CN113359069B - High-efficiency full Stokes component polarization measurement method - Google Patents

Abstract

The invention discloses a high-efficiency full Stokes component polarization measurement method, which comprises the following steps: designing a polarization measuring device, wherein the polarization measuring device comprises a lambda/2 micro-phase retarder array, a 3 lambda/4 micro-phase retarder array and a linear polaroid, and optimizing to obtain the fast axis azimuth angle of each micro-phase retarder in the two micro-phase retarder arrays; obtaining the arrangement of the two micro-phase retarder arrays and the linear polaroid based on the optimization result; the incident light enters a polarization measuring device to correspondingly obtain a light intensity signal L after 4 kinds of polarization modulation₁，L₂，L₃，L₄(ii) a From the light intensity signal L₁，L₂，L₃，L₄Resolving to obtain full Stokes component(s)₀，s₁，s₂，s₃)^TWhere T denotes the vector transpose sign. The method can realize the same measurement efficiency of the linear polarization component and the circular polarization component, maximize the overall efficiency, and is beneficial to reducing the uncertainty in the measurement process and improving the measurement efficiency.

Description

A high-efficiency full Stokes component polarization measurement method

technical field

The invention relates to the field of solar magnetic field measurement, in particular to a high-efficiency full Stokes component polarization measurement method.

Background technique

The magnetic field plays an important role in the study of the sun's atmospheric structure and various solar activity phenomena. Measuring the solar magnetic field is of great significance for understanding the physical mechanism and dynamic process of various activity phenomena on the sun's surface. In particular, the research on the effects of the solar magnetic field and the solar wind on the earth's magnetic field and the earth's ionosphere has practical application value for short-wave wireless communications, navigation systems, and spacecraft flight safety.

With the help of the Zeeman effect and the Hanle effect, the polarization measurement technology can effectively measure the solar magnetic field, and through the polarization radiation transfer theory, the measured polarization signal can be converted into magnetic field information to realize the analysis of the solar magnetic field information. Therefore, the development of polarization technology can effectively promote the level of solar magnetic field measurement.

The first step in the solar magnetic field polarization measurement process is to perform polarization modulation on the incident light of the solar incident polarization measurement instrument. After that, the image intensity signal obtained by polarization modulation is collected by the camera, and finally the polarization information of the incident light is obtained through numerical calculation, and the magnetic field information is further obtained through the radiation transfer theory. Considering that the Stokes component signal is usually weak in the solar magnetic field measurement, it is necessary to achieve high-efficiency full Stokes component measurement to realize the inverse solution of the solar magnetic field signal. To this end, this patent proposes a high-efficiency full Stokes component polarization measurement method for solar magnetic field measurement.

Chinese patent document CN 104216135 A discloses a polarizer array for obtaining full polarization parameters, a preparation method and an application thereof. The invention discloses a 2x2 size micro-polarizer unit. However, the polarization measurement method described in the invention has low polarization measurement efficiency and is difficult to apply to the field of solar magnetic field measurement.

Chinese patent document CN 103063300 B discloses a micro-polarization modulation array that realizes full-polarization imaging. The invention discloses a micro-polarization modulation array for realizing full-polarization imaging, which is composed of a micro-phase retarder array and a micro-polarizer. However, the polarization measurement efficiency of the polarization measurement method described in the invention is low, and it is difficult to apply to the field of solar magnetic field measurement.

To sum up, in the field of solar magnetic field measurement, how to develop a set of polarization measurement methods with high efficiency, strong reliability, and a smaller instrument volume for the full Stokes component is an urgent problem for those skilled in the art.

SUMMARY OF THE INVENTION

In order to realize the high-polarization-efficiency full-Stokes component polarization measurement of the solar magnetic field, the present invention proposes a high-efficiency full-Stokes-component polarization measurement method for the solar magnetic field measurement.

The present invention adopts following technical scheme:

A high-efficiency full Stokes component polarization measurement method, comprising:

Step 1: Design a polarization measurement device, which includes a λ/2 micro-phase retarder array, a 3λ/4 micro-phase retarder array, and a linear polarizer. Fast-axis azimuth of the micro-phase retarder;

Step 2: Based on the optimization results, obtain the arrangement of two micro-phase retarder arrays and linear polarizers;

Step 3: the incident light enters the polarization measuring device, and correspondingly obtains four polarization-modulated light intensity signals L _l , L ₂ , L ₃ , and L ₄ ;

Step 4: Calculate the full Stokes component (s ₀ , s ₁ , s ₂ , s ₃ ) ^T from the light intensity signals L ₁ , L ₂ , L ₃ , and L ₄ , where T represents the vector transposition symbol.

且总体效率为1，即偏振效率最大。Further, the measurement efficiency of the linearly polarized component and the circularly polarized component is the same, both

And the overall efficiency is 1, that is, the polarization efficiency is the largest.

