JP2912784B2 - Optical isolator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator.

[0002]

2. Description of the Related Art Conventionally, a Faraday rotator has been disposed in a cylindrical magnet, and a pair of polarizers has been disposed on an optical axis with the Faraday rotator interposed therebetween. There is known an optical isolator configured to be inclined by 45 ° so that light from the forward direction passes with little loss and light from the reverse direction is blocked and cannot pass.

When an optical isolator having such a structure is manufactured, a small polarizer is used.
In order to facilitate the angle adjustment and the fixing work of the polarization plane, a polarizer is fixed to a pair of holders each having a light transmitting hole in advance, and the holder is rotated at both ends of the cylindrical magnet to adjust the angle. In this state, the holder and the cylindrical magnet are fixed.

[0004]

By the way, since the holder for fixing the polarizer is disposed at both ends of the cylindrical magnet,
Generally, a non-magnetic material is used. This is because a ferromagnetic material is considered to affect the central magnetic field condition of the cylindrical magnet.

To use an optical isolator, it is combined with a lens system in an optical transmission line. FIG. 5 shows a state where the optical isolator 41 is combined with a lens holder 44 that holds a lens 43. Since the holder holding the polarizer is disposed at both ends of the optical isolator, if a ferromagnetic material is used as the material, if the lens holder 44 to be combined is a ferromagnetic material, the magnet and the A new magnetic circuit is formed between the materials, which may degrade the condition of the central magnetic field in the optical isolator.

Therefore, when an optical isolator is incorporated in an optical transmission line, for example, as described above,
The holder for fixing the polarizer should be a non-magnetic material so that the normal function can be maintained even if the material of the case 4 or the case 42 is ferromagnetic.

However, the selection of the holder depends not only on the conditions such as the strength, reliability and workability of the material, but also on the matching with the thermal expansion coefficient of the fixed polarizer.
In addition, solder or low melting point glass is generally used for fixing the optical element, and a holder material having good wettability is preferable. Materials that satisfy all of these conditions are not necessarily in non-magnetic materials.In practice, the above conditions are almost satisfied in order to fix lenses and polarizing glass with low-melting glass and solder. The holder member used is made of a ferromagnetic material such as 50-Aroy. Therefore, if the material used in the optical isolator can be selected regardless of whether it is ferromagnetic or non-magnetic, an optical isolator with extremely high reliability and productivity can be provided.

An object of the present invention is to solve the above-mentioned problems of the prior art by using a ferromagnetic material for a holder for fixing a polarizer, and furthermore, an optical isolator that does not matter the material of an optical transmission line to be incorporated. It is to provide.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems in the prior art, the present invention provides a cylindrical magnet, a Faraday rotator disposed in the opening of the cylindrical magnet, and both ends of the opening of the cylindrical magnet. And a pair of polarizers respectively disposed on the optical axis and sandwiching a Faraday rotator, wherein a pair of cylindrical holders made of a ferromagnetic material having a polarizer fixed on an optical axis are provided by the cylindrical magnet. The optical isolator includes a configuration disposed at both ends of the optical isolator, and the configuration is included in a shield member made of a non-magnetic material.

[0010]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1A is a sectional view of an optical isolator showing one embodiment of the present invention, and FIG. 1B is an exploded perspective view thereof.
FIGS. 3 and 4 are cross-sectional views of an optical isolator showing a comparative example of the embodiment of the present invention. In addition, the same reference numerals are given to the same parts in each drawing so that the comparison can be made clearly.

First, an optical isolator shown in FIG. 1 which is an embodiment of the present invention will be described. In the optical isolator of the present embodiment, a Faraday rotator FR and polarizers P1 and P2 of the same size are disposed in the opening of the cylindrical magnet M on both sides of the Faraday rotator FR. Is P
The respective polarization planes are 4 while being held by the holders 2 respectively.
It has a basic structure manufactured by adjusting the rotation by 5 ° and a shield structure (4, 5, 6) made of a non-magnetic material including the basic structure.

