CN102645281B - Method for measuring degree of polarization by means of polarization beam splitter prism - Google Patents

Abstract

The invention discloses a method for measuring a degree of polarization by means of a polarization beam splitter prism. Devices for measuring comprise a polarization light source, an element to be tested, the polarization beam splitter prism and an optical power meter. The measurement method includes that the polarization light source passes by the element to be tested, then shoots into the polarization beam splitter prism and is divided into o light and e light; an optical power Po (0) of the o light and an optical power Pe (0) of the e light are measured respectively, wherein the o light and the e light are emitted by the polarization beam splitter prism; the polarization beam splitter prism is rotated, the position of the o light keeps unchanged, and the e light rotates around the o light with the rotation of the polarization beam splitter prism; and when the polarization beam splitter prism is rotated by 45 degrees, the optical power value Po (pi/4) of the o light is measured, and the degree of polarization (DOP) is confirmed by means of correlation formulas. The method for measuring the degree of polarization by means of the polarization beam splitter prism is wide in wavelength coverage, simple in structure, convenient to measure and operate, and capable of measuring the degree of polarization and simultaneously observing space distribution features of polarizations of lights.

Description

A kind of utilization plays the method that inclined to one side beam splitter prism is measured degree of polarization

Technical field

The present invention relates to optical measurement field.

Background technology

Degree of polarization (DOP) is a physical quantity describing light beam polarization situation, is an important parameter of light source characteristic, degree of polarization with the feature measurement of optical device, the optical signal quality of the sensitivity of optical sensor system, optical communication system is directly related.Polarisation of light degree is defined as the ratio that polarized light accounts for total light intensity,

wherein, P _prefer to the power of polarized component in light beam, P _urefer to the power of unpolarized component in light beam, DOP has characterized the number of polarized component in light beam.

The method of measuring degree of polarization has following several at present:

1. the stokes parameter method of testing of degree of polarization

As shown in Figure 1, light source is that degree of polarization is 100% polarized light to its apparatus structure, for test light is by the stokes parameter after device under test, need to insert respectively three polarizers, and when inserting 0 ° of polarizer, recording power is P ₀; When inserting 45 ° of polarizers, recording power is P ₄₅; When inserting left-handed rotatory polarization, rise when inclined to one side, recording power is P _cl; The power of testing while not inserting the polarizer is P _total.

Definition by stokes parameter obtains S ₀=P _total, suppose that polarized light light intensity is P _tp, nonpolarized light light intensity is P _un, the light intensity that nonpolarized light sees through after the polarizer is P _min=0.5P _un, polarized light light intensity can be decomposed into two orthogonal polarisation state light intensity sums.Therefore can obtain stokes parameter is:

S ₀＝P _total

S ₁＝2P ₀-P _total

S ₂＝2P ₄₅-P _total

S ₃＝2P _cl-P _total

The formula that represents degree of polarization with stokes parameter is:

$\mathrm{DOP}=\frac{\sqrt{{{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="120426153113.png"\; state="\{\{state\}\}">S</figure-callout>}}^2}_1+{{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="120426153113.png"\; state="\{\{state\}\}">S</figure-callout>}}_2}^2+{{\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="120426153113.png"\; state="\{\{state\}\}">S</figure-callout>}}_3}^2}}{{S_0}^2}$

2. the full polarization state extinction ratio method of testing of degree of polarization

Its apparatus structure as shown in Figure 2, changes output polarisation of light state, the maximum output intensity P of test in all polarization states by Polarization Controller _max, minimum output intensity P _min.

Suppose that polarized light light intensity is P _tp, nonpolarized light light intensity is P _un, polarized light, partly by the effect of Polarization Controller, is P by the largest light intensity after analyzer _tp, minimum is 0, nonpolarized light by analyzer after light intensity be 0.5P _un.Therefore maximum is exported light P _max=0.5P _un+ P _tp, minimum output intensity P _min=0.5P _un.By the definition of degree of polarization (DOP), i.e. the ratio of complete polarized light part intensity and total intensity.So can obtain:

$\mathrm{DOP}=\frac{P_{\mathrm{tp}}}{P_{\mathrm{tp}}+P_{\mathrm{un}}}=\frac{P_{\max }-P_{\min }}{P_{\max }+P_{\min }}$

