Spatial light modulation spectrometer and its measurement method

Abstract

The present invention provides a spatial light modulation spectrometer and a measurement method thereof, comprising: a light source system, a liquid crystal phase modulation array, a digital micromirror array, and a detector system; the light source system is used to emit a linearly polarized light beam, and after distributed phase modulation by the phase modulation array, a light field array composed of M×M light field units is obtained; the digital micromirror array is used to gate the light field array, so that the light beams corresponding to at least two light field units are incident on the detector system to generate interference, and an interference pattern signal is obtained to acquire the spectral information of the linearly polarized light beam. The present invention realizes the precise modulation of the optical path difference and the precise sampling of the interference signal. This invention patent proposes a Fourier transform spectrometer based on a liquid crystal phase modulation array and a digital micromirror array for precise scanning without optical path difference and energy splitting, avoiding the difficulties in the fabrication and control of the scanning moving mirror, reducing the volume and weight of the system, and at the same time improving the energy utilization rate of the system.

Description

Technical Field

[0001] The present invention relates to the field of spectral technology, and particularly relates to a spatial light modulation spectrometer and a measurement method thereof. Background Art

[0002] Spectral technology can obtain the composition and content information of target substances, and has been increasingly widely used in fields such as physical experiments, chemical analysis, biological characterization, medical tests, ecological environment protection, etc., and has played an important role in the exploration and discovery of new materials, new energy sources, and the unknown world. In order to obtain the spectral characteristics of the target, it is necessary to perform spectral decomposition on the detected polychromatic light. Currently, the commonly used spectral instruments mainly adopt technologies such as filter spectroscopy, prism spectroscopy, grating spectroscopy, and interference spectroscopy. Among them, the Fourier transform spectroscopy technology using interference spectroscopy technology has become a high-end instrument and equipment in many application fields due to its advantages such as multi-channel, high throughput, accurate wavenumber, and low stray light.

[0003] In recent years, with the emergence and development of emerging scientific and technological fields such as space exploration, aerial remote sensing, earth exploration, atmospheric monitoring, and military reconnaissance, due to their special application fields and usage environments, there is an urgent need for miniaturized and static Fourier transform spectrometers. And with the continuous upgrading of the demand, it has made it difficult for traditional Fourier transform spectrometers to overcome technical bottlenecks. Currently, the Fourier transform spectrometers commonly used in laboratories adopt a time modulation type structure, and the interferometer generates an optical path difference through the scanning of a moving mirror to obtain spectral information. It contains a set of high-precision moving mirror scanning mechanisms, and the precise sampling of the interference pattern is carried out through the high-precision moving mirror scanning mechanisms. This mechanism is very complex to manufacture, sensitive to vibration, has relatively strict requirements for the usage environment, and the moving mirror scanning mechanism has a large volume and weight; at the same time, due to the use of a beam splitter for spectroscopy, there will be an energy loss of half, reducing the stability and reliability of the system, which is not conducive to aerospace applications such as meteorological observation and atmospheric remote sensing. Thus, it limits its application in high-tech fields such as space exploration, meteorological remote sensing, and military reconnaissance. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to propose a spatial light modulation spectrometer and a measurement method thereof. Through a liquid crystal phase modulation array and a digital micromirror array, spatial distributed phase modulation of the transverse light field and gated interference of light field units are carried out, so as to obtain the interference pattern signals of each sampling optical path difference, avoiding the moving mirror scanning mechanism and beam splitting system of traditional Fourier transform spectrometers, reducing the volume and weight of the system, and improving the energy utilization rate. The proposed micro-spectrometer structure of the invention has the characteristics of miniaturization, light weight, and high energy utilization rate. It is applicable to applications in complex environments such as aerospace, earth remote sensing, and military reconnaissance.

[0005] To achieve the above purpose, the present invention adopts the following specific technical solutions:

[0006] A spatial light modulation spectrometer provided by the present invention includes: a light source system, a liquid crystal phase modulation array, a digital micromirror array, and a detector system;

[0007] The light source system is used to emit a linearly polarized light beam, and after distributed phase modulation by the phase modulation array, an optical field array composed of M×M optical field units is obtained; the digital micromirror array is used to gate the optical field array, so that at least two light beams corresponding to at least two optical field units are incident into the detector system to interfere, obtaining an interference pattern signal and acquiring the spectral information of the linearly polarized light beam.

[0008] Preferably, the light source system includes: a light source, a collimator, and a polarizer;

[0009] The light source is used to emit a divergent light beam with a spectral radiation range, and the divergent light beam is collimated by the collimator and then forms a parallel light beam incident on the polarizer; the polarizer is used to output the parallel light beam as a linearly polarized light beam.

[0010] Preferably, the liquid crystal phase modulation array includes: a row liquid crystal phase modulation array and a column liquid crystal phase modulation array;

[0011] The row liquid crystal phase modulation array is used to perform distributed phase modulation on the optical field of the linearly polarized light beam in the horizontal direction, obtaining M rows of horizontal optical fields;

[0012] The column liquid crystal phase modulation array is used to perform distributed phase modulation on the horizontal optical field again in the vertical direction, obtaining an optical field array composed of M×M optical field units.

