JPH02309227A - Measuring method and apparatus of distribution of index of refraction - Google Patents

Abstract

PURPOSE:To shorten the measuring time of the distribution of the index of refraction by projecting a plurality of light beams from a projecting optical system to be incident upon a coaxial columnar glass and measuring projecting angles of said incident light beams from said coaxial columnar glass. CONSTITUTION:The light beams from a light source 5 are incident upon the rotational center of a rotary mirror 7. When the rotary mirror 7 is rotated, the light beams passing through a lens 9 which has its focus on the rotating center of the rotary mirror 7 is allowed to enter a coaxial columnar glass 1 as a plurality of parallel light beams. In other words, a plurality of light beams are made incident upon the coaxial columnar glass 1 from the optical system and, each projecting angle of the incident light beams from the coaxial columnar glass 1 is measured. Therefore, the distribution of the index of refraction at a plurality of points can be measured at one time. Since a plurality of light beams are allowed to be incident in parallel to the direction of the central axis of the coaxial columnar glass 1, the distribution of the index of refraction at a plurality of points in the axial direction can be measured at one time. Accordingly, the distribution of the index of refraction can be measured with high accuracy in a short time.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a measuring method and a measuring device for measuring the refractive index distribution of cylindrical glass used, for example, in optical fiber preforms and rod lenses, and in particular to measuring the refractive index distribution of preforms having different refractive indexes. This is useful for simplification and high precision.

[Conventional technology]

Cylindrical glass used for optical fiber preforms (base materials) and rod lenses has a refractive index in the radial direction that has a substantially square distribution, and a refractive index in the axial direction that is uniform. An optical fiber is formed by drawing this. Accurately measuring the refractive index distribution of the preform before drawing is necessary to obtain a good product. As a method for measuring refractive index distribution, for example, Japanese Patent Application Laid-Open No. 1983-1995
Japanese Patent Application No. 336 discloses a method in which a light beam is made incident in a direction perpendicular to the central axis of a preform for an optical fiber, and its exit angle is determined to measure the refractive index distribution of the preform. FIG. 4 shows a refractive index distribution measuring device disclosed in the publication. As shown in the figure, an incident optical system consisting of a light source 5 and a lens 6 enters the preform 1 installed in the matching oil 3 in the cell 2, and the output light that passes through the preform 1 is sent to the lens. The light passes through an output optical system having 21 and is projected onto the viewing surface of the TV camera 22. This projected image is taken out by the TV camera 22, and the coordinates of the projected image
The output angle φ is determined from the focal path tlif of the output optical system as follows: φ=jan-' (x/f). Then, the refractive index distribution n (r) of the preform 1 is calculated using the following equation % using the exit angle φ obtained while moving the movable table 4 on which the preform is placed by a pulse motor. Alternatively, an image of the output light that has passed through the output optical system is formed on a screen, and the projected image on the screen is observed with the TV camera 22 to determine the output angle φ.

[Problem to be solved by the invention]

For example, in a preform for an optical fiber, the refractive index distribution in the axial direction changes due to slight variations in conditions during the manufacturing process, and the refractive index distribution may become asymmetrical with respect to the central axis of the preform. In order to measure such axial refractive index distribution fluctuations using the conventional refractive index distribution measuring device described above, it is necessary to repeatedly measure the refractive index distribution while moving the preform in the axial direction, which makes it difficult to accurately measure the refractive index distribution. There is a problem in that it takes time to obtain a refractive index distribution. Furthermore, when measuring the asymmetry of the preform with respect to its central axis, it was necessary to rotate the preform 90 degrees and repeat the measurement, which also required time to obtain an accurate refractive index distribution. The present invention has been made to eliminate these drawbacks, and aims to provide a refractive index distribution measuring method and measuring device that can measure refractive index distribution with high precision in a short time. It is.

