CN211043859U

CN211043859U - Polarized light Stokes parameter selector

Info

Publication number: CN211043859U
Application number: CN201922171639.7U
Authority: CN
Inventors: 黄春晖
Original assignee: Yango University
Current assignee: Yango University
Priority date: 2019-12-06
Filing date: 2019-12-06
Publication date: 2020-07-17
Anticipated expiration: 2029-12-06

Abstract

The utility model relates to a polarized light Stokes parameter's selector, including half-wave plate, electro-optic modulator, wollaston prism, photoelectric conversion module, half-wave plate be 1/2 wave plates that can accurately rotate, realize the rotation to the Q of input polarized light, U parameter, and reflect parameter V and operate as-V, the electro-optic modulator be Z type L iNbO₃The crystal electro-optic modulator can rotate two parameters of input polarized light U and V by any angle; the photoelectric conversion module comprises two photodiodes which have the same performance parameters and are connected in series, and the photodiodes receive the vertical component light beam and the horizontal component light beam from the Wollaston prism respectivelyThe component beams are converted into corresponding photocurrents, and differential residual currents related to the selected parameters are obtained by applying +/-12V voltage. The utility model discloses can realize online selection Stokes polarization parameter and real-time measurement, can be used to technical field such as polarization characteristic of analysis spectrum, coherent light communication's signal identification and decoding, Stokes parameter formation of image and face identification.

Description

Polarized light Stokes parameter selector

Technical Field

The utility model relates to a polarized light application technique field especially relates to a polarized light Stokes parametric selector.

Background

Polarized light includes four basic properties of amplitude, frequency, phase and polarization. Each basic attribute contains important information. The polarization of light provides abundant information as the intensity and wavelength of light, and has wide application prospect. Polarization of arbitrary partially or fully polarized lightThe vibration state can be completely described by using Stokes parameters, and the method has the advantages that I, Q, U, V4 Stokes parameters have the dimension of light intensity, the parameter selection and separation of polarized light are realized by an optical method, and the polarized light is directly converted into photocurrent by a photodiode to realize high-sensitivity measurement, or the polarization parameters are received by SiCCD to realize Stokes polarization imaging. Polarization imaging and polarization recognition technology based on Stokes parameters is rapidly and successfully applied to systems around satellites for atmospheric measurement, remote sensing, aerial photography of landforms, military target recognition, radar imaging and the like in recent years. In the aspect of material structure research, the characteristics of surface roughness, geometric shape, material, structure and the like of an object can be acquired by utilizing the polarization property of object reflected light. In optical communication, a single-beam coherent optical communication is realized by encoding a carrier component of polarized light using a polarization multiplexing technique of light. The above applications all relate to parametric selection, separation and conversion of polarized light. For obtaining polarization state information S of incident light_in＝[I Q U V]^TThe optical system for polarization splitting needs to be adjusted to perform 4 measurements. The measurement method comprises a mode of rotating a polaroid, a mode of fixing the polaroid and a rotating wave plate and a mode of fixing the polaroid and reinforcing the fixed variable delay wave plate.

Based on under the above background, the utility model provides a combine rotatory wave plate and electro-optic phase modulation technique organically, develop a swift, efficient polarized light Stokes parameter selector, it has optical axis of sharing and simple structure, stable and the fast characteristics of measuring speed for solve the shortcoming that exists among the prior art.

SUMMERY OF THE UTILITY MODEL

The utility model aims at solving the defects existing in the prior art and providing a polarized light Stokes parameter selector. The selector organically combines the rotating wave plate and the phase modulation technology to realize the online selection of the Stokes parameters of the polarized light, and can be used for spectral polarization measurement, coherent light communication decoding, Stokes parameter imaging and face recognition.

In order to achieve the above purpose, the technical scheme of the utility model is that: polarized light Stokes parameterThe selector comprises a half-wave plate, an electro-optical modulator, a Wollaston prism and an optical-to-electrical converter, wherein the half-wave plate is an 1/2 wave plate capable of rotating accurately, and the electro-optical modulator is a Z-shaped L iNbO₃The electro-optical modulator firstly rotates two components of polarization state input light through rotating two component axes; the Wollaston prism decomposes the rotated component into two orthogonal polarized light components; the photoelectric converter converts the selected output light into corresponding photocurrent, and selection of Stokes parameters of the polarized light is realized through photocurrent difference; the two photoelectric tubes of the photoelectric converter have the same performance, and are equidistantly arranged on the output end surface of the earth Wollaston prism, and a shielding wiring technology is adopted in a homodyne measurement circuit. The utility model discloses can realize online selection Stokes polarization parameter and real-time measurement, can be used to spectral polarization measurement, coherent light communication decoding, Stokes parameter formation of image and face identification, have the usage extensive, advantages such as measuring speed is fast, and it is significant to the measurement analysis and the application meaning of polarized light. A Stokes parameter selector for any light polarization state is suitable for polarized light with the wavelength of 808 nm.

