CN105403382A - Wave plate phase retardation and fast axis azimuth measurement device and method - Google Patents

Abstract

A measuring device for wave plate phase retardation and fast axis azimuth, comprising collimated light source, circular polarizer, first variable retarder, second variable retarder, analyzer, photodetector and signal processing system. The invention can measure the phase delay amount and the fast axis azimuth of the wave plate in real time, and has no mechanical rotating device, no complex signal modulation and demodulation unit, simple structure, short measurement time and wide measurement range.

Description

Device and method for measuring wave plate phase delay and fast axis azimuth

technical field

The invention relates to wave plate measurement, in particular to a real-time measuring device and method for wave plate phase delay and fast axis azimuth.

Background technique

With the continuous development of polarized light technology, the requirements of the polarization system for resolution, accuracy, signal-to-noise ratio and other indicators are getting higher and higher. The wave plate is widely used in the field of polarization technology and is the most commonly used device in the polarization system. Therefore, it is particularly important to simultaneously accurately measure the phase delay and the fast axis azimuth of the two most important technical parameters of the wave plate.

Prior technology [1] (see Cui Xiangxia, Wu Fuquan, Chen Jun, etc. Four-step phase shift method measurement of wave plate phase delay. Journal of Qufu Normal University. Vol.36, No.2, 2010) through the Muller wave plate The general expression for measuring the phase delay of the wave plate is deduced from the matrix and Stokes vector, and a four-step phase shift method for splitting the correction beam in the optical path is proposed. This method can measure the phase delay of the wave plate without knowing the specific orientation of the optical axis of the wave plate and without judging the extinction position. However, during the measurement process, the analyzer needs four mechanical rotations, which will reduce the efficiency of the experiment and affect the accuracy of the experiment.

The prior art [2] (see Xu Wendong, Li Xishan. A New Method for Precise Measurement of Waveplate Phase Retardation. Acta Optics. Vol.14, No.10, 1994) proposed a polarization interference technology using rotating waveplate, combined with mechanical -A method for precisely determining the phase delay of the wave plate by judging the presence or absence of a square wave signal for the modulation of the optical phase by the optical rotatory modulator. However, this method introduces a rotatable mechanical-optical optical rotation modulator, which has a complex structure, difficult installation and adjustment, and large errors.

Prior art [3] (see BaoliangWang, C.OwenGriffiths, RickR.Rockwell, Etc.The DUVBirefringenceMeasurementSystemandItsApplicationtoMeasuringLithographyGradeCaF2LensBlanks.SPIE.Vol.5192,2003) proposed a method for measuring phase delay and fast axis azimuth using dual photoelastic modulators, but in this method, it is difficult to calibrate the modulator and the signal processing process is also relatively complicated .

Contents of the invention

The object of the present invention is to overcome above-mentioned deficiencies in the prior art, provide a kind of phase delay amount and fast axis azimuth angle measuring device and method of wave plate, can measure the phase delay amount and fast axis azimuth angle of wave plate simultaneously.

Technical solution of the present invention is as follows:

A measuring device for phase retardation and fast axis azimuth of a wave plate, characterized in that the device consists of a collimated light source, a circular polarizer, a first variable retarder, a second variable retarder, and a polarizer , a photodetector and a signal processing system, and its positional relationship is: along the forward direction of the light beam of the collimated light source, there are the circular polarizer, the first variable retarder, and the second variable retarder in sequence A device, a polarizer, a photodetector, the socket of the wave plate to be measured is set between the circular polarizer and the first variable retarder;

The first variable delay device and the second variable delay device can be composed of a single variable delay device or a combination of multiple variable delay devices. The phase delays of the first variable retarder and the second variable retarder change simultaneously, which are δ ₁ , δ ₂ , δ ₃ and δ ₄ respectively, and the values of δ ₁ , δ ₂ , δ ₃ and δ ₄ are The value range is (0°, 180°). The azimuth angle of the fast axis of the first variable retarder is θ ₁ , the azimuth angle of the fast axis of the second variable retarder is θ ₂ , and the value range of θ ₁ and θ ₂ is (0°, 180°);

The angle between the direction of the transmission axis of the analyzer and the horizontal direction is α, and the value range of α is (0°, 180°);

θ ₁ , θ ₂ and α can be in any combination, and phase delays δ ₁ , δ ₂ , δ ₃ and δ ₄ can also be in many different combinations, but the following transfer matrix T(α; θ ₁ , θ ₂ ; δ ₁ , δ ₂ , δ ₃ , δ ₄ ) are non-singular matrices.

