Wide spectrum response detection reconstruction spectrum imaging system

Abstract

The utility model discloses a wide spectrum response detection reconstruction spectrum imaging system comprising a bias voltage coding wide spectrum detection device which comprises a liquid crystal phase modulator, a polarizer, a beam splitter prism, an analyzer and a detector. The liquid crystal phase modulator adopts an electric control birefringence orientation mode, and the orientation direction of liquid crystal molecules is parallel to the X axis; a polarizer is arranged in front of the liquid crystal phase modulator, and the included angle between the polarization direction of the polarizer and the X axis is 45 degrees; a beam splitter prism is arranged between the liquid crystal phase modulator and the polarizer; the polarization analyzer is arranged behind the liquid crystal phase modulator, and the included angle between the polarization direction of the polarization analyzer and the X axis is-45 degrees; and a detector is arranged behind the polarization analyzer and is used for receiving an image signal passing through the liquid crystal phase modulator and the polarization analyzer. According to the utility model, the number of spectrum coding channels which can be modulated is large, and spectrum response curves of different channels have strong irrelevance, so that the incident spectrum can be accurately reconstructed.

Description

Technical Field

[0001] The utility model relates to the field of photoelectric imaging, in particular to spectral imaging technology. Background Art

[0002] Photoelectric imaging refers to converting the spatial light intensity distribution of the imaging plane into the corresponding electrical signal distribution. With the development of information technology, photoelectric imaging has penetrated into people's daily life, industrial production, medical diagnosis and other fields. In the conventional photoelectric imaging process, the detector obtains a two-dimensional array, and each data point represents the light intensity distribution of each spatial point in the imaging plane.

[0003] In addition to obtaining the light intensity information of each spatial point in the imaging plane, spectral imaging also obtains the wavelength information of each spatial point. Therefore, the spectral imaging detector obtains a three-dimensional data set, such as Figure 1 As shown, it includes spectral channel 1 and spectral distribution 2 of a certain spatial point. Since different substances have their own specific spectral distribution, spectral imaging can not only reflect the geometric morphology of the imaged object, but also obtain its material distribution characteristics. Spectral imaging has important applications in remote sensing measurement, material analysis, space science, and national security.

[0004] In order to obtain a three-dimensional spectral data cube, people have proposed spectral channel separation detection methods and spectral reconstruction detection methods. In the spectral channel separation detection method, people use dispersive optical elements such as gratings to separate the incident polychromatic light into independent spectral channels, and then use conventional CCD or CMOS detectors to obtain the information of each spectral channel, such as Figure 2a As shown, it includes incident polychromatic light 3, grating 4, outgoing light 5 formed after spectral channels are separated, and conventional photodetector 6. Figure 2bSeveral commonly used spectral image acquisition methods are given: a one-dimensional line array detector 7 can be used to obtain one-dimensional spectral line array 9 data through a prism spectrometer 8. In order to obtain a three-dimensional spectral data cube, the one-dimensional line array detector 7 needs to perform two-dimensional sweeping according to the sweeping path 10 of the detector; a two-dimensional array detector 11 can also be used to read the one-dimensional line array information of the imaging object through the prism spectrometer 8 to form two-dimensional spectral plane data 12 of the line array. In order to obtain a three-dimensional spectral data cube, the two-dimensional array detector 11 needs to perform one-dimensional push sweeping according to the push sweeping path 13 of the detector; the prism spectrometer 8 can also be replaced with a color wheel 14 with a color filter, and the signal of a specific spectral channel of the imaging object is output at a certain moment through the rotation of the color wheel, which also constitutes a two-dimensional plane spectral data. The color wheel rotates in a time series, outputs signals of different spectral channels, and finally forms a complete three-dimensional spectral data cube. Whether it is two-dimensional sweeping, one-dimensional push sweeping or color wheel rotation, they are all mechanical movements. Because the detector needs to move mechanically along a certain path, this type of spectral shaping system is large in size, heavy, low in integration, and low in working stability. In response to the above series of problems, a snapshot spectral imaging method that does not require mechanical scanning or rotation has been proposed. It uses a first group of photoelectric elements 15 and a second group of photoelectric elements 16 to obtain a three-dimensional spectral data cube 18 on an ultra-large-size high-resolution detector 17. However, in this solution, the pixel data of the ultra-large-size high-resolution detector 17 is required to be 2 orders of magnitude higher than that of a conventional photoelectric detector, and its resolution requirement is also much higher than that of a conventional detector.