[0013] Preferably, the row liquid crystal phase modulation array includes M rows of liquid crystal phase modulation units; the column liquid crystal phase modulation array includes M columns of liquid crystal phase modulation units;

[0014] By regulating the driving voltages on the liquid crystal phase modulation units in the row liquid crystal phase modulation array and the column liquid crystal phase modulation array, the distributed phase modulation of the linearly polarized light beam is realized.

[0015] Preferably, the row liquid crystal phase modulation array or the column liquid crystal phase modulation array from top to bottom sequentially includes: an upper transparent substrate, an upper transparent electrode, an upper alignment film, a liquid crystal layer, a lower alignment film, a strip electrode unit, and a lower transparent substrate;

[0016] The upper transparent substrate and the lower transparent substrate serve as the optical windows of the liquid crystal phase modulation array, jointly forming a liquid crystal cell for fixing the liquid crystal layer;

[0017] The upper transparent electrode and the strip electrode unit form the driving electrode of the liquid crystal layer, and drive the liquid crystal layer after applying a voltage to it;

[0018] The upper alignment film and the lower alignment film are used to align the nematic liquid crystal molecules in the liquid crystal layer.

[0019] Preferably, the detector system includes: a focusing mirror and a single-point detector;

[0020] The light beams of different light field units are incident on the single-point detector after being converged by the focusing mirror and interfere to obtain an interference pattern signal, and the single-point detector is used to convert the interference light signal into an electrical signal.

[0021] Preferably, when the row-wise liquid crystal phase modulation array and the column-wise liquid crystal phase modulation array are loaded with the same voltage distribution V, the liquid crystal layer thickness L of the column-wise liquid crystal phase modulation array y is N times that of the liquid crystal layer thickness L of the row-wise liquid crystal phase modulation array x , that is, L y = NL x ;

[0022] The refractive index difference corresponding to the voltages loaded on the adjacent strip units of the row-wise liquid crystal phase modulation array and the column-wise liquid crystal phase modulation array satisfies

[0023] When the row-wise liquid crystal phase modulation array and the column-wise liquid crystal phase modulation array have the same liquid crystal layer thickness L, the voltage V loaded on the adjacent strip units of the column-wise liquid crystal phase modulation array y causes a refractive index difference Δn y which is N times that of the refractive index difference Δn x caused by the voltage V loaded on the adjacent strip units of the row-wise liquid crystal phase modulation array x , that is, Δn y (V y ) = NΔn x (V x );

[0024] The refractive index differences corresponding to the voltages loaded on the adjacent strip units of the row-wise liquid crystal phase modulation array and the column-wise liquid crystal phase modulation array respectively satisfy Δn y (V y ) = NΔn x (V x );

[0025] where λ min is the minimum wavelength in the linearly polarized light beam.

[0026] Preferably, the digital micromirror array includes M×M digital micromirror units; at the same moment, two digital micromirror units at (0,0) and (i,j) are kept in the on state; i = 0, 1, 2…M; j = 0, 1, 2…M;

[0027] At the same moment, two light beams from different optical field units are incident into the detector system to generate interference;

[0028] When the light beam passing through the (i,j)th optical field unit interferes with the light beam passing through the (0,0)th optical field unit, the optical path difference between the two coherent light beams is:

[0029] δ(i,j) = [n(i) - n(0)]L x + [n(j) - n(0)]L y

[0030] By demodulating the interference pattern signal through discrete Fourier transform, the spectral information of the linearly polarized light beam is obtained.

[0031] The present invention also provides a measurement method for a spatial light modulation spectrometer, including the following steps:

[0032] S1. Adjust the linearly polarized light beam emitted from the light source system so that the polarization direction of the linearly polarized light beam is parallel to the light incident plane;

[0033] S2. The linearly polarized light beam is sequentially subjected to distributed phase modulation by the row liquid crystal phase modulation array and the column liquid crystal phase modulation array to obtain an optical field array composed of M×M optical field units, and is incident on the digital micromirror array;

[0034] S3. By controlling the M×M digital micromirror units in the digital micromirror array, the selection of different optical field units in the optical field array is realized;

[0035] S4. At least two optical field units with a preset optical path difference selected by the digital micromirror array enter the detector system to generate an interference pattern signal after interference, and then the spectral information of the linearly polarized light beam is obtained.

[0036] Preferably, step S1 includes the following steps:

[0037] S11. Use the scattered light beam emitted by the light source as the incident light beam, and make the emission point of the light source located at the front focal point of the collimating mirror;

[0038] S12. After the incident light beam is collimated by the collimating mirror, it becomes a parallel light beam and is incident on the polarizer;

[0039] S13. Adjust the polarization direction of the polarizing sheet in the polarizer until the polarization direction of the emitted linearly polarized light beam is parallel to the light incident plane.

[0040] Preferably, step S2 includes the following steps:

[0041] S21. Adjust the driving voltages of the strip-shaped liquid crystal phase modulation units in the row-direction liquid crystal phase modulation array and the column-direction liquid crystal phase modulation array respectively, so that the refractive index differences between adjacent strip-shaped liquid crystal phase modulation units are equal;

[0042] S22. After the linearly polarized light beam undergoes distributed phase modulation by the row-direction liquid crystal phase modulation array, M rows of transverse light fields are obtained;

[0043] S23. After the M rows of transverse light fields undergo distributed phase modulation by the column-direction liquid crystal phase modulation array, a light field array composed of M×M light field units is obtained.

