JPH0458120A - Polarized light measuring instrument - Google Patents

Abstract

PURPOSE:To measure the polarized state of luminous flux which has specific divergence without making any mechanical scanning by assuming that variation in the intensity of the quantity of light detected by a light receiving means due to the rotation of an analyzer is sine-shaped variation and judging the polarized states of the luminous flux at parts corresponding to respective picture elements from sampled intensity. CONSTITUTION:This instrument is equipped with a light source part 10 which makes the linear polarized light having specific divergency incident on an optical element 20 as a sample 20, the analyzer 30 which is provided rotatably in the optical path of luminous flux transmitted through the sample 20, a two-dimensional image sensor 40 such as a CCD sensor which photodetects the luminous flux transmitted through the analyzer 30, a frame memory 50 where the output of the image sensor 40 is stored after being A/D-converted, a computer 60 which analyzes the data in the frame memory 50 when at least the analyzer is set at three different angles, and a display 70 which displays the analytic result. Consequently, the polarized state of the luminous flux which is diverged as specified can be inputted as two-dimensional information without any mechanical scanning and the field of polarization of the whole luminous flux can be measured.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a device for measuring the polarization state of a beam of light that enters with a predetermined spread. [Prior Art and Problems to be Solved by the Invention] Conventionally, a polarization measuring device has been used to measure the polarization characteristics of a test object such as a plane-parallel plate. A conventional polarization measurement device places a polarizer and an analyzer between a light source that generates a narrow beam of light and a light receiving element, sets the object to be measured between these polarizers, and measures the amount of transmitted light while rotating the analyzer. This is a configuration that detects. From the amount of detected light and the rotation angle of the analyzer, at least the slope of the polarization ellipse of the transmitted polarized light can be determined. However, since the conventional polarization measurement device described above performs measurement using a single beam, a mechanism for mechanically scanning the sample is required in order to obtain two-dimensional information. There are problems in that the device becomes complicated and the measurement takes time. Furthermore, since conventional devices perform measurements using a light beam with a diameter of about 1 mm, the resolution during scanning can only be obtained to the same extent as the diameter of the light beam, which poses the problem of not being able to perform precise measurements. [Object of the invention] This invention was made in view of the above problems, and
It is an object of the present invention to provide a polarization measuring device that can measure the polarization state of a light beam having a predetermined spread without mechanical scanning and has high spatial resolution for measurement. [Means for Solving the Problems] In order to achieve the above object, the polarization measuring device according to the present invention includes a light receiving means that has two-dimensionally arranged pixels and receives polarized light with a predetermined spread, and a light receiving means. an analyzer that is provided in front of the analyzer and rotated to change the amount of transmitted light;
A sampling means that sets the analyzer at at least three different angles and samples the intensity of each pixel of the light receiving means at each set angle, and a sinusoidal change in the intensity of the amount of light detected by the light receiving means due to rotation of the analyzer. The present invention is characterized by comprising an analysis means for determining the polarization state of a portion of the light beam corresponding to each pixel based on the sampled intensity.

[Effect]

According to the above configuration, the polarization state of a light beam having a predetermined spread can be captured as two-dimensional information without mechanical scanning, and in other words, the polarization field of the entire light beam can be measured.

