JPH01153939A - Calibrating method for measuring instrument for laser beam deflection angle - Google Patents

Abstract

PURPOSE:To accurately calibrate the device even in liquid whose refractive index is close to that of glass by arranging a hollow prism which has a parallel part and a slanting part in its opposite flanks in the liquid. CONSTITUTION:While a laser beam from a laser generator 1 does not passes through the hollow prism 11, the light spot position P0 of the beam on a photodetector 8 is measured. Then the prism 11 is put in the oil 4 in a liquid tank 3 and while the beam passes through the parallel surfaces A and C of the prism 11, the arrangement angle (tilt angle and horizontal rotation) of the prism 11 are so adjusted that the light spot position on the photodetector 8 is at the same position with P0. Consequently, the surfaces A and C become perpendicular to the optical axis. While this state is maintained, the prism 11 is lifted to allow the beam pass through the slanting part (surfaces A and B: vertical angle theta), thereby measuring the position P2 of the light spot on the photodetector 8 at this time. Then a microcomputer finds the distance L between the positions P0-P2 and the conversion coefficient of the deflection angle phi of the beam is found from the distance.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an apparatus for measuring the deflection angle of a laser beam passing through an object to be measured immersed in liquid, or a device for measuring the deflection angle of a laser beam passing through an object to be measured that is immersed in liquid, or The present invention relates to a method for calibrating a laser beam deflection angle measuring device, which is used, for example, in a device for determining the refractive index distribution of an optical fiber base material.

[Prior Art] As a device for measuring the refractive index distribution of a cylindrical body such as an optical fiber base material, devices based on a spatial filtering method using collimated light have been provided. A system that uses a laser beam and reads the deflection angle of the laser beam has not been put to practical use.

Furthermore, there was no means to perform absolute calibration of the measured value of the deflection angle.

° [Problems to be solved by the invention] In the laser beam deflection angle measuring device to which the invention is applied, the spot position of the laser beam on the receiver is read,
A method is used in which this reading position is converted into a deflection angle of a laser beam through computer processing. Therefore, the measurement accuracy of the beam deflection angle depends on the accuracy of this conversion coefficient, but since this conversion coefficient changes depending on the adjustment position of the imaging optical system, in order to improve the measurement accuracy of the deflection angle, it is necessary to It is necessary to perform absolute calibration of the reading angle under the same adjustment conditions. In addition, when measuring the refractive index distribution of an optical fiber base material or the like as an object to be measured, the area around the object to be measured is filled with oil having a refractive index close to that of glass. It was difficult to obtain the desired deflection angle using a glass prism of

In view of the above-mentioned problems, the present invention makes it possible to refract a light beam at a desired angle even in a liquid having a refractive index close to that of glass, and makes it possible to accurately calibrate a laser beam deflection angle measuring device. The purpose of the present invention is to provide a method for calibrating a laser beam deflection angle measuring device.

Means for Solving Problem E] To achieve the above object, the present invention provides a device for measuring the deflection angle of a laser beam passing through an object to be measured immersed in liquid, in which a hollow prism is disposed in the liquid. The feature is that absolute calibration of the deflection angle is performed by doing this.

Further, as an example of the present invention, the prism is characterized in that opposing side surfaces have a parallel portion and an inclined portion.

Furthermore, as an example, the present invention is characterized in that the top surface of the prism is open.

[Function] The hollow prism used for calibration according to the present invention has a cavity (hollow) inside, so when it is immersed in a liquid having a refractive index close to that of glass, the light rays incident on the prism are It is possible to refract the liquid by an angle corresponding to the apex angle θ and the difference in refractive index between the liquid and the air. Furthermore, in the prism according to the present invention shown in FIGS. 2 and 3, the surface A
and surface C are arranged in parallel, and by calibrating using the light beam passing through surfaces A1 and C, the prism (surface A1 and C
) can be adjusted so that it is perpendicular to the optical axis. In particular, since the top surface of the prism shown in Figure 3 is open, it is possible to inject a liquid with a known refractive index into the prism, thereby making it possible to freely adjust the laser beam deflection angle. Can be done.

Therefore, according to the present invention, it is possible to refract light rays at a desired angle even in a liquid having a refractive index close to that of glass, and by providing a parallel portion in the prism, it is possible to change the folding angle of the prism, etc. Since the adjustment can be performed with high precision, the laser beam deflection angle measuring device can be calibrated accurately.

[Embodiment 1] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Figures 1 to 3 each show an example of a hollow prism used in the calibration method of the present invention, each of which has surfaces A to C made of quartz plates, and the inside thereof is hollow. There is. In addition, the hollow prism lla in FIG. 1 is formed into a wedge-shaped triangular prism, and the hollow prism llb in FIG. The hollow prism ll formed in FIG.
The upper surface facing the inclined surface B is open, and a predetermined liquid can be injected from above.

FIG. 4 shows an example of a laser beam deflection angle measuring device for measuring refractive index distribution using the deflection angle of a laser beam, and FIG. 5 shows a laser beam deflection angle according to the present invention using the hollow prism shown in FIG. An example of a calibration method is shown below.

