CN210863099U - Device for measuring performance of broadband wave plate by using AOTF monochromatic light - Google Patents

Abstract

This patent discloses a device for measuring the performance of a broadband wave plate using AOTF monochromatic light. The device consists of a wavelength-tunable monochromatic light source module, a polarizer, a wave plate to be detected, an analyzer, and an energy detection component. The detector plate is located between the polarizer and the analyzer. Rotating the wave plate to be detected causes the energy of the outgoing light to change, and the phase delay of the wave plate can be accurately calibrated by measuring the change of the light energy. The patent has the advantages that the measurement method is simple, the phase retardation angles of the wave plates at different wavelengths can be measured, and the measurement accuracy is high.

Description

A device for measuring the performance of broadband waveplates using AOTF monochromatic light

technical field

This patent relates to the detection and calibration of wave plate parameters, in particular to a device for measuring the performance of broadband wave plates using AOTF monochromatic light. It is suitable for polarization-related measurement and detection fields such as polarization optical systems, ellipsometry, and laser technology.

Background technique

Light is a transverse wave and has the property of being polarized. Depending on the nature of the change in the polarization state of light as it travels through a polarizing device, one can change its polarization state as desired. With the deepening of the research on the polarization of light, it is found that polarization has a wide range of application prospects, so the polarization technology begins to enter the practical stage. Polarization information can detect targets and play an important role in meteorological detection, remote sensing detection of ground objects, underwater space detection, astronomical detection, medical diagnosis, image processing and military applications; especially in the field of quantum communication, the use of photons The polarization state replaces the classical binary code (bit) to carry different encoded information. Combined with the quantum entanglement effect, it can realize the distribution of quantum keys and achieve the purpose of quantum secure communication, such as the Mozi quantum communication satellite successfully developed and launched in my country. Therefore, how to better apply the polarization information of light has become a popular scientific research direction, which requires researchers to continuously develop and improve, and the obtained research results also have a wide range of applications.

Wave plate is a commonly used optical element in the field of polarization optics. It is a polarization optical device based on the birefringence characteristics of crystals, also known as a phase retarder. It can change the polarization state of light. The specific principle is that it can generate an additional optical path difference (or phase difference), which is coupled to the two vertical components of the polarized light to change the polarization state of the light. The optical path difference is called the phase of the wave plate. amount of delay. Commonly used wave plates are 1/4 wave plate and 1/2 wave plate. The phase retardation characteristic of the wave plate can not only change the polarization state of light, but also can be applied to the fields of optical fiber communication, photoelasticity, polarization state inspection of light waves, and various polarization technology, and has a wide application prospect. At present, block wave plates and fiber wave plates are widely used, and block wave plates are parallel thin slices with uniform thickness and uniform thickness made by cutting uniaxial crystals along the optical axis. According to the manufacturing process, the block wave plate can be divided into true zero-order wave plate, multi-order wave plate, glued zero-order wave plate and achromatic wave plate. Optical fiber waveplates are made of birefringent fibers, which are divided into stress birefringent fibers and geometric birefringence fibers.

In order to detect the retardation accuracy and effect of the wave plate, it is necessary to measure the phase retardation of the wave plate. At present, there are optical compensation method, phase shift method, electro-optic crystal modulation method and laser frequency splitting method to detect the phase retardation of wave plate. Patent No. CN201810536990 provides a method and device for detecting the phase retardation of the wave plate surface. The ZYGO interferometer is used to measure the surface phase retardation of the wave plate, and the phase retardation of the wave plate is inverted through the thickness. This method is an indirect measurement of the phase retardation. The test accuracy is limited; the patent CN201710229703 provides a wave plate fast and slow axis detection method, which only provides the optical axis detection method, and does not involve the measurement of the phase delay; the patent CN201610029435 provides a wave plate detection device and method, This method can measure parameters including phase retardation, fast axis azimuth angle, optical rotation angle, fast and slow axis transmittance amplitude ratio angle, depolarization index and other parameters. The test process of this method is too complicated.

From the point of view of easy detection and operation, this patent proposes a Mueller matrix and Stokes vector representation method based on the propagation of polarized light in the device. In the middle of the plate, only by rotating the wave plate to test the maximum and minimum light energy, the corresponding relationship between the phase retardation angle of the wave plate to be measured and the maximum and minimum values of the output energy can be deduced, so as to accurately and quickly calibrate the wave plate to be measured. phase delay amount. In the actual production, processing and detection process, the method can meet the detection requirements of convenience and operability.

