CN101319958B - Quarter-wave plate fast axis orientation real-time measurement device and method - Google Patents

Abstract

A device and method for real-time measurement of the fast axis azimuth of a quarter wave plate, the device is composed of a collimated light source, a polarizer, a standard quarter wave plate, a diffraction beam splitter element, a focusing lens, an analyzer array, a photodetector array, an amplifier circuit and a signal processing system. The measurement method is that a parallel light beam emitted by the collimated light source passes through a polarizer and a standard quarter wave plate to form a circularly polarized light, the circularly polarized light passes through the quarter wave plate to be measured and is split by the diffraction beam splitter element, a plurality of sub-beams with equal intensity are focused on the analyzer array by a focusing lens, each of which generates polarization interference, forming interference light intensity with a certain phase shift amount in sequence and received by a photodetector array, the electrical signal output by the photodetector array passes through an amplifier circuit and is processed by a signal processing system, so that the fast axis azimuth angle of the quarter wave plate to be measured can be obtained in real time.

Description

Quarter-wave plate fast axis orientation real-time measurement device and method

technical field

The invention relates to the field of polarization measurement, in particular to a device and method for real-time measurement of the fast axis orientation of a quarter-wave plate.

Background technique

Quarter-wave plate is a commonly used polarizing optical element, which is widely used in modern optical measurement technology and polarized light application technology and other fields. The fast-axis orientation is one of the important optical parameters of the quarter-wave plate. Usually, the fast-axis orientation of the quarter-wave plate is not marked, and it is necessary to accurately measure the quarter-wave plate’s The orientation of the fast axis and make adjustments based on this.

The prior art [1] (refer to Wang Wei, Li Guohua, Wu Fuquan, etc. A new method for measuring wave plate retardation and fast axis orientation. China Laser, Vol.30, 1121-1123, 2003) describes a method that can measure four One-third wave plate fast axis orientation device, the device is mainly composed of light source, polarizer, analyzer and photodetector. During the measurement process, rotate the measured quarter-wave plate at a constant speed and continuously measure the outgoing light intensity to obtain the curve of the outgoing light intensity changing with time. The rotation speed of the quarter-wave plate is used to calculate the fast-axis orientation of the quarter-wave plate under test. Since the measured quarter-wave plate needs to be rotated continuously, the device cannot realize real-time measurement of the fast axis orientation, and requires a precision rotating mechanism that can continuously and stably rotate the quarter-wave plate, while the light intensity fluctuation of the light source will change The curve of the emitted light intensity changing with time will introduce a large measurement error.

Prior technology [2] (see Zhengping Wang, Qingbo Li, Qiao Tan, et al..Method of measuring practical retardance and judging the fast or slow axis of a quarter-wave plate. Measurement, Vol.39, 729-735, 2006 ) describes a device for measuring the orientation of the fast axis of a quarter-wave plate, which is mainly composed of a light source, a polarizer, a reflecting prism, an analyzer and an optical power meter. In the fast-axis azimuth measurement process, first use other measurement methods such as extinction method to find a certain main axis of the quarter-wave plate to be measured, take this main axis as the selected axis and make it 45° to the transmission axis of the polarizer ° angle. Then rotate the polarizer so that the light transmission axis is parallel and perpendicular to the light transmission axis of the polarizer, and the optical power meter obtains two light intensity signals in the two states. Then turn the quarter-wave plate to be tested by 90°, and obtain two light intensity signals under the two states that the light transmission axis of the analyzer is parallel to the light transmission axis of the polarizer, and they are vertical. Finally, the phase delay is calculated by using these four light intensity signals, and whether the selected axis is the fast axis or the slow axis is determined by judging the positive or negative of the phase delay. Due to the need to rotate the measured quarter-wave plate and polarizer multiple times, this device cannot achieve real-time measurement of the fast axis orientation, and its measurement accuracy is affected by light intensity fluctuations, which requires high stability of the light source and requires precise rotation The mechanism makes the structure of the device complex.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art, to provide a kind of real-time measuring device and method for the fast axis orientation of a quarter wave plate, the device and method should be able to measure the fast axis orientation of a quarter wave plate in real time, The measurement result is not affected by the light intensity fluctuation of the light source, and the measurement device has the characteristics of simple structure, stable performance and convenient operation.