[0005] In addition to obtaining spectral images by separating spectral channels, reconstructing the incident spectrum through wavelength division multiplexing algorithm is another method to obtain spectral images. In this method, people use wide-spectrum filters to filter the incident light to obtain a wide-spectrum image of the imaging object, such as Figure 3a The spectral response curve 19 obtained by the detector after the first filter, the spectral response curve 20 obtained by the detector after the second filter, and the spectral response curve 21 obtained by the detector after the third filter. This method requires that each wide-spectrum filter has randomness, so the spectral curves they generate have strong linear non-correlation. Under this premise, the incident spectrum can be reconstructed more accurately through the wavelength division multiplexing algorithm to obtain the spectral curve 22 obtained by spectral reconstruction, such as Figure 3b. Compared with the spectral channel separation method, the spectral reconstruction method has some obvious advantages: first, it does not require the detector to be mechanically scanned or rotated, so the spectral imaging system can be very compact; second, each time the detector obtains a wide-spectrum image, compared with the narrow-spectrum image separated by spectral channels, the wide-spectrum image has a larger light flux and the detector produces a higher responsivity. In the process of spectral reconstruction imaging, setting randomly distributed wide-spectrum filters is the key, and the number of these wide-spectrum filters must be much larger than the number of spectral channels for imaging, only in this way can the reconstructed spectrum be guaranteed to have sufficient accuracy. People have proposed a variety of filtering methods such as dye filters, quantum dot filters, Fabry-Perot optical microcavities, photonic crystals, and metasurfaces, but in these structures, the wide-spectrum filters are arranged according to spatial distribution and encode the incident spectrum, so its spectral resolution and spatial resolution are mutually restricted, that is, in order to obtain higher spectral resolution (identify more spectral channels), the spatial resolution of the image will be reduced.

[0006] In summary, although spectral imaging has important applications in many fields, the existing spectral channel separation imaging method requires mechanical scanning of dispersive optical elements, and the imaging system is large in size, heavy in weight, and has low integration. Although the spectral imaging method of spectral reconstruction does not require mechanical scanning, the spectral resolution and spatial resolution of the image restrict each other, which seriously affects the quality of the spectral image. Utility Model Content

[0007] The purpose of the utility model is to address the problems existing in the existing spectral imaging methods and propose a wide-spectrum response detection and reconstruction spectral imaging system. The core technology is to adjust the refractive index of the liquid crystal by bias voltage, thereby changing its optical path for incident light of different wavelengths to obtain a wide-spectrum filtered spectral output. The utility model can modulate a large number of spectral coding channels, and the spectral response curves of different channels have strong non-correlation, which is conducive to accurately reconstructing the incident spectrum; the incident spectrum is encoded in time series by using electrically controlled liquid crystal phase modulation, so it solves the contradiction between spectral resolution and spatial resolution.

[0008] The technical solution adopted by the utility model is: a wide-spectrum response detection and reconstruction spectrum imaging system, including a bias voltage encoding wide-spectrum detection device, which includes a liquid crystal phase modulator, a polarizing plate, a beam splitter, an analyzer and a detector;

[0009] The liquid crystal phase modulator adopts an electrically controlled birefringence orientation mode, and the orientation direction of the liquid crystal molecules is parallel to the X-axis;

[0010] A polarizer is arranged in front of the liquid crystal phase modulator, and its polarization direction is at an angle of 45° with the X-axis;

[0011] A beam splitter prism is provided between the liquid crystal phase modulator and the polarizing plate;

[0012] A polarizer is arranged behind the liquid crystal phase modulator, and the angle between its polarization direction and the X-axis is -45°;

[0013] A detector is arranged behind the polarizer to receive the image signal passing through the liquid crystal phase modulator and the polarizer.

