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

Abstract

The invention belongs to the related technical field of optical field wavefront measurement, and discloses an on-chip optical 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 which are connected in sequence, the grating coupler array is arranged on the silicon photon chip and is used for coupling a wavefront to be measured into the waveguide and converting a wavefront angle into a light intensity signal in the waveguide; the optical fiber array is used for transmitting the light intensity signal coupled into the waveguide to the photoelectric detector; and the photoelectric detector is used for receiving the light intensity signal and carrying out photoelectric conversion processing on the light intensity signal to obtain characteristic parameters of the wavefront to be detected. The wavefront angle is converted into the light intensity signal in the waveguide through the grating coupler array, the wavefront to be measured is reconstructed according to the light intensity signal received by the photoelectric detector, and the measurement method is simple in device, high in spatial resolution and large in dynamic angle range.

Description

Technical Field

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

[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. The main methods for implementing traditional wavefront phase sensing include: Shack-Hartmann wavefront sensor, digital holographic quantitative phase imaging, etc.

[0003] Traditional phase measurement technology usually uses complex optical devices that are difficult to meet many practical application requirements. The quantitative phase measurement method based on interference requires a large number of complex optical components and is very sensitive to environmental perturbations, which limits its application scenarios; although the traditional Shack-Hartmann sensor based on microlens arrays is a relatively simple device, its imaging resolution is low and its dynamic range is small, which can only meet some wavefront measurement requirements with low resolution requirements.

[0004] In recent years, silicon photonic chips have been widely used in optical communications, 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 micro-scale traditional optical measurement equipment. Summary of the invention

[0005] In view of the defects of the prior art and the need for improvement, the present invention provides an on-chip light field wavefront measurement system and method based on a grating coupler, which utilizes a grating coupler to convert the angle information of the wavefront to be measured into the light intensity information in the waveguide, and measures the light intensity signal in the waveguide through an optical fiber array and a photodetector to determine the angle information of the wavefront to be measured at each spatial position, so as to realize a high-resolution, high-dynamic range wavefront measurement system.

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

[0007] 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, wherein 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;

[0008] 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;

[0009] 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.

[0010] Furthermore, the grating coupler unit array includes four grating couplers that are at an angle of 90 degrees to each other in the same plane, and a waveguide is arranged at one end of each grating coupler that is away from each other, and each grating coupler couples the wavefront to be measured into the interior of the waveguide, and the waveguide is used to form the waveguide array.

[0011] Furthermore, 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] Furthermore, 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 invention, the present invention also provides a method for measuring a wavefront characteristic parameter to be measured using the above-mentioned measurement system, comprising:

[0014] 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:

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

[0016] S3: Calculating the wavefront angle of the wavefront to be measured under 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;

[0017] 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.

[0018] Further, in steps S2-S3, the plane is a plane composed of xy directions, the grating coupler array includes grating couplers distributed in the plane along four directions of +x, -x, +y, and -y, 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:

[0019]

[0020] The normalized coupling power ratio of the grating coupler in the +y and -y directions is:

[0021]

[0022] Among them, the normalized coupling power ratio R in the x-direction and y-direction 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 +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 +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 maximum, 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, which uses a grating coupler to convert the angle information of the wavefront to be measured into the light intensity information in the waveguide. The light intensity signal in 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 the traditional wavefront sensor based on microlens array.

[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 Schematic diagram of the structure of an on-chip light field wavefront measurement system based on a grating coupler provided in an embodiment of the present invention;

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

[0031] Figure 3 is the waveguide coupling power in the +x direction and the -x direction provided in the embodiment of the present invention as a function of the measured wavefront angle θ x The change curve diagram of

[0032] Figure 4 is the normalized power ratio R in the x direction provided in the embodiment of the present invention x With the wavefront angle θ x 's change curve graph.

[0033] Throughout the drawings, the same reference numerals are used to denote 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 solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention 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 invention provides an on-chip light field measurement system based on a grating coupler, such as Figure 1 As shown, 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 photonic 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 the wavefront to be measured and couple the wavefront to be measured into the waveguide array 102, and convert the wavefront angle signal into a light intensity signal in the waveguide array 102.

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

[0039] The photoelectric detector 300 is used to receive the light intensity signal in the optical fiber array 200 and perform photoelectric conversion processing on the light intensity signal to obtain characteristic parameters of the wavefront to be measured.

[0040] Furthermore, if Figure 2 As shown, the grating coupling unit 101 includes grating couplers distributed in the plane along the four directions of +x, -x, +y, and -y, and each of the grating couplers is provided with a waveguide at one end away from each other, and each of the grating couplers couples the wavefront to be measured into the inside of 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 the power P in four independent waveguides. +x , P -x , P +y , P -y The grating couplers in the +x and -x directions are used to measure the angle θ between the wavefront to be measured and the x-axis in the xz plane. x The grating couplers in the +y and -y directions are used to measure the angle θ between the wavefront to be measured and the y-axis projected into the yz plane. y θ x and θ y The measurement structure and principle are the same. x The grating coupler in the +x direction couples the wavefront to be measured to the power P in the waveguide. +x is about the wavefront angle θ to be measured x The Gaussian curve of the coupling peak angle is θ1, such as Figure 3 As shown. -x The response curve and P +x Symmetric about the yz plane. The normalized coupling power ratio of the grating coupler in the +x and -x directions is:

[0041]

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

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

[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. Determine the light intensity signal in the waveguide 102 by receiving the light intensity signal in the optical fiber array 200 through the photodetector 300: +x , P -x , P +y , P -y ;

[0048] 2. Calculate the normalized coupling power ratio R in the x-direction and the y-direction through 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 The distribution of the wavefront to be measured can be determined by integrating the wavefront angle measurements at different positions using the regional wavefront reconstruction algorithm.

[0051] It will be easily understood by those skilled in the art that the above description is only 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 protection scope of the present invention.

Claims

1. An on-chip light 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, wherein 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 that are at an angle of 90 degrees to each other in the same plane, and a waveguide is arranged at one end of each grating coupler that is away from each other. Each grating coupler couples the wavefront to be measured into the inside of the waveguide, and the waveguide is used to form the waveguide array.

3. The on-chip optical 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 optical 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 the 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 under 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 composed of xy directions, the grating coupler array includes grating couplers distributed in the plane along four directions of +x, -x, +y, and -y, 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 x and R y 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 +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 +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: 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 maximum, and using the intelligent optimization algorithm to solve and calculate to obtain the optimal grating coupling unit structure.

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