JPH0331812A - Laser module with optical isolator - Google Patents

Abstract

PURPOSE:To considerably reduce the feedback of reflected light to a laser by slanting the normal of the incidence end surface of the optical isolator in a plane containing a main axis within a range of 1 - 10 deg. from the optical axis. CONSTITUTION:In the plane (X-Z plane) which is perpendicular to a plane containing the electric vector of the projection light 6a of the semiconductor laser 1 and the optical axis and contains the optical axis, the normal of the incidence end surface of the optical isolator is slanted within a range of 1 - 10 deg. from the optical axis. When the inclination is <=1 deg., the reflected light is fed back to the semiconductor laser. When the inclination exceeds 10 deg., on the other hand, the opposite-directional loss and insertion loss of the optical isolator 8 are considerably deteriorated. It is not evident why the good effect is obtained when the normal is slanted, but this may relate to the backward incidence of no reflected light from the optical isolator 8 on an active layer 2.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a module equipped with an optical isolator that is used in high-speed long-distance optical communication systems, etc. The present invention relates to a laser module with an optical isolator that defines the direction.

[Conventional technology]

In recent years, due to the amazing progress of optical fibers, research and development and practical application of optical fiber-based communication devices to increase the speed of communication devices are being seriously considered. Semiconductor lasers with narrow spectral line widths are often used as light emitting sources in these devices. In particular, in high-performance semiconductor lasers used in optical communication systems, etc., the blue frequency sound characteristics are sensitively affected by the feedback from the optical fiber, etc., and the laser module with an optical isolator deteriorates. has become essential.

FIG. 5 is a diagram showing the basic configuration of a laser module with an optical isolator. In FIG. 5, 1 is a semiconductor laser, 2 is an active layer (evitor 1t shear layer) provided inside the semiconductor laser, and 3 is a semiconductor laser. Polarized light r, 4 is a Faraday rotator, 5 is an analyzer, 6a is light emitted from a semiconductor laser, 6b
8 is the output light from the optical isolator whose polarization plane has been rotated by 45 degrees, and 8 is the entire optical isolator.

The electric vector of the emitted light 6a from the active layer 2 is parallel to the epitaxial layer of the active layer. Here, the electric vector refers to the -\ vector of the electric field (electric force wave) of light. This light passes through a polarizer 3, the plane of polarization is rotated by 45 degrees by a Faraday rotator 4, and passes through an analyzer 5, which is attached with the plane rotated by exactly 45 degrees. The emitted light 6b from the optical isolator is coupled to the optical fiber by another lens or the like.

The problem here is that the reflected light 7a from the optical fiber, lens, etc. is removed by the optical isolator 8, but the reflected light 7b from the incident surface of the optical isolator, that is, the end face of the polarizer 3, is not removed and remains as it is in the semiconductor laser 1. It is to return to the active layer.

In order to avoid this, conventional optical isolators, as shown in FIG.
-Z plane) by θ'. x shown here,
The y and z coordinates match those shown in FIG. This method has the advantage that a slight inclination prevents the reflected light 7b from reaching the active layer of the semiconductor laser, thereby preventing deterioration of the semiconductor laser and allowing stable emitted light to be extracted.

Furthermore, Japanese Patent Laid-Open No. 54-29661 discloses an optical isolator having a polarizer plate, a Faraday rotation plate, and a quarter-wave plate, in which the normal line of the surface of each plate is inclined with respect to the direction of incident light. , it is disclosed that a device with a large extinction ratio and a small size can be obtained.

Alternatively, JP-A-59-204293 discloses a device in which the optical axis of a semiconductor laser diode is tilted with respect to the optical axis of an optical isolator to eliminate the influence of reflection at the incident angle.

[Problems to be solved by the present invention]

The conventional laser module with an optical isolator described above certainly has the advantage of reducing the return of reflected light from the incident end facet of the optical isolator to the semiconductor laser, but the optical axis of the incident light and the incidence of the optical isolator There is a drawback that the inclination with respect to the normal vector of the end face significantly deteriorates the reverse direction loss and insertion loss, which are the characteristics of an optical isolator.

That is, in such a configuration, although the influence of the reflected light 7b can be reduced, there is a problem in that the inherently good characteristics of the optical isolator cannot be utilized.

Furthermore, the optical isolator described in the above-mentioned Japanese Patent Application Laid-Open No. 54-29661 requires a 174-wavelength plate, and since the direction in which it is tilted is not specified, there is a problem that the characteristics vary widely. there were. This was also the case with the one described in the above-mentioned Japanese Patent Application Laid-Open No. 59-204293. That is, until now, no one had recognized that the tendency and angle of the optical isolator were important.

An object of the present invention is to provide a high-performance laser module that reduces reflected light returning from an optical isolator to a semiconductor laser and does not deteriorate the characteristics of the optical isolator.