[Means to solve the problem]

The refractive index distribution measurement method to which the present invention is applied in order to solve the above problems is to emit light from a direction perpendicular to the central axis of a cylindrical glass whose refractive index is uniform in the axial direction and whose refractive index distribution changes in the radial direction. In the refractive index distribution measurement method, in which the refractive index distribution in the radial direction of a coaxial cylindrical glass is determined by making the incident light beam incident on the coaxial cylindrical glass and measuring its exit angle, a plurality of light rays are made incident on the coaxial cylindrical glass from an input optical system, and the coaxial cylindrical shape of the incident rays is measured. The feature is that each angle of emission from the glass is measured. By arranging a plurality of light beams that enter the coaxial cylindrical glass from this incident optical system in parallel in the direction of the central axis of the coaxial cylindrical glass, it is possible to simultaneously measure the refractive index distribution fluctuation in the axial direction. In addition, by orthogonally making multiple light beams incident on the coaxial cylindrical glass from the incident optical system,
The asymmetry of the refractive index distribution can be measured simultaneously. To measure the emission angle from the coaxial cylindrical glass, the emitted light from the coaxial cylindrical glass is directly received by an image pickup tube without going through an optical system, and the emission angle is measured. Similarly, a refractive index distribution measuring device to which the present invention is applied to solve the above problem includes an incident optical system that includes a light source, a rotating mirror that makes the light beam from the light source enter the center of rotation and reflects it, and the center of rotation of the rotating mirror. A plurality of light rays are made incident on the coaxial cylindrical glass. Another configuration of the refractive index distribution measuring device to which the present invention is applied is that the incident optical system includes a half mirror that transmits a part of the light beam that is reflected by the rotating mirror and passes through the lens, and reflects a part of the light beam. By providing mirrors that are parallel to the reflecting surfaces of the half mirror and reflect the transmitted light and reflected light of the half mirror, it is possible to make orthogonal light rays enter the coaxial cylindrical glass.These refractive index distributions In this measurement device, an image pickup tube is placed on the optical path of the light emitted from the coaxial cylindrical glass without passing through an optical system.

