阅读说明：本技术 一种大量程成像式双折射分布测量装置及方法 (Wide-range imaging type birefringence distribution measuring device and method ) 是由 陈宽 陈国飞 曾爱军 葛士军 胡伟 于 2019-12-04 设计创作，主要内容包括：本发明公开了一种大量程成像式双折射分布测量装置及方法,该测量装置包括：光源模块,其接收控制与数据处理模块信号,选择并输出测量所用波长的光束,透射照明被测材料样品；成像镜组,其将经被测材料样品的出射光束投影到光电探测器上；可变偏振态发生器,其位于被测材料样品两侧的光路中,根据控制与数据处理模块输入的电信号,改变光束的偏振态,提供光束的起偏、检偏或相位延迟；光电探测器,其将采集的光强分布转化为电信号输出给控制与数据处理模块运算,最终呈现被测物双折射分布结果。本发明解决了现有双折射分布测量技术存在的测量速度相对较慢、相位延迟量量程受限的问题。(The invention discloses a wide-range imaging type birefringence distribution measuring device and a method thereof, wherein the measuring device comprises: the light source module receives the signals of the control and data processing module, selects and outputs light beams with wavelengths used for measurement, and transmits and illuminates the measured material sample; the imaging lens group projects the emergent light beam of the tested material sample onto the photoelectric detector; the variable polarization state generator is positioned in the light paths at two sides of the tested material sample, changes the polarization state of the light beam according to the electric signal input by the control and data processing module, and provides polarization, polarization detection or phase delay for the light beam; and the photoelectric detector converts the acquired light intensity distribution into an electric signal and outputs the electric signal to the control and data processing module for operation, and finally, a measured object birefringence distribution result is presented. The invention solves the problems of relatively low measurement speed and limited phase delay measurement range in the existing birefringence distribution measurement technology.)

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.

10. The method of claim 1, comprising the steps of:

focusing a light source module and an imaging lens group on the surface of a tested material sample, carrying out conversion of the output light wavelength of the light source module through a control and data processing module, simultaneously switching variable polarization state generators in two side light paths of the tested material sample according to the delay amount corresponding to the wavelength, acquiring a light intensity distribution image under the delay amount of each variable polarization state generator by a photoelectric detector, calculating the delay amount and azimuth angle distribution of the acquired image under each wavelength, calculating the total delay amount order by utilizing the fractional part of the delay amount of each wavelength, and finally obtaining the absolute value and the delay azimuth angle of the delay amount distribution.

Technical Field

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

Background

The phenomenon that light is decomposed into linearly polarized light with two vibration planes perpendicular to each other when passing through an anisotropic transparent medium is called birefringence, and birefringence distribution parameters refer to a phase retardation amount δ and an azimuth angle θ of a measured material. Birefringence characteristics are widely present in natural mineral crystals and in synthetic materials such as mechanically stressed glass, plastics, liquid crystals, and in addition cellular materials such as nucleoproteins, spindles, myofibrils, and the like also have optical anisotropy. Measuring the birefringence properties of materials is useful to help us understand in depth and to make more rational use of optical materials.

The measurement of birefringence distribution is based on the principle of polarization optics, and the birefringence distribution can be qualitatively obtained by the conventional polarization measurement instrument through a polarizing plate polarization-analyzing mode. In recent years, with the development of scientific technology, a plurality of new birefringence distribution measuring methods are proposed, which adopt various phase delay modulation modes, overcome the defects of the traditional method, quantitatively acquire the birefringence distribution of the measured material and have important application prospects. The existing birefringence distribution measurement method mostly adopts a single-wavelength light source and is limited by the periodicity of a trigonometric function in Stokes vector calculation, and the upper limit of the measuring range of birefringence phase delay quantity does not exceed pi; secondly, the detection method obtains the two-dimensional distribution of birefringence in a point-by-point scanning mode, has relatively slow measurement speed, and cannot be applied to large-area sample or pipeline detection.

Disclosure of Invention

The purpose of the invention is as follows: in order to overcome the defects of the prior art, the invention provides an optical device for realizing wide-range imaging type birefringence distribution measurement based on a multi-wavelength polarization phase modulation method and multiple planar array detection, and further realizes birefringence distribution measurement of a phase delay sample exceeding pi under the condition of no mechanical transmission.

