CN108593105A - The Hyperspectral imaging devices and its imaging method of birefringent polarizing interference-type - Google Patents

Abstract

The invention discloses a birefringent polarization interference type hyperspectral imaging device and an imaging method thereof, comprising a front imaging objective lens, a diaphragm, a collimating objective lens, a polarizer, a birefringent shearing plate, Birefringence compensation plate, analyzer, rear imaging objective lens and area array detector. After the incident light from the target passes through the polarization interference system, interference information is generated on the area array detector. After the overall scanning of the system, the area array detector obtains the interference image information of the target under different optical path difference modulation states, and finally obtains the spectral information of the target after Fourier transform spectral restoration processing. The hyperspectral imaging device of the birefringent polarization interference type in the present invention only uses two birefringent crystals, which not only can better solve the nonlinear problem of optical path difference, but also has the advantages of compact structure and low complexity, and is suitable for light Small, high-precision hyperspectral imaging applications.

Description

Hyperspectral imaging device and imaging method of birefringent polarization interference type

technical field

The invention relates to the field of optical imaging, in particular to a birefringent polarization interference hyperspectral imaging device and an imaging method thereof.

Background technique

Interferometric hyperspectral imaging technology is one of the important technical means for spectral subdivision imaging. In recent years, a variety of interferometer schemes have been gradually developed, mainly based on Michelson interferometer, Sagnac interferometer, Mach-Zehnder interferometer, Fabry- Perot interferometer, and birefringent interferometer based on Wollaston prism and Savart prism, etc. These hyperspectral imaging technologies have been widely used in remote sensing detection, environmental monitoring, biomedicine and other fields.

Among them, the birefringent polarization interference hyperspectral imager has been intensively studied by researchers because of its compact structure and simple optical path. Chinese patent 01213109.1 proposes an "ultra-small steady-state polarization interference imaging spectrometer" (as shown in Figure 3), which is a birefringent polarization interference hyperspectral imager based on a traditional Savart plate. The structural features are as follows: birefringence interferometer It consists of two birefringent crystals with the same thickness; the angle between the optical axis of the first birefringent crystal and the positive direction of the X-axis is 45°, the angle between the optical axis of the first birefringent crystal and the negative direction of the Y-axis is 45°, and the angle between the optical axis of the first birefringent crystal and the positive direction of the Z-axis is 45°; the angle between the optical axis direction of the second birefringent crystal and the positive direction of the X-axis is 45°, the angle between the positive direction of the Y-axis is 45°, and the angle between the positive direction of the Z-axis is 45°; the polarizer and The transmittance axis of the analyzer is parallel to the X axis. The characteristics of the sheared beam are as follows: after passing through crystal 1 and crystal 2, the two rays propagate along the Z-axis direction, the plane formed by the two outgoing beams is parallel to the YOZ plane, and the two outgoing beams are symmetrical about the XOZ plane. The interference mechanism is as follows: Since the thickness of the two birefringent crystals is equal, the two birefringent crystals both introduce the same amount of transverse shear, and can eliminate the constant term optical path difference, and adjust the zero-order fringe to the center of the field of view. However, the combination of the square-term optical path differences of the two birefringent crystals still introduces a linear optical path difference with a difference in the longitudinal field of view. Therefore, there are large differences in the total optical path difference value of the longitudinal field of view at the same wavelength produced by the traditional Savart scheme. Since the total optical path difference value and the spectral resolution are reciprocally proportional to each other, the difference in the total optical path difference value will lead to different spectral resolutions and wavenumber positions at different imaging positions, which is not conducive to the slice representation of the three-dimensional spectral data cube.

The present invention proposes a new birefringent interferometer, which is characterized in that it is composed of two birefringent crystal plates with unequal thicknesses, a shearing plate and a compensating plate, the optical axis of the birefringent shearing plate is perpendicular to the X axis, and The included angle with the Y axis is 45°, the optical axis of the birefringent compensation plate is parallel to the X axis, the thickness of the birefringent shear plate is larger than that of the birefringent compensation plate; the transmission axes of the polarizer and the analyzer are both in line with the X axis The included axis angle is 45°. Its shear beam characteristics: one beam of light propagates along the original optical path; the other beam of light propagates in the negative direction of the Y axis when passing through the birefringent shear plate, and propagates along the direction of the Z axis when passing through the birefringent compensation plate; The plane formed by the rays coincides with the YOZ plane, and one ray coincides with the Z axis. The interference mechanism is as follows: the shear plate introduces the optical path difference related to the viewing angle, and realizes the wide-band transverse shear interference of the incident beam. The compensation plate compensates the constant-term optical path difference and the square-term optical path difference of the shearing plate, so as to realize the position adjustment of the zero-order fringe and the difference correction of the total optical path difference. This double-chip structure can effectively solve the nonlinear problem of optical path difference in the traditional Savart scheme.

