JPS62115404A - Optical coupler - Google Patents

Abstract

PURPOSE:To improve the environmental resistance and reliability of an optical coupler by forming the end face on the near parabolic rod lens side of an optical fiber to a convex face and forming the end face on the optical fiber side of the near parabolic rod lens diagonally with the optical axis. CONSTITUTION:The 2nd end face 7b of the 2nd near parabolic rod lens 7 disposed apart at a prescribed distance from the 1st near parabolic rod lens 6 is polished diagonally with the optical axis and said lens 7 is disposed in contact with the end face 8a of an optical fiber 8. The end face 8a of the optical fiber 8 is formed to the convex face by electric discharge machining or polishing. The need for adhering and fixing an antireflection film plate to the top end of the optical fiber is thereby substantially eliminated and therefore, the generation of exfoliation and foam in the adhered part as in the conventional practice is surely averted and the environmental resistance and reliability are improved. The laboriousness of the operation required for diagonal polishing or adhering of the optical fiber is further eliminated and the working time is shortened.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is applicable to optical communication and optical information processing for coupling emitted light from a semiconductor laser used in optical communication and optical information processing to an optical fiber. This relates to an optical coupler for use.

[Conventional technology]

In conventionally known optical couplers, in order to prevent light from being reflected from the end face of the optical fiber, the end face of the optical fiber is polished diagonally with respect to the optical axis, or polished diagonally. A method such as fixing a glass plate coated with an antireflection film (hereinafter referred to as an antireflection film plate) with an adhesive to the end face of the optical fiber has been adopted.

[Problem that the invention seeks to solve]

By the way, the former method, in which the end face of the optical fiber is cut obliquely to the optical axis, has the advantage of reducing the amount of light that returns to the semiconductor laser due to reflection at this end face, but it also reduces the amount of light emitted from the semiconductor laser. It is not possible to efficiently introduce the fiber into the optical fiber, and when the inclination is, for example, 8 degrees, there is a drawback that a coupling loss of 10 dB or more occurs.

For this reason, a means using an anti-reflection film plate is usually adopted as in the latter case. However, this method not only requires the cumbersome work of diagonally grinding the optical fiber and gluing the anti-reflection coating to the surface of the grinder, but also causes drastic changes in the thermal environment because adhesive is used. Otherwise, differences in expansion coefficients of the materials may cause peeling or bubbles to form in the bonded area, resulting in problems in terms of environmental resistance and long-term stability.

Further, as a means for reducing the coupling loss, for example, applied optics (Appl 1eclOp
tics) 1980, Volume 19, Page 2578, which uses a tapered spherical fiber described in the paper by Mr. Kuwabara, Utility Application 51137440r spherical convergence optical transmitter'' and Utility Application (Reference number 4580526 VO dispatched) An example of this method is to use a converging rod lens with a spherical tip as described in ``Optical coupler using Wooden lens with convex curved surface''. It is already known that in these optical couplers, the coupling efficiency between the semiconductor laser and the optical fiber is considerably improved. for example,
When a single mode fiber is used as the optical fiber, 3.5 dB and 2.5 dB, respectively. ．． The output light beams from the semiconductor lasers are combined with a coupling loss of 7 dB.

The purpose of the present invention was made in view of the above-mentioned problems,
The basic characteristics of optical couplers such as return loss and coupling loss are not degraded compared to conventional ones, and the work is complicated by diagonal polishing of optical fibers and the use of adhesives, as well as environmental resistance and reliability. An object of the present invention is to provide an optical coupler that can solve the problem of a decrease in

[Means for solving problems]

In the optical coupler of the present invention, a focusing rod lens is arranged on the semiconductor laser side of an optical fiber so as to be in optical contact with it, and the end surface of the optical fiber on the focusing rod lens side is formed into a convex curved shape, and the focusing rod lens is arranged so as to be in optical contact with the semiconductor laser side of the optical fiber. The rod lens has a structure in which the end surface on the optical fiber side is formed obliquely with respect to the optical axis, thereby achieving the above-mentioned object.

〔Example〕

Hereinafter, the present invention will be explained in detail using embodiments shown in the drawings.

The figure is a schematic configuration diagram showing an embodiment of an optical coupler according to the present invention. Define the coordinate system as shown.

