JPS597312A - Optical isolator - Google Patents

Abstract

PURPOSE:To provide an inexpensive and small sized optical isolator having easy constitution by providing a reflection film having a fine hole of the diameter smaller than the core diameter of an optical transmission body to which light is made incident to the one end of said optical transmission body. CONSTITUTION:The forward end of an optical fiber 100 is polished roughly perpendicularly to the optical axis of the optical fiber and a reflection preventing film 300 is attached to the end face thereof; further a reflection film 200 of Al having a fine hole 201 of about 8mu diameter is vapor deposited thereon. The fiber 100 is a focusing type fiber of 80mu core diameter as a core part 101 is shown by a broken line in the figure. Now, the light emitted from a semiconductor laser is restricted to about 2mu spot size by a lens, and is propagated in the core part 101 of the fiber 100 through the fine hole 201 provided to the film 200, whereby the coupling is accomplished with high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical isolator used to prevent reflected light from an optical fiber from returning to a semiconductor laser, particularly an optical isolator for a multimode optical fiber.

In an optical fiber transmission system that uses a semiconductor laser as a light source and an optical fiber as a transmission path, a portion of the output light of the semiconductor laser is reflected by the light input/output end face of the optical fiber and returns to the active layer of the semiconductor laser. However, there is a problem that noise and waveform distortion occur in the output light. In particular, when the coupling efficiency between the semiconductor laser and the optical fiber is high, the reflected light tends to return to the semiconductor laser, which tends to cause W sound and waveform distortion. Therefore, optical isolators inserted between a semiconductor laser and an optical fiber have been developed for the purpose of preventing reflected light from returning to the semiconductor laser.

Conventionally, this type of optical isolator uses the Faraday rotation effect of the plane of polarization of light in a crystal such as YIG (for example, Seki et al., Proceedings of the National Conference of the Institute of Electronics and Communication Engineers, 1981, Lecture No. 83- 3) etc. are often used.

However, this optical isolator uses expensive parts such as YTG and other expensive Faraday rotation crystals, polarizers, and analyzers, requires a large number of assembly steps due to the large number of parts, and is difficult to assemble. It has the disadvantage of being expensive because it requires a lot of man-hours. Furthermore, 0
In the 8 μm wavelength range, use a Faraday rotation element.

Since the Y I G crystal cannot be used because of its large loss, lead glass, etc., whose Verdet constant is smaller than the Y I G crystal, is used. Therefore, a large magnet is used to increase the length of the Faraday rotation element or to strengthen the magnetic field. This also has the disadvantage that it is difficult to realize a compact optical isolator.

The purpose of this invention is to eliminate the above-mentioned drawbacks, and to create an inexpensive and compact
Particularly, it is desired to provide an optical isolator suitable for an optical fiber transmission system using a semiconductor laser and a multimode optical fiber.

The optical isolator of the present invention has a pore having a diameter smaller than the core diameter of the optical transmission body at at least one tip of the optical transmission body into which light enters or the optical member provided at the tip of the optical transmission body. It has a configuration with a reflective film.

The present invention will be explained in detail below using the drawings.

FIG. 1 is a schematic diagram showing a first embodiment of the invention.

The tip of the optical fiber 00 is polished perpendicular to the optical axis of the optical fiber, and an anti-reflection coating 300 is attached to the end face, and an aluminum film 300 having a pore 201 with a diameter of about 8 μm is attached to the end face. A reflective film 200 is provided by vapor deposition. The fine holes 201 were formed by conventional photo+)/graphic techniques. The optical fiber oo is a focusing fiber with a core diameter of 80 μm (the core portion 101 is indicated by a broken line in the figure). In the above configuration, the light emitted from the semiconductor laser is narrowed down to a spot size of approximately 2 μm by a lens (not shown in the figure), and is
01 and propagates through the core portion 101 of the optical fiber 100. The losses when the focused light beam passes through the pores are almost negligible, resulting in highly efficient coupling.

Further, since the antireflection film 300 is provided on the end face of the optical fiber 100, there is almost no return of reflected light from this end face to the semiconductor laser.