Expressing the Stokes vector of any polarized light as S_in＝[I Q U V]^TWherein I, Q, U, V the 4 Stokes parameters have intensity dimensions representing total intensity, horizontally and vertically polarized light, ± 45 ° polarized light, and right-and left-handed circularly polarized light, respectively. The Stokes parameter description method is selected to be easy to realize receiving and measuring, the Ponga ball mark can be intuitively marked, the Stokes parameter description method is suitable for partial polarized light and full polarized light, each polarization optical device can be described by one Muller matrix, and analysis is easy.

The half-wave plate converts the polarization state into S_in＝[I Q U V]^TIs incident upon the 1/2 wave plate of figure 1. The Muller matrix using 1/2 waveplates is:

in the formula, theta is the included angle between the fast axis of the 1/2 wave plate and the horizontal direction. The light polarization state after passing through 1/2 wave plate is S_out1＝M(HWP,θ)*S_in＝[I Q₁U₁V₁]^TThis corresponds to rotating Q, U two components by 4 θ about the V-axis and then rotating V by 180 °.

As shown in FIG. 1 and FIGS. 3 to 6, a Z-type L iNbO₃The electro-optical modulator comprises a Muller matrix as follows:

handle S_out1The output light obtained after incidence on the electro-optic modulator is S_out2＝[I Q₂U₂V₂]^T，M(EOM,_z) Has the function of_out1Q of (2)₁、V₁Two components wound around U₁Rotation of the shaft_zWherein

Is the phase delay angle and is proportional to the modulation voltage Vz.

As shown in FIG. 7, the Wollaston prism bundle S_out2Split into two orthogonal polarized light components, consisting of the mueller matrix:

(the horizontal component),

(vertical component)

Act on S_out2So as to obtain the compound with the characteristics of,

and

as a result, the Wollaston prism functions as a polarizing beam splitter PBS for splitting an incident beam into two beams, wherein the vibration direction of the beams is determined when the incident beam enters the first BBOThe vibration direction of the e light is parallel to the optical axis, and although the two lights have the same propagation direction, the wave fronts are separated into two linearly polarized lights due to the different refractive indexes of the two lights. At the interface between the two BBOs, the incident angles of the two beams are both i equal to 45 °. The two beams are further refracted from the air interface to form two separated linearly polarized light beams with mutually perpendicular polarization directions.

As shown in FIG. 1, FIG. 7 and FIG. 8, the photoelectric converters are two semiconductor photodiodes with the same technical parameters, and respectively receive two beams of light S emitted from the PBS_HoutAnd S_VoutObtain corresponding converted light current I_HoutAnd I_VoutPhotocurrent I_HoutAnd I_VoutThe sum-only Q is obtained by the homodyne detection circuit shown in FIG. 8₂Related differential photocurrent I_out＝I_Hout-I_VoutThen handle I_outAnd sending the data to a computer acquisition card for acquisition, storage and display. Two photocurrents received from the photodiodes in the homodyne detection circuit and two currents output from the middle points of the two photodiodes according to kirchhoff's law are residual current signals.

Photocurrent I_out＝(I_Hout-I_Vout)∞S_out，S_outThe specific expression of (a) is as follows:

S_out＝(PBS_H-PBS_V)*M(EOM,_z)*M(HWP,θ)

or

S_out＝(Qcos4θ+Usin4θ)cos_z+Vsin_z(1)

By selecting different rotation angles theta and phase delay angles_zCan be prepared from (S)_Hout-S_Vout) And obtaining the required Stokes parameters, and realizing the selection of the polarized light Stokes parameters.

Drawings

FIG. 1 is a schematic view of a Stokes parameter selector;

FIG. 2 is a wave plate fast axis view of the 1/2 wave plate;

FIG. 3 is a schematic diagram of an electro-optic modulator;

FIG. 4 is L iNbO₃A geometric structure diagram of the crystal;

FIG. 5 is a perspective view of an electro-optic modulator mount;

FIG. 6 is a schematic view of a parametric selector enclosure;

FIG. 7 is a Wollaston prism and photodiode position distribution diagram;

fig. 8 is a graph of bias versus residual photocurrent output for a photodiode.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments.