In order to achieve the purpose, the invention adopts the following technical scheme: a wide-range imaging birefringence distribution measuring 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, changes the polarization state of the light beams according to electric signals input by the control and data processing module, provides polarization, polarization detection or phase delay for the light beams, the photoelectric detector converts collected light intensity distribution into electric signals to be output to the control and data processing module for operation, and finally presents a measured object birefringence distribution result.

Furthermore, 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 the tested material sample through the wavelength selection device and the light source lens group.

Furthermore, 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.

Furthermore, the object image conjugate plane of the light source lens group is respectively the emission end plane of the multi-wavelength light source and the sample plane of the tested material.

Furthermore, the optical path of the imaging lens group is an object space telecentric optical path.

Furthermore, the object-image conjugate surfaces of the imaging lens group are the surface of the sample of the material to be detected and the surface of the target of the photoelectric detector.

Furthermore, the variable polarization state generator comprises a linear polarizer and a liquid crystal variable retarder, the polarization state of the light beam is changed after the light beam sequentially passes through the linear polarizer 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 magnitude of the retardation corresponds to the magnitude of the electric signal one to one.

Furthermore, the number of the variable polarization state generators is at least two, and the light paths on the two sides of the measured material sample respectively comprise at least one variable polarization state generator.

Further, the photodetector is an area array detector.

The measuring method of the wide-range imaging type birefringence distribution measuring device comprises the following steps:

focusing a light source module and an imaging lens group on the surface of a tested material sample, carrying out conversion of the output light wavelength of the light source module through a control and data processing module, simultaneously switching variable polarization state generators in two side light paths of the tested material sample according to the delay amount corresponding to the wavelength, acquiring a light intensity distribution image under the delay amount of each variable polarization state generator by a photoelectric detector, calculating the delay amount and azimuth angle distribution of the acquired image under each wavelength, calculating the total delay amount order by utilizing the fractional part of the delay amount of each wavelength, and finally obtaining the absolute value and the delay azimuth angle of the delay amount distribution.

Compared with the prior art, the wide-range imaging type birefringence distribution measuring device provided by the invention has the beneficial effects that:

(1) an imaging detection mode is adopted, a liquid crystal variable delay device is combined, and a mechanical transmission device is not arranged in a measurement system, so that the measurement stability is improved, and the measurement speed is increased;

(2) through multi-wavelength delay measurement, the detection of a large-delay material sample with phase delay larger than pi is realized, and the measuring range of a measuring system is expanded.

Drawings

FIG. 1 is a schematic structural view of one embodiment of the apparatus of the present invention;

FIG. 2 is a wavelength selection scheme for a multi-wavelength light source according to the embodiment of the present invention;

FIG. 3 is a schematic diagram of the operation of a variable polarization state generator according to the embodiment of the present invention;

FIG. 4 illustrates a polarization state modulation pattern of one side of a light source optical path at a single wavelength in accordance with one embodiment of the present invention;

FIG. 5 shows a polarization state modulation pattern on one side of an imaging optical path in a three-wavelength measurement mode according to an embodiment of the present invention;

FIG. 6 is a flow chart of a wide-range birefringence distribution measurement using the present apparatus in accordance with the embodiment of the present invention.

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

The specific implementation mode is as follows:

the invention is further explained below with reference to the drawings.

The invention relates to a wide-range imaging birefringence distribution measuring device which 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.

FIG. 1 is a schematic diagram of the structure of one embodiment of the apparatus of the present invention. In this example, the variable polarization state generator used includes a first variable polarization state generator 4 and a second variable polarization state generator 8, and both the first variable polarization state generator 4 and the second variable polarization state generator 8 are composed of a linear polarizer and a Liquid Crystal Variable Retarder (LCVR). The polarization state of the 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 magnitude of the retardation corresponds to the magnitude of the electric signal one by 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 lens group 2. The wavelength selection device 3 is a liquid crystal tunable filter which can allow narrow light wave transmission in a certain spectral range, the center wavelength of the transmitted light can be tuned, and the passband range of the filter used herein is matched with the emission spectrum band of the light source. The light beam emitted by the multi-wavelength light source 1 in the light source module is projected to the tested material sample through the wavelength selection device 3 and the light source lens group 2.

