CN104931234A - Device for precisely calibrating inclined angle between wave plate and polaroid, and calibration method - Google Patents

Abstract

The invention discloses a device for precisely calibrating an inclined angle between a wave plate and a polaroid, and a calibration method. Based on Fourier series relation between light intensity of a target scene and a direction angle of a polarization device in a polarization imaging test, the method employs a rotatable linear polaroid and a polarization imaging device. The rotatable linear polaroid is driven by a stepping motor to rotate. The polarization imaging device consists of a rotatable phase delayer and a fixed linear polaroid. A to-be-measured light beam is transmitted to the linear polaroid, thereby forming linear polarized light. The linear polarized light passes through the polarization imaging device, and a target image containing a group of polarization state information on a target surface of an imaging detector. The stepping motor drives the linear polaroid to rotate continuously for one circle, and the information of light intensity of the target scene is detected continuously. Finally, the direction angle of the polarization device is calibrated through matrix multiplication, Fourier integration and trigonometric function operation. According to the invention, the precision is high, the device is simple, and the operation is easy.

Description

The device of a kind of Accurate Calibration wave plate and polaroid angle and scaling method

Technical field

The invention belongs to optical device and demarcate field, be specifically related to device and the scaling method of a kind of Accurate Calibration wave plate and polaroid angle, the deflection of polarizer can be gone out by Accurate Calibration, be applicable to polarization imaging experiment.

Background technology

Polarization imaging is a kind of technology detecting scenery optical polarization.This technology not only can obtain the intensity signal of target, can also obtain the information such as frequency, amplitude, degree of polarization and polarization angle, improve the recognition capability of target.In recent years, polarization imaging technology has become the domestic focus for research, and is applied to numerous areas, as fields such as military surveillance, environmental monitoring and biomedicines.

Wave plate, as phase delay device, is most basic a kind of optical component in modern polarization imaging technology, is widely used.In polarization imaging, for obtaining four whole Stokes (Stokes) vectors of light wave, need to introduce wave plate and polaroid, and the Accurate Calibration of the fast axle of wave plate and polaroid light transmission shaft deflection, be one of key factor guaranteeing polarization information detected with high accuracy.At present, the main method of demarcating wave plate quick shaft direction has tower to pause method of inspection, right-angle prism method, Fresnel rib body method, minimax photon flux method, heterodyne interferometry and second harmonic extremum method etc.

In said method, the tower method of inspection that pauses can only detect mica waveplate, does not possess general applicability; Right-angle prism method first need be found out wave plate optical axis direction and could demarcate further; Fresnel rib body method and minimax photon flux method require very high to detector sensitivity; Difference interference complex structure, data handling procedure is loaded down with trivial details; Second harmonic extremum method precision is lower.

Summary of the invention

The object of the present invention is to provide device and the scaling method of a kind of Accurate Calibration wave plate and polaroid angle, achieve in polarization experiment, the Accurate Calibration of wave plate quick shaft direction and polaroid light transmission shaft angular separation.

The technical solution realizing the object of the invention is: the device of a kind of Accurate Calibration wave plate and polaroid angle and scaling method, comprises rotatable linear polarizer and polarization imaging device that same optical axis arranges in turn; Wherein rotatable linear polarizer is by stepper motor driven rotary; Polarization imaging device comprises the rotatable phase delay device set gradually along optical path direction, fixing linear polarizer and imaging detector.From the incident light of target each point to be measured through rotatable linear polarizer, form a branch of linearly polarized light, arrive polarized imaging system, form the emergent light carrying one group of polarization state information, and on the target surface of imaging detector, obtain the image that a group is carried target scene polarization information.

The device of Accurate Calibration wave plate and polaroid angle and a scaling method, comprise the following steps:

The first step, places rotatable linear polarizer, rotatable phase delay device, fixing linear polarizer and imaging detector successively by optical axis direction, and now the quick shaft direction of phase delay device and the light transmission shaft direction of linear polarizer exist angle α;

Second step, drives linear polarizer continuous rotation one week by stepper motor, the light intensity I of continuous probe target scene while of imaging detector;

3rd step, according to the above-mentioned light intensity I detected, determines the size of α, completes the Accurate Calibration to wave plate and polaroid angle.

In above-mentioned second step, light intensity I:

I=S ₀+S ₀cos ²2αcos2θ+S ₀sin2αcos2αsin2θ

In above formula, S ₀first parameter of incident light Stokes polarization information; α is the quick shaft direction of phase delay device and the axial angle of printing opacity of fixing linear polarizer, and θ is the printing opacity axial angle of light transmission shaft direction relative to fixing linear polarizer of rotatable linear polarizer.

