Detection system and method based on vortex phase circular polarization vector superposition

Abstract

The present invention relates to the field of optical detection technology, and discloses a detection system and method based on vortex phase circular polarization vector superposition to accurately measure the thickness uniformity of a transparent object to be detected. The method includes: a processor obtains a first vector polarization field collected by a phase detector when there is no object to be detected, and after placing the object to be detected between a polarization grating and a first vortex wave plate or a second vortex wave plate, obtains a second vector polarization field collected by the phase detector, and compares the polarization state difference between the superimposed vector polarization field when there is an object to be detected and the superimposed vector polarization field when there is no object to be detected, and obtains the phase distribution of each coordinate point on the cross section perpendicular to the optical axis in the transparent part of the object to be detected according to the principle of circular polarization vector superposition, and then unpacks the phase distribution of each coordinate point to obtain the phase delay amount caused by the thickness of each coordinate point on the cross section, and then solves the thickness uniformity of the transparent part of the object to be detected according to the phase delay amount of each coordinate point on the cross section.

Description

Technical Field

[0001] The present invention relates to the field of optical detection technology, and in particular to a detection system and method based on vortex phase circular polarization vector superposition. Background Art

[0002] With the development of modern industrial technology, the requirements for high-precision detection technology are getting higher and higher.

[0003] Traditional optical inspection mostly infers the parameter information of the object being inspected through the changes in the phase information in the interference fringes caused by the reflection of the object being inspected. In addition, to obtain more accurate surface information, four-step phase shift interference is required, which is complicated to operate and has high requirements for the accuracy of phase shift. At the same time, the reflection-based inspection mechanism is not suitable for measuring the thickness uniformity of transparent objects. Summary of the invention

[0004] The present invention aims to disclose a detection system and method based on vortex phase circular polarization vector superposition to accurately measure the thickness uniformity of a light-transmitting object.

[0005] To achieve the above-mentioned purpose, the detection system based on vortex phase circular polarization vector superposition disclosed by the present invention comprises:

[0006] A left-handed circularly polarized light generating component, used for generating left-handed circularly polarized light;

[0007] A right-handed circularly polarized light generating component, used for generating right-handed circularly polarized light;

[0008] The wavelength of the laser light source in the left-handed circularly polarized light generating component is equal to the wavelength of the laser light source in the right-handed circularly polarized light generating component;

[0009] A first vortex wave plate located between the left-handed circularly polarized light generating assembly and the polarization grating;

[0010] A second vortex wave plate located between the right-handed circularly polarized light generating assembly and the polarization grating;

[0011] The first vortex wave plate and the second vortex wave plate are vortex wave plates of equal and integer orders;

[0012] The incident light axis of the first vortex wave plate and the incident light axis of the second vortex wave plate are respectively located at the positive and negative first-order diffraction angles of the polarization grating, so as to deflect the two incident vortex lights into a combined light beam with the same propagation direction and vector superposition;

[0013] A phase detector located in the exit direction of the polarization grating, used for collecting the vector polarization field of the combined light beam after superposition;

[0014] A transparent object to be detected located between the polarization grating and the first vortex wave plate or the second vortex wave plate, wherein the light beam phase delay amount of the object to be detected is changed due to the thickness of the light-transmitting portion;

[0015] The processor connected to the phase detector is used to compare the polarization state difference between the superimposed vector polarization field when there is a detected object and the superimposed vector polarization field when there is no detected object, and obtain the phase distribution of each coordinate point on the cross section perpendicular to the optical axis in the transparent part of the detected object according to the principle of circular polarization vector superposition, and then unwrap the phase distribution of each coordinate point to obtain the phase delay caused by the thickness of each coordinate point on the cross section, and then solve the thickness uniformity of the transparent part of the detected object according to the phase delay of each coordinate point on the cross section.

[0016] Preferably, the order of the first vortex wave plate and the order of the second vortex wave plate are both 1.