[0044] Compared with the existing technologies, the present invention performs spatial distributed phase modulation of the transverse light field and gating interference of the light field units through the liquid crystal phase modulation array and the digital micromirror array, so as to obtain the interference pattern signals of each sampling optical path difference, avoiding the moving mirror scanning mechanism and beam splitting system of the traditional Fourier transform spectrometer, reducing the volume and weight of the system, and improving the energy utilization rate. The miniaturized spectrometer structure proposed by the invention has the characteristics of miniaturization, light weight, and high energy utilization rate, and is applicable to complex environments such as aerospace, earth remote sensing, and military reconnaissance. Description of the Drawings

[0045] Figure 1 is a schematic structural diagram of a spatial light modulation spectrometer provided according to an embodiment of the present invention.

[0046] Figure 2 is a schematic structural diagram of a liquid crystal phase modulation array in a spatial light modulation spectrometer provided according to an embodiment of the present invention.

[0047] Figure 3 is a schematic structural diagram of a liquid crystal phase modulation unit in a spatial light modulation spectrometer provided according to an embodiment of the present invention.

[0048] Figure 4 is a schematic diagram of the voltage loading drive of a row-direction liquid crystal phase modulation array in a spatial light modulation spectrometer provided according to an embodiment of the present invention.

[0049] Figure 5 is a schematic diagram of the voltage loading drive of a column-direction liquid crystal phase modulation array in a spatial light modulation spectrometer provided according to an embodiment of the present invention.

[0050] Figure 6 is a schematic flow diagram of a measurement method of a spatial light modulation spectrometer provided according to an embodiment of the present invention.

[0051] Figure 7 is a program block diagram of a measurement method of a spatial light modulation spectrometer provided according to an embodiment of the present invention.

[0052] The reference numerals therein include: light source 1, collimator 2, polarizer 3, columnar liquid crystal phase modulation array 4, row liquid crystal phase modulation array 5, digital micromirror array 6, focusing mirror 7, single-point detector 8, upper transparent substrate 9, upper transparent electrode 10, upper alignment film 11, liquid crystal layer 12, lower alignment film 13, strip electrode unit 14, lower transparent substrate 15, driving voltage 16, and nematic liquid crystal molecules 17. Detailed implementation manners

[0053] In the following, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are denoted by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, their detailed descriptions will not be repeated.

[0054] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation to the present invention.

[0055] Figure 1 The structural schematic diagram of a spatial light modulation spectrometer provided according to an embodiment of the present invention is shown.

[0056] As Figure 1 shown, the spatial light modulation spectrometer provided by the embodiment of the present invention includes: a light source system, a liquid crystal phase modulation array, a digital micromirror array 6, and a detector system.

[0057] The light source system is used to emit a linearly polarized light beam and enter the phase modulation array.

[0058] The light source system includes: a light source 1, a collimator 2, and a polarizer 3. The light source 1 is used to emit a divergent light beam having a certain spectral radiation range. The divergent light beam is collimated by the collimator 2 to form a parallel light beam, and the parallel light beam is incident on the polarizer 3. The polarizer 3 contains a polarizing plate, and the polarization direction of the polarizing plate is parallel to the incident plane of the parallel light beam. The incident plane is the plane formed by the incident light, the reflected light of the digital micromirror array 6, and the surface normal of the digital micromirror array 6, that is Figure 1 the YZ plane in. The Z-axis is parallel to the optical axis of the light source system, and the XYZ coordinate system is a right-handed coordinate system.

[0059] Polarize the incident light from the collimator to make the linearly polarized light with the vibration direction parallel to the incident plane of the parallel light beam transmit. The transmitted light is a linearly polarized light with the polarization direction parallel to the incident plane of the parallel light beam.

[0060] The linearly polarized light beam is incident on the liquid crystal phase modulation array. The liquid crystal phase modulation array is used to perform phase modulation on the linearly polarized light beam and divide the linearly polarized light beam into M×M regions.

[0061] The liquid crystal phase modulation array includes: a row - direction liquid crystal phase modulation array 4 and a column - direction liquid crystal phase modulation array 5.

[0062] The row - direction liquid crystal phase modulation array 4 is used to perform distributed phase modulation on the optical field of a linearly polarized light beam in the horizontal direction; the linearly polarized light beam is divided into M row regions to obtain M horizontal optical fields.

[0063] The column - direction liquid crystal phase modulation array 5 is used to perform distributed phase modulation on the horizontal optical field again in the vertical direction, thereby dividing the aperture of the horizontal optical field into M columns to obtain an optical field array composed of M×M optical field units, so that each optical field unit in the optical field array corresponds to a specific phase delay.

[0064] The row - direction liquid crystal phase modulation array 4 and the column - direction liquid crystal phase modulation array 5 are loaded with different driving voltages V, so that when the linearly polarized light beam transmits through the row - direction liquid crystal phase modulation array 4 and the column - direction liquid crystal phase modulation array 5, it passes through different optical paths respectively.

[0065] Figure 2 It shows a schematic structural diagram of the liquid crystal phase modulation array in the spatial light modulation spectrometer provided by the embodiment of the present invention.