3. measurement target is in the method for the light intensity of a plurality of polarization directions

Its apparatus structure as shown in Figure 3, from the intensity I of the partial poolarized light of target light _in, can be expressed as I _in=I _n+ I _p, I in formula _nfor the intensity of natural light component, I _pintensity for linearly polarized light component.Allow the vertical normal incidence of this partial poolarized light by an analyzer, analyzer output light intensity can be expressed as:

$I_{\mathrm{out}}=\frac{I_{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="120426153113.png"\; state="\{\{state\}\}">n</figure-callout>}}}{2}+{\left(A\cos \mathrm{\&alpha;}\right)}^2=\frac{I_{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="120426153113.png"\; state="\{\{state\}\}">n</figure-callout>}}}{2}+{\mathrm{<figure-callout\; id="2"\; label="A"\; filenames="120426153113.png"\; state="\{\{state\}\}">A</figure-callout>}}^2{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="120426153113.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;}$

$=\frac{I_{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="120426153113.png"\; state="\{\{state\}\}">n</figure-callout>}}}{2}+I_{\mathrm{<figure-callout\; id="2"\; label="p\; cos"\; filenames="120426153113.png"\; state="\{\{state\}\}">p</figure-callout>}}{\cos }^{}{}^2\mathrm{\&alpha;}=\frac{I_{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="120426153113.png"\; state="\{\{state\}\}">n</figure-callout>}}}{2}+\frac{I_{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="120426153113.png"\; state="\{\{state\}\}">p</figure-callout>}}}{2}+\frac{I_{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="120426153113.png"\; state="\{\{state\}\}">p</figure-callout>}}}{2}\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="120426153113.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&alpha;}$

In formula, α is from the advantage vibration orientation of the partial poolarized light of target and the angle between analyzer light transmission shaft direction, the amplitude that A is linearly polarized light, I _outoutput light intensity for analyzer.In the interval value that changes α of 0-π,, can obtain I _outand the relation between α, by calculating, derives, and obtains

$\mathrm{DOP}=\frac{I_p}{I_p+I_n}=\frac{\underset{i=1}{\overset{k/2}{\mathrm{\&Sigma;}}}\left(\right|I_{\mathrm{out}\left(i\right)}-I_{\mathrm{out}(k/+i)}\left|\right)\frac{\mathrm{\&pi;}}{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="120426153113.png"\; state="\{\{state\}\}">k</figure-callout>}}}{2\underset{i=1}{\overset{k}{\mathrm{\&Sigma;}}}{I}_{\mathrm{out}\left(i\right)}/k}$

$=\frac{\mathrm{\&pi;}}{2}\&CenterDot;\frac{\underset{i=1}{\overset{k/2}{\mathrm{\&Sigma;}}}\left(\right|I_{\mathrm{out}\left(i\right)}-I_{\mathrm{out}(k/2+i)}\left|\right)\frac{\mathrm{\&pi;}}{2}}{\underset{i=1}{\overset{k}{\mathrm{\&Sigma;}}}{I}_{\mathrm{out}\left(i\right)}/k}$

By measurement target, at the polarized light intensity of k different directions, can calculate the degree of polarization of target light.

Measure now the method for degree of polarization, multiplex is greatly the stokes parameter method of testing of degree of polarization and the full polarization state extinction ratio method of testing of degree of polarization, measurement target is the method for the light intensity of a plurality of polarization directions use few also, the method of the measurement degree of polarization that the polarization analysis instrument of selling in the market adopts substantially use be all the stokes parameter method of testing of degree of polarization and the full polarization state extinction ratio method of testing of degree of polarization, and control by the improved employing closed-loop feedback circuit of full polarization state extinction ratio method of testing of degree of polarization the extremum search method forming, but the essence of extremum search method is the full polarization state extinction ratio method of testing of degree of polarization.

The stokes parameter method of testing of degree of polarization, has stronger wavelength dependence, but operate fairly simple, use more; The full polarization state extinction ratio method of testing of degree of polarization, simple to operate, there is wavelength dependence, measuring accuracy and measurement operation have much relations; Measurement target, in the method for the light intensity of a plurality of polarization directions, is repeatedly measured, cumbersome, time-consuming; In some occasion, should measure polarisation of light degree, observe again the spatial characteristics of polarisation of light state simultaneously, on one side above 3 kinds of methods all can not measure polarisation of light degree, Yi Bian observe the spatial characteristics of polarisation of light state simultaneously.

