CN211122503U - Wide-range imaging type birefringence distribution measuring device - Google Patents

Abstract

The utility model discloses a large-range imaging type birefringence distribution measuring device. The measuring device comprises: a light source module, which receives a signal from a control and data processing module, selects and outputs a light beam with a wavelength used for measurement, and transmits and illuminates a material sample to be measured; Imaging lens group, which projects the outgoing beam of the tested material sample onto the photodetector; variable polarization state generator, which is located in the optical path on both sides of the tested material sample, according to the electrical signal input by the control and data processing module , change the polarization state of the beam, and provide polarization, analysis or phase delay of the beam; photodetector, which converts the collected light intensity distribution into electrical signals and outputs them to the control and data processing module for calculation, and finally presents the birefringence of the measured object distribution results. The utility model solves the problems existing in the existing birefringence distribution measurement technology that the measurement speed is relatively slow and the phase delay range is limited.

Description

A large-range imaging birefringence distribution measuring device

technical field

The utility model relates to the field of optical detection, in particular to a device for measuring the birefringence distribution of a transparent medium.

Background technique

The phenomenon that the light is decomposed into two linearly polarized light whose vibration planes are perpendicular to each other when passing through an anisotropic transparent medium is called birefringence, and the birefringence distribution parameter refers to the phase retardation δ and azimuth angle θ of the measured material. Birefringence is widely found in natural mineral crystals and mechanically stressed synthetic materials such as glass, plastics, and liquid crystals. In addition, cellular substances such as nucleoproteins, spindles, and myofibrils also have optical anisotropy. Measuring the birefringence properties of materials is beneficial to help us understand and apply optical materials more rationally.

The measurement of birefringence distribution is based on the principle of polarization optics, and the birefringence distribution can be qualitatively obtained by the traditional polarization measuring instrument through the polarization-analyzer method of polarizer. In recent years, with the development of science and technology, some new birefringence distribution measurement methods have been proposed. They use various phase delay modulation methods, overcome the shortcomings of traditional methods, and quantitatively obtain the birefringence distribution of the measured material, which has important application prospects. Most of the existing birefringence distribution measurement methods use a single-wavelength light source, which is limited by the periodicity of the trigonometric function in the Stokes vector solution, and the upper limit of the range of the birefringence phase retardation does not exceed π; secondly, the detection method is obtained by point-by-point scanning. Two-dimensional distribution of birefringence, the measurement speed is relatively slow, and it is not suitable for large-area samples or pipeline inspection.

Utility model content

Purpose of the utility model: In order to overcome the above-mentioned defects of the prior art, the present utility model creates and provides an optical device for realizing large-scale imaging type birefringence distribution measurement based on the multi-wavelength polarization phase modulation method and multiple surface array detection, and furthermore, without The birefringence distribution measurement of samples with more than π phase retardation is achieved under any mechanical transmission.

In order to achieve the above purpose, the present utility model adopts the following technical scheme: a large-range imaging birefringence distribution measurement device, comprising a light source module, an imaging mirror group, a variable polarization state generator, a photodetector, and control and data processing Module; the light source module receives the signal from the control and data processing module, selects and outputs the light beam of the wavelength used for measurement, transmits the illumination of the material sample to be measured, and the imaging lens group projects the outgoing beam of the material sample to be measured on the photodetector, variable polarization The state generator is located in the optical path on both sides of the material sample to be tested. According to the electrical signal input by the control and data processing module, the polarization state of the beam is changed to provide polarization, analysis or phase delay of the beam, and the photodetector will collect the data. The light intensity distribution is converted into an electrical signal and output to the control and data processing module for operation, and finally presents the birefringence distribution result of the measured object.

Further, the light source module includes a multi-wavelength light source, a wavelength selection device, and a light source mirror group, and the multi-wavelength light source in the light source module projects the light beam to the material sample under test through the wavelength selection device and the light source mirror group.

Further, the multi-wavelength light source contains at least three or more wavelength components with a wavelength interval of not less than 10 nanometers; the wavelength selective device has sub-passbands with no less than three wavelength ranges, and the sub-pass The central wavelength of the band corresponds to the wavelength components of the multi-wavelength light source one-to-one, and the bandwidth of each sub-pass band is not greater than 10 nanometers.