[0066] Figure 3 It shows a schematic structural diagram of the liquid crystal phase modulation unit in the spatial light modulation spectrometer provided by the embodiment of the present invention.

[0067] As Figure 2 and Figure 3 shown, the row - direction liquid crystal phase modulation array 4 and the column - direction liquid crystal phase modulation array 5 are one - dimensional liquid crystal phase modulation arrays connected in series.

[0068] The column - direction liquid crystal phase modulation array 5 is placed perpendicular to the optical axis and is composed of N bar - shaped liquid crystal phase modulation units. The width of each bar - shaped liquid crystal phase modulation unit is a, the length is Na, and the length is along the y - direction. By controlling the voltage loaded on each bar - shaped liquid crystal phase modulation unit, distributed modulation of the phase delay amount of the linearly polarized light beam is achieved.

[0069] The row - direction liquid crystal phase modulation array 4 is placed perpendicular to the optical axis and is composed of N bar - shaped liquid crystal phase modulation units. The direction of the bar - shaped units is perpendicular to the direction of the bar - shaped units of the column - direction liquid crystal phase modulation array 5. The width of each bar - shaped liquid crystal phase modulation unit is a, the length is Na, and the length is along the x - direction. By controlling the voltage loaded on each bar - shaped liquid crystal phase modulation unit, distributed modulation of the phase delay amount of the linearly polarized light beam is achieved.

[0070] The row - direction liquid - crystal phase - modulation array 4 and the column - direction liquid - crystal phase - modulation array 5 have different liquid - crystal layer thicknesses. Both the row - direction liquid - crystal phase - modulation array 4 and the column - direction liquid - crystal phase - modulation array 5 include liquid - crystal phase - modulation units.

[0071] The liquid - crystal phase - modulation units, from top to bottom, sequentially include: an upper transparent substrate 9, an upper transparent electrode 10, an upper alignment film 11, a liquid - crystal layer 12, a lower alignment film 13, a strip - shaped electrode unit 14, and a lower transparent substrate 15.

[0072] The upper transparent substrate 9 and the lower transparent substrate 15 serve as the optical windows of the liquid - crystal phase - modulation array, jointly forming a liquid - crystal cell, transmitting the incident light beam, and fixing the middle liquid - crystal layer 12. The materials of the upper transparent substrate 9 and the lower transparent substrate 15 are transparent materials such as glass, quartz, and sapphire. Anti - reflection films are coated on the front and back surfaces of the upper transparent substrate 9 and the lower transparent substrate 15.

[0073] The upper transparent electrode 10 and the strip - shaped electrode unit 14 form the driving electrodes of the liquid - crystal layer 12, and a voltage is applied to drive the liquid - crystal layer 12. The materials of the upper transparent electrode 10 and the strip - shaped electrode unit 14 are indium tin oxide materials.

[0074] The number of strip - shaped electrode units 14 is N, the width b is slightly less than a, and the length is N×a. The material is indium tin oxide, which is formed on the lower transparent substrate 7 through photolithography and etching.

[0075] The upper alignment film 11 and the lower alignment film 13 align the nematic liquid - crystal molecules in the liquid - crystal layer 12. The materials are polyimide polymer films, which are formed on the transparent cover plate through printing.

[0076] The liquid - crystal material of the liquid - crystal layer 12 is nematic liquid crystal, and there are nematic liquid - crystal molecules 17 inside the liquid - crystal layer 12;

[0077] When there is no driving voltage 16 between the upper transparent electrode 10 and the strip - shaped electrode unit 14 of the liquid - crystal phase - modulation unit, the long axis of the nematic liquid - crystal molecule 17 points in the horizontal direction.

[0078] When a driving voltage 16 is applied between the upper transparent electrode 10 and the strip - shaped electrode unit 14 of the liquid - crystal phase - modulation unit, the long axis of the nematic liquid - crystal molecule 17 generates an inclination angle relative to the horizontal direction.

[0079] Figure 4 It shows a schematic diagram of the voltage - loading drive of the row - direction liquid - crystal phase - modulation array in the spatial light - modulating spectrometer provided by the embodiment of the present invention.

[0080] Figure 5 It shows a schematic diagram of the voltage - loading drive of the column - direction liquid - crystal phase - modulation array in the spatial light - modulating spectrometer provided by the embodiment of the present invention.

[0081] As shown in Figure 4 and Figure 5 shown, the refractive index differences between adjacent row units caused by the voltage distribution V applied to the row - direction liquid - crystal phase - modulation array 4 are equal;

[0082] The refractive index differences between adjacent column units caused by the voltage distribution V applied to the column - direction liquid - crystal phase - modulation array 5 are also equal.

[0083] The liquid - crystal layer thickness of the row - direction liquid - crystal phase - modulation array 4 is Lx, and the liquid - crystal layer thickness of the column - direction liquid - crystal phase - modulation array 5 is Ly.

