CN102494877B - Method for demodulating extinction ratio test data of polarizing device by white light interference method - Google Patents

Abstract

The invention discloses a method for demodulating extinction ratio test data of a polarizing device by a white light interference method. The method comprises the following steps: collecting an interference signal by a white light interference system so as to obtain voltage data V(t) which represents the interference signal; averaging V(t) at every N points to obtain new voltage data, wherein N is an integer and is greater than 0 and less than M, and M is a data size of V(t); carrying out wavelet denoising to obtain V0(t); calculating a polarization crosstalk intensity of V0(t) to obtain Vc(t); finding a threshold polarization crosstalk intensity a'th by a programmed algorithm; taking polarization crosstalk points which are greater than or equal to a'th in the Vc(t), utilizing the polarization crosstalk intensities of the points to obtain PER'', dividing the residual data points into data segments, and calculating a maximum polarization crosstalk intensity of each data segment to obtain PER0''; and at last, obtaining the extinction ratio of the polarizing device. According to the method provided by the invention, the characteristics of high white light interference precision and large dynamic range are used for detecting the small polarization crosstalk point and calculating the extinction ratio, so that the result is more precise. The threshold polarization crosstalk intensity is automatically selected according to the extinction ratio performance of the measured polarizing device, and the method has very strong self-adaptability, so that the test result is more reliable.

Description

Method for demodulating extinction ratio test data of polarizing device by white light interference method

Technical field

The present invention relates to the extinction ratio measuring technology of polarizer, relate in particular to a kind of self-adaptation polarizer extinction ratio test data demodulation method based on White Light Interferometer, belong to field of optical measuring technologies.

Background technology

Extinction ratio is the important indicator that tolerance polarizer (as waveguide, polarization maintaining optical fibre, polarization-maintaining fiber coupler, polarizer, prism, crystal) keeps polarisation of light state stability.The extinction ratio of polarizer is higher, and the ability of the maintenance polarization state that polarizer has had is described.Yet the impact due to the various internal and external factors such as internal residual stress, processing technology and external disturbance of polarizer, makes the extinction ratio of polarizer can not reach request for utilization, therefore to the extinction ratio of polarizer, need to make accurate test calibration.

The method of testing of extinction ratio mainly contains the direct method of measurement and polarized light interference method at present.The direct method of measurement is many to be risen partially and rotation analyzer based on the polarizer, by measuring polarizer light transmission shaft luminous energy P _yluminous energy P with non-light transmission shaft _xratio weigh its extinction ratio size, generally can be expressed as

directly measuring in the method for extinction ratio, conventionally need to use attenuator, and regulate frequently light path, tend to cause larger measuring error.If use highly sensitive photomultiplier to measure, also need effectively to suppress the interference of parasitic light, simultaneously owing to being subject to the impact of polarizer extinction ratio performance, theoretical measuring accuracy also only limits to 60dB.And polarized light interference rule can make full use of high spatial resolution and wide dynamic range that white light interference has advantages of, the polarization interference point that more accurate detecting polarization device inside exists.Just because of the high precision feature of white light interference, extinction ratio test macro based on White Light Interferometer can detect the very little polarization interference point in polarizer inside, and how to utilize these polarization interference points to calculate more accurately the extinction ratio of polarizer, need the intensity of the polarization interference point surveyed according to system, select a kind of extinction ratio calculating method with adaptivity.

The present invention is based on white light interference principle, collecting on the basis of all polarization interference point interference data, by data pre-service and self-adaptation extinction ratio algorithm, make extinction ratio measurement result more accurate.

Goal of the invention

The object of the invention is to solve the data demodulates problem that interferometric method is surveyed polarizer extinction ratio, a kind of extinction ratio test data demodulation method of the polarizer based on white light interference is provided, by the adaptive threshold polarization interference intensity proposing, carry out the extinction ratio of accurate Calculation polarizer, further improve precision and the fiduciary level of utilizing White Light Interferometer to measure polarizer extinction ratio.

