CN103712781A - Device and method for measuring multi-incidence-angle polarization interference in birefringence optical wedge optical axis direction - Google Patents

Abstract

The invention discloses a device and method for measuring multi-incidence-angle polarization interference in the birefringence optical wedge optical axis direction. The device comprises a laser source (1), an optical attenuator (2), a beam expanding mirror (3), a polarizer (4), a birefringence optical wedge (5), a sample testing platform (6), a polarization detecting device (7), an area array detector (8) and a signal processing system (9). Compared with the prior art, the device has the advantages that the three-dimensional direction measuring can be fast carried out on the birefringence optical wedge optical axis by collecting three polarization interference patterns under different incident angles, the problem that there is no system or method for measuring the birefringence optical wedge optical axis at present is solved. The measuring precision can be further improved by adding the number of times of adjusting the incident angles. The device and method are suitable for traditional birefringence test pieces with the incident plane being parallel to the emitting plane as well, the error range is small, the measuring precision can be guaranteed, and therefore the device and method are wide in application range.

Description

Multiple angles of incidence polarization interference measurement mechanism and the method for birefringent wedge optical axis direction

Technical field

The present invention relates to birefringece crystal parameter detecting field, particularly relate to a kind of multiple angles of incidence polarization interference measurement mechanism of birefringent wedge optical axis direction.

Background technology

The optical axis of crystal is the important optical parametric of crystal, and its difference with respect to the three-dimensional of quartz crystal device incidence surface can affect quartz crystal device performance, therefore the detection technique of optical axis of crystal three-dimensional is seemed to extremely important.

In definite optical axis of crystal direction, some measuring methods have been there are at present.M.Laue(FriedrichW, Knipping P, LaueM.Interference appearances in x-rays[J] .Ann.Phys. (Berlin), 1913,41:971-988.) optical axis of crystal direction X-ray diffraction method that proposes, measuring accuracy is high, but method is complicated, and need to know in advance the structural parameters of this crystal and the corresponding relation of crystal face and diffraction peak; (the Zhang Yi such as Zhang Yi, Shen Weimin. the theoretical and experimental study of uniaxial crystal conoscopic interference [J]. journal of Zhejiang university (report of science), 2005,32 (4): 403-406.) utilize the polarization interference figure of crystal to determine optical axis of crystal direction, crystal polarization interference figure gathers by polarizing microscope, according to optical axis dew point (being the point that is parallel to refracted ray correspondence in interferogram of optical axis direction in crystal, namely black cross intersection point), with respect to the position at ken center, measure optical axis direction; D.Su (Su D C, HsuCC.Method for determining the optical axis and (no, ne) of a birefringent crystal[J] .Applied optics, 2002,41 (19): 3936-3940.) etc. a kind of interference with common path type of employing process of heterodyning is measured optical axis direction; (the Duan Cunli such as Duan Cunli, Han Jun, Lu Shaojun, Deng. based on Huygens' principle, determine the new method research [J] of uniaxial crystal optical axis direction. optical instrument, 2008,30 (4): 55-59.) adopt Huygens' principle to analyze light wave propagation direction, the relational expression according to optical axis and plane of crystal normal, realizes the measurement of optical axis of crystal direction; Shen Weimin etc. (Lie group, waits .CCD image method to measure optical axis of crystal direction [J] for Shen Weimin, Li Weitao. semiconductor optoelectronic, 2006,27 (4): 485-488.) judge that plane of crystal normal carries out the measurement of optical axis direction; Xing Jinhua etc. (Xing Jinhua. with Brewster horn cupping, measure refractive index and the optical axis direction [J] of uniaxial crystal simultaneously. College Physics, 2004,23 (6): the optical axis direction of 49-50.) determining uniaxial crystal by measuring three surperficial Brewster angles of crystal prototype.

Said method is normally measured being processed into the optical axis direction of standard specimen, requires the plane of incidence of test specimen and exit facet to be parallel to each other to guarantee that o light and e light two emergent light exit directions are parallel to each other, and requires test specimen o light and e light to have large refringence.And the plane of incidence of birefringent wedge and exit facet exist angle, this causes two emergent lights (o light and e light) not parallel, and two-beam refringence is less, is not easily distinguishable out, and this all brings difficulty to the measurement of birefringent wedge optical axis three-dimensional.The present invention is intended to overcome above-mentioned difficulties, realizes the three-dimensional of birefringent wedge optical axis is accurately measured.

