CN107421641B - A kind of broadband full polarization imaging device based on Mach Zehnder interferometer - Google Patents

Abstract

The invention discloses a wide-band full-polarization imaging device based on a Mach-Zehnder interferometer. Light carrying target polarization information enters a polarization modulation module through a collimation system, and the beam is divided into reflected light and transmitted light through a polarization beam splitter. The two beams of light pass through the half-wave plate placed at 22.5°, the vibration direction is rotated by 45°, and then pass through the diffraction grating to cause dispersion, pass through the plane mirror, change the propagation direction, and enter the polarization beam splitter for secondary light splitting, according to The propagation direction is divided into two groups. One group of light passes through the analyzer, and the vibration direction is the same. Under the action of the imaging lens, stable interference fringes are obtained on the CCD array, and the other group of light passes through the 1/4 wave plate placed at 0° , the values of circular polarization and linear polarization are exchanged, and after passing through the polarizer, under the action of the imaging lens, the CCD detection array obtains interference fringes. Finally, the two groups of interference fringes are demodulated to obtain the linear full polarization information of the target.

Description

A wide-band full-polarization imaging device based on Mach-Zehnder interferometer

【Technical field】

The invention belongs to the field of optical remote sensing detection, and relates to a wide-band full-polarization imaging device based on a Mach-Zehnder interferometer.

【Background technique】

Polarization imaging is an advanced detection technology that can obtain the intensity information and polarization information of the target at the same time. It has certain potential in improving the efficiency and accuracy of target detection, identification, and classification. , Natural disaster forecasting, atmospheric detection, astronomical observation, machine vision release, biomedical diagnosis and many other fields have great application value and development prospects. As a new type of remote sensing detection technology, channel-modulated polarization imaging technology has attracted the attention of domestic and foreign institutions due to its unique remote sensing detection advantages. Foreign research institutions are mainly concentrated in major engineering project support units, The military, universities, etc.; domestic research institutions mainly include Anhui Institute of Optics and Mechanics, Xi'an Institute of Optics and Mechanics, Xi'an Jiaotong University, etc., and the reported polarization imaging detection technologies have their own characteristics.

The core components of channel-modulated polarization imagers generally use birefringent crystals or interferometers. According to the imaging method, it can be divided into active imaging and passive imaging. Active imaging is represented by Mueller matrix polarization imaging, and its light source is known or controllable, so as to detect the polarization state of the target; Not limited by the light source, the practical application range is wider. According to the data processing method, it can be divided into data simplification mode, Fourier analysis method, and channel modulation mode. According to the time sequence, it can be divided into sequential polarization imaging and non-sequential polarization imaging. The timing mainly includes the rotating polarizer type and the liquid crystal control type: the rotating polarizer type is to place a rotating stage in front of the imaging camera and rotate the polarizer to obtain the target polarization state; the liquid crystal control type is to electronically control the sorting of liquid crystals to realize the function of the polarizer. The polarization state of the target can also be obtained. The disadvantage of the two is that it cannot image a dynamic target; non-sequential can be divided into amplitude-divided, aperture-divided, focal-plane-divided and channel-modulated. The sub-amplitude type generally requires multiple detectors, the data synchronization is difficult, the instrument is relatively large and complex, and the robustness is low; the sub-aperture type divides the aperture of the optical system into multiple, and each aperture detects the target separately. The polarization information of the detector is low, and the production is difficult; the split focal plane type adds a polarizing plate in front of the detector, and every four pixels can detect the polarization information of a target pixel, the spatial resolution is low, and the process is difficult to manufacture. ; The channel modulation type is to modulate the polarization information of the target to different spatial frequencies, so as to obtain the target polarization information on an image. It has the advantages of low cost and high spatial resolution.

【Content of invention】

The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art, and provide a wide-band full-polarization imaging device based on a Mach-Zehnder interferometer. The two technologies of amplitude-type polarization imaging and channel-modulated polarization imaging not only reduce the number of detectors that only divide the amplitude, but also expand the imaging band width of the channel-modulated polarization imaging method, and this method can realize self-calibration, solving the problem of Sub-amplitude polarization imaging matching problem. This scheme uses the dispersion of the blazed grating and the light splitting of the interferometer to obtain the shear amount of the beam proportional to the wavelength. Through the interference of two beams of light, the Stokes parameters (S ₀ , S ₁ , S ₂ ) or (S ₀ , S ₂ , S ₃ ) are two images modulated to the amplitude of the interference fringes, the frequency of the interference fringes is inversely proportional to the wavelength and proportional to the shear amount, eliminating the influence of the wavelength.