[0017] Preferably, in the process of solving the thickness uniformity of the light-transmitting portion of the object to be detected based on the phase delay amount of each coordinate point on the cross section, the processor is specifically used to: first combine the phase delay amount of each coordinate point with the wavelength of the laser light source and the refractive index of the object to be detected to calculate the thickness information of each coordinate point on the cross section extending along the direction parallel to the optical axis; and then obtain the thickness uniformity of the light-transmitting portion of the object to be detected based on the thickness information of each coordinate point on the cross section extending along the direction parallel to the optical axis.

[0018] To achieve the above object, the present invention further discloses a detection method based on vortex phase circular polarization vector superposition, comprising:

[0019] Deploy a detection system based on vortex phase circular polarization vector superposition as described above;

[0020] The processor acquires a first vector polarization field collected by the phase detector when there is no object to be detected;

[0021] After placing the object to be detected between the polarization grating and the first vortex wave plate or the second vortex wave plate, the processor obtains the second vector polarization field collected by the phase detector, and compares the polarization state difference between the superimposed vector polarization field when there is a detected object and the superimposed vector polarization field when there is no detected object, and obtains the phase distribution of each coordinate point on the cross section perpendicular to the optical axis in the transparent part of the detected object according to the principle of circular polarization vector superposition, and then unpacks the phase distribution of each coordinate point to obtain the phase delay caused by the thickness of each coordinate point on the cross section, and then solves the thickness uniformity of the transparent part of the detected object according to the phase delay of each coordinate point on the cross section.

[0022] The present invention has the following beneficial effects:

[0023] The system is simple, practical and easy to deploy. By comparing the polarization state difference between the superimposed vector polarization field when there is an object to be detected and the superimposed vector polarization field when there is no object to be detected, and according to the principle of circular polarization vector superposition, the phase distribution of each coordinate point on the cross section perpendicular to the optical axis in the transparent part of the object to be detected is obtained, and then the phase distribution of each coordinate point is unwrapped to obtain the phase delay caused by the thickness of each coordinate point on the cross section, and then the thickness uniformity of the transparent part of the object to be detected is solved according to the phase delay of each coordinate point on the cross section, which can effectively eliminate system errors and ensure that high precision can reach the nanometer level.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0026] Figure 1 It is a block diagram of a detection system based on vortex phase circular polarization vector superposition disclosed in an embodiment of the present invention.

[0027] Figure 2 It is a schematic diagram of the principle of superposition of circular polarization vectors based on vortex phase disclosed in an embodiment of the present invention.

[0028] Figure 3 It is a flow chart of a detection method based on vortex phase circular polarization vector superposition disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0030] Example 1

[0031] This embodiment discloses a detection system based on vortex phase circular polarization vector superposition, such as Figure 1 As shown, including:

[0032] The left-handed circularly polarized light generating component 1 is used for generating left-handed circularly polarized light.

[0033] The right-handed circularly polarized light generating component 2 is used to generate right-handed circularly polarized light.

[0034] Among them, the wavelength of the laser light source in the left-handed circularly polarized light generating component is equal to the wavelength of the laser light source in the right-handed circularly polarized light generating component.

[0035] The first vortex wave plate 3 is located between the left-handed circularly polarized light generating assembly and the polarization grating 5.

[0036] The second vortex wave plate 4 is located between the right-handed circularly polarized light generating assembly and the polarization grating.

[0037] The first vortex wave plate and the second vortex wave plate are vortex wave plates of equal and integer orders. Preferably, the orders of the first vortex wave plate and the second vortex wave plate are both 1. The smaller the order, the simpler the complexity of subsequent calculation of phase distribution. As an alternative, the orders of the first and second vortex wave plates can also be 2 or 3 or other positive integers.

[0038] The incident light axis of the first vortex wave plate and the incident light axis of the second vortex wave plate are respectively at the positive and negative first-order diffraction angles of the polarization grating, so as to deflect the two incident vortex lights into a combined light beam with the same propagation direction and vector superposition.