Further, the phase retardation of the λ/2 micro-phase retarder array is λ/2, which is used to measure the linear polarization components s ₁ and s ₂ , and the phase retardation of the 3λ/4 micro-phase retarder array is 3λ/ 4. Used to measure the circular polarization component s ₃ , the linear polarizer is used as the analyzer to perform polarization modulation on the full Stokes component; the two micro-phase retarder arrays and the linear polarizer are arranged in sequence to perform polarization modulation on the incident light.

Further, the relationship between the Stokes component of the incident light and the measured light intensity signal is:

The beneficial effects and advantages of the present invention are:

1. The high-efficiency full Stokes component polarization measurement method proposed by the present invention can realize the same measurement efficiency of the linear polarization component and the circular polarization component, and maximize the overall efficiency, which is beneficial to reduce the uncertainty in the measurement process and improve the measurement efficiency. , which is conducive to the development of solar magnetic field polarization measurement.

2. The micro-phase retarder array and the linear polarizer used in the present invention are small in size, thereby reducing the system installation and calculation errors, facilitating installation and adjustment, and easy implementation;

3. The present invention can be connected with various optical systems, such as telescopes, optical elements, etc., through the mechanical interface structure, so as to facilitate integration with other optical systems.

Description of drawings

Fig. 1 is the overall structure diagram of the present invention;

Fig. 2 is the array distribution schematic diagram of λ/2 micro-phase retarder array in the present invention;

FIG. 3 is a schematic diagram of the array distribution of the 3λ/4 micro-phase retarder array in the present invention.

Reference numerals: 100: polarization measurement device; 101: interface mechanism; 102: measurement device housing; 103: image sensor; 110: λ/2 micro-phase retarder array; 120: 3λ/4 micro-phase retarder array; 130: Linear polarizer; 111: λ/2 micro phase retarder in fast axis 112.5° direction; 112: λ/2 micro phase retarder in fast axis 157.5° direction; 121: 3λ/4 micro phase retarder in fast axis 112.5° direction ;122: 3λ/4 micro-phase retarder in fast axis 67.5° direction.

Detailed ways

Embodiments of the present invention are given below in conjunction with the accompanying drawings to describe the technical solutions in detail.

且总体效率为1，即偏振效率最大。这样的设计可以降低测量过程中的不确定度，提升测量效率，利于太阳磁场偏振测量的开展。The method of the invention includes the design of a high-efficiency polarization measurement method and a set of polarization measurement devices. The polarization efficiency measurement method proposed in the present invention can make the measurement efficiency of the linear polarization component and the circular polarization component the same, both of which are

And the overall efficiency is 1, that is, the polarization efficiency is the largest. Such a design can reduce the uncertainty in the measurement process, improve the measurement efficiency, and facilitate the development of solar magnetic field polarization measurement.

The polarization measurement device proposed in the present invention uses two micro-phase retarder arrays and a linear polarizer as a polarization modulation device. One of the micro-phase retarder arrays has a phase retardation of λ/2, which can be used to measure the linear polarization components s ₁ and s ₂ . Another micro-phase retarder array has a phase retardation of 3λ/4, which can be used to measure the circular polarization component s ₃ . Linear polarizers can be used as analyzers for polarization modulation of the full Stokes component. Two micro-phase retarder arrays and linear polarizers are arranged in sequence to realize polarization modulation of incident light.

In this embodiment, the specific structure of the polarization measurement device is shown in FIG. 1 . The polarization measurement device 100 is composed of a mechanical interface structure 101 , a measurement device housing 102 , an image sensor 103 , a λ/2 micro-phase retarder array 110 , a 3λ/4 micro-phase retarder array 120 , and a linear polarizer 130 .

The mechanical interface structure 101 can connect the polarization measurement device 100 to various optical systems. The measuring device housing 102 can be used to fix various components in the mechanical measuring device 100 .

The λ/2 micro-phase retarder array 110 , the 3λ/4 micro-phase retarder array 120 , and the linear polarizer 130 are used for polarization modulation of incident light, and the image sensor 103 is used to collect and record the polarization-modulated light intensity signal. The phase retardation amount of the λ/2 micro-phase retarder array 110 is λ/2. The phase retardation amount of the λ/2 micro-phase retarder array 120 is 3λ/4. The azimuth angle of the fast axis of the linear polarizer 130 is 0°.

The array distribution of the λ/2 micro-phase retarder array 110 is shown in FIG. 2 . In the λ/2 micro-phase retarder array 110, every 4 micro-phase retarders are grouped in a periodic distribution, wherein the upper right corner and the upper left corner are the λ/2 micro phase retarders 111 in the direction of the fast axis 112.5°, and the lower left The corner and the lower right corner are the fast axis 157.5° direction λ/2 microphase retarder 112 .