Summary of the invention

The problem existing in order to overcome prior art, the present invention is directed to above deficiency, multiple angles of incidence polarization interference measurement mechanism and the method for birefringent wedge optical axis direction have been proposed, be used for the measurement of the three-dimensional of birefringent wedge optical axis, also can measure for the Axis Azimuth of other birefringence devices simultaneously.

The present invention proposes a kind of multiple angles of incidence polarization interference measurement mechanism of birefringent wedge optical axis direction, this device comprises LASER Light Source (1), optical attenuator (2), beam expanding lens (3), the polarizer (4), birefringent wedge (5), sample test platform (6), analyzer (7), planar array detector (8) and signal processing system (9) wherein:

LASER Light Source (1), for the input light source of this device is provided, adopts the good visible light wave range laser instrument of spatial coherence, comprises He-Ne laser instrument and semiconductor laser;

Optical attenuator (2), for reducing laser energy, controls LASER Light Source power stability, avoids planar array detector saturated;

Beam expanding lens (3), for laser beam expanding, guarantees the parallel outgoing of LASER Light Source, obtains the spatial coherence laser facula that covers birefringent wedge lateral dimension;

The polarizer (4), does up partially for laser light, and light transmission shaft direction and horizontal reference are at 45 °;

Sample test platform (6), for placing birefringent wedge to be measured (5) and controlling birefringent wedge incident angle, test board can, around the axle rotation vertical with placing its plane, be realized at least three kinds of different angles and be incident to birefringent wedge surface generation polarization interference;

Analyzer (7), for realizing polarization interference, light transmission shaft direction and horizontal reference are at 45 °, simultaneously perpendicular with the polarizer or parallel;

Planar array detector (8), comprises CCD and cmos detector, for receiving polarization interference figure signal; And

Signal processing system (9), comprises image pick-up card and computing machine, and for gathering polarization interference figure signal, computing machine is processed according to Measurement Algorithm, calculates birefringent wedge optical axis three-dimensional;

The parallel incident of LASER Light Source (1) Output of laser, when optical attenuator (2) reduces laser energy, controls laser power stability and avoids detector saturated, beam expanding lens (3) expands laser, obtain the spatial coherence laser facula that covers birefringent wedge lateral dimension, through polarizer (4), rise partially, light transmission shaft direction and horizontal reference are at 45 °, at the tested birefringent wedge 5 of the upper placement of sample test platform (6), by regulating sample test platform (6), rotation birefringent wedge (5), thereby realize different angles incident wedge surface and produce polarization interference, by the light beam after birefringent wedge (5), after analyzer (7), realize polarized light interference, adopt planar array detector (8) receive polarization interference figure and be passed in signal processing system 9.

The multiple angles of incidence polarization interference measuring method that the invention allows for a kind of birefringent wedge optical axis direction, the method comprises the following steps:

The parallel incident of LASER Light Source (1) Output of laser, when optical attenuator (2) reduces laser energy, controls laser power stability and avoids detector saturated, beam expanding lens (3) expands laser, obtain the spatial coherence laser facula that covers birefringent wedge lateral dimension, through polarizer (4), rise partially, light transmission shaft direction and horizontal reference are at 45 °, at the upper tested birefringent wedge (5) of placing of sample test platform (6), by regulating sample test platform (6), rotation birefringent wedge (5), thereby realize different angles incident wedge surface and produce polarization interference, by the light beam after birefringent wedge (5), after analyzer (7), realize polarized light interference, adopt planar array detector (8) receive polarization interference figure and be passed in signal processing system (9), under each incident angle, record a width polarization interference figure, when collecting the polarization interference figure of three different incidence angles, in signal processing system (9), polarization interference signal is carried out to greyscale transformation and hough conversion process, extract the bright fringes of polarization interference figure, calculate interference fringe spacing, by the simultaneous optical path difference system of equations of three angle incidents formations, solve the three-dimensional of birefringent wedge optical axis,

The process that described birefringent wedge forms simultaneous optical path difference system of equations by three angle incidents is as follows:

Set up adjacent bright fringe spacing h and crystal wedge surface thickness t corresponding relation formula:

Adjacent bright striped optical path difference δ Δ=λ in polarization interference, thus polarization interference light adjacent stripes optical path difference δ Δ formula obtained:

$\mathrm{\δ\Δ}=\mathrm{\δd}\·n_{\mathrm{re}}-\sin \mathrm{\θ}({\mathrm{\δx}}_e-{\mathrm{\δz}}_e\tan {\mathrm{\θ}}_{\mathrm{ro}})-n_o\frac{{\mathrm{\δz}}_e}{\cos {\mathrm{\θ}}_{\mathrm{ro}}}=\mathrm{\λ}---\left(1\right)$

In formula (1), θ is incident angle, n _refor the refractive index of e light light on its direction of propagation; θ _roangle for o light light and plane of crystal normal; δ d is the path length difference that adjacent e light is propagated in birefringent wedge; δ x _efor the propagation difference of adjacent e light on x direction of principal axis; δ z _efor the propagation difference of adjacent e light on z direction of principal axis;

When incidence angle θ is constant, n _re, θ _roconstant, only have δ d, δ x _e, δ z _echange.

Choose 0 °, 30 °, 45 ° three different incidence angles, obtain system of equations:

$\left\{\begin{array}{c}{\mathrm{\&delta;\&Delta;}}_1={\mathrm{\&delta;<figure-callout\; id="1"\; label="d"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">d</figure-callout>}}_1\&CenterDot;n_{\mathrm{re}1}-{\mathrm{\&delta;x}}_{e1}-n_o{\mathrm{\&delta;<figure-callout\; id="1"\; label="z\; e"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">z</figure-callout>}}_e=\mathrm{\&lambda;}\\ {\mathrm{\&delta;\&Delta;}}_2={\mathrm{\&delta;<figure-callout\; id="2"\; label="d"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">d</figure-callout>}}_2\&CenterDot;n_{\mathrm{re}2}-\frac{1}{2}({\mathrm{\&delta;x}}_{e2}-0.39{\mathrm{\&delta;z}}_{e2})-n_0{\mathrm{\&delta;<figure-callout\; id="2"\; label="z\; e"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">z</figure-callout>}}_e=\mathrm{\&lambda;}\\ {\mathrm{\&delta;\&Delta;}}_3={\mathrm{\&delta;<figure-callout\; id="3"\; label="d"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">d</figure-callout>}}_3\&CenterDot;n_{\mathrm{re}3}-\frac{\sqrt{2}}{2}({\mathrm{\&delta;x}}_{e3}-0.514{\mathrm{\&delta;z}}_{e3})-n_o{\mathrm{\&delta;<figure-callout\; id="3"\; label="z\; e"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">z</figure-callout>}}_e=\mathrm{\&lambda;}\end{array}\right.---\left(2\right)$

And

In formula (3),

be respectively wedge surface and x, y, z axle angle, α, β, γ be birefringent wedge optical axis and x, y, z axle angle, θ _kefor the angle of e light light wave vector and plane of crystal normal, M ₁, M ₂for corresponding coefficient.

Compared with prior art, the present invention has following good effect:

1. multiple angles of incidence polarization interference measurement mechanism and the method for birefringent wedge optical axis direction have been proposed, by gathering the polarization interference figure under three width different incidence angles degree, can realize rapidly the three-dimensional of birefringent wedge optical axis and measure, overcome a difficult problem that in the past there is no birefringent wedge optical axis measuring system and method;

2. propose multiple angles of incidence polarization interference measurement mechanism and the method for birefringent wedge optical axis direction, can further improve measuring accuracy by increasing the number of incident angle adjustment;

3. the measurement mechanism proposing and method are applicable to traditional plane of incidence birefringence test specimen parallel with exit plane equally, therefore adapt to wide.