Still further, the object-image conjugate surfaces of the light source lens group are respectively the emission end surface of the multi-wavelength light source and the sample surface of the material to be measured.

Further, the optical path of the imaging lens group is an object-side telecentric optical path.

Further, the object-image conjugate surfaces of the imaging lens group are the sample surface of the material to be measured and the target surface of the photodetector, respectively.

Further, the variable polarization state generator includes a linear polarizer and a liquid crystal variable retarder, and the light beam passes through the linear polarizer and the liquid crystal variable retarder in turn, and the polarization state changes, and the liquid crystal variable retarder delays. The amount can vary with the change of the electrical signal applied to it, and the magnitude of the delay corresponds to the magnitude of the electrical signal.

Further, there are at least two variable polarization state generators, and the optical paths on both sides of the material sample to be tested each include at least one variable polarization state generator.

Further, the photodetector is an area array detector.

According to the measurement method of the large-range imaging birefringence distribution measurement device, the following steps are included:

Focus the light source module and imaging lens group on the surface of the material sample to be tested, and convert the wavelength of the light output from the light source module through the control and data processing module. The photodetector collects the light intensity distribution image under the delay amount of the variable polarization state generator each time, calculates the delay amount and azimuth angle distribution for the collected image at each wavelength, and uses the fractional part of the delay amount of each wavelength to calculate the total amount. , and finally obtain the absolute value of the delay distribution and the delay azimuth.

Compared with the prior art, the beneficial effects of the large-scale imaging birefringence distribution measuring device proposed by the present utility model include:

(1) Using the imaging detection method, combined with the liquid crystal variable retardation device, there is no mechanical transmission device in the measurement system, which increases the stability of the measurement and improves the measurement speed;

(2) Through the measurement of retardation at multiple wavelengths, the detection of large retardation material samples with a phase delay greater than π is realized, and the range of the measurement system is expanded.

Description of drawings

1 is a schematic structural diagram of a specific embodiment of the device of the present invention;

Fig. 2 is a kind of wavelength selection mode of the multi-wavelength light source in the embodiment of the present utility model;

3 is a schematic diagram of the working principle of the variable polarization state generator in the embodiment of the present invention;

4 is a polarization state modulation mode on one side of the light path of the light source at a single wavelength in the embodiment of the present utility model;

5 is a polarization state modulation mode on one side of the imaging optical path in the three-wavelength measurement mode in the embodiment of the present utility model;

FIG. 6 is a flow chart of measuring the birefringence distribution of a large range by using the device in the embodiment of the present invention.

In the figure: 1-multi-wavelength light source; 2-light source mirror group; 3-wavelength selective device; 4-variable polarization state generator 1; 5-tested material sample; 6-imaging mirror group; 7-aperture diaphragm; 8- -Variable polarization state generator two; 9-photodetector; 10-data processing module.

Detailed ways:

The present utility model will be further explained below in conjunction with the accompanying drawings.

A large-range imaging type birefringence distribution measuring device of the utility model comprises a light source module, an imaging mirror group, a variable polarization state generator, a photoelectric detector and a control and data processing module. The light source module receives the signal from the control and data processing module, selects and outputs the light beam of the wavelength used for measurement, transmits and illuminates the material sample to be measured, and the imaging lens group projects the outgoing beam of the material sample to be measured onto the photodetector, and the variable polarization state occurs. The detector is located in the optical path on both sides of the material sample to be tested. According to the electrical signal input by the control and data processing module, the polarization state of the beam is changed to provide polarization, analysis or phase delay of the beam. The photodetector will collect the light intensity distribution. Convert it into an electrical signal and output it to the control and data processing module for operation, and finally present the birefringence distribution result of the measured object.

FIG. 1 is a schematic structural diagram of a specific embodiment of the device of the present invention. In this example, the variable polarization state generators used include variable polarization state generator one 4 and variable polarization state generator two 8, and variable polarization state generator one 4 and variable polarization state generator two 8 are both It is composed of linear polarizer and liquid crystal variable retarder (Liquid CrystalVariable Retarder, LCVR). After the light beam passes through the linear polarizer and the liquid crystal variable retarder in turn, the polarization state changes, and the retardation of the liquid crystal variable retarder can be changed with the change of the electrical signal applied to it, and the retardation value corresponds to the size of the electrical signal one-to-one.

