JPH09292212A - Method for measuring optical axial angle of wedge-like double refracting plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of measuring optical axial angle of a wedge-like double refracting plate in which the angle formed by a reference surface and an optical axis in the wedge-like double refracting plate can be precisely measured, whereby the quality as a part can be easily judged. SOLUTION: This measuring method comprises measuring the angle θformed by a reference surface 66 and an optical axis in a wedge-like double refracting plate 6 having the reference surface 66 parallel to the transmitting direction of light, an end surface 62 orthogonal to the transmitting direction in which the optical axis is present, and an inclined surface 64 opposed to the end surface 62 with an inclination of a prescribed angle. In this case, the double refracting plate 6 is placed on a measuring base 22 with the reference surface 66 being matched thereto, a light polarized by a rotary polarizing plate 28 is transmitted thereby, the quantity of transmitted light only of ordinary light or abnormal light after transmission is measured, the rotating position of the polarizing plate 28 where the quantity of transmitted light is minimized is determined from two direction of the end surface 62 side and the inclined surface 64 side, respectively, and the angle θ [=(π-α)/2] formed by the reference surface 66 and the optical axis is calculated from the angle difference α of both the rotating positions and measured.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for measuring the optical axis direction of a wedge-shaped birefringent plate used in an optical device such as a polarization independent optical isolator.

[0002]

2. Description of the Related Art FIG. 5 is a perspective view for explaining a schematic configuration of a polarization independent optical isolator and its operating principle. As shown in FIGS. 2A and 2B, the polarization-independent optical isolator 2 has a pair of wedge-shaped birefringent plates 6 of the same shape arranged symmetrically with the Faraday rotator 4 interposed therebetween. An optical fiber 1 with a pair of lenses 8 arranged in front and back
It is tied to 0.

Here, the polarization plane rotation angle by the Faraday rotator 4 is set to 45 degrees, and the pair of wedge-shaped birefringent plates 6 before and after the Faraday rotator 4 are arranged rearward with respect to the optical axis direction of the front first birefringent plate 6a. The optical axis direction of the second birefringent plate 6b is shifted by 45 degrees in correspondence with the polarization plane rotation angle by the Faraday rotator 4, and the first and second birefringent plates 6a and 6b have wedge-shaped inclined surfaces outside. And are arranged symmetrically in parallel. The wedge-shaped birefringent plate 6 has an end face 62 perpendicular to the light transmission direction, and an inclined face 64 that faces the end face 62 at a predetermined angle.
And the optical axis lies in the plane of the end face 62.

In the polarization-independent optical isolator 2 constructed as described above, as shown in FIG. 3A, the light from the front optical fiber 10a in the forward direction is converted into parallel rays by the first lens 8a. And is incident on the first birefringent plate 6a,
The light transmitted through the first birefringent plate 6a is separated into ordinary light and extraordinary light. Then, the ordinary light and the extraordinary light thus separated are further rotated by 45 degrees in polarization planes by the Faraday rotator 4 and are incident on the rear second birefringent plate 6b.

At this time, in relation to the first birefringent plate 6 b, the optical axis direction of the second birefringent plate 6 b is adjusted by the rotation angle of the plane of polarization by the Faraday rotator 4 and shifted by 45 °, and tilted. Since the surfaces are parallel to each other and are symmetrically arranged, the relation between the ordinary ray and the extraordinary ray when passing through the second birefringent plate 6b is the same as when passing through the first birefringent plate 6a. The ordinary ray and the extraordinary ray transmitted through the second birefringent plate 6b are returned to parallel rays and enter the second lens 8b at the rear. Therefore, the ordinary light and the extraordinary light are condensed on the rear optical fiber 10b and propagated in the forward direction.

On the other hand, as shown in FIG. 6B, the reflected light returning in the opposite direction from the rear optical fiber 10b is made into parallel rays by the second lens 8b and then abnormal by the second birefringent plate 6b. The light is separated into light, and the plane of polarization is rotated by 45 degrees by the Faraday rotator 4, and then the light is incident on the first birefringent plate 6a.