【Example】

The present invention will be explained below based on the drawings. FIG. 1 is a configuration diagram showing an embodiment of a polarization measuring device according to the present invention. This device transmits linearly polarized light with a predetermined spread to the sample 20.
A light source unit 10 that makes the light enter an optical element, and an analyzer 3 that is rotatably provided in the optical path of the light beam that has passed through the sample 20.
0, a two-dimensional image sensor 40 such as a CCD sensor that receives the light beam transmitted through the analyzer 30, a frame memory 50 that A/D converts and stores the output of the image sensor 40, and at least the analyzer 3 The frame memory 50 includes a computer 60 for analyzing data stored in the frame memory 50 when set at two different angles, and a display 70 for displaying the analyzed results. The light source section 10 includes a light source 11 that is a combination of a laser device that generates linearly polarized light or a light source that emits a light beam with a random polarization state and a polarizer, and a beam expander 12 that expands the diameter of the light beam emitted from this light source. configured. The analyzer 30 is automatically rotated by a motor 31, and the rotation angle is input to the computer 60 by an angle sensor 32. When measuring the polarization characteristics of a sample using the above device, the sample 20 is placed between the light source section 10 and the analyzer 30, the light source is turned on to transmit the light beam, and the analyzer 30 is rotated. The computer 60 samples the output of the image sensor when the rotation angle of the analyzer 30 reaches a predetermined value based on the output of the angle sensor 32, and stores it in the frame memory 50. Since it can be assumed that the intensity change of the light flux due to the rotation of the analyzer 30 is sinusoidal, the polarization state of the light flux can be measured for each pixel by performing measurements at least three times. FIG. 2 shows the analyzer 30 and image sensor 4 having the above configuration.
An example is shown in which an imaging lens 41 is provided between the sample 20 and the image sensor 40 so that an image of the sample 20 is formed on the image sensor 40. Next, the principle of polarization measurement will be explained. When expressing elliptically polarized light, as shown in Figure 3, the three parameters of the ellipse drawn by the tip of the electric field vector in the plane opposite to the direction of light travel: major axis a1, minor axis b, and slope ψ. is necessary. When either a or b is O, the light becomes linearly polarized, and when a=b, the light becomes circularly polarized. The intensity when the above elliptically polarized light is received through an analyzer is expressed by formula (1), where the rotation angle of the analyzer is θ. Ideally, it changes sinusoidally as shown in FIG. Here, the maximum value Imax and the minimum value 1a+in of the intensity can be respectively expressed by the following formulas. I++ax = C2 Imin = b2 Since there are three unknown variables α, β, and ψ representing polarization characteristics in equation (1), the output intensity when the analyzer 30 is rotated to at least three different angular positions By measuring (2), the values of the three unknowns can be found. Here, in order to simplify the calculation, it is assumed that measurements are performed four times at every 45°. Intensity IO, I4 from 4 measurements
5.190. l135 has the following relationships for each of the three variables. ■0−α+β・cos(−2ψ): α+β・cos2ψ
I45 = a + β・C08 (90°-2ψ): α
+β-5in2ψl90-α+β・cos(180°-
2ψ)=α−β・cos2ψ1135=a+β・
cos(135°-2ψ)=α-β·5in2ψ These intensities are measured as independent data for each pixel of the image sensor 40, and are stored in the frame memory 50 as image information for each of the four measurement angles. Ru. When the four measurements are completed, the computer 60 uses the four intensity data to find a variable expressing the polarization characteristic for each pixel according to the following formula. IO+I45+I90+1135 α = When the analysis is completed, for example, the angle of the polarization inclination ψ is converted into a bright/dark gradation and displayed on the display 70, or converted into the size of a dot and printed out. The above variables analyzed are not as single data per pixel, but
It has meaning as a relative difference to adjacent pixels,
By displaying this difference, it is possible to visually grasp the variation in the polarization characteristics of the sample as a whole. Note that the measurement resolution depends on the number of pixels of the image sensor 40, but in view of the recent increase in pixel density, it is possible to perform measurements with considerably higher precision than the conventional measurement in units of 1 mm in diameter. I can do it. If noise is present in the above measurement due to dirt or the like on the sample surface, the slope ψ can be accurately determined, but α and β cannot be accurately determined. For example, if a point P without noise and a point Q with noise are set on the sample, the pixel of the image sensor that receives the light flux from point P will output a sine wave as shown by P in Figure 5. The pixel corresponding to point Q outputs a sine wave as shown by Q in FIG. These sine waves have different amplitudes depending on the presence or absence of noise, but have the same wavelength, and the phase difference between the two sine waves, that is, the difference between the slopes ψP and ψQ, can be accurately determined. On the other hand, when the influence of noise can be ignored, that is,
When the reliability of the values of α and β is high, information on the birefringence of the sample can also be obtained by determining the phase difference between the ordinary ray and the extraordinary ray based on the light emitted from the sample into which linearly polarized light is incident. I can do it. Further, in the above embodiment, only the example of measuring the light emitted from the sample was described, but the scope of application of the present invention is not limited to this example. It is also effective for measurement, that is, for measuring the polarization characteristics of the light beam itself, regardless of the configuration of the light emitting side. [Effects] As explained above, according to the polarization measuring device of the present invention, the polarization state of a light beam having a predetermined spread can be captured at once without mechanically scanning the light beam, and the mechanical configuration can be simplified. It is possible to simplify the process and shorten the processing time. Furthermore, the measurement resolution can be improved compared to scanning with a single light beam.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the polarization measuring device according to the present invention, FIG. 2 is an explanatory diagram showing a modification of the first embodiment, FIG. 3 is a graph showing a polarization ellipse, and FIG. FIG. 5 is a graph showing changes in the amount of light received by the light receiving means due to rotation of the analyzer. 10... Laser light source 20... Sample 30... Analyzer 31... Motor 32... Angle sensor 40... Image sensor 50... Frame memory 60... Computer

Claims (3)

[Claims] (1) A light-receiving means having two-dimensionally arranged pixels and receiving polarized light with a predetermined spread; an analyzer provided in front of the light-receiving means and rotated to change the amount of transmitted light; sampling means for setting the analyzer at at least three different angles and sampling the intensity of each pixel of the light receiving means at each set angle; 1. A polarization measurement device comprising: analysis means for determining the polarization state of a portion of the light beam corresponding to each pixel based on the sampled intensity, assuming that the change is a change in polarization measurement device. (2) a light source unit that makes linearly polarized light with a predetermined spread enter the sample; a light receiving unit that has two-dimensionally arranged pixels and receives the light beam that has passed through the sample; and a combination of the sample and the light receiving unit. In between, there is an analyzer rotatably provided around an axis substantially parallel to the traveling direction of the light flux, and the analyzer is set at at least three different angles, and each pixel of the light receiving means at each set angle is Assuming that the change in intensity of the amount of light detected by the light receiving means due to the rotation of the analyzer is a sinusoidal change, the polarization characteristics of the sample in the portion corresponding to each pixel are determined by the sampled intensity. A polarization measuring device characterized by comprising: an analysis means for making a determination. (3) The polarization measuring device according to claim 2, wherein the light receiving means receives the light beam reflected by the sample.