CN102135450A - Liquid crystal tunable filter based static full stokes imaging spectropolarimeter - Google Patents

Abstract

The invention relates to a liquid crystal tunable filter based static full stokes imaging spectropolarimeter. The imaging spectropolarimeter comprises a front optical system, a collimating lens, a liquid crystal tunable filter and a phase modulation module, wherein the liquid crystal tunable filter is positioned in the same optical axis as the front optical system and the collimating lens; and the phase modulation module is arranged between the collimating lens and the liquid crystal tunable filter and is positioned in the same optical axis as the collimating lens and the liquid crystal tunable filter. The liquid crystal tunable filter based static full stokes imaging spectropolarimeter provided by the invention has the advantages of no moving part, static measurement, full stokes polarization-state measurement, high spatial resolution, simple structure and high stability.

Description

Static full Stokes imaging spectral polarimeter based on the liquid crystal tunable optical filter

Technical field

The invention belongs to optical field, relate to a kind of imaging spectral polarizing instrument, relate in particular to a kind of static full Stokes imaging polarimeter based on the liquid crystal tunable optical filter.

Background technology

Imaging spectral polarimetry (Imaging Spectropolarimetry) technology is a kind ofly can obtain target image, and a kind of optical information of the spectrum polarizing information of each pixel is obtained technology in the acquisition image, the imaging spectral polarimeter can obtain image, spectrum and the polarization information of target simultaneously, having important use and be worth in industrial or agricultural, remote sensing and military affairs, is one of forward position research topic in the world.

Generally speaking, two-dimentional focus planardetector single exposure can only obtain two-dimensional signal, obtain image, spectrum and the polarization information of target, must experience the mechanical scanning or the electric tuning scanning process of certain form.Computed tomography spectrum polarizing instrument [the Eustace L.Dereniak of design such as Eustace L.Dereniak, Nathan A.Hagen, William R.Johnson, et.al. " Imaging Spectropolarimetry " .Proceedings of SPIE Vol.5074,272～285 (2003)] can in single exposure, obtain the space of target, spectrum and full Stokes polarization information, but be subjected to calculation holographic optical grating diffraction angle, the influence of focal plane array detector size, spectral resolution and spatial resolution all are restricted, and have " losing awl " phenomenon of principle.Imaging spectral polarimeter [the Kevin W.Peters that in the collimated light path of spatial modulation imaging spectrometer, adds the liquid crystal tunable phase delay device that Japan scholar Kevin W.Peters proposes, Theodore S.Turner, Jr.et.al. " Portable visible imaging spectropolarimeter for remote sensingapplications " .SPIE Vol.3498,223～230 (1998)] can obtain the full Stokes spectrum polarization information of target, just can finish but need carry out repeatedly scanning imagery, image registration is brought very big difficulty same target.The imaging spectral polarimeter that Japanese national aerospace laboratory proposes based on the liquid crystal tunable optical filter, when obtaining the polarization information of target, need the rotation of step motor drive liquid crystal tunable mating plate, because moving component is arranged, stability decreases, it can only carry out the measurement of linear polarization simultaneously, can not finish the measurement of full Stokes polarization state.Snap formula imaging spectral polarimeter [the Stephen H.Jones of U.S. aerodyne research company development, Frank J.Iannarilli, and Paul L.Kebabian. " Relazation ofquantitative-grade fiedable snapshot imaging spectropolarimeter " .Optics Express, Vol.12,6559～6573 (2004)] needs move through platform or scenery moves the two dimensional image that obtains target.

Summary of the invention

In order to solve the above-mentioned technical matters that exists in the background technology, the invention provides a kind of static full Stokes imaging spectral polarimeter based on the liquid crystal tunable optical filter with movement-less part, static measurement, full Stokes measuring polarization state, high spatial resolution, simple in structure and good stability.