However, in the case of this opposite direction, the optical axis of the first birefringent plate 6a is set in a direction opposite to that of the Faraday rotator 4 with respect to the optical axis of the second birefringent plate 6b.
Since they are shifted by 5 degrees, the relationship between the ordinary light and the extraordinary light separated when passing through the second birefringent plate 6b is reversed when passing through the first birefringent plate 6a. become.

Therefore, even though the first birefringent plate 6a is transmitted, the ordinary and extraordinary rays of the reflected return light do not return to parallel rays,
Therefore, the ordinary light and the extraordinary light are not condensed by the first lens 8a on the front optical fiber 10a, and therefore, the reflected return light is prevented from propagating in the opposite directions.

By the way, as is clear from the above-mentioned principle of operation, the polarization-independent optical isolator 2 has a pair of wedge-shaped birefringent plates 6a and 6b having the same inclined surface angles and arranged in parallel. The angle directions of the optical axes are 45
It is necessary to shift them, and these accuracies must be set extremely precisely.

Therefore, the pair of wedge-shaped birefringent plates 6a, 6a,
6b is a process in which the optical material such as rutile (TiO ₂ ) is cut from the block material to the formation of the inclined surface 64 by polishing, and is simultaneously processed in the same step, and then two birefringent plates 6a and 6b are formed. The two wedge-shaped birefringent plates 6a and 6b to be combined in a pair are made at the same time without fail so that the shapes are equalized to the error level of the processing accuracy.

Further, the pair of wedge-shaped birefringent plates 6a and 6b thus produced in a pair as shown in FIG.
Before and after the Faraday rotator 4, the respective inclined surfaces 64 are arranged outside and symmetrically arranged with a high degree of parallelism. At that time, not only the parallelism but also the direction of the optical axis <001> is accurately 45 degrees. You have to shift it.

Here, as described above, the pair of wedge-shaped birefringent plates 6a, 6b are cut out from the same block material in pairs and processed, so that they are formed at right angles to the periphery of the end face 62 where the optical axis <001> exists. If the formed common peripheral side surface is used as the reference surface 66, the optical axis <001 with respect to the reference surface 66.
>, That is, the angle θ is equal, and if the pair of wedge-shaped birefringent plates 6a and 6b are symmetrically arranged with their inclined surfaces 64 in parallel, the angle formed by both optical axes <001>, that is, the optical axis <0.
01> The mutual deviation angle is 2θ. Therefore, in order to set the shift angle to 45 degrees, the optical axis angle θ from the reference plane 66 is set.
Should be 22.5 degrees.

Therefore, from the above, the pair of wedge-shaped birefringent plates 6a and 6b have been conventionally manufactured as shown in FIG. That is, first, the optical axis <001> of the block material 12 of the optical material is measured by X-ray diffraction, and the two parallel surfaces that include the optical axis <001> in the plane and the optical axis <001> are orthogonal to these two surfaces. A rectangular columnar body 14 surrounded by two parallel surfaces forming an angle of 22.5 degrees with respect to the axis <001> is cut out. Next, one of the two parallel surfaces including the optical axis <001> is polished and tilted at a predetermined angle to form the tilted surface 64.
To form After that, cut at a plane orthogonal to the above four planes,
Two wedge-shaped birefringent plates 6a and 6b having the same shape are obtained.

[0014]

By the way, in order to satisfy the performance of the polarization independent optical isolator 2 above a specified value, the optical axes of the wedge-shaped birefringent plates 6a and 6b are oriented with respect to the reference plane. Therefore, it is necessary to put it within the processing accuracy of about 22.5 degrees ± 10 minutes. However, after processing up to the wedge-shaped birefringent plate 6, the measurement of the optical axis <001> of the wedge-shaped birefringent plate 6 is too small to be accurately performed by X-ray diffraction, and in the related art, the measurement is accurately performed. Optical axis <001
There is no other way to measure>, therefore the dimensional accuracy of the wedge-shaped birefringent plate 6 cannot be controlled, and it is practically impossible to make a pass / fail judgment as a component.