SUMMARY OF THE INVENTION

The purpose of this patent is to provide a device for measuring the performance of a broadband wave plate using AOTF monochromatic light, mainly to meet the detection requirements for the convenience and operability of the wave plate detection method in the actual large-scale production and processing process.

The method of this patent is shown in FIG. 1 , which includes a wavelength-tunable monochromatic light source module 1 , a wave plate to be measured 2 with a rotating structure, an analyzer 3 and an energy detection component 4 . The wavelength-tunable monochromatic light source module 1 is composed of a wide-spectrum light source 1-1 output by an optical fiber, a collimating lens 1-2, an acousto-optic tunable filter 1-3, and a shading plate 1-4. During the test, the light emitted from the wide-spectrum light source 1-1 output by the optical fiber becomes parallel light after passing through the collimating lens 1-2, and then enters the acousto-optic tunable filter 1-3 with adjustable radio frequency. Diffracted light, the negative first-order diffracted light and zero-order light are blocked by the shading plates 1-4, and the generated positive first-order diffracted light passes through the analyzer to be measured wave plate 2 and the analyzer 3, and then is detected by the energy detection component 4. , the polarization state of the outgoing light is changed by rotating the wave plate to be measured 2 with a rotating structure, so that the energy detection component 4 detects the energy change of the light, and the wave plate to be measured 2 with a rotating structure is accurately and quickly calibrated by the energy change. The wavelength of the outgoing light is changed by the wavelength tunable monochromatic light source module 1, so as to obtain the phase retardation of the broadband wave plate.

The wavelength range of the wavelength-tunable monochromatic light source module 1 and the analyzer 3 needs to be adapted to the wavelength plate 2 to be tested with a rotating structure; the analyzer 3 is a polarizing plate with a rotating structure, The use wavelength range of the polarizer needs to cover the wavelength of the wavelength plate 2 with a rotating structure to be tested, and the polarization extinction ratio of this wavelength band is better than 5000:1; Waveplate 2 measures the wavelength range.

This patent provides a device and method for measuring the performance of a broadband wave plate using AOTF monochromatic light. The specific implementation steps are as follows:

由斯托克斯矢量表示为；1) Fixed wavelength tunable monochromatic light source module 1 and energy detection component 4, the light emitted by the wide-spectrum light source 1-1 output by the optical fiber becomes parallel light after passing through the collimating lens 1-2, and incident on the radio frequency tunable acousto-optic Adjustable filter 1-3, after the radio frequency is turned on, the diffracted light with wavelength λ _i is output, and the shading plate 1-4 is used to block the negative first-order diffracted light and zero-order light, and the generated positive first-order diffracted light is detected by the energy detection component. 4 Receive, since the output positive first-order diffracted light is horizontally polarized light, the polarization state of the diffracted light with the output wavelength λ _i at this time

Represented by the Stokes vector as;

2) The analyzer 3 is placed between the wavelength tunable monochromatic light source module 1 and the energy detection component 4, and the detected energy is minimized by rotating the analyzer 3. At this time, the light transmittance of the analyzer 3 is located. The axis angle is orthogonal to the polarization direction of the outgoing light, and then the analyzer 3 is rotated by 90 degrees. At this time, the light transmission axis angle of the polarizer 3 is 0, which is in the horizontal direction. The Mueller matrix M3 of the analyzer ₃ can be expressed as:

此时带旋转结构的待测波片2快轴所处角度为θ，其中θ是带旋转结构的待测波片2快轴与水平方向的夹角。此时带旋转结构的待测波片2的穆勒矩阵M₂可以表示为：3) Place the wave plate to be measured 2 with a rotating structure between the wavelength tunable monochromatic light source module 1 and the analyzer 3, and adjust the position and angle of the wave plate to be measured 3 with a rotating structure to make the wavelength tunable. The outgoing light of the monochromatic light source module 1 is vertically incident through the center of the wave plate 2 to be measured with a rotating structure. It is assumed that the phase retardation of the wave plate 2 to be measured with a rotating structure corresponding to the wavelength λ _i is