[0084] When the same voltage distribution V is applied to the row - direction liquid - crystal phase - modulation array 4 and the column - direction liquid - crystal phase - modulation array 5, the liquid - crystal layer thickness of the column - direction liquid - crystal phase - modulation array 5 is N times that of the row - direction liquid - crystal phase - modulation array 4, that is, L y y x = NL

[0085] The refractive index differences corresponding to the voltages applied to adjacent strip - shaped units of the row - direction liquid - crystal phase - modulation array 4 and the column - direction liquid - crystal phase - modulation array 5 satisfy

[0086] When the row - direction liquid - crystal phase - modulation array 4 and the column - direction liquid - crystal phase - modulation array 5 have the same liquid - crystal layer thickness L, the refractive index difference caused by the voltage V applied to adjacent strip - shaped units of the column - direction liquid - crystal phase - modulation array 5 y is N times the refractive index difference caused by the voltage V applied to adjacent strip - shaped units of the row - direction liquid - crystal phase - modulation array 4, that is, Δn x (V y y y ) = NΔn x (V x x

[0087] The refractive index differences corresponding to the voltages applied to adjacent strip - shaped units of the row - direction liquid - crystal phase - modulation array 4 and the column - direction liquid - crystal phase - modulation array 5 respectively satisfy Δn y (V y ) = NΔn x (V x )

[0088] When different driving voltages are applied, the long - axis orientation angles of liquid - crystal molecules in the liquid - crystal layer of the strip - shaped liquid - crystal phase - modulation unit will be different, and different long - axis orientation angles of liquid - crystal molecules result in different refractive indices. Thus, when light travels through different strip - shaped liquid - crystal phase - modulation units of the liquid - crystal phase - modulation array, it travels different optical paths.

[0089] For the row - direction liquid - crystal phase - modulation array, when a driving voltage V(i) is applied to the strip - shaped electrode of its i - th strip - shaped liquid - crystal phase - modulation unit, the long - axis pointing inclination angle of the liquid - crystal molecules in the i - th strip - shaped liquid - crystal phase - modulation unit of the row - direction liquid - crystal phase - modulation array is θ(i). Therefore, the extraordinary - light refractive index corresponding to the i - th row - direction strip - shaped liquid - crystal phase - modulation unit in the row - direction liquid - crystal phase - modulation array is The equivalent refractive index is where n o and n e are the refractive indices of the ordinary light and the extraordinary light in the nematic liquid crystal without voltage, respectively. Thus, the optical path that light travels through in the i - th strip - shaped liquid - crystal phase - modulation unit of the row - direction liquid - crystal phase - modulation array is OP x (i)=n(i)L x .

[0090] Similarly, for the column - direction liquid - crystal phase - modulation array, when a driving voltage V(j) is applied to the strip - shaped electrode of its j - th strip - shaped liquid - crystal phase - modulation unit, the long - axis pointing inclination angle of the liquid - crystal molecules in the j - th strip - shaped liquid - crystal phase - modulation unit of the column - direction liquid - crystal phase - modulation array is θ(j). Therefore, the extraordinary - light refractive index corresponding to the j - th column - direction strip - shaped liquid - crystal phase - modulation unit in the column - direction liquid - crystal phase - modulation array is The equivalent refractive index is Thus, the optical path that light travels through in the j - th strip - shaped liquid - crystal phase - modulation unit of the column - direction liquid - crystal phase - modulation array is OP y (j)=n(j)L y .

[0091] The electrode directions of the row - direction liquid - crystal phase - modulation array 4 and the column - direction liquid - crystal phase - modulation array 5 are orthogonal in the transverse space, thus dividing the light field into M×M light - field array units in the transverse space. Each light - field unit corresponds to a specific row - direction strip - shaped electrode unit of the row - direction liquid - crystal phase - modulation array and a specific column - direction strip - shaped electrode unit of the column - direction liquid - crystal phase - modulation array. The size of each light - field unit is a×a.

[0092] After the linearly polarized light beam exits from the row - direction liquid - crystal phase - modulation array 4 and the column - direction liquid - crystal phase - modulation array 5, it is incident on the digital micromirror array 6.

[0093] The digital micromirror array 6 is composed of M×M digital micromirror units. Each digital micromirror unit corresponds to a specific light - field unit formed by the row - direction strip - shaped electrode unit of the row - direction liquid - crystal phase - modulation array 5 and the column - direction strip - shaped electrode unit of the column - direction liquid - crystal phase - modulation array 4. The digital micromirror array can be placed perpendicular to the incident optical axis or tilted at a certain angle. Each digital micromirror unit of the digital micromirror array can rotate at a certain angle along its rotation axis, thereby realizing the gating interference of the spatial light - field units.

[0094] Turn on the digital micromirror unit corresponding to the optical field unit formed by the row - oriented strip - shaped electrode unit of the row - oriented liquid - crystal phase modulation array 4 with \(i = 0\) (\(i=[0,1,\cdots,M]\)) and the column - oriented strip - shaped electrode unit of the column - oriented liquid - crystal phase modulation array 5 with \(j = 0\) (\(j=[0,1,\cdots,M]\)), that is, turn on the digital micromirror unit \((i,j)=(0,0)\), and keep the remaining digital micromirror units off at the same time.

[0095] Then, turn on the remaining digital micromirror units row - by - row and column - by - column in sequence. At each moment, only keep two digital micromirror units \((0,0)\) and \((i,j)\) (\((i,j)\neq(0,0)\)) on.

[0096] Therefore, at the same moment, only two beams of light from different optical field units are incident into the detector system and interfere inside.

[0097] The detector system includes: a focusing mirror 7 and a single - point detector 8.