Therefore, the wedge-shaped birefringent plate 6 depends on the optical axis measurement by the X-ray diffraction in the step 12 of the block material in the process of processing, and for the sake of convenience, the parts are expediently improved by improving the processing accuracy thereafter. There is no choice but to guarantee the dimensional accuracy, and there is no choice but to make a pass / fail judgment in the performance test of the completed polarization-independent optical isolator 2.

For this reason, even if the optical axis angle of the component is bad, the assembly is performed wastefully, resulting in a reduction in the yield and a hindrance to cost reduction.

The present invention has been made in view of the above circumstances, and an object thereof is to be able to accurately measure an angle formed by a reference plane and an optical axis in a wedge-shaped birefringent plate, and thus, a component. An object of the present invention is to provide a method for measuring an optical axis angle of a wedge-shaped birefringent plate, which can easily perform pass / fail judgment as described above.

[0018]

In order to achieve the above object, in the method of measuring the optical axis angle of a wedge-shaped birefringent plate according to the present invention, a reference plane 66 parallel to the light transmission direction and a direction orthogonal to the light transmission direction are provided. And the end face 62 in which the optical axis <001> exists in the plane,
The inclined surface 6 that faces the end surface 62 at a predetermined angle.
When measuring the angle θ formed by the reference plane 66 and the optical axis <001> in the wedge-shaped birefringence plate 6 having the reference numeral 4, the birefringence plate 6 is mounted on the measurement table 22 with the reference plane 66 thereof aligned. Then, the polarized birefringent plate 6 is caused to transmit the light polarized by the rotary polarizing plate 28, and the transmitted light amount of only the ordinary light or the extraordinary light after the transmission is measured, and the transmitted light amount becomes the minimum value. The rotating position of the polarizing plate 28 is set from the end face 62 side to the inclined surface 64.
And the angle between the reference plane 66 and the optical axis <001> is measured from the angle difference α between the two rotational positions.

Here, the rotational position of the rotary polarizing plate 28 where the transmitted light amount of only the ordinary light or the extraordinary light is the minimum value is shown by accurately measuring the optical axis <001> direction, and from the end face 62 side. Optical axis <001> direction and inclined surface 6 when viewed
The optical axis <001> direction when viewed from the 4 side is, of course, a position rotated by the same angle θ in the opposite direction with respect to the reference plane 66. Therefore, when the rotational positions in the respective optical axis <001> directions when viewed from these two directions are respectively obtained and the angular difference α between them is obtained, this angular difference α becomes the reference plane 66 and the optical axis <001>. The angle θ is (π−α) /
It becomes 2 and can be easily calculated. Further, since the respective optical axis directions obtained by measuring from two directions, that is, the rotational positions are substantially directly measuring the optical axis <001>, the angular difference α between them can be measured with extremely high accuracy, Therefore, the angle θ can also be measured with high accuracy. For this reason, it becomes possible to perform highly reliable component quality control, and it is possible to appropriately perform pass / fail determination of components.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION An optical axis angle measuring method for a wedge-shaped birefringent plate according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a diagram showing a schematic configuration of a measuring system used for carrying out the measuring method according to the present invention. As shown in the figure, the measurement system 20 irradiates a measuring table 22 on which the wedge-shaped birefringent plate 6 to be measured is placed and a parallel light beam toward the wedge-shaped birefringent plate 6 placed on the measuring table 22. Irradiator 24 and its light source 26 for transmitting light through the measuring table 22 and irradiator 2
4, a rotary polarizing plate 28 capable of polarizing parallel rays irradiated with the polarized light into a plane of polarization having an arbitrary angle, and an angle measuring means 3 for measuring a rotation angle of the rotary polarizing plate 28.
0, and a detector 32 for measuring the amount of transmitted light after passing through the wedge-shaped birefringent plate 6 and its power source 34.