The signal processing system is composed of a signal amplification circuit, a signal acquisition circuit and a computer with data processing and analysis software.

The method for measuring the phase delay and the fast axis azimuth of the wave plate by using the measuring device of the wave plate phase delay and the fast axis azimuth is characterized in that it comprises the following steps:

① Insert the wave plate to be tested into the socket of the wave plate to be tested between the circular polarizer and the first variable retarder and adjust the optical path so that the light beam passes through the wave plate to be tested vertically;

② Turn on the collimated light source, control the phase delays of the first variable retarder and the second variable retarder to be δ1 _; use the photodetector to detect the light intensity ^I1 And the light intensity ^I1 is converted into an electrical signal and input to the signal processing system;

③ controlling the phase delays of the first variable retarder and the _second variable retarder to be δ2; utilizing the photodetector to detect the light intensity ^I2 and converting the light intensity ^I2 into The electrical signal is input to the signal processing system;

④ control the phase delay of the first variable retarder and the second variable retarder to be _δ3 ; utilize the photodetector to detect the light intensity ^I3 and convert the light intensity ^I3 into The electrical signal is input to the signal processing system;

5. Control the phase delays of the first variable retarder and the second variable retarder to be _δ4 ; utilize the photodetector to detect the light intensity ^I4 and convert the light intensity ^I4 into The electrical signal is input to the signal processing system;

6. The signal processing system described in the following calculations:

From the above formula, the azimuth angle θ of the fast axis and the amount of phase delay δ of the wave plate to be tested can be solved. in, is the transfer matrix

The elements of T(α; θ ₁ , θ ₂ ; δ ₁ , δ ₂ , δ ₃ , δ ₄ ), T(α; θ ₁ , θ ₂ ; δ ₁ , δ ₂ , δ ₃ , δ ₄ ) can be expressed as :

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

1. There is no mechanical rotating device, no complicated signal modulation and demodulation unit, simple structure, and short measurement time.

2. The phase delay and fast axis azimuth can be measured at the same time, and the measurement range is wide. The phase delay measurement range is 0°~180° and the fast axis azimuth angle measurement range is 0°~180°.

Description of drawings

Fig. 1 is a structural block diagram of an embodiment of a device for measuring wave plate phase delay and fast axis azimuth of the present invention.

detailed description

The present invention will be further described below in conjunction with the embodiments and accompanying drawings, 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 device for measuring wave plate phase delay and fast axis azimuth of the present invention. As can be seen from Fig. 1, the measuring device of the wave plate phase retardation amount and the fast axis azimuth angle of the present invention consists of a collimated light source 1, a circular polarizer 2, a first variable retarder 4, a second variable retarder 5, a detector Polarizer 6, photodetector 7, and signal processing system 8. The positional relationship is: along the forward direction of the light beam of the collimated light source 1 , there are circular polarizer 2 , first variable retarder 4 , second variable retarder 5 , analyzer 6 , and photodetector 7 in sequence. The electrical signal output by the photodetector 7 is input into the signal processing system 8 for signal amplification and data processing.

Both the first variable retarder 4 and the second variable retarder 5 are nematic liquid crystal retarders, and the phase delays of the first variable retarder and the second variable retarder change simultaneously, are δ ₁ , δ ₂ , δ ₃ and δ ₄ respectively, and the value ranges of δ ₁ , δ ₂ , δ ₃ and δ ₄ are (0°, 180°). The azimuth angle of the fast axis of the first variable retarder 4 is θ ₁ , the azimuth angle of the fast axis of the second variable retarder 5 is θ ₂ , and the value range of θ ₁ and θ ₂ is (0 °, 180°);

Described analyzer 6 is a polarizer, and its transmission axis direction is α, and the value range of α is (0 °, 180 °);

The signal processing system 8 is composed of a signal amplification circuit, a signal acquisition circuit and a computer with data processing and analysis software.