In 3rd step, determine that the step of α is as follows:

I=S ₀+S ₀cos ²2αcos2θ+S ₀sin2αcos2αsin2θ

Can find, I is the Fourier series of θ, and progression n=2,

Make a _n=S ₀cos ²2 α, b _n=S ₀sin2 α cos2 α, then

I=S ₀+a _ncos2θ+b _nsin2θ

$a_n=\frac{1}{\mathrm{\π}}{\∫}_0^{2\mathrm{\π}}I\cos 2\mathrm{\θd\θ}$

$b_n=\frac{1}{\mathrm{\π}}{\∫}_0^{2\mathrm{\π}}I\sin 2\mathrm{\θd\θ}$

$\tan 2\mathrm{\α}=\frac{b_n}{a_n}$

By inverse trigonometric function, α can be obtained, i.e. the quick shaft direction of phase delay device and the axial angle of printing opacity of fixing linear polarizer.

Compared with prior art, its remarkable advantage: 1) without the need to independently light channel structure, is applicable to polarization imaging experiment in the present invention.

2) structure is simple, and be easy to operation, precision is high, can the small angle of Accurate Calibration.

Accompanying drawing explanation

Fig. 1 is light path principle figure of the present invention.

Fig. 2 is process flow diagram of the present invention

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in further detail.

Composition graphs 1 and Fig. 2, the present invention is device and the scaling method of a kind of Accurate Calibration wave plate and polaroid angle, and experimental provision comprises the rotatable linear polarizer 1 and polarization imaging device 2 that same optical axis arranges in turn; Wherein rotatable linear polarizer 1 is by stepper motor driven rotary; Polarization imaging device 2 comprises the rotatable phase delay device 21 set gradually along optical path direction, fixing linear polarizer 22 and imaging detector 23.

A scaling method for the device of Accurate Calibration wave plate and polaroid angle, to demarcate small angle α (0< α <5 °), step is as follows:

The first step, place rotatable linear polarizer 1, fixing linear polarizer 22 and imaging detector 23 successively by optical axis direction, rotational line polaroid 1 is to extinction position;

Second step, between rotatable linear polarizer 1 and fixing linear polarizer 22, add rotatable phase delay device 21, rotatable phase delayer 21, the light intensity that detector is detected is minimum.Now, there is a small angle α in the quick shaft direction of phase delay device 21 and the light transmission shaft direction of linear polarizer 22;

3rd step, drives linear polarizer 1 continuous rotation one week by stepper motor, the light intensity I of continuous probe target scene while of imaging detector 23;

4th step, according to the above-mentioned light intensity I detected, determines the size of α, completes the Accurate Calibration to wave plate and polaroid angle.

A branch of incident light from target each point to be measured is through rotatable linear polarizer 1, form a branch of linearly polarized light, arrive polarized imaging system 2, form the emergent light carrying one group of polarization state information, and on the target surface of imaging detector 23, obtain the image that a group is carried target scene polarization information.

The linearly polarized light that incident light is formed after rotatable linear polarizer 1, its Stokes vector can be expressed as by Muller matrix:

S _in(S ₀,S ₁,S ₂,S ₃)=(S ₀,S ₀cos2θ,S ₀sin2θ,0) ^T

In above formula, S _in(S ₀, S ₁, S ₂, S ₃) be the Stokes vector of incident light, be one group of parameter representing the polarization state information of incident light.S ₀first parameter of incident light Stokes polarization information; θ is the printing opacity axial angle of light transmission shaft direction relative to fixing linear polarizer of rotatable linear polarizer.

This linearly polarized light through the Stokes vector of the emergent light of polarization imaging device is:

S _out(S' ₀,S ₁',S' ₂,S ₃')=M ₂₂(0°)·M ₂₁(α,90°)·S _in（S ₀,S ₀cos2θ,S ₀sin2θ,0) ^T

In above formula, S _out(S' ₀, S ₁', S' ₂, S ₃') be one group of Stokes polarization information, wherein S' representing emergent light ₀equal the size of the light intensity I detected, M ₂₂(0 °) is the Muller matrix of fixing linear polarizer, M ₂₁(α, 90 °) are the Muller matrixes of phase delay device, i.e. the Muller matrix of quarter wave plate, and α is the quick shaft direction of phase delay device and the axial angle of printing opacity of fixing linear polarizer.

By matrix multiple, can draw:

$\left(\begin{array}{c}{S}_0^{\&prime;}\\ S_1^{\&prime;}\\ S_2^{\&prime;}\\ S_3^{\&prime;}\end{array}\right)=\left[\begin{array}{cccc}1& {\cos }^{2}2\mathrm{\&alpha;}& \sin 2\mathrm{\&alpha;}\cos 2\mathrm{\&alpha;}& -\sin 2\mathrm{\&alpha;}\\ 0& {\cos }^{2}2\mathrm{\&alpha;}& \sin 2\mathrm{\&alpha;}\cos 2\mathrm{\&alpha;}& -\sin 2\mathrm{\&alpha;}\\ 0& 0& 0& 0\\ 0& 0& 0& 0\end{array}\right]\&CenterDot;\left(\begin{array}{c}{S}_0\\ S_0\cos 2\mathrm{\&theta;}\\ S_0\sin 2\mathrm{\&theta;}\\ 0\end{array}\right),---\left(3\right)$