The extinction ratio test of the polarizer based on white light interference that the present invention proposes, making full use of the feature that white light interference precision is high, dynamic range is large surveys the little polarization interference point of polarizer inside, and then calculate algorithm by data pre-service and self-adaptation extinction ratio, make test result more accurate, reliable.

Method for demodulating extinction ratio test data of polarizing device by white light interference method provided by the invention comprises:

1st, use the White Light Interferometer extinction ratio test macro shown in Fig. 2 to gather interference signal, test macro receives white light interference signal and carries out opto-electronic conversion with detector, obtain continuous analog electrical signal, after capture card sampling, quantification, obtain characterizing the discrete voltage data V(t of interference signal), as shown in Figure 3;

2nd, by the voltage data V(t gathering in the 1st step) carry out data pre-service;

2.1st, to voltage data V(t) in the every N of data point do average, the value of a point using the mean value obtaining as this N, in the random noise in effective erasure signal by N times of data volume M reduction, thereby obtain new voltage data

wherein N, M are integer, and 0<N<M, and M is V(t) data amount check; Note voltage data

data volume size be a, a=[M/N] represent M/N to round;

2.2nd, right

carry out Wavelet Denoising Method, on the basis of mean denoising, utilize the adaptivity of small echo to remove noise and retain useful signal, obtain voltage data V ₀(t);

Wherein the number of plies of Wavelet Denoising Method is generally selected 5 layers, can reduce the background noise of system;

3rd, the voltage data V obtaining after data pre-service is carried out in utilization ₀(t) carrying out local polarization interference intensity calculates;

3.1st, find V ₀(t) maximum of points V _0max(t), and to V _0max(t) near 100 data are done and are on average tried to achieve V _0max(t) the DC voltage value V at some place _0DC(t), calculate Δ V _m, Δ V _m=V _0max(t)-V _0DC(t), Δ V _mmeaning as shown in Figure 3, the amplitude of the interference signal of gained when having characterized the quiet arm catoptron of test macro and swing arm catoptron optical path difference and being zero.

3.2nd, get V ₀(t) the magnitude of voltage V of every bit in _0i(t), and to V _0i(t) near 100 data are done and are on average obtained V _0i(t) the DC voltage value V at some place _0iDC(t), calculate Δ V _ci, V _0i(t)-V _0iDC(t), wherein, i is integer, and 0≤i≤a; Δ V _cimeaning as shown in Figure 3, the amplitude of the interference signal of gained when having characterized the quiet arm catoptron of test macro and swing arm catoptron optical path difference and having compensated the optical path difference between two polarization state lights in polarizer.

3.3rd, by Δ V _ciwith Δ V _mwork, suc as formula the calculating of (1), obtains data V _ci(t), use V _c(t) represent by data V _ci(t) the polarization interference intensity data forming, data volume size is i.From data V _c(t) in, can obtain the polarization interference intensity of local polarization interference point

$V_{\mathrm{ci}}\left(t\right)=10\lg {\left(\frac{{\mathrm{\&Delta;V}}_{\mathrm{ci}}}{{\mathrm{\&Delta;V}}_m}\right)}^2,0\&le;i\&le;a---\left(1\right);$

4th, the V that utilizes the 3.3rd step to obtain _c(t) calculate the extinction ratio of polarizer;

Be located at data V _c(t) in, have n local polarization interference point, polarization interference intensity is respectively: α _j, 0<j<n;

, at polarizer exit end, the energy on non-light transmission shaft is:

$p_x=\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}{V_{\mathrm{<figure-callout\; id="2"\; label="cj"\; filenames="HDA0000123681580000021.png,HDA0000123681580000023.png"\; state="\{\{state\}\}">cj</figure-callout>}}}^2=\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}({10}^{0.1{\mathrm{\&alpha;}}_j}\&CenterDot;{V_m}^2)---\left(2\right)$

V in formula _mfor the energy of polarizer exit end light transmission shaft, used P _yrepresent, by formula the extinction ratio of known polarizer can be with the polarization interference intensity α of a plurality of polarization interference points _jrepresent:

$\mathrm{PER}=-10\lg \left\{\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}\left({10}^{0.1{\mathrm{\&alpha;}}_j}\right)\right\}(0<j<n)---\left(3\right)$

And the polarization interference intensity of how to take out this n local polarization interference point in actual measurement data is calculated the measurement result that the extinction ratio of polarizer will affect extinction ratio to a great extent; And the adaptive threshold polarization interference intensity that the present invention proposes has made up above-mentioned defect, and can do according to image data the adjustment of polarization interference intensity threshold, the calculating extinction ratio local polarization interference point used of choosing more accurately, concrete choosing method is as follows:

4.1st, find V _ci(t) in, characterize the polarization interference hot spot of joint, device under test two ends, all data points that characterize polarizer polarization interference intensity between two joints are taken out, be designated as V' _c(t);

4.2nd, find V' _c(t) in, maximum of points is designated as α _max, α _max=max{V' _c(t) }, calculate ${\mathrm{PER}}^{\&prime;}=10\lg \left\{{10}^{0.1{\mathrm{\&alpha;}}_{\max }}\right\};$

4.3rd, by α _maxnear this polarization interference hot spot of crosstalking a little that characterizes is removed, and residual polarization crosstalk strength point is designated as V'' _c(t);

4.4th, find V'' _c(t) in, maximum of points is designated as α ' _max, α ' _max=max{V'' _c(t) }, calculate ${\mathrm{PER}}^{\&prime;\&prime;}=-10\lg \{\mathrm{\&Sigma;}{10}^{-0.1{\mathrm{PER}}^{\&prime;}}+{10}^{{{0.1\mathrm{\&alpha;}}^{\&prime;}}_{\max }}\};$

4.5th, judge whether PER''-PER' is greater than σ, σ is by α ' _maxcorresponding polarization interference point when calculating the extinction ratio of polarizer, the extinction ratio of the device obtaining and not by α ' _maxthe difference of the delustring ratio of the measured polarizer of system when corresponding polarization interference point calculates for extinction ratio, general σ=0.01dB or less numerical value;

4.6th, when PER''-PER' is more than or equal to σ, illustrate that the polarization interference point of newly getting is larger on the result of calculation impact of polarizer extinction ratio, need to participate in extinction ratio calculating, PER'' note is done to PER', α ' _maxnote is α _max, return to the 4.3rd step and continue to carry out; When PER''-PER' is less than σ, illustrate the polarization interference point newly got on the result of calculation of polarizer extinction ratio without impact, the PER'' now obtaining is the extinction ratio of polarizer, is designated as PER;

4.7th, when PER''-PER' is less than σ, the α ' that programmed algorithm obtains _maxbe threshold value polarization interference intensity, be designated as α ' _th.With at light source resolution L _cthe data point number b comprising in length is as demarcation interval length, by the polarization interference intensity V'' when PER''-PER' is less than σ _c(t) be divided into r data segment, wherein

right

round.Data segment note after division is V'' _ck(t), represent k segment data; Wherein,

λ ₀for testing the centre wavelength of wideband light source used, Δ λ is light source spectrum width; K is integer, and 0<k≤r; Take out V'' _ck(t) the maximal value α in _kmax, i.e. α _kmax=max{V'' _ck(t) }, 0<k≤r, utilizes α by (4) formula _kmaxcalculate PER ₀:

${\mathrm{<figure-callout\; id="0"\; label="PER"\; filenames="HDA0000123681580000023.png,HDA0000123681580000031.png"\; state="\{\{state\}\}">PER</figure-callout>}}_0=-10\lg \left\{\underset{k=1}{\overset{r}{\mathrm{\&Sigma;}}}\left({10}^{0.1{\mathrm{\&alpha;}}_{k\max }}\right)\right\}(0<k\&le;r)---\left(4\right);$

4.8th, by PER ₀the PER'' that while being less than σ with the 4.7th judgement PER''-PER', programmed algorithm obtains, according to the extinction ratio PER of (5) formula calculating polarizer _final:

${\mathrm{PER}}_{\mathrm{final}}=-10\lg \{\mathrm{\&Sigma;}{10}^{{-0.1\mathrm{PER}}^{\&prime;\&prime;}}+{10}^{-0.1{\mathrm{PER}}_0}\}---\left(5\right).$

Advantage of the present invention and good effect:

1, the present invention makes full use of the feature that white light interference precision is high, dynamic range is large the little polarization interference point of polarizer inside is surveyed, and makes extinction ratio test result more accurate.

