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高光谱偏振成像全Stokes参量获取新方法

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考虑到现有Stokes参量获取方法测量速度慢、测量精度低、系统结构复杂等特点,提出了一种基于双液晶可调相位延迟器(liquid crystal variable retarder,LCVR)和声光可调滤波器(acousto-optic tunable filter,AOTF)的光谱偏振成像系统中全Stokes参量的新获取方法.从AOTF和LCVR的工作原理出发,介绍了系统的基本探测原理;根据偏振分析提出了快速获取全Stokes参量的新方法——该方法选取四个固定的LCVR控制电压,同时控制两个相同的LCVR对光波进行相位调制,得到四组(八个)两两相同的相位延迟量即可求得Stokes参量.此外,设计了能够稳定输出均方根为0~+8.72 V连续可调方波的LCVR控制器,并对其进行定标,实现了不同波长下光波的精确调制.搭建实验样机,以偏振方向分别为0°,90°和45°的三个偏振片P1,P2,P3作为偏振测量目标,测得了波长为632 nm时的全Stokes参量图;以画有夹角为30°的红色、绿色、蓝色三色线条的实验板作为光谱测量目标,对400~750 nm光谱范围的71个通道(光谱带宽为5 nm)进行光谱成像,得到了与红色、绿色和蓝色的分析谱段范围相一致的光谱曲线.结果表明,该系统不仅可以快速准确地获取全部Stokes参量,而且系统结构简单、成像质量良好.

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第３７卷，第１２期

２０１７年１２月

光

谱

学

与

光

谱

分

析

Vol.３７，No.１２，３９５３‐３９５８

Spectroscopy and Spectral Analysis

December ，２０１７

New Method for Obtaining Full‐Stokes Parameters of

High‐Spectral Polarization Imaging System

１，３

１，２ *

１

LI Xiao ，LIU Shun ，WANG Zhi‐bin ，XUE Peng ，ZHANG Rui ，

１

WANG Yao‐li ，JING Ning

１．Engineering and Technology Research Center of Shanxi Province for Optical‐electric Information

and Instrument ，Taiyuan ０３００５１，China

２．School of Computer and Control Engineering ，North University of China ，Taiyuan ０３００５１，China

３．School of Electrical and Control Engineering ，North University of China ，Taiyuan ０３００５１，China

Abstract Taking into account of the slow measuring speed ，low measuring accuracy and complex system

structure of the existing Stokes parameters acquisition method ，a new acquisition method of full‐Stokes param‐

eters in double Liquid Crystal Variable Retarder （LCVR）and Acousto‐Optical Tunable Filter （AOTF）combi‐

ning spectral polarization imaging system is established ．Based on the working principle of AOTF and LCVR ，

this paper has explored the basic detection principles of the system before a new method for fast acquisition of

full‐Stokes parameters is proposed ．According to polarization analysis ，fixed control voltage is selected as the

basis ，in which four fixed voltages are selected as the control voltages of LCVR ，and two identical LCVR are

controlled at the same time to complete phase modulation of optical waves ．The Stokes parameters can be ob‐

tained with four groups of phase delay which are plunging the same ．Besides ，a LCVR controller is designed to

stabilize the output square wave whose root mean square is ０ to ＋８.７２ V ．Then ，its calibration is carried out

in order to realize precise modulation of different optical waves ．Finally ，an experimental prototype is set up to

test the target ，with three polarizing plates P

１

，P

２

and P

３

whose polarization directions being ０，９０ and ４５ de‐

rees respectively as the targets of polarization measurement ．The full‐Stokes parameter figures with a wave‐

length of ６３２ nm is obtained ； aper painted with red ， reen and blue lines and the angle of ３０ degrees are used

as the target of spectral measurement ，spectral imaging on ７１channels of ４００～７５０ nm spectral range （spectral

bandwidth of ５ nm），the spectrum curves of red ， reen ，blue are acquired which accordant with their theoreti‐

cal spectral graphs ．The results show that not only all the Stokes parameters can be obtained quickly and accu‐

rately with the system ，but also the structure of system is simplified and the imaging quality is improved ．

Keywords High‐spectral polarization imaging ；Full‐Stokes parameters ；Double LCVR ；AOTF ；LCVR controller

中图分类号：O４３３

文献标识码：A

DOI ：１０.３９６４／.issn.１０００‐０５９３（２０１７）１２‐３９５３‐０６

nology and space imaging technology ，which can obtain the

spectral information ， olarization information and image in‐

Introduction

［１‐６］

formation of the object simultaneously

．Besides ，being

Spectral polarization imaging is an organic combination of

helpful to improve the detection and recognition ability of tar‐

spectral analysis technology ， olarization measurement tech‐

et effectively ，it is widely used in medical imaging ，environ‐

Received ：２０１６‐０５‐０４；accepted ：２０１６‐１０‐２９

Foundation item ：National Natural Science Foundation for Special of China（６１１２７０１５），International Science and Technology Cooperative Pro‐

ect（２０１３DFR１０１５０），Science and Technology Research Fund for Youth of Shanxi（２０１４０２１０１２）

