Optical field wavefront measurement module and method based on integrated photon chip

Abstract

The invention belongs to the related technical field of optical information measurement, and discloses an optical field wavefront measurement module and method based on an integrated photon chip. The measurement module is arranged on the integrated photon chip and comprises a coupling unit, a transmission waveguide and a photoelectric detector, and the coupling unit is used for receiving wavefront to be measured and coupling the wavefront to be measured to the transmission waveguide; the periphery of the coupling unit is connected with transmission waveguides, the periphery comprises a transverse forward direction and a transverse reverse direction and a longitudinal forward direction and a longitudinal reverse direction, the tail end of each transmission waveguide is connected with a photoelectric detector, and the transmission waveguides are used for transmitting optical signals on the coupling unit to the photoelectric detectors; the photoelectric detector is used for measuring the light intensity of the optical signal from the transmission waveguide. According to the invention, high-resolution and high-dynamic-range wavefront measurement is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field related to optical information measurement, and more specifically, relates to a light field wavefront measurement module and method based on an integrated photonic chip. Background Art

[0002] The wavefront and phase measurement of light fields are widely used in wafer defect detection, biological imaging, micro-nano 3D topography measurement, adaptive optics, etc. The traditional methods for implementing light field wavefront and phase measurement mainly include: digital holographic quantitative phase imaging, shearing interferometry phase measurement, Shack-Hartmann wavefront sensor, etc.

[0003] Quantitative phase measurement methods based on interference usually use complex optical devices and are very sensitive to environmental perturbations, making it difficult to meet many practical application requirements. Although the measurement device of the Shack-Hartmann sensor based on a microlens array is relatively simple, its imaging resolution is low, its dynamic range is small, and its measurement accuracy is limited. It can only meet some wavefront measurement requirements with low resolution requirements.

[0004] In recent years, integrated photonic chips have been widely used in optical communications, optical computing, optical sensing, etc. Integrated photonic chips make it possible to miniaturize and micro-scale traditional optical measurement equipment due to their flexible control of optical polarization, phase, and amplitude. Summary of the invention

[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a light field wavefront measurement module and method based on an integrated photonic chip to solve the problem of measuring wavefront using a photonic chip.

[0006] To achieve the above object, according to one aspect of the present invention, a light field wavefront measurement module based on an integrated photonic chip is provided, the measurement module comprising a coupling unit, a transmission waveguide and a photodetector, wherein:

[0007] The coupling unit is used to receive the wavefront to be measured and couple the wavefront to be measured to the transmission waveguide; the coupling unit is connected with transmission waveguides on all sides, including the forward and reverse directions in the transverse direction and the forward and reverse directions in the longitudinal direction; each end of the transmission waveguide is connected with the photodetector, the transmission waveguide is used to transmit the optical signal on the coupling unit to the photodetector, and the photodetector is used to measure the light intensity of the optical signal from the transmission waveguide.

[0008] Further preferably, the coupling unit is made of silicon or silicon nitride, and the transmission waveguide is made of silicon or silicon nitride.

[0009] Further preferably, the coupling unit has yz plane symmetry, xz plane symmetry and z-axis center symmetry.

[0010] Further preferably, the structure of the coupling unit is obtained according to the following method: constructing the objective function of the coupling unit structure so that the forward transmission waveguide along the transverse direction is at the wavefront angle θ to be measured x1 The power is maximum when the coupling unit is connected to the yz plane, the xz plane and the z axis, and the symmetry of the coupling unit is taken as a constraint condition, and the optimal coupling unit structure is obtained by solving and calculating using an intelligent optimization algorithm.

[0011] Further preferably, the objective function is as follows:

[0012]

[0013] Where FoM is the objective function, E0 and H0 are the electric and magnetic field distributions of the fundamental mode of the waveguide in the forward direction, and are the conjugates of E0 and H0 respectively, E and H are the actual electric field and magnetic field distributions of the waveguide along the lateral forward transmission direction, S is the cross-section of the waveguide along the lateral forward transmission direction, and Re is the real part operation of the complex number.

[0014] According to another aspect of the present invention, a method for measuring light field wavefront using the above-mentioned measurement module is provided, the method comprising the following steps:

[0015] Arrange a plurality of the measurement modules in an array;

[0016] Using each measuring module to calculate and obtain the wavefront angle of the wavefront to be measured irradiated on the coupling unit of each measuring module;

[0017] The wavefront reconstruction algorithm is used to reconstruct the wavefront angles of the wavefront to be measured obtained by all measurement modules, so as to obtain the position of the wavefront to be measured.

