JPS63281126A - Optical isolator - Google Patents

Abstract

PURPOSE:To prevent the deterioration in characteristic due to the approach of a ferromagnetic material from the outside, by providing a magnetic shield use ferromagnetic metallic structure of a specific shape. CONSTITUTION:In about the center of a ferromagnetic metallic structure 4 of a cylindrical shape, an optical isolator is placed, and it is constituted so that length (h) of a cylindrical magnet 3 is shorter than length l in the traveling direction of a light beam of the ferromagnetic metallic structure 4. Accordingly, to the respective parts of the ferromagnetic metallic structure 4, a magnetic charge of an opposite code to N and S of a magnet is induced, and a magnetic field applied to a magneto-optical material is weakened to some extent, but it is scarcely influenced from the outside. In such a way, even if other ferromagnetic metallic structure approaches, the original characteristic of the optical isolator is not damaged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical isolator that has the function of suppressing light propagating in the opposite direction along the same optical path when light propagates in one direction.

[Conventional technology]

For example, light generated by a semiconductor laser as a light source can be used as a light source.
When trying to propagate through an eyeper, reflected light is generated due to the dispersion of light inside the optical fiber, local non-uniformity of the refractive index, the presence of connections, etc., and the light propagates in the opposite direction along the optical path to the semiconductor of the light source. It may recombine with the laser. In such a state, the oscillation of the semiconductor laser becomes unstable and the noise of the generated light increases, which is undesirable.

Therefore, in such cases, it is effective to use an optical isolator to suppress the reflected light.

Figure fjS6 shows an example of the configuration of a conventional optical isolator.

In the figure, light incident from point a is converted into parallel light by a lens 1, and then enters a polarizer P1. The polarizer P selectively passes only polarized light in a certain direction, for example, vertically polarized light, from the incident light.

The light emitted from the polarizer P1 is Y I G (Y 20 s, F
The light enters a 7 Alladay rotary element FR made of a single crystal such as an oxide single crystal whose main component is e203, and output light whose polarization direction is rotated by 45 degrees is generated.

Normally, the 77 Rady rotation element FR is placed at the center of a cylindrical magnet 3 magnetized in the direction of the rotation axis as shown in the figure, and is magnetized in a direction substantially parallel to the optical path.

The light emitted from the Alladay rotary element FR enters the analyzer P2, but the polarization direction of the analyzer P2 is tilted by 45 degrees from the vertical direction.

Therefore, the light incident from the 7 Allady rotary element FR is
The light passes through the analyzer P2 and exits, passes through the lens 2, and produces an output converged at point b.

Therefore, for example, if the end of the optical fiber is placed at point b, then a
It is possible to couple light incident from a point to a light fiber.

On the other hand, as mentioned above, the reflected light generated in the optical fiber etc. enters the polarizer P2 (acted as an analyzer last time) from point b through the lens 2, and the component light that matches the polarization direction of the polarizer P2 is The light passes through the polarizer P2 and enters the 7 Alladay rotation element FR.

As is well known, in the 7 Alladay rotation element FR, the direction of rotation of the plane of polarization changes depending on the relationship between the direction of incidence of light and the magnetization direction of the 7 Alladay rotation element material.

In this case, the coordinate system of the arrangement is 4 in the same direction as the incident light.
Since it is rotated by 5 degrees, the polarization direction of the emitted light from the Faraday rotation element FR becomes perpendicular to the propagation direction of the analyzer P (which previously acted as an analyzer). Therefore, the incident light from the seven Alladay rotary elements FR is blocked by the analyzer P1 and is not propagated to the side a.

Therefore, reversely entering light coupled to the semiconductor laser placed at point a is blocked, and deterioration of S/N in the semiconductor laser is prevented.

Now, as optical communications become more dense and faster each year, research into high-speed modulation optical communications has become active in various places. Such high-speed modulation optical communications require small, high-performance optical isolators.

Also, several optical isolators may be used in close proximity.

However, as shown in Figure 6, the magnetic circuit of a conventional optical isolator is an open magnetic circuit, and if two or more optical isolators are used in close proximity, they will interfere with each other and impair the characteristics of the optical isolator. I'm worried.

Furthermore, when an optical isolator is mounted on a printed board, there is a possibility that other ferromagnetic metal structures may come close to the optical isolator, and in this case as well, the characteristics of the optical isolator may be impaired.

[Problem that the invention seeks to solve]

In the structure of conventional optical fisulators, little attention has been paid to the deterioration of characteristics due to the approach of ferromagnetic material from the outside.

The object of the present invention is to provide an optical isolator equipped with a ferromagnetic metal structure that serves as a suitable magnetic shield to solve this problem.

[Means for solving problems]

In order to achieve the above object, the present invention includes a seven Alladay rotating element arranged at the center of a cylindrical magnet magnetized in the direction of the rotation axis;
In an optical isolator whose main components include a polarizer, an analyzer, a prism, etc. arranged on both sides of the 77 Rady rotary element, there is a ferromagnetic metal structure containing the optical isolator, and the ferromagnetic metal structure The main points are that the length of the object in the traveling direction of light is treated as greater than the length of a cylindrical magnet, and that the ferromagnetic metal structure is splittable and has a structure in which the optical isolator can be contained by splitting it. It is a feature.

[For production]

By using the ferromagnetic metal hη structure of the present invention, it becomes possible to realize an optical isolator that is stable against disturbances caused by the proximity of a ferromagnetic material from the outside.

〔Example〕

The effects of the present invention will be explained in detail below using Examples.