[0039] The phase detector 6 located in the outgoing direction of the polarization grating is used to collect the vector polarization field of the combined light beam after superposition.

[0040] The transparent object to be detected is located between the polarization grating and the first vortex wave plate or the second vortex wave plate. The thickness of the transparent part of the object changes the phase delay of the light beam.

[0041] The processor 7 connected to the phase detector is used to compare the polarization state difference between the superimposed vector polarization field when there is a detected object and the superimposed vector polarization field when there is no detected object, and obtain the phase distribution of each coordinate point on the cross section perpendicular to the optical axis in the transparent part of the detected object according to the principle of circular polarization vector superposition, and then unwrap the phase distribution of each coordinate point to obtain the phase delay caused by the thickness of each coordinate point on the cross section, and then solve the thickness uniformity of the transparent part of the detected object according to the phase delay of each coordinate point on the cross section.

[0042] Preferably, in the process of solving the thickness uniformity of the light-transmitting portion of the object to be detected based on the phase delay amount of each coordinate point on the cross section, the processor is specifically used to: first combine the phase delay amount of each coordinate point with the wavelength of the laser light source and the refractive index of the object to be detected to calculate the thickness information of each coordinate point on the cross section extending along the direction parallel to the optical axis; and then obtain the thickness uniformity of the light-transmitting portion of the object to be detected based on the thickness information of each coordinate point on the cross section extending along the direction parallel to the optical axis.

[0043] In this embodiment, the detection principle based on the superposition of circularly polarized light vectors is described as follows:

[0044] Any left-handed circularly polarized light and any right-handed circularly polarized light of the same frequency and amplitude can be vector-superimposed to obtain linearly polarized light. Therefore, we only need to know the law of vector superposition to obtain the overall polarization state distribution of the superimposed light field. The following is the specific derivation process.

[0045] like Figure 2As shown, according to the representation method of the Jones matrix, any polarized light field distribution can be represented by the vector E: Where C is the intensity amplitude (since the light intensity at the corresponding points is consistent, the subsequent light intensity amplitude is represented by C); The initial phase is The matrix represents the direction of the unit polarization state The first element of the matrix represents the x polarization component The second element represents the y polarization component For example This means left-hand circular deviation).

[0046] Consider the superposition of arbitrary left-handed circularly polarized light and arbitrary right-handed circularly polarized light of the same frequency and amplitude at a certain point.

[0047] Arbitrary left circularly polarized field vector E LCP It can be expressed as in The initial phase of the left circularly polarized light is E; and the light field vector E in any right circularly polarized light field is RCP It can be expressed as in For this reason, the initial phase of the right circularly polarized light is defined as the phase difference mode. and phase common mode satisfy:

[0048] Then we have: Therefore, the light field vector E of any superposition point P It can be calculated as:

[0049]

[0050] The results show that any left-handed circularly polarized light and any right-handed circularly polarized light of the same frequency and amplitude can be vector-superimposed to obtain linearly polarized light, and the polarization direction is determined by (That is, half of the phase difference between left-handed circularly polarized light and right-handed circularly polarized light at that point). Therefore, at different position coordinates of the superimposed light field, the left-hand and right-handed phase differences are different, so the corresponding linear polarization states are different.

[0051] The angle θ between the polarization direction and the positive x direction is used to represent the linear polarization direction, and the polarization angle θ satisfies:

[0052]

[0053] The linear polarization angle θ obtained by superimposing any left-hand circular polarization light and any right-hand circular polarization light of the same frequency and amplitude is the same as the phase angle of the left-hand circular polarization light. and right-hand circular polarization phase The relationship is:

[0054]

[0055] At this time, when the right-handed circular polarization phase changes by Δφ, the linear polarization direction θ′ obtained by superposition satisfies:

[0056]

[0057] The relationship between the right-hand circularly polarized light phase change Δφ and the difference in the angles of the two superimposed linear polarization directions can be obtained:

[0058] Δφ=2(θ′-θ)

[0059] Therefore, the polarization state direction θ0(x, y) of each point measured when there is no object to be detected and the polarization state direction θ1(x, y) of each point measured when there is an object to be detected are substituted into the formula to obtain the phase distribution of each point of the object to be detected.