Accompanying drawing explanation

Fig. 1 is the measuring system schematic diagram of birefringent wedge optical axis direction in the present invention;

Fig. 2 gathers polarization interference and reduction polarization interference comparison diagram;

Fig. 3 is the polarization direction schematic diagram that produces polarization interference after birefringent wedge;

Fig. 4 is two-beam interference intensity distributions contrast schematic diagram;

In figure, 1, He-Ne laser instrument, 2, optical attenuator, 3, beam expanding lens, 4, the polarizer, 5, birefringent wedge, 6, sample test platform, 7, analyzer, 8, planar array detector, 9, signal processing system, 10 gather polarization interference figure, 11, reduction polarization interference figure, 12, polarizer light transmission shaft direction, 13, birefringent wedge optical axis direction, 14, analyzer light transmission shaft direction, 15, o light amplitude after incident wedge, 16, o light is by the projection amplitude of analyzer, 17, the amplitude of incident light, 18, e light amplitude after incident wedge, 19, e light is by the projection amplitude of analyzer, 20, the angle of birefringent wedge optical axis deviation y axle, 21, two polarizers are assembled joining true origin, 22, angle between polarizer optical axis direction and coordinate axis x, 23, angle between analyzer optical axis direction and coordinate axis x, 24 polarization interference normalized intensity variation delta I, 25, the variation delta x of the wedge position that low coherence interference striped peak value is corresponding.

Embodiment

Below in conjunction with drawings and Examples, further describe the specific embodiment of the present invention.

Embodiment 1: the multiple angles of incidence polarization interference measurement mechanism of birefringent wedge optical axis direction and method implementation process

As shown in Figure 1, the present invention takes multiple angles of incidence polarization interference figure to realize the measurement of birefringent wedge optical axis direction, and measurement mechanism is comprised of LASER Light Source (1), optical attenuator (2), beam expanding lens (3), the polarizer (4), sample test platform (6), analyzer (7), planar array detector (8) and signal processing system (9).

He-Ne laser instrument (1) Output of laser, parallel incident, when optical attenuator (2) reduces laser energy, is controlled laser power stability and is avoided detector saturated, beam expanding lens (3) expands laser, obtain the spatial coherence laser facula that covers birefringent wedge lateral dimension, through polarizer (4), rise partially, polarization direction is from the horizontal by 45 °, at the upper tested birefringent wedge (5) of placing of sample test platform (6), by regulating sample test platform, thereby rotation birefringent wedge is realized different angles and is incident to wedge surface generation polarization interference, by the light beam after birefringent wedge, after analyzer (7), realize polarized light interference, adopt planar array detector (8) receive polarization interference figure and be passed in signal processing system (9), under each incident angle, record a width polarization interference figure, when collecting the polarization interference figure of three different incidence angles, in signal processing system, polarization interference signal is carried out to greyscale transformation and hough conversion process, extract the bright fringes of polarization interference figure, calculate interferogram fringe spacing, the simultaneous optical path difference system of equations forming by three angle incidents, solve the three-dimensional of birefringent wedge optical axis.

Embodiment 2: polarization interference figure fringe spacing leaching process specific embodiments

Take 0 °, 30 °, 45 ° three different angles to incide birefringent wedge surface, by planar array detector (8), gather polarization interference signal, extract interferogram fringe spacing.Leaching process is: first polarization interference figure is carried out to greyscale transformation, obtain gray-scale map; Again gray-scale map is carried out to hough conversion, extract the bright fringes of polarization interference figure.After hough conversion, read bright fringes and count the margin of image element p=p1-p2 between N, according to each pixel size ε of planar array detector, calculating interference fringe spacing is h=ε p/N=ε (p ₁-p ₂)/N.

Embodiment 3:: the detailed process that birefringent wedge optical axis direction solves

After interference fringe spacing is extracted, the expression formula of theoretical analysis different angles incident light path difference, adjacent bright fringe spacing h and crystal wedge surface thickness difference t corresponding relation formula are

and adjacent bright striped optical path difference is δ Δ=λ; Therefore polarization interference signal adjacent stripes optical path difference formula is:

$\mathrm{\&delta;\&Delta;}=\mathrm{\&delta;d}\&CenterDot;n_{\mathrm{re}}-\sin \mathrm{\&theta;}({\mathrm{\&delta;x}}_e-{\mathrm{\&delta;z}}_e\tan {\mathrm{\&theta;}}_{\mathrm{ro}})-n_o\frac{{\mathrm{\&delta;z}}_e}{\cos {\mathrm{\&theta;}}_{\mathrm{ro}}}=\mathrm{\&lambda;}---\left(1\right)$

In formula, θ is incident angle, n _refor the refractive index of e light light on its direction of propagation; θ _roangle for o light light and plane of crystal normal; δ d is the path length difference that adjacent e light is propagated in birefringent wedge; δ x _efor the propagation difference of adjacent e light on x direction of principal axis; δ z _ethe propagation difference of adjacent e light on z direction of principal axis;

When incidence angle θ is constant, n _re, θ _roconstant, only have δ d, δ x _e, δ z _echange.

