A device and method for measuring the performance of a wide-band wave plate using AOTF monochromatic light

Abstract

The present invention discloses a device and method for measuring the performance of a wide-band wave plate using AOTF monochromatic light. The device is composed of a wavelength tunable monochromatic light source module, a polarizer, a wave plate to be detected, an analyzer, and an energy detection component. The wave plate to be detected is located between the polarizer and the analyzer. Rotating the wave plate to be detected causes the energy of the emitted light to change. The phase delay of the wave plate is accurately calibrated by testing the change of the emitted light energy. The method of the present invention is based on the Mueller matrix and Stokes vector representation of polarized light propagating in a device. The wave plate to be detected is placed between two analyzers with the same light transmission axis direction. The maximum and minimum values ​​of the emitted light energy are tested by rotating the wave plate. The corresponding relationship between the phase delay angle of the wave plate to be tested and the maximum and minimum values ​​of the emitted energy is derived according to the Stokes vector method, so that the phase delay of the wave plate to be tested can be accurately and quickly calibrated by measuring the emitted energy.

Description

Technical Field

[0001] The present invention relates to the detection and calibration of wave plate parameters, and in particular to a device and method for measuring the performance of a wide-band wave plate using AOTF monochromatic light. The device is applicable to polarization optical systems, elliptical polarization measurement, laser technology and other polarization-related measurement and detection fields. Background Art

[0002] Light is a transverse wave with polarization characteristics. According to the property of the change in the polarization state of light when it propagates in a polarization device, people can change its polarization state as needed. With the deepening of the study of the polarization of light, it is found that polarization has a wide range of application prospects, so polarization technology has begun to enter the practical stage. Polarization information can detect targets and plays an important role in meteorological detection, remote sensing of land objects, underwater space detection, astronomical detection, medical diagnosis, image processing and military applications. Especially in the field of quantum communication, the polarization state of photons is used instead of classical binary codes (bits) to carry different information. Combined with the quantum entanglement effect, the distribution of quantum keys can be realized to achieve the purpose of quantum secure communication, such as the Micius quantum communication satellite successfully developed and launched by my country. Therefore, how to better apply the polarization information of light has become a hot scientific research direction, which requires researchers to continuously develop and improve, and the research results obtained also have a wide range of applications.

[0003] Wave plates are commonly used optical elements in the field of polarization optics. They are polarization optical devices made based on the birefringence characteristics of crystals, also known as phase delay devices. They can change the polarization state of light. The specific principle is that they can generate additional optical path difference (or phase difference) and couple to the two perpendicular components of polarized light to change the polarization state of light. The optical path difference is called the phase delay of the wave plate. Common wave plates include 1 / 4 wave plates and 1 / 2 wave plates. The phase delay characteristics of wave plates can not only change the polarization state of light, but also be applied to fields such as optical fiber communication, photoelasticity, polarization state inspection of light waves, and various polarization light technologies. The application prospects are very broad. Currently, block wave plates and fiber wave plates are widely used. Block wave plates are parallel thin plates with uniform thickness made by cutting uniaxial crystals along the optical axis. Block wave plates are divided into true zero-order wave plates, multi-order wave plates, glued zero-order wave plates, and achromatic wave plates according to the manufacturing process. Fiber wave plates are made of birefringent optical fibers, which are divided into stress birefringent optical fibers and geometric birefringent optical fibers.

[0004] In order to detect the delay accuracy and effect of the wave plate, it is necessary to measure the phase delay of the wave plate. At present, there are optical compensation method, phase shift method, electro-optic crystal modulation method and laser frequency splitting method for detecting the phase delay of the wave plate. Patent No. CN201810536990 provides a method and device for detecting the surface phase delay of the wave plate, which uses a ZYGO interferometer to measure the surface phase delay of the wave plate and inverts the phase delay of the wave plate through the thickness. This method is an indirect measurement of the phase delay, and its test accuracy is limited; Patent CN201710229703 provides a wave plate fast and slow axis detection method, which only provides a method for detecting the optical axis and does not involve the measurement of phase delay; Patent CN201610029435 provides a wave plate detection device and method, which can measure parameters including phase delay, fast axis azimuth, optical rotation angle, fast and slow axis transmittance amplitude ratio angle, depolarization index, etc. The test process of this method is too complicated.