The wave plate to be tested 3 is inserted into the wave plate to be tested socket between the circular polarizer 2 and the first variable retarder 4 and the optical path is adjusted so that the light beam passes through the wave plate to be tested vertically. The parallel light beam emitted by the collimated light source 2 sequentially passes through the circular polarizer 2 to form a circularly polarized light, and the circularly polarized light passes through the wave plate to be measured 3 and reaches the second variable retarder 4 and The third variable retarder 5 controls the phase delays of the first variable retarder 4 and the second variable retarder 5 to be δ ₁ , and generates a phase delay for the incident light. After described polarizer 6, the light intensity ^I1 of optical path is received by described photodetector 7; Control the phase delay of described first variable retarder 4 and described second variable retarder 5 The quantities are all δ ₂ , which produces a phase delay for the incident light. After passing through the analyzer 6, the light intensity I ² of the optical path is received by the photodetector 7; the first variable retarder 4 is controlled The phase delays of the second variable retarder 5 and the second variable retarder 5 are both δ ₃ , which produces a phase delay to the incident light. After passing through the polarizer 6, the light intensity I ³ of the optical path is detected by the photodetector 7 receiving; controlling the phase delays of the first variable retarder 4 and the second variable retarder 5 to be δ ₄ , thereby generating a phase delay for the incident light, passing through the analyzer 6 Finally, the light intensity I ⁴ of the optical path is received by the photodetector 7 .

The collimated laser beam becomes circularly polarized light after passing through the circular polarizer, and the Stokes vector of the circularly polarized light is S _I , which can be expressed as

Among them, I ₀ is the light intensity of the incident beam of the wave plate to be tested.

The Muller matrix M _S of described wave plate to be measured can be expressed as

Where: δ is the phase delay of the wave plate to be tested, and θ is the azimuth of the fast axis of the wave plate to be tested. Then the Stokes vector S _II of the outgoing beam of the wave plate to be measured is

Among them, I ₁ is the light intensity of the outgoing beam of the wave plate under test, Q ₁ and U ₁ are the linear polarization components of the outgoing beam of the wave plate under test, and V ₁ is the circular polarization component of the outgoing beam of the wave plate under test

The Muller matrix M _L of the retarder with any fast axis azimuth and phase delay can be expressed as

Where: δ is the phase delay of the retarder, and θ is the azimuth of the fast axis of the retarder.

Therefore, the four Muller matrices of the first variable delay device can be expressed as M _L1 (θ ₁ , δ ₁ ), M _L1 (θ ₁ , δ ₂ ), M _L1 (θ ₁ , δ ₃ ), M _L1 (θ ₁ , δ ₄ ). The four Muller matrices of the second variable retarder can be expressed as _ML2 (θ ₂ , δ ₁ ), _ML2 (θ ₂ , δ ₂ ), _ML2 (θ ₂ , δ ₃ ), _ML2 ( θ ₂ , δ ₄ ).

The Muller matrix M _A of the analyzer with any azimuth angle of the transmission axis can be expressed as

where α is the azimuth of the polarization axis of the analyzer.

Therefore, the Muller matrix of the polarizer can be expressed as M _A (α).

Then the polarization state S of the outgoing light from the analyzer can be expressed as

Wherein, I is the light intensity of the outgoing beam of the analyzer, Q and U are the linear polarization components of the outgoing beam of the analyzer, and V is the circular polarization component of the outgoing beam of the analyzer.

The light intensity I detected by the photodetector can be expressed as

I＝m ₁₁ I ₁ +m ₁₂ Q ₁ +m ₁₃ U ₁ +m ₁₄ V ₁

Therefore, the four measurements in the experiment can be expressed as

Among them, the transfer matrix

Available

but

From the above formula, the azimuth angle θ of the fast axis and the amount of phase delay δ of the wave plate to be tested can be solved.

The structure of the preferred embodiment of the present invention is as shown in Figure 1, and its concrete structure and parameters are as follows:

The collimated light source 1 is a stable He-Ne laser with a laser wavelength of 632.8nm and a light intensity stability of ±0.2%. The linear polarizer in the circular polarizer 2 is a polarizer with an extinction ratio of 10 ⁻² . The quarter-wave plate in the circular polarizer 2 is a zero-order quartz wave plate with a phase retarder precision of λ/300. Both the first variable retarder 4 and the second variable retarder 5 are nematic liquid crystal retarders with a clear aperture of 10mm and a suitable wavelength range of 350-700nm. The azimuth angle of the fast axis of the first variable retarder 4 is 45°, and the azimuth angle of the fast axis of the second variable retarder 5 is 30°. The analyzer 6 is a polarizer with an extinction ratio of 10 ^-2 . The photodetector 7 is a PIN tube. The signal processing system 8 is composed of an amplifying circuit for converting 2.5mA current into 3V voltage, a 100M data acquisition circuit and a computer with LabView software.