In order to achieve the above object, the present invention adopts the following technical solutions to achieve:

A wide-band full-polarization imaging device based on a Mach-Zehnder interferometer, including a pre-optical mirror group for collimating incident light, a polarization modulation module, a first imaging lens, a second imaging lens, and a second imaging lens arranged sequentially on the optical path One side array detector and the second side array detector; the incident light enters the front optical mirror group and then enters the polarization modulation module, and after passing through the polarization modulation module, two groups of four beams of light with the same vibration direction are formed, one of which is in the first imaging Under the action of the lens, interference fringes are formed on the first area detector, and the other group passes through a broadband 1/4 wave plate placed at 0° in the direction of the fast axis, and under the action of the second imaging lens, on the second surface Interference fringes are formed on the array detector; both the first area array detector and the second area array detector are connected with a data acquisition and processing system for performing Fourier transformation, filtering and Fourier inverse transformation on the interference fringes.

The further improvement of the present invention is:

The front optical lens group includes an objective lens, a field diaphragm and a collimating lens arranged in sequence along the incident light.

The objective lens is a telescopic objective lens, a microscopic objective lens or an ordinary objective lens.

The polarization modulation module includes a first polarizing beam splitter. After the incident light passes through the first polarizing beam splitter, it is divided into transmitted light and reflected light. The angle between the reflected light and the transmitted light is 90°; The first broadband half-wave plate, the first diffraction grating, the second diffraction grating and the first plane mirror placed at 22.5°, the transmitted light passes through the first plane mirror, and is parallel to the reflected light after passing through the first polarizing beam splitter ; The second broadband half-wave plate placed at 22.5°, the third diffraction grating, the fourth diffraction grating and the second plane reflector are arranged successively on the reflected light path, after the reflected light passes through the second plane reflector, it passes through the first polarization splitter The transmitted light after the beam splitter is parallel; the transmitted light passing through the first plane mirror and the reflected light passing through the second plane mirror converge at the second polarizing beam splitter, and the transmitted light and reflected light pass through the second polarizing beam splitter The rear vibration directions are perpendicular to each other.

The first diffraction grating, the second diffraction grating, the third diffraction grating and the fourth diffraction grating are transmission diffraction gratings.

Fast axis 0° placement of broadband 1/4 wave plate.

A first polarizer is arranged between the first imaging lens and the polarization modulation module.

A second polarizer is arranged between the second imaging lens and the polarization modulation module.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention combines the split-amplitude and channel-modulated polarization imaging methods, which makes up for the inability of the channel-modulated polarization imaging to realize wide-band full polarization, and also reduces the number of detectors and optical paths required when only using the split-amplitude polarized imaging method. Simple and easy to adjust, low cost, this method has both the advantages of the two methods. The imaging band of the invention is wide, and the intensity information and polarization information of the target can be obtained at the same time under weak light conditions; only one frame image of the space target is needed to obtain its full polarization imaging information, and the dynamic target can be detected, and the work efficiency is high . Finally, the data processing is simple and fast, and the target can be detected in real time.

【Description of drawings】

Fig. 1 realizes the dispersion type Mach-Zehnder interferometer type full polarization imaging device of the present invention;

Figure 2 shows the principle of dispersion compensation for blazed gratings;

Fig. 3 is a beam distribution diagram of the polarization modulation module.

Among them: 100-front optical mirror group; 200-polarization modulation module; 211-first polarizing beam splitter; 212 second polarizing beam splitter; 221-first broadband half-wave plate; 222-second broadband half-wave plate 231-the first diffraction grating; 232-the second diffraction grating; 233-the third diffraction grating; 234-the fourth diffraction grating; 241-the first plane mirror; 4 wave plates; 301-the first polarizer; 302-the second polarizer; 401-the first imaging lens; 402-the second imaging lens; 501-the first area detector; 502-the second area detector; 110-objective lens; 120-field diaphragm; 130-collimating lens.