Technical solution of the present invention:

A quarter-wave plate fast-axis orientation real-time measuring device is characterized in that the device consists of a collimated light source, a polarizer, a standard quarter-wave plate, a diffractive beam splitting element, a focusing lens, an analyzer array, It consists of a photodetector array, an amplifying circuit and a signal processing system, and its positional relationship is: along the forward direction of the light beam of the collimated light source, the polarizer, the standard quarter-wave plate, the diffraction beam element, focusing lens, analyzer array, photodetector array, the socket of the quarter wave plate to be measured is set between the standard quarter wave plate and the diffraction beam splitting element, so The signal detected by the photodetector array is amplified by the amplifying circuit and then input to the signal processing system for data processing.

The polarizer is a polarizer, a polarizing prism or a polarizing phase mask.

The standard quarter-wave plate is a crystal material type quarter-wave plate, a multi-component compound type quarter-wave plate, a reflective prism type quarter-wave plate or a birefringent film type quarter-wave plate The plate, whose phase retardation is equal to or very close to 90°, and the angle formed by its fast axis and the light transmission axis of the polarizer is 45° or 135°.

The diffractive beam-splitting element is an orthogonal amplitude grating, an orthogonal phase grating or a Damman grating, which utilizes the diffraction effect to form a beam of incident light into multiple outgoing sub-beams, and at least three sub-beams have equal intensities.

The array of polarizers is a combination of multiple analyzers formed in one plane, and the analyzers are polarizers or polarization phase masks.

The polarizer array is formed by four first polarizers, second polarizers, third polarizers and fourth polarizers with the same structure arranged in four quadrants in the same plane. The angles formed by the light transmission axis of the first polarizer, the second polarizer, the third polarizer, and the fourth polarizer and the light transmission axis of the polarizer are 0°, 45° respectively , 90° and 135°.

The photodetector array is a combination of multiple photodetectors, or multiple photodetectors, and the photodetectors are photodiodes, phototransistors, photomultiplier tubes or photocells.

The photodetector array corresponds to the structure of the analyzer array, and is composed of a first photodetector, a second photodetector, and a third photodetector arranged in four quadrants in the same plane with the same structure. detector and a fourth photodetector.

The signal processing system is composed of a multi-channel high-speed data acquisition card with A/D conversion function and a computer with corresponding data processing and analysis software, or is composed of a signal processing circuit and a microprocessor with corresponding processing functions .

The method for measuring the fast-axis orientation of the quarter-wave plate by using the above-mentioned real-time measuring device for the fast-axis orientation of the quarter-wave plate is characterized in that it comprises the following steps:

① Establish the quarter-wave plate fast-axis orientation real-time measurement device;

② Insert the quarter-wave plate to be measured between the standard quarter-wave plate and the diffraction beam splitting element and adjust the optical path;

③ Utilize the first photodetector, the second photodetector, the third photodetector and the fourth photodetector of the photodetector array to record the first polarizer, the first polarizer and the fourth photodetector of the polarizer array respectively. The interference light intensities I ₁ , I ₂ , I ₃ , and I ₄ of the second polarizer, the third polarizer, and the fourth polarizer are converted into electrical signals, and the electrical signals are amplified at the same time through the amplifying circuit. After inputting the described signal processing system;

④ The signal processing system carries out the following operations:

$\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\sqrt{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; ,</span>$

$\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{\sqrt{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; ,</span>$

Calculate the value of θ in the range of 0° to 180°, that is, obtain the fast axis orientation of the quarter wave plate to be measured.

Compared with prior art, technical effect of the present invention is as follows:

1. It can measure the fast axis orientation of the quarter wave plate in real time. Multiple sub-beams with equal intensity can be obtained by using diffractive beam-splitting elements. These sub-beams are focused on the analyzer array at the same time to generate polarization interference. The photodetector array simultaneously receives the interference light intensity with a certain phase shift and Converted to an electrical signal, the electrical signal is simultaneously amplified by the amplifier circuit and then processed at high speed by the signal processing system, so the fast axis orientation of the quarter-wave plate can be measured in real time.

2. The light intensity fluctuation of the light source does not affect the measurement results. When using multiple interfering light intensities with a certain amount of phase shifting to calculate the fast axis azimuth angle, the numerator and denominator in the calculation formula have the same initial light intensity factor, so that the measurement result has nothing to do with the initial light intensity, so the measured 1/4 The measurement result of the fast axis orientation of a wave plate is not affected by the light intensity fluctuation of the light source.

3. The structure is simple and stable. The quarter-wave plate fast axis orientation real-time measuring device of the present invention has no rotating optical element and no rotating mechanism, so the measuring device has a simple structure and high stability.

