JPH05306995A - Polarized light measuring device - Google Patents

Abstract

PURPOSE:To measure information of double refraction of a specimen in a short time by detecting correction output subtracting the inherent bias output of a light receiving means from the light receiving output of light flux transmitting a polarized light element. CONSTITUTION:A lambda/4 plate 20 circularly polarizes light flux from a light source part 10 and the light flux transmitting a specimen 30 is received by an analyzer 50. The analyzer 50 is automatically rotated by the use of a motor 51 and a rotating angle is input to a computer 62 through an angle sensor 52. And the sinsoidal change of the quantity of light received due to the rotation of the analyser 50 is converted into an angle, sampling is conducted a plurality of times and a polarized light condition is measured. The light flux passing the analyzer 50 is received by a two-dimensional image sensor 60, its output is A/D-converted and a frame grabber serves to store it. An input correction circuit 65 to which this signal is input serves to subtract stored 64 bias output from a measured value and output to the computer 62. The computer 62 serves to analyze the information of double refraction on the basis of the correction measurement value and display 63 is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring birefringence information due to strain of molecular orientation of an optical component.

[0002]

2. Description of the Related Art Polymer compounds such as plastics generally have anisotropy similar to that of crystals and cause birefringence.

As a device for measuring the birefringence, a device disclosed in, for example, Japanese Patent Application Laid-Open No. 4-58138 is known.

As shown in FIG. 3, the apparatus described in this publication converts a light beam emitted from a light source section 10 composed of a laser light source 11 and a beam expander 12 into circularly polarized light by a first λ / 4 plate 20. Then, the luminous flux transmitted through the sample 30 is set to the second λ /
4 Plate 40 converts to elliptically polarized light close to linearly polarized light and analyzer
Light is received by the image sensor 60 via 50.

The output of the image sensor 60 is A / D converted and stored in the frame grabber 61. The signal from the frame grabber 61 is output to the computer 62. The computer 62 analyzes the birefringence information based on this measurement value and displays it on the display 63.

[0006]

However, in order to measure the birefringence by the above-mentioned conventional apparatus, the light intensity is measured by setting the angle of the analyzer 50 to at least three angles, and the influence of noise is measured. To remove it, change the angle of the λ / 4 plate 40 at least twice, that is, at least 6 in total.
There is a problem in that it has to be performed once, the measurement takes time, and the processing time becomes long because there is a lot of data to be processed.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a birefringence measuring method capable of measuring birefringence information of a sample in a short time.

[0008]

In order to achieve the above-mentioned object, a polarization measuring apparatus according to the present invention comprises a light source for making a specific polarized light incident on a sample and a polarized light for changing the polarization state of a light beam emitted from the sample. Element, light receiving means for receiving the light flux transmitted through the polarizing element, storage means for storing the bias output specific to the light receiving means measured without making the light flux enter the light receiving means, and the output of the storage means from the output of the light receiving means It is characterized in that it has a correcting means for outputting the light reception signal corrected by the above, and a measuring means for measuring the birefringence of the sample by detecting the output of the correcting means while rotating the polarizing element.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.
FIG. 1 shows an embodiment of a polarization measuring device according to the present invention.

This apparatus comprises a light source section 10 which emits linearly polarized light having a predetermined spread, a λ / 4 plate 20 which converts a light beam emitted from the light source section into circularly polarized light, and an optical path of a light beam which has passed through a sample 30. And a two-dimensional image sensor 60 such as a CCD sensor for receiving the light flux transmitted through the analyzer 50.

The output of the image sensor 60 is A / D converted and stored in the frame grabber 61. The signal from the frame grabber 61 is output to the correction circuit 65 in the computer 62. The correction circuit 65 subtracts the bias output stored in the memory 64 from the measured value, as described later, and then the computer 62
Then, the computer 62 analyzes the birefringence information based on the corrected measurement value and displays it on the display 63.

The light source unit 10 includes a laser device for generating linearly polarized light, or a light source 11 in which a light source for emitting a light beam having a random polarization state and a polarizer are combined, and a beam expander for expanding the diameter of the light beam emitted from the light source. It is composed of 12 and.

The analyzer 50 is automatically rotated by the motor 51, and the rotation angle is input to the computer 62 by the angle sensor 52.

First, the sample 3 is placed between the λ / 4 plate 20 and the analyzer 50.
0 is arranged, circularly polarized light is made incident on the sample, and the polarized light emitted from the sample is received via the second λ / 4 plate 40 and the analyzer 50.

When circularly polarized light is made incident on a sample having birefringence, due to the difference in refractive index between the slow axis and the fast axis of the sample, the traveling speeds of the two orthogonal axes differ, and the light is emitted as elliptically polarized light. It

When the analyzer is rotated, the amount of light received changes sinusoidally. Therefore, the polarization state can be measured by changing the angle of the analyzer and sampling this change a plurality of times.