[0005] From the perspective of easy detection and operation, the present invention proposes a Mueller matrix and Stokes vector representation method based on the propagation of polarized light in the device. The wave plate to be detected is placed between two polarizers with the same transmission axis direction. The maximum and minimum values ​​of the output light energy are tested by rotating the wave plate, and the corresponding relationship between the phase delay angle of the wave plate to be tested and the maximum and minimum values ​​of the output energy can be derived, thereby accurately and quickly calibrating the phase delay of the wave plate to be tested. In the actual production, processing and detection process, this method can meet the detection requirements of convenience and easy operation. Summary of the invention

[0006] The purpose of the present invention is to provide a device and method for measuring the performance of a wide-band wave plate using AOTF monochromatic light, mainly to meet the requirements for convenient and easy-to-operate wave plate detection in actual large-scale production and processing.

[0007] The method of the present invention is as follows Figure 1As shown, it includes a wavelength tunable monochromatic light source module 1, a wave plate 2 to be tested 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 light shielding plate 1-4. 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 is incident on the radio frequency adjustable acousto-optic tunable filter 1-3. The emitted light will generate diffracted light of corresponding wavelength. The negative first-order diffracted light and the zero-order light are shielded by the shading plate 1-4. The generated positive first-order diffracted light passes through the polarizer wave plate 2 to be tested and the polarizer 3, and is detected by the energy detection component 4. The polarization state of the emitted light is changed by rotating the wave plate 2 to be tested with a rotating structure, so that the energy detection component 4 detects the energy change of the light, and the phase delay of the wave plate 2 to be tested with a rotating structure is accurately and quickly calibrated according to the energy change; the wavelength of the emitted light is changed by the wavelength tunable monochromatic light source module 1, so as to obtain the phase delay of the wide-band wave plate.

[0008] The wavelength ranges of the wavelength tunable monochromatic light source module 1 and the analyzer 3 need to be adapted to the wave plate 2 to be tested with a rotating structure; the analyzer 3 is a polarizer with a rotating structure, and the use wavelength range of the polarizer needs to cover the wavelength of the wave plate 2 to be tested with a rotating structure, and the polarization extinction ratio of this band is better than 5000:1; the wavelength range measured by the energy detection component 4 covers the test wavelength range of the wave plate 2 to be tested with a rotating structure.

[0009] The present invention provides a device and method for measuring the performance of a wide-band wave plate using AOTF monochromatic light, and the specific implementation steps are as follows:

[0010] 1) Fix the wavelength tunable monochromatic light source module 1 and the 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 is incident on the radio frequency tunable acousto-optic tunable filter 1-3. After turning on the radio frequency, the output wavelength is λ i The diffracted light of 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 is received by the energy detection component 4. Since the output positive first-order diffracted light is horizontally linearly polarized, the output wavelength is λ i The polarization state of the diffracted light It is represented by the Stokes vector as;

[0011]

[0012] 2) Place the polarizer 3 between the wavelength tunable monochromatic light source module 1 and the energy detection component 4, and rotate the polarizer 3 to minimize the detected energy. At this time, the transmission axis angle of the polarizer 3 is orthogonal to the polarization direction of the outgoing light. Then rotate the polarizer 3 90 degrees. At this time, the transmission axis angle of the polarizer 3 is 0, which is in the horizontal direction. The Mueller matrix M3 of the polarizer 3 can be expressed as:

[0013]

