JP3465804B2 - Method for measuring light transmission characteristics of wedge-type birefringent plate - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a method for measuring light transmission characteristics of a wedge-shaped birefringent plate, which is performed after manufacturing a wedge-shaped birefringent plate which is a component of an optical isolator.

[0002]

2. Description of the Related Art As a typical optical isolator,
The following structure is known (for example, Japanese Patent Publication No. 61-5).
8809 publication). As shown in FIG. 3, between the two wedge-shaped birefringent plates 1a and 1b, which serve as a polarizer and an analyzer, 45
The Faraday rotator 2 is installed, and the optical fiber 3 on the input side is provided.
And the coupling lens 4 on the side of the wedge-shaped birefringent plate 1a, and the optical fiber 5 on the output side and the coupling lens 6 are combined.
On the side of the wedge-shaped birefringent plate 1b.

The angle formed by the optical axis of the wedge type birefringent plate 1b as an analyzer with respect to the optical axis of the wedge type birefringent plate 1a as a polarizer is 45 degrees in the rotation direction of the plane of polarization by the Faraday rotator 2. Is set to. Two wedge-shaped birefringent plates 1
Since a and 1b have the same structure, they are referred to as wedge-shaped birefringent plate 1 in the following description when they are not distinguished from each other.

As is well known, a large number of wedge-shaped birefringent plates 1 are cut out from a large ingot of a birefringent crystal and finished. The shape is shown in detail in FIG. The wedge-shaped birefringent plate 1 of this example is a thin plate having a substantially square outer shape, and is wedged between a main plane R parallel to the optical axis Q and an inclined plane S inclined at an appropriate angle with respect to the main plane R. It is processed into a mold. Then, the main plane R and the inclined plane S are mirror-finished and further coated with an antireflection film.

In the process of manufacturing and assembling the optical isolator, it is desirable to measure the light transmittance of the finished wedge-type birefringent plate for the purpose of eliminating defective parts. Explaining an example of the measuring method, as shown in FIG. 5, the light projector 7 and the photodetector 8 which emit the measuring light are arranged so as to face each other with their optical axes aligned (see the chain double-dashed line), and measure at an intermediate position therebetween. The wedge-shaped birefringent plate 1 is placed. In this state, the measurement light from the light projector 7 is vertically incident on the main plane R of the wedge-shaped birefringent plate 1, and the light emitted from the inclined plane S is received by the photodetector 8. Thereby, the light transmittance of the wedge-shaped birefringent plate 1 can be obtained by obtaining the difference in luminous intensity between the incident light and the emitted light.

[0006]

However, the above-mentioned conventional measuring method has a problem that the transmitted light of the wedge-shaped birefringent plate 1 cannot be measured with high accuracy by the photodetector 8.
That is, as shown in FIG. 5, even if the measurement light is incident perpendicularly to the main plane R of the wedge-shaped birefringent plate 1, the light emitted from the inclined plane S is not parallel to the incident light, and is an ordinary ray and an extraordinary ray. And are emitted in directions away from each other at different angles. Therefore, as shown in FIG. 3, even if the optical axes of the projector 7 and the photodetector 8 are simply made to coincide with each other in a state before the wedge-shaped birefringent plate 1 is installed, the wedge-shaped birefringent plate 1 as shown by the broken line in FIG. The emitted light transmitted through the refraction plate 1 cannot be entirely received by the photodetector 8, and the receiving portion is not the highest sensitivity point of the photodetector 8 and accurate measurement cannot be performed.

Therefore, in order to receive the emitted light that is divided into ordinary light and extraordinary light and spread at the highest sensitivity point of the photodetector 8 and measure it with high accuracy, a certain object to be measured (a wedge-shaped compound) It is necessary to set the refraction plate 1) and finely adjust the position of the photodetector 8 so as to show the maximum sensitivity to the emitted light. Although accurate measurement can be performed in this way, the position of the photodetector 8 must be adjusted again when the object to be measured is replaced next time. This makes it impossible to measure a large number of wedge-shaped birefringent plates one after another efficiently, and it is the actual situation that such an exhaustive test is hardly conducted.