2, realize threshold value polarization interference intensity and automatically chosen according to the extinction ratio performance of tested polarizer, there is very strong adaptivity, made extinction ratio test result more reliable.

Accompanying drawing explanation

Fig. 1 is White Light Interferometer extinction ratio test data demodulation process flow diagram.

Fig. 2 is White Light Interferometer extinction ratio proving installation figure.

Fig. 3 is the voltage data schematic diagram that characterizes interference signal

Fig. 4 is the original interference data schematic diagram of 3m wire jumper.

Fig. 5 is 3m wire jumper polarization interference intensity data schematic diagram.

Fig. 6 is the original interference data schematic diagram of 12m wire jumper.

Fig. 7 is 12m wire jumper polarization interference intensity data schematic diagram.

Embodiment

The invention process case is tested the extinction ratio of polarization maintaining optical fibre.Extinction ratio proving installation adopts Michelson interferometer simple in structure as demodulated interferential instrument.Fig. 1 is White Light Interferometer extinction ratio testing algorithm process flow diagram; Fig. 2 is hardware testing installation drawing of the present invention, wherein, and the 1st, SLD light source, the 2nd, isolator, the 3rd, the polarizer, the 4th, polarization maintaining optical fibre, the 5th, polarizer to be measured, the 6th, demodulated interferential instrument tail optical fiber, the 7th, beam-expanding collimation lens, the 8th, half-wave plate, the 9th, Glan prism, the 10th, beam splitter, the 11st, quiet arm catoptron, the 12nd, scanning guide rail, the 13rd, swing arm catoptron, the 14th, photodetector, the 15th, capture card, the 16th, computing machine, the 17, the 18th, stepper motor.

Super continuum source is provided by Japanese Amonics Limited, the light source of model ASLD84-PM-150-B-FA, and the spectrum shape of light source is gaussian shaped profile, and centre wavelength is 850nm, and spectrum width is 49nm, and peak power output is 15mW; The Glan prism of the extinction ratio of analyzer use Thorlabs company more than 100dB; High-accuracy guide rail is Japanese THK company ball-screw guide rail, and model is KR2602AFM+200LP0F-000E; Detector adopts Newport818-SL, and detection wavelength coverage is 400nm-1000nm, dark current 5nA, dynamic range 0-4.6 * 10 ^-3w; The NI-USB6251 data collecting card of NI company is counted collection; Controllor for step-by-step motor is east motor CRK544APB.

In extinction ratio test experiments, by super continuum source 1, send super continuous spectrums light, by optoisolator 2, after the polarizer 3, become line polarisation, along a certain spindle coupled of polarizer tail optical fiber (polarization maintaining optical fibre) 4, enter polarizer 5 to be measured, by the light of the outgoing of polarizer outgoing after 6 transmission of demodulation tail optical fiber by beam-expanding collimation lens 7 collimations, through rotation half-wave plate 8 change polarization states and in conjunction with Glan prism 9 analyzings, make the light wave of two vertical polarization states of polarizer exit end all project to same polarization state, then enter adjustable Michelson interferometer, by beam splitter 10, the light after projection is divided into two bundles, the quiet arm catoptron 11 of a branch of arrival, another bundle arrives the swing arm catoptron 13 being fixed on scanning guide rail 12, by mobile swing arm catoptron compensating light path difference, the light wave that projects to same polarization state is interfered, by photodetector 14, receive interference light intensity, capture card 15 converts the light signal of detector collection to digital electric signal and sends computing machine 16 to and carry out data processing afterwards.In experimental provision, the movement of the rotation of half slide 8 and guide rail 12 is given capture card 14 signals by computing machine 16, and capture card is controlled motor 17 and motor 18 is realized.Because polarizer has the characteristic that keeps polarization state, when polarization maintaining optical fibre is subject to external disturbance or itself has defect, along the line polarisation of its a certain polarization principal axis transmission, will be crosstalked into another with it on vertical polarization principal axis, thereby cause polarization state to crosstalk, position and the intensity of final polarization interference point all can be obtained by the interference light signal demodulation collecting, and then carry out the measurement of polarizer extinction ratio.