[0014] 3) Place the wave plate 2 with a rotating structure to be tested between the wavelength tunable monochromatic light source module 1 and the analyzer 3, and adjust the position and angle of the wave plate 3 with a rotating structure to be tested so that the outgoing light of the wavelength tunable monochromatic light source module 1 passes through the center of the wave plate 2 with a rotating structure and is vertically incident. Assume that the wave plate 2 with a rotating structure to be tested corresponds to a wavelength of λ i The phase delay is At this time, the angle of the fast axis of the wave plate 2 to be tested with the rotating structure is θ, where θ is the angle between the fast axis of the wave plate 2 to be tested with the rotating structure and the horizontal direction. At this time, the Mueller matrix M2 of the wave plate 2 to be tested with the rotating structure can be expressed as:

[0015]

[0016] 4) The wavelength generated by the wavelength tunable monochromatic light source module 1 is λ i The light passes through the wave plate 2 with a rotating structure and the analyzer 3 in turn, and is detected by the energy detection component 4. The final polarization state of the emitted light is It can be expressed as:

[0017]

[0018] Through calculation, we know that:

[0019]

[0020] 5) The final polarization state of the outgoing light It can be seen that the energy E of the emitted light can be expressed as:

[0021]

[0022] By rotating the wave plate 2 with a rotating structure to be tested, the maximum energy value E detected by the energy detection component 4 during the rotation process max and the minimum value E min , and its output value satisfies:

[0023]

[0024]

[0025] but:

[0026]

[0027] 6) Changing the radio frequency drive of the acousto-optic tunable filter 1-3 so that the wavelength tunable monochromatic light source module 1 outputs different wavelengths λ in turn i , and repeat step 5, and finally the phase delay amount corresponding to the wave plate 2 with a rotating structure to be tested at different wavelengths can be obtained, so that the wave plate 2 with a rotating structure to be tested obtains the phase delay δ(λ) in a wide spectrum range, wherein the phase delay amount δ is a function of the wavelength λ, and the wavelength λ is its independent variable.

[0028] The specific principles of the method of the present invention are as follows:

[0029] In optical theory, polarized light is divided into linear polarized light, circular polarized light and elliptically polarized light. Any kind of polarized light can be represented by the Stokes vector, as shown in the following figure. Figure 1 As shown, the wavelength tunable monochromatic light source module 1 uses an AOTF crystal to generate a positive first-order output wavelength of λ i The emitted light is ideal horizontal linear polarized light, and its Stokes vector It can be expressed as:

[0030]

[0031] The polarized light passes through the wave plate 2 with a rotating structure to be measured. Assume that the wave plate 2 with a rotating structure to be measured corresponds to a light wavelength of λ i The phase delay is The angle of the fast axis is θ, where θ is the angle between the fast axis of the wave plate 2 to be measured with a rotating structure and the horizontal direction. At this time, the Mueller matrix M2 of the wave plate 2 to be measured with a rotating structure can be expressed as:

[0032]

[0033] Then the state of the horizontal polarized light generated by the wavelength tunable monochromatic light source module 1 after passing through the wave plate to be tested 2 with a rotating structure is:

[0034]

[0035] Finally, the polarization is analyzed by the polarizer 3, and its polarization angle is in the horizontal direction. Its Mueller matrix M3 can be expressed as:

[0036]

[0037] The polarization state after polarization analysis is:

[0038]

[0039] The final polarization state of the outgoing light It can be seen that the energy E of the emitted light can be expressed as:

[0040]

[0041] During the process of rotating the wave plate 2 to be tested with the rotating structure, the maximum energy value E can be detected by the energy detection component 4. max and E min , due to the incident light polarization state To determine the state,

[0042]

[0043]

[0044] but:

[0045]

[0046] Change the wavelength λ output by the wavelength tunable monochromatic light source module 1 i , the phase delay of the wave plate 2 to be tested with a rotating structure at different wavelengths can be obtained, thereby obtaining the phase delay δ(λ) within a wide spectrum range, where the phase delay δ is a function of the wavelength λ, and the wavelength λ is its independent variable.

