JPH01261616A - Optical isolator - Google Patents

Abstract

PURPOSE:To eliminate the difficulty in adjustment of an optical isolator and, at the same time, to reduce the size of the isolator further by forming holders for fixing a pair of polarizing elements of a magnetic substance. CONSTITUTION:A pair of holders 3 respectively provided with holes suitable for the outer shapes of a polarizer 1 and analyzer 2 which are polarizing elements so that the polarizer 1 and analyzer 2 can be put in the holes are formed of a magnetic substance and the polarizer 1 and analyzer 2 are put in and fixed to the holes. Then the polarizing elements 1 and 2 are respectively fixed to both sides of a permanent magnet 4 after the magnet 4 is magnetized and a Farady rotator 5 is inserted into the central part of the magnet 4. The holders are attracted by the magnet 4 and remain attracted unless external force is applied. Therefore, necessity of tentatively setting the constituents of this isolator in the course of optical axis alignment and 45 deg. adjustment is eliminated and, moreover, since the holders 3 maintain their attracted states after their positions are adjusted, the holders 3 can be fixed permanently by means of a resin bonding or metallic fusion. Thus the assemblage and adjustment of the optical isolator become easier and the whole volume of the isolator can be minimized. In addition, the angle of the optical axis can be adjusted easily.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is used in optical communication, optical measurement, etc., and is particularly applicable to applications where a semiconductor laser is used as a light source. The present invention relates to the structure of an optical isolator, which is a device, and has a function of blocking reflected return light.

[Prior Art] Recent remarkable technological developments in semiconductor lasers, optical fibers, light receiving elements, etc. have made it possible to perform high-density optical transmission of several Qbits/Sec, and are expected to make rapid progress in the future. -As optical systems for right-handed conductor lasers become more dense, malfunctions in laser oscillation caused by reflected light returning from the optical circuit to the semiconductor laser have become an important issue. As a solution to this problem, a method has been proposed in which an optical isolator with a function similar to the isolators used in microwave communications etc. is inserted into the optical circuit to block the reflected return light, and some are now commercially available. It has been reached.

[Problem to be solved by the invention] The optical isolators that have been proposed so far can be roughly divided into two types: one uses Faraday glass as a Faraday rotator, and the other uses Y[G or Bi-substituted LPE garnet. When constructed as follows, the overall size is in the following order: - Faraday glass in the shell > YIQ > Bi-substituted LPE garnet. One field of use each,
They are used depending on their performance. However, considering the future use of multiple devices, devices will need to be made smaller.

(Is it formed by the Bi-converted LPE method in terms of productivity and low cost?) A method using a love-rotor is considered advantageous. On the other hand, polarizing elements such as polarizers and analyzers are polarizing beam splitters (PBS).

Various prisms made from calcite, rutile (TtO)
Birefringent crystals such as e) are used, and rare earth magnets are used as the permanent magnets that give the Faraday rotation effect due to the need to downsize the entire structure.

The performance of an optical isolator is to have as little transmission loss as possible in the forward direction, and to have a high ability to block returning light in the reverse direction. When actually assembling an optical isolator, in order to solve the above performance requirements, it is necessary to strictly adjust the optical axis of each element, and precisely adjust the polarization planes of the polarizer, Faraday rotator, and analyzer at 45 degrees to each other. In the optical isolator configurations proposed in the past, optical axis adjustment and angle adjustment are complicated, and fine adjustment is difficult. - If the ease of force adjustment was the main focus of the design, the entire device would become large and it would be difficult to downsize it, which is a contradictory problem.

In view of this, the first objective of the present invention is to eliminate the adjustment ability of the conventional optical isolator as described above and realize further miniaturization, and the second objective is to provide an optical isolator that is cheaper and easier to mass produce. It provides an isolator.

[Means for Solving the Problems] The main structure of the present invention is to provide an optical isolator including a polarizer, a Faraday rotator, an analyzer, and a permanent magnet for magnetically saturating the Faraday rotator. The fixing holder is made of a magnetic material. That is, as shown in FIG. 1, a polarizer 1 which is a polarizing element
゜A pair of holders 3 are made of a magnetic material and have a hole in the center that matches the outer shape of the polarizing element so that the analyzers 2 can be inserted and bonded to each other. Insert and fix analyzer 2.

