JPH07159660A - Light emitting module for optical communication - Google Patents

Abstract

PURPOSE:To provide a light emitting module capable of dealing with noise by return light with inexpensive and simple constitution by providing one surface of a lens or half surface of both surfaces with light shielding parts. CONSTITUTION:A reflection film 21 which is the light shielding part fo shield about upper half of the laser beam from a semiconductor laser 1 is formed by vapor deposition, etc., on the surface of the aspherical lens 20 between the semiconductor laser 1 and an optical fiber 3. The laser beam emitted from the semiconductor laser 1 is condensed by the aspherical lens 20 and is made incident on the optical fiber 3. The upper half of the laser beam by the reflection film 21 is reflected and is not made incident on the optical fiber 3 so that the laser of about lower half part arrives at the optical fiber 3. Consequently, the incidence is eventually the same as the incidence on the optical fiber end face 3a from diagonally on the lower side. The reflected light 22 reflected by the optical fiber end face 3a returns to the upper half part of the aspherical lens face 20 but is shielded by the reflection film 21 formed thereon and is no longer returned to the semiconductor laser 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupling device for optical communication using an optical fiber, and more particularly to a light emitting module for optically coupling a semiconductor laser and an optical fiber.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional example. In a conventional light emitting module composed of a semiconductor laser 1, a lens 2 and an optical fiber 3, when the laser light from the semiconductor laser 1 enters the optical fiber 3, it is refracted. Due to the difference in the ratio, a few% of the incident laser light is reflected by the end face 3a of the optical fiber 3.
The reflected light 4 directly passes through the lens 2 and the semiconductor laser 1
Return to. As a result, the oscillation state of the semiconductor laser 1 becomes extremely unstable, causing changes in both static and dynamic characteristics such as increased noise and changes in current-optical output characteristics. In optical fiber communication, this characteristic change is a fatal obstacle mainly due to deterioration of direct modulation characteristic.

As a countermeasure against this, there is a method of using an optical isolator as shown in FIG. This is a configuration in which the laser light from the semiconductor laser 1 is once made into parallel light using the collimator lens 7, is again condensed by the collimator lens 8 through the optical isolator 9, and is incident on the optical fiber 3. In this way, the reflected light 10 from the end face 3a of the optical fiber 3 passes through the collimator lens 8 and is incident on the optical isolator 9. The optical isolator 9 allows the light from one direction to pass but the light from the opposite direction. It has a property of not allowing light to pass therethrough, acts to prevent the return light 11 from reaching the semiconductor laser 1, and prevents the return light due to reflection.

Further, as shown in FIG. 5, there is a method of using an oblique cut fiber 12 in which the end face of the optical fiber is obliquely cut. The end face 12a of this oblique cut fiber 12
The laser light is obliquely incident on the optical fiber 1 and the coupling efficiency is not impaired, and the reflected light 13 from the end face 12a of the oblique cut fiber is prevented from returning to the semiconductor laser 1.

[0005]

However, the optical isolator is expensive, and the use of the oblique cut fiber complicates the optical axis alignment with the laser beam and the lens, and the mechanism becomes complicated.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a light emitting module which is inexpensive and has a simple structure and which can prevent noise due to returning light.

[0007]

The present invention is characterized in that a light-shielding portion is provided on one or both half surfaces of a lens.

[0008]

In the present invention, since the light shielding portion is provided on the half surface of the lens, about half of the laser light from the semiconductor laser is obliquely incident on the optical fiber, and the reflected light from the end surface of the optical fiber is reflected by the lens. The light will be reflected by the light-shielding portion and will not return to the semiconductor laser.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a light emitting module for optical communication.
FIG. 2 is a diagram showing an aspherical lens having a reflective film formed thereon. As shown in the figure, on the surface of the aspherical lens 20 between the semiconductor laser 1 and the optical fiber 3, a reflection film 21 of a light shielding portion that blocks approximately the upper half of the laser light from the semiconductor laser 1 is formed by vapor deposition or the like. . By doing so, the laser light emitted from the semiconductor laser 1 is condensed by the aspherical lens 20 and is incident on the optical fiber 3.
The upper half of the laser light is reflected by 1 and is not incident on the optical fiber 3, and about the lower half of the laser light reaches the optical fiber 3. As a result, the light is incident on the optical fiber end face 3a obliquely downward, and the reflected light 22 reflected by the optical fiber end face 3a returns to the upper half side of the aspherical lens 20. , And is not blocked by the formed reflection film 21 and returns to the semiconductor laser 1.

A reflective film 2 formed on the aspherical lens 20.
2 is formed in the upper half (about 50%) as shown in FIG. 2, but the range of the reflection film 21 depends on the balance between the incident power to the optical fiber 3 and the output stability of the semiconductor laser 1. If power is needed and output stability can be sacrificed a little, it will be reduced to about 40%, and conversely, if transmission quality is a problem, it will be increased to about 60% to make it as noise-free as possible. As described above, it is effective to set the range of the reflective film 21 depending on the situation.

Although the light-shielding reflection film 21 is formed on one surface of the aspherical lens 20 on the optical fiber 3 side, it may be on the opposite surface, that is, the surface on the semiconductor laser 1 side.
It may also be formed on both sides.

It should be noted that not only the reflection film 21 formed on the aspherical lens 20 as the light shielding portion for the laser light of the semiconductor laser 1 but also
The same effect can be obtained by affixing a sheet-shaped light shielding member on the surface of the aspherical lens 20 or by inserting the light shielding member between the semiconductor laser 1 or the optical fiber 3 and the aspherical lens 20.

[0013]

According to the present invention described above, the light shielding portion is formed on the upper half surface of the lens without shifting the optical axes of the semiconductor laser, the lens system and the optical fiber, and without using special parts. It is possible to prevent the reflected return light from the incident end face of the optical fiber from returning to the semiconductor laser simply by blocking the light.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a light emitting module showing an embodiment of the present invention.

FIG. 2 is a view showing a reflection film formed on the lens of FIG.

FIG. 3 is a schematic configuration diagram of a conventional light emitting module.

FIG. 4 is a schematic configuration diagram of a conventional light emitting module using an optical isolator.

FIG. 5 is a schematic configuration diagram of a conventional light emitting module using a diagonal cut fiber.

[Explanation of symbols]

 1 Semiconductor Laser 3 Optical Fiber 3a Optical Fiber End Face 20 Aspherical Lens 21 Reflective Film 22 Reflected Light

Claims (1)

[Claims] 1. A light-emitting module for optical communication, comprising a semiconductor laser and a lens for condensing light emitted from the semiconductor laser on an optical fiber, wherein one or both half surfaces of the lens are provided with the semiconductor laser. A light-emitting module comprising a light-shielding portion that blocks laser light.