【Detailed ways】

The present invention is described in further detail below in conjunction with accompanying drawing:

Referring to Fig. 1-Fig. 3, the wide-band full-polarization imaging device based on Mach-Zehnder interferometer of the present invention, the front optical mirror group 100, the polarization modulation module 200, the first polarizer 301, the second polarizer 301, and the second Polarizer 302, first imaging lens 401, second imaging lens 402, first area array detector 501, second area array detector 502 and data acquisition and processing system;

As shown in FIG. 1 , the front optical lens group 100 is composed of an objective lens 110 , a diaphragm 120 and a collimator lens 130 sequentially arranged on the optical path; the objective lens 110 is a telescopic objective lens, a microscopic objective lens or an ordinary objective lens.

As shown in Figure 2, the key technology for the Mach-Zehnder interferometer to produce a transverse shear that is positively correlated with the wavelength is composed of two identical diffraction gratings: the beam is vertically incident on the diffraction grating, and diffraction occurs, where the diffraction angle is the same as The wavelength has a relationship of dsinθ _λ =mλ (d diffraction grating period, θ _λ is the diffraction angle, m is the diffraction order, and λ is the wavelength), and the shear amount Δ/2=Ltanθ _λ , when the angle is small enough, the above relationship is approximate Δ/2=Lsinθ _λ =Lmλ/d , that is, the shear amount positively related to the wavelength is obtained.

As shown in Figure 3, after the two beams of light pass through the polarization modulation module, the shear amount of each band is positively correlated with the wavelength, and modulated with different phase factors.

The polarization modulation module 200 consists of a first polarization beam splitter 211, a first broadband half-wave plate 221 placed at 22.5°, a first diffraction grating 231, a second diffraction grating 232, a plane mirror 241, and a broadband 1/4 wave plate placed at 0° wave plate 250; where the blazed grating is located on the branch of the Mach-Zehnder optical path, the distance between the two groups of gratings is the same, and the lengths of the two branches are equal; under the action of the first polarizing beam splitter 211, the s light is reflected, and the p light Transmission, divided into two paths; after the light beam passes through the broadband half-wave plate placed at 22.5°, the vibration direction is rotated by 45°, and dispersion occurs after passing through the first diffraction grating 231. Different wavelengths have different diffraction angles, which satisfy the diffraction formula. After the second diffraction grating 232, the propagation direction of the light changes again, and the light beam becomes parallel light; after passing through the plane mirror placed at 45°, the propagation route is changed; similarly, the other path of light undergoes the same change. The two beams of light meet at the second polarizing beam splitter 212 , and after passing through the second polarizing beam splitter 212 , the two beams of light are respectively split for the second time. After the light beam passes through the first polarizer 301 , the vibration direction is the same, and it converges at the focal plane under the action of the first imaging lens 401 , where interference occurs, and the first area array detector 501 can capture a set of interference fringe patterns. In addition, the light beam first passes through the broadband 1/4 wave plate 250 placed at 0° in the direction of the fast axis, and the linear polarization information S ₁ carried by it and the circular polarization information S ₃ exchange positions, and the polarization state is determined by S=[S ₀ , S ₁ , S ₂ , S ₃ ] ^T transforms into S=[S ₀ , S ₃ , S ₂ , S ₁ ] ^T , and then passes through the second polarizer 302 with the same vibration direction. Under the action of the second imaging lens 402, the second surface Array detector 502 can detect a set of interference fringes. Theoretically, there is a phase difference of one wavelength between the two beams of light when interference occurs (here, the machining precision is extremely high, the four sides of the Mach-Zehnder interferometer have exactly the same arm length), and when interference occurs, the central fringes are shifted, but It does not affect the measurement results; finally, the two-dimensional spatial distribution map corresponding to the linear polarization information can be obtained through the acquisition, extraction and processing of the data acquisition system.

Principle and working process of the present invention:

The light carrying the polarization information of the space target enters the polarization detection imaging system through the collimation system, and the beam is divided into reflected light and transmitted light under the action of the polarization beam splitter. The plane mirror changes the propagation direction, and then enters the beam splitter, half of the light is reflected and half of the light is transmitted, and the transmitted two beams of light converge after passing through the polarizer, and the vibration direction is the same. Under the action of the imaging lens, Stable interference fringes can be obtained on the CCD detection array, and finally Fourier transform, filter and Fourier inverse transform are performed on the interference fringes to obtain a two-dimensional image of the linear polarization component, and the reflected two beams of light pass through the fast axis direction The 1/4 wave plate placed at 0° exchanges the linear polarization information S1 of the target with the circular polarization information value. After passing through the polarizer, the vibration direction is the same. Under the action of the imaging lens, it can be obtained on the CCD detection array. Stable interference fringes, and finally perform Fourier transformation, filtering and Fourier inverse transformation on the interference fringes to obtain a two-dimensional image of the linear polarization component, and combine the information obtained by the two detectors to obtain the full polarization of the target at the same time information.