[0018] Further preferably, each measurement module calculates the measurement angle of the wavefront to be measured according to the following method:

[0019] Each photoelectric detector of each measuring module measures and obtains the light intensity in the forward and reverse directions in the horizontal direction and the forward and reverse directions in the longitudinal direction of the wave front to be measured;

[0020] The current light intensity coupling power ratio in the transverse direction and the longitudinal direction is solved respectively by using the light intensity in the transverse forward and reverse directions and the light intensity in the longitudinal forward and reverse directions;

[0021] According to the relationship between the pre-calibrated coupling power ratio and the wavefront angle of the wavefront to be measured, the wavefront angle of the wavefront to be measured corresponding to the current coupling power ratio is calculated.

[0022] Further preferably, the calculation formula of the light intensity coupling power ratio is as follows:

[0023]

[0024]

[0025] Among them, R x (θ x ) is the light intensity coupling power ratio along the lateral direction, R y (θ y ) is the optical intensity coupling power ratio along the longitudinal direction, P +x , P -x , P +y and P -y are the light intensities along the transverse positive direction, direction, and the longitudinal positive direction, θ x is the lateral wavefront angle, θ y is the longitudinal wavefront angle.

[0026] Further preferably, the transverse and longitudinal light intensity coupling power ratios are monotonic functions of the transverse wavefront angle and the longitudinal wavefront angle, respectively.

[0027] According to another aspect of the present invention, a light field wavefront measurement system based on an integrated photonic chip is provided. The system includes an actuator for executing the above-mentioned light field wavefront measurement method based on an integrated photonic chip.

[0028] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0029] 1. The measurement module provided by the present invention uses a coupling unit to convert the angle information of the wavefront to be measured into the light intensity information in the transmission waveguide. The angle of the wavefront to be measured at each spatial position can be uniquely determined by measuring the light intensity signal in the waveguide through a photodetector, thereby realizing high-resolution and high-dynamic range wavefront measurement;

[0030] 2. The spatial resolution of the light field wavefront measurement module proposed in the present invention only depends on the size of the coupling unit and the photodetector, and can achieve higher spatial resolution than the traditional wavefront sensor based on microlens array;

[0031] 3. The measurement method proposed in the present invention can uniquely determine the angle of the wavefront to be measured at each spatial position through the ratio of the lateral and longitudinal coupling powers. The data processing process is simple and the amount of calculation is small, thereby further improving the measurement efficiency;

[0032] 4. The coupling unit of the present invention is to construct an objective function so that the forward transmission waveguide along the lateral direction is at the angle θ of the wavefront to be measured. x1The power is maximum when the coupling unit is symmetrically constrained in the yz plane, xz plane and z axis, so that the transverse and longitudinal light intensity coupling power ratios are monotonic functions of the transverse wavefront angle and the longitudinal wavefront angle, respectively, which facilitates the use of the coupling power to determine the angle of the wavefront to be measured in the later stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a structural schematic diagram of a light field wavefront measurement module based on an integrated photonic chip constructed according to a preferred embodiment of the present invention;

[0034] Figure 2 is a top view of a light field wavefront measurement module based on an integrated photonic chip constructed according to a preferred embodiment of the present invention;

[0035] Figure 3 is a scanning electron microscope picture of a coupling unit constructed according to a preferred embodiment of the present invention;

[0036] Figure 4 The normalized power ratio Rx in the x direction constructed according to the preferred embodiment of the present invention varies with the wavefront angle θ to be measured. x and θ y , wherein (a) is a graph showing the variation of the transmission waveguide light intensity along the positive lateral direction with the wavefront angle to be measured, (b) is a graph showing the variation of the transmission waveguide light intensity along the reverse lateral direction with the wavefront angle to be measured, and (c) is a graph showing the variation of the light intensity coupling power ratio along the lateral direction with the wavefront angle to be measured;

[0037] Figure 5 Schematic diagram of the coupling unit array structure constructed according to the preferred embodiment of the present invention. In all the drawings, the same reference numerals are used to represent the same elements or structures, wherein:

[0038] 100-wavefront to be measured, 200-coupling unit, 300-transmission waveguide, 400-photodetector. DETAILED DESCRIPTION

[0039] 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.