[0047] The present invention provides a device and method for measuring the performance of a wide-band wave plate by using AOTF monochromatic light. The advantages of the method are: 1. The measuring method is simple. After the optical path is built, it is only necessary to rotate the wave plate 3 to be measured with a rotating structure, and the phase delay angle of the wave plate can be obtained by outputting the maximum and minimum energy values; 2. The phase delay angle of the wave plate at different wavelengths can be measured; 3. The direct measurement method is used to calibrate the phase delay. Compared with the thickness measurement method, the material property difference can be eliminated and the measurement accuracy is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A device for quickly measuring the phase delay of a wide-band wave plate. DETAILED DESCRIPTION

[0049] The following is combined with Figure 1 The implementation examples of the method of the present invention are described in detail.

[0050] The main components used in the present invention are described as follows:

[0051] 1) Broad spectrum light source 1-1: In this embodiment, the broad spectrum light source 1-1 outputted by optical fiber adopts a stable infrared tungsten lamp light source of Thorlabs, model SLS202L, and has a spectrum range of 450-5500nm;

[0052] 2) Collimating lens 1-2: In this embodiment, the collimating lens 1-2 is a self-designed component, and its use wavelength range is 900-2500nm. The purpose is to collimate the wide spectrum light source 1-1 output by the optical fiber into a parallel light beam incident on the acousto-optic tunable filter 1-3;

[0053] 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 Institute of China Electronics Technology Group Corporation, and its main technical indicators are:

[0054] a) Working wavelength: 850nm-2400nm

[0055] b) Spectral resolution: 2nm-12nm

[0056] c) Primary deflection angle: 2.6°

[0057] d) Separation angle: >=6.1°

[0058] e) Diffraction efficiency: >=60%

[0059] f) Dimensions: 560mm*400mm*315mm

[0060] g) Driving power: <=2W

[0061] h) Driving frequency range: 37MHz-112MHz;

[0062] 4) Wave plate 2 to be tested with a rotating structure: Wave plate 3 to be tested is a wave plate with a rotating structure. Wave plate 3 needs to measure the phase delay from 600 to 900 nm The rotating structure adopts the product of Daheng Optoelectronics, model WPA-30. The rotation angle is 0 to 360 degrees, the clamping diameter is 30mm, and the minimum reading is 0.5 degrees;

[0063] 5) Analyzer 3: Analyzer 3 is a polarizer with a rotating structure, in which the polarizer is a Thorlabs product, model LPVIS100, and its main performance parameters are: working band 600-1200nm; polarization extinction ratio is 10000:1; aperture size is 25mm, effective aperture is 90% of the aperture; polarization angle is ±20°. The rotating structure is a Thorlabs product, model RSP1D, and its main performance parameters are: rotation angle is 0 to 360 degrees, clamping diameter is 1 inch. The minimum reading is 0.5 degrees;

[0064] 6) Energy detection component 4: It uses the product of Thorlabs, model PM120D, and its main performance parameters are: working band is 400-1100nm; power test range is 50nw-50mw; the probe is Si detector;

[0065] The main optical path schematic diagram of the method of the present invention is shown in the attached Figure 1 The specific situation is described as follows:

[0066] 1) According to the attached Figure 1 The wavelength tunable monochromatic light source module 1 and the energy detection component 4 are fixed. 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 is incident on the radio frequency tunable acousto-optic tunable filter 1-3. After the radio frequency is turned on, the output wavelength is λ i The diffracted light is blocked by the shading plates 1-4 to block the negative first-order diffracted light and the zero-order light, and the generated positive first-order diffracted light is received by the energy detection component 4. In the embodiment, the wavelength range of the wave plate 3 to be measured with a rotating structure is required to be 600 to 900 nm, and the wavelength range to be measured is divided into a light wavelength λ with each 10 nm as a measurement point. i The sequence is:

[0067] λ i =600+10i(i=0,1,…30)

[0068] The wide-band phase delay of the wave plate 2 with a rotating structure is measured. Where i is a natural number from 0 to 30. As i increases by 1 each time, the output wavelength is λ i The output positive first-order diffraction light is horizontally polarized. It is expressed by the Stokes vector as:

[0069]

[0070] 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 transmission axis angle of the analyzer 3 is orthogonal to the polarization direction of the outgoing light. The analyzer 3 is then rotated 90 degrees. At this time, the transmission axis direction of the polarizer 3 is horizontal. The Mueller matrix M3 of the analyzer 3 can be expressed as:

[0071]

[0072] 3) The wave plate 2 with a rotating structure to be tested is placed between the wavelength tunable monochromatic light source module 1 and the analyzer 3, and the position and angle of the wave plate 3 with a rotating structure to be tested are adjusted so that the outgoing light of the wavelength tunable monochromatic light source module 1 passes through the center of the wave plate 2 with a rotating structure to be tested and is vertically incident. Assuming that the wavelength of light corresponding to the wave plate 2 with a rotating structure to be tested is λ i The phase delay is At this time, the angle of the fast axis of the wave plate 2 to be tested with the rotating structure is θ, where θ is the angle between the fast axis of the wave plate 2 to be tested with the rotating structure and the horizontal direction. At this time, the Mueller matrix M2 of the wave plate 2 to be tested with the rotating structure can be expressed as:

[0073]

[0074] 4) The wavelength generated by the wavelength tunable monochromatic light source module 1 is λ i The light passes through the wave plate 2 with a rotating structure and the analyzer 3 in turn, and is detected by the energy detection component 4. The final polarization state of the emitted light is It can be expressed as:

[0075]

[0076] Through calculation, we know that:

[0077]

[0078] 5) Final polarization state of the output light It can be seen that the energy E of the emitted light can be expressed as:

[0079]

[0080] By rotating the wave plate 2 with a rotating structure to be tested, the maximum energy value E detected by the energy detection component 4 during the rotation process max and the minimum value E min , and its output value satisfies:

[0081]

[0082]

[0083] but:

[0084]

[0085] 6) Changing the radio frequency drive of the acousto-optic tunable filter 1-3 so that the wavelength tunable monochromatic light source module 1 outputs different wavelengths λ in turn i , and repeat step 5, and finally the phase delay amount of the wave plate 2 to be tested with a rotating structure at different wavelengths can be obtained, so that the wave plate 2 to be tested with a rotating structure obtains the phase delay δ(λ) in a wide spectrum range, wherein the phase delay amount δ is a function of the wavelength λ, and the wavelength λ is its independent variable.

Claims

1. A device for measuring the performance of a wide-band wave plate using AOTF monochromatic light, comprising a wavelength tunable monochromatic light source module (1), a wave plate to be measured with a rotating structure (2), an analyzer (3) and an energy detection component (4), characterized in that: 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 light shielding plate (1-4); during testing, the light emitted by the wide-spectrum light source (1-1) output by the optical fiber passes through the collimating lens (1-2) to become parallel light, which is incident on the radio frequency tunable acousto-optic tunable filter (1-3), and the emitted light generates diffracted light of corresponding wavelength, and the light shielding plate (1-4) is used to shield the negative first-order diffracted light and the zero-order light, and the generated After the positive first-order diffracted light passes through a wave plate to be tested with a rotating structure (2) and a polarizer (3), it is detected by an energy detection component (4). The polarization state of the emitted light is changed by rotating the wave plate to be tested with a rotating structure (2), thereby causing the energy detection component (4) to detect the energy change of the light. The phase delay amount of the wave plate to be tested with a rotating structure (2) is accurately and quickly calibrated according to the energy change. The wavelength of the emitted light is changed by a wavelength-tunable monochromatic light source module (1), thereby obtaining the phase delay amount of the wide-band wave plate.