Description of drawings

Fig. 1 is the structural block diagram of the embodiment of the real-time measurement device of quarter-wave plate fast axis azimuth of the present invention

Fig. 2 is the structural diagram of analyzer array in the embodiment of the present invention

Fig. 3 is the structural diagram of photodetector array in the embodiment of the present invention

Fig. 4 is a diagram of the interference light intensity formation and receiving optical path with sequential phase shift of 90° in the embodiment of the present invention

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited thereby.

Please refer to FIG. 1 first. FIG. 1 is a structural block diagram of an embodiment of a quarter-wave plate fast-axis azimuth real-time measurement device according to the present invention. As can be seen from the figure, the quarter-wave plate fast axis orientation real-time measuring device of the present invention is composed of a collimated light source 1, a polarizer 2, a standard quarter-wave plate 3, a diffractive beam splitting element 5, and a focusing lens 6 , an analyzer array 7, a photodetector array 8, an amplifying circuit 9 and a signal processing system 10, and its positional relationship is: along the forward direction of the beam of the collimated light source 1, followed by the polarizer 2. Standard quarter wave plate 3, diffractive beam splitting element 5, focusing lens 6, analyzer array 7, photodetector array 8, described diffractive beam splitting element 5 is a quadrature phase grating, and its grating engraved The line direction is at an angle of 45° to the direction of the light transmission axis of the polarizer 2, and the signal detected by the photodetector array 8 is amplified by the amplifier circuit 9 and then input to the signal processing system 10 for further processing. data processing.

In this example

The diffraction beam splitting element 5 is a quadrature phase grating, and the direction of the grating lines is at an angle of 45° to the direction of the transmission axis of the polarizer 2 . The incident light is diffracted after passing through the diffraction beam-splitting element 5, wherein the zero-order and even-order diffracted lights disappear and only odd-order diffracted lights are present, and the four ±1-order diffracted lights have equal intensities and are the highest-intensity diffracted lights.

The structure of the described polarizer array 7 is as shown in Figure 2, by the first polarizer 701, the second polarizer 702, the 3rd polarizer 703, the 4th polarizer 704 with the same structure in In the same plane, they are arranged and combined in four quadrants. The light transmission axes of the first polarizer 701, the second polarizer 702, the third polarizer 703, and the fourth polarizer 704 are in line with the starting The angles formed by the transmission axes of the polarizer 2 are 0°, 45°, 90° and 135° respectively.

The structure of described photodetector array 8 is as shown in Figure 3, corresponds to the structure of described polarizer array 7, is by the first photodetector arranged in four quadrants in the same plane by the same structure 801, a second photodetector 802, a third photodetector 803 and a fourth photodetector 804.

Described signal processing system 10 is constituted by a multi-channel high-speed data acquisition card with A/D conversion function and a computer with corresponding data processing and analysis software,

The structure of the preferred embodiment of the present invention is shown in Fig. 1, Fig. 2, Fig. 3, and its concrete structure and parameter are as follows:

The collimated light source 1 is a He-Ne laser, the polarizer 2 is a Glan-Taylor prism made of calcite crystal material, the standard quarter wave plate 3 is a quartz wave plate with a phase retardation error less than 0.3°, and the diffraction beam splitting element The width of the grating lines of 5 is 10 μm, and the focusing lens 6 is a doublet lens with a focal length equal to 100 mm. The first analyzer 701, the second analyzer 702, and the third analyzer in the analyzer array 7 703. The fourth polarizer 704 is a polarizer with an extinction ratio better than 10 ⁻² , the photodetector array 8 is a four-quadrant photodiode, the amplifier circuit 9 is a four-channel signal amplifier circuit, and the signal processing system 10 consists of 100M four-way synchronous data acquisition card and computer.

The method for measuring the fast axis orientation of the quarter wave plate by using the real-time measuring device for the fast axis orientation of the quarter wave plate is characterized in that it comprises the following steps:

① Establish the quarter-wave plate fast-axis orientation real-time measurement device;

② Insert the quarter wave plate 4 to be measured between the standard quarter wave plate 3 and the diffraction beam splitting element 5 and adjust the optical path;

③ Utilize the first photodetector 801, the second photodetector 802, the third photodetector 803 and the fourth photodetector 804 of the photodetector array 8 to record the first photodetector of the analyzer array 7 respectively. The interference light intensities I ₁ , I ₂ , I ₃ , and I ₄ of the first polarizer 701, the second polarizer 702, the third polarizer 703, and the fourth polarizer 704 are converted into electrical signals, and the electrical signals pass through The amplifying circuit 9 is simultaneously amplified and then input to the signal processing system 10;

4. the signal processing system 10 performs the following operations:

$\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sin"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">sin</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\sqrt{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; ,</span>$

$\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{\sqrt{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; ,</span>$

Calculate the value of θ within the range of 0° to 180°, that is, obtain the fast axis orientation of the quarter wave plate 4 to be measured.