[0060]

[0061] Since the polarization state direction in the detection process ranges from [0,2π), for example, the actual polarization state direction should be π+2*N*π (N is an arbitrary integer), and the polarization direction detected is π. Therefore, the phase directly calculated It can only be truncated within the range of [0,2π) and cannot obtain a true continuous phase.

[0062] At this time, the calculated phase Unwrapping is performed to connect the truncated phase into a continuous phase. Common two-dimensional unwrapping algorithms are divided into two categories: one is a path tracking phase unwrapping algorithm that seeks the path-independent condition of the integral result, and the other is a path-independent phase unwrapping algorithm that seeks to satisfy the minimum norm solution. In this embodiment, the least squares algorithm in the second category can be used to perform unwrapping calculations to obtain the unwrapped continuous phase ΔΦ(x, y). The core idea is that the gradient difference of the phase before and after unwrapping should be minimized.

[0063] After obtaining the actual continuous phase ΔΦ(x,y) of each point, the thickness d(x,y) of each point of the object can be estimated:

[0064]

[0065] Where λ is the wavelength of the laser light source, and n is the refractive index corresponding to the material of the object to be detected.

[0066] Example 2

[0067] Corresponding to the above embodiment, this embodiment discloses a detection method based on vortex phase circular polarization vector superposition, such as Figure 3 As shown, the following steps are included:

[0068] Step S1: deploy a detection system based on vortex phase circular polarization vector superposition. The system is the system of the above embodiment, and the specifics can be referred to Figure 1 , no further elaboration is given.

[0069] Step S2: The processor obtains a first vector polarization field collected by the phase detector when there is no object to be detected.

[0070] Step S3, after placing the object to be detected between the polarization grating and the first vortex wave plate or the second vortex wave plate, the processor obtains the second vector polarization field collected by the phase detector, and compares the polarization state difference between the superimposed vector polarization field when there is a detected object and the superimposed vector polarization field when there is no detected object, and obtains the phase distribution of each coordinate point on the cross section perpendicular to the optical axis in the light-transmitting part of the detected object according to the principle of circular polarization vector superposition, and then unpacks the phase distribution of each coordinate point to obtain the phase delay caused by the thickness of each coordinate point on the cross section, and then solves the thickness uniformity of the light-transmitting part of the detected object according to the phase delay of each coordinate point on the cross section.

[0071] Preferably, the process of the processor solving the thickness uniformity of the light-transmitting portion of the detected object according to the phase delay amount of each coordinate point on the cross section specifically includes:

[0072] Step S31, firstly combine the phase delay of each coordinate point with the wavelength of the laser light source and the refractive index of the object to be detected to calculate the thickness information of each coordinate point on the cross section extending along the direction parallel to the optical axis.

[0073] Step S32, then obtaining the thickness uniformity of the light-transmitting portion of the object to be inspected according to the thickness information of each coordinate point of the cross section extending in a direction parallel to the optical axis.

[0074] Thus, in this embodiment, the second vector polarization field is compared with the first vector polarization field, thereby effectively avoiding interference caused by noise of the system itself when no detection object is placed.