Next, the backscattered light of the light propagating through the optical fiber 100,
The reflected light at the output end of the optical fiber 1oo is reflected by the core portion 101.
Since it spreads over the whole area and propagates, most of it is covered by the reflective film 200 (however, only a small amount of light that passes through the pores 201 returns to the semiconductor laser), so the reflected light is transmitted to the semiconductor laser. It has almost no effect and almost never generates noise or waveform distortion. With this optical isolator, insertion loss of 0.1 dll and optical isolation of 20 dll were obtained. Note that the larger the ratio between the diameter of the pore 201 and the core diameter of the optical fiber, the greater the isolation can be achieved.
The coupling efficiency to 0 is reduced, and some of the light that has hit the reflective film 200 is returned to the semiconductor laser, resulting in a reduction in isolation. Therefore, there is an optimum value for the pore diameter. In this example, the diameter of the pores is approximately 8 μm.

FIG. 2 is a schematic diagram showing a second embodiment of the invention. The difference from the first embodiment shown in FIG. 1 is that the optical fiber 100 and the antireflection coating 30 shown in FIG.
0, a transparent optical member 400 is inserted between the two.

The optical member 400 is a quartz plate with a thickness of 200 μm and both end faces polished, with an antireflection film 300′ on one side and a thin +tz
A reflective film 200' having oi' is provided.

The side of the optical member 400 facing the optical fiber 100 is fixed to the end surface of the optical fiber 100 with an optically transparent adhesive.

By adopting such a structure, the antireflection film 300
', and the reflective film 200' having the pores 2o1' is characterized in that it is easier to manufacture.

Although quartz crystal is used as the optical member 400, other optical glass plates or the like may be used, or an optical fiber having the same or smaller core diameter than the optical fiber 100 may be used.

The optical member 400 and the optical fiber 100 may be fixed together by fusion.

FIG. 3 is a schematic diagram showing a third practical IXa example according to the present invention. The difference from the first embodiment shown in FIG. 11 is that the end face of the optical fiber IOO is provided obliquely to the optical axis and that the antireflection film 300 is not provided. The end face of the optical fiber 100 is polished along the optical axis (with an angle λ of approximately 8°), and directly connects the pore 201".
A reflective film 200'' is provided.

Since the end of the optical fiber 100 has a slanted surface in this way, the reflected light hardly returns to the i+ body, resulting in high isolation.

Therefore, the antireflection film 3 shown in the first embodiment also
Since there is no need to provide 00, the number of man-hours can be reduced, and a cheaper original isolator can be obtained.

Incidentally, the optical advantage inserted between the optical fiber and the reflective film having pores as shown in the second embodiment is the same as the light inserted between the optical fiber and the reflective film having pores! The gear part 11 may be provided with a reflective film that covers the pores, and may have an inclined surface.

1st. As shown in us 2 and the third example, τ
In the first method, r may be a different value.

The positions of the pores 201, 201', and 202'' may be offset from the optical axis as long as they are located in relation to the core' portion of the optical fiber.

The name of this place is also that the light emitted from the semiconductor laser is efficiently
There is almost no reflected light that couples into the fiber and returns to the semiconductor laser, resulting in high isolation. 1) The reflective films 200, 209' and 200'' may be made of a metal vapor deposited film other than aluminum shims, a metal plate with pores, a dielectric multimetallic film, or the like.

＼ Hata et al. reported that even if the optical fiber end is misaligned, the emitted light from the semiconductor laser will be reflected by the reflective film 200°200',
Even if it hits the 200" part, the reflective film 200.20
By providing an antireflection film on the 0" and 200", it is possible to prevent the emitted light from returning to the semiconductor laser.

Although the optical isolator according to the present invention has been explained in detail using examples, the isolator according to the present invention is a simple one that only has a reflective film with pores at the tip of the optical transmitter. , Extremely cheap and small 9 isolake is great! ) is prepared for the Lord Chamberlain, who will be! It is well suited for optical fiber transmission systems using semiconductor lasers and multimode I optical fibers.

[Brief explanation of drawings]

Figures 1, 2, and 3 MV [first and second according to the present invention]
and a schematic diagram showing a third example. In the figure, there are 100 optical fibers, 101 is the core part, 2
00.200', 200" is a reflective film, 201.201
'. 201" is a pore, 300 is an antireflection film. 69

Claims (3)

[Claims] (1) A reflective film having a pore having a diameter smaller than the core diameter of the optical transmitter is provided on at least one tip of the optical member on which light enters or the optical member provided at the tip of the optical transmitter. An optical isolator characterized by: (2) Claim 1, characterized in that at least one tip of the optical transmission body or an optical member provided at the tip of the optical transmission body is formed to be oblique with respect to the optical axis of the optical transmission body.
Optical isolator as described in section. (3) The optical isolator according to claim 1, characterized in that the thin (L) of the reflective film is shifted from the optical axis of the optical transmission body.