In view of the above problems, the present inventors have
The following light transmittance tests are conducted. A sample for a light transmittance test is cut out from a birefringent crystal ingot which is a material for a wedge-shaped birefringent plate. The sample is not a wedge type like the actual product, but a flat plate whose front and back surfaces are parallel. Moreover, processing is performed so that the optical axis is perpendicular to the front and back surfaces. Then, this sample is arranged perpendicular to the measurement light between the light projector 7 and the photodetector 8 as shown in FIG. In this case, since the incident light and the direction of the optical axis coincide with each other, the ordinary light and the extraordinary light are not separated inside and the light travels straight through the sample and is emitted as it is.
Therefore, since the incident light and the emitted light are located on the same straight line,
If the optical axes of the projector 7 and the photodetector 8 are aligned with each other, all the emitted light can be received. However, this test only measures the light transmittance of the material ingot, and is unsuitable as a test for finding defects in a large number of individual wedge-shaped birefringent plates processed from this ingot.

The present invention has been made in view of the above background, and an object of the present invention is to solve the above-mentioned problems and to adjust the position of the measuring device every time the object to be measured is replaced. Another object of the present invention is to provide a method for measuring the light transmission characteristics of each wedge-shaped birefringent plate that efficiently and accurately measures the light transmission characteristics of each wedge-shaped birefringence plate.

[0010]

In order to achieve the above object, in the method for measuring the light transmission characteristics of a wedge-shaped birefringent plate according to the present invention, a main plane R parallel to the optical axis Q and this main plane R On the other hand, two wedge-shaped birefringent plates are prepared in order to measure the light transmission characteristics of the wedge-shaped birefringent plate which is sandwiched between the inclined plane S inclined by an appropriate angle. Then, the inclined plane S of one wedge-shaped birefringent plate and the main plane R of the other wedge-shaped birefringent plate are opposed to each other, and both are arranged so that the optical axes of both wedge-shaped birefringent plates are aligned. In this state, the measuring light is made incident on the main plane R of one wedge-shaped birefringent plate or the inclined plane S of the other wedge-shaped birefringent plate, and the emitted light is received by the photodetector (claim 3). 1).

Preferably, when disposing the both wedge-shaped birefringent plates, the main plane R of the one wedge-shaped birefringent plate and the inclined plane S of the other wedge-shaped birefringent plate are parallel to each other. (Claim 2).

When the measuring light is vertically incident on the two wedge-shaped birefringent plates which are superposed in a predetermined relative positional relationship,
In the wedge-shaped birefringent plate on the incident side, it goes straight as it is, but when it exits from the wedge-shaped birefringent plate, it is separated into ordinary light and extraordinary light. Further, in the present invention, since the optical axes of both wedge-shaped birefringent plates are aligned with each other, the ordinary light and the extraordinary light similarly maintain the ordinary light and the extraordinary light in the next wedge-shaped birefringence number. Therefore, as described above, the ordinary light and the extraordinary light, which are once separated and proceed in a direction away from each other, proceed in a direction approaching each other while proceeding in the next wedge-shaped birefringent plate. Therefore, the birefringence generated in each wedge-shaped birefringent plate is canceled, and the emitted light becomes parallel to the incident light. Therefore, the emitted light can be accurately received and measured by the photodetector.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a method for measuring light transmission characteristics of a wedge-shaped birefringent plate according to the present invention will be described in detail below with reference to the accompanying drawings. 1 and 2 show an embodiment of the measuring method of the present invention. As shown in the figure, the light transmission characteristic of the wedge-shaped birefringent plate 1 having a shape sandwiched between a main plane R parallel to the optical axis Q and an inclined plane S inclined at an appropriate angle with respect to the main plane R is shown. In measuring, two wedge-shaped birefringent plates 1a,
Prepare 1b. The inclined plane S of the one wedge-shaped birefringent plate 1a and the main plane R of the other wedge-shaped birefringent plate 1b are opposed to each other, and the main plane R of the wedge-shaped birefringent plate 1a and the wedge-shaped birefringent plate 1a. Both are superposed so that the inclined plane S of 1b is parallel. Since the two wedge-shaped birefringent plates 1a and 1b to be measured are cut out under the same directional condition with respect to the optical axis of the material ingot, both are seen in the direction perpendicular to the main plane R of the wedge-shaped birefringent plate 1a. The optical axes Q of the wedge-shaped birefringent plates are aligned in parallel.