The wedge-shaped birefringent plate 6 is, as described in the above-mentioned prior art, perpendicular to the light transmission direction and the optical axis <001.
>, An inclined surface 64 that is inclined at a predetermined angle and faces the end surface 62, and a reference surface 66 that is orthogonal to the end surface 62 and is parallel to the light transmission direction. Has a wedge shape in which one surface of a rectangular parallelepiped is formed into an inclined surface.

By the way, the reference surface 6 of the wedge-shaped birefringent plate 6
In order to measure the optical axis <001> direction with respect to 6, that is, the angle θ formed by the reference plane 66 and the optical axis <001>,
As shown in FIG. 2, first, the wedge-shaped birefringent plate 6 is placed on the measurement table 22 with the reference surface 66 aligned, and the end face 62 or the inclined surface 64 of the wedge-shaped birefringent plate 6 is placed on the irradiator 24. (See FIG. 2A), the irradiator 24 irradiates a parallel light beam and transmits it. Then, the detector 32 is positioned on the optical axis of either ordinary light or extraordinary light separated by the wedge-shaped birefringent plate 6, and the amount of transmitted light after transmission is measured. In the illustrated example, the detector 3 is placed on the optical axis of ordinary light.
2 is arranged to measure the amount of transmitted light of only ordinary light, and in order to obtain the optical axis <001> direction when viewed from the end face 62 side including the optical axis <001> in advance, The end surface 62 side faces the irradiator 24 side.

Next, the rotary polarizing plate 28 is rotated to find the rotational position where the measured value of the transmitted light amount becomes the minimum value, the optical axis <001> direction is obtained, and the optical axis <001> direction is obtained. If so, the rotational position of the rotary polarizing plate 28 at this time is set as the angle measurement starting point, and the scale of the angle measuring means 30 is reset.

Next, while leaving the reference surface 66 of the wedge-shaped birefringent plate 6 to be placed as it is, the wedge-shaped birefringent plate 6 is rotated 180 degrees so that the inclined surface 64 side faces the irradiator 24 (FIG. 2B).
Optical axis <00 when viewed from the inclined surface 64 side.
The 1> direction is obtained in the same manner as described above. Then, the rotation angle of the rotary polarizing plate 28 at this time is determined by the angle measuring device 30.
If read from, the optical axis <00 when viewed from the end face 62 side
Since the scale is reset in advance in the angle direction of 1>, the read value becomes the angular difference α in each optical axis <001> direction when viewed from the two directions as it is. The angular difference α thus obtained is, so to speak, two optical axes <0.
Since the angle between 01> is substantially equal to the direct measurement, the measurement accuracy is extremely high.

Since the angle difference α is obtained by subtracting twice the angle θ formed by the reference plane 66 and the optical axis <001> from π, the angle θ is (π-α) / 2. It is possible to easily calculate and measure, and obtain a highly accurate measured value.

When obtaining the angle difference α, the scale initial value of the angle measuring means 30 is set to an arbitrary value,
The scale display value of the rotational position when the optical axis <001> direction from each direction is searched for may be read as it is, and the angular difference α may be obtained from the difference between the read values. Even if calculated in this manner, the arbitrarily set initial value disappears when the subtraction is performed, so that there is no effect. That is, the scale of the angle measuring means 30 does not need to be initially set when the rotary polarizing plate 28 is rotated to find the direction of each optical axis <001>. Further, as the reference surface 66 of the wedge-shaped birefringent plate 6, any of the four surfaces around the inclined surface can be selected.