[0014] In the bias voltage coded wide spectrum detection device, the multi-color incident light comes from the reflection of the illumination light source or the imaging object, and forms linear polarized light after passing through the polarizer, and the polarization direction is 45° with the horizontal positive angle; the multi-color incident light is irradiated to the liquid crystal phase modulator through the beam splitter prism, and the initial orientation direction of the liquid crystal molecules is the horizontal direction, resulting in phase delay; after the phase delay is generated, the input light forms output light after passing through the analyzer, and the polarization direction of the output light is -45° with the horizontal axis; a detector is arranged behind the analyzer to record the intensity change of the output light under different bias voltage changes.

[0015] The bias voltage coded wide spectrum detection imaging system adopts a liquid crystal phase modulator. Different wavelengths of incident light produce different phase delays after passing through the liquid crystal layer. After applying the bias voltage, the change in the refractive index of the liquid crystal modulates the phase delay of the incident light, but the modulation amount for incident light of different wavelengths is different, so the phase delay of the transmitted light (reflected light) changes nonlinearly.

[0016] The bias voltage coded wide spectrum detection imaging system adopts a modulation structure of polarizer / liquid crystal phase modulator / analyzer / photodetector to control the polarization angle and liquid crystal orientation angle (typical angles are polarizer 45° / liquid crystal layer 0° / analyzer-45°) to convert the phase change of incident light into intensity change through the liquid crystal phase modulator.

[0017] Furthermore, the liquid crystal phase modulator includes, from bottom to top, a substrate, a bottom electrode, an alignment layer, a liquid crystal layer and a top electrode.

[0018] The bias voltage coded wide spectrum detection device of the utility model performs phase modulation on incident light of different wavelengths, and constructs a voltage-regulated random spectrum filter for spectral imaging; the bias voltage coded wide spectrum detection device uses bias voltage to regulate the refractive index of liquid crystal, thereby generating different phase delays for incident light of different wavelengths.

[0019] Beneficial effects of the utility model:

[0020] (1) The utility model proposes to use liquid crystal electrically controlled phase modulation to enable the detector to obtain wide-spectrum response curves under different bias voltages, and then reconstruct the incident spectrum through a wavelength division multiplexing algorithm based on these wide-spectrum responses. No mechanical scanning is required, and the spectral imaging system has a high degree of integration.

[0021] (2) The utility model utilizes liquid crystal phase modulation to obtain a series of wide-spectrum response curves with strong non-correlation, thereby improving the calculation accuracy of spectrum reconstruction. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the three-dimensional data cube obtained by spectral imaging;

[0023] Figure 2a The spectral channel separation detection method adopts grating to separate the spectral channels;

[0024] Figure 2b Several methods for obtaining spectral images for spectral channel separation detection method;

[0025] Figure 3a Spectral response curve of incident light after passing through random broadband filter for wavelength division multiplexing reconstructed spectrum;

[0026] Figure 3b A spectrum curve obtained after the spectrum reconstruction of the wavelength division multiplexing reconstructed spectrum;

[0027] Figure 4a Liquid crystal molecular orientation before and after voltage application for liquid crystal phase modulation in electrically controlled birefringence mode;

[0028] Figure 4b The phase change of the transmitted light before and after the applied voltage in the liquid crystal phase modulation in the electrically controlled birefringence mode;

[0029] Figure 5 To convert the phase change of incident light into intensity change;

[0030] Figure 6 is the angle between the polarizer and the liquid crystal phase modulator;

[0031] Figure 7a Based on liquid crystal phase modulation, the modulation curve of liquid crystal to incident light with a wavelength of 1550nm under different bias voltages for spectral detection is obtained;

[0032] Figure 7b The change of the spectral response curve of changing the bias voltage is obtained based on the phase modulation of liquid crystal to obtain spectral detection;