Biography ：LI Xiao ，（１９７２— ），associate professor ，North University of China

e‐mail ：lixiaoydx＠１６３．com

万方数据

* Corresponding author

e‐mail ：liushun＿ls＠ eah ．net

光谱学与光谱分析

第３７卷

３９５４

mental monitoring ，military identification ，deep space explo‐

ration and other fields ．In terms of polarization imaging sys‐

tems ，the Stokes vector method does not limit the spectral

voltage that is loaded on both ends of the liquid crystal ，then

the phase delay of the incident light is adjusted continuously ，

and finally different polarization states can be detected ．The

relationship between the voltage applied to the liquid crystal

electrode and the tilt angle of the liquid crystal molecule

range ，and contains almost all the shapes of beams in na‐

［７‐１２］

ture

，moreover ，it can describe both full polarized light

［２１‐２２］

and partial polarized light as well as non‐ olarized light ．

Therefore ，Stokes vector method is widely used as a macro‐

scopic and measurable description method ．

０，

（U

）

≤

＞

＝

０

－

２

２arctan exp

，（U

）

－

In recent years ，the N ．Gupta group of U ．S ．Army Re‐

（２）

search Laboratory proposed an acquisition method of Stokes

［１３‐１５］

in which ，U is the threshold voltage ，U is the corresponding

voltage of a ^tl^hiquid crystal molecule to a s^０pecific angle ．We can

know that ，when the applied voltage is less than or equal to

the threshold voltage ，the tilt angle of the liquid crystal mole‐

cules is ０°；when the applied voltage is greater than the

threshold voltage ，the tilt angle of the liquid crystal molecules

arameters of high spectral polarization imaging system

．

This method requires constant replacement of the drive volt‐

age to achieve the same phase delay at different wavelengths ，

which prolongs the measurement time ，and reduces the meas‐

［１６］

urement accuracy

．In ２０１５，a method based on an Acous‐

to‐Optic Tunable Filter （AOTF） and a Liquid Crystal Varia‐

ble Retarder （LCVR）^{［１６‐１８］}is proposed ．However ，this meth‐

od has the same problem as that of N ．Gupta group ．In fact ，

is θ，the specific function relationship between deflection angle

［１６］

and the applied voltage is given in

．

When the light passed through a phase retarder with a

the use of two CCD for AOTF １ diffraction imaging increases

［１６］

thickness of d ，the phase delay is

the complexity of system construction greatly

．

２π（n

（θ）－ n

）d ２π（n

）d

－

２

Based on the previous studies ，a fast acquisition method

for all Stokes parameters of hyperspectral polarization imaging

systems is proposed referring to two LCVR and one AOTF ．

Four driving voltage is chosen as reference to control two

identical LCVR simultaneously ，obtaining full‐Stokes parame‐

ters through four sets of polarization image ．Besides ，a CCD

camera is applied to detect the ＋１ diffraction light of AOTF ，

which can not only overcomes the existing defects of the sys‐

tem ，but also improves the imaging quality further ．

cos θ

（３）

＝

and n

is the reflection rate of o light and e light ，respec‐

tively ，and λis wavelength ．

According to equation （３），it is found that the phase de‐

lay δ is related to the deflection angle θ，and equation （２）

shows that the deflection angle θis related to the voltage U

applied to the LCVR ．In conclusion ，the phase‐modulation of

the incident light wave can be realized by changing the voltage

that is loaded on the LCVR ．

１ Basic Principle

２

Hyperspectral Polarization Imaging Sys‐

tem

1.1 The Principle of AOTF

AOTF is an electrically turntable filter based on the in‐

2.1 Fundamentals of System Detection

teraction of acoustic wave with light wave ．When the incident

The principle of hyperspectral polarization imaging sys‐

light‐wave and the ultrasonic wave is suitable for the momen‐

tem based on dual‐LCVRs and AOTF is shown in figure １．

［１９‐２０］

tum‐matching ，the incident light will be diffracted

，and

The polarization direction of the polarizer P

１

is the reference

the corresponding length of the diffracted light wave λ

０

can be

direction of ０° ，the fast axis direction of LCVR１ and LCVR２

are ９０° and －４５° ，respectively ，the polarization direction of

expressed as

２

０

２n

cos（θ

）

（１）

＝

＋

－

the polarizer P

１

and P

２

laced on the both sides of AOTF are

erpendicular to each other ，which can effectively eliminate

in which ，V

is the speed of sound ，

is frequency of sound

the influence of grade ０ and grade ‐１ diffraction light ．The

target light passed through the pre‐optical system ，LCVR１，

LCVR２ and AOTF ，and then imaged on the CCD camera ．

During the operation of the whole system ，we used personal

computer to realize the control of dual‐LCVRs and AOTF ，

and finally achieved the polarization imaging of the target ．

wave ，θ

and θ

are the polar angles of incident light and dif‐

fracted light ，respectively ，n

and n

are the refractive index of

incident light and diffracted light ，respectively ．

1.2 The Principle of LCVR

LCVR is an optical phase retarder based on the electrical‐

ly controlled birefringence of liquid crystal ，the refractive in‐

dex of liquid crystal molecules is controlled by changing the

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