The parallel light beam emitted by the collimated light source 1 passes through the polarizer 2 and the standard quarter-wave plate 3 in turn to form circularly polarized light, and the circularly polarized light passes through the measured quarter-wave plate 4 and then is processed by the diffraction beam splitting element 5 Diffraction splitting, in which only four ±1st-order diffracted beams with equal intensity are effectively utilized sub-beams. The four sub-beams form an interference light intensity with a phase shift of 90° in sequence and are received. Please refer to Figure 4 for the specific optical path. The four sub-beams form a certain angle with each other and are focused by the focusing lens 6. The four sub-beams respectively pass through the analyzer. After the first polarizer 701, the second polarizer 702, the third polarizer 703 and the fourth polarizer 704 in the detector array 7 perform polarization interference, the interference light intensity is correspondingly determined by the photodetector array 8 The first photodetector 801 , the second photodetector 802 , the third photodetector 803 and the fourth photodetector 804 receive.

The light vector E of the circularly polarized light emitted from the standard quarter-wave plate 3 can be expressed by Jones vector as:

$\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; 1</span>}\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}\end{array}\right]<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Where: E ₀ is the amplitude of the outgoing beam of the polarizer 2. The Jones matrix G of the quarter-wave plate 4 to be tested can be expressed as:

$\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; =</span>\left[\begin{array}{cc}\mathrm{<span\; class="notranslate">\; cos</span>}\frac{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\frac{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\frac{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sin"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">sin</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\frac{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sin"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">sin</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& \mathrm{<span\; class="notranslate">\; cos</span>}\frac{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\frac{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\end{array}\right]<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Where: δ and θ are the phase retardation and fast axis azimuth angle of the quarter-wave plate 4 to be tested respectively, δ is close to 90°, and θ varies from 0° to 180°. The first polarizer 701, the second polarizer 702, the third polarizer 703, and the fourth polarizer 704 in the described polarizer array 7 can be jointly expressed as

$\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; =</span>\left[\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">cos</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}& \frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sin"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">sin</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\\ \frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sin"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">sin</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}& {\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sin"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">sin</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\end{array}\right]<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Wherein: α is the angle between the light transmission axis of the first polarizer 701, the second polarizer 702, the third polarizer 703, and the fourth analyzer 704 and the light transmission axis of the polarizer 2, that is 0°, 45°, 90° and 135° respectively. The polarized interference beams emitted from the first analyzer 701, the second analyzer 702, the third analyzer 703, and the fourth analyzer 704 can be jointly expressed by the Jones vector S as

S=AGE. (4)

The interference light intensity received by the first photodetector 801, the second photodetector 802, the third photodetector 803 and the fourth photodetector 804 in the photodetector array 8 can be jointly expressed as

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; S</span>}}^{<span\; class="notranslate">\; *</span>}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sin"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">sin</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sin"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">sin</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

where * means Hermitian operation. In formula (5), α takes 0°, 45°, 90° and 135° respectively, that is, the interference light intensities I ₁ , I ₂ , I ₃ and I ₄ received by the photodetectors 801, 802, 803 and 804 are respectively for

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sin"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">sin</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sin"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">sin</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

It can be seen that the phase shifts among the interference light intensities I ₁ , I ₂ , I ₃ and I ₄ are 90° in sequence.

The phase delay of the quarter-wave plate 4 to be tested is close to 90°, and the value of sinδ in the formulas (6)～(9) is always a positive value, which can be obtained from the formulas (6)～(9)

$\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sin"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">sin</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\sqrt{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="S2008100406147E00011.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}{\sqrt{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

The value of θ in the range of 0° to 180° can be calculated by using formulas (10) and (11), that is, the fast axis orientation of the quarter wave plate 4 to be measured is obtained.

The photodetectors 801, 802, 803, and 804 respectively convert the interference light intensities I ₁ , I ₂ , I ₃ , and I ₄ into electrical signals at the same time, and the electrical signals are simultaneously amplified by the amplifier circuit 9 and then processed by the signal processing system 10. High-speed processing, so the orientation of the fast axis of the quarter-wave plate under test is measured in real time. When calculating the fast axis azimuth angle of the measured quarter-wave plate, the E ₀ ² factor term exists in the numerator and denominator of the formulas (10) and (11) and is canceled, that is, the measured quarter-wave plate The measurement result of the fast axis orientation has nothing to do with the initial light intensity, so the measurement result of the fast axis orientation is not affected by the light intensity fluctuation of the collimated light source 1 . At the same time, the quarter-wave plate fast axis orientation real-time measuring device shown in Fig. 1 does not have rotating optical elements and does not need a rotating mechanism, so the present invention has a simple structure and high stability.