Preferably, the multiwavelength light source 1 comprises at least three or more wavelength components having a wavelength interval of not less than 10 nm; the wavelength selection device 3 has 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 source 1 one by one, and the bandwidth of each sub-pass band is not more than 10 nanometers. The object-image conjugate surface of the light source lens group 2 is the emission end surface of the multi-wavelength light source 1 and the surface of the tested material sample 5 respectively.

In the embodiment, at least one first variable polarization state generator 4 is arranged in the light source module, and can output emergent light with any complete polarization by polarizing and delaying unpolarized light or partially polarized light. The broadband partial polarized light emitted by the multi-wavelength light source 1 is filtered by the wavelength selection device 3 to obtain narrow-band partial polarized light, then the narrow-band partial polarized light is converted into narrow-band completely polarized light by the variable polarization state generator 4, and finally the narrow-band completely polarized light is projected on the surface of a tested material sample 5 through the light source lens group 2.

The measured material sample 5 spatially forms a distribution of retardation amounts and azimuth angles (i.e., birefringence distribution parameters) due to its optical anisotropy, and the retardation of each point spatially modulates the fully polarized light transmitted therethrough. According to the principle of polarization optics, the tested material sample 5 is a delay device with a spatial distribution Muller matrix, and after the Stokes vector of the completely polarized light is delayed and modulated to be emitted, the Stokes vector of the emitted light beam carries delay distribution information of a tested object.

The imaging lens group 6 is generally required to be telecentric on the object side, that is, the aperture stop 7 of the imaging lens group 6 is on the image side focal plane at the front part of the lens group, the object image conjugate plane of the imaging lens group 6 is the surface of the material sample to be detected 5 and the target surface of the photoelectric detector 9, and at least one second variable polarization state generator 8 is located near the aperture stop 7. The photodetector 9 is an area array detector. Therefore, the emergent light beam of the tested material sample 5 passes through the imaging lens group 6 and the polarization state demodulation device 8 in the lens group, and is finally projected on the photoelectric detector 9.

During measurement, voltages applied to the first variable polarization state generator 4 and the second variable polarization state generator 8 are changed according to a certain rule, and the polarization state of a transmission light beam in the light path is changed accordingly. The light intensity distribution of the image received by the area array detector 9 changes with the change of the polarization state of the light beam, the polarization state data and the image are transmitted to the control and data processing module, and the Muller matrix distribution of the tested sample material 5 can be calculated through the light intensity distribution images in a plurality of polarization states, namely the birefringence distribution data of the tested sample material is obtained.

FIG. 2 is a wavelength selection scheme for a multi-wavelength light source according to the embodiment of the present invention. The multi-wavelength light source 1 selects a white light LED and emits visible light with a typical spectrum range of 400-700 nm. When the measurement is performed, the wavelength selection device 3 sequentially selects wavelength components including at least three or more wavelength components at a wavelength interval of not less than 10 nm. As shown, three sets of measurements selected narrow band light outputs of 460 + -5 nm, 520 + -5 nm, and 630 + -5 nm, respectively.

Fig. 3 is a schematic diagram of the operation principle of the variable polarization state generator in the embodiment of the invention. The variable polarization state generator 4 in this embodiment 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), and the transmission axis of the linear polarizer 4a and 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 polarized light emitted by the LED light source 1 passes through the polarizing plate 4a and then emits vertical linearly polarized light, and when the retardation of the first liquid crystal retarder 4b is pi/2, the transmitted linearly polarized light is modulated into circularly polarized light. When the retardation amounts of the second liquid crystal retarder 4c are 0, pi/2, pi, 3 pi/2, respectively, the outgoing light beam is modulated to right circularly polarized light, +/-45 ° linearly polarized light, left circularly polarized light, and-45 ° linearly polarized light. Similarly, when the first and second liquid crystal retarders 4a and 4b are combined with different retardation amounts, the polarization state of the exiting light beam may be modulated into any linearly polarized, circularly polarized, or elliptically polarized light beam.