[Operation] The measurement method of the present invention described above is based on the refractive index distribution at multiple locations by inputting a plurality of light rays from an incident optical system to a coaxial cylindrical glass and measuring the exit angle of each of the incident rays from the coaxial cylindrical glass. are measured at the same time. By arranging a plurality of light beams in the direction of the central axis of the coaxial cylindrical glass and making them incident in parallel, it is possible to simultaneously measure the refractive index distribution at a plurality of locations in the axial direction. Furthermore, by making a plurality of light beams perpendicular to each other and incident on the coaxial cylindrical glass, it is possible to simultaneously measure the refractive index in directions different by 90 degrees. The refractive index distribution measuring device of the present invention rotates a rotating mirror that reflects a light beam from a light source by making it incident on the rotation center, and converts the light beam passing through a lens having a focal point at the rotation center of the rotating mirror into multiple parallel light beams. Inject it into a coaxial cylindrical glass. Furthermore, by splitting the rays passing through the lens with a half mirror and reflecting the split rays with mirrors installed parallel to the reflecting surfaces of the half mirror, the orthogonal rays can be simultaneously incident on the coaxial cylindrical glass. I can do it. Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of an embodiment of a refractive index distribution measuring apparatus to which the present invention is applied. In the figure, 1 is a preform, 2 is a cell in which the preform 1 is mounted, and the cell 2 is filled with matching oil 3 to eliminate sudden changes in the refractive index on the surface of the preform 1. Reference numeral 4 denotes a moving table on which the cell 2 is installed, and the moving table 4 is driven by a pulse motor (not shown), and moves the preform l whose center axis coincides with the X-axis direction in the X-axis and Y-axis directions. 5 is a light source made of, for example, a He-Ne laser oscillator, 6 is a lens that condenses the light from the light source 5. 7 is a rotating mirror mounted on a moving table 8; The light from the light source 5 is incident on the rotation center and reflected on the rotating mirror 8 while rotating in the six directions of the arrows.The lens 9 has a focal point at the rotation center of the rotating mirror 7. A camera tube 11 receives the light that has passed through the camera tube 10, a frame memory 11 stores electrical signal data obtained by the camera tube 10, and a central processor 2 stores data in the frame memory 11. The output angle φ is calculated by performing linear approximation of the data and outputted to the display section 13.Next, the operation when measuring the refractive index distribution of the preform l with the refractive index distribution measuring device configured as described above. The light that is focused from the light source 5 through the lens 6 is reflected at the rotation center of the rotating mirror 7 and enters the lens 9. Since the focal point of this lens 9 is at the rotation center of the rotating mirror 7, The light incident on the lens 9 is refracted parallel to the optical axis of the lens 9,
The light enters the preform l in a direction perpendicular to the central axis, is refracted by the preform l, and exits. This emitted light is observed by the image pickup tube IO, and image data of the image is sent to the frame memory 11 and stored. This data is sent to the central processing unit 12, which calculates the output angle φ from the ridge value of the image of the output light and sends it to the display unit 13. Then, while moving the moving table 4 on which the preform l is mounted in the y-axis direction, which is perpendicular to the optical axis of the lens 9, the position of the light incident on the preform l is changed in the radial direction of the preform l. Find the change in the exit angle φ. As described above, for example, as shown in FIG.
The relationship between the incident position r and the output angle φ is measured, and the refractive index distribution n(r) is determined from the measured output angle φ. On the other hand, since the rotating mirror 7 is rotating on the moving table 8, the light sent from the rotating mirror 7 to the lens 9 rotates around the optical axis of the lens 9, changing the point of incidence on the lens 9. Therefore, the light beam parallel to the optical axis emitted from the lens 9 moves in the X-axis direction and scans the preform l in the X-axis direction. As a result, without moving preform 1 in the X-axis direction,
It is possible to simultaneously measure the exit angle φ at a plurality of locations in the direction of the central axis of the preform 1. In this way, the three light beams are scanned in the direction of the central axis of the preform 1, the output angle φ is repeatedly measured, and the relative refractive index difference Δ Δ=(n+−nt)X100/nl is determined by the following formula. , the result of finding the difference 0 in the relative refractive index difference Δ is o = 0.
It turned out to be 006. When measuring the same measurement range, it took 33 minutes for three measurements using the conventional method, but in the case of this example, it took 1.
The i1 fixed time could be shortened to 16 minutes. In the above embodiment, a case where a plurality of parallel light beams are incident from the direction of the central axis of the preform 1 has been explained. It is also possible to obtain the symmetry of the refractive index distribution in the radial direction of the preform l in one measurement by simultaneously making the light beams incident on the preform l. FIG. 3 shows a schematic configuration for measuring the symmetry of the refractive index distribution in the radial direction of the preform l. In this figure, the same reference numerals as in FIG. 1 indicate the same parts as in the above embodiment. A half mirror 14 transmits a part of the light beam refracted by the lens 9 and reflects a part thereof, and the half mirror 14 is installed with its reflecting surface inclined at 45 degrees with respect to the optical axis of the lens 9. Reference numerals 15 and 16 are mirrors in which the reflecting surfaces of the half mirror 14 are parallel to each other, and the mirror 15 is 8-
The half mirror 14 reflects the transmitted light, and the mirror 16 reflects the reflected light from the half mirror 14, and each of the reflected lights enters the preform 1. loa is an image pickup tube installed perpendicularly to the image pickup tube 10, lla is a frame memory, 1
2a is a central processing unit, and 13a is a display section. When measuring the refractive index distribution of the preform 1 with the refractive index distribution measuring device configured as described above, a light ray parallel to the optical axis refracted by the lens 9 is divided into orthogonal rays by the half mirror 14, Each split light is mirror 1
5.16, and the mutually orthogonal lights enter the preform 1 from the radial direction. The emitted light from the preform l of the incident light is observed with the image pickup tube 10.1 oa and stored in the frame memories it and lla. Then, the data stored in the frame memories 11 and lla are transferred to the central processing unit 1.
2.12a to measure the refractive index distribution in directions 90 degrees apart from each other with respect to the radial direction of the preform l. In this way, the refractive index distributions in directions 90 degrees apart relative to the radial direction of the preform l are actually measured, and the eccentricities C3 and C3 in each direction of the refractive index distribution are determined,
The symmetry degree ε expressed by the following equation was calculated from the eccentricity F, 1.52. C・(ε, "+ c *') "" As a result, we were able to obtain a degree of symmetry C of 0.37125. Compared to the case where the same measurement was performed using the conventional method, in the case of this example, We were able to cut the measurement time in half.