2. The device for measuring the performance of a wide-band wave plate using AOTF monochromatic light according to claim 1, characterized in that: The wavelength ranges of the wavelength-tunable monochromatic light source module (1) and the polarizer (3) need to be compatible with the wave plate (2) to be tested with a rotating structure.

3. The device for measuring the performance of a wide-band wave plate using AOTF monochromatic light according to claim 1, characterized in that: The polarizer (3) is a polarizing plate with a rotating structure. The use wavelength range of the polarizing plate needs to cover the wavelength of the wave plate (2) to be measured with a rotating structure, and the polarization extinction ratio of this band is better than 5000:

1.

4. The device for measuring the performance of a wide-band wave plate using AOTF monochromatic light according to claim 1, characterized in that: The wavelength range measured by the energy detection component (4) covers the test wavelength range of the wave plate (2) to be tested with a rotating structure.

5. A method for measuring phase delay based on the device for measuring the performance of a wide-band wave plate using AOTF monochromatic light according to claim 1, characterized in that it comprises the following steps: 1) A wavelength tunable monochromatic light source module (1) and an energy detection component (4) are fixed. Light emitted from a wide spectrum light source (1-1) output by an optical fiber passes through a collimating lens (1-2) and becomes parallel light. The light is incident on a radio frequency tunable acousto-optic tunable filter (1-3). After the radio frequency is turned on, the output wavelength is λ i The diffracted light is diffracted by the light shielding plate (1-4), and the negative first-order diffracted light and the zero-order light are shielded. The generated positive first-order diffracted light is received by the energy detection component (4). Since the output positive first-order diffracted light is horizontally linearly polarized light, the output wavelength is λ i The polarization state of the diffracted light It is 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 transmission axis angle of the analyzer (3) is orthogonal to the polarization direction of the outgoing light. The analyzer (3) is then rotated 90 degrees. At this time, the 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: 3) placing the wave plate (2) to be tested with a rotating structure between the wavelength tunable monochromatic light source module (1) and the analyzer (3), and adjusting the position and angle of the wave plate (3) to be tested with a rotating structure so that the outgoing light of the wavelength tunable monochromatic light source module (1) passes through the center of the wave plate (2) to be tested with a rotating structure and is vertically incident. Assuming that the wave plate (2) to be tested with a rotating structure corresponds to a wavelength λ i The phase delay is At this time, the angle of the fast axis of the wave plate (2) to be tested with a rotating structure is θ, where θ is the angle between the fast axis of the wave plate (2) to be tested with a rotating structure and the horizontal direction; then the Mueller matrix M2 of the wave plate (2) to be tested with a rotating structure can be expressed as: 4) The wavelength generated by the wavelength tunable monochromatic light source module (1) is λ i The light passes through the wave plate (2) to be measured with a rotating structure and the polarizer (3) in sequence, and is then detected by the energy detection component (4). The final polarization state of the emitted light is It can be expressed as: Through calculation, we know that: 5) The final polarization state of the outgoing light It can be seen that the energy E of the emitted light can be expressed as: By rotating the wave plate (2) to be tested with the rotating structure, the maximum energy value E detected by the energy detection component (4) during the rotation process is max and the minimum value E min , and its output value satisfies: but: 6) Changing the radio frequency drive of the acousto-optic tunable filter (1-3) so that the wavelength tunable monochromatic light source module (1) outputs different wavelengths λ in sequence i , and repeating step 5), the phase delay corresponding to the wave plate (2) with a rotating structure to be tested at different wavelengths can be finally obtained, so that the wave plate (2) with a rotating structure to be tested obtains the phase delay δ(λ) within a wide spectrum range, wherein the phase delay δ is a function of the wavelength λ, and the wavelength λ is its independent variable.

Images