Technical solution of the present invention is: the invention provides a kind of static full Stokes imaging spectral polarimeter based on the liquid crystal tunable optical filter, comprise preposition optical system, collimating mirror and be in liquid crystal tunable optical filter on the same optical axis together with preposition optical system and collimating mirror, its special character is: described static full Stokes imaging spectral polarimeter based on the liquid crystal tunable optical filter also comprises the phase modulation (PM) module; Described phase modulation (PM) module places between collimating mirror and the liquid crystal tunable optical filter and with collimating mirror and liquid crystal tunable optical filter and is co-located on the same optical axis.

Above-mentioned phase modulation (PM) module comprises first phase delay device and second phase delay device, and described first phase delay device and second phase delay device bond together.

Above-mentioned phase modulation (PM) module comprises first phase delay device and second phase delay device, and described first phase delay device and second phase delay device are successively set between collimating mirror and the liquid crystal tunable optical filtering.

The plane that the fast axle and the slow axis of above-mentioned first phase delay device formed and the fast axle of second phase delay device are vertical with systematic optical axis respectively with the plane that slow axis is formed.

The quick shaft direction of above-mentioned first phase delay device is identical with the analyzer polarization direction of liquid crystal tunable optical filter; The angle of the quick shaft direction of the quick shaft direction of described second phase delay device and first phase delay device is 45 °.

Above-mentioned first phase delay device and second phase delay device all are by the single axial birefringence crystalline material.

Above-mentioned first phase delay device and second phase delay device are to be made by kalzit or quartz.

The model of above-mentioned liquid crystal tunable optical filter is VariSpec VISR type or VariSpec NIRR type.

Advantage of the present invention is:

The present invention has thoroughly save mechanical scanning mechanism, can be under static condition the spectrum of liquid crystal tunable optical filter by electric tuning scan and finish obtaining of object space, spectrum and full Stokes polarization information.Also have simultaneously simple in structure, volume is little, the advantage of in light weight and good stability, particularly, the present invention has the following advantages:

1, can obtain full Stokes polarization information, and not need special mechanical type polarization state scanning.The present invention utilizes static phase delay device and linear polarizer that polarization information is modulated in the spectrum and goes, and then from restore spectrum, demodulate polarization of incident light attitude information, can obtain full Stokes polarization information, and not need special mechanical type polarization state scanning.

2, stability is strong, resolution is high.The present invention can static staring imaging, do not need moving of target or instrument platform to obtain the spatial information of target, stability improves greatly, simultaneously, spatial resolution mainly by the pixel number restriction of focal plane array detector, utilizes bigger face battle array can obtain higher spatial resolution.

3, volume is little, and is with low cost.The present invention has utilized the liquid crystal tunable optical filter to can be used as the linear polarizer characteristics, has saved the linear polarizer in polarization-spectrum modulation type spectrum polarizing instrument, has reduced volume.Simultaneously, the preposition optical system of imaging spectral polarimeter provided by the present invention, collimating mirror, liquid crystal tunable optical filter, imaging mirror, focal plane array detector and computing machine etc. greatly reduce instrument cost all from spot commodities.

Description of drawings

Fig. 1 is the static structural representation of Stokes imaging spectral polarimeter entirely based on the liquid crystal tunable optical filter provided by the present invention;

Fig. 2 is polarization of the present invention-spectral modulation structural representation.

Embodiment

Referring to Fig. 1, a kind of static full Stokes imaging spectral polarimeter that the present invention proposes based on the liquid crystal tunable optical filter, be that the mode of placing phase delay device in based on the collimated light path before the liquid crystal tunable optical filter 6 of the imaging spectrometer of liquid crystal tunable optical filter realizes, the full Stokes polarization information that to import light by phase delay device and linear polarizer is modulated in the spectrum and goes, utilize the Computer signal treatment technology that each stokes component spectrum recovering is come out at last, can be used for visible light and near infrared spectral coverage.

Static full Stokes imaging spectral polarimeter based on the liquid crystal tunable optical filter provided by the present invention, preposition optical system 1 is with target imaging; Collimating mirror 2 is with beam collimation, in collimated light path, put into the phase modulation (PM) module of forming by phase delay device 3 and phase delay device 45, and liquid crystal tunable optical filter 6, imaged on the focal plane array detector 8 by the picture of imaging mirror 7 with target, computing machine 9 is connected with focal plane array detector 8 with liquid crystal tunable optical filter 6 again.

