the grating coupler structure so that when the wavefront angle to be measured is θ1, the power of the transmission waveguide along the +x direction is maximized, and using the intelligent optimization algorithm to solve and calculate to obtain the optimal grating coupling unit structure.

[0025] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0026] 1. The present invention proposes an on-chip light field wavefront measurement system and a new method based on a grating coupler. The grating coupler is used to convert the angle information of the wavefront to be measured into the light intensity information within the waveguide. The light intensity signal within the waveguide is measured by an optical fiber array and a photodetector to uniquely determine the angle information of the wavefront to be measured at each spatial position.

[0027] 2. The measurement spatial resolution of the on-chip light field wavefront measurement system proposed in the present invention only depends on the size of the grating coupler, and can achieve higher spatial resolution than traditional wavefront sensors based on microlens arrays.

[0028] 3. The preferred measurement method of the present invention can uniquely determine the angle information of the wavefront to be measured by calculating the normalized coupling power ratio in four different directions in the same plane. The data processing process is simple and the amount of calculation is small, thereby further improving the measurement efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a structure diagram of an on-chip light field wavefront measurement system based on a grating coupler provided in an embodiment of the present application;

[0030] Figure 2 is a schematic diagram of a grating coupler array provided in an embodiment of the present application;

[0031] Figure 3 is a curve diagram of the variation of the power coupled by the waveguide in the +x direction and the -x direction with the angle θ of the wavefront to be measured provided in an embodiment of the present application; x

[0032] Figure 4 is a curve diagram of the variation of the normalized power ratio R in the x direction with the angle θ of the wavefront to be measured provided in an embodiment of the present application. x x

[0033] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein:

[0034] Grating coupler array 100, grating coupler 101, waveguide array 102, optical fiber array 200, photodetector 300. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0036] The first aspect of the present application proposes an on-chip light field measurement system based on a grating coupler, as shown in Figure 1 The system includes a grating coupler array 100, an optical fiber array 200, an optical fiber and a photodetector 300 connected in sequence, wherein the direction of light propagation is the z-axis, and the grating coupler array 100 is located in the xy plane, wherein:

[0037] The grating coupler array 100 is arranged on a silicon photonics chip and includes a grating coupling unit array 101 and a waveguide array 102 located in the same plane, the grating coupling unit array 101 is used to receive a wavefront to be measured and couple the wavefront to be measured into the waveguide array 102, and convert the wavefront angle signal into an optical intensity signal in the waveguide array 102.

[0038] The optical fiber array 200 is used to couple the optical intensity signal in the waveguide array 102 into an optical fiber and transmit it to the photodetector 300.

[0039] ​​​The photoelectric detector 300 is used for receiving the light intensity signal in the optical fiber array 200, and performing photoelectric conversion processing on the light intensity signal to obtain the characteristic parameter of the wavefront to be measured.

[0040] Further, as shown in Figure 2 , the grating coupling unit 101 includes grating couplers distributed in +x, -x, +y and -y directions in the plane, and each grating coupler is provided with a waveguide at one end away from each other, and each grating coupler respectively couples the wavefront to be measured into the waveguide, and the waveguide is used to form the waveguide array 102, and each grating coupler simultaneously converts the angle of the wavefront to be measured into four independent powers P +x , P -x , P +y , P -y in the waveguide. Among them, the grating couplers in the +x direction and the -x direction are used to measure the included angle θ x of the wavefront to be measured projected into the xz plane with the x axis, and the grating couplers in the +y direction and the -y direction are used to measure the included angle θ y of the wavefront to be measured projected into the yz plane with the y axis. The measurement structure and principle of θ x and θ y are the same, and the measurement principle of θ x will be described. The grating coupler in the +x direction couples the wavefront to be measured into the waveguide, and the power P +x is a Gaussian curve about the angle θ x of the wavefront to be measured, and the coupling peak angle is θ1, as shown in Figure 3 . The response curve of P -x and P +x are symmetrical about the yz plane. The normalized coupling power ratio of the grating couplers in the +x and -x directions is:

[0041]

[0042] As shown in Figure 4 , the normalized coupling power ratio R x of the x direction is a monotonic function about θ x . By measuring R x , the angle θ x of the wavefront to be measured can be uniquely determined. The measurement principle of θ y is the same as that of θ x , and by measuring R y , the angle θ y of the wavefront to be measured can be uniquely determined.

[0043] Furthermore, the design of the grating coupler must be optimized based on the performance requirements of wavefront detection and the wavelength of the wavefront to be measured. Since the grating couplers arranged along the four directions are of the same size, only a single grating coupler needs to be optimized. Taking the grating coupler along the +x direction as an example, an objective function for the grating coupler structure is constructed so that the power of the transmission waveguide along the +x direction is maximized when the angle of the measured wavefront is θ1. Using commonly used intelligent optimization algorithms such as particle swarm optimization and simulated annealing, the optimal grating coupling unit structure is calculated.

