CN201373959Y - Device for measuring twisty angle and optical retardation of liquid crystal device - Google Patents

Abstract

The utility model belongs to the technical field of optoelectronics and measurement, and relates to a device for measuring the twisty angle and the optical retardation of a reflection type liquid crystal device; the device comprises a double-frequency Zeeman laser, a lambada/4 wave plate, a beam splitter, an analyzer, a photoelectric detector and a signal processor. When in testing, an optical axis is taken as an axis to rotate a tested liquid crystal device; when the rotation angle of the tested liquid crystal device is 0 degree, 60 degrees and 120 degrees respectively, the phase differences obtained by the signal processor are recorded, wherein the phase differences are respectively psi1, psi2 and psi3, and a computer utilizes heterodyne measurement equation to conduct curve fitting on the psi1, psi2, and psi3 and 0, pi/3, and 2pi/3, thus obtaining the twisty angle and the optical retardation data of the tested liquid crystal device. The device has the beneficial effects that the generated beat frequency signal can avoid errors caused by the fluctuation of light source or environmental influence, and an alternating current amplifier replaces a conventional direct current amplifier, thus avoiding direct current level shifting caused by external disturbance.

Description

Measure the device of liquid crystal device twist angle and light delay

Technical field

The utility model belongs to optoelectronics and field of measuring technique, relates to the device of measuring reflection type liquid crystal device twist angle and light delay.

Background technology

Liquid crystal device since have low in energy consumption, volume is little and plurality of advantages such as in light weight, be used in very in the extensive fields.The twist angle of the measurement liquid crystal device of widespread use now and the method for light delay mainly are Stokes parametric method (Susumu Sato etc., Japan), spectral scanning method (S.T.Tang etc., Hong Kong) and interferometric method etc.These methods all belong to two classes: monochromatic light method and spectroscopic methodology.There is following shortcoming in they:

1, adopt spectroscopy measurements, can be because the Fabry-Perot effect that the reflection between the inner multilayer film of liquid crystal device produces causes measuring error.

2, adopt spectroscopy measurements, complex structure, expense is higher.

3, adopt monochromatic light to measure, because the fluctuation of light source or the influence of environment, light intensity value easily produces measuring error.

4, adopt spectral measurement and employing monochromatic light to measure, because the electric signal of light intensity signal and electrooptical device output all is a DC quantity, dc shift also will produce measuring error.

The optical heterodyne measuring technique has the advantage of precision height, strong interference immunity, is usually used in the accurate measurement of physical quantitys such as length, displacement, speed, but is not applied in the field tests of liquid crystal device as yet.

The utility model content

The purpose of this utility model provides a kind of device of measuring liquid crystal device twist angle and light delay, the error that the beat signal that produces can avoid light source fluctuation or environmental impact to cause, replace conventional direct current amplifier by AC amplifier, can completely cut off the DC level drift that causes by external interference.

In order to achieve the above object, the technical solution of the utility model is as follows:

Measure the device of liquid crystal device twist angle and light delay, comprise double frequency zeeman laser, λ/4 wave plates, beam splitter, tested reflection type liquid crystal device, first analyzer, first photodetector, second analyzer, second photodetector and signal processor, the output optical axis of double frequency zeeman laser and λ/4 wave plates surperficial orthogonal, the output optical axis of double frequency zeeman laser and the reflecting surface of beam splitter are in angle of 45 degrees; The Surface Vertical of tested reflection type liquid crystal device is in the transmitted light of beam splitter; The Surface Vertical of the surface of first analyzer and first photodetector is in the secondary reflected light of beam splitter, and first analyzer is between first photodetector and beam splitter; Look along the light working direction, the light transmission shaft of first analyzer becomes miter angle with the slow axis of λ/4 wave plates; The Surface Vertical of the surface of second analyzer and second photodetector is in the primary reflected light of beam splitter, and second analyzer is between second photodetector and beam splitter; Look along the light working direction, the light transmission shaft of second analyzer becomes miter angle with the slow axis of λ/4 wave plates; First photodetector and second photodetector are electrically connected with signal processor respectively.