When linearly polarized light is made incident on a linearly birefringent crystal such as plastic, when the incident light coincides with the intrinsic polarized light, the polarization state is not changed and is transmitted. Cannot be detected. When circularly polarized light is incident, the sample has no insensitive direction, unlike the case where linearly polarized light is used, and the polarization state can be measured in any direction.

To represent elliptically polarized light, as shown in FIG. 2, the major radius a, the minor radius b, and the slope ψ of the ellipse drawn by the tip of the electric field vector in the plane opposed to the traveling direction of light are 3 One parameter is required.

The intensity I when elliptically polarized light is received through the analyzer can be obtained by the equation (1), where θ is the rotation angle of the analyzer.

[0020]

## EQU1 ## I = α + βcos2 (θ-ψ) (1) However, α = (a ² + b ² ) / 2 β = (a ² -b ² ) / 2.

In equation (1), 3 of α, β, and ψ, which represent polarization characteristics, are used.
Since there are three unknown variables, three unknown values can be obtained by measuring the output intensity I when the analyzer 50 is rotated to at least three different angular positions. Here, in order to simplify the calculation, four measurements are performed every 45 °. Assuming that the intensities obtained by the four measurements are I ₀ , I ₄₅ , I ₉₀ , and I ₁₃₅ , the variables expressing the polarization characteristics can be obtained according to the following formula.

[0022]

[Equation 2] α = (I ₀ + I ₄₅ + I ₉₀ + I ₁₃₅ ) / 4 β = √ (((I ₀ -I ₉₀ ) ² + (I ₄₅ -I ₁₃₅ ) ² ) / 4) ψ = 1 / 2 ・ tan ^-1 ((I ₄₅ -I ₁₃₅ ) / (I ₀ -I ₉₀ ))

However, in the case of measuring the polarization characteristic based on only the intensity as described above, there is a problem that the polarization characteristic cannot be accurately measured if the signal has noise.

The largest cause of noise is the mixing of the sync signal into the video signal of the television. In a normal television system, setting of both signals is often inaccurate, which makes matching with the input of the frame grabber difficult.

If such noise is present, α and β cannot be accurately obtained. However, the inclination ψ of the principal axis of the polarization ellipse can be accurately obtained without being affected by noise.

In order to remove noise, the apparatus of the present invention measures the bias output Ibias for each pixel of the image sensor in advance in a state where no light is incident on the image sensor 60, and measures this during actual measurement. Correct by subtracting from the value.

To obtain the bias output Ibias, the output from the frame grabber 61 is input to the computer 62,
The measured value is stored in the memory 64. At the time of actual measurement, the correction circuit 65 subtracts the bias output Ibias stored in the memory 64 from the measurement value Im input from the frame grabber 61 to input the correction measurement value I to the computer 62.

This bias output Ibias corresponds to the electrical noise component of the image sensor. If the electrical system is completely adjusted, the bias output Ibias of each pixel at this time becomes zero.

By such calculation, it is possible to obtain the intensity without the influence of noise, and it is possible to accurately measure α and β.

The birefringence axis direction θ and the retardance δ are calculated by the following equations.

[0031]

[Mathematical formula-see original document] θ = ψ -π / 4 δ = 2 · tan ^-1 (√ (Imin / Imax))-π / 2 However, Imax = α + β Imin = α-β.

The above calculation is executed for each pixel of the image sensor, and the birefringence information of the entire area of the sample can be analyzed at one time.

When the analysis is completed, for example, the retardance δ
Is converted into light and dark gradation and displayed on the display 63, or converted into dot size and printed out. Thereby, the variation of birefringence of the sample can be visually grasped as a whole.

When linearly polarized light is made incident on the sample, if the incident light matches the intrinsic polarized light of the linearly birefringent crystal such as plastic, the polarization state is not changed and the light is transmitted. Although no information can be detected, the use of circularly polarized light as in the embodiment makes it possible to eliminate the insensitive direction with respect to the sample.

[0035]

As described above, according to the present invention, the birefringence of the sample can be accurately analyzed by subtracting and measuring the noise of other electric systems including the light receiving means.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a polarization measuring device according to the present invention.

FIG. 2 is a graph showing a polarization ellipse.

FIG. 3 is an explanatory view showing a conventional polarization measuring device.

[Explanation of symbols]

 10 ... Light source section 20 ... λ / 4 plate 30 ... Sample 50 ... Analyzer 60 ... Image sensor 62 ... Computer 64 ... Memory 65 ... Correction circuit

Claims (2)

[Claims] 1. A light source for making a specific polarized light incident on a sample, a polarizing element for changing a polarization state of a light beam emitted from the sample, a light receiving means for receiving the light beam transmitted through the polarizing element, and the light receiving device. Storage means for storing a bias output peculiar to the light receiving means measured without making the light flux incident on the means, correction means for outputting a light reception signal corrected by subtracting the output of the storage means from the output of the light receiving means, and the polarization A polarization measuring apparatus, comprising: a measuring unit that measures the birefringence of the sample by detecting the output of the correcting unit while rotating the element. 2. The polarization measuring device according to claim 1, wherein the light source makes circularly polarized light incident on the sample.