[0033] In the figure: 1. Spectral channel; 2. Spectral distribution at a certain spatial point; 3. Incident polychromatic light; 4. Grating; 5. Outgoing light formed after the spectral channel is separated; 6. Conventional photodetector; 7. One-dimensional line array detector; 8. Prism spectroscopic element; 9. One-dimensional spectral line array; 10. Detector sweep path; 11. Two-dimensional array detector; 12. Two-dimensional spectral plane data; 13. Detector push sweep path; 14. Color wheel with color filter; 15. First group of spectral elements; 16. Second group of spectral elements; 17. Ultra-large size high-resolution detector; 18. Three-dimensional spectral data cube; 19. Through the first filter Spectral response curve obtained by the detector after the optical plate; 20. Spectral response curve obtained by the detector after the second filter; 21. Spectral response curve obtained by the detector after the third filter; 22. Spectral curve obtained by spectral reconstruction; 23. Liquid crystal molecule orientation when no electric field is applied; 24. Liquid crystal molecule orientation after electric field is applied; 25. Substrate; 26. Bottom electrode; 27. Orientation layer; 28 Liquid crystal layer; 29. ​​Top electrode; 30. Incident light; 31. Outgoing light; 32. Multicolor incident light; 33. Polarizer; 34. Spectral prism; 35. Liquid crystal phase modulator; 36. Analyzer; 37. Detector; 38. θ 1 =θ 2 =θ 3 = 0 when the output light intensity changes; 39.θ 1 =45°,θ 2 =-45°,θ 3 =0° when the output light intensity changes. DETAILED DESCRIPTION

[0034] The utility model is described in detail below. This embodiment is implemented on the premise of the technical solution of the utility model, and a detailed implementation method and a specific operation process are given, but the protection scope of the utility model is not limited to the following embodiments.

[0035] like Figure 4a , 4b , 5, 6, 7a and 7b, a wide spectrum response detection and reconstruction spectrum imaging system, including a bias voltage encoding wide spectrum detection device, the device includes a liquid crystal phase modulator 35, a polarizer 33, a beam splitter prism 34, an analyzer 36 and a detector 37;

[0036] The liquid crystal phase modulator 35 adopts an electrically controlled birefringence orientation mode, and the orientation direction of the liquid crystal molecules is parallel to the X axis;

[0037] A polarizer 33 is arranged in front of the liquid crystal phase modulator 35, and its polarization direction is at an angle of 45° with the X-axis;

[0038] A beam splitter prism 34 is provided between the liquid crystal phase modulator 35 and the polarizing plate 33;

[0039] A polarizer 36 is disposed behind the liquid crystal phase modulator 35, and its polarization direction has an angle of -45° with the X-axis;

[0040] A detector 37 is disposed behind the analyzer 46 to receive image signals passing through the liquid crystal phase modulator 35 and the analyzer 36 .

[0041] Liquid crystal is a soft material with a birefringence effect. Under the action of an external electric field, the liquid crystal molecules produce a certain spatial rotation, thereby changing the refractive index of the liquid crystal layer. Liquid crystal photonic devices have different operating modes, among which the electrically controlled birefringence mode is used to modulate the phase of the incident light. Figure 4a and 4b The phase modulation of the liquid crystal molecules on the transmitted light in this working mode is given. The liquid crystal phase modulator includes a substrate 25, a bottom electrode 26, an orientation layer 27, a liquid crystal layer 28 and a top electrode 29 from bottom to top. When no voltage is applied, the liquid crystal molecules are oriented to 23, and after the voltage is applied, the liquid crystal molecules are oriented to 24. After the voltage is applied, the phase delay of the outgoing light 31 increases by △φ compared with the incident light 30.

[0042] Assume that the refractive index of the liquid crystal molecule is n when no voltage is applied, and the refractive index changes by △n after the bias voltage is applied, and the thickness of the liquid crystal layer is d; the phase delay of the incident light with a wavelength of λ after passing through the liquid crystal layer is

[0043] δ(λ)=d·(n+Δn) / λ·2π (1)

[0044] The bias voltage coded wide spectrum detection device converts the liquid crystal phase modulation into the intensity modulation of the output light by designing a certain polarizer angle. It can be seen from formula (1) that the phase delay of the incident light passing through the liquid crystal layer is related to the wavelength of the incident light. The utility model uses the correlation between the phase delay and the wavelength to obtain a random wide spectrum response curve. Since the photodetector only responds to the intensity (power) of the incident light, and the incident light phase does not affect the photocurrent of the detector, the utility model proposes Figure 5 The structure converts phase changes of incident light into intensity changes.