At this time, the angle at which the fast axis of the wave plate 2 to be measured with the rotating structure is located is θ, where θ is the angle between the fast axis of the wave plate 2 to be measured with the rotating structure and the horizontal direction. At this time, the Mueller matrix M ₂ of the wave plate 2 to be tested with a rotating structure can be expressed as:

可以表示为：4) The light with a wavelength of λ _i generated by the wavelength tunable monochromatic light source module 1 passes through the wave plate to be measured 2 and the analyzer 3 with a rotating structure in turn, and then is detected by the energy detection component 4, and the final outgoing light is polarized. state

It can be expressed as:

By calculation, it can be known that:

可知，出射光的能量E可以表示为：5) By the final outgoing light polarization state

It can be seen that the energy E of the outgoing light can be expressed as:

By rotating the wave plate 2 to be measured with a rotating structure, the maximum value E _max and the minimum value E _min of the energy detected by the energy detection component 4 during the rotation process, the output value of which satisfies:

but:

6) Change the radio frequency drive of the acousto-optic tunable filters 1-3, so that the wavelength-tunable monochromatic light source module 1 outputs different wavelengths λ _i in turn, and repeats step 5, and finally a wave to be measured with a rotating structure can be obtained The corresponding phase retardation of plate 2 at different wavelengths, so that the wave plate 2 to be tested with a rotating structure can obtain the phase retardation δ(λ) in a wide spectral range, where the phase retardation δ is a function of the wavelength λ, and the wavelength λ is its independent variable.

The concrete principle of this patented method is as follows:

可以表示为：In optical theory, polarized light is divided into linearly polarized light, circularly polarized light and elliptically polarized light. Any kind of polarized light can be represented by the Stokes vector. As shown in Figure 1, the wavelength-tunable monochromatic light source module 1 uses an AOTF crystal to generate a positive first-order output wavelength of λ _i , and the outgoing light is Ideal horizontal linearly polarized light, its Stokes vector

It can be expressed as:

快轴所处角度为θ，其中θ是带旋转结构的待测波片2快轴与水平方向的夹角。此时带旋转结构的待测波片2的穆勒矩阵M₂可以表示为：The polarized light passes through the wave plate to be measured 2 with a rotating structure, and it is assumed that the phase retardation of the wave plate to be measured 2 with a rotating structure corresponding to the light wavelength λ _i is

The angle at which the fast axis is located is θ, where θ is the included angle between the fast axis of the wave plate 2 under test with the rotating structure and the horizontal direction. At this time, the Mueller matrix M ₂ of the wave plate 2 to be tested with a rotating structure can be expressed as:

Then the state of the horizontally polarized light generated by the wavelength-tunable monochromatic light source module 1 after passing through the wave plate to be measured 2 with a rotating structure is:

Finally, the analyzer 3 is used for analysis, and its analysis angle in the horizontal direction, its Mueller matrix M ₃ can be expressed as,

The polarization state after analysis is:

可知，出射光的能量E可以表示为：By the final outgoing light polarization state

It can be seen that the energy E of the outgoing light can be expressed as:

为确定状态，则During the process of rotating the wave plate 2 to be measured with the rotating structure, the maximum energy values E _max and E _min that can be detected by the energy detection component 4 , due to the polarization state of the incident light

To determine the state, then

but:

By changing the wavelength λ _i output by the wavelength-tunable monochromatic light source module 1 , the phase retardation of the wave plate 2 under test with a rotating structure at different wavelengths can be obtained, so as to obtain the phase retardation δ(λ) in a wide spectral range. , where the phase retardation δ is a function of the wavelength λ, and the wavelength λ is its independent variable.

This patent provides a device and method for measuring the performance of a broadband wave plate by using AOTF monochromatic light. The advantages of this method are: 1. After the simple optical path of the measurement method is completed, only the wave plate 3 to be measured with a rotating structure needs to be rotated, The phase retardation angle of the wave plate can be obtained by outputting the maximum and minimum values of the energy; 2. The phase retardation angle of the wave plate at different wavelengths can be measured; 3. The direct measurement method is used to calibrate the phase retardation. Compared with the thickness measurement method, it can be excluded Differences in material properties result in higher measurement accuracy.

Description of drawings

Figure 1 shows a device for rapidly measuring the phase retardation of broadband waveplates.

Detailed ways

Embodiments of the patented method will be described in detail below with reference to FIG. 1 .