FIG. 1 is a diagram showing one embodiment of the present invention.

An optical isolator is arranged approximately in the center of the cylindrical ferromagnetic structure 4. h is the length of the cylindrical magnet 3, and l is the length of the ferromagnetic metal structure 4 in the direction in which the light advances. In this figure, h is shorter than r.

By doing this, magnetic charges with opposite signs to the N and S of the magnets are induced in each part of the ferromagnetic metal structure 4, and although the magnetic field applied to the magneto-optic material is somewhat weakened, It becomes extremely difficult to be affected.

The fjtJ2 diagram shows an example in which this was actually confirmed.
In this embodiment, the optical isolator 7.8 of conventional structure is
We are conducting experiments by preparing individual pieces and bringing them together in close contact with each other.

A cylindrical iron plate 4 is placed over only one of the optical isolators 8 as a cylindrical ferromagnetic metal structure, and the length l of the cylindrical iron plate 4 is varied to reduce the deterioration of the reverse direction loss of one of the optical isolators 8. That's what I saw.

As can be seen from this figure, in the region where β is sufficiently longer than h, the characteristics of one optical isolator 8 do not deteriorate, but... is smaller than h, the other optical isolator 7
Under the influence of this, the characteristics of one optical isolator 8 rapidly deteriorate.

According to the embodiment of the present invention, when two optical isolators are used close to each other, mounting the cylindrical iron plate 4 is extremely effective, and it is more effective if its length is longer than the length of the cylindrical magnet. I understand that.

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

In this case, the ferromagnetic metal structure 4 can be divided into c-cod-d or e-e, and is characterized by the addition of a disk-shaped ferromagnetic structure 5.5'. .

Structures 4.4' and 5.5' can be manufactured as one piece, but even if they are ultimately sealed by laser welding, it is necessary to include the magnets, etc., which are the main components of the optical isolator, during manufacture. In order to do so, it must be divisible. Hole 6 in the center of the disk-shaped ferromagnetic metal structure 5.5'.

6' is a hole through which light passes. If the purpose is magnetic shielding, this hole should be as small as possible.

Further, the distance f between the magnetic pole face of the magnet and the cylindrical structure is extremely important in terms of design. From the point of view of downsizing the optical isolator, it is better to make r as small as possible, but if it becomes too small, the magnetic charges N and S on the magnetic pole surfaces will be effectively diluted.
This is inconvenient because the magnetic field applied to the 7T araditic element FR becomes too weak.

In this example, in order to sufficiently magnetize the 7 Alladay diversion element FR, f was required to be DL/2 or more. However, DL is the inner diameter of the magnet.

FIG. 4 shows the deterioration of the characteristics of one of the optical isolators 10 by varying the distance Rx between the two optical isolators 9 and 10 in order to investigate the effect of the Pt53 diagram embodiment of the present invention. be. The Δ mark is when the structure of the embodiment of the present invention is used, and the ○ mark is when the structure of the prior art is used.

As can be seen from this figure, when the distance between two optical isolators is 5- or more, no deterioration in the characteristics of the optical isolators is observed, but when the distance approaches 5-1 or less, the characteristics of the optical isolator with the conventional structure rapidly deteriorate. I can see it sticking.

On the other hand, in the embodiment of the present invention, almost no change in the characteristics of the optical isolator 10 is observed even when the two optical isolators 9 and 10 are brought into close contact with each other.

FIG. 5 shows another embodiment of the invention in which two optical isolators are included in a ferromagnetic metal structure 4''.

Ps, P<, 3', and FR' represent the polarizer, analyzer, cylindrical magnet, and 7 Alladay rotating elements of the second optical isolator, respectively.

Those skilled in the art who are interested in the present technology will easily understand that the effects of the present invention do not change even if two or more optical isolators are included.

〔Effect of the invention〕

As described above in detail using the embodiments, the optical isolator using the ferromagnetic metal structure of the present invention is resistant to external magnetic influences and has extremely stable characteristics.

[Brief explanation of the drawing]

Figures 1, 3, and 5 are structural diagrams of optical isolators according to embodiments of the present invention, Figures 2 and 4 are characteristic change diagrams showing the effects of the present invention, and Figure 6 is a diagram of conventional optical isolators. FIG. 3: Cylindrical magnet, 4: Ferromagnetic metal structure, FR
Near Allady rotating element, Pl: polarizer,
P2: analyzer, l binary magnetic metal v I relic length,
h: Length of cylindrical magnet Agent Patent attorney Books
Kai Takashi J: Round armored stone P2: Ken #:
, Hand 4: Obscure & 4 structural pieces No: Ferromagnetic metal structure FR Nib-Aradi rotation element + A: Length of cylindrical magnet Pl: A1 to ε-C-child/l Fig. 3 Suff (mη hun

Claims (4)

[Claims] (1) An optical isolator whose main components include a Faraday rotating element placed in the center of a cylindrical magnet magnetized in the direction of the rotation axis, and a polarizer, analyzer, or prism placed on both sides of the Faraday rotating element. An optical isolator characterized in that there is a ferromagnetic metal structure that encloses the optical isolator, and the length of the ferromagnetic metal structure in the direction in which light travels is longer than the length of the cylindrical magnet. (2) The optical isolator according to claim 1, wherein the ferromagnetic metal structure is splittable and has a structure in which the optical isolator can be included by splitting the structure. (3) The optical isolator according to claim 2, characterized in that the ferromagnetic metal structure has two or more holes for transmitting light. (4) The optical isolator according to claim 2, wherein the ferromagnetic metal structure includes two or more optical isolators.