Preposition optical system 1 is used for the interesting target imaging, and image space is on the front focal plane of collimating mirror 2.Collimating mirror 2 will enter the beam collimation of optical system, first phase delay device 3 and second phase delay device 4 are positioned in the collimated light path behind the collimating mirror successively, by the single axial birefringence crystalline material, can adopt kalzit (icelandspar) or quartz material to make, for reducing volume, two phase delay devices can bond together.

Preposition optical system 1, collimating mirror 2, liquid crystal tunable optical filter 6 and computing machine all are the commodity (COTS) of stock in hand supply, and phase delay device carries out design customization according to instrument parameter.

The wavelength that sees through of liquid crystal tunable optical filter 6 is controlled by computing machine 9, and the exposure and the image acquisition of simultaneous computer 9 control focal plane array detectors 8 finally utilize algorithm to finish the spectrum of each pixel of target and the recovery of full Stokes polarization state on computing machine 9.Liquid crystal tunable optical filter 6 has the tuning capability of transmitted beam wavelength, the characteristics that also have linear polarizer simultaneously, can finish polarization-spectral modulation function with 5 combinations of phase modulation (PM) module, the wave number (inverse of wavelength) that the spectrum polarizing attitude that is about to incident light is modulated to incident light gets on, and demodulates full Stokes polarization information through demodulating algorithm from restore spectrum then.

Liquid crystal tunable optical filter 6 adjacent phase delay devices 4 are placed, and the liquid crystal tunable optical filter can adopt VariSpec VISR type or two kinds of products of VariSpec NIRR type of U.S. CRI company.Wherein the spectral range of VariSpec VISR is 480～720nm, and resolution is 0.25nm, and the spectral range of VariSpec NIRR is 650～1100nm, and resolution is 0.75nm.The liquid crystal tunable optical filter can realize seeing through continuously changing of wavelength as required by computer software control;

Imaging mirror 7 will through liquid crystal tunable optical filter 6 directional light image in once more on the focal plane array detector 8, focal plane array detector 8 is also by computer control, finish collection to the quasi-monochromatic light image, the wavelength shift of the collection of image and liquid crystal tunable optical filter 6 is coordinated, every adjustment once sees through wavelength, piece image is gathered in stable back, adjusts wavelength again one time after having gathered image, finishes the collection of entire image sequence in this manner.

Computing machine 9 is formed a spectroscopic data cube with image sequence after gathering complete image sequence, comprises two dimensional image and one dimension spectrum, and each pixel in the image all has a specific curve of spectrum.The curve of spectrum to each pixel carries out Fourier transform, each Stokes spectral components of this pixel will be separated at frequency domain this moment, adopt different window functions that the Fourier transform curve of each stokes component is separated, again each Fourier transform curve is carried out the spectrum that inverse Fourier transform can restore full stokes component.

Referring to Fig. 2, the present invention is when work, and its spectrum polarizing modulation detailed process is as follows:

The fast axle 11 of first phase delay device 3 is vertical with optical axis 10 with the plane that slow axis 12 is formed, and the fast axle 13 of second phase delay device 4 is also vertical with optical axis 10 with the plane that slow axis 14 is formed;

Fast axle 11 directions of first phase delay device 3 are parallel with the linear polarization 15 of the polarizer of liquid crystal tunable optical filter 6, the angle of the direction of the fast axle 13 of second phase delay device 4 and the quick shaft direction 11 of first phase delay device 3 is 45 degree, the two phase place delayer is glued together, and thickness is respectively L ₁And L ₂

For the input of any Stokes vector, output can be represented with following formula:

$s_{\mathrm{out}}=\left(\begin{array}{cccc}1/2& 1/2& 0& 0\\ 1/2& 1/2& 0& 0\\ 0& 0& 0& 0\\ 0& 0& 0& 0\end{array}\right)\left(\begin{array}{cccc}1& 0& 0& 0\\ 0& \cos \left({\mathrm{\δ}}_2\right)& 0& -\sin \left({\mathrm{\δ}}_2\right)\\ 0& 0& 1& 0\\ 0& \sin \left({\mathrm{\δ}}_2\right)& 0& \cos \left({\mathrm{\δ}}_2\right)\end{array}\right)\left(\begin{array}{cccc}1& 0& 0& 0\\ 0& 1& 0& 0\\ 0& 0& \cos \left({\mathrm{\δ}}_1\right)& \sin \left({\mathrm{\δ}}_1\right)\\ 0& 0& -\sin \left({\mathrm{\δ}}_1\right)& \cos \left({\mathrm{\δ}}_1\right)\end{array}\right)\left(\begin{array}{c}{s}_0\\ s_1\\ s_2\\ s_3\end{array}\right)---\left(1\right)$

S in the following formula _OutBe the Stokes vector of output beam, s _In=(s ₀, s ₁, s ₂, s ₃) ^TStokes vector for input beam.The mueller matrix of the polarizer that three matrixes in equation the right are liquid crystal tunable optical filter 6 successively, first phase delay device 3, second phase delay device 4.δ ₁And δ ₂Be respectively the phase-delay quantity of first phase delay device 3 and second phase delay device 4, they all are the functions of wave number σ (inverse of wavelength), are determined by formula (2):

δ(σ)＝2πdΔnσ(2)

In the following formula, d is the thickness of delayer material, and Δ n is refractive index poor of ordinary light and unusual light.

Matrix multiple in the formula (1) is obtained:

$s_{\mathrm{out}}=1/2\left(\begin{array}{c}{s}_0+{\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="H201010013654XE00011.png"\; state="\{\{state\}\}">s</figure-callout>}}_1\cos \left({\mathrm{\&delta;}}_2\right)+{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="H201010013654XE00011.png"\; state="\{\{state\}\}">s</figure-callout>}}_2\sin \left({\mathrm{\&delta;}}_1\right)\sin \left({\mathrm{\&delta;}}_2\right)-{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="H201010013654XE00011.png,H201010013654XE00012.png"\; state="\{\{state\}\}">s</figure-callout>}}_3\cos \left({\mathrm{\&delta;}}_1\right)\sin \left({\mathrm{\&delta;}}_2\right)\\ s_0+{\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="H201010013654XE00011.png"\; state="\{\{state\}\}">s</figure-callout>}}_1\cos \left({\mathrm{\&delta;}}_2\right)+{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="H201010013654XE00011.png"\; state="\{\{state\}\}">s</figure-callout>}}_2\sin \left({\mathrm{\&delta;}}_1\right)\sin \left({\mathrm{\&delta;}}_2\right)-{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="H201010013654XE00011.png,H201010013654XE00012.png"\; state="\{\{state\}\}">s</figure-callout>}}_3\cos \left({\mathrm{\&delta;}}_1\right)\sin \left({\mathrm{\&delta;}}_2\right)\\ 0\\ 0\end{array}\right)---\left(3\right)$

Because detector itself only has response to light intensity signal, and polarization state is not had response, the signal that detector receives is the whole intensity that see through the light of linear polarizer, corresponding to first element of output Stokes vector.Therefore, the light intensity that detector receives is the function of wave number σ, as shown in the formula.

2I(σ)＝s ₀+s ₁cos(δ ₂)+s ₂sin(δ ₁)sin(δ ₂)-s ₃cos(δ ₁)sin(δ ₂)(4)

Above-mentioned equation has been described the Polarization Modulation module will modulate the into mechanism of spectrometer output spectrum with the full stokes component that wave number changes.