The main devices employed in this patent are described as follows:

1) wide-spectrum light source 1-1: the wide-spectrum light source 1-1 of optical fiber output in the present embodiment adopts Thorlabs company stable infrared tungsten light source, and the model is the optical fiber output light source of SLS202L, and its spectral range is 450-5500nm;

2) Collimating lens 1-2: In this embodiment, the collimating lens 1-2 is a self-designed component, and its wavelength range is 900-2500 nm, the purpose is to collimate the wide-spectrum light source 1-1 output by the optical fiber into parallel The light beam is incident on the acousto-optic tunable filters 1-3;

3) Acousto-optic tunable filter 1-3: The acousto-optic tunable filter 1-3 used in this embodiment is a customized product of the 26th Research Institute of China Electronics Technology Group, and its main technical indicators are:

a) Working wavelength: 850nm-2400nm

b) Spectral resolution: 2nm-12nm

c) Primary deflection angle: 2.6°

d) Separation angle: >=6.1°

e) Diffraction efficiency: >= 60%

f) Size: 560mm*400mm*315mm

g) Drive power: <= 2W

h) Drive frequency range: 37MHz-112MHz;

其中旋转结构采用大恒光电的产品，型号为WPA-30。旋转角度为0到360度，夹持口径30mm。最小读数为0.5度；4) Wave plate 2 with a rotating structure: The wave plate 3 to be measured is a wave plate with a rotating structure. Among them, the wave plate 3 needs to measure the phase retardation from 600 to 900 nm

Among them, the rotating structure adopts the product of Daheng Optoelectronics, the model is WPA-30. The rotation angle is 0 to 360 degrees, and the clamping diameter is 30mm. The minimum reading is 0.5 degrees;

5) Analyzer 3: The analyzer 3 is a polarizer with a rotating structure, and the polarizer is a product of Thorlabs, the model is LPVIS100, and its main performance parameters: the working band is 600-1200nm; the polarization extinction ratio is 10000:1 ; The size of the aperture is 25mm, and the effective aperture is 90% of the aperture; the angle of polarization and analysis is ±20°. The rotating structure adopts Thorlabs products, model RSP1D, its main performance parameters: the rotation angle is 0 to 360 degrees, and the clamping diameter is 1 inch. The minimum reading is 0.5 degrees;

6) Energy detection component 4: The product of Thorlabs is used, the model is PM120D, and its main performance parameters: the working band is 400-1100nm; the power test range is 50nw-50mw; the probe is a Si detector;

The schematic diagram of the main optical path of the patented method is shown in accompanying drawing 1, and the specific situation is described as follows:

1) Fix the wavelength tunable monochromatic light source module 1 and the energy detection assembly 4 according to the accompanying drawing 1, the light emitted by the wide-spectrum light source 1-1 output by the optical fiber becomes parallel light after passing through the collimating lens 1-2, and the incident radio frequency can Adjusted acousto-optic tunable filters 1-3, after the radio frequency is turned on, the diffracted light with wavelength λ _i is output, and the shading plate 1-4 is used to block the negative first-order diffracted light and zero-order light, and the generated positive first-order diffracted light Received by the energy detection assembly 4, the wavelength range required to measure the wavelength plate 3 to be measured with a rotating structure is 600 to 900 nm in the embodiment, and the wavelength range to be measured is divided into a light wavelength λ _i sequence by every 10 nm as a measurement point. :

λ _i =600+10i (i=0,1,...30)

由斯托克斯矢量表示为：The broadband phase retardation measurement is performed on the wave plate 2 to be tested with a rotating structure. where i is a natural number from 0 to 30. According to i each step of 1, the light beams with wavelength λ _i are sequentially emitted. Since the output positive first-order diffracted light is horizontally polarized light, its polarization state

Represented by the Stokes vector as:

2) The analyzer 3 is placed between the wavelength tunable monochromatic light source module 1 and the energy detection component 4, and the detected energy is minimized by rotating the analyzer 3. At this time, the light transmittance of the analyzer 3 is located. The axis angle is orthogonal to the polarization direction of the outgoing light, and then the analyzer 3 is rotated by 90 degrees. At this time, the direction of the light transmission axis of the polarizer 3 is the horizontal direction, and the Mueller matrix M ₃ of the analyzer 3 can be expressed as:

此时带旋转结构的待测波片2快轴所处角度为θ，其中θ是带旋转结构的待测波片2快轴与水平方向的夹角。此时带旋转结构的待测波片2的穆勒矩阵M₂可以表示为：3) Place the wave plate to be measured 2 with a rotating structure between the wavelength tunable monochromatic light source module 1 and the analyzer 3, and adjust the position and angle of the wave plate to be measured 3 with a rotating structure to make the wavelength tunable. The emitted light of the monochromatic light source module 1 is vertically incident through the center of the wave plate to be measured 2 with a rotating structure. Assume that the phase retardation of the wave plate to be measured 2 with a rotating structure corresponding to the wavelength of λ _i is

At this time, the angle at which the fast axis of the wave plate 2 to be measured with the rotating structure is located is θ, where θ is the angle between the fast axis of the wave plate 2 to be measured with the rotating structure and the horizontal direction. At this time, the Mueller matrix M ₂ of the wave plate 2 to be tested with a rotating structure can be expressed as:

可以表示为：4) The light with a wavelength of λ _i generated by the wavelength tunable monochromatic light source module 1 passes through the wave plate to be measured 2 and the analyzer 3 with a rotating structure in turn, and then is detected by the energy detection component 4, and the final outgoing light is polarized. state

It can be expressed as:

By calculation, it can be known that:

可知，出射光的能量E可以表示为：5) The final polarization state of the outgoing light

It can be seen that the energy E of the outgoing light can be expressed as:

By rotating the wave plate 2 to be measured with a rotating structure, the maximum value E _max and the minimum value E _min of the energy detected by the energy detection component 4 during the rotation process, the output value of which satisfies:

but:

6) Change the radio frequency drive of the acousto-optic tunable filters 1-3, so that the wavelength-tunable monochromatic light source module 1 outputs different wavelengths λ _i in turn, and repeats step 5, and finally a wave to be measured with a rotating structure can be obtained The phase retardation of plate 2 at different wavelengths, so that the wave plate 2 to be tested with a rotating structure can obtain the phase retardation δ(λ) in a wide spectral range, where the phase retardation δ is a function of the wavelength λ, and the wavelength λ is independent variable.

Claims (4)

1. A device for measuring the performance of a broadband wave plate using AOTF monochromatic light, comprising a wavelength-tunable monochromatic light source module (1), a wave plate to be measured (2) with a rotating structure, an analyzer (3) and An energy detection assembly (4), characterized in that: The wavelength-tunable monochromatic light source module (1) includes a wide-spectrum light source (1-1) output by an optical fiber, a collimating lens (1-2), an acousto-optic tunable filter (1-3), a light shielding The board (1-4) is composed of, during the test, the light emitted by the wide-spectrum light source (1-1) output by the optical fiber becomes parallel light after passing through the collimating lens (1-2), and incident on the acousto-optic tunable filter with adjustable radio frequency. (1-3), the outgoing light will generate diffracted light of the corresponding wavelength, the negative first-order diffracted light and the zero-order light are blocked by the shading plate (1-4), and the generated positive first-order diffracted light passes through the waiting device with the rotating structure. After the wave plate (2) and the analyzer (3) are detected by the energy detection component (4), the polarization state of the outgoing light is changed by rotating the wave plate to be measured (2) with a rotating structure, thereby causing the energy detection component (4) The energy change of the light is detected, and the phase retardation of the wave plate to be measured (2) with the rotating structure is accurately and quickly calibrated according to the energy change; the outgoing light is changed by the wavelength tunable monochromatic light source module (1). wavelength, so as to obtain the phase retardation of the broadband wave plate. 2. a kind of device utilizing AOTF monochromatic light to measure the performance of broadband wave plate according to claim 1, is characterized in that: described wavelength tunable monochromatic light source module (1), analyzer (3) The wavelength range needs to be adapted to the wavelength plate (2) to be measured with a rotating structure. 3. a kind of device utilizing AOTF monochromatic light to measure broadband wave plate performance according to claim 1, is characterized in that: described analyzer (3) is the polarizer with rotating structure, the use of polarizer The wavelength range needs to cover the wavelength of the wave plate (2) to be measured with the rotating structure, and the polarization extinction ratio of this wavelength band is better than 5000:1. 4. A device for measuring the performance of a broadband wave plate using AOTF monochromatic light according to claim 1, wherein the measured wavelength range of the energy detection assembly (4) covers the wave to be measured with a rotating structure Sheet (2) Test wavelength range.

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