First, the P-holder 1 and the P-holder 2 are flat cylindrical bodies having substantially the same outer diameter as the cylindrical magnet M and having a light-transmitting hole passing through the center at the center. Is provided with a step for fixing the polarizer with solder or low-melting glass. Suitable for using solder or low melting point glass for the material of P holder 1 and P holder 2
Considering the good wettability and the good matching of the thermal expansion coefficients of the polarizers P1 and P2, the ferromagnetic material Ni-Fe 50-
Aroy's alloy is used. The inner diameter φa of the light transmitting hole has a minimum size that does not hinder the passage of light.

The Faraday rotator FR is connected to a cylindrical magnet M.
A cylindrical F holder 3 using a 50-Aroy alloy for the light transmitting hole of the P holder 1 in order to dispose it in the opening
And a Faraday rotator FR at the tip of the F holder 3.
Are fixed with solder or low melting point glass, respectively. Therefore, the P holder 1 is assembled in a state where the polarizer P1 and the Faraday rotator FR are fixed on the light transmitting holes in this order in advance. On the other hand, the P holder 2 is assembled in a state where only the polarizer P2 is fixed in advance.

Next, a shield 4, a shield 5, and a cylindrical case 6 using Sus304 as a nonmagnetic material are used for the shield structure. Shields 4 and 5 are P holders 1 and 2
As in the case of (1), it is a flat cylindrical body having an outer diameter substantially the same as that of the cylindrical magnet M and having a light-transmitting hole through which light passes in the center. The inner diameter φb of the shields 4 and 5 and the inner diameter φa of the P holders 1 and 2 satisfy φb ≧ φa. Since the shields 4 and 5 form the outermost end face of the optical isolator, a keyway for facilitating the adjustment of the optical isolator and other components in the optical transmission line is provided, and the polarization is not provided. A marking indicating the direction may be added. This is useful for automation and labor saving.

When the cylindrical magnet M, the P holder 1 to which the polarizer P1 and the Faraday rotator FR are fixed, the P holder 2 to which the polarizer P2 is fixed, and the shields 4 and 5 are ready, the cylindrical case 6 Assemble inside. Other parts fit into this cylindrical case 6 exactly. The assembling order is as follows. First, the P holder 1, the cylindrical magnet M, and the P holder 2 are put in the cylindrical case 6, and the mutual polarization planes of the polarizers P1 and P2 are set at 45 °.
The rotation of the P holder is adjusted so as to be inclined, and when the rotation adjustment is completed, the P holders 1 and 2 and the inner wall of the cylindrical case 6 are welded with a YAG laser. Finally, the shields 4 and 5 are put in the cylindrical case 6 and fixed by welding with a YAG laser to complete the optical isolator.

Next, the optical isolator of FIG. 3 shown as a comparative example has a structure in which the shields 4 and 5 are removed from the optical isolator of FIG. 1 described above. And the results are shown in Table 1.

[0017]

[Table 1]

In this test, a sample and a sample using a 50-Aroy alloy of Ni—Fe as a ferromagnetic material were used as the materials of the P holders 1 and 2, and a sample was made of S as a nonmagnetic material.
For the sample using us304 and the sample, the forward loss and the backward loss were measured in a single state.

As can be seen from the results, the use of either a ferromagnetic material or a non-magnetic material for the P holder has no relation to the characteristics of the optical isolator. Heretofore, it has been considered that the P holder cannot be used unless it is a non-magnetic material because it is disposed near the cylindrical magnet M. However, there are conditions that the cylindrical magnet M sufficiently satisfies the saturation magnetic field of the Faraday rotator FR and that the light transmitting hole of the P holder has a smaller diameter than the opening of the cylindrical magnet M so as not to deteriorate the central magnetic field. If
It can be assumed that the material of the P holder is not particularly limited, and the conditions for selecting the material of the P holder can be relaxed. Therefore, a ferromagnetic material can be used for the P holder so as to match the thermal expansion coefficients of the polarizers P1 and P2 and to fix the polarizers P1 and P2 with solder or low-melting glass from the viewpoint of good wettability . In the case of solder or low-melting-point glass, no gas is generated unlike an adhesive, so that a semiconductor laser or the like is not adversely affected. Specifically, an alloy such as 50-Aroy of Ni—Fe, which is a ferromagnetic material, is suitable.