The effect of each device in the device of the present utility model: the double frequency zeeman laser sends the left and right rounding polarized light with frequency difference, λ/4 wave plates make the emergent light of double frequency zeeman laser become the mutually perpendicular double frequency linearly polarized light in polarization direction, beam splitter makes light portion transmission, partial reflection, two analyzers make the direction of vibration unanimity of double frequency light and produce beat frequency interference, two photodetectors are gathered beat signal respectively, and send into signal processor, signal processor is made comparisons to obtain the phase differential of two paths of signals to two paths of signals.

The beneficial effects of the utility model are as follows:

1, tested liquid crystal device makes the flashlight phase place that variation take place, and when flashlight and reference light produced beat respectively and interfere, the phase differential of these two cadence signals equaled the phase change that flashlight takes place tested liquid crystal device.

2, the utility model uses the optical heterodyne method to measure the phase change of optical beat signal, because the frequency of beat signal has only several megahertzes, photodetector can response signal frequency and phase change, the error that beat signal can avoid light source fluctuation or environmental impact to cause.

3, the utility model replaces conventional direct current amplifier by AC amplifier, can completely cut off the DC level drift that is caused by external interference like this.

4, need not to know the direction of liquid crystal top layer molecule before the utility model test, and in twist angle that obtains liquid crystal device and light delay, can obtain liquid crystal top layer molecular orientation.

Description of drawings

Fig. 1 is the structural representation that the utility model is measured the device of reflection type liquid crystal device twist angle and light delay.

Fig. 2 is the coordinate system synoptic diagram of signal light path of the present utility model.

Fig. 3 be the phase difference that obtains of signal processor of the present utility model and tested reflection type liquid crystal device corner γ concern profile.

Among the figure: 1, double frequency zeeman laser, 2, λ/4 wave plates, 3, beam splitter, 4, tested reflection type liquid crystal device, 5, first analyzer, 6, first photodetector, 7, second analyzer, 8, second photodetector, 9, signal processor.

Embodiment

Below in conjunction with accompanying drawing the utility model is done description in further detail:

As shown in Figure 1, the device that the utility model is measured liquid crystal device twist angle and light delay comprises: double frequency zeeman laser 1, λ/4 wave plates 2, beam splitter 3, tested reflection type liquid crystal device 4, first analyzer 5, first photodetector 6, second analyzer 7, second photodetector 8 and signal processor 9, the output optical axis of double frequency zeeman laser 1 and λ/4 wave plates 2 surperficial orthogonal, the reflecting surface of the output optical axis of double frequency zeeman laser 1 and beam splitter 3 is in angle of 45 degrees; The Surface Vertical of tested reflection type liquid crystal device 4 is in the transmitted light of beam splitter 3; The Surface Vertical of the surface of first analyzer 5 and first photodetector 6 is in beam splitter 3 secondary reflected light, and first analyzer 5 is between first photodetector 6 and beam splitter 3; Look along the light working direction, the light transmission shaft of first analyzer 5 becomes miter angle with the slow axis of λ/4 wave plates 2; The Surface Vertical of the surface of second analyzer 7 and second photodetector 8 is in beam splitter 3 primary reflected light, and second analyzer 7 is between second photodetector 8 and beam splitter 3; Look along the light working direction, the light transmission shaft of second analyzer 7 becomes miter angle with the slow axis of λ/4 wave plates 2; First photodetector 6 and second photodetector 8 are electrically connected with signal processor 9 respectively.

Course of work when device of the present utility model is used to measure the twist angle of reflection type liquid crystal device and light delay is: the left and right rounding polarized light with frequency difference is sent by double frequency zeeman laser 1, become the mutually perpendicular double frequency linearly polarized light in polarization direction through behind λ/4 wave plates 2, pass through beam splitter 3 back separated into two parts then: transmitted light and reflected light, transmitted light is called flashlight, and reflected light is called reference light; Reference light produces optical beat through second analyzer 7 interferes, and beat signal is gathered by second photodetector 8; When flashlight arrives tested reflection type liquid crystal device 4, produced the phase change different, and reflected back into beam splitter 3, reflexed to the reverse direction of reference light then by beam splitter 3 with reference light, produce beat frequency interference through first analyzer 5 again, beat signal is gathered by first photodetector 6; First photodetector 6, second photodetector 8 change beat signal into ac signal, send into signal processor 9, obtain the phase differential of reference light and flashlight interference signal; According to the phase differential of reference light and flashlight interference signal, calculate the twist angle and the light delay data of tested liquid crystal device 4.

The twist angle of the utility model measurement reflection type liquid crystal device and the test philosophy of light delay are as follows:

Is that axle rotates a tested liquid crystal device 4 with the optical axis, when the corner of tested liquid crystal device 4 be 0 degree, when 60 degree and 120 are spent, the phase difference that tracer signal processor 9 obtains ₁, Ψ ₂And Ψ ₃, utilize reflective heterodyne measurement equation solution by computing machine.

Reflective heterodyne measurement equation:

$c\tan \mathrm{\&Psi;}=\frac{2\&CenterDot;\mathrm{\&delta;}\&CenterDot;\sin \mathrm{\&beta;}\&CenterDot;\sqrt{{\mathrm{\&beta;}}^2-{\mathrm{\&delta;}}^2{\sin }^2\mathrm{\&beta;}}\&CenterDot;[{\mathrm{\&beta;}}^2\cos 2(\mathrm{\&alpha;}+\mathrm{\&gamma;})-\mathrm{\&phi;}\&CenterDot;\sin 2(\mathrm{\&alpha;}+\mathrm{\&gamma;})\&CenterDot;\tan \mathrm{\&beta;}]}{({\mathrm{\&beta;}}^2-2{\mathrm{\&delta;}}^2{\sin }^2\mathrm{\&beta;})\sqrt{{\mathrm{\&beta;}}^2+{\mathrm{\&phi;}}^2{\mathrm{<figure-callout\; id="2"\; label="tan"\; filenames="Y2009200932560009H1.png"\; state="\{\{state\}\}">tan</figure-callout>}}^2\mathrm{\&beta;}}}$

δ and β are expressed as follows in the equation

δ＝π·Δnd/λ，β ²＝δ ²+φ ²

Use Ψ ₁, Ψ ₂And Ψ ₃Replace heterodyne system and measure Ψ in the equation, with 0, π/3 and 2 π/3 replace the γ in the heterodyne systems measurement equations, are carried out curve fitting by computing machine, obtain the twist angle and the light delay data of tested liquid crystal device 4.

Heterodyne system measurement equation of the present utility model and derivation process thereof are as follows:

The coordinate system of signal light path as shown in Figure 2, all projections all are the projections of looking along the light working direction.The light transmission shaft of first analyzer 5 is taken as the x axle, is taken as the y axle with the light transmission shaft vertical direction of first analyzer 5.A is the molecule director projection on the light entering surface of tested liquid crystal device 4 among the figure; B is the molecule director projection on the light outgoing plane of tested liquid crystal device 4; α is that the corner of tested liquid crystal device 4 is 0 when spending, and the liquid crystal molecule director orientation on the light entering surface of tested liquid crystal device 4 is at the projection and the axial angle of x on x-y plane; φ is the twist angle of tested liquid crystal device 4.

Below employed mathematic sign be unitedly described as follows:

Unknown parameter:

φ is that twist angle, the Δ nd of tested liquid crystal device 4 is the light delay of tested liquid crystal device 4;

α is that the corner of tested liquid crystal device 4 is 0 when spending, and the liquid crystal molecule director orientation on the light entering surface of tested liquid crystal device 4 is at the projection and the axial angle of x on x-y plane.α, φ, Δ nd will be found the solution simultaneously.

Known parameters, the i.e. parameter that can directly obtain by device of the present utility model:

Ψ is the phase differential that signal processor 9 obtains;

γ is the corner of tested liquid crystal device 4;

λ is the wavelength of zeeman laser 1.

The derived object that heterodyne system is measured equation promptly is that above-mentioned unknown parameter and known parameters are combined into the equation that can find the solution.For this reason, following formula (1) (2) (3) (4) (5) (6) (7) promptly is in order to utilize known formula to express Ψ ₁, Ψ ₂, Ψ ₃Relational expression with α, φ, Δ nd, γ, λ.

The phase difference that signal processor 9 obtains satisfies following known formula

$\mathrm{\&Psi;}=\arg (E_{\mathrm{Exit}1}^{*}\&CenterDot;E_{\mathrm{Exit}2})---\left(1\right)$

E _Exit1, E _Exit2Represent that respectively the different two-beam of the frequency of x, y direction of principal axis vibration is by the expression formula behind first analyzer 5

$E_{\mathrm{Exit}1}=[\cos \mathrm{\&theta;},\sin \mathrm{\&theta;}]\&CenterDot;R(-\mathrm{\&alpha;}-\mathrm{\&gamma;})\&CenterDot;M\&CenterDot;R(\mathrm{\&alpha;}+{\mathrm{\&phi;}}_D)\&CenterDot;\left[\begin{array}{c}1\\ 0\end{array}\right]---\left(2\right)$

${\mathrm{<figure-callout\; id="2"\; label="E\; Exit"\; filenames="Y2009200932560009H1.png"\; state="\{\{state\}\}">E</figure-callout>}}_{\mathrm{Exit}}=[\cos \mathrm{\&theta;},\sin \mathrm{\&theta;}]\&CenterDot;R(-\mathrm{\&alpha;}-\mathrm{\&gamma;})\&CenterDot;M\&CenterDot;R(\mathrm{\&alpha;}+{\mathrm{\&phi;}}_D)\&CenterDot;\left[\begin{array}{c}0\\ 1\end{array}\right]---\left(3\right)$

(2) R is a rotation matrix in (3) formula

$R(*)=\left[\begin{array}{cc}\cos (*)& \sin (*)\\ -\sin (*)& \cos (*)\end{array}\right]---\left(4\right)$

M is the Jones matrix that light transmits in liquid crystal, $M=M_a^T\&CenterDot;M_a$

$M_a=R(-\mathrm{\&phi;})\&CenterDot;\left[\begin{array}{cc}\cos \mathrm{\&beta;}-\mathrm{i\&delta;}\frac{\sin \mathrm{\&beta;}}{\mathrm{\&beta;}}& \mathrm{\&phi;}\frac{\sin \mathrm{\&beta;}}{\mathrm{\&beta;}}\\ -\mathrm{\&phi;}\frac{\sin \mathrm{\&beta;}}{\mathrm{\&beta;}}& \cos \mathrm{\&beta;}+\mathrm{i\&delta;}\frac{\sin \mathrm{\&beta;}}{\mathrm{\&beta;}}\end{array}\right]---\left(5\right)$

M _a ^TExpression M _aTransposed matrix.

(5) R in the formula is with (4) formula, in (5) formula

δ＝π·Δnd/λ (6)

β ²＝δ ²+φ ² (7)

So far, the relational expression of having listed Ψ and α, φ, Δ nd, λ, γ i.e. (1) (2) (3) (4) (5) (6) (7) formula, and the heterodyne measurement equation (8) that obtains reflection type liquid crystal device twist angle and light delay of continuing to derive is as follows,

$c\tan \mathrm{\&Psi;}=\frac{2\&CenterDot;\mathrm{\&delta;}\&CenterDot;\sin \mathrm{\&beta;}\&CenterDot;\sqrt{{\mathrm{\&beta;}}^2-{\mathrm{\&delta;}}^2{\sin }^2\mathrm{\&beta;}}\&CenterDot;[{\mathrm{\&beta;}}^2\cos 2(\mathrm{\&alpha;}+\mathrm{\&gamma;})-\mathrm{\&phi;}\&CenterDot;\sin 2(\mathrm{\&alpha;}+\mathrm{\&gamma;})\&CenterDot;\tan \mathrm{\&beta;}]}{({\mathrm{\&beta;}}^2-2{\mathrm{\&delta;}}^2{\sin }^2\mathrm{\&beta;})\sqrt{{\mathrm{\&beta;}}^2+{\mathrm{\&phi;}}^2{\mathrm{<figure-callout\; id="2"\; label="tan"\; filenames="Y2009200932560009H1.png"\; state="\{\{state\}\}">tan</figure-callout>}}^2\mathrm{\&beta;}}}---\left(8\right)$

δ and β are expressed as follows in the equation

δ＝π·Δnd/λ，β ²＝δ ²+φ ²。

An embodiment of the present utility model is:

As shown in Figure 1, the wavelength X of double frequency zeeman laser 1 is 0.6328 μ m, frequency difference 2.7MHz; First analyzer 5, second analyzer 7 all adopt polarizing prism, and first photodetector 6, second photodetector 8 all adopt photomultiplier, and signal processor 9 adopts phasometer.