Contents of the invention

The purpose of the present invention is to provide a birefringent polarization interference type hyperspectral imaging device and its imaging method, which solves the technical problem of inconsistency in the total optical path difference of each vertical field of view in the traditional Savart interference system.

The technical solution to realize the object of the present invention is: a hyperspectral imaging device of birefringent polarization interference type, comprising a front imaging objective lens, a diaphragm, a collimating objective lens, a polarizer, a birefringent shearing plate, birefringence compensation plate, analyzer, rear imaging objective lens and area array detector; the imaging plane of the front imaging objective lens coincides with the front focal plane of the collimating objective lens, and the aperture is at the imaging surface of the front imaging objective lens; The angle between the transmission axis of the polarizer and the X-axis is 45°, the angle between the transmission axis of the analyzer and the X-axis is 45°; the optical axis of the birefringent shear plate is perpendicular to the X-axis, and The angle between the axes is 45°; the optical axis of the birefringence compensation plate is parallel to the X axis.

An imaging method based on a birefringent polarization interference type hyperspectral imaging device, the method steps are as follows:

In the first step, the incident beam is imaged on the diaphragm through the front imaging objective lens, and then passes through the collimating objective lens to form a collimated beam, which enters the polarizer in the form of a collimated beam, and the polarizer converts the collimated beam into linear polarization Light;

In the second step, the above-mentioned linearly polarized light is decomposed into o light and e light whose vibration directions are orthogonal to each other after passing through the birefringent shear plate, because the optical axis of the birefringent shear plate is orthogonal to the optical axis of the birefringent compensation plate , the o light in the birefringent shearing plate becomes e light in the birefringent compensation plate, and this beam is oe light, and the other polarized light is eo light; these two beams of polarized light pass through the birefringent compensation plate Afterwards, it turns into two beams of orthogonally polarized light beams that emerge in parallel, one of which propagates along the original optical path, and the other beam propagates in the negative direction of the Y axis when passing through the birefringent shear plate, and along the Propagate in the Z-axis direction; the plane composed of two outgoing rays coincides with the YOZ plane, and one ray coincides with the Z-axis.

Step 3: After the two outgoing rays pass through the analyzer, they become two beams with the same polarization direction and a certain optical path difference.

In the fourth step, the two light beams with a certain optical path difference converge on the target surface of the area array detector after passing through the post-imaging objective lens and interfere.

Step 5. Since different positions on the imaging surface correspond to different optical path differences, the image obtained by the area array detector is an interference image modulated by the optical path difference. In the window scan mode, the light of each image point The intensity is modulated by different optical path differences at different times, and the spectral information of each target point can be obtained by extracting the interference information of each point of the detection target in the interference image sequence and performing spectral restoration.

Compared with the prior art, the present invention has significant advantages in that: (1) it can suppress the difference in linear total optical path difference in different longitudinal fields of view at the same wavelength, and better ensure the spectral resolution and spectral resolution of the restored spectra at different positions on the imaging surface. Consistency of wavenumber position; (2) It can suppress the difference of linear total optical path difference in the same longitudinal field of view at different wavelengths, and has an excellent effect in suppressing the difference in wavenumber resolution caused by the dispersion effect.

Description of drawings

FIG. 1 is a schematic structural diagram of a birefringent polarization interference type hyperspectral imaging device of the present invention.

Fig. 2 is a schematic structural diagram of the birefringence interferometer part of the present invention.

Fig. 3 is a schematic structural diagram of the birefringent interferometer part in the background art.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Combining Figures 1 and 2, a birefringent polarization interference type hyperspectral imaging device includes a front imaging objective lens 1, a diaphragm 2, a collimating objective lens 3, a polarizer 4, and a birefringent shear placed in sequence along the optical axis. Cutting plate 5 , birefringent compensation plate 6 , analyzer 7 , rear imaging objective lens 8 and area array detector 9 .

The imaging plane of the front imaging objective lens 1 coincides with the front focal plane of the collimating objective lens 3 , and the diaphragm 2 is located at the imaging plane of the front imaging objective lens 1 . Both the transmission axes of the polarizer 4 and the analyzer 7 have an included angle of 45° with the X axis. The optical axis of the birefringent shear plate 5 is perpendicular to the X-axis and has an included angle of 45° with the Y-axis, and the optical axis of the birefringent compensation plate 6 is parallel to the X-axis.

The thickness of the birefringent shear plate 5 is greater than that of the birefringent compensation plate 6 .