FIG. 4 shows the polarization state modulation pattern of one side of the light source optical path at a single wavelength in the embodiment of the present invention. According to the working principle of the variable polarization state generator, after the incident beams with different polarization states are modulated and emitted by the tested sample material 5, the Stokes vector of the emitted beam is the interaction result of the Stokes vector of the incident beam and the Muller matrix of the tested sample material 5. In order to obtain the information of the delay delta and the azimuth theta in the Muller matrix, the incident light in various polarization states and the signal of the corresponding emergent light are required to participate in the solution. In this embodiment, four elliptical polarized light beams are selected as the incident light as shown in fig. 4, and the four elliptical polarization states satisfy the condition that the ellipticity is the same and the direction angles are different. The effect of the Stokes vector of the beam on the Muller matrix of the sample material 5 under test can be expressed by the following equation:

where the ellipticity x and the direction angle ψ of the incident beam are modulated by the control system 10 applied to the variable polarization state generator 4, the light intensity of the outgoing beam can be solved by multi-polarization state measurement, and then the distribution of the retardation δ and the azimuth θ in the Muller matrix can be obtained by matrix inversion.

Fig. 5 shows a polarization state modulation mode on the imaging optical path side in the three-wavelength measurement mode according to the embodiment of the present invention. The polarization state generator is usually a circular polarizer, and for the multi-wavelength measurement in this embodiment, the polarization demodulation device composed of the birefringent crystal wave plate and the linear polarizer cannot behave as a circular polarizer at each wavelength. In this embodiment, the variable polarization demodulation device 8 used is a variable retardation circular polarizer in which a birefringent crystal waveplate is replaced with a liquid crystal variable retarder in consideration of the retardation variation of different wavelengths, and if the current measurement wavelength is λ₁The control system 10 applies a liquid crystal variable retarderVoltage to make its delay amount equal to lambda₁/4. In the multi-wavelength measurement, the retardation of the liquid crystal variable retarder is switched in accordance with the used wavelength in turn to obtain a circularly polarizing plate of the corresponding wavelength.

The measuring method of the wide-range imaging birefringence distribution measuring device comprises the following steps: focusing a light source module and an imaging lens group on the surface of a tested material sample, carrying out conversion of the output light wavelength of the light source module through a control and data processing module, simultaneously switching variable polarization state generators in two side light paths of the tested material sample according to the delay amount corresponding to the wavelength, acquiring a light intensity distribution image under the delay amount of each variable polarization state generator by a photoelectric detector, calculating the delay amount and azimuth angle distribution of the acquired image under each wavelength, calculating the total delay amount order by utilizing the fractional part of the delay amount of each wavelength, and finally obtaining the absolute value and the delay azimuth angle of the delay amount distribution.

Fig. 6 is a flow chart of a measurement method in the embodiment of the present invention. Before the measurement is started, the number of the testing wavelengths is selected according to the estimated sample delay range and the required measurement precision, and the measuring range and the precision are positively correlated with the number of the used wavelengths. Number of measurement wavelengths N and wavelength λ to be used₁、λ₂、……λ_NThe input control and data processing module 10 controls the voltage combination of the liquid crystal device corresponding to the selected wavelength in the self-contained database of the data processing module 10. After the test is started, the control module 10 first selects the voltage of the wavelength selective device 3 to obtain the central wavelength λ₁And narrow-band light output with the bandwidth not more than 10 nm. Then, the voltage of the second polarization demodulation device 8 is selected to constitute λ₁The voltage V of the first 4 variable polarization state generator is selected₁(λ₁) The photodetector 9 records and transmits the two-dimensional light intensity distribution to the control and data processing module 10. Sequentially obtaining I according to the modulation mode of the variable polarization state generator₂(λ₁)、I₃(λ₁) And I₄(λ₁). The four times of measured light intensity distribution can be used for obtaining lambda according to the Stokes vector operation formula₁Retardation delta at wavelength₁And azimuth angle theta₁And (4) distribution.

According to the method, the retardation and the azimuth angle distribution delta under each wavelength can be obtained₂～θ₂、δ₃～θ₃、……δ_N～θ_N. For measured material samples 5, delta, less than the pi retardation₁＝δ₂＝…＝δ_N(ii) a And m is satisfied for the tested sample 5 with the retardation larger than pi₁λ₁/2+δ₁＝m₂λ₂/₂+δ₂＝…＝m_Nλ_N/2+δ_NWhere m is the delay order and is a positive integer. For example, the measured retardation amounts are 30nm (460nm), 200nm (520nm) and 90nm (630nm) for the three wavelengths employed in fig. 2, respectively, and it is not difficult to obtain 3-stage, 2-stage and 2-stage retardations for the three wavelengths, respectively, whose absolute retardation amount is 720 nm. After the operation is finished, the control and data processing module 10 outputs the measurement result of the birefringence distribution.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.