Summary of the invention

The present invention is that a kind of utilization plays the method that inclined to one side beam splitter prism is measured degree of polarization, and applicable wavelengths scope is larger, simple in structure, measures easy to operately, can also observe the spatial characteristics of polarisation of light state when measuring degree of polarization.

Technical scheme of the present invention is as follows:

Utilization plays the method that inclined to one side beam splitter prism is measured degree of polarization, measures needed device and comprises polarized light source, device under test, plays inclined to one side beam splitter prism and light power meter; Measuring method is: polarized light source has been injected inclined to one side beam splitter prism after device under test, is divided into o light and e light two-beam, has measured respectively the o light of inclined to one side beam splitter prism outgoing and the optical power value P of e light _o[0] and P _e[0], then rotated inclined to one side beam splitter prism, the invariant position of o light, e light, rotates after 45 ° around the rotation of o light along with playing the rotation of inclined to one side beam splitter prism, measures the wherein optical power value P of o light _o[π/4], degree of polarization DOP determines by following formula:

$\mathrm{DOP}=\frac{P_p}{P_p+P_u}=\frac{\sqrt{{\left(2P_o\right[\mathrm{\&pi;}/4]-P_o[0]-P_e[0\left]\right)}^2+{\left(P_e\right[0]-P_o[0\left]\right)}^2}}{P_o\left[0\right]+P_e\left[0\right]}$

In formula, P _prefer to the power of polarized component in light beam, P _urefer to the power of unpolarized component in light beam.

Further, polarized light source obtains through the polarizer by unpolarized light source.

In the present invention, playing inclined to one side beam splitter prism is the various effects partially that both had, and has again the prism that has beam splitting effect, for example: Rochon prism, wollaston prism, the special prism of San'a awns; After playing inclined to one side beam splitter prism, add the spatial characteristics that an imaging screen can be observed polarisation of light state, while surveying invisible light, need to observe polarization state space distribution situation with CCD or other electrooptical device; The optical power value substitution formula of the o light measuring by light power meter and e light just can calculate degree of polarization.To same device under test, under equal conditions, the result that the full polarization state extinction ratio measurement of the inventive method and degree of polarization records is basic identical, and the relative error of the two is less than 1%.

Principle of work of the present invention is as follows:

According to the design feature that plays inclined to one side beam splitter prism, it can produce two bundles are separated from each other, the mutually perpendicular complete linearly polarized light of direction of vibration.Spatial beam after depolarization can be regarded as by nonpolarized light and a part of polarized light and form, and wherein, nonpolarized light is all identical along the intensity of all directions vibration, according to any two orthogonal directionss, be decomposed into o light, e light, two-beam luminous power equates, is all half of nonpolarized light, that is:

$P_{o\left(u\right)}=P_{e\left(u\right)}=\frac{1}{2}{P}_u---\left(1\right)$

For remaining polarization part, orientation and the rectangular coordinate system in space X-axis angle of establishing its polarization principal axis are θ, play second optical axis of crystal of inclined to one side beam splitter prism parallel with X-Y plane, with X-axis angle be α, as shown in figure 11.

For calculating incident light polarization part, after playing inclined to one side beam splitter prism, be separated into the light intensity of o light, e light, can be first by the amplitude A of polarized light ₀to the X of space coordinates, Y-axis projection, obtain at the amplitude of X, Y both direction be

A _x＝A ₀ cosθ

A _y＝A ₀ sinθ

By amplitude, the component at X-axis, Y-axis both direction decomposes according to the optical axis direction of second crystal respectively again, obtains

The amplitude component perpendicular to principal section of X-direction: A _{⊥ 1}=A _xsin α

The amplitude component perpendicular to principal section of Y direction: A _{⊥ 2}=A _ycos α

The amplitude component that is parallel to principal section of X-direction: A _{// 1}=A _xcos α

The amplitude component that is parallel to principal section of Y direction: A _{// 1}=A _ysin α

To synthetic o light, the e optical vibration direction oscillator intensity of obtaining of above-mentioned amplitude component

A _o＝A _⊥1+A _⊥2＝A _xsinα+A _ycosα＝A ₀sinαcosθ+A ₀cosαsinθ＝A ₀sin(α+θ)