Collimated laser beam becomes circularly polarized light after described circular polarizer 2, and the Stokes vector S ₁ of this circularly polarized light is

Among them, I ₀ is the light intensity of the incident beam of the wave plate to be tested.

The Muller matrix M _S of described wave plate 3 to be tested can be expressed as

Where: δ is the phase delay of the wave plate 3 to be tested, and θ is the azimuth of the fast axis of the wave plate 3 to be tested. The Stokes vector S _II of the outgoing beam of the wave plate 3 to be measured is

Among them, I ₁ is the light intensity of the outgoing beam of the wave plate under test, Q ₁ and U ₁ are the linear polarization components of the outgoing beam of the wave plate under test, and V ₁ is the circular polarization component of the outgoing beam of the wave plate under test

The Muller matrix M _L of the retarder with any fast axis azimuth and phase delay can be expressed as

Where: δ is the phase delay of the retarder, and θ is the azimuth of the fast axis of the retarder. Therefore, the fast axis azimuth angle of the first variable retarder 4 is 45°, and the Muller matrix M _L1 (θ ₁ , δ ₁ ), M _L1 (θ ₁ , δ ₂ ), M _L1 (θ ₁ , δ ₃ ), M _L1 (θ ₁ , δ ₄ ) are respectively

The fast axis azimuth angle of the second variable retarder 5 is 30°, and the Muller matrix M _L2 (θ ₂ , δ ₁ ), M _L2 (θ ₂ , δ ₂ ), M _L2 (θ ₂ , δ ₃ ), M _L2 (θ ₂ , δ ₄ ) are respectively

The Muller matrix M _A of the analyzer with any azimuth angle of the transmission axis can be expressed as

where α is the azimuth of the polarization axis of the analyzer. Described polarizer 5 transmission axis azimuth angles are 0 °, so its Muller matrix M _A (α) is

The polarization state S of the outgoing light from the analyzer can be expressed as

Wherein, I is the light intensity of the outgoing beam of the analyzer, Q and U are the linear polarization components of the outgoing beam of the analyzer, and V is the circular polarization component of the outgoing beam of the analyzer.

The light intensity I detected by the photodetector 6 can be expressed as

I＝m ₁₁ I ₁ +m ₁₂ Q ₁ +m ₁₃ U ₁ +m ₁₄ V ₁

Therefore, the four measurements in the experiment can be expressed as

Among them, the transfer matrix

Available

can be obtained by calculation

The phase delay of the wave plate can be obtained by calculating the value of δ, and the fast axis azimuth of the wave plate can be obtained by calculating the value of θ, so the phase delay and fast axis of the wave plate 3 to be measured can be measured at the same time azimuth.

The collimated light source 1 adopts a 632.8nm stable He-Ne laser, and its light intensity stability is ±0.2%, so during the measurement process, _I0 can be regarded as constant. The measurement results are independent of the initial light intensity.

Utilize above-mentioned embodiment to measure the one-eighth wave plate 3 that the phase delay amount is 45 ° to be measured, the experimental result shows that the measurement accuracy of the phase delay amount of the one-eighth wave plate to be measured is 0.1 °, fast axis azimuth angle The accuracy is 1°.

Claims (6)

1. A device for measuring the phase retardation and the fast axis azimuth angle of a wave plate is characterized by comprising a collimated light source (1), a circular polarizer (2), a first variable retarder (4), a second variable retarder (5), an analyzer (6), a photoelectric detector (7) and a signal processing system (8);

the positional relationship of the above components is:

the device comprises a circular polarizer, a first variable retarder, a second variable retarder, an analyzer and a photoelectric detector in sequence along the advancing direction of a light beam of the collimation light source, wherein the output end of the photoelectric detector is connected with the input end of the signal processing system, and a socket for placing a wave plate to be detected is arranged between the circular polarizer and the first variable retarder.