[0075] In summary, the detection system and method based on vortex phase circular polarization vector superposition disclosed in the above embodiments of the present invention have at least the following beneficial effects:

[0076] The system is simple, practical and easy to deploy. By comparing the polarization state difference between the superimposed vector polarization field when there is an object to be detected and the superimposed vector polarization field when there is no object to be detected, and based on the principle of circular polarization vector superposition, the phase distribution of each coordinate point on the cross section perpendicular to the optical axis in the transparent part of the object to be detected is obtained. Then, the phase distribution of each coordinate point is unwrapped to obtain the phase delay caused by the thickness of each coordinate point on the cross section. Then, the thickness uniformity of the transparent part of the object to be detected is solved based on the phase delay of each coordinate point on the cross section, ensuring that high precision can be achieved at the nanometer level.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A detection system based on vortex phase circular polarization vector superposition, characterized in that: include: A left-handed circularly polarized light generating component, used for generating left-handed circularly polarized light; A right-handed circularly polarized light generating component, used for generating right-handed circularly polarized light; The wavelength of the laser light source in the left-handed circularly polarized light generating component is equal to the wavelength of the laser light source in the right-handed circularly polarized light generating component; A first vortex wave plate located between the left-handed circularly polarized light generating assembly and the polarization grating; A second vortex wave plate located between the right-handed circularly polarized light generating assembly and the polarization grating; The first vortex wave plate and the second vortex wave plate are vortex wave plates of equal and integer orders; The incident light axis of the first vortex wave plate and the incident light axis of the second vortex wave plate are respectively located at the positive and negative first-order diffraction angles of the polarization grating, so as to deflect the two incident vortex lights into a combined light beam with the same propagation direction and vector superposition; A phase detector located in the exit direction of the polarization grating, used for collecting the vector polarization field of the combined light beam after superposition; A transparent object to be detected located between the polarization grating and the first vortex wave plate or the second vortex wave plate, wherein the light beam phase delay amount of the object to be detected is changed due to the thickness of the light-transmitting portion; The processor connected to the phase detector is used to compare the polarization state difference between the superimposed vector polarization field when there is a detected object and the superimposed vector polarization field when there is no detected object, and obtain the phase distribution of each coordinate point on the cross section perpendicular to the optical axis in the transparent part of the detected object according to the principle of circular polarization vector superposition, and then unwrap the phase distribution of each coordinate point to obtain the phase delay caused by the thickness of each coordinate point on the cross section, and then solve the thickness uniformity of the transparent part of the detected object according to the phase delay of each coordinate point on the cross section.

2. The detection system based on vortex phase circular polarization vector superposition according to claim 1 is characterized in that: The orders of the first vortex wave plate and the second vortex wave plate are both 1.

3. The detection system based on vortex phase circular polarization vector superposition according to claim 1 or 2, characterized in that: In the process of solving the thickness uniformity of the light-transmitting portion of the object to be detected based on the phase delay amount of each coordinate point on the cross section, the processor is specifically used to: first combine the phase delay amount of each coordinate point with the wavelength of the laser light source and the refractive index of the object to be detected to calculate the thickness information of each coordinate point on the cross section extending along the direction parallel to the optical axis; then obtain the thickness uniformity of the light-transmitting portion of the object to be detected based on the thickness information of each coordinate point on the cross section extending along the direction parallel to the optical axis.

4. A detection method based on vortex phase circular polarization vector superposition, characterized in that: include: Deploy a detection system based on vortex phase circular polarization vector superposition as described in any one of claims 1 to 3; The processor acquires a first vector polarization field collected by the phase detector when there is no object to be detected; After placing the object to be detected between the polarization grating and the first vortex wave plate or the second vortex wave plate, the processor obtains the second vector polarization field collected by the phase detector, and compares the polarization state difference between the superimposed vector polarization field when there is a detected object and the superimposed vector polarization field when there is no detected object, and obtains the phase distribution of each coordinate point on the cross section perpendicular to the optical axis in the transparent part of the detected object according to the principle of circular polarization vector superposition, and then unpacks the phase distribution of each coordinate point to obtain the phase delay caused by the thickness of each coordinate point on the cross section, and then solves the thickness uniformity of the transparent part of the detected object according to the phase delay of each coordinate point on the cross section.

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