Is that axle rotates a tested liquid crystal device 4 with the optical axis, when the corner of tested liquid crystal device 4 be 0 degree, when 60 degree and 120 are spent, the phase difference that tracer signal processor 9 obtains ₁, Ψ ₂And Ψ ₃, utilize heterodyne system to measure equation solution by computing machine, heterodyne system is measured equation and is:

$c\tan \mathrm{\&Psi;}=\frac{2\&CenterDot;\mathrm{\&delta;}\&CenterDot;\sin \mathrm{\&beta;}\&CenterDot;\sqrt{{\mathrm{\&beta;}}^2-{\mathrm{\&delta;}}^2{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="Y2009200932560009H1.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&beta;}}\&CenterDot;[{\mathrm{\&beta;}}^2\cos 2(\mathrm{\&alpha;}+\mathrm{\&gamma;})-\mathrm{\&phi;}\&CenterDot;\sin 2(\mathrm{\&alpha;}+\mathrm{\&gamma;})\&CenterDot;\tan \mathrm{\&beta;}]}{({\mathrm{\&beta;}}^2-2{\mathrm{\&delta;}}^2{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="Y2009200932560009H1.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&beta;})\sqrt{{\mathrm{\&beta;}}^2+{\mathrm{\&phi;}}^2{\tan }^2\mathrm{\&beta;}}}$

δ and β are expressed as follows in the equation

δ＝π·Δnd/λ，β ²＝δ ²+φ ²

Use Ψ ₁, Ψ ₂And Ψ ₃Replace heterodyne system and measure Ψ in the equation, with 0, π/3 and 2 π/3 replace the γ in the heterodyne systems measurement equations, are carried out curve fitting by computing machine, obtain the twist angle and the light delay data of tested transmission-type liquid crystal device 4.

Fig. 3 is in the present embodiment, the relation curve synoptic diagram of the corner γ of phase difference that signal processor 9 obtains and tested liquid crystal device 4.Stain be make in the present embodiment corner γ of tested liquid crystal device 4 equal 0 degree, when 60 degree and 120 are spent, the phase difference that records by signal processor 9 respectively ₁, Ψ ₂And Ψ ₃

Claims (3)

1, measures the device of liquid crystal device twist angle and light delay, comprise double frequency zeeman laser (1), λ/4 wave plates (2), beam splitter (3), tested reflection type liquid crystal device (4), first analyzer (5), first photodetector (6), second analyzer (7), second photodetector (8) and signal processor (9), it is characterized in that, the output optical axis of double frequency zeeman laser (1) and λ/4 wave plates (2) surperficial orthogonal, the reflecting surface of the output optical axis of double frequency zeeman laser (1) and beam splitter (3) is in angle of 45 degrees; The Surface Vertical of tested reflection type liquid crystal device (4) is in the transmitted light of beam splitter (3); The Surface Vertical of the surface of first analyzer (5) and first photodetector (6) is in the secondary reflected light of beam splitter (3), and first analyzer (5) is positioned between first photodetector (6) and the beam splitter (3); Look along the light working direction, the light transmission shaft of first analyzer (5) becomes miter angle with the slow axis of λ/4 wave plates (2); The Surface Vertical of the surface of second analyzer (7) and second photodetector (8) is in the primary reflected light of beam splitter (3), and second analyzer (7) is positioned between second photodetector (8) and the beam splitter (3); Look along the light working direction, the light transmission shaft of second analyzer (7) becomes miter angle with the slow axis of λ/4 wave plates (2); First photodetector (6) and second photodetector (8) are electrically connected with signal processor (9) respectively.

2, the device of measurement liquid crystal device twist angle according to claim 1 and light delay, it is characterized in that, first analyzer (5), second analyzer (7) are polarizing prism, first photodetector (6), second photodetector (8) are photomultiplier, and signal processor (9) is a phasometer.

3, the device of measurement liquid crystal device twist angle according to claim 1 and light delay is characterized in that, the wavelength X of described double frequency zeeman laser (1) is 0.6328 μ m, frequency difference 2.7MHz.

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