[0045] exist Figure 5 In the structure shown in the figure, the phase change shown in formula (1) can be converted into intensity change by adjusting the angle between the polarizer 33, the liquid crystal phase modulator 35 and the analyzer 36. In order to more clearly describe this conversion process, the angle between the polarizer 33, the liquid crystal phase modulator 35 and the analyzer 36 is adjusted according to Figure 6 definition.

[0046] exist Figure 6 In the structure shown, θ 1 is the polarization angle of the polarizer 33, θ 2is the polarization angle of the analyzer 36, θ 3 is the orientation angle of the liquid crystal phase modulator 35; the modulation of the incident light by the polarizer, analyzer and liquid crystal phase modulator can be described by Mueller matrix, which are respectively expressed as M P1 、M P2 、M LC

[0047]

[0048] Where δ is the phase delay of the sample to be tested, and the Stokes parameter is used to represent the state of the light wave. Then the light wave modulated by the polarizer and the sample can be written as

[0049]

[0050] Where [IQUV] T with [I o Q o U o V o ] T are the Stokes parameters of the outgoing light and the incident light respectively; if the incident light is natural light with a wavelength of λ, its Stokes parameter can be expressed as I o [1 0 0 0] T Substituting into formula (3), we can get the incident light intensity as

[0051]

[0052] According to formula (4), take the deflection angle θ 1 =45°, analysis angle θ 2 =-45° It is known that the orientation angle of liquid crystal molecules is θ 3 = 0° can make the intensity I have the maximum modulation amount, which can be expressed as

[0053]

[0054] It can be seen from formulas (1) and (5) that different wavelengths of incident light can produce different spectral responses after passing through the liquid crystal phase modulation layer. Figure 7a and 7b This is a typical spectral response curve based on liquid crystal phase modulation obtained from actual testing. 38 in the figure is θ 1 =θ 2 =θ 3 = 0 when the output light intensity changes, 39 is θ 1 =45°,θ 2 =-45°,θ 3=0°. It can be seen from the figure that after applying different bias voltages to the liquid crystal phase modulator, the obtained spectral response curves have obvious differences, and the calculated Pearson correlation coefficient of the curve group is only 0.36, so these curves are highly uncorrelated.

[0055] The bias voltage coded wide spectrum detection device is as follows: Figure 5 As shown, the multi-color incident light 32 may come from the illumination source or the reflection of the imaging object. After passing through the polarizer 33, it forms linear polarized light, and the polarization direction is 45° with the horizontal positive angle. The multi-color incident light is irradiated to the liquid crystal phase modulator 35 through the beam splitter prism 34. The initial orientation direction of the liquid crystal molecules is horizontal, generating a phase delay φ o +△φ; after the phase delay is generated, the input light passes through the polarizer 36 to form the output light, and the polarization direction of the output light is at an angle of -45° with the horizontal axis; a detector 37 is arranged behind the polarizer 36 to record the intensity change of the output light under different bias voltage changes.

[0056] The detector 37 records the following Figure 7b The spectral response curves under different bias voltages are shown. These curves have strong nonlinear correlation.

[0057] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the claims attached to the utility model.

Claims

1. A wide spectrum response detection and reconstruction spectral imaging system, characterized in that: The invention comprises a bias voltage coded wide spectrum detection device, which comprises a liquid crystal phase modulator, a polarizing plate, a beam splitter, an analyzer and a detector; The liquid crystal phase modulator adopts an electrically controlled birefringence orientation mode, and the orientation direction of the liquid crystal molecules is parallel to the X-axis; A polarizer is arranged in front of the liquid crystal phase modulator, and its polarization direction is at an angle of 45° with the X-axis; A beam splitter prism is provided between the liquid crystal phase modulator and the polarizing plate; A polarizer is arranged behind the liquid crystal phase modulator, and the angle between its polarization direction and the X-axis is -45 degrees; A detector is arranged behind the polarizer to receive the image signal passing through the liquid crystal phase modulator and the polarizer.

2. The wide spectrum response detection and reconstruction spectral imaging system according to claim 1, characterized in that: The liquid crystal phase modulator comprises, from bottom to top, a substrate, a bottom electrode, an orientation layer, a liquid crystal layer and a top electrode.

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