Embodiment 1:

By centre wavelength, be 850nm, in the long Nufern polarization maintaining optical fibre connecting system for 3m, start after all devices, carry out white light interference data acquisition, when Fig. 4 has provided light source power and has been 8mW, the original interference data schematic diagram of collection.The raw data gathering is carried out to demodulation by the data demodulation method shown in Fig. 1, first calculating interference principal maximum is that fiber lengths is the interference signal amplitude at 0 place, then in interference data, the amplitude of the amplitude of every bit and main pole general goal calculates the data that characterize polarization interference intensity, as shown in Figure 5, AB segment data represents the polarization interference intensity of interferometer tail optical fiber, and BC segment data represents the polarization interference intensity of tested polarization maintaining optical fibre.The BC segment data of utilizing the polarization interference intensity that characterizes tested 3m polarization maintaining optical fibre, finds threshold value polarization interference intensity α ' by loop program algorithm _th; Take out polarization interference intensity and be more than or equal to α ' _thpolarization interference point, and utilize the polarization interference intensity of these points to calculate PER''; To be less than α ' _thpolarization interference hot spot be divided into data segment, the maximum polarization interference intensity of taking out each data segment calculates PER ₀; Finally by PER'' and PER ₀obtain the extinction ratio of polarizer ${\mathrm{PER}}_{\mathrm{final}}=-10\lg \{\mathrm{\&Sigma;}{10}^{{-0.1\mathrm{PER}}^{\&prime;\&prime;}}+{10}^{-0.1{\mathrm{PER}}_0}\}.$

Experiment has been carried out 5 experiments to 3m polarization maintaining optical fibre, and the extinction ratio obtaining and Thorlabs polarization extinction ratio tester are recorded to extinction ratio compares, as shown in table 1.The extinction ratio standard deviation that adopts extinction ratio calculating algorithm of the present invention to obtain is little, and the test result of test result and Thorlabs polarization extinction ratio tester only differs 0.42dB.

3 meters of polarization maintaining optical fibre wire jumper extinction ratio test results of table 1

Embodiment 2:

By centre wavelength, be 850nm, long in Japanese Teng storehouse polarization maintaining optical fibre of 12m and polarizer tail optical fiber and demodulated interferential instrument tail optical fiber connecting system, carry out white light interference data acquisition, when Fig. 5 has provided light source power and has been 8mW, the original interference data schematic diagram of collection.The raw data gathering is processed by the extinction ratio testing algorithm shown in Fig. 1, first calculating interference principal maximum is that fiber lengths is the interference signal amplitude at 0 place, then in interference data, the amplitude of the amplitude of every bit and main pole general goal calculates the data that characterize polarization interference intensity, as shown in Figure 7, EF segment data represents the polarization interference intensity of interferometer tail optical fiber, and FG segment data represents the polarization interference intensity of tested polarization maintaining optical fibre.The FG segment data of utilizing the polarization interference intensity that characterizes tested 12m polarization maintaining optical fibre, finds threshold value polarization interference intensity α ' by loop program algorithm _th; Take out polarization interference intensity and be more than or equal to α ' _thpolarization interference point, and utilize the polarization interference intensity of these points to calculate PER''; To be less than α ' _thpolarization interference hot spot be divided into data segment, the maximum polarization interference intensity of taking out each data segment calculates PER ₀; Finally by PER'' and PER ₀obtain the extinction ratio of polarizer ${\mathrm{PER}}_{\mathrm{final}}=-10\lg \{\mathrm{\&Sigma;}{10}^{{-0.1\mathrm{PER}}^{\&prime;\&prime;}}+{10}^{-0.1{\mathrm{PER}}_0}\}.$