The array distribution of the 3λ/4 micro-phase retarder array 120 is shown in FIG. 3 . In the 3λ/4 micro-phase retarder array 120, every 4 micro-phase retarders are grouped in a periodic distribution, wherein the upper left corner and the lower right corner are the 3λ/4 micro phase retarders 121 in the direction of the fast axis 112.5°, and the lower left corner is the 3λ/4 micro phase retarder 121. The corner and upper right corner are the 3λ/4 micro-phase retarders 122 in the 67.5° direction of the fast axis.

During the installation process, the horizontal and vertical positions of the λ/2 micro-phase retarder array 110, the 3λ/4 micro-phase retarder 122, the linear polarizer 130, and the image sensor 103 are exactly the same, and there is no offset between the relative positions of the four. This ensures that the incident light can be completely modulated by polarization, and all the incident light can enter the image sensor 103 .

The advantages of using the micro-phase retarder array include: reducing redundant mechanical fixed structures, facilitating the lightweight and miniaturized design of polarization measurement devices; reducing the image rotation phenomenon generated in the process of polarization modulation, and reducing the difficulty of modulation signal solution; Liquid crystal polarizers, micro-phase retarder arrays have more stable optical properties and are not easily affected by the environment. In addition, if the four components of the full Stokes are measured, at least four modulations of the polarization signal are required. Therefore, the two micro-phase retarder arrays both take 4 micro-phase retarders as one cycle.

After numerical calculation, the relationship between the Stokes component of the incident solar light and the measured light intensity signal can be obtained as:

Thus, the fast calculation of the full Stokes component is realized.

The theoretical basis of the present invention is as follows:

The incident light from the sun has a certain polarization signal, and the Stokes component of the incident light is (s ₀ , s ₁ , s ₂ , s ₃ ) ^T . The polarization modulation process can modulate the Stokes component of the incident light into a light intensity signal, which can then be collected by the image sensor.

The present invention selects two micro-phase retarder arrays 110 and 120 and a linear polarizer 130 as polarization modulation devices. The phase retardation of the λ/2 micro-phase retarder array 110 is λ/2, which can be used to measure the linear polarization components s ₁ and s ₂ . The phase retardation of the 3λ/4 micro-phase retarder array 120 is 3λ/4, which can be used to measure the circular polarization component s ₃ . The linear polarizer 130 can be used as an analyzer to perform polarization modulation on the full Stokes component. The micro-phase retarder arrays 110, 120 and the linear polarizer 130 are arranged in sequence, which can realize polarization modulation of the incident light.

The advantages of using the micro-phase retarder array include: reducing redundant mechanical fixed structures, facilitating the lightweight and miniaturized design of polarization measurement devices; reducing the image rotation phenomenon generated in the process of polarization modulation, and reducing the difficulty of modulation signal solution; Liquid crystal polarizers, micro-phase retarder arrays have more stable optical properties and are not easily affected by the environment. In addition, if the four components of the full Stokes are measured, at least four modulations of the polarization signal are required. Therefore, the two micro-phase retarder arrays both take 4 micro-phase retarders as one cycle.

The Stokes component of the incident light from the sun is (s ₀ , s ₁ , s ₂ , s ₃ ) ^T . After the incident light passes through the λ/2 micro-phase retarder array 110 , the 3λ/4 micro-phase retarder 120 and the linear polarizer 130 , the light intensity is subjected to four polarization modulations. The fast-axis azimuth reference of the polarization measurement device is the horizontal baseline of the bottom of the camera. The Mueller matrix of the micro-phase retarder is denoted as M _ij (θ _ij , φ _i ), where i=1, 2 correspond to the micro-retarder array 110 and micro-retarder array 120 respectively, and j=1, 2, 3, and 4 correspond respectively Four micro-phase retarders, θ _ij is the fast axis azimuth, and φ _i is the phase delay amount. The Mueller matrix of the linear polarizer 130 is denoted as M _P (0°), and 0° in parentheses is the azimuth angle of the fast axis of the linear polarizer. The four-order polarization modulation effect produced by the above three devices can be expressed as M _P (0°)·M _2j (θ _2j ,3λ/4)·M _1j (θ _1j ,λ/2). Taking the first row element of the matrix product of four polarization modulation effects, a new 4×4 instrument modulation matrix M can be formed. The light intensity signal corresponding to each unit combination in the array is (L ₁ , L ₂ , L ₃ , L ₄ ) The relationship between ^T and the Stokes component of the incident light from the sun is (L ₁ , L ₂ , L ₃ , L ₄ ) ^T = M·(s ₀ , s ₁ , s ₂ , s ₃ ) ^T .