Next, the permanent magnet 4 is magnetized, and the Faraday rotator 5 is placed in the center.
After inserting each polarizing element 1.2 into a permanent magnet 4
Fix it on both sides. At this time, since the holder 3 is a magnetic material, it is attracted to the permanent magnet 4 and maintains that state unless an external force is applied. Therefore, optical axis alignment, 45
There is no need to temporarily fix the component parts during the adjustment process, and moreover, once the holder 3 is adjusted, it can be permanently fixed by resin adhesion or metal welding while maintaining the adsorbed state of the holder 3.

At this time, so that there is no optical axis displacement during the 45° rotation adjustment,
As shown in FIG. 2, a stepped portion is formed on the end surface of the magnetic material holder 3 on the Faraday rotor side so that the central axis of the permanent magnet 4 coincides with the central axis of the holder 3, and the protruding portion is placed inside the permanent magnet. Preferably, it is configured to fit into the circumferential portion.

If the step is large, a portion of the magnetic holder will enter the permanent magnet too much and disturb the magnetic flux distribution, so the design standard is to maintain the magnetic saturation state of the Faraday rotor over the entire surface. Furthermore, if the outer diameter of a part of the holder is larger than the outer diameter of the permanent magnet, a magnetic circuit is formed at the outer circumference, and the amount of magnetic flux returning from the center path decreases, reducing the amount of magnetic flux necessary to magnetically saturate the Faraday element. It will not be possible to secure it. Therefore, the volume of the permanent magnet must be designed to be large to compensate for the external leakage valve. When considering these phenomena, the outside diameter of the holder should be designed to be the same as or smaller than the outside diameter of the permanent magnet (Fig. 3). In such a holder, the leakage of magnetic flux from the outer circumference is reduced, By concentrating the return magnetic flux into the inner peripheral space, it becomes possible to reduce the volume of the permanent magnet accordingly, and the optical isolator as a whole can be significantly downsized.

[Example] Table 1 shows each part used in this example.

Assemble the parts 1 to 5 above into the structure shown in Figure 4, and
A notch is provided on the sloped surface of the holder 3 on the entrance/exit surface side so that the rotation can be adjusted for adjustment.

Light was incident from the direction of the arrow, and the holder 3 was rotated and adjusted so that the insertion loss was at the minimum position. At this time, isolation characteristics of an extinction ratio of -36 dB and an insertion loss of 0.9 dB at a wavelength of 1.3 μ were obtained.

[Effects of the Invention] Since the polarizing element holder is attracted to the permanent magnet according to the present invention, the angle adjustment can be made by simply transmitting the light beam and rotating the holder to match the maximum light transmission intensity, making assembly and adjustment extremely easy. Since the total volume of the optical isolator can be designed to a minimum and the optical axis angle can be easily adjusted, a great mass production effect can be expected, and it has become possible to supply the market with low-cost optical isolators.

[Brief explanation of the drawing]

1, 2, 3, and 4 are cross-sectional views of embodiments of the present invention. 1: Polarizer 2: Analyzer 3: Holder 4: Permanent magnet 5: Faraday rotator Patent applicant Namiki Precision Jewelry Co., Ltd. [Figure 1 Figure 3 Light Figure 2 Figure 4v! J

Claims (3)

[Claims] (1) In an optical isolator consisting of a polarizer, a Faraday rotator, an analyzer, and a permanent magnet for magnetically saturating the Faraday rotator, the polarizer and analyzer are installed inside,
An optical isolator characterized by a pair of fixed holders made of a magnetic material. (2) The optical isolator according to claim (1), wherein a stepped portion is formed on the Faraday rotor side end surface of the magnetic material holder, and the protruding portion thereof is fitted into the inner peripheral portion of the permanent magnet. (3) The optical isolator according to claim 1 or 2, wherein the outer diameter of the magnetic holder is the same as or smaller than the outer diameter of the permanent magnet.