Adopt Eulerian equation e ^Ix=cosx+isinx makes amendment to above-mentioned equation, can get:

$I\left(\mathrm{\&sigma;}\right)=\frac{1}{2}{s}_0+\frac{1}{4}{s}_1(e^{i{\mathrm{\&delta;}}_2}+e^{-i{\mathrm{\&delta;}}_2})+\frac{1}{8}[(s_2-{\mathrm{is}}_3)e^{i({\mathrm{\&delta;}}_2+{\mathrm{\&delta;}}_1)}+$

$({\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="H201010013654XE00011.png"\; state="\{\{state\}\}">s</figure-callout>}}_2+{\mathrm{is}}_3)e^{-i({\mathrm{\&delta;}}_2+{\mathrm{\&delta;}}_1)}+({-s}_2-{\mathrm{is}}_3)e^{i({\mathrm{\&delta;}}_2-{\mathrm{\&delta;}}_1)}+({-\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="H201010013654XE00011.png"\; state="\{\{state\}\}">s</figure-callout>}}_2+{\mathrm{is}}_3)e^{-i({\mathrm{\&delta;}}_2-{\mathrm{\&delta;}}_1)}]---\left(5\right)$

By formula (5) as can be known the intensity that receives of detector include 7 different frequency components based on delayer: 0, ± δ ₂, ± (δ ₂+ δ ₁) and ± (δ ₂-δ ₁).If two detectors adopt same material, when the thickness of second phase delay device 4 was the twice of first phase delay device 3, so above-mentioned seven frequency channels will uniformly-spaced separate.Carry out Fourier transform by the intensity spectrum that spectrometer is collected and to obtain seven separated frequency channels.Each passage is separated, can reach s through inverse Fourier transform ₀(σ), s ₁(σ), s ₂(σ) and s ₃(σ).

Claims (8)

1. static full Stokes imaging spectral polarimeter based on the liquid crystal tunable optical filter, comprise preposition optical system, collimating mirror and be in liquid crystal tunable optical filter on the same optical axis with preposition optical system and collimating mirror, it is characterized in that: described static full Stokes imaging spectral polarimeter based on the liquid crystal tunable optical filter also comprises the phase modulation (PM) module; Described phase modulation (PM) module places between collimating mirror and the liquid crystal tunable optical filter and with collimating mirror and liquid crystal tunable optical filter and is on the same optical axis.

2. the static full Stokes imaging spectral polarimeter based on the liquid crystal tunable optical filter according to claim 1, it is characterized in that: described phase modulation (PM) module comprises first phase delay device and second phase delay device, and described first phase delay device and second phase delay device bond together.

3. the static full Stokes imaging spectral polarimeter based on the liquid crystal tunable optical filter according to claim 1, it is characterized in that: described phase modulation (PM) module comprises first phase delay device and second phase delay device, and described first phase delay device and second phase delay device are successively set between collimating mirror and the liquid crystal tunable optical filtering.

4. according to claim 2 or 3 described static full Stokes imaging spectral polarimeters based on the liquid crystal tunable optical filter, it is characterized in that: the plane that the fast axle and the slow axis of described first phase delay device formed and the fast axle of second phase delay device are vertical with systematic optical axis respectively with the plane that slow axis is formed.

5. the static full Stokes imaging spectral polarimeter based on the liquid crystal tunable optical filter according to claim 4, it is characterized in that: the quick shaft direction of described first phase delay device is identical with the analyzer polarization direction of liquid crystal tunable optical filter; The angle of the quick shaft direction of the quick shaft direction of described second phase delay device and first phase delay device is 45 °.

6. the static full Stokes imaging spectral polarimeter based on the liquid crystal tunable optical filter according to claim 5, it is characterized in that: described first phase delay device and second phase delay device all are by the single axial birefringence crystalline material.

7. the static full Stokes imaging spectral polarimeter based on the liquid crystal tunable optical filter according to claim 6, it is characterized in that: described first phase delay device and second phase delay device are to be made by kalzit or quartz.

8. the static full Stokes imaging spectral polarimeter based on the liquid crystal tunable optical filter according to claim 1, it is characterized in that: the model of described liquid crystal tunable optical filter is VariSpec VISR type or VariSpec NIRR type.

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