Both the birefringent shear plate 5 and the birefringent compensation plate 6 are made of birefringent crystals.

The birefringent crystals used in the birefringent shear plate 5 and the birefringent compensating plate 6 are uniaxial crystals.

Both the birefringent shear plate 5 and the birefringent compensation plate 6 are positive crystals or negative crystals.

An imaging method based on a birefringent polarization interference type hyperspectral imaging device, the method steps are as follows:

In the first step, the incident beam is imaged on the diaphragm 2 through the front imaging objective lens 1, and then passes through the collimating objective lens 3 to form a collimated beam, which is incident on the polarizer 4 in the form of a collimated beam, and the polarizer 4 collimates The light beam becomes linearly polarized light;

In the second step, the above-mentioned linearly polarized light is decomposed into o light and e light whose vibration directions are orthogonal to each other after passing through the birefringent shear plate 5 . Since the optical axis of the birefringent shearing plate 5 is perpendicular to the optical axis of the birefringent compensation plate 6, the o light in the birefringent shearing plate 5 becomes e light in the birefringent compensation plate 6, and the light beam is oe light, and another beam of polarized light is eo light. After the two beams of polarized light pass through the birefringence compensation plate 6, they become two beams of orthogonally polarized beams that exit in parallel. A beam of light propagates along the original optical path; another beam of light propagates in the negative direction of the Y axis when passing through the birefringent shear plate, and propagates along the direction of the Z axis when passing through the birefringent compensation plate; the plane formed by the two outgoing rays is the same as the YOZ The planes coincide, and there is a ray coincident with the Z axis;

In the third step, after the two light beams pass through the analyzer 7, they become two light beams with the same polarization direction and a certain optical path difference;

In the fourth step, the two light beams with a certain optical path difference converge on the target surface of the area array detector 9 after passing through the post-imaging objective lens 8 and interfere;

In the fifth step, since different positions on the imaging surface correspond to different optical path differences, the image obtained by the area array detector 9 is an interference image modulated by the optical path difference. In the window scan mode, the light intensity of each image point is modulated by different optical path differences at different times. The spectral information of each target point can be obtained by extracting the interference information of each point of the detection target in the interference image sequence and performing spectral restoration.

Example 1

The spectral range of the system is set to be 400-1000 nm, and the wavenumber resolution at the central wavelength of 700 nm is 91.2 cm ^-1 . The focal lengths of the pre-imaging objective lens 1, the collimating objective lens 3, and the rear imaging objective lens 8 are all 75 mm, and the number of sampling pixels of the area array detector 9 is 1024×1024, and the pixel size is 6.5 μm. In the present invention, the birefringent crystals are all made of iceland stone, wherein the thickness of the birefringent shear plate 5 is 11.55 mm, and the thickness of the birefringent compensation plate 6 is 6.24 mm. The thickness of the birefringent crystals used in the traditional Savart scheme is 8.17mm.

Table 1 shows the total optical path difference values at different row positions (lines 1, 512 and 1024) on the image plane at 400nm, 700nm and 1000nm for the two schemes. It can be seen from Table 1 that the total optical path difference of the upper field of view of the traditional Savart scheme is significantly greater than that of the lower field of view, and the maximum difference of the total optical path difference at 400nm is 5.232μm, and the total optical path difference at 700nm The maximum difference in path difference is 4.868 μm, and the maximum difference in total optical path difference at 1000 nm is 4.743 μm. The maximum difference of the total optical path difference of the solution of the present invention is 0.116 μm, so it can be seen that the difference of the optical path difference of the solution of the present invention is significantly improved.

Table 1 The total optical path difference (μm) of the two schemes at different row positions on the image plane

Table 2 shows the spectral resolutions of the two schemes at different row positions on the image plane. The spectral resolution of the upper field of view of the traditional Savart scheme is significantly higher than that of the lower field of view. The spectral resolution at 400nm differs by 0.060nm, the spectral resolution at 700nm differs by 0.199nm, and the spectral resolution at 1000nm differs. 0.417nm. The spectral resolution of the solution of the present invention has a maximum difference of 0.009 nm, which shows that the spectral resolution of the solution of the present invention has better consistency.

Table 2 Spectral resolution (nm) of the two schemes at different row positions on the image plane

Table 3 shows the wavelength positions of the restored spectra at different row positions on the image plane for the two schemes. In the traditional Savart scheme, the maximum wavelength difference at 400nm is 16.16nm, the maximum wavelength difference at 700nm is 28.59nm, and the maximum wavelength difference at 1000nm is 41.14nm. The wavelength position of the solution of the present invention has a maximum difference of 0.85 nm, which shows that the wavelength position of the solution of the present invention has better consistency.