[0098] The two beams of light are converged by the focusing mirror 7 and then incident into the single - point detector 8, where they interfere to obtain an interference pattern signal. The single - point detector 8 is used to convert the interference light signal into an electrical signal.

[0099] When the light beam passing through the \((i,j)\) - th optical field unit interferes with the light beam passing through the \((0,0)\) - th optical field unit, the optical path difference of the two coherent light beams is:

[0100] \(\delta(i,j)=[n(i)-n(0)]L\) x +[n(j)-n(0)]L y

[0101] Therefore, the intensity \(I\) of the \((i,j)\) - th interference pattern signal is:

[0102]

[0103] In the formula, \(\nu\) is the wave number of the interference light signal. For light with a wavelength of \(\lambda\), \(\nu = 1 / \lambda\).

[0104] By performing discrete Fourier transform demodulation on the interference pattern sequence, the spectral information of the incident light can be restored.

[0105] To achieve equally - spaced sampling, there is the same refractive index difference \(\Delta n\) between adjacent strip - shaped liquid - crystal phase modulation units in the row - oriented liquid - crystal phase modulation array 4 x , and there is also the same refractive index difference \(\Delta n\) between adjacent strip - shaped liquid - crystal phase modulation units in the column - oriented liquid - crystal phase modulation array 5 y .

[0106] To form a continuous sequence of optical path differences, the two liquid crystal phase modulation arrays must satisfy optical path compensation, which can be achieved in two ways.

[0107] One way is to achieve optical path complementarity by matching the liquid crystal layer thicknesses of the two liquid crystal phase modulation arrays, such that the liquid crystal layer thickness of one liquid crystal phase modulation array is N times that of the other liquid crystal phase modulation array, i.e., L y = NL x At this time, the adjacent strip liquid crystal phase modulation units of the two liquid crystal phase modulation arrays have the same refractive index difference Δn x = Δn y = Δn;

[0108] Another way is to keep the two liquid crystal phase modulation arrays having the same liquid crystal layer thickness L x = L y = L, and achieve optical path complementarity by matching the refractive index differences of the adjacent strip liquid crystal phase modulation units of the two liquid crystal phase modulation arrays, such that the refractive index difference of the adjacent strip liquid crystal phase modulation units of one liquid crystal phase modulation array is N times that of the adjacent strip liquid crystal phase modulation units of the other liquid crystal phase modulation array, i.e., Δn y = NΔn x .

[0109] When the first optical path complementarity method is adopted, the adjacent strip liquid crystal phase modulation units of the two liquid crystal phase modulation arrays have the same refractive index difference Δn x = Δn y = Δn, and the relationship between the liquid crystal layer thicknesses of the two liquid crystal phase modulation arrays is L y = NL x , and at this time the optical path difference sampling array is:

[0110] δ(i,j) = iΔnL x + jΔnL y = ΔnL x (jN + i)

[0111] In order not to produce spectral aliasing during the spectral restoration process, the optical path difference sampling interval must be less than or equal to twice the minimum wavelength of the optical signal, i.e.:

[0112]

[0113] Therefore, the refractive index differences of the adjacent strip liquid crystal phase modulation units of the two liquid crystal phase modulation arrays must satisfy the following formula:

[0114]

[0115] At this time, the form of the restored spectrum is:

[0116]

[0117] According to the discrete Fourier transform theory, the spectral resolution is the reciprocal of the maximum optical path difference, i.e., Therefore, the liquid crystal layer thicknesses of the two liquid crystal phase modulation arrays satisfy the following relationship:

[0118]

[0119] Meanwhile, the number of sampling points needs to satisfy the relationship where n max and n min are the maximum refractive index value and the minimum refractive index value that the liquid crystal material can reach, respectively.

[0120] When the second optical path complementary method is adopted, the two liquid crystal phase modulation arrays have the same liquid crystal layer thickness L x = L y = L, and the relationship between the refractive index differences of adjacent strip liquid crystal phase modulation units of the two liquid crystal phase modulation arrays is Δn y = NΔn x , and at this time, the optical path difference sampling array is:

[0121] δ(i, j) = iΔn x L + jΔn y L = Δn x L(jN + i)

[0122] In order not to generate spectral aliasing during the spectral restoration process, the optical path difference sampling interval must be less than or equal to twice the minimum wavelength of the optical signal, i.e.:

[0123]

[0124] Therefore, the refractive index differences of adjacent strip liquid crystal phase modulation units of the two liquid crystal phase modulation arrays must satisfy the following relationship:

[0125]

[0126] At this time, the form of the restored spectrum is:

[0127]

[0128] According to the discrete Fourier transform theory, the spectral resolution is the reciprocal of the maximum optical path difference, i.e., Therefore, the liquid crystal layer thicknesses of the two liquid crystal phase modulation arrays satisfy the following relationship:

[0129]

[0130] Meanwhile, the number of sampling points needs to satisfy the relationship where nmax and n min are respectively the maximum refractive index value and the minimum refractive index value that the liquid crystal material can reach.

[0131] Figure 6 Fig. shows a schematic flow chart of a spatial light modulation spectrometer according to an embodiment of the present invention.

[0132] Figure 7 Fig. shows a program block diagram of a measurement method of a spatial light modulation spectrometer according to an embodiment of the present invention.

