JPH09269428A - Reflective return light compensation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compensation circuit capable of eliminating reflective return light from an optical fiber to a semiconductor laser without using an optical isolator. SOLUTION: This circuit is constituted so that outgoing beam from the semiconductor laser is divided by a Y branch coupler 3, and one side branch A is connected to a communicating optical fiber of an optical fiber communication system 5, and the other side branch B is connected to a light reflection circuit 4. In the regular optical fiber communication system 5, the reflective return light 6 from an optical connector, etc., occurs. By making incident compensation light 7 of the same intensity as/a phase opposite to the reflective return light 6 returned to the branch A on the branch B of the Y branch coupler 3, since the total light power of the reflective return light 6 is radiated to the outside of the Y branch coupler 3 as the result of multiplex-/interference, the reflective return light isn't made incident on the semiconductor laser 1 as a result. That is, the reflective return light 6 from the optical fiber is canceled, and is prevented from again making incident it on 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 a reflected return light compensation circuit, and more particularly to a reflected return light compensation circuit for eliminating the adverse effect of reflected return light from an optical fiber in an optical fiber communication system or the like.

[0002]

2. Description of the Related Art Semiconductor lasers are now widely used as light sources for ultrafast and long-distance optical fiber communications. However, the semiconductor laser has a problem that a slight amount of reflected return light from the optical fiber causes noise inside the semiconductor laser to cause a transmission code error. Therefore, in the conventional semiconductor laser module, an optical isolator is used as a reflected return light compensation circuit for removing the reflected return light to the semiconductor laser. This optical isolator is a magneto-optical crystