JPH046010Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a light source switch with low insertion loss used in the field of optical communication.

(Prior art) Semiconductor lasers, which are light sources for optical communications, currently lack reliability compared to semiconductor devices, so improvements in their reliability are desired in the field of optical communications, which requires high reliability. ing. Currently, as a means to increase the reliability of light sources for optical communications, a redundant configuration is being considered in which two semiconductor lasers are used as a working laser and a backup laser. When such a redundant configuration is used, a changeover switch as shown in FIG. 8 has conventionally been used to switch from the active light source to the standby light source.

This switch is composed of a movable prism 5, and when guiding the optical signal from the light source 1 propagating through the fiber 3 to the main optical fiber 6, the movable prism 5 is moved upward to the dotted line position. Furthermore, when guiding the optical signal from the light source 2 propagating through the optical fiber 4 to the main optical fiber 6, the movable prism 5 is moved to the position shown by the solid line below. In this way, by the switch consisting of the movable prism 5,
The optical signal from light source 1 and the optical signal from light source 2 are switched.

(Problem that the invention aims to solve) Although this switch has the feature of low crosstalk, since the prism moves mechanically, the prism may be misaligned, resulting in problems with switching reproducibility and reliability. There was a problem.

The purpose of the present invention is to provide a low-insertion-loss light source switcher useful for optical communication systems, which has no problems with switching reproducibility and reliability, and can switch between two light sources without momentary interruption. There is a particular thing.

(Means and effects for solving the problem) The present invention is characterized by a first surface and a second surface on which polarized light orthogonal to each other is incident, and a third surface and a fourth surface opposite to the two surfaces. a polarizing beam splitter having a surface, a working light source disposed from a first surface of the polarizing beam splitter via a first polarization maintaining optical fiber, and a second surface of the polarizing beam splitter. a auxiliary light source disposed through a second polarization-maintaining optical fiber from the polarization beam splitter; a main optical fiber disposed directly from the third surface of the polarization beam splitter or via a quarter-wave plate; and a monitoring optical fiber arranged to take out the monitor light from the fourth surface of the beam splitter, so that a part of the light emitted from the active light source and the standby light source leaks into the monitoring optical fiber. The present invention is characterized in that the polarization axes of the first and second polarization maintaining optical fibers are rotated from the first and second polarization axes of the polarization beam splitter, respectively.

(Principle of the invention) The polarization state of light waves propagating through optical fibers currently made for optical communications changes due to temperature changes or bending of the optical fiber, but the output In recent years, polarization-maintaining optical fibers have been developed that are less susceptible to these effects and can always maintain the output polarization state as linearly polarized light under normal conditions. The present invention uses such a polarization-maintaining optical fiber, and will be explained in detail below with reference to the drawings.

FIG. 2 shows the principle of the present invention, and 7 has a first surface and a second surface into which mutually orthogonal polarized light is incident, and a third surface and a fourth surface opposite to the two surfaces. The polarizing beam splitters 8, 9 are polarization-maintaining optical fibers having the properties described above. Further, the symbols other than these indicate the same things as those in FIG. As is clear from the figure, the optical coupler according to this embodiment has a configuration in which polarization-maintaining optical fibers 8 and 9 are coupled to a polarization beam splitter 7.

Next, the operation of FIG. 2 will be explained with reference to FIGS. 3 and 4. An input polarized light wave 1 consisting of a P polarized light wave 11 and an S polarized light wave 12, which are linearly polarized waves orthogonal to each other.
0 is input to the polarizing beam splitter 7, as shown in FIG. Ru. On the other hand, if this polarizing beam splitter 7 is used as shown in FIG.
The polarized light wave 11 and the S-polarized light wave 12 can be combined with low loss.

According to the optical coupler shown in FIG. 2, the linearly polarized light waves propagating through the polarization preserving optical fibers 8 and 9 are sent to the polarizing beam splitter 7 in an almost completely linearly polarized state.
This allows light to be separated or combined with low loss. If a lens such as a self-occurring lens or a ball lens is inserted between the polarization maintaining optical fibers 8 and 9 and the polarizing beam splitter 7, the light waves can be guided to the main optical fiber 6 more efficiently.

FIG. 1 is a diagram showing the principle of the light source switching device of the present invention.

In the figure, 1 and 2 indicate a working light source and a standby light source that output linearly polarized waves arranged in the same direction, respectively, and the lights output from the working light source 1 and standby light source 2 are connected to polarization-maintaining optical fibers, respectively. 8 and 9 with almost no loss. The other ends of the polarization-maintaining optical fibers 8 and 9 are rotated and coupled to two light incident surfaces of the polarization beam splitter 7 having mutually orthogonal polarization axes so that the polarization axes coincide with each other. There is. One end of a normal main optical fiber 6 is coupled to the light exit surface of the beam splitter.