Referring to fig. 1, a selector for Stokes parameters of polarized light includes a half-wave plate, an electro-optic modulator, a wollaston prism, and a photoelectric conversion module.

In an embodiment of the present invention, fig. 1-a shows that the 1/2 wave plate is a 1/2 wave plate with a wavelength of 808nm and with a precision rotation frame according to the formula of Thor L ab, and the precision of the rotation angle is ± 0.5 degree, fig. 2 shows the rotation frame and the wave plate of 1/2 wave plate.

Type Z L iNbO depicted in section 1-b₃The electro-optical modulator is the core device of the utility model, which selects Z-shaped L iNbO₃The electro-optical modulator has the advantages of low price, small size, high light intensity bearing capacity, large working temperature range and the like, and is wider in application. According to the analysis of the formula (1),_zwhen the voltage is 0, the electro-optical crystal does not apply voltage;_zwhen pi/2, according to

Determining the required modulation voltage Vz, where n_oThe structure of the electro-optic crystal is shown in FIG. 5 for ordinary refractive index, and has the specific dimensions of light passing length L, width D, light wavelength λ, and light wavelength γ of L iNbO₃Electro-optic crystal coefficient.

The semiconductor DC voltage conversion chip is selected to generate DC high voltage, and the highest voltage is set not to exceed 120V considering the working condition of the chipLine-fabricated semiconductor DC high voltage source, L iNbO is customized according to the high voltage source parameters₃Electro-optic crystal, the side to which voltage is applied is gold-plated, and the specific dimensions are as shown in table 1:

TABLE 1L iNbO₃Size and correlation coefficient of electro-optic crystal

The actual debugging result is_zAt pi/2, the bias voltage is 103 volts.

L iNbO plated with gold electrode₃The crystal is mounted on the base as shown in FIG. 4, and is adjusted and fixed by M2 screw on the side of the base, so that L iNbO₃The crystal is horizontally fixed, and the circular arc-shaped groove on the base is used for connecting L iNbO₃L iNbO as side leading-out connecting wire₃The connecting wire and the aluminum alloy packaging box are subjected to silver paste low-temperature baking process, the bonding effect is shown in figure 3, 1 is an aluminum alloy packaging box, 2 is a polytetrafluoroethylene base, 3 is an adjusting screw, and 4 is L iNbO₃The crystal, 5 is a connecting electrode, 6 is a silver paste electrode, and 7 is a screw adjusting hole.

In order to reduce the influence of external stray light on measurement, as shown in fig. 6, the base is installed in the aluminum alloy installation box, the small circular hole on the side surface in the installation box corresponds to the adjusting screw on the base, and the screw can be timely inserted from the outside to adjust L iNbO by rotating the screw₃And an observation hole is arranged above the light inlet and outlet hole at the position of the crystal, so that whether the incident light is aligned to the incident end face of the crystal or not and whether all emergent light beams are emitted from the light outlet hole or not can be observed in real time.

The wollaston prism described in section c of fig. 1 as a Polarizing Beam Splitter (PBS) is capable of splitting incident polarized light into 50:50, the two lights are symmetrically distributed with the center line as the reference, which is very beneficial to the installation of the photodiode. BBO Wollaston prisms with a size of 10mm were selected as PBS. As shown in fig. 7, the two photodiodes are mounted by welding and debugging other components on the circuit board except the two photodiodes, then fixing the wollaston prism at the reserved position of the circuit board, measuring the path of the marker PBS beam splitting light, cutting out the equal length on the two paths as the position of the incident end face of the photodiode, fixing the photodiode, and then welding the pins to be connected. This enables two beams of light to be incident perpendicularly to the center of the incident end face of the semiconductor photodiode, respectively, and receives 50:50 beams of light.

The photodiode in the photoelectric conversion module described in section d of fig. 1 receives two polarized lights with polarization directions orthogonal to each other from the wollaston edge, and converts the two polarized lights into a photocurrent. As shown in fig. 8, the two photodiodes have two pairs of transistors of the BPX61 semiconductor photodiode type with identical performance parameters. The two ends of the two photodiodes connected in series are applied with 12 voltages, and the shielding wiring technology is adopted, so that the connection midpoint of the two photodiodes outputs residual photocurrent which is only equal to S_out＝(Qcos4θ+Usin4θ)cos_z+Vsin_zIt is related. By selecting different rotation angles theta and phase delay angles_zThe required Stokes parameters can be obtained, and the selection of the polarized light Stokes parameters is realized.