The two wedge-shaped birefringent plates 1a and 1b are placed in the middle of the projector 7 and the photodetector 8 to form the wedge-shaped birefringent plate 1.
The measurement light is incident perpendicularly to the main plane R of a, and the wedge-shaped birefringent plate 1
Light emitted from the inclined plane S of b is received by the photodetector 8.

Then, since the incident direction of the incident light on the one wedge-shaped birefringent plate 1a which is first irradiated is equal to the normal direction of the horizontal plane R (incident angle is 0), the ordinary ray and the extraordinary ray are Continue straight ahead. Then, when the ordinary light and the extraordinary light traveling in the wedge-shaped birefringent plate 1a are incident on the inclined plane S at a predetermined angle with respect to the normal line of the inclined plane S, the emitted light is the ordinary light. Since the extraordinary light is refracted in a direction approaching the normal line and the extraordinary light is refracted in a direction away from the normal line, the emitted ordinary light and extraordinary light travel away from each other as shown in FIG.

Then, the light enters the other wedge-shaped birefringent plate 1b as it is. Then, while each light is refracted in a predetermined direction when passing through the main plane R, the two wedge-shaped birefringent plates 1a, 1
Since b has its optical axis aligned, the ordinary light and the extraordinary light when entering the wedge-shaped birefringent plate 1b maintain the same state, so that the extraordinary light has a larger refraction angle and refraction before and after the boundary surface. Since the magnitude relationship of the indices is opposite to that in the inclined plane S of the wedge-shaped birefringent plate 1a, the two-ray splitting effect due to the birefringence generated in the wedge-shaped birefringent plate 1a is refracted in a direction canceling the wedge-shaped birefringent plate 1a. Proceed inside the birefringent plate 1b. Further, in this embodiment, since the opposing surfaces of the wedge-shaped birefringent plates 1a and 1b are arranged in parallel, the inclined plane S which is the emission surface of the wedge-shaped birefringent plate 1b.
When the light reaches, the ordinary light and the extraordinary light converge to one point, and then both lights are emitted in a state of being coincident (combined). The emitted light at this time is parallel to the incident light and is on the same straight line.

Therefore, by making the optical axes of the light projector 7 and the photodetector 8 coincident with each other, the transmitted light can be measured accurately, and it is not necessary to readjust the position of the measuring system even if the object to be measured is replaced. . As a result, the quality of the characteristics such as the transmittance can be continuously determined in a short time in the state of the final product, which is an actual product processed into a wedge shape.

If the same ingot is processed under the same conditions, both wedge-shaped birefringent plates 1 are unknown.
The measurement target may be a and 1b, or the measurement may be performed by combining a known birefringent plate that has been measured and an unknown wedge-shaped birefringent plate. In either case, it is possible to judge whether the wedge-shaped birefringent plate is good or defective without any problem.

* Experimental Results A wafer was arbitrarily extracted from the birefringent crystal ingot, and two wedge-shaped birefringent plates and one parallel plate were manufactured from this wafer. The thickness of this parallel plate was set to be half the thickness when two wedge-shaped birefringent plates were superposed in a predetermined positional relationship. The surface of each plate was mirror-finished.

Then, the parallel flat plate alone and the two wedge-shaped birefringent plates arranged facing each other were inserted between the light projector 7 and the photodetector 8 to measure the light transmittance. Then, while the light transmittance of the parallel plate is 0.01 dB, the light transmittance of the two wedge-shaped birefringent plates is 0.02 dB, which is twice that of the parallel plate, which is equal to the thickness ratio. Become. This confirmed that the light transmittance of the wedge-shaped birefringent plate can be accurately measured.