[0040] A light field wavefront measurement system and method based on an integrated photonic chip, comprising: a coupling unit 200, a transmission waveguide 300, and a photodetector 400, wherein the direction of light propagation is defined as the z-axis, the plane where the wavefront to be measured is located is defined as the xy plane, and the angle between the wavefront to be measured and the x-axis projected into the xz plane is θx , the angle between the wavefront to be measured and the y-axis projected into the yz plane is θ y .

[0041] The coupling unit 200 is used to couple the measured wavefront into the transmission waveguide 300, and convert the angle information of the measured wavefront 100 into the light intensity information in the transmission waveguide 300; that is, the change in angle causes the change in light intensity, and the coupling efficiency of the measured wavefront incident on the coupling unit from different angles is different, and silicon and silicon nitride are generally used.

[0042] The transmission waveguide 300 is used to transmit the light intensity signal coupled to the optical chip to the photodetector 400; it is made of the same material as the coupling unit;

[0043] The photodetector 400 is used to receive the light intensity signal in the transmission waveguide 300 and perform photoelectric conversion on the light intensity signal to obtain the characteristic parameter of the wavefront to be measured, that is, the magnitude of the light intensity.

[0044] like Figure 2 The schematic diagram of the integrated photonic chip is shown in top view. The coupling unit 200 has yz plane symmetry, xz plane symmetry and z-axis center symmetry. The objective function of the coupling unit 200 is constructed so that the transverse forward transmission waveguide is at the angle θ of the wavefront to be measured. x1 (θ x1 >0) is the maximum. The expression of the objective function is:

[0045]

[0046] Where FoM is the objective function, E0 and H0 are the electric and magnetic field distributions of the fundamental mode of the waveguide in the forward direction, and are the conjugates of E0 and H0, respectively. E and H are the actual electric and magnetic field distributions of the waveguide in the transverse forward transmission direction. S is the cross section of the waveguide in the transverse forward transmission direction. Re is the real part of the complex number. The coupling unit 200 couples the wavefront to be measured to the inside of the +x, -x, +y, -y transmission waveguides respectively, and converts the angle of the wavefront to be measured into the power P in four independent waveguides. +x , P -x , P +y , P -y .

[0047] like Figure 3 The figure shows a scanning electron microscope image of the coupling unit 200 prepared in this embodiment. The coupling unit and the transmission waveguide material can be silicon or silicon nitride.

[0048] The photodetector is used to convert the optical signal in the transmission waveguide into an electrical signal, and the photodetector is an integrated photodetector or an off-chip photodetector.

[0049] like Figure 4 As shown in (a), the power P in the +x direction transmission waveguide 300 +x is about the wavefront angle θ to be measured x Gaussian distribution, the coupling peak angle is θ x1 ; -x-direction transmission waveguide power P -x Response curves of wavefront angles and P +x Symmetrical about the yz plane, its coupling peak angle is -θ x1 ,like Figure 4 As shown in (b). The normalized coupling power ratio of the +x and -x direction transmission waveguides is:

[0050]

[0051] The normalized coupling power ratio of the transmission waveguide in the +y and -y directions is:

[0052]

[0053] Among them, the normalized coupling power ratio R of the transmission waveguide in the x-direction and y-direction is x and R y They are respectively about the wavefront angle θ to be measured x and θ y A monotonic function of .

[0054] like Figure 4 As shown in (c), the normalized coupling power ratio R of the waveguide 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 .

[0055] Furthermore, the optimal design of the coupling unit 200 should be optimized according to the performance requirements of the wavefront detection and the wavelength of the wavefront to be measured. The optimal design can adopt the commonly used intelligent optimization algorithm, direct binary search algorithm or adjoint method for reverse design optimization.

[0056] Furthermore, the photodetector 400 may be an integrated photodetector or an off-chip photodetector.

[0057] Furthermore, in order to measure the wavefront angles at different positions, the coupling unit 200, the transmission waveguide 300 and the photodetector 400 are arranged in an array on the integrated photonic chip, such as Figure 5A certain gap is left between the coupling units 200 to allow the transmission waveguide 300 to be routed, and the transmission waveguide 300 array transmits the light intensity signal to the photodetector 400 array for photoelectric conversion.

[0058] In specific implementation, the light field wavefront measurement method proposed by the present invention includes the following steps:

[0059] (1) Receive the light intensity signal in the transmission waveguide 300 through the photodetector 400: P +x , P -x , P +y , P -y ;

[0060] (2) Calculate the normalized coupling power ratio R in the x-direction and y-direction by the light intensity signal in the transmission waveguide 300 x and R y ;

[0061] (3) According to the pre-calibrated R x With θ x Between, R y With θ y The relationship between the current coupling power ratio R x and R y The corresponding angle θ of the wavefront to be measured x and θ y .