【Effect of the invention】

As explained in detail above, according to the measurement method of the present invention, a plurality of light rays are incident on the coaxial cylindrical glass from the incident optical system, and the exit angle of each of the incident light rays from the coaxial cylindrical glass is measured. Since the refractive index distributions at multiple locations are measured simultaneously, the time required to measure the refractive index distributions can be significantly shortened. In addition, by arranging multiple light beams and making them incident in parallel in the direction of the central axis of the coaxial cylindrical glass, it is possible to simultaneously measure the refractive index distribution at multiple locations in the axial direction, and also to measure the refractive index distribution in the axial direction continuously. Since it can be measured, even minute fluctuations in the refractive index distribution in the axial direction can be detected. By making a plurality of light beams perpendicular to each other and incident on the coaxial cylindrical glass, the refractive index in 90-degree directions can be measured simultaneously, and the asymmetry of the refractive index can also be measured at the same time. In measuring the emission angle from the coaxial cylindrical glass, the emission angle can be measured by directly receiving the emitted light from the coaxial cylindrical glass with an image pickup tube without passing through an optical system. The refractive index distribution measuring device of the present invention rotates a rotating mirror that reflects light beams from a light source by entering them at the rotation center, and converts the light rays that pass through a lens having a focal point at the rotation center of the rotating mirror into multiple parallel rays coaxially. Since the light is made incident on the cylindrical glass, it is possible to easily make a plurality of parallel lights incident on the coaxial cylindrical glass. Furthermore, by splitting multiple parallel rays passing through the lens with a half mirror and reflecting the split rays with mirrors installed parallel to the reflective surface of the half mirror, orthogonal rays can be simultaneously directed to the coaxial cylindrical glass. Since it can be made incident, the asymmetry of the refractive index can be measured with a simple structure. Further, since the image pickup tube is placed on the optical path of the light emitted from the coaxial cylindrical glass without passing through the optical system, the effort of aligning the axis of the optical system is reduced, resulting in a simple device.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an apparatus to which the present invention is applied;
Figure 2 is a characteristic diagram showing the refractive index distribution of the preform, Figure 3 is a characteristic diagram showing the refractive index distribution of the preform.
The figure is a schematic configuration diagram of another embodiment, and FIG. 4 is a schematic configuration diagram showing an example of a conventional device. l...Preform 2...Cell 4...Moving table 5...Light source 6.9...Lens
7...Rotating mirror 8...Moving table lO・
... Image pickup tube 11 ... Frame memory I 2 - ... Central processing unit 13 ... Display section 14 ... Half mirror - 15, 16 ... Mirror

Claims (1)

[Claims] 1. Light is incident from a direction perpendicular to the central axis of a cylindrical glass whose refractive index is uniform in the axial direction and changes in the radial direction,
In the refractive index distribution measurement method that measures the exit angle and determines the refractive index distribution in the radial direction of coaxial cylindrical glass, multiple light rays are incident on coaxial cylindrical glass from an input optical system, and the incident light rays are measured from coaxial cylindrical glass. A method for measuring refractive index distribution characterized by measuring each output angle. 2. The method for measuring refractive index distribution according to claim 1, wherein a plurality of light beams are arranged in parallel in the direction of the central axis of the coaxial cylindrical glass. 3. The method for measuring refractive index distribution according to claim 1, wherein the plurality of light beams are incident on the coaxial cylindrical glass at right angles. 4. The method for measuring refractive index distribution according to claim 1, 2, or 3, characterized in that the emitted light from the coaxial cylindrical glass is directly received by an image pickup tube and the emission angle is measured respectively. . 5. Light is incident from a direction perpendicular to the central axis of the cylindrical glass, which has a uniform refractive index in the axial direction and a varying refractive index in the radial direction,
A refractive index distribution measuring device that measures the emission angle and determines the refractive index distribution in the radial direction of a coaxial cylindrical glass, includes a light source, a rotating mirror that makes the light ray from the light source incident on the center of rotation and reflects it, and the rotating mirror. 1. A refractive index distribution measuring device comprising: an input optical system comprising a lens having a focal point at the center of rotation of the lens. 6. The input optical system includes a light source, a rotating mirror that makes the light ray from the light source enter the rotation center and reflects it, a lens that has a focal point at the rotation center of the rotation mirror, and a part of the light ray that passes through the lens. Claim 5, characterized in that it consists of a half mirror that transmits light and partially reflects the light, and mirrors that are provided parallel to the reflecting surfaces of the half mirror and reflect the transmitted light and the reflected light of the half mirror, respectively. The refractive index distribution measuring device described in 1. 7. The refractive index distribution measuring device according to claim 5 or 6, characterized in that an imaging tube is disposed on the optical path of the light emitted from the coaxial cylindrical glass.