Although the opposing surfaces of the wedge-shaped birefringent plates 1a and 1b are arranged in parallel in the above embodiment, the present invention does not necessarily have to be arranged in parallel, and the main plane and the inclined plane are opposed to each other. If the optical axes coincide with each other, the angle is arbitrary. Further, the angle of the incident light with respect to the incident surface does not necessarily have to be vertical, and may be inclined by a predetermined angle. However, when the parallelism between the two plates is deviated or the incident light is not radiated vertically, the emitted light emitted from the pair of wedge-shaped birefringent plates becomes parallel to the incident light, but the ordinary light and the extraordinary light. And will be emitted in a separated state. However, the emitted light is in a position close to the same straight line as the incident light, and both lights are not parallel and do not spread. Therefore, even if the projector and the photodetector are placed in the positional relationship as shown in FIG. The emitted light can be received by the central portion of the photodetector with high detection sensitivity.

However, the separation distance between the ordinary ray and the extraordinary ray emitted in parallel becomes larger as the deviation of the parallelism becomes larger and the incident angle becomes larger, so that they are set to be parallel as in the above-mentioned embodiment. It is best to make it vertically incident with. In other words, the amount of deviation from parallelism,
The upper limit of the incident angle is determined by the light receiving range of the photodetector.

Further, in disposing the both wedge-shaped birefringent plates 1a and 1b, in the example shown in the figure, the both plates are separated from each other.
The separation distance is arbitrary, and the width may be wide or narrow as long as the two lights emitted once can enter the next wedge-shaped birefringent plate.

[0024]

According to the measuring method of the present invention, when the measuring light is incident on the two wedge-shaped birefringent plates which are stacked as described above at a predetermined angle, the birefringence generated in each wedge-shaped birefringent plate is canceled. The emitted light becomes parallel to the incident light. Therefore,
By making the optical axes of the light projector and the photodetector coincide with each other, the transmitted light can be accurately measured, and it is not necessary to readjust the position of the measurement system even if the measurement object is replaced. Therefore, the light transmission characteristics of each wedge-shaped birefringent plate can be measured efficiently and highly accurately.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a method for measuring light transmission characteristics of a wedge-shaped birefringent plate according to the present invention.

FIG. 2 is a perspective view showing how to combine the two wedge-shaped birefringent plates shown in FIG.

FIG. 3 is a schematic configuration diagram of an optical isolator using a wedge-shaped birefringent plate which is an object of the present invention.

FIG. 4 is a perspective view showing an example of a wedge-shaped birefringent plate.

FIG. 5 is a schematic view showing a conventional method for measuring the light transmission characteristics of a wedge-shaped birefringent plate.

[Explanation of symbols]

1,1a, 1b Wedge type birefringent plate 2 Faraday rotator 3 Input side optical fiber 4 coupling lens 5 Output side optical fiber 6 coupling lens 7 Floodlight 8 Photodetector Q optical axis R main plane S inclined plane

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-34916 (JP, A) JP-A-6-51244 (JP, A) Fukui Sho 62-39229 (JP, U) JP-B Sho 61- 58809 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01M 11/00-11/08 G01N 21/23 G01N 21/59 G02B 27/00-27/64

Claims (2)

(57) [Claims] 1. When measuring a light transmission characteristic of a wedge-shaped birefringent plate having a shape sandwiched by a main plane R parallel to an optical axis Q and an inclined plane S inclined at an angle with respect to the main plane R. ,
Two wedge-shaped birefringent plates (1a and 1b) are prepared, and the inclined plane S of one wedge-shaped birefringent plate (1a) and the main plane R of the other wedge-shaped birefringent plate (1b) are opposed to each other. With
The two wedge-shaped birefringent plates are arranged so that their optical axes are aligned with each other, and the measurement light is placed on the main plane R of one wedge-shaped birefringent plate (1a) or the inclined plane S of the other wedge-shaped birefringent plate (1b). Incident,
A method for measuring light transmission characteristics of a wedge-shaped birefringent plate, characterized in that the emitted light is received by a photodetector (8). 2. When disposing the both wedge-shaped birefringent plates,
The main plane R of the one wedge-shaped birefringent plate (1a) and the inclined plane S of the other wedge-shaped birefringent plate (1b) are made parallel to each other. Measuring method of light transmission characteristics of wedge-shaped birefringent plate.