An integrated photonic chip-based optical field wavefront measurement module and method

Abstract

The application belongs to the technical field of optical information measurement, and discloses an optical field wave front 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. The coupling unit is used for receiving a wave front to be measured and coupling the wave front to be measured to the transmission waveguide. The coupling unit is connected with the transmission waveguide around the four sides, which includes the forward and reverse directions in the transverse direction and the forward and reverse directions in the longitudinal direction. The end of each transmission waveguide is connected with the photoelectric detector. The transmission waveguide is used for transmitting the optical signal on the coupling unit to the photoelectric detector. The photoelectric detector is used for measuring the light intensity of the optical signal from the transmission waveguide. Through the application, the wave front measurement with high resolution and high dynamic range is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical information measurement, and more particularly relates to an optical field wavefront measurement module and method based on an integrated photonic chip. BACKGROUND

[0002] Wavefront and phase measurement of optical field has a wide range of applications in wafer defect detection, biological imaging, micro-nano three-dimensional topography measurement, adaptive optics and other fields. Traditional methods for realizing wavefront and phase measurement of optical field mainly include digital holographic quantitative phase imaging, shearing interference phase measurement, and Shack-Hartmann wavefront sensor.

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

[0004] In recent years, integrated photonic chips have been widely used in optical communication, optical computing, optical sensing and other fields. Due to the flexible control of optical polarization, phase and amplitude, the integrated photonic chip makes it possible to miniaturize and microminiaturize traditional optical measurement devices. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the present application provides an optical field wavefront measurement module and method based on an integrated photonic chip, which solves the problem of wavefront measurement using a photonic chip.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present application, an optical field wavefront measurement module based on an integrated photonic chip is provided, which comprises a coupling unit, a transmission waveguide and a photodetector, wherein:

[0007] The coupling unit is used to accept a wavefront to be measured and couple the wavefront to be measured to the transmission waveguide; the coupling unit is connected with a transmission waveguide around its periphery, the periphery including the forward and reverse directions in the lateral direction and the forward and reverse directions in the longitudinal direction, the end of each 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 silicon or silicon nitride, and the transmission waveguide is silicon or silicon nitride.

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

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

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

[0012]

[0013] wherein FoM is the objective function, E0 and H0 are the electric field and magnetic field distribution of the fundamental mode of the forward transmission waveguide along the transverse direction, and are the conjugate of E0 and H0, respectively, E and H are the actual electric field and magnetic field distribution of the forward transmission waveguide along the transverse direction, S is the cross section of the forward transmission waveguide along the transverse direction, and Re is the real part operation of a complex number.

[0014] According to another aspect of the present application, a method for measuring the wavefront of an optical field by using the measurement module is provided, which comprises the following steps:

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

[0016] Calculating the wavefront angle of the wavefront to be measured irradiated on the coupling unit of each measurement module by using each measurement module;

[0017] Reconstructing the wavefront of the wavefront to be measured by using a wavefront reconstruction algorithm according to the wavefront angles of the wavefront to be measured obtained by all the measurement modules, so as to obtain the position of the wavefront to be measured.

[0018] Further preferably, the measurement of the wavefront to be measured by each measurement module is performed according to the following method:

[0019] Each photodetector of each measurement module measures the light intensity along the forward and reverse directions of the transverse direction and the forward and reverse directions of the longitudinal direction of the wavefront to be measured;

[0020] Solving the current light intensity coupling power ratio of the transverse direction and the longitudinal direction by using the light intensity along the forward and reverse directions of the transverse direction and the forward and reverse directions of the longitudinal direction, respectively;

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

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

[0023] ​

[0024]

[0025] wherein R x (θ x ) is the lateral light intensity coupling power ratio, R y (θ y ) is the longitudinal light intensity coupling power ratio, P +x , P -x , P +y and P -y are the light intensities along the lateral forward, backward, longitudinal forward and backward directions, respectively, θ x is the lateral wavefront angle, and θ y is the longitudinal wavefront angle.

[0026] Further preferably, the lateral and longitudinal light intensity coupling power ratios are monotonic functions with respect to the lateral and longitudinal wavefront angles, respectively.

[0027] According to yet another aspect of the present application, there is provided an integrated photonic chip-based optical field wavefront measurement system, which comprises an executor configured to execute the above-mentioned integrated photonic chip-based optical field wavefront measurement method.

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

[0029] 1. The measurement module provided by the present application converts the angle information of the wavefront to be measured into light intensity information in the transmission waveguide by using the coupling unit, and 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 by using the photodetector, thereby realizing high-resolution and high-dynamic-range wavefront measurement.

[0030] 2. The spatial resolution of the optical field wavefront measurement module proposed by the present application only depends on the size of the coupling unit and the photodetector, and compared with the conventional wavefront sensor based on a microlens array, the spatial resolution can be higher.

