JPH08101360A - Fixing structure of optical element - Google Patents

Abstract

PURPOSE: To obviate the generation of the tensile stress by a thermal expansion difference of an azimuth rotator by arranging the azimuth rotator on the inner side of a Faraday rotator holder and another azimuth rotator holder, inserting a spacer on the inner side of both holders and holding the Faraday rotator and the azimuth rotator at their respective ends. CONSTITUTION: The Faraday rotator holder 1 is formed to a cylindrical shape and has a collar part 1a on the outer periphery at one end. The holder has a first stage 1b and a second stage 1c. The Faraday rotator 4 is held in the first step part 1b and the Faraday rotator 4 is joined by the low melting glass 6 of the second step part 1c. The one end 3a of the cylindrical spacer 3 is inserted into the Faraday rotator holder 1 and the Faraday rotator holder 1 and the spacer 3 are joined. On the other hand, the azimuth rotator holder 2 is placed with the azimuth rotator 5 in the step part 2a. The other end 3b of the spacer 3 is inserted into the inner periphery of the azimuth rotator holder 2 and the end 3b of the spacer 3 is pressed to the azimuth rotator 5 and is connected by a melting point 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for fixing an optical element constituting an optical isolator or optical circulator used for optical fiber communication or the like.

[0002]

2. Description of the Related Art As a structure for fixing an optical element such as a lens to a holder, as shown in FIG. 5, an annular groove 31a is formed on the inner periphery of a cylindrical holder 31, and a low melting point glass 33 is filled in this groove. And firing with the optical element 32 mounted,
There is a structure for fusion bonding (see Japanese Patent Laid-Open No. 3-271704).

Utilizing this, as shown in FIG. 6, the Faraday rotator holder 21 in which the Faraday rotator 24 is fixed by the low melting point glass 26 and the optical rotator 25 are set in the low melting point glass 2.
YAG at the welding point 28 with the optical rotator holder 22 fixed at 7.
A fixing structure of an optical element fixed by welding is used.

The optical element shown in FIG. 6 is used as an optical isolator. That is, the Faraday rotator 24 is made of garnet and has the function of rotating the polarization plane of linearly polarized light by 45 °. The optical rotator 25 is made of crystal, and when linearly polarized light having an angle of θ with respect to its crystal axis is incident,
Since it has a function of rotating the plane of polarization of this linearly polarized light by 2θ and allowing it to pass, θ is set beforehand to be 22.5 °. Now, the linearly polarized light incident from the direction of the arrow in FIG. 6 rotates its polarization plane by 45 ° when passing through the Faraday rotator 24, and then rotates by −45 ° when passing through the optical rotator 25. Match the azimuth. On the other hand, the linearly polarized light incident in the direction opposite to the arrow has a polarization plane of 45 ° when passing through the optical rotator 25.
It rotates, and because it passes through the Faraday rotator 24 and rotates 45 °, it is
° It will be rotated.

As described above, the polarization direction of the emitted light can be made orthogonal depending on the incident direction of the light. Therefore, if polarizers having absorption azimuths are arranged at both ends of the optical element shown in FIG.
It is possible to allow light in only a certain direction to pass and not allow light in the opposite direction to pass, and it is possible to provide an optical isolator.

If this optical isolator is connected, for example, immediately after the laser light source, even if the light emitted from the laser light source is reflected and returned, it does not enter the laser light source and the laser oscillation becomes unstable. Can be prevented.

[0007]

However, in the fixing structure shown in FIG. 6, the low-melting glass 27 has a coefficient of thermal expansion of 83 × 10 ⁻⁷ / ° C., and the optical rotator holder 22 has a coefficient of thermal expansion of 100 × 10 ^−7. In contrast, the optical rotator 25 made of quartz has a high coefficient of thermal expansion at 300 ° C. of 300 × 10 ⁻⁷ / ° C. and a high coefficient of thermal expansion at a high temperature, and a large difference in thermal expansion with other members. there were. Therefore, when the low melting point glass 27 is fired and fused and then cooled, the optical rotator 25 largely contracts, and a tensile residual stress is generated between the optical rotation element 25 and the low melting point glass 27.

As a result, the birefringence of the optical rotator 25 changes to cause a phase difference, and the normal extinction ratio is about 50 dB, but the extinction ratio is greatly deteriorated to 30 dB or less. It was When the extinction ratio becomes small, there is a disadvantage that both the forward loss characteristic and the backward loss characteristic are deteriorated when used as an optical isolator, for example.

Further, since the angle of rotation of the linearly polarized light of the optical rotator 25 differs depending on the angle formed by the vibration direction of the linearly polarized light and the optical axis, it is necessary to adjust the rotation around the optical axis. Since it also has the effect of rotating the linearly polarized light having such an oscillation direction by a predetermined angle, it is not necessary to adjust the rotation. Therefore, the Faraday rotator 24 and the optical rotator 25 can be integrated, but in the structure of FIG. 6, the Faraday rotator 24 and the optical rotator 25 are separately assembled and finally joined, so that there are many work steps. There was also a problem.