A _e＝A _//1+A _//2＝A _xcosα+A _ysinα＝A ₀cosαcosθ+A ₀sinαsinθ＝A ₀cos(α+θ)

According to the relation of luminous power and oscillator intensity

$\frac{P_o}{P_e}=\frac{A_o^2}{A_e^2}=\frac{{\sin }^2(\mathrm{\&alpha;}+\mathrm{\&theta;})}{{\cos }^2(\mathrm{\&alpha;}+\mathrm{\&theta;})}$

And,

P _p＝P _o(p)+P _e(p)

So, polarization part according to two orthogonal directionss be decomposed into o light, e light light intensity is respectively

P _o(p)＝P _psin ²(α+θ) (2)

P _e(u)＝P _pcos ²(α+θ) (3)

Therefore, can obtain o light, the e light luminous power after inclined to one side beam splitter prism separation

$P_o=P_{o\left(p\right)}+P_{o\left(u\right)}=P_p{\sin }^2(\mathrm{\&alpha;}+\mathrm{\&theta;})+\frac{1}{2}{P}_u---\left(4\right)$

$P_e=P_{e\left(p\right)}+P_{e\left(u\right)}=P_p{\cos }^2(\mathrm{\&alpha;}+\mathrm{\&theta;})+\frac{1}{2}{P}_u---\left(5\right)$

Regulated inclined to one side beam splitter prism, make two hot spot line levels of emergent light separation, now second optical axis of crystal is positioned at vertical direction, measured respectively the optical power value of two bundle separated lights of inclined to one side beam splitter prism outgoing, namely parallel, perpendicular to the luminous power component of two polarization directions of second optical axis of crystal

$P_o\left[0\right]={\mathrm{<figure-callout\; id="2"\; label="P\; p\; sin"\; filenames="120426153113.png"\; state="\{\{state\}\}">P</figure-callout>}}_p{\sin }^{}{}^2\mathrm{\&theta;}+\frac{1}{2}{P}_u---\left(6\right)$

$P_e\left[0\right]={\mathrm{<figure-callout\; id="2"\; label="P\; p\; cos"\; filenames="120426153113.png"\; state="\{\{state\}\}">P</figure-callout>}}_p{\cos }^{}{}^2\mathrm{\&theta;}+\frac{1}{2}{P}_u---\left(7\right)$

By rotation, play inclined to one side beam splitter prism again, make 45 ° of two hot spot lines, optical axis direction also changes 45 ° thereupon, and light beam is decomposed according to the polarization direction of two other quadrature, measures the wherein optical power value of o light

$P_o[\mathrm{\&pi;}/4]=P_p{\sin }^2(\mathrm{\&pi;}/4+\mathrm{\&theta;})+\frac{1}{2}{P}_u---\left(8\right)$

According to above-mentioned (6), (7), (8) three groups of optical power value P _o[0], P _e[0], P _o[π/4], can calculate the optical power value of obtaining polarized component and unpolarized component in the light beam that has incided inclined to one side beam splitter prism, further can obtain the degree of polarization of incident light.

$\mathrm{DOP}=\frac{P_p}{P_p+P_u}=\frac{\sqrt{{\left(2P_o\right[\mathrm{\&pi;}/4]-P_o[0]-P_e[0\left]\right)}^2+{\left(P_e\right[0]-P_o[0\left]\right)}^2}}{P_o\left[0\right]+P_e\left[0\right]}---\left(9\right)$

Accompanying drawing explanation

Fig. 1 is the apparatus structure schematic diagram of the stokes parameter method of testing of degree of polarization;

Fig. 2 is the apparatus structure schematic diagram of the full polarization state extinction ratio method of testing of degree of polarization;

Fig. 3 is that measurement target is at the apparatus structure schematic diagram of the method for the survey degree of polarization of the light intensity of a plurality of polarization directions;

Fig. 4 is for having utilized inclined to one side beam splitter prism to measure the apparatus structure schematic diagram of the method for degree of polarization;

Fig. 5 when having utilized inclined to one side beam splitter prism measurement degree of polarization during with the incident light incident of 120 ° of relative device under tests, the o polarization state space distribution situation that CCD records;