[0133] As Figure 6 and Figure 7 shown, the measurement method of the spatial light modulation spectrometer provided by the embodiment of the present invention includes the following steps:

[0134] S1. Adjust the linearly polarized light beam emitted from the light source system so that the polarization direction of the linearly polarized light beam is parallel to the light incident plane.

[0135] Step S1 includes the following steps:

[0136] Fix the collimating mirror on the platform base;

[0137] S11. Use the laser beam emitted by the laser light source as the incident beam, and make the emission point of the laser light source located at the front focal point of the collimating mirror.

[0138] The wavelength of the divergent laser beam emitted by the laser light source is within the working spectral band of the system. First, a laser is used for the convenience of alignment because the laser has high brightness and is convenient for alignment and testing. In practical applications, a broadband light source is used for spectral analysis.

[0139] S12. After the incident beam is collimated by the collimating mirror, it is collimated into a parallel beam and incident into the polarizer.

[0140] Place the polarizer in the collimated parallel optical path and perform central alignment;

[0141] S13. Adjust the polarization direction of the polarizing plate in the polarizer until the polarization direction of the emitted linearly polarized light beam is parallel to the light incident plane.

[0142] Detect the polarization direction of the emitted laser beam through the analyzer. If the polarization direction of the emitted laser beam is not parallel to the light incident plane, continue to adjust the polarization direction of the polarizing plate in the polarizer.

[0143] S2. The linearly polarized light beam successively undergoes distributed phase modulation by the row - direction liquid crystal phase modulation array and the column - direction liquid crystal phase modulation array to obtain a light field array composed of M×M light field units, and is incident into the digital micromirror array.

[0144] Step S2 includes the following steps:

[0145] Place the row - oriented liquid - crystal phase - modulation array in the transmission optical path of the polarizer and perform central alignment;

[0146] Place the column - oriented liquid - crystal phase - modulation array in the transmission optical path of the row - oriented liquid - crystal phase - modulation array and perform central alignment;

[0147] Adjust the relative position between the row - oriented liquid - crystal phase - modulation array and the column - oriented liquid - crystal phase - modulation array to ensure that the electrode directions of the row - oriented and column - oriented liquid - crystal phase - modulation arrays are perpendicular to each other;

[0148] S21. Adjust the driving voltages of the strip - shaped liquid - crystal phase - modulation units in the row - oriented liquid - crystal phase - modulation array and the column - oriented liquid - crystal phase - modulation array respectively, so that there is an equal refractive - index difference between adjacent strip - shaped liquid - crystal phase - modulation units.

[0149] S22. After the linearly polarized light beam undergoes distributed phase modulation by the row - oriented liquid - crystal phase - modulation array, M rows of transverse light fields are obtained.

[0150] S23. After the M rows of transverse light fields undergo distributed phase modulation by the column - oriented liquid - crystal phase - modulation array, an optical - field array composed of M×M optical - field units is obtained.

[0151] The order of step S22 and step S23 can be interchanged.

[0152] S3. By controlling the M×M digital - micromirror units in the digital - micromirror array, the gating of different optical - field units is achieved.

[0153] Place the digital - micromirror array in the transmission optical path of the column - oriented liquid - crystal phase - modulation array and perform central alignment; adjust the angle of the digital - micromirror array so that the digital - micromirror units correspond one - to - one with the liquid - crystal phase - modulation array units;

[0154] S4. At least two optical - field units with a preset optical path difference selected by the digital - micromirror array enter the detector system, interfere with each other to obtain an interference - pattern signal, and then obtain spectral information.

[0155] Although the embodiments of the present invention have been shown and described above, it can be understood that the above - mentioned embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above - mentioned embodiments within the scope of the present invention.

[0156] The above - mentioned specific embodiments of the present invention do not constitute a limitation to the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A spatial light modulation spectrometer, characterized in that, it includes: a light source system, a liquid crystal phase modulation array, a digital micromirror array, and a detector system; The light source system is used to emit a linearly polarized light beam, and after distributed phase modulation by the liquid crystal phase modulation array, an optical field array composed of M×M optical field units is obtained; the digital micromirror array is used to gate the optical field array, so that at least two light beams corresponding to at least two optical field units are incident into the detector system to interfere, obtaining an interference pattern signal and acquiring the spectral information of the linearly polarized light beam; When the same voltage distribution V is applied to the row-direction liquid crystal phase modulation array and the column-direction liquid crystal phase modulation array, the liquid crystal layer thickness L of the column-direction liquid crystal phase modulation array y is N times the liquid crystal layer thickness L of the row-direction liquid crystal phase modulation array, that is x ; ; The refractive index difference corresponding to the voltages applied to adjacent strip units of the row-direction liquid crystal phase modulation array and the column-direction liquid crystal phase modulation array satisfies ; When the row - direction liquid - crystal phase - modulation array and the column - direction liquid - crystal phase - modulation array have the same liquid - crystal layer thickness L, the voltage applied to adjacent strip - shaped units of the column - direction liquid - crystal phase - modulation array V y causes a refractive index difference which is N times the refractive index difference caused by the voltage applied to adjacent strip - shaped units of the row - direction liquid - crystal phase - modulation array V x That is ; ​ The refractive index differences corresponding to the voltages applied to adjacent strip units of the row-direction liquid crystal phase modulation array and the column-direction liquid crystal phase modulation array respectively satisfy , ; where λ min is the minimum wavelength in the linearly polarized light beam.