[0044] Furthermore, the optical fiber array 200 can couple the light intensity signal in the waveguide into the array optical fiber through an edge coupler or a vertical coupler.

[0045] Furthermore, the photodetector 300 may be a CMOS camera, a CCD camera, or a multi-channel optical power meter.

[0046] In specific implementation, the on-chip light field wavefront measurement method proposed in the present invention includes the following steps:

[0047] 1. The light intensity signal in the optical fiber array 200 is received by the photodetector 300 to determine the light intensity signal in the waveguide 102: P +x , P -x , P +y , P -y ;

[0048] 2. Calculate the normalized coupling power ratio R in the x-direction and y-direction using the light intensity signal in the waveguide array 102 x and R y ;

[0049] 3. Calculate the current R according to the pre-calibrated normalized coupling power ratio and the response curve of the wavefront angle to be measured. x and R y The wavefront angle θ corresponding to the wavefront to be measured x and θ y ;

[0050] 4. According to the wavefront angle θ to be measured x and θ y By integrating the wavefront angle measurements at different positions using the regional wavefront reconstruction algorithm, the distribution of the wavefront to be measured can be determined.

[0051] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An on-chip optical field wavefront measurement system based on a grating coupler, characterized in that: It includes a grating coupler array, an optical fiber array, an optical fiber, and a photodetector connected in sequence; The grating coupler array is arranged on the silicon photonic chip, and includes a grating coupling unit array and a waveguide array located in the same plane. The grating coupling unit array is used to receive the wavefront to be measured and couple the wavefront to be measured into the waveguide array, and convert the wavefront angle signal into a light intensity signal in the waveguide array; The optical fiber array is used to couple the light intensity signal in the waveguide array into the optical fiber, and transmit it to the photodetector through the optical fiber; The photoelectric detector is used to perform photoelectric conversion processing on the light intensity signal to obtain characteristic parameters of the wavefront to be measured.

2. The on-chip optical field wavefront measurement system based on a grating coupler according to claim 1, characterized in that: The grating coupler unit array includes four grating couplers in the same plane that are at a 90-degree angle to each other. A waveguide is provided at one end of each grating coupler that is away from each other. Each grating coupler couples the wavefront to be measured into the interior of the waveguide. The waveguides are used to form the waveguide array.

3. The on-chip light field wavefront measurement system based on a grating coupler according to claim 1 or 2, characterized in that: The optical fiber array couples the light intensity signal in the waveguide into the optical fiber through an edge coupler or a vertical coupler.

4. The on-chip light field wavefront measurement system based on a grating coupler according to claim 1 or 2, characterized in that: The photoelectric detector is a CMOS camera, a CCD camera or a multi-channel optical power meter.

5. A method for measuring a wavefront characteristic parameter to be measured using the measurement system according to any one of claims 1 to 4, characterized in that: include: S1: Determine the light intensity signal in the waveguide array according to the light intensity signal in the optical fiber array received by the photodetector: S2: calculating a normalized coupling power ratio of the in-plane grating coupler array according to the light intensity signal in the waveguide array; S3: Calculating the wavefront angle of the wavefront to be measured at the current normalized coupling power ratio according to a pre-calibrated response curve of the normalized coupling power ratio and the wavefront angle to be measured; S4: According to the wavefront angle, a regional wavefront reconstruction algorithm is used to integrate the wavefront angle measurement values ​​at different positions to determine the wavefront distribution to be measured.

6. The measuring method according to claim 5, characterized in that In steps S2-S3, the plane is a plane consisting of the xy directions, the grating coupler array includes grating couplers distributed along the four directions of +x, -x, +y, and -y in the plane, the direction of the wavefront to be measured is the z direction perpendicular to the plane, and the normalized coupling power ratio of the grating couplers in the +x and -x directions is: The normalized coupling power ratio of the grating coupler in the +y and -y directions is: Among them, the normalized coupling power ratio R in the x-direction and y-direction is x and R y They are respectively about the wavefront angle θ x and the wavefront angle θ y A monotonic function of Where, the power in the waveguide P +x is about the wavefront angle θ x Gaussian distribution, the coupling peak angle is θ1, the wavefront angle θ x P is the angle between the wavefront to be measured and the x-direction projected into the xz plane; -x is the wavefront angle θ x The response curve of P +x Symmetric about the yz plane; P +y is about the wavefront angle θ y Gaussian distribution, where θ y P is the angle between the wavefront to be measured and the y direction projected into the yz plane; -y is the wavefront angle θ y The response curve of P +y Symmetric about the xz plane.

7. The measuring method according to claim 6, characterized in that The grating coupler structure distributed along the +x direction is obtained according to the following method: an objective function of the grating coupler structure is constructed so that when the wavefront angle to be measured is θ1, the power of the transmission waveguide along the +x direction is maximized, and an intelligent optimization algorithm is used to solve and calculate the optimal grating coupling unit structure.

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