A blazed grating is an ideal case of a diffraction grating element, which will utilize the first-order diffracted light with extremely high diffraction efficiency, and the beam splitter will evenly divide the light into two parts without introducing polarization errors. The light passing through the dispersion-type polarization modulation module based on the Mach-Zehnder interferometer has a transverse shearing effect, and the shearing amount is approximately proportional to the wavelength.

The above content is only to illustrate the technical ideas of the present invention, and cannot limit the protection scope of the present invention. Any changes made on the basis of the technical solutions according to the technical ideas proposed in the present invention shall fall within the scope of the claims of the present invention. within the scope of protection.

Claims (8)

1. A wide-band full-polarization imaging device based on a Mach-Zehnder interferometer, characterized in that it includes a pre-optical mirror group (100) and a polarization modulation module (200) for collimating incident light that are sequentially arranged on the optical path , the first imaging lens (401), the second imaging lens (402), the first area array detector (501) and the second area array detector (502); the incident light enters the front optical mirror group (100) and enters The polarization modulation module (200), forms two groups of four bundles of light with the same vibration direction after passing through the polarization modulation module (200), one group of which is under the action of the first imaging lens (401), and is placed on the first area array detector (501 ) to form interference fringes, another group passes through a broadband 1/4 wave plate (250) placed at 0° in the direction of the fast axis, and under the action of the second imaging lens (402), the second area array detector (502 ) to form interference fringes; the first area detector (501) and the second area detector (502) are all connected to the data acquisition process for carrying out Fourier transform, filtering and Fourier inverse transform to the interference fringes system. 2. The wide-band full-polarization imaging device based on Mach-Zehnder interferometer according to claim 1, wherein the front optical lens group (100) includes an objective lens (110) arranged in sequence along the incident light, a field of view light diaphragm (120) and collimating lens (130). 3. The wide-band full-polarization imaging device based on Mach-Zehnder interferometer according to claim 2, characterized in that the objective lens (110) is a telescopic objective lens, a microscopic objective lens or an ordinary objective lens. 4. The broadband full-polarization imaging device based on Mach-Zehnder interferometer according to claim 1, characterized in that, the polarization modulation module (200) comprises a first polarization beam splitter (211), and the incident light undergoes a first polarization After the beam splitter (211), it is divided into transmitted light and reflected light, and the angle between the reflected light and the transmitted light is 90 °; the first broadband half-wave plate (221) placed at 22.5 ° is sequentially arranged on the transmitted light path, The first diffraction grating (231), the second diffraction grating (232) and the first plane mirror (241), after the transmitted light passes through the first plane mirror (241), and after passing through the first polarizing beam splitter (211) The reflected light is parallel; the second broadband half-wave plate (222), the third diffraction grating (233), the fourth diffraction grating (234) and the second plane reflector (242) placed at 22.5° are arranged successively on the reflected light path, After the reflected light passes through the second plane reflector (242), it is parallel to the transmitted light after passing through the first polarizing beam splitter (211); the transmitted light through the first plane reflector (241) and the second plane reflector ( The reflected light of 242) is converged at the second polarizing beam splitter (212), and the vibration directions of the transmitted light and the reflected light are perpendicular to each other after passing through the second polarizing beam splitter (212). 5. the broadband full-polarization imaging device based on Mach-Zehnder interferometer according to claim 4, is characterized in that, the first diffraction grating (231), the second diffraction grating (232), the third diffraction grating (233) And the fourth diffraction grating (234) is a transmission diffraction grating. 6. The broadband full-polarization imaging device based on Mach-Zehnder interferometer according to claim 4 or 5, characterized in that the fast axis of the broadband 1/4 wave plate is placed at 0°. 7. the wide-band full-polarization imaging device based on Mach-Zehnder interferometer according to claim 1, is characterized in that, a first polarizer ( 301). 8. the wide-band full-polarization imaging device based on Mach-Zehnder interferometer according to claim 1, is characterized in that, a second polarizer ( 302).