2. The spatial light modulation spectrometer according to claim 1, characterized in that, the light source system includes: a light source, a collimating mirror, and a polarizer; The light source is used to emit a divergent light beam with a spectral radiation range, and the divergent light beam is collimated by the collimating mirror to form a parallel light beam incident on the polarizer; the polarizer is used to output the parallel light beam as a linearly polarized light beam.

3. The spatial light modulation spectrometer according to claim 2, characterized in that, the liquid crystal phase modulation array includes: a row liquid crystal phase modulation array and a column liquid crystal phase modulation array; The row liquid crystal phase modulation array is used to perform distributed phase modulation on the optical field of the linearly polarized light beam in the horizontal direction to obtain M rows of transverse optical fields; The column liquid crystal phase modulation array is used to perform distributed phase modulation on the transverse optical field again in the vertical direction to obtain an optical field array composed of M×M optical field units.

4. The spatial light modulation spectrometer according to claim 3, characterized in that, the row liquid crystal phase modulation array includes M rows of liquid crystal phase modulation units; the column liquid crystal phase modulation array includes M columns of liquid crystal phase modulation units; By adjusting the driving voltages on the liquid crystal phase modulation units in the row liquid crystal phase modulation array and the column liquid crystal phase modulation array, the distributed phase modulation of the linearly polarized light beam is realized.

5. The spatial light modulation spectrometer according to claim 4, characterized in that, the row liquid crystal phase modulation array or the column liquid crystal phase modulation array from top to bottom sequentially includes: an upper transparent substrate, an upper transparent electrode, an upper alignment film, a liquid crystal layer, a lower alignment film, a strip electrode unit, and a lower transparent substrate; The upper transparent substrate and the lower transparent substrate serve as the optical windows of the liquid crystal phase modulation array, jointly forming a liquid crystal cell for fixing the liquid crystal layer; The upper transparent electrode and the strip electrode unit form the driving electrodes of the liquid crystal layer, and drive the liquid crystal layer after applying a voltage; The upper alignment film and the lower alignment film are used to make the nematic liquid crystal molecules in the liquid crystal layer be aligned.

6. The spatial light modulation spectrometer according to claim 5, characterized in that, the detector system includes: a focusing mirror and a single-point detector; The light beams of different optical field units are incident into the single-point detector after being converged by the focusing mirror to interfere, and the single-point detector is used to convert the interference light signal into an electrical signal.

7. The spatial light modulation spectrometer according to claim 1, characterized in that, The digital micromirror array includes M×M digital micromirror units; at the same moment, two digital micromirror units at (0, 0) and (i, j) are kept in the on state; i = 0, 1, 2…M; j = 0, 1, 2…M; At the same moment, two beams of light from different light field units are incident on the detector system and interfere. When the beam passing through the (i, j)th light field unit interferes with the beam passing through the (0, 0)th light field unit, the optical path difference between the two coherent light beams is: By performing discrete Fourier transform demodulation on the interference pattern signal, the spectral information of the linearly polarized light beam is obtained.

8. A measurement method of a spatial light modulation spectrometer according to any one of claims 1-7, characterized in that, it includes the following steps: S1. Adjust the linearly polarized light beam emitted from the light source system so that the polarization direction of the linearly polarized light beam is parallel to the light incident surface; S2. The linearly polarized light beam passes through the distributed phase modulation of the row-direction liquid crystal phase modulation array and the column-direction liquid crystal phase modulation array in sequence to obtain a light field array composed of M×M light field units, and is incident on the digital micromirror array; S3. By controlling the M×M digital micromirror units in the digital micromirror array, the gating of different light field units in the light field array is realized; S4. At least two light field units with a preset optical path difference selected by the digital micromirror array enter the detector system to interfere and obtain an interference pattern signal, and then the spectral information of the linearly polarized light beam is obtained.

9. The measurement method of a spatial light modulation spectrometer according to claim 8, characterized in that, the step S1 includes the following steps: S11. Take the scattered light beam emitted by the light source as the incident light beam, and make the emission point of the light source located at the front focal point of the collimator; S12. After the incident light beam is collimated by the collimator, it becomes a parallel light beam and is incident on the polarizer; S13. Adjust the polarization direction of the polarizing plate in the polarizer until the polarization direction of the emitted linearly polarized light beam is parallel to the light incident surface.

10. The measurement method of a spatial light modulation spectrometer according to claim 9, characterized in that, the step S2 includes the following steps: S21. Adjust the driving voltages of the strip-shaped liquid crystal phase modulation units in the row-direction liquid crystal phase modulation array and the column-direction liquid crystal phase modulation array respectively, so that the refractive index differences between adjacent strip-shaped liquid crystal phase modulation units are equal; S22. After the linearly polarized light beam passes through the distributed phase modulation of the row-direction liquid crystal phase modulation array, M rows of transverse light fields are obtained; S23. After the M rows of transverse light fields pass through the distributed phase modulation of the column-direction liquid crystal phase modulation array, a light field array composed of M×M light field units is obtained.

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