Table 3 The wavelength position (nm) of the restored spectrum of the two schemes at different row positions on the image plane

Due to the strong wavelength dependence of the refractive index of birefringent materials, there are differences in the total optical path difference at different wavelengths. The total optical path difference of the short wavelength is significantly larger than that of the long wavelength, resulting in a large difference in the wavenumber resolution at different wavelengths. The maximum difference in wavenumber resolution of the traditional Savart scheme is 13.248cm ^-1 , and the maximum difference in wavenumber resolution of the scheme of the present invention is 9.377cm ^-1 . Therefore, the scheme of the present invention is better than the traditional Savart scheme in suppressing the wavenumber resolution difference caused by the dispersion effect.

Claims (7)

1. a kind of Hyperspectral imaging devices of birefringent polarizing interference-type, it is characterised in that：Include before optical axis is sequentially placed Set image-forming objective lens（1）, diaphragm（2）, collimator objective（3）, the polarizer（4）, birefringence shear plate（5）, birefringence compensating plate（6）、 Analyzer（7）, postposition image-forming objective lens（8）And planar array detector（9）；Preposition image-forming objective lens（1）Imaging surface and collimator objective（3） Front focal plane overlap, diaphragm（2）In preposition image-forming objective lens（1）Imaging surface at；The polarizer（4）Light transmission shaft and X-axis folder Angle is 45 °, analyzer（7）Light transmission shaft and the angle of X-axis be 45 °；Birefringence shear plate（5）Optical axis perpendicular to X-axis, and with Y-axis angle is 45 °；Birefringence compensating plate（6）Optical axis be parallel to X-axis.

2. the Hyperspectral imaging devices of birefringent polarizing interference-type according to claim 1, it is characterised in that：It is described two-fold Penetrate shear plate（5）Thickness be more than birefringence compensating plate（6）Thickness.

3. the Hyperspectral imaging devices of birefringent polarizing interference-type according to claim 1, it is characterised in that：It is described two-fold Penetrate shear plate（5）And birefringence compensating plate（6）Birefringece crystal is all made of to be made.

4. the Hyperspectral imaging devices of birefringent polarizing interference-type according to claim 3, it is characterised in that：It is described two-fold Penetrate shear plate（5）And birefringence compensating plate（6）The birefringece crystal used is uniaxial crystal.

5. the Hyperspectral imaging devices of birefringent polarizing interference-type according to claim 4, it is characterised in that：It is described two-fold Penetrate shear plate（5）And birefringence compensating plate（6）It is positive crystal.

6. the Hyperspectral imaging devices of birefringent polarizing interference-type according to claim 4, it is characterised in that：It is described two-fold Penetrate shear plate（5）And birefringence compensating plate（6）It is negative crystal.

7. a kind of Hyperspectral imaging devices based on the birefringent polarizing interference-type described in any one of claim 1-6 at Image space method, which is characterized in that method and step is as follows：

The first step, incident beam pass through preposition image-forming objective lens（1）It is imaged on diaphragm（2）On, then pass through collimator objective（3）, shape At collimated light beam, the polarizer is incident in the form of collimated light beam（4）, the polarizer（4）Collimated light beam is become linearly polarized light；

Second step, above-mentioned linearly polarized light pass through birefringence shear plate（5）Afterwards, direction of vibration mutually orthogonal o light and e are broken down into Light, due to birefringence shear plate（5）Optical axis and birefringence compensating plate（6）Optical axis it is orthogonal, birefringence shear plate（5）In o Light is in birefringence compensating plate（6）In become e light, be oe light by the light beam, same in addition a branch of polarised light is eo light；This two Beam polarised light passes through birefringence compensating plate（6）Become the orthogonal polarized light beam of two beam exiting parallels afterwards, wherein Ray Of Light is along former Paths, another Ray Of Light are passing through birefringence shear plate（5）When to Y-axis negative direction propagate, by birefringence compensating plate （6）When propagated along Z-direction；The plane of two emergent rays composition is overlapped with YOZ planes, and has a light and Z axis It overlaps；

Third step, this two emergent rays pass through analyzer（7）Afterwards, become that polarization direction is identical, and with certain optical path difference Two light beams；

4th step, two articles of light beams with certain optical path difference pass through postposition image-forming objective lens（8）Post-concentration is in planar array detector（9）Target On face and interfere；

5th step corresponds to different optical path differences, planar array detector due to position different on imaging surface（9）It is obtained Image is the interference image modulated by optical path difference, and in the case where window sweeps pattern, the light intensity of each picture point is different in different moments Optical path difference modulation, the interference information of extraction interference image sequence detection target each point simultaneously carries out spectrum recovering, you can obtains every The spectral information of a target point.