The light wave guided by the polarization preserving optical fiber 8 is, for example, P polarized light, and the light wave guided by the polarization preserving optical fiber 9 is polarized, for example, S polarized light. Under normal conditions, only the current light source 1 is working. Therefore, only the light waves emitted from the light source 1 are guided to the main optical fiber 6. When switching from active to standby, light source 2 is turned on, and then light source 1 is turned off. As a result, only the light waves emitted from the light source 2 are guided to the main optical fiber 6, and the switching is completed.

According to the principle of the present invention, switching between light source 1 and light source 2 can be performed simply by controlling on/off of light source 1 and light source 2, so that the light waves from light source 1 and light source 2 can be switched with low loss and without momentary interruption. It can be led to the main optical fiber 6. Note that as another method, the light source 1 and the light source 2 may be always turned on.

(Example) A first example of the present invention is shown in FIG. In this embodiment, the polarization axes of the polarization maintaining optical fibers 8 and 9 are slightly tilted from the P polarization axis and the S polarization axis of the polarization beam splitter, so that a part of the light waves emitted from the light sources 1 and 2 is transferred to the optical fiber 12. It was designed so that it would leak into the room. According to this embodiment, the optical fiber 1
Since the optical signal leaked into the main line system can be used for monitoring the light source 1 and the light source 2, the monitor system and the main line system can be integrated without causing a large loss to the main line system.

Still another embodiment of the present invention is shown in FIG. In this embodiment, a 1/4 wavelength plate 13 is inserted between the polarizing beam splitter 7 and the main optical fiber 6 to reduce the influence of reflected light from the main optical fiber 6 on the light sources 1 and 2. .

This principle will be explained using the equivalent diagram shown in FIG. The P-polarized light wave 10 emitted from the light source 1 is transmitted through the polarization beam splitter 7, and its axis is aligned with respect to the P-polarization axis.
It passes through a 1/4 wavelength plate 13 tilted at 45°. This results in a circularly polarized light wave 14. When this circularly polarized light wave 14 is reflected back by the prism 15 and passes through the quarter-wave plate 13 again, it becomes an S-polarized light wave 11. The S-polarized light wave 11 is reflected by the polarized beam splitter 7,
By not facing the direction of the light source 1, the influence of reflected light on the light source 1 can be avoided.

According to the above-mentioned principle, when only the light source 1 is on in FIG. 6, the reflected light from the main optical fiber 6 of the light emitted from the light source 1 propagates toward the light source 2, and the influence on the light source 1 can be avoided. . Further, since the light source 2 is in an off state, this reflected light has no influence on the light source 2.
Conversely, if light source 2 is on and light source 1 is off,
Since the reflected light from the main optical fiber 6 of the light emitted from the light source 2 is directed toward the light source 1, an adverse effect on the light source 2 can be avoided.

(Effects of the invention) As described above, according to the invention, switching between the active light source and the standby light source is performed by turning the light source on and off, and no mechanical movement is involved, making it possible to switch the light source with high reliability. It can be done with Furthermore, it is possible to avoid instantaneous interruptions in the optical communication system due to switching. Furthermore, switching of light sources can be performed with low losses. Furthermore, by adjusting the polarization axes of the polarization maintaining optical fibers 8 and 9,
Monitor light can be extracted at a desired branching ratio.

[Brief explanation of drawings]

Figures 1 to 4 are schematic diagrams for explaining the principle of the present invention, Figure 5 is a schematic diagram of the first embodiment according to the present invention, and Figure 6 is a schematic diagram of the second embodiment according to the present invention. 7 is a schematic diagram of the operation of the second embodiment,
FIG. 8 is a schematic diagram of a conventional light source changeover switch. 6... Main optical fiber, 7... Polarizing beam splitter, 8, 9... Polarization preserving optical fiber.

Claims (1)

[Claims for Utility Model Registration] A polarizing beam splitter having a first surface and a second surface into which mutually orthogonal polarized light is incident, and a third surface and a fourth surface opposing the two surfaces. , a working light source disposed from a first surface of the polarizing beam splitter via a first polarization-maintaining optical fiber;
an auxiliary light source disposed via a polarization-maintaining optical fiber of the polarizing beam splitter; a main optical fiber disposed directly from the third surface of the polarizing beam splitter or via a quarter-wave plate; and the polarizing beam splitter. a monitoring optical fiber disposed to take out the monitoring light from the fourth surface of the first light source, and a monitoring optical fiber disposed to extract the monitoring light from the fourth surface of the first and a light source switching device, characterized in that the polarization axis of the second polarization-maintaining optical fiber is rotated from the first and second polarization axes of the polarization beam splitter, respectively.