Utilize the preferred embodiment to measure the measured quarter-wave plate 3 whose phase delay is 88°, the experimental results show that the measurement accuracy of the measured quarter-wave plate fast axis orientation is higher than 0.1°, and the measurement time is less than 1μs.

Claims (7)

1. A quarter-wave plate fast axis orientation real-time measuring device is characterized in that the device consists of a collimated light source (1), a polarizer (2), a standard quarter-wave plate (3), a diffraction beam element (5), focusing lens (6), analyzer array (7), photodetector array (8), amplification circuit (9) and signal processing system (10), its positional relationship is: along the In the forward direction of the light beam of the collimated light source (1), the polarizer (2), the standard quarter-wave plate (3), the diffraction beam splitting element (5), the focusing lens (6), Analyzer array (7), photodetector array (8), between described standard quarter-wave plate (3) and described diffraction beam-splitting element (5), a quarter wave plate to be measured is set Wave plate (4), described polarizer array (7) is made up of the first polarizer (701), the second polarizer (702), the 3rd polarizer (703), the 4th polarizer The polarizers (704) are arranged and combined in four quadrants in the same plane, the first polarizer (701), the second polarizer (702), the third polarizer (703) and the fourth The angles formed by the transmission axis of the polarizer (704) and the transmission axis of the polarizer (2) are respectively 0°, 45°, 90° and 135°; the photodetector array (8 ) is corresponding to the structure of the described analyzer array (7), and is composed of the first photodetector (801), the second photodetector (802), the second photodetector (802), Composed of a third photodetector (803) and a fourth photodetector (804); the signal detected by the photodetector array (8) is amplified by the amplifier circuit (9) and then input to the signal processing system (10) Perform data processing. 2. The quarter-wave plate fast axis orientation real-time measuring device according to claim 1, characterized in that said polarizer (2) is a polarizer, a polarizing prism, or a polarization phase mask. 3. quarter-wave plate fast-axis orientation real-time measuring device according to claim 1, is characterized in that described standard quarter-wave plate (3) is crystal material type quarter-wave plate, multiple Composite quarter-wave plate, reflective prism-type quarter-wave plate, or birefringent film-type quarter-wave plate, whose phase retardation is equal to or very close to 90°, and whose fast axis is The angle formed by the transmission axes of the polarizer (2) is 45° or 135°. 4. The quarter-wave plate fast axis azimuth real-time measuring device according to claim 1, characterized in that the diffraction beam splitting element (5) is a quadrature amplitude grating, a quadrature phase grating, or a Damman grating , using the diffraction effect to form a beam of incident light into four outgoing sub-beams, and the intensities of the four sub-beams are equal. 5. The quarter-wave plate fast-axis orientation real-time measuring device according to claim 1, characterized in that said photodetector is a photodiode, a phototransistor, a photomultiplier tube or a photocell. 6. quarter wave plate fast-axis orientation real-time measuring device according to claim 1, is characterized in that described signal processing system (10) is the multi-channel high-speed data acquisition card with A/D conversion function and has It is composed of a computer with corresponding data processing and analysis software, or a signal processing circuit and a microprocessor with corresponding processing functions. 7. Utilize the quarter wave plate fast axis orientation real-time measuring device of claim 1 to measure the method for quarter wave plate fast axis orientation, it is characterized in that comprising the following steps: ① Establish the quarter-wave plate fast-axis orientation real-time measurement device; ② Insert the quarter wave plate (4) to be measured between the standard quarter wave plate (3) and the diffraction beam splitting element (5) and adjust the optical path; 3. Utilize the first photodetector (801), the second photodetector (802), the third photodetector (803) and the fourth photodetector (804) of the photodetector array (8) to record respectively The interference light intensity of the first polarizer (701), the second polarizer (702), the third polarizer (703) and the fourth polarizer (704) of the polarizer array (7) I ₁ , I ₂ , I ₃ , and I ₄ are converted into electrical signals, and the electrical signals are simultaneously amplified by the amplifier circuit (9) and input to the signal processing system (10); 4. described signal processing system (10) carries out following operation:

Calculate the value of θ within the range of 0° to 180°, that is, obtain the fast axis orientation of the quarter wave plate (4) to be measured.

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