The Y-axis is oriented perpendicular to the plane of the paper. A semiconductor laser 2 having a junction surface 1 has an optical axis 51 of an output light beam 4 from a light emitting surface 3.
is fused and fixed on the heat sink 5 so that it is parallel to the Z-axis. In the first focusing rod lens 6 whose refractive index distribution is approximately given by the following equation, an end surface 6a disposed close to the light emitting surface 3 of the semiconductor laser 2 is polished into a convex curved shape.

n(r,) −n. 1 (f a
lrl') Here, nol is the refractive index on the central axis 52, a
l is the focusing parameter of the first focusing rod lens 6, and rl is the central axis 52 of the first focusing rod lens 6.
Each represents the distance from.

A second focusing rod lens 7 arranged a predetermined distance apart from the first focusing rod lens 6 has a first end surface 7 thereof.
The second end surface 7b facing the first focusing rod lens 6 side and opposite to the first end surface 7a is polished obliquely with respect to the optical axis. This second end face 7
b is placed in contact with the end surface 8a of the optical fiber 8.

In particular, the second converging rod lens 7 and the optical fiber 8 are both fixed together. In addition, optical fiber 8
The end surface 8a is formed into a convex curved surface by electric discharge machining, grinding machining, or the like.

Regarding the refractive index distribution of the second focusing rod lens 7,
is given by the following equation.

n (r2) = no2 (l −-32r22) now,
For two focusing rod lenses 6.7, al>a2
, not>no2. In other words, by increasing the numerical aperture of the first focusing rod lens 6, as much of the output light beam 4 from the semiconductor laser 2 as possible is captured into the first focusing rod lens 6, and the second focusing rod lens 7 The incident light is gently narrowed down to the size of the optical fiber 8. In this embodiment, as the first focusing rod lens 6,
no, = 1.63, al = 0.175-2 mm.

r, == o, 9 mm, lens pitch 0.23 pitch, and as the second focusing rod lens 7, no.
2=1.59, a2=0.107-2mm.

r2=Q, 9mm, lens pitch Q, 20pi, and those from Sochi were used. Further, the optical fiber 8 has an end face 8a at the tip.
A single mode fiber with a radius of curvature of the convex curved surface of 60 μm, a core diameter of 10 mm, and a cutoff wavelength of 1.1 μm is used.
The semiconductor laser 2 used had an oscillation wavelength of 1.3 μm. The coupling loss at this time was 2.7 dB, which was about the same low loss as the conventional one. Also, the return loss is 3
0 dB or more was obtained, which was equivalent to or higher than when an antireflection film plate was used.

In the above embodiment, the end surface 7b of the second focusing rod lens 7 and the end surface 8a of the optical fiber 8 are arranged in contact with each other. That's fine.

Optical contact here means that two surfaces face each other at a distance within 1/4 of the wavelength of light.

In addition, in the present invention, the same effect can be obtained even if a ball lens is used instead of the first focusing rod lens 6.

〔Effect of the invention〕

As explained above, according to the optical coupler according to the present invention,
The basic characteristics of the optical coupler, such as return loss and coupling loss, are equivalent to or better than conventional ones. In addition, since there is no need to adhesively fix an anti-reflection film plate to the tip of the optical fiber during mounting, it is possible to reliably avoid peeling of the adhesive part and generation of bubbles as in the past, improving environmental resistance and reliability. be able to. Furthermore, it is possible to eliminate the complexity of operations required for oblique polishing and bonding of optical fibers, and it is also possible to shorten the working time.

[Brief explanation of drawings]

The figure is a schematic configuration diagram showing an embodiment of an optical coupler according to the present invention. 2... Semiconductor laser, 7... Second focusing rod lens, 7b...
...Second end surface, 8...Optical fiber, 8a.
·····End face.

Claims (1)

[Claims] In an optical coupler that couples a light beam emitted from a semiconductor laser to an optical fiber, a focusing rod lens is arranged on the semiconductor laser side of the optical fiber so as to be in optical contact with the optical fiber, and a focusing rod lens is arranged on the focusing rod lens side of the optical fiber. An optical coupler characterized in that an end face is formed into a convex curved shape, and the end face on the optical fiber side of the focusing rod lens is formed obliquely with respect to the optical axis.