2. The apparatus of claim 1, wherein the first variable retarder and the second variable retarder are nematic liquid crystal retarders, and the retardation amounts of the first variable retarder and the second variable retarder are simultaneously changed to be respectively nematic liquid crystal retarders₁、₂、₃And₄，₁、₂、₃and₄is (0 DEG, 180 DEG).

3. The apparatus of claim 1, wherein the first variable retarder has a fast axis azimuth θ₁The fast axis azimuth angle of the second variable retarder is theta₂，θ₁And theta₂Is (0 DEG, 180 DEG).

4. The apparatus of claim 1, wherein the analyzer is a polarizer, and the transmission axis direction is α, and the range of the analyzer is (0 °, 180 °).

5. The apparatus for measuring the retardation and azimuth angle of the fast axis of a wave plate of claim 1, wherein the signal processing system comprises a signal amplification circuit, a signal acquisition circuit and a computer with data processing and analysis software.

6. A method for measuring the phase retardation and fast axis azimuth of a wave plate using the measuring apparatus of claim 1, comprising the steps of:

inserting a wave plate to be measured into a socket of the wave plate to be measured between a circular polarizer and a first variable retarder, and adjusting a light path to enable light beams to vertically pass through the wave plate to be measured;

② turning on the collimated light source, controlling the phase delay amount of the first variable retarder and the second variable retarder₁(ii) a Detecting light intensity I using a photodetector¹And the light intensity I¹Converting the signal into an electric signal and inputting the electric signal into a signal processing system;

③ controlling the phase delay of the first variable delayer and the second variable delayer₂(ii) a Detecting the light intensity I by the photoelectric detector²And the light intensity I²Converting the signal into an electric signal and inputting the electric signal to the signal processing system;

④ controlling the phase delay of the first variable delayer and the second variable delayer₃(ii) a Detecting the light intensity I by the photoelectric detector³And the light intensity I³Converting the signal into an electric signal and inputting the electric signal to the signal processing system;

⑤ controlling the phase delay of the first variable delayer and the second variable delayer₄(ii) a Detecting the light intensity I by the photoelectric detector⁴And the light intensity I⁴Converting the signal into an electric signal and inputting the electric signal to the signal processing system;

sixthly, calculating the fast axis azimuth angle theta and the phase delay of the wave plate to be measured, wherein the formula is as follows:

$\mathrm{\θ}=\frac{1}{2}arctan\frac{m_{11}^2{I}^1+m_{12}^2{I}^2+m_{13}^2{I}^3+m_{14}^2{I}^4}{m_{11}^3{I}^1+m_{12}^3{I}^2+m_{13}^3{I}^3+m_{14}^3{I}^4}$

$\mathrm{\δ}=arctan\frac{\sqrt{{(m_{11}^2{I}^1+m_{12}^2{I}^2+m_{13}^2{I}^3+m_{14}^2{I}^4)}^2+{(m_{11}^3{I}^1+m_{12}^3{I}^2+m_{13}^3{I}^3+m_{14}^3{I}^4)}^2}}{m_{11}^4{I}^1+m_{12}^4{I}^2+m_{13}^4{I}^3+m_{14}^4{I}^4}$

wherein,is a transfer matrix T (α; theta)₁，θ₂；₁，₂，₃，₄) α is the polarization axis azimuth of the analyzer;

T(α；θ₁，θ₂；₁，₂，₃，₄) Expressed as:

$T\left(\begin{array}{ccccccc}\mathrm{\α};& {\mathrm{\θ}}_1,& {\mathrm{\θ}}_2;& {\mathrm{\δ}}_1,& {\mathrm{\δ}}_2,& {\mathrm{\δ}}_3,& {\mathrm{\δ}}_4\end{array}\right)=\left[\begin{array}{cccc}{m_{11}}^1& {m_{12}}^1& {m_{13}}^1& {m_{14}}^1\\ {m_{11}}^2& {m_{12}}^2& {m_{13}}^2& {m_{14}}^2\\ {m_{11}}^3& {m_{12}}^3& {m_{13}}^3& {m_{14}}^3\\ {m_{11}}^4& {m_{12}}^4& {m_{13}}^4& {m_{14}}^4\end{array}\right].$