Matrix the first row is mutually multiplied:

I=S ₀+S ₀cos ²2αcos2θ+S ₀sin2αcos2αsin2θ， (4)

Can find, I is the Fourier series of θ, and progression n=2,

Make a _n=S ₀cos ²2 α, b _n=S ₀sin2 α cos2 α, then

I=S ₀+a _ncos2θ+b _nsin2θ， (5)

$a_n=\frac{1}{\mathrm{\&pi;}}{\&Integral;}_0^{2\mathrm{\&pi;}}I\cos 2\mathrm{\&theta;d\&theta;},---\left(6\right)$

$b_n=\frac{1}{\mathrm{\&pi;}}{\&Integral;}_0^{2\mathrm{\&pi;}}I\sin 2\mathrm{\&theta;d\&theta;},---\left(7\right)$

$\tan 2\mathrm{\&alpha;}=\frac{b_n}{a_n},---\left(8\right)$

By inverse trigonometric function, α can be obtained, i.e. the fast axle of quarter wave plate and the angle of polaroid 2 light transmission shaft.The present invention can go out the deflection of polarizer by Accurate Calibration, and structure is simple, is easy to operation, and without the need to independently light channel structure, is applicable to polarization imaging experiment.

Claims (5)

1. a device for Accurate Calibration wave plate and polaroid angle, is characterized in that: comprise rotatable linear polarizer (1) and polarization imaging device (2) that same optical axis arranges in turn; Wherein rotatable linear polarizer (1) is by stepper motor driven rotary; Polarization imaging device (2) comprises the rotatable phase delay device (21) set gradually along optical path direction, fixing linear polarizer (22) and imaging detector (23); Incident light from target each point to be measured enters rotatable linear polarizer (1), form a branch of linearly polarized light, enter into polarized imaging system (2), form the emergent light carrying one group of polarization state information, and on the target surface of imaging detector (23), obtain the image that a group is carried target scene polarization information.

2. the device of Accurate Calibration wave plate according to claim 1 and polaroid angle, it is characterized in that: the rotatable phase delay device (21) in polarization imaging device, fixing linear polarizer (22) and imaging detector (23) and rotatable linear polarizer (1) common optical axis, phase delay device (21) selects quarter wave plate.

3., based on the scaling method of the device of Accurate Calibration wave plate according to claim 1 and polaroid angle, it is characterized in that, comprise the following steps:

The first step, place rotatable linear polarizer (1), rotatable phase delay device (21), fixing linear polarizer (22) and imaging detector (23) successively by optical axis direction, now there is angle α in the quick shaft direction of phase delay device (21) and the light transmission shaft direction of linear polarizer (22);

Second step, drives linear polarizer (1) continuous rotation one week by stepper motor, the light intensity I of continuous probe target scene while of imaging detector (23);

3rd step, according to the above-mentioned light intensity I detected, determines the size of α, completes the Accurate Calibration to wave plate and polaroid angle.

4. the scaling method of the device of Accurate Calibration wave plate according to claim 3 and polaroid angle, is characterized in that: the light intensity I in second step:

I=S ₀+S ₀cos ²2αcos2θ+S ₀sin2αcos2αsin2θ

In above formula, S ₀first parameter of incident light Stokes polarization information; α is the quick shaft direction of phase delay device (21) and the axial angle of printing opacity of linear polarizer (22), and θ is the printing opacity axial angle of light transmission shaft direction relative to linear polarizer (22) of linear polarizer (1).

5. the scaling method of the Accurate Calibration wave plate according to claim 3 or 4 and the device of polaroid angle, is characterized in that: in the 3rd step, determines that the step of α is as follows:

Fourier integral and trigonometric function operation are carried out to light intensity I:

I=S ₀+S ₀cos ²2αcos2θ+S ₀sin2αcos2αsin2θ

I is the Fourier series of θ, and progression n=2

Make a _n=S ₀cos ²2 α, b _n=S ₀sin2 α cos2 α, then

I=S ₀+a _ncos2θ+b _nsin2θ

$a_n=\frac{1}{\mathrm{\&pi;}}{\&Integral;}_0^{2\mathrm{\&pi;}}I\cos 2\mathrm{\&theta;d\&theta;}$

$b_n=\frac{1}{\mathrm{\&pi;}}{\&Integral;}_0^{2\mathrm{\&pi;}}I\sin 2\mathrm{\&theta;d\&theta;}$

$\tan 2\mathrm{\&alpha;}=\frac{b_n}{a_n}$

By inverse trigonometric function, α can be drawn, i.e. the quick shaft direction of phase delay device (21) and the axial angle of printing opacity of linear polarizer (22).