In this example, the light source module is composed of a multi-wavelength light source 1 , a wavelength selection device 3 , and a light source mirror group 2 . The wavelength selection device 3 is a liquid crystal tunable filter, which can allow very narrow light wave transmission within a certain spectral range, and the center wavelength of the transmitted light can be tuned. The passband range of the filter used here matches the emission spectrum of the light source. In the light source module, the light beam emitted by the multi-wavelength light source 1 is projected to the material sample to be measured through the wavelength selection device 3 and the light source lens group 2 .

Preferably, the multi-wavelength light source 1 contains at least three or more wavelength components with a wavelength interval of not less than 10 nanometers; The wavelength components are in one-to-one correspondence, and the bandwidth of each sub-passband is not greater than 10 nanometers. The object-image conjugate surfaces of the light source lens group 2 are the emission end surface of the multi-wavelength light source 1 and the surface of the material sample 5 to be measured, respectively.

In this embodiment, at least one variable polarization state generator-4 is placed in the light source module, and can output any fully polarized outgoing light through polarization-retardation for unpolarized light or partially polarized light. The broadband partially polarized light emitted by the multi-wavelength light source 1 is first filtered by the wavelength selective device 3 to obtain the narrow-band partially polarized light, and then converted into the narrow-band fully polarized light by the variable polarization state generator 4, and finally projected on the light source lens group 2. The surface of the material sample 5 to be tested.

Due to its optical anisotropy, the measured material sample 5 forms a distribution of retardation and azimuth angle (ie birefringence distribution parameter) in space, and the retardation of each point in space modulates the fully polarized light transmitted through it. According to the principle of polarization optics, the tested material sample 5 is a retardation device with a spatially distributed Muller matrix. When the Stokes vector of the fully polarized light is delayed and modulated, the Stokes vector of the outgoing light beam carries the retardation distribution information of the tested object.

Generally, the imaging mirror group 6 is required to be telecentric in the object side, that is, the aperture stop 7 of the imaging mirror group 6 is on the focal plane of the image side in the front part of the mirror group, and the object image conjugate plane of the imaging mirror group 6 is the material to be measured. The sample 5 surface and the photodetector 9 target surface, and at least one variable polarization state generator two 8 is located in the vicinity of the aperture stop 7 . The photodetector 9 is an area array detector. Therefore, the outgoing light beam from the tested material sample 5 passes through the imaging mirror group 6 and the polarization state demodulation device 8 in the mirror group, and finally projects on the photodetector 9 .

During measurement, the voltage applied to the variable polarization state generator 1 4 and the variable polarization state generator 2 8 changes according to a certain law, and the polarization state of the transmission beam in the optical path changes accordingly. The light intensity distribution of the image received on the area array detector 9 changes with the change of the polarization state of the beam, and these polarization state data and images are transmitted to the control and data processing module. The Muller matrix distribution of the tested sample material 5, that is, its birefringence distribution data is obtained.

FIG. 2 is a wavelength selection method of the multi-wavelength light source in the embodiment of the present invention. The multi-wavelength light source 1 selects a white LED, which emits a typical spectrum of visible light in the range of 400-700 nm. When performing the measurement, the wavelength selection device 3 sequentially selects at least three or more wavelength components with a wavelength interval of not less than 10 nanometers. As shown in the figure, narrowband light outputs of 460 ± 5 nm, 520 ± 5 nm and 630 ± 5 nm were selected for the three sets of measurements, respectively.

FIG. 3 is a schematic diagram of the working principle of the variable polarization state generator in the embodiment of the present invention. In this embodiment, the variable polarization state generator 4 is composed of a linear polarizer 4a and a pair of liquid crystal variable retarders (a first liquid crystal retarder 4b and a second liquid crystal retarder 4c). The transmission axis of the linear polarizer 4a is the same as the The fast axis directions of the first liquid crystal retarder 4b and the second liquid crystal retarder 4c are 90°, 45°, and 90°, respectively. Part of the polarized light emitted by the LED light source 1 passes through the linear polarizer 4a and then emits vertical linearly polarized light. When the retardation of the first liquid crystal retarder 4b is π/2, the linearly polarized light transmitted through it is modulated into circularly polarized light . When the retardation of the second liquid crystal retarder 4c is 0, π/2, π, 3π/2, respectively, the outgoing light beam is modulated into right circularly polarized light, +45° linearly polarized light, left circularly polarized light and -45° Linearly polarized light. Similarly, when the first liquid crystal retarder 4a and the second liquid crystal retarder 4b are combined with different retardation, the polarization state of the outgoing light beam can be modulated to any linearly polarized, circularly polarized or elliptically polarized light beam.