The present invention has been made in view of the above points, and an object thereof is to provide a fixing structure in which tensile stress due to a difference in thermal expansion does not occur in an optical rotator. Another object of the present invention is to obtain a fixing structure in which a Faraday rotator and an optical rotator are integrated.

[0011]

In view of the above, the present invention provides:
In the structure in which the Faraday rotator and the rotator are coaxially fixed, the Faraday rotator is placed in the inner step of the cylindrical Faraday rotator holder, and the rotator is placed in the inner step of the other cylindrical rotator holder. Is arranged, a cylindrical spacer is inserted into both holders, and the Faraday rotator and / or the optical rotator are sandwiched and held at each end of the spacer.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the Faraday rotator holder 1 is a cylindrical member made of metal and has a flange 1a on the outer circumference at one end, and a first step 1b and a second step 1c on the inner peripheral surface. have. Then, the Faraday rotator 4 is held on the first step portion 1b, and the Faraday rotator 4 is joined by the low melting point glass 6 provided on the second step portion 1c. Further, one end 3a of the cylindrical spacer 3 is inserted into the inner circumference of the Faraday rotator holder 1, and the Faraday rotator holder 1 and the spacer 3 are joined by YAG welding.

On the other hand, the optical rotator holder 2 is a cylindrical body made of metal and has a step portion 2a on its inner peripheral surface, and the optical rotator 5 is mounted on the step portion 2a. Then, the other end 3 of the spacer 3
b is inserted into the inner circumference of the optical rotator holder 2 and the end 3b of the spacer 3 is pressed against the optical rotator 5, and the spacer 3 and the optical rotator holder 2 are connected by laser welding at the welding point 8. is there. At this time, the optical rotator 5 is held by being sandwiched between the spacer 3 and the optical rotator holder 2, and is not fixed using a low melting point glass or the like.

Further, a permanent magnet 7 for applying a magnetic field to the Faraday rotator 4 is mounted on the outer periphery of the Faraday rotator holder 1, and the permanent magnet 7 is provided by including the collar portion 1a. Does not shift in the optical axis direction. When a sintered magnet is used as the permanent magnet 7,
It is desirable to make the outer diameter of the collar portion 1 a larger than the outer diameter of the permanent magnet 7 because chipping or cracking may occur due to external impact.

According to such a fixing structure of the optical element of the present invention, since the Faraday rotator 4 and the optical rotator 5 are integrated, the manufacturing process can be simplified. Moreover, since both ends of the spacer 3 are inserted into and joined to the inner peripheral surfaces of the Faraday rotator holder 1 and the optical rotator holder 2, the overall coaxiality can be increased.

Further, since the optical rotator 5 is held by being sandwiched between the spacer 3 and the optical rotator holder 2, the tensile stress due to the difference in thermal expansion does not occur in the optical rotator 5 because the low melting point glass is not used.

The Faraday rotator 4 has a function of rotating the angle of the plane of polarization of the incident linearly polarized light, and is usually made of garnet. Further, when the linearly polarized light having an angle of θ with respect to the crystal axis is incident, the optical rotator 5 has a function of rotating the polarization plane of this linearly polarized light by 2θ and emitting it.
Usually consists of a half-wave plate such as a crystal.

Next, a method of manufacturing the optical element fixing structure of the present invention will be described. First, as shown in FIG. 2 (a), which is turned upside down from FIG. 1, the Faraday rotator 4 is attached to the first step 1b of the Faraday rotator holder 1, and the low melting point glass 6 is attached to the second step 1c. After arranging the preform, it is fired to fusion-bond the Faraday rotator 4. Then, the permanent magnet 7 is mounted on the outer circumference of the Faraday rotator holder 1, the end 3a of the spacer 3 is further inserted on the inner circumference of the Faraday rotator holder 1, and the spacer 3 and the rotor holder 1 are joined by YAG welding. To do.

Next, as shown in FIG. 2 (b), after the optical rotator 5 is mounted on the step portion 2a on the inner circumference of the optical rotator holder 2,
The other end 3 of the spacer 3 in the assembly shown in (a)
Insert b into the inner peripheral surface of the optical rotator holder 2. Then, the end portion 3b of the spacer 3 is pressed against the optical rotator 5, and the side surface of the spacer 3 and the optical rotator 5 are pressed in a state in which the optical rotator 5 is not displaced and the stress does not cause birefringence. Laser welding may be performed at the welding point 8 between the holder 2 and the inner peripheral surface.

Further, in the above embodiment, since the outer diameter A of the large diameter portion of the spacer 3 is made larger than the inner diameter B of the permanent magnet 7, the permanent magnet 7 is held at both ends by the flange portion 1a and the spacer 3. can do. However, as another embodiment, the outer diameter A of the large diameter portion of the spacer 3 can be made smaller than the inner diameter B of the permanent magnet 7. In this case, the permanent magnet 7 can be mounted after the Faraday rotator holder 1, the Faraday rotator 4, and the spacer 3 are joined.