In combination with the application example, in the natural atmospheric background and the polarization effect of the target object on the incident sunlight, the circular polarization component is very little, and V is assumed to be 0, so that the polarization effect only needs to be obtained in_zWhen θ is 0, the parameter Q is selected, and when θ is pi/8, the parameter U is selected.

The identification and decoding of signals in single-beam coherent optical communication are only related to two Stokes parameters, U and V, under the condition that theta is equal to pi/8,_zselecting a parameter V when the parameter V is 0;_zthe parameter U is chosen pi/2.

In general, when θ is 0,_zselecting a parameter Q under an initial condition of 0; the 1/2 waveplate is then rotated to θ ═ π/8:_zselecting a parameter V when the parameter V is 0;_zthe parameter U is chosen pi/2.

It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modifications, equivalents and the like which do not depart from the spirit and scope of the present invention should be construed as being included therein.

Above is the utility model discloses a preferred embodiment, all rely on the utility model discloses the change that technical scheme made, produced functional action does not surpass the utility model discloses during technical scheme's scope, all belong to the utility model discloses a protection scope.

Claims

1. A selector for Stokes parameters of polarized light comprises a half-wave plate, an electro-optic modulator, a Wollaston prism and an electro-optic conversion module, and is characterized in that the half-wave plate is an 1/2 wave plate capable of being precisely rotated, Q and U parameters of input polarized light are rotated, and V is reflected and operated as-V, and the electro-optic modulator is a Z-shaped L iNbO₃The electro-optical modulator can rotate the U and V parameters by any angle; the Wollaston prism decomposes the rotated parameters into two orthogonal polarized light components; the photoelectric conversion module converts the selected output light into corresponding photocurrent, and realizes selection of polarized light Stokes parameters by photocurrent difference.

2. The selector of Stokes parameters for polarized light of claim 1, wherein the Stokes parameter selector comprises precisely rotatable 1/2 wave plate, Z-type L iNbO₃Electro-optical modulator, Wollaston prism, in which a precisely rotatable 1/2 waveplate converts the input light into S_in＝[I Q U V]^TQ, U two components of polarized light are rotated by 4 theta around V polarization axis, and the rotation of V by 180 DEG is used to obtain S_out1＝[I Q₁U₁V₁]^TZ type L iNbO₃Electro-optical modulator_out1Q of (2)₁、V₁Two components wound around U₁Rotation of the shaft_zTo obtain S_out2＝[I Q₂U₂V₂]^TWollaston prism handle S_out2Split into two orthogonal polarized light components:

and

where theta is the rotation angle of the fast axis of the 1/2 wave plate relative to the horizontal,_zis Z-type L iNbO₃Phase delay angle of electro-optic modulator, proportional to modulation voltage Vz, Q₂＝(Q cos4θ+U sin4θ)cos_z+Vsin_z。

3. The selector of a Stokes parameter of a polarized light as claimed in claim 1, wherein said photoelectric conversion module is a current differentiator formed by two semiconductor photodiodes for receiving two orthogonal polarized light components S_HoutAnd S_VoutConversion of a light beam into a photocurrent I_HoutAnd I_VoutAnd differencing to obtain only the sum Q₂The residual photocurrent I involved_out＝I_Hout-I_VoutUsing Q₂With rotation angle theta and phase delay angle_zAnd (3) selecting different Stokes parameters to play a role in selecting the Stokes parameters.

4. The selector for Stokes parameters of polarized light as claimed in claim 2, wherein said Z-type L iNbO₃An electro-optical modulator is composed of a Z-type L iNbO₃The electro-optical crystal, the mounting box and the modulation voltage source, wherein the Z type L iNbO₃Delay phase generated by electro-optic crystal

The Q is₁、V₁Two components wound around U₁Rotation of the shaft_zWhere n is_oL is the light passing length of the electro-optic crystal, D is the width of the electro-optic crystal, λ is the wavelength of light, and γ is L iNbO₃Electro-optic crystal factor, Z-type L iNbO₃The electro-optical crystal is arranged on a polytetrafluoroethylene base, the base is arranged in an aluminum alloy packaging box, an electro-optical crystal lead wire connecting joint and a wafer adjusting screw are arranged on the packaging box, the electro-optical crystal is connected with a lead wire through low-temperature silver paste, and a 0-120V direct-current voltage source is externally arranged.

5. The selector for Stokes parameters of claim 1, wherein the two photodiodes of the photoelectric conversion module have the same performance parameters, and are equidistantly installed on the output end faces of the wollaston prism, and ± 12 voltages are applied to the two ends of the two photodiodes connected in series, and the shielding wiring technology is adopted, so that the connection midpoint of the two photodiodes outputs the residual photocurrent.