FIG. 4 is a polarization state modulation mode on one side of the light path of the light source at a single wavelength in the embodiment of the present invention. According to the above working principle of the variable polarization state generator, after the incident beams with different polarization states are modulated and emitted by the sample material 5 to be tested, the Stokes vector of the outgoing beam is the result of the interaction between the Stokes vector of the incident beam and the Muller matrix of the sample material 5 to be tested. . In order to obtain the information of the retardation δ and the azimuth angle θ in the Muller matrix, the signals of the incident light and the corresponding outgoing light of various polarization states are required to participate in the solution. In this embodiment, four elliptically polarized light beams are selected as incident light as shown in FIG. 4 , and the four elliptically polarized states satisfy the same ellipticity but different direction angles. The interaction between the Stokes vector of the beam and the Muller matrix of the sample material 5 under test can be expressed by the following formula:

In the formula, the ellipticity x and the direction angle ψ of the incident beam are modulated on the variable polarization state generator 4 by the control system 10, and the light intensity of the outgoing beam can be solved by the multi-polarization state measurement, then for the Muller matrix in The distribution of delay amount δ and azimuth angle θ can be obtained by matrix inversion operation.

FIG. 5 is a polarization state modulation mode on one side of the imaging optical path in the three-wavelength measurement mode in the embodiment of the present invention. Usually the polarization state generator is a circular polarizer. For the multi-wavelength measurement in this embodiment, the polarization demodulation device composed of a birefringent crystal waveplate and a linear polarizer cannot behave as a circular polarizer at each wavelength. In this embodiment, considering the change of retardation at different wavelengths, the variable polarization demodulation device 8 used is a variable retardation circular polarizer, and the birefringent crystal wave plate is replaced by a liquid crystal variable retarder. If the current measurement wavelength is λ ₁ , the control system 10 applies the voltage of the liquid crystal variable retarder to make the retardation equal to λ ₁ /4. In the multi-wavelength measurement, the wavelengths are used in sequence, and the retardation of the liquid crystal variable retarder is switched to obtain a circular polarizer corresponding to the wavelength.

The measurement method of the above-mentioned large-scale imaging type birefringence distribution measuring device includes the following steps: focusing the light source module and the imaging lens group on the surface of the material sample to be measured, converting the output light wavelength of the light source module through the control and data processing module, and simultaneously using the control and data processing module. The variable polarization state generators in the optical paths on both sides of the material sample are switched according to the delay corresponding to the wavelength, and the photodetector collects the light intensity distribution image under the delay amount of the variable polarization state generator each time, and collects images at each wavelength. Calculate the retardation and azimuth distribution, use the fractional part of the retardation of each wavelength to calculate the total retardation order, and finally obtain the absolute value of the retardation distribution and the retardation azimuth.

FIG. 6 is a flow chart of the measurement method in the embodiment of the present invention. Before starting the measurement, select the number of test wavelengths according to the estimated delay range of the sample and the required measurement accuracy. Both the range and accuracy are positively related to the number of wavelengths used. The number N of measurement wavelengths used and wavelengths λ ₁ , λ ₂ , . . . λ _N are input to the control and data processing module 10 , and the control and data processing module 10 selects the liquid crystal device voltage combination corresponding to the wavelength in its own database. After starting the test, the control module 10 first selects the voltage of the wavelength selective device 3 to obtain a narrow-band light output with a center wavelength of λ ₁ and a bandwidth not greater than 10 nm. Then, the voltage of the polarization demodulation device 2 8 is selected to form a circular polarizer of λ ₁ , and then the voltage V ₁ (λ ₁ ) of the variable polarization state generator 1 4 is selected, and the photodetector 9 records and sends the control and data The processing module 10 transmits a two-dimensional light intensity distribution. According to the modulation mode of the variable polarization state generator described above, I ₂ (λ ₁ ), I ₃ (λ ₁ ) and I ₄ (λ ₁ ) are obtained in sequence. The distribution of the retardation δ ₁ and the azimuth angle θ ₁ at the wavelength of λ ₁ can be obtained by applying the four measured light intensity distributions according to the above-mentioned Stokes vector operation formula.