Next, the performance of the optical isolator having the shields 4 and 5 attached as shown in FIG. 1 was tested, and the results are shown in Table 2 and 3.

[0021]

[Table 2]

First, in the test, the forward loss and the backward loss were measured in a state where only the optical isolator of FIG. 1 was used alone. On the other hand, in the test, the forward loss and the backward loss were measured in the experimental apparatus shown in FIG. FIG.
In the experimental device of the first embodiment, an optical isolator is combined with a ferromagnetic lens holder or the like to realize a state in which the optical isolator is incorporated in an optical transmission line. As shown in the results in Table 2, almost the same characteristics were obtained in the test using the single unit and the test in the experimental apparatus, and the effect of the shield according to the present invention was confirmed.

After this test, the optical isolator having the structure shown in FIG. 3 was measured in the experimental apparatus shown in FIG.
The result is the test in Table 2. As the result, it was completely different from the result of Table 1. Therefore, when a material using a ferromagnetic material for the P holder is directly incorporated into an optical transmission line, a new magnetic circuit is formed by the P holder and the ferromagnetic material for the transmission line as described in the problem to be solved by the present invention. Is formed, which causes the function of the optical isolator to be completely lost.

Next, in the optical isolator shown in FIG. 4 as a comparative example, the positions of the shields 4 and 5 of the optical isolator shown in FIG. Is the same as that of FIG.
Roy's alloy is used. Table 1 shows the results of testing this optical isolator in the experimental apparatus shown in FIG. The results show that the forward loss is almost satisfactory, but the reverse loss is much worse than the test. This is because the F-holder 3 holding the Faraday rotator FR also uses an alloy of 50-Aroy, which is a ferromagnetic material, between the end face of the cylindrical magnet M and the P holders 1 and 2. This is because even if the shields 4 and 5 are interposed, a sufficient shielding effect cannot be obtained. Therefore, the shield is not necessarily located anywhere outside the magnet, and it is understood that the configuration of the present invention is the optimum position.

As is apparent from the above comparative example, as in the embodiment of the present invention, the P holders 1 and 2 have good wettability and good matching of the thermal expansion coefficient with the polarizers P1 and P2. If a ferromagnetic material such as a 50-Aroy alloy of Ni-Fe is used, and a shield made of a non-magnetic material such as Sus304 is disposed outside the ferromagnetic material, the light can be transmitted to any optical transmission line. The same characteristics as those of the isolator alone can be maintained.

In the above embodiment, Sus304 is used as the non-magnetic material because of ease of welding, but other metals or ceramics may be used as long as they are non-magnetic. Further, the P-holder and the F-holder have good wettability and good matching of the thermal expansion coefficient with the polarizer.
Ni alloy was used, but it was ferromagnetic and required strength,
Other metals and alloys may be used as long as they have reliability and processing accuracy.

[0027]

As described above, according to the present invention, a ferromagnetic material can be used for the P holder to which the polarizer is fixed, and the function of the material of other components combined in the optical transmission line can be improved. Unaffected.

[Brief description of the drawings]

1A and 1B show an optical isolator according to one embodiment of the present invention, wherein FIG. 1A is a cross-sectional view and FIG. 1B is an exploded perspective view.

FIG. 2 is a sectional view of an experimental apparatus.

FIG. 3 is a cross-sectional view of an optical isolator according to a comparative example.

FIG. 4 is a sectional view of an optical isolator according to another comparative example.

FIG. 5 is a sectional view showing an example of use of the optical isolator.

[Explanation of symbols]

 1, 2P holder 3 F holder 4, 5 Shield 6 Cylindrical case (shield member) M Cylindrical magnet P1, P2 Polarizer FR Faraday rotator

Claims (1)

(57) [Claims] 1. A cylindrical magnet, a Faraday rotator disposed in an opening of the cylindrical magnet, and a pair of polarizers disposed at both ends of the opening of the cylindrical magnet and sandwiching the Faraday rotator. In the optical isolator, a pair of cylindrical holders made of a ferromagnetic material having a polarizer fixed on an optical axis are provided at both ends of the cylindrical magnet, respectively. An optical isolator, which is included in a shield member made of a material.