Experiment has been carried out 5 experiments to 12 meters of long polarization maintaining optical fibres, and the extinction ratio obtaining and Thorlabs polarization extinction ratio tester are recorded to extinction ratio compares, as shown in table 2.The extinction ratio that extinction ratio calculating algorithm described in employing this patent obtains and the test result of Thorlabs polarization extinction ratio tester only differ 0.35dB.

12 meters of polarization maintaining optical fibre wire jumper extinction ratio test results of table 2

Claims (1)

1. a method for demodulating extinction ratio test data of polarizing device by white light interference method, is characterized in that the method comprises:

1st, use White Light Interferometer extinction ratio test macro to gather interference signal, test macro receives white light interference signal and carries out opto-electronic conversion with detector, obtain continuous analog electrical signal, after capture card sampling, quantification, obtain characterizing the discrete voltage data V(t of interference signal);

2nd, by the voltage data V(t gathering in the 1st step) carry out data pre-service;

2.1st, to voltage data V(t) in the every N of data point do average, the value of a point using the mean value obtaining as this N, in the random noise in effective erasure signal by N times of data volume M reduction, thereby obtain new voltage data wherein N, M are integer, and 0<N<M, and M is V(t) data amount check; Note voltage data

data volume size be a, a=[M/N] represent M/N to round;

2.2nd, right carry out Wavelet Denoising Method, on the basis of mean denoising, utilize the adaptivity of small echo to remove noise and retain useful signal, obtain voltage data V ₀(t);

Wherein the number of plies of Wavelet Denoising Method is generally selected 5 layers, can reduce the background noise of system;

3rd, the voltage data V obtaining after data pre-service is carried out in utilization ₀(t) carrying out local polarization interference intensity calculates;

3.1st, find V ₀(t) maximum of points V _0max(t), and to V _0max(t) near 100 data are done and are on average tried to achieve V _0max(t) the DC voltage value V at some place _0DC(t), calculate Δ V _m, Δ V _m=V _0max(t)-V _0DC(t), Δ V _mthe amplitude of meaning interference signal of gained when having characterized the quiet arm catoptron of test macro and swing arm catoptron optical path difference and being zero;

3.2nd, get V ₀(t) the magnitude of voltage V of every bit in _0i(t), and to V _0i(t) near 100 data are done and are on average obtained V _0i(t) the DC voltage value V at some place _0iDC(t), calculate Δ V _ci, Δ V _ci=V _0i(t)-V _0iDC(t), wherein, i is integer, and 0≤i≤a; Δ V _cithe amplitude of the interference signal of gained when having characterized the quiet arm catoptron of test macro and swing arm catoptron optical path difference and having compensated the optical path difference between two polarization state lights in polarizer;

3.3rd, by Δ V _ciwith Δ V _mwork, suc as formula the calculating of (1), obtains data V _ci(t), use V _c(t) represent by data V _ci(t) the polarization interference intensity data forming, data volume size is i; From data V _c(t) in, can obtain the polarization interference intensity of local polarization interference point

$V_{\mathrm{ci}}\left(t\right)=10\lg {\left(\frac{{\mathrm{\&Delta;V}}_{\mathrm{ci}}}{{\mathrm{\&Delta;V}}_m}\right)}^2,0\&le;i\&le;a---\left(1\right);$

4th, the V that utilizes the 3.3rd step to obtain _c(t) calculate the extinction ratio of polarizer;

Be located at data V _c(t) in, have n local polarization interference point, polarization interference intensity is respectively: α _j, 0<j<n;

, at polarizer exit end, the energy on non-light transmission shaft is:

$p_x=\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}{V_{\mathrm{cj}}}^2=\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}({10}^{0.1{\mathrm{\&alpha;}}_j}\&CenterDot;{V_m}^2)---\left(2\right)$