In this way, the retardation and azimuth distributions δ ₂ to θ ₂ , δ ₃ to θ ₃ , . . . δ _N to θ _N at each wavelength can be obtained. For the measured material sample 5 less than the π retardation, δ ₁ =δ ₂ =...=δ _N ; and for the tested sample 5 greater than the π retardation, m ₁ λ ₁ /2+δ ₁ =m ₂ λ ₂ /2+δ ₂ =...=m _N λ _N /2+δ _N , where m is the delay order and is a positive integer. For example, for the three wavelengths used in Figure 2, the measured retardation is 30nm (460nm), 200nm (520nm) and 90nm (630nm), it is not difficult to find that the absolute retardation is 720nm for the three wavelengths respectively Level 3, Level 2 and Level 2 delays. After the calculation, the control and data processing module 10 outputs the measurement result of the birefringence distribution.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. These improvements and Retouching should also be regarded as the protection scope of the present invention.

Claims (9)

1. A wide-range imaging birefringence distribution measuring device is characterized in that: the device comprises a light source module, an imaging lens group, a variable polarization state generator, a photoelectric detector and a control and data processing module; the light source module receives signals of the control and data processing module, selects and outputs light beams with wavelengths used for measurement, transmits and illuminates a measured material sample, the imaging lens group projects the emergent light beams passing through the measured material sample to the photoelectric detector, the variable polarization state generator is positioned in light paths on two sides of the measured material sample, the polarization state of the light beams is changed according to electric signals input by the control and data processing module, polarization detection or phase delay of the light beams is provided, the photoelectric detector converts collected light intensity distribution into electric signals to be output to the control and data processing module for operation, and a measured object birefringence distribution result is finally presented.

2. A wide-range imaging birefringence distribution measuring device as set forth in claim 1, wherein: the light source module comprises a multi-wavelength light source, a wavelength selection device and a light source lens group, and emergent light beams of the multi-wavelength light source in the light source module are projected to a tested material sample through the wavelength selection device and the light source lens group.

3. A wide-range imaging birefringence distribution measuring device as set forth in claim 2, wherein: the multi-wavelength light source at least comprises three or more wavelength components with the wavelength interval not less than 10 nanometers; the wavelength selection device is provided with sub-pass bands in not less than three wavelength ranges, the central wavelengths of the sub-pass bands correspond to the wavelength components of the multi-wavelength light sources one by one, and the bandwidth of each sub-pass band is not more than 10 nanometers.

4. A wide-range imaging birefringence distribution measuring device as set forth in claim 3, wherein: the object image conjugate surface of the light source lens group is respectively a multi-wavelength light source emission end surface and a tested material sample surface.

5. A wide-range imaging birefringence distribution measuring device as set forth in claim 1, wherein: the optical path of the imaging lens group is an object space telecentric optical path.

6. A wide-range imaging birefringence distribution measuring device as set forth in claim 5, wherein: the object-image conjugate surface of the imaging lens group is the surface of the tested material sample and the surface of the photoelectric detector target respectively.

7. A wide-range imaging birefringence distribution measuring device as set forth in claim 1, wherein: the variable polarization state generator comprises a linear polaroid and a liquid crystal variable retarder, the polarization state of a light beam is changed after the light beam sequentially passes through the linear polaroid and the liquid crystal variable retarder, the retardation of the liquid crystal variable retarder can be changed along with the change of an electric signal applied to the liquid crystal variable retarder, and the retardation of the liquid crystal variable retarder corresponds to the electric signal in a one-to-one mode.

8. A wide-range imaging birefringence distribution measuring device as set forth in claim 7, wherein: the number of the variable polarization state generators is at least two, and the light paths on two sides of the measured material sample respectively comprise at least one variable polarization state generator.

9. A wide-range imaging birefringence distribution measuring device as set forth in claim 1, wherein: the photoelectric detector is an area array detector.

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