Fig. 6 when having utilized inclined to one side beam splitter prism measurement degree of polarization during with the incident light incident of 120 ° of relative device under tests, the e polarization state space distribution situation that CCD records;

Fig. 7 when having utilized inclined to one side beam splitter prism measurement degree of polarization during with the incident light incident of 135 ° of relative device under tests, the o polarization state space distribution situation that CCD records;

Fig. 8 when having utilized inclined to one side beam splitter prism measurement degree of polarization during with the incident light incident of 135 ° of relative device under tests, the e polarization state space distribution situation that CCD records;

Fig. 9 when having utilized inclined to one side beam splitter prism measurement degree of polarization during with the incident light incident of 140 ° of relative device under tests, the o polarization state space distribution situation that CCD records;

Figure 10 when having utilized inclined to one side beam splitter prism measurement degree of polarization during with the incident light incident of 140 ° of relative device under tests, the e polarization state space distribution situation that CCD records;

Figure 11 has been the optical axis schematic diagram of inclined to one side beam splitter prism.

In Fig. 3,1,3,6: lens, 2: diaphragm, 4: optical filter, 5: analyzer, 7: detector.

Embodiment

According to Fig. 4 shown device structural representation, regulate device, when incident beam, light is by after polarization beam splitter prism, to be divided into o light and e light two-beam, regulate polarization beam splitter prism, make two hot spot line levels of emergent light separation, measure respectively the optical power value P of two bundle separated lights of polarization beam splitter prism outgoing _o[0] and P _e[0], then by rotatory polarization beam splitter prism, the invariant position of o light, e light around the rotation of o light, after 45 ° of rotations, is measured the wherein optical power value P of o light along with playing the rotation of inclined to one side beam splitter prism _o[π/4], degree of polarization DOP determines by following formula:

$\mathrm{DOP}=\frac{P_p}{P_p+P_u}=\frac{\sqrt{{\left(2P_o\right[\mathrm{\&pi;}/4]-P_o[0]-P_e[0\left]\right)}^2+{\left(P_e\right[0]-P_o[0\left]\right)}^2}}{P_o\left[0\right]+P_e\left[0\right]}$

Value substitution above formula by measuring, can calculate degree of polarization.

Claims (5)

1. a method of having utilized inclined to one side beam splitter prism to measure degree of polarization, measuring needed device comprises polarized light source, device under test, plays inclined to one side beam splitter prism and light power meter, it is characterized in that measuring method is: polarized light source has been injected inclined to one side beam splitter prism after device under test, be divided into light o and e light two-beam, regulated inclined to one side beam splitter prism, make two hot spot line levels of emergent light separation, measured respectively the o light of inclined to one side beam splitter prism outgoing and the optical power value P of e light _o[0] and P _e[0], then rotated inclined to one side beam splitter prism, the invariant position of o light, e light around the rotation of o light, after 45 ° of rotations, is measured the wherein optical power value P of o light along with playing the rotation of inclined to one side beam splitter prism _o[π/4], degree of polarization DOP determines by following formula:

$\mathrm{DOP}=\frac{P_p}{P_p+P_u}=\frac{\sqrt{{\left({2P}_o\right[\mathrm{\&pi;}/4]-P_o[0]-P_e[0\left]\right)}^2+{\left(P_e\right[0]-P_o[0\left]\right)}^2}}{P_o\left[0\right]+P_e\left[0\right]}$

In formula, p _prefer to the power of polarized component in light beam, p _urefer to the power of unpolarized component in light beam.

2. utilization according to claim 1 plays the method that inclined to one side beam splitter prism is measured degree of polarization, it is characterized in that: after polarized light source has been injected inclined to one side beam splitter prism after device under test, by imaging screen or electrooptical device, obtain polarization state space distribution situation.

3. utilization according to claim 2 plays the method that inclined to one side beam splitter prism is measured degree of polarization, it is characterized in that: described electrooptical device is CCD.

4. utilization according to claim 1 plays the method that inclined to one side beam splitter prism is measured degree of polarization, it is characterized in that: polarized light source obtains through the polarizer by unpolarized light source.

5. utilization according to claim 1 plays the method that inclined to one side beam splitter prism is measured degree of polarization, it is characterized in that: playing inclined to one side beam splitter prism is the special prism of Rochon prism, wollaston prism or San'a awns.

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