[0031] 3. The measurement method proposed by the present application can uniquely determine the angle of the wavefront to be measured at each spatial position by using the lateral and longitudinal coupling power ratios, the data processing process is simple, the amount of calculation is small, and thus the measurement efficiency is further improved.

[0032] 4. The coupling unit of the present application is configured to construct an objective function so that the lateral forward transmission waveguide is in the wavefront angle θ x1The power is maximum at the moment, and the symmetry constraints of the coupling unit in the yz plane, the xz plane and the z axis make the transverse and longitudinal light intensity coupling power ratios be monotonic functions of the transverse wave front angle and the longitudinal wave front angle, respectively, which facilitates the determination of the angle of the to-be-measured wave front by using the coupling power. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 FIG. 1 is a structural schematic diagram of an integrated photonic chip-based optical field wave front measurement module constructed according to a preferred embodiment of the present application;

[0034] Figure 2 FIG. 2 is a top view of an integrated photonic chip-based optical field wave front measurement module constructed according to a preferred embodiment of the present application;

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

[0036] Figure 4 FIG. 4 is a graph showing the variation of the x-direction normalized power ratio Rx with the to-be-measured wave front angle θ x and θ y , wherein (a) is a graph showing the variation of the light intensity along the transverse forward transmission waveguide with the to-be-measured wave front angle, (b) is a graph showing the variation of the light intensity along the transverse reverse transmission waveguide with the to-be-measured wave front angle, and (c) is a graph showing the variation of the light intensity coupling power ratio along the transverse direction with the to-be-measured wave front angle;

[0037] Figure 5 FIG. 5 is a structural schematic diagram of a coupling unit array constructed according to a preferred embodiment of the present application. In all the drawings, the same reference signs are used to represent the same elements or structures, wherein:

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

[0039] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0040] An integrated photonic chip-based optical field wave front measurement system and method, 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 in which the to-be-measured wave front is located is defined as the xy plane, and the angle between the to-be-measured wave front projected into the xz plane and the x axis is θx , the angle between the to-be-tested wave front and the y-axis in the yz plane is θ y .

[0041] The coupling unit 200 is used for coupling the to-be-tested wave front into the transmission waveguide 300 and converting the angle information of the to-be-tested wave front 100 into the light intensity information in the transmission waveguide 300; that is, the change of the angle causes the change of the light intensity, and the coupling efficiency of the to-be-tested wave front incident into the coupling unit from different angles is different, and silicon and silicon nitride are generally used.

[0042] The transmission waveguide 300 is used for transmitting the light intensity signal coupled onto the optical chip to the photodetector 400; the same material as the coupling unit is used;

[0043] The photodetector 400 is used for receiving the light intensity signal in the transmission waveguide 300 and performing photoelectric conversion processing on the light intensity signal to obtain the characteristic parameter of the to-be-tested wave front, that is, the size of the light intensity.

[0044] As shown in Figure 2 , the top view of the integrated photonic chip is shown, the coupling unit 200 has yz plane symmetry, xz plane symmetry and z-axis central symmetry; the target function of the coupling unit 200 is constructed so that the power of the to-be-tested wave front angle θ x1 (θ x1 >0) along the transverse forward transmission waveguide is maximum. The expression of the target function is:

[0045]

[0046] Wherein, FoM is the target function, E0 and H0 are the electric field and magnetic field distribution of the basis mode along the transverse forward transmission waveguide, and are the conjugate of E0 and H0, E and H are the actual electric field and magnetic field distribution along the transverse forward transmission waveguide, S is the cross section of the transverse forward transmission waveguide, and Re is the real part operation of the complex number. The coupling unit 200 respectively couples the to-be-tested wave front into the +x, -x, +y and -y transmission waveguide, and simultaneously converts the angle of the to-be-tested wave front into the power P +x , P -x , P +y , P -y .

[0047] As shown in Figure 3 , the scanning electron microscope picture of the coupling unit 200 prepared in the embodiment is shown. The materials of the coupling unit and the transmission waveguide can be selected from silicon or silicon nitride.

[0048] The photodetector is used for converting the light signal in the transmission waveguide into an electric signal, and the photodetector is an integrated photodetector or an off-chip photodetector.

[0049] like Figure 4 As shown in (a), the power P within the +x direction transmission waveguide 300 is... +x It concerns the wavefront angle θ to be measured. x The Gaussian distribution has a coupling peak angle of θ. x1 -x direction transmission waveguide power P -x The response curves for wavefront angle and P +x Symmetric 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 propagation waveguides in the +x and -x directions is:

[0050]

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

[0052]

[0053] Among them, the normalized coupling power ratio R of the transmission waveguides in the x and y directions x and R y These are related to the wavefront angle θ to be measured. x and θ y It is a monotonic function.