Choose 0 °, 30 °, 45 ° three different incidence angles, obtain system of equations:

$\left\{\begin{array}{c}{\mathrm{\&delta;\&Delta;}}_1={\mathrm{\&delta;<figure-callout\; id="1"\; label="d"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">d</figure-callout>}}_1\&CenterDot;n_{\mathrm{re}1}-{\mathrm{\&delta;x}}_{e1}-n_o{\mathrm{\&delta;<figure-callout\; id="1"\; label="z\; e"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">z</figure-callout>}}_e=\mathrm{\&lambda;}\\ {\mathrm{\&delta;\&Delta;}}_2={\mathrm{\&delta;<figure-callout\; id="2"\; label="d"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">d</figure-callout>}}_2\&CenterDot;n_{\mathrm{re}2}-\frac{1}{2}({\mathrm{\&delta;x}}_{e2}-0.39{\mathrm{\&delta;z}}_{e2})-n_0{\mathrm{\&delta;<figure-callout\; id="2"\; label="z\; e"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">z</figure-callout>}}_e=\mathrm{\&lambda;}\\ {\mathrm{\&delta;\&Delta;}}_3={\mathrm{\&delta;<figure-callout\; id="3"\; label="d"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">d</figure-callout>}}_3\&CenterDot;n_{\mathrm{re}3}-\frac{\sqrt{2}}{2}({\mathrm{\&delta;x}}_{e3}-0.514{\mathrm{\&delta;z}}_{e3})-n_o{\mathrm{\&delta;<figure-callout\; id="3"\; label="z\; e"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">z</figure-callout>}}_e=\mathrm{\&lambda;}\end{array}\right.---\left(2\right)$

And

In formula (3),

be respectively wedge surface and x, y, z axle angle, α, β, γ be birefringent wedge optical axis and x, y, z axle angle, θ _kefor the angle of e light light wave vector and plane of crystal normal, M ₁, M ₂for corresponding coefficient.

Solving equation group obtains solution of equations, i.e. birefringent wedge optical axis three-dimensional angle (α, β, γ).

Contrast with desired light direction of principal axis, optical axis direction angular error is controlled in 0.5 °, has guaranteed measuring accuracy.Fig. 3 is for gathering polarization interference and reduction polarization interference contrast schematic diagram.The polarization interference that wherein reduces is updated in the expression formula of optical path difference δ Δ by solving the optical axis three-dimensional angle [alpha], β, the γ that obtain, the optical path difference in communication process according to o light and e light, obtain reducing polarization interference light light intensity distributions, and contrast with collection polarization interference, show that measuring error scope is little, guaranteed measuring accuracy.

Embodiment 4: to the impact analysis of pressure demodulating system

In actual conditions, optical axis direction is not ideal situation when (being parallel to y direction of principal axis), there will be certain deflection angle β, and now polarized light interference figure as shown in Figure 4.

Now obtain e light and the o light projection amplitude on analyzer

with

wherein interference strength is:

$\begin{array}{c}I={|{\hat{E}}^{\&prime;}+{\hat{E}}^{\&prime;\&prime;}|}^2={\left|{\hat{E}}^{\&prime;}\right|}^2+{\left|{\hat{E}}^{\&prime;\&prime;}\right|}^2+2{\hat{E}}^{\&prime;}*{\hat{E}}^{\&prime;\&prime;}\\ =a^2\&CenterDot;{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">sin</figure-callout>}}^{2}2\mathrm{\&beta;}+a^2\&CenterDot;\mathrm{<figure-callout\; id="2"\; label="c\; os"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">c</figure-callout>}{\mathrm{os}}^{}{}^{2}2\mathrm{\&beta;}\&CenterDot;\left[\frac{1}{2}(1-\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">cos</figure-callout>}\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}\mathrm{\&Delta;})\right]\end{array}---\left(4\right)$

Correlation parameter is as follows: β=0.4 °

Centre wavelength: λ ₀=580nm, ν ₀=5.1724 * 10 ¹⁴hz

Bandwidth corresponding wavelength is: λ ₁=530nm, λ ₂=633nm, Δ ν=0.92167 * 10 ¹⁴hz

Wedge parameter: the angle of wedge long L=25mm, wide d ₁=3mm, d ₂=6.51mm

Only consider the actual contrast with ideal situation of mutual dry interference portion in two-beam interference, obtain the interference light intensity figure that receives by planar array detector in two situations, after normalization as shown in Figure 4.

The variation delta x25 of the wedge position that wherein, dry interference fringe peak value is corresponding mutually:

$\mathrm{\&Delta;x}=2l\&CenterDot;(\frac{1}{k}-\frac{1}{k^{\&prime;}})=0.776\mathrm{\&mu;m}---\left(5\right)$

In formula (5), l is long length, ideally coefficient of corresponding cavity

actual conditions k ' has light with deviation angle.

Mutual dry interference peak respective intensities variation delta I24:

$\mathrm{\&Delta;I}=\frac{1}{2}-\frac{1}{2}\&CenterDot;\frac{n}{m}=\frac{1}{2}(1-S)=1.9996\&times;{10}^{-4}---\left(6\right)$

In formula (6), $m={\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">sin</figure-callout>}}^{2}2\mathrm{\&beta;}+\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">cos</figure-callout>}}^{2}2\mathrm{\&beta;},$ $n=\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000446502700000011.png"\; state="\{\{state\}\}">cos</figure-callout>}}^{2}2\mathrm{\&beta;},$ S is the sensitivity of two-beam interference striped.According to analysis, variable quantity and the peak value respective intensities variable quantity of the wedge position that mutually dry interference fringe peak value is corresponding are all less, therefore when fleet angle β scope control is in 0.5 °, can ignore its impact on birefringent wedge demodulation, in pressure demodulating system, can not take in.

Claims (2)

1. the multiple angles of incidence polarization interference measurement mechanism of a birefringent wedge optical axis direction, it is characterized in that, this device comprises LASER Light Source (1), optical attenuator (2), beam expanding lens (3), the polarizer (4), birefringent wedge (5), sample test platform (6), analyzer (7), planar array detector (8) and signal processing system (9); Wherein:

LASER Light Source (1), for the input light source of this device is provided, adopts the good visible light wave range laser instrument of spatial coherence, comprises He-Ne laser instrument and semiconductor laser;

Optical attenuator (2), for reducing laser energy, controls LASER Light Source power stability, avoids planar array detector saturated;

Beam expanding lens (3), for laser beam expanding, guarantees the parallel outgoing of LASER Light Source, obtains the spatial coherence laser facula that covers birefringent wedge lateral dimension;

The polarizer (4), does up partially for laser light, and light transmission shaft direction and horizontal reference are at 45 °;

Sample test platform (6), for placing birefringent wedge to be measured (5) and controlling birefringent wedge incident angle, test board can, around the axle rotation vertical with placing its plane, be realized at least three kinds of different angles and be incident to birefringent wedge surface generation polarization interference;

Analyzer (7), for realizing polarization interference, light transmission shaft direction and horizontal reference are at 45 °, simultaneously perpendicular with the polarizer or parallel;

Planar array detector (8), comprises CCD and cmos detector, for receiving polarization interference figure signal;

Signal processing system (9), comprises image pick-up card and computing machine, and for gathering polarization interference figure signal, computing machine is processed according to Measurement Algorithm, calculates birefringent wedge optical axis three-dimensional;

The parallel incident of LASER Light Source (1) Output of laser, when optical attenuator (2) reduces laser energy, controls laser power stability and avoids detector saturated, beam expanding lens (3) expands laser, obtain the spatial coherence laser facula that covers birefringent wedge lateral dimension, through polarizer (4), rise partially, light transmission shaft direction and horizontal reference are at 45 °, at the tested birefringent wedge 5 of the upper placement of sample test platform (6), by regulating sample test platform (6), rotation birefringent wedge (5), thereby realize different angles incident wedge surface and produce polarization interference, by the light beam after birefringent wedge (5), after analyzer (7), realize polarized light interference, adopt planar array detector (8) receive polarization interference figure and be passed in signal processing system (9).

2. a multiple angles of incidence polarization interference measuring method for birefringent wedge optical axis direction, is characterized in that, the method comprises the following steps:

The parallel incident of LASER Light Source (1) Output of laser, when optical attenuator (2) reduces laser energy, controls laser power stability and avoids detector saturated, beam expanding lens (3) expands laser, obtain the spatial coherence laser facula that covers birefringent wedge lateral dimension, through polarizer (4), rise partially, light transmission shaft direction and horizontal reference are at 45 °, at the upper tested birefringent wedge (5) of placing of sample test platform (6), by regulating sample test platform (6), rotation birefringent wedge (5), thereby realize different angles incident wedge surface and produce polarization interference, by the light beam after birefringent wedge (5), after analyzer (7), realize polarized light interference, adopt planar array detector (8) receive polarization interference figure and be passed in signal processing system (9), under each incident angle, record a width polarization interference figure, when collecting the polarization interference figure of three different incidence angles, in signal processing system (9), polarization interference signal is carried out to greyscale transformation and hough conversion process, extract the bright fringes of polarization interference figure, calculate interference fringe spacing, by the simultaneous optical path difference system of equations of three angle incidents formations, solve the three-dimensional of birefringent wedge optical axis,

The process that described birefringent wedge forms simultaneous optical path difference system of equations by three angle incidents is as follows:

Set up adjacent bright fringe spacing h and crystal wedge surface thickness t corresponding relation formula:

Adjacent bright striped optical path difference δ Δ=λ in polarization interference, thus polarization interference light adjacent stripes optical path difference δ Δ formula obtained:

$\mathrm{\&delta;\&Delta;}=\mathrm{\&delta;d}\&CenterDot;n_{\mathrm{re}}-\sin \mathrm{\&theta;}({\mathrm{\&delta;x}}_e-{\mathrm{\&delta;z}}_e\tan {\mathrm{\&theta;}}_{\mathrm{ro}})-n_o\frac{{\mathrm{\&delta;z}}_e}{\cos {\mathrm{\&theta;}}_{\mathrm{ro}}}=\mathrm{\&lambda;}---\left(1\right)$

In formula (1), θ is incident angle, n _refor the refractive index of e light light on its direction of propagation; θ _roangle for o light light and plane of crystal normal; δ d is the path length difference that adjacent e light is propagated in birefringent wedge; δ x _efor the propagation difference of adjacent e light on x direction of principal axis; δ z _efor the propagation difference of adjacent e light on z direction of principal axis;

When incidence angle θ is constant, n _re, θ _roconstant, only have δ d, δ x _e, δ z _echange.

Choose 0 °, 30 °, 45 ° three different incidence angles, obtain system of equations:

$\left\{\begin{array}{c}{\mathrm{\&delta;\&Delta;}}_1={\mathrm{\&delta;d}}_1\&CenterDot;n_{\mathrm{re}1}-{\mathrm{\&delta;x}}_{e1}-n_o{\mathrm{\&delta;z}}_{e1}=\mathrm{\&lambda;}\\ {\mathrm{\&delta;\&Delta;}}_2={\mathrm{\&delta;d}}_2\&CenterDot;n_{\mathrm{re}2}-\frac{1}{2}({\mathrm{\&delta;x}}_{e2}-0.39{\mathrm{\&delta;z}}_{e2})-n_0{\mathrm{\&delta;z}}_{e2}=\mathrm{\&lambda;}\\ {\mathrm{\&delta;\&Delta;}}_3={\mathrm{\&delta;d}}_3\&CenterDot;n_{\mathrm{re}3}-\frac{\sqrt{2}}{2}({\mathrm{\&delta;x}}_{e3}-0.514{\mathrm{\&delta;z}}_{e3})-n_o{\mathrm{\&delta;z}}_{e3}=\mathrm{\&lambda;}\end{array}\right.---\left(2\right)$

And

In formula (3),

be respectively wedge surface and x, y, z axle angle, α, β, γ be birefringent wedge optical axis and x, y, z axle angle, θ _kefor the angle of e light light wave vector and plane of crystal normal, M ₁, M ₂for corresponding coefficient.

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