In FIG. 4, 1 is a He-Ne (helium-neon) laser generator that generates a laser beam;
2 is a lens that condenses the laser beam emitted from the laser generator 1; 3 is a liquid tank disposed in the optical path of the laser beam passing through the lens 2; this liquid tank 3 collects light as shown by the arrow; It is configured to be movable in the vertical direction with respect to the axis. 4 is the oil filled in the liquid tank 3, 5 is the liquid ai3
The sample to be measured is immersed in the oil 4, and is, for example, an optical fiber base material.

6.7 is a pair of lenses for imaging the laser beam that has passed through the sample to be measured 5, and 8 is a light receiver, such as a TV camera, that receives the laser beam that has passed through the lens 6.7. Note that the solid line 9 indicates the path of the laser beam, and the broken line 10 indicates the optical axis.

Further, in the figure, φ is the deflection angle of the laser beam, and the dimension on the light receiver 8 indicates the distance (positional shift) between the position of the laser beam on the light receiver 8 and the optical axis.

In the measuring device shown in FIG. 4, by moving the liquid tank 3 in the vertical direction, the position of the sample to be measured 5 and the corresponding deflection angle φ of the laser beam can be determined by moving the liquid tank 3 up and down.
The refractive index distribution of the sample 5 to be measured is determined by integrating the data of the deflection angle φ obtained by this measurement. Here, the deflection angle φ of the laser beam is
This corresponds to the distance between the position of the laser beam on the light receiver 8 and the optical axis lO. The deflection angle φ is determined by multiplying L by a predetermined conversion coefficient, but since the conversion coefficient also changes by adjusting the position of the lens 6.7, it is necessary to calibrate the measured value of the deflection angle φ.

Therefore, if a hollow prism 11 is placed in place of the sample to be measured 5 as shown in FIG.
If the apex angle θ is known, the deflection angle φ can be determined by Snell's law. By measuring the distance IIL between the position of the laser beam on the light receiver 8 and the optical axis 10 at this time via the light receiver 8, the conversion coefficient of the deflection angle φ is determined.

A specific procedure for calibrating the laser beam deflection angle measuring device shown in FIG. 4 using the hollow prism 11 shown in FIG. 3 will be described below with reference to FIG. 5.

The calibration procedure is performed in the following order:

Step 1: Measure the optical spot position P0 of the laser beam on the photoreceiver 8 with the laser beam not passing through the prism 11.

Step 2: Next, put the prism 11 into the oil 4 in the liquid tank, and the laser beam will hit the parallel part of the prism 11 (surface A1, surface C
), the arrangement angle (tilt angle/horizontal rotation) of the prism 11 is adjusted so that the optical spot position PI of the laser beam on the photoreceiver 8 is the same as the above-mentioned position P0. Thereby, the surfaces A1 and C are adjusted to be perpendicular to the optical axis.

Step 3: Furthermore, the state of the arrangement angle in step 2 (surface A1
While keeping the plane C perpendicular to the optical axis, move the prism 11
The laser beam is directed to the inclined part of the prism 11 (surface A) by slightly lifting the prism 11.

The light spot position P2 of the laser beam on the light receiver 8 at that time is measured. At this time, if necessary, the position of the prism 11 in the optical axis direction is also adjusted (see FIG. 5).

Step 4: L by a microcomputer, etc. (not shown)
(Distance from P2 to Po or distance from P1 to eo!!1)
Calculate and find.

Through the above procedure, the ITV image pickup tube is used as the light receiver 8, and the apex angle θ=11.92 (de
g) As a result of calibrating the angle using a hollow prism as shown in Figure 3, where the distance between planes A and C is 10 (mm),
As a calibration value, φ/L = 5.52 (deg)/
A value of 178 (pixels) was obtained. Here, φ is the deflection angle of the laser beam, and L is the position change (p+~Pa) of the laser beam on the ITV image.

[Effects of the Invention] As explained above, according to the present invention, since the laser beam deflection angle is calibrated using a hollow prism, the desired angle can be adjusted even in a liquid having a refractive index close to that of glass. In addition, by providing a parallel part in the hollow prism, it is possible to accurately adjust the deflection angle of the prism, so it is possible to use a laser beam deflection angle measuring device. The effect is that calibration can be performed accurately.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are perspective views showing configuration examples of hollow prisms applicable to the present invention, respectively. Figure 4 shows a laser beam deflection for measuring the refractive index distribution using the deflection angle of the laser beam. FIG. 5 is a schematic diagram showing an example of the configuration of an angle measuring device. FIG. 5 is a schematic diagram showing an example of a laser beam deflection angle reading calibration method according to the present invention. DESCRIPTION OF SYMBOLS 1... Laser generator, 2... Lens, 3... Liquid type, 4... Oil, 5... Sample to be measured, 6... Lens, 7... Lens, 8... ...Light receiver, 9...Laser beam path, lO...Optical axis, 11...Hollow prism, φ...Deflection angle, θ...Vertex angle. Patent applicant Sumitomo Electric Industries, Ltd. Representative Patent attorney Yoshi Tani - deceased

Claims (1)

[Claims] 1) In a device for measuring the deflection angle of a laser beam passing through a measured object immersed in liquid, absolute calibration of the deflection angle is performed by placing a hollow prism in the liquid. A method for calibrating a laser beam deflection angle measuring device. 2) The method for calibrating a laser beam deflection angle measuring device according to claim 1, wherein the prism has opposing side surfaces having a parallel portion and an inclined portion. 3) The method for calibrating a laser beam deflection angle measuring device according to claim 1 or 2, wherein the prism has an open top surface.