Further, in the above embodiment, an example in which the Faraday rotator holder 1 and the spacer 3 are joined by welding is shown. However, the end portion 3a of the spacer 3 is extended and the end portion 3a is brought into contact with the low melting point glass 6. The Faraday rotator holder 1 and the spacer 3 may also be joined with the low melting point glass 6.

In the above embodiment, the Faraday rotator 4 is used.
Shows an example of fixing with the low melting point glass 6, but as shown in FIG. 3 of another embodiment of the present invention, the Faraday rotator 4 may be held by being held between the Faraday rotator holder 1 and the spacer 3. it can. Moreover, in the example of FIG.
The cylindrical portion 2b of the Faraday rotator holder 1 is made longer by covering the cylindrical portion 2b of the Faraday rotator holder 1.
The whole is joined by laser welding at a welding point 9 between b and 1d. With such a structure, all the joining can be performed by one welding, and the manufacturing becomes easy.

Further, although the Faraday rotator holder 1 and the spacer 3 are separately formed and joined in the above embodiment, they may be integrally formed in advance.

Next, FIG. 4 shows an optical isolator using the fixing structure of the present invention. The fixing structure 10 of the optical element of the present invention is disposed between the polarizer holders 13 and 14 in which the polarizers 11 and 12 that absorb the linearly polarized light of a specific vibration direction are fusion-bonded to each other with a low-melting glass, and both ends are arranged. Polarizers 11 and 1
After adjusting around the optical axis so that the absorption direction of 2 becomes vertical, the respective members are joined and fixed by laser welding, and the case 15 is attached, whereby the optical isolator can be manufactured.

This optical isolator is easy to manufacture because the Faraday rotator 4 and the optical rotator 5 are integrated in advance, and since the extinction ratio of the optical rotator 5 is high, the forward loss characteristic and the reverse loss characteristic are obtained. Can be improved.

In addition to this, the optical element fixing structure of the present invention can also be applied to an optical circulator used for switching the input / output direction of light between a plurality of ports. Although not shown, this optical circulator comprises birefringent crystal bodies such as rutile and calcite before and after the optical element fixing structure of the present invention. That is, since the birefringent crystal has a different refractive index depending on the angle of the plane of polarization of the linearly polarized light, the angle of the plane of polarization of the linearly polarized light is changed by the Faraday rotator or optical rotator, and the birefringent crystal causes The emission direction of can be switched.

Here, the fixing structure of the present invention shown in FIG.
As a comparative example, the extinction ratio of the optical rotator was measured for the conventional fixed structure shown in FIG. Note that the extinction ratio is the ratio of the major axis to the minor axis of the elliptically polarized light, although an unnecessary component is added to the elliptically polarized light when the linearly polarized light passes through the optical element. The larger the value, the better the characteristics. As a result, as shown in FIG.
While the extinction ratio was 0 dB or less, it was found that the extinction ratio can be increased to 35 to 50 dB in the examples of the present invention. Therefore, it can be seen that when the fixed structure of the present invention is used for the optical isolator, the loss of light in the forward direction is small and the effect of blocking the light in the reverse direction is extremely high.

[0029]

As described above, according to the present invention, in the structure in which the Faraday rotator and the optical rotator are coaxially fixed, the Faraday rotator is arranged at the inner step of the cylindrical Faraday rotator holder, and The optical rotator is arranged on the inner step of the cylindrical optical rotator holder, and the cylindrical spacers are inserted inside both holders, and the Faraday rotator and / or the optical rotator is inserted at each end of the spacer. By sandwiching and holding, the working process at the time of manufacturing can be simplified and the coaxiality between the Faraday rotator and the optical rotator can be increased.

Further, since the optical rotator is held by being sandwiched between the optical rotator holder and the spacer, tensile stress is not generated because the optical rotator is not bonded with the low melting point glass, and the extinction ratio can be increased. . As a result, the forward loss can be reduced when applied to an optical isolator or the like.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a fixing structure of an optical element of the present invention.

2A and 2B are cross-sectional views showing a manufacturing process of a fixing structure for an optical element of the present invention.

FIG. 3 is a sectional view showing another embodiment of the present invention.

FIG. 4 is a cross-sectional view showing an optical isolator using the optical element fixing structure of the present invention.

FIG. 5 is a cross-sectional view showing a conventional fixing structure for an optical element.

FIG. 6 is a cross-sectional view showing a conventional fixing structure for an optical element.

FIG. 7 is a graph showing the extinction ratio of the optical rotator in the example of the present invention and the comparative example.

[Explanation of symbols]

 1: Faraday rotator holder 2: Optical rotator holder 3: Spacer 4: Faraday rotator 5: Optical rotator 6: Low melting point glass 7: Permanent magnet

Claims (1)

[Claims] 1. In a structure in which a Faraday rotator and an optical rotator are coaxially fixed, the Faraday rotator is arranged on the inner step of a cylindrical Faraday rotator holder, and the inner side of another cylindrical rotator holder. An optical rotator is arranged in the step portion, a cylindrical spacer is inserted into both holders, and the Faraday rotator and / or the optical rotator are held by being sandwiched at each end of the spacer. Fixing structure for optical elements.