[Means to solve the problem]

The present invention provides a laser module with an optical isolator in which light emitted from a semiconductor laser is transmitted through an isolator and then inputted into an optical fiber. A laser module with an optical isolator, characterized in that the normal line of the incident end face of the optical isolator is set within a plane (X-Z plane) including the optical axis within a range of 1 degree or more and 10 degrees or less from the optical axis. be.

The present invention is more effective than conventional methods by tilting the normal line of the incident end face of the optical isolator within the plane containing the electric vector of the emitted light of the semiconductor laser and the optical axis within the range of 1 degree or more and 10 degrees or less from the optical axis. This is based on the discovery that a laser module with less deterioration in the characteristics of the optical isolator can be obtained. The reason why the inclination is defined as 1 degree or more and 10 degrees or less is because if it is less than 1 degree, the reflected light will return to the semiconductor laser, which is undesirable.If it exceeds 10 degrees, the reverse direction loss and insertion loss of the optical isolator will increase. In the present invention, the distance between the semiconductor laser 1 and the optical isolator 8 is generally on the order of divergence, and although it is not yet clear why the effects of the present invention can be obtained, the optical isolator This seems to be related to the fact that the reflected light from the active layer does not enter the active layer.

Example C] Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.

FIG. 1 is a configuration diagram illustrating an embodiment of the present invention.

The X, Y, and Z coordinates shown here are completely different from those shown in FIG. FIG. 1 shows a laser module with an optical isolator in which light 6a emitted from a semiconductor laser 1 is transmitted through an optical isolator 8 and then input into an optical fiber. In this laser module, the optical beam is isolated in a plane perpendicular to the plane containing the electric vector of the emitted light 6a of the semiconductor laser 1 and the optical axis. It has become. Optical isolator 8 used here
is a polarizer 3 consisting of a polarizing beam splitter, a Faraday rotation P4, and an analyzer 5 consisting of a polarizing beam splitter 7.
It consists of

FIG. 2 is shown as a comparative example, and the difference from the above embodiment is that the normal n' of the incident end face of the optical isolator is set to θ in a plane containing the electric vector of the output light 6a of the semiconductor laser.
′ is tilted.

Figure 4 shows the incident angle θ of the backward direction Il loss and insertion 14 loss in the comparative example.
′ shows the relationship between As shown here, it has been found that when the incident angle becomes 1 degree or more, the reverse direction loss and insertion loss, which are the characteristics of the optical isolator, deteriorate rapidly.

In this case, when tilted from the optical axis by 4 degrees, the reverse direction loss is 8 dB.
The insertion loss also decreased by 0.15 dB.

FIG. 3 shows measurements of changes in reverse direction loss and insertion loss with respect to the incident angle θ of the present invention. As can be seen from a comparison with the comparative example shown in FIG. 4, the laser module of the present invention has an extremely large reverse direction loss with respect to the incident angle. Also, unlike the comparative example, this backward jii loss occurs when the incident angle θ is 1.
There is almost no change below 0 degrees. In this way, the angle of incidence θ
It has been found that it is possible to greatly reduce the feedback of the reflected light from the semiconductor laser because it is possible to increase the . However, even in this case, there was a tendency that the insertion loss increased when the incident angle θ was 10 degrees or more. Also,
It has been found that unless the number of injections per meter of the incident end of the optical isolator is one or more times, the reflected light will return to the semiconductor laser, which is not preferable.

In the embodiment, the entire optical isolator is tilted, but the polarizer alone may be tilted.

(Effects of the Invention) According to the present invention, it is possible to significantly reduce the return of reflected light from the incident end face of the optical isolator to the semiconductor laser while preventing the deterioration of the reverse direction loss and insertion t1 loss of the optical isolator. You can get the module.

[Brief explanation of drawings]

Fig. 1 shows an embodiment of the present invention, Fig. 2 shows a comparative example, Fig. 3 shows the characteristics of the optical isolator shown in Fig. 1, and Fig. 4 shows a comparative example. FIG. 2 is a diagram showing the characteristics of the optical isolator of the comparative example shown in FIG. 2, and FIG. 5 is a diagram showing the basic configuration of a laser module with an optical isolator. 2: Epitaxial layer, 3: Polarizer, 4: Faraday rotator, 5: Analyzer, 6a: Light emitted from the laser, 6b; Light emitted from the optical isolator, 7a
: Reflected light from optical fibers, lenses, etc., 7b: Reflected light from the incident end face of optical isolake, 8: Optical isolake. Applicant Hitachi Metals, Ltd. Figure 1 Figure 5 Figure 5 Angle of incidence θ Angle of incidence θ'

Claims (1)

[Claims] (1) In a laser module with an optical isolator in which light emitted from a semiconductor laser is transmitted through an optical isolator and then input into an optical fiber, a plane perpendicular to a plane containing the electric vector and optical axis of the emitted light from the semiconductor laser. A laser module with an optical isolator, characterized in that the normal line of the incident end face of the optical isolator is tilted within a plane including the optical axis within a range of 1 degree or more and 10 degrees or less from the optical axis.