When measuring the optical axis direction of a pair of wedge-shaped birefringent plates 6a and 6b incorporated in a polarization independent optical isolator, one wedge-shaped birefringent plate 6a is wedge-shaped as shown in FIG. The peripheral side surface on the long side, which is wide in the trapezoidal cross section of the above, is measured as the reference surface 66, and the other wedge-shaped birefringent plate 6b
Alternatively, as shown in FIG. 3, the peripheral side surface on the short side, which becomes narrow in the wedge-shaped trapezoidal cross section, may be measured as the reference surface 66. In this way, when the reference planes are separately measured, the optical axes <00 of the pair of wedge-shaped birefringent plates 6a and 6b are <00.
1> direction is within the allowable dimensional accuracy (as a specific example, 2
When the polarization independent optical isolator is assembled, the pair of wedge-shaped birefringent plates 6a and 6b are mounted on the assembly jig base if the acceptance judgment is made as a part after entering the temperature of 2.5 degrees ± 10 minutes). The optical axis directions can be shifted from each other by 45 degrees simply by placing them on the reference surface 36a of 36, and the optical axis adjustment becomes unnecessary.

[0029]

As described above in detail in the embodiments of the invention, according to the method for measuring the optical axis angle of the wedge-shaped birefringent plate according to the present invention, the transmitted light amount of only ordinary light or extraordinary light is a minimum value. Accurately find the optical axis direction from the rotation position of the rotating polarizing plate, and measure the angular difference α between the optical axis direction when viewed from the end face side and the optical axis direction when viewed from the inclined surface side,
The angle difference α in the optical axis direction when viewed from these two directions is obtained by subtracting twice the angle θ formed by the reference surface and the optical axis from π, and the angle θ is (π−α) / 2. Therefore, the angle θ can be easily calculated and measured from the calculated angle difference α.

Further, since the rotational positions in the respective optical axis directions obtained by measuring from the two directions substantially directly measure the optical axis, the angular difference α between them can be measured with extremely high accuracy, Therefore, the angle θ can also be measured with high accuracy.

For this reason, it becomes possible to perform highly reliable component accuracy control, and it becomes possible to appropriately perform the component pass / fail judgment.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a measurement system used for carrying out a measurement method according to the present invention.

FIG. 2 shows a wedge-shaped birefringent plate placed on a measuring table with a reference surface aligned. FIG. 2 (a) shows a case of measuring from the end face side, (i) is a side view thereof, ) Is its front view,
The same figure (b) shows the case of measuring from the inclined surface side, (i)
Is a side view thereof, and (ii) is a front view thereof.

FIG. 3 shows a wedge-shaped birefringent plate mounted on a measuring table with different reference planes aligned. FIG. 3 (a) shows a case where measurement is performed from the end face side, and FIG. , (Ii) is a front view thereof, (b) is a case of measuring from the inclined surface side, (i) is a side view thereof, and (ii) is a front view thereof.

FIG. 4 is a diagram showing a state in which a polarization independent optical isolator is assembled on an assembly jig base.

FIG. 5 is a perspective view for explaining a schematic configuration of a polarization independent optical isolator and its operation principle.

FIG. 6 is an enlarged perspective view showing a main part of a polarization independent optical isolator.

FIG. 7 is a diagram illustrating a procedure for forming a wedge-shaped birefringent plate used in a polarization-independent optical isolator.

[Explanation of symbols]

 6 wedge-shaped birefringent plate 22 measuring table 28 rotary polarizing plate 62 end surface 64 inclined surface 66 reference plane <001> optical axis

Claims (1)

[Claims] 1. A reference surface 66 parallel to a light transmitting direction, an end surface 62 orthogonal to the light transmitting direction and having an optical axis <001> within the surface, and a facing surface inclined at a predetermined angle with respect to the end surface 62. When measuring the angle θ formed by the reference plane 66 and the optical axis <001> in the wedge-shaped birefringent plate 6 having the inclined surface 64, the birefringent plate 6 is placed on the measuring table 22.
6 is placed together, the birefringent plate 6 placed thereon is caused to transmit the light polarized by the rotary polarizing plate 28, and the transmitted light amount of only the ordinary or extraordinary light after the transmission is measured. The minimum rotation angle of the polarizing plate 28 is determined both from the end face 62 side and from the inclined surface 64 side, and the reference plane 66 and the optical axis < The method of measuring an optical axis angle of a wedge-shaped birefringent plate, which comprises measuring an angle θ formed by 001>.