JPH0815644A - Inline type optical isolator - Google Patents

Abstract

PURPOSE:To realize an optical isolator for a spherically pointed coupling semiconductor laser of a small size and high performance. CONSTITUTION:Both ends of an optical isolator element constituted of an integrated structure formed by tightly holding a Faraday rotor 1 by polarizing elements 2, 3 are tightly connected and fixed by core expanded fibers 4, 5 and the front end of the core expanded fiber 5 on which the light of the semiconductor laser LD is made incident is formed as a spherically pointed fiber, by which this inline type optical isolator is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser used in an optical communication network or an optical interconnection, and an in-line type optical isolator used for removing a return light of a semiconductor laser array.

[0002]

2. Description of the Related Art Conventionally, a semiconductor laser is coupled with a fiber through a lens. In addition, as a measure against the return light, an optical isolator was installed between the fiber and the semiconductor laser and removed. However, when using a semiconductor laser that performs the spherical coupling, there is no space to install such an optical isolator, and it is virtually impossible to install the optical isolator.

[0003]

Therefore, in the case of performing such coupling, it is difficult to take a measure for returning light to the semiconductor laser, and the only method is to install an in-line type optical isolator between the optical fibers. The above problems are listed as follows: (1) Since the focal length is as small as several tens of μm, there is no place to install an optical isolator, and it is not possible to remove the returning light before the semiconductor laser.

(2) Further, when the in-line type optical isolator is installed between the fibers, the in-line type optical isolator is very expensive and it is impossible to remove the return light generated between the light sources.

[0005]

In order to solve the above-mentioned problems, the present invention installs an optical isolator in the vicinity of the front ball coupling portion, which allows the return light to be removed before the semiconductor laser by an inexpensive means. This is an enabled in-line optical isolator.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of an in-line type optical isolator according to the present invention, in which both ends of an optical isolator element are fixedly connected by core expanding fibers, and an incident side fiber is made into a front spherical fiber. There is.

The optical isolator element is one in which the Faraday rotator 1 is sandwiched between the polarizers 2 and 3, and they are tightly fixed and integrated. The integration is realized by a method such as adhesion or low melting point glass fixing. It

The core expanding fiber is made up of 150 optical fibers.
It is obtained by heating around 0 ° C. and diffusing a dopant such as Ge inside the core, and the mode field diameter can be expanded to about 2 to 4 times. The end face core expanding fiber 4 is an expanded core only at the tip. The end surface of the core-expanding front-end spherical fiber 5 on which the light of the semiconductor laser LD is incident is formed into a front-end sphere, and in this case, the core is expanded over the entire region.

For example, when an optical isolator element having a mode field diameter expanded four times and a thickness of 0.75 mm is connected, an in-line type optical isolator having an insertion loss of about 1 dB can be realized. Although the optical isolator element is configured as a polarization-dependent type here, it is also possible to configure it as a polarization-independent type that is closely integrated with a Faraday rotator using a birefringent element (or structural birefringent element). It doesn't matter. Even if it is configured as a polarization-dependent optical isolator, the propagation distance in the core-expanding front-end fiber 5 having the front-end coupling portion is very small, and since it has a fixed structure, the polarization direction of the incident guided light hardly changes there. .

FIG. 2 shows an in-line type optical isolator according to the present invention which is three-dimensionally constructed in an array form and is very effective when the array core wire 6 or the like is used. In this case, the optical isolator element is formed in a flat plate shape, and the fiber spacing is maintained by the fiber array support 7. Although the structure is three-dimensional here, a simpler two-dimensional array structure is naturally possible and is included in the present invention.

[0011]

As described above, the present invention has the following excellent advantages.

(1) Even in the case of coupling with a spherical fiber, it is possible to completely eliminate the return light from the semiconductor laser almost immediately.

(2) In addition, it is possible to form a compact lensless lens,
It can also be applied to array fibers.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment of an in-line type optical isolator according to the present invention.

FIG. 2 shows an in-line type optical isolator according to the present invention applied to an array fiber,
(A) is a longitudinal sectional view and (b) is an AA sectional view.

[Explanation of Codes] 1: Faraday rotator 2, 3: Polarizer 4: End face core expansion fiber 5: Core expansion tip spherical fiber 7: Fiber array support M: Cylindrical magnet LD: Semiconductor laser

Claims (3)

[Claims] 1. An in-line type optical isolator which is arranged between optical fibers to allow light in one direction to pass therethrough and to block light in the opposite direction, in which a plurality of optical elements constituting the optical isolator are integrated. The core expanding end faces of the end face core expanding fibers are closely fixed to both ends of the element, and the light incident end face of the end face core expanding fiber on the signal light incident side of the end face core expanding fibers is a sphere. In-line type optical isolator. 2. The in-line optical isolator according to claim 1, wherein the core of the end face core expanding fiber on the signal light incident side is expanded in the entire region. 3. An in-line type optical isolator, characterized in that the end face core expanding fibers are arranged in a two-dimensional or three-dimensional array and fixed in close contact with both ends of the optical isolator element.