[0062] (4) According to the measured wavefront angle θ x and θ y By integrating the wavefront angle measurements at different positions using the wavefront reconstruction algorithm, the distribution of the wavefront to be measured can be obtained.

[0063] 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. A light field wavefront measurement module based on an integrated photonic chip, characterized in that: The measurement module comprises a coupling unit (200), a transmission waveguide (300) and a photodetector (400), wherein: The coupling unit (200) is used to receive a wavefront to be measured and couple the wavefront to be measured to the transmission waveguide (300); the coupling unit (200) is connected to transmission waveguides (300) on all sides, including transverse positive and reverse directions and longitudinal positive and reverse directions; the end of each transmission waveguide (300) is connected to the photodetector (400); the transmission waveguide (300) is used to transmit the optical signal on the coupling unit (200) to the photodetector (400); and the photodetector (400) is used to measure the light intensity of the optical signal from the transmission waveguide (300).

2. The light field wavefront measurement module based on an integrated photonic chip as claimed in claim 1, characterized in that: The coupling unit (200) is made of silicon or silicon nitride, and the transmission waveguide (300) is made of silicon or silicon nitride.

3. The light field wavefront measurement module based on an integrated photonic chip as claimed in claim 1 or 2, characterized in that: The coupling unit (200) has yz plane symmetry, xz plane symmetry and z-axis center symmetry.

4. The light field wavefront measurement module based on an integrated photonic chip as claimed in claim 3, characterized in that: The structure of the coupling unit (200) is obtained according to the following method: constructing the objective function of the coupling unit structure so that the forward transmission waveguide (300) along the transverse direction is at the angle θ of the wavefront to be measured. x1 The power is maximum when the coupling unit is connected to the yz plane, the xz plane and the z axis, and the symmetry of the coupling unit is taken as a constraint condition, and the optimal coupling unit structure is obtained by solving and calculating using an intelligent optimization algorithm.

5. The light field wavefront measurement module based on an integrated photonic chip as claimed in claim 4, characterized in that: The objective function is as follows: Where FoM is the objective function, E0 and H0 are the electric and magnetic field distributions of the fundamental mode of the waveguide in the forward direction, and are the conjugates of E0 and H0 respectively, E and H are the actual electric field and magnetic field distributions of the waveguide along the lateral forward transmission direction, S is the cross-section of the waveguide along the lateral forward transmission direction, and Re is the real part operation of the complex number.

6. A method for measuring light field wavefront using the measurement module according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: Arrange a plurality of the measurement modules in an array; Using each measurement module to calculate and obtain the wavefront angle of the wavefront (100) to be measured irradiated on the coupling unit (200) of each measurement module; The wavefront reconstruction algorithm is used to reconstruct the wavefront angles of the wavefront to be measured (100) obtained by all measurement modules, so as to obtain the position of the wavefront to be measured.

7. The method according to claim 6, characterized in that Each measurement module calculates the measurement angle of the wavefront to be measured according to the following method: Each photoelectric detector (400) of each measuring module measures and obtains the light intensity in the forward and reverse directions in the transverse direction and the forward and reverse directions in the longitudinal direction of the wave front to be measured; The current light intensity coupling power ratio in the transverse direction and the longitudinal direction is solved respectively by using the light intensity in the transverse forward and reverse directions and the light intensity in the longitudinal forward and reverse directions; According to the relationship between the pre-calibrated coupling power ratio and the wavefront angle of the wavefront to be measured, the wavefront angle of the wavefront to be measured corresponding to the current coupling power ratio is calculated.

8. The method according to claim 7, characterized in that The calculation formula of the optical intensity coupling power ratio is as follows: Among them, R x (θ x ) is the light intensity coupling power ratio along the lateral direction, R y (θ y ) is the optical intensity coupling power ratio along the longitudinal direction, P +x , P -x , P +y and P -y are the light intensities along the transverse positive direction, direction, and the longitudinal positive direction, θ x is the lateral wavefront angle, θ y is the longitudinal wavefront angle.

9. The method according to claim 7 or 8, characterized in that The transverse and longitudinal light intensity coupling power ratios are monotonic functions of the transverse wavefront angle and the longitudinal wavefront angle, respectively.

10. A light field wavefront measurement system based on an integrated photonic chip, characterized in that: The system includes an actuator, which is used to execute the light field wavefront measurement method based on an integrated photonic chip as described in any one of claims 6 to 9.

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