The design of the fast axis azimuth angle of the micro phase retarder needs to meet the following conditions: the difference between the fast axis azimuth angles is 45°, which is convenient for processing; the polarization measurement device has the same measurement efficiency for the Stokes circular polarization component and the linear polarization component. Considering the above two points, in the λ/2 microphase retarder array 110, the upper right corner and the upper left corner are the fast axis 112.5° direction λ/2 microphase retarder 111, and the lower left corner and the lower right corner are the fast axis 157.5° direction λ/ 2 micro-phase retarder 112; 3λ/4 micro-phase retarder array 120, the upper left corner and lower right corner are fast axis 112.5° direction 3λ/4 micro phase retarder 121, the lower left corner and upper right corner are fast axis 67.5° direction 3λ /4 micro phase retarder 122 .

With the above configuration, the modulation matrix of the polarization measurement device can be expressed as:

Correspondingly, the demodulation matrix of the polarization measurement device can be expressed as:

The measurement efficiency of the polarization measurement device can be expressed as:

即线性偏振分量测量效率为

圆偏振分量测量效率为

整体测量效率为

达到最大值。从而实现高效率测量。这样的设计可以降低测量过程中的不确定度，提升测量效率，利于太阳磁场偏振测量的开展。In the formula, i=1, 2, 3, and 4 correspond to the I, Q, U, and V components of Stokes, respectively. Corresponding solution, get

That is, the measurement efficiency of the linear polarization component is

The measurement efficiency of the circularly polarized component is

The overall measurement efficiency is

Reaches the maximum value. This enables high-efficiency measurement. Such a design can reduce the uncertainty in the measurement process, improve the measurement efficiency, and facilitate the development of solar magnetic field polarization measurement.

The light intensity signals corresponding to each unit combination in the array are L ₁ , L ₂ , L ₃ , and L ₄ , which correspond to the upper right corner, upper left corner, lower left corner, and lower right corner, respectively. The relationship between the light intensity signal and the Stokes component can be expressed as:

After numerical calculation, the Stokes component of the incident light from the sun can be obtained as:

In practical application, the present invention can complete the measurement of the full Stokes component of incident solar light through the polarization measurement device 100, and the specific implementation steps are as follows:

Step 1: Design the high-efficiency measurement scheme of the polarization measurement device. The design is based on a λ/2 micro-phase retarder array, a 3λ/4 micro-phase retarder array, and a linear polarizer, and two micro-phase retarders are optimized. the fast axis azimuth of each micro-phase retarder in the array;

Step 2: Based on the design results, obtain the arrangement of two micro-phase retarder arrays and linear polarizers, and build a polarization measurement device accordingly;

Step 3: The incident light enters the polarization measurement device, and correspondingly obtains four polarization-modulated light intensity signals L ₁ , L ₂ , L ₃ , and L ₄ ;

Step 4: Calculate the full Stokes component (s ₀ , s ₁ , s ₂ , s ₃ ) ^T from the light intensity signals L ₁ , L ₂ , L ₃ , and L ₄ , where T represents the vector transposition symbol.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (3)

1. A high-efficiency full Stokes component polarization measurement method is characterized by comprising the following steps:

step 1: designing a polarization measuring device, wherein the polarization measuring device comprises a lambda/2 micro-phase retarder array, a 3 lambda/4 micro-phase retarder array and a linear polaroid, and optimizing to obtain the fast axis azimuth angle of each micro-phase retarder in the two micro-phase retarder arrays; the phase delay amount of the lambda/2 micro-phase retarder array is lambda/2, and the lambda/2 micro-phase retarder array is used for measuring a linear polarization component s₁、s₂The 3 lambda/4 micro-phase retarder array has the phase retardation of 3 lambda/4 and is used for measuring the circular polarization component s₃The linear polaroid is used as an analyzer for carrying out polarization modulation on the full Stokes component; the two micro phase retarder arrays and the linear polaroid are sequentially arranged in sequence to carry out polarization modulation on incident light;

step 2: obtaining the arrangement of the two micro-phase retarder arrays and the linear polaroid based on the optimization result;

and step 3: the incident light enters a polarization measuring device to correspondingly obtain a light intensity signal L after 4 kinds of polarization modulation₁，L₂，L₃，L₄；

And 4, step 4: from the light intensity signal L₁，L₂，L₃，L₄Resolving to obtain full Stokes component(s)₀，s₁，s₂，s₃)^TWhere T denotes the vector transpose sign.

2. The method as claimed in claim 1, wherein the linear polarization component and the circular polarization component have the same measurement efficiency and are all measured with the same measurement efficiency

And the overall efficiency is 1, i.e. the polarization efficiency is maximum.

3. The method as claimed in claim 1, wherein the relationship between the Stokes component of the incident light and the measured light intensity signal is:

Images