[0054] like Figure 4 As shown in (c), the normalized coupling power ratio R of the waveguide in the x-direction direction is... x It's about θ x It is a monotonic function. This is determined by measuring R. x This allows for the unique determination of the wavefront angle θ to be measured. x θ y The measurement principle and θ x Similarly, by measuring R y This allows for the unique determination of the wavefront angle θ to be measured. y .

[0055] Furthermore, the optimization design of the coupling unit 200 should be carried out according to the performance requirements of wavefront detection and the wavelength of the wavefront to be measured. The optimization design can be carried out by using common intelligent optimization algorithms, direct binary search algorithms or adjoint methods for reverse design optimization.

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

[0057] Furthermore, to measure the wavefront angle at different locations, the coupling unit 200, the transmission waveguide 300, and the photodetector 400 are arranged in an array on an integrated photonic chip, such as... Figure 5The coupling units 200 are left with a certain gap for the transmission waveguide 300 to run, and the transmission waveguide 300 array transmits the light intensity signal to the photodetector 400 array and performs photoelectric conversion.

[0058] In a specific implementation, the method for measuring a light field wavefront includes the following steps:

[0059] (1) receiving the light intensity signal in the transmission waveguide 300 by the photodetector 400: P +x , P -x , P +y , and P -y .

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

[0061] (3) determining the angles θ x and θ y of the wavefront to be measured corresponding to the coupling power ratios R x and R y , according to the relationship between R x and θ x , and the relationship between R y and θ y .

[0062] (4) obtaining the distribution of the wavefront to be measured by integrating the wavefront angle measurement values at different positions by using a wavefront reconstruction algorithm according to the measured angles θ x and θ y of the wavefront to be measured.

[0063] Those skilled in the art will easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement, and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A wavefront measurement module for optical fields based on an integrated photonic chip, characterized in that, The measurement module includes a coupling unit (200), a transmission waveguide (300), and a photodetector (400), wherein: The coupling unit (200) is used to receive the wavefront to be measured and couple the wavefront to be measured to the transmission waveguide (300); the coupling unit (200) is connected to the transmission waveguide (300) on all four sides, the four sides including the forward and reverse directions in the lateral direction and the forward and reverse directions in the longitudinal direction, and 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). The structure of the coupling unit (200) is obtained by the following method: the objective function of the coupling unit structure is constructed such that the forward transmission waveguide (300) along the transverse direction is at the wavefront angle θ to be measured. x1 The power is maximized when the symmetry of the coupling unit in the yz plane, xz plane and z axis is used as a constraint condition, and the optimal coupling unit structure is obtained by solving the problem using an intelligent optimization algorithm. The objective function is as follows: Where FoM is the objective function, E 0 and H 0 represents the electric and magnetic field distribution of the fundamental mode of the transverse positive propagation waveguide. and They are E 0 and H The conjugate of 0, E and H It represents the actual electric and magnetic field distribution along the transverse forward transmission waveguide. S It is the cross section of the transverse forward propagation waveguide, and Re is the operation of taking the real part of the complex number.

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

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

4. A method for measuring the wavefront of an optical field using the measurement module according to any one of claims 1-3, characterized in that, The method includes the following steps: Arrange multiple of the measurement modules in an array; The wavefront angle of the wavefront to be measured (100) illuminating the coupling unit (200) of each measurement module is calculated using each measurement module; The wavefront reconstruction algorithm is used to reconstruct the wavefront angle of the wavefront to be measured (100) obtained by all measurement modules, thereby obtaining the position of the wavefront to be measured.

5. The method as described in claim 4, characterized in that, Each measurement module calculates the measurement angle of the wavefront to be measured according to the following method: Each photodetector (400) of each measurement module measures the light intensity in the forward and reverse directions of the transverse direction and in the forward and reverse directions of the longitudinal direction of the wavefront to be measured. The current light intensity coupling power ratio in the lateral and longitudinal directions is calculated by using the light intensity in the forward and reverse directions in the lateral direction and the forward and reverse directions in the longitudinal direction, respectively. Based on the pre-calibrated relationship between the 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.

6. The method as described in claim 5, characterized in that, The formula for calculating the optical intensity coupling power ratio is as follows: in, R x ( θ x () is the optical intensity coupling power ratio along the transverse 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 These represent the light intensity along the horizontal forward and reverse directions, and the vertical forward and reverse directions, respectively. θ x It is the transverse wavefront angle. θ y It is the longitudinal wavefront angle.

7. The method as described in claim 5 or 6, characterized in that, The transverse and longitudinal light intensity coupling power ratios are monotonic functions of the transverse and longitudinal wavefront angles, respectively.

8. A wavefront measurement system for optical fields based on an integrated photonic chip, characterized in that, The system includes an actuator for performing a wavefront measurement method for an integrated photonic chip as described in any one of claims 4-7.

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