V in formula _mfor the energy of polarizer exit end light transmission shaft, used P _yrepresent, by formula

the extinction ratio of known polarizer can be with the polarization interference intensity α of a plurality of polarization interference points _jrepresent:

$\mathrm{PER}=-10\lg \left\{\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}\left({10}^{0.1{\mathrm{\&alpha;}}_j}\right)\right\}(0<j<n)---\left(3\right)$

Concrete choosing method is as follows:

4.1st, find V _ci(t) in, characterize the polarization interference hot spot of joint, device under test two ends, all data points that characterize polarizer polarization interference intensity between two joints are taken out, be designated as V' _c(t);

4.2nd, find V' _c(t) in, maximum of points is designated as α _max, α _max=max{V' _c(t) }, calculate ${\mathrm{PER}}^{\&prime;}=10\lg \left\{{10}^{0.1{\mathrm{\&alpha;}}_{\max }}\right\};$

4.3rd, by α _maxnear this polarization interference hot spot of crosstalking a little that characterizes is removed, and residual polarization crosstalk strength point is designated as V'' _c(t);

4.4th, find V'' _c(t) in, maximum of points is designated as α ' _max, α ' _max=max{V'' _c(t) }, calculate ${\mathrm{PER}}^{\&prime;\&prime;}=-10\lg \{\mathrm{\&Sigma;}{10}^{-0.1{\mathrm{PER}}^{\&prime;}}+{10}^{{{0.1\mathrm{\&alpha;}}^{\&prime;}}_{\max }}\};$

4.5th, judge whether PER''-PER' is greater than σ, σ is by α ' _maxcorresponding polarization interference point when calculating the extinction ratio of polarizer, the extinction ratio of the device obtaining and not by α ' _maxthe difference of the delustring ratio of the measured polarizer of system when corresponding polarization interference point calculates for extinction ratio, general σ=0.01dB or less numerical value;

4.6th, when PER''-PER' is more than or equal to σ, illustrate that the polarization interference point of newly getting is larger on the result of calculation impact of polarizer extinction ratio, need to participate in extinction ratio calculating, PER'' note is done to PER', α ' _maxnote is α _max, return to the 4.3rd step and continue to carry out; When PER''-PER' is less than σ, illustrate the polarization interference point newly got on the result of calculation of polarizer extinction ratio without impact, the PER'' now obtaining is the extinction ratio of polarizer, is designated as PER;

4.7th, when PER''-PER' is less than σ, the α ' that programmed algorithm obtains _maxbe threshold value polarization interference intensity, be designated as α ' _th, with at light source resolution L _cthe data point number b comprising in length is as demarcation interval length, by the polarization interference intensity V'' when PER''-PER' is less than σ _c(t) be divided into r data segment, wherein r=[a/b], a/b is rounded, the data segment note after division is V'' _ck(t), represent k segment data; Wherein,

λ ₀for testing the centre wavelength of wideband light source used, Δ λ is light source spectrum width; K is integer, and 0<k≤r; Take out V'' _ck(t) the maximal value α in _kmax, i.e. α _kmax=max{V'' _ck(t) }, 0<k≤r, utilizes α by (4) formula _kmaxcalculate PER ₀:

${\mathrm{PER}}_0=-10\lg \left\{\underset{k=1}{\overset{r}{\mathrm{\&Sigma;}}}\left({10}^{0.1{\mathrm{\&alpha;}}_{k\max }}\right)\right\}(0<k\&le;r)---\left(4\right);$

4.8th, by PER ₀the PER'' that while being less than σ with the 4.7th judgement PER''-PER', programmed algorithm obtains, according to the extinction ratio PER of (5) formula calculating polarizer _final:

${\mathrm{PER}}_{\mathrm{final}}=-10\lg \{\mathrm{\&Sigma;}{10}^{{-0.1\mathrm{PER}}^{\&prime;\&prime;}}+{10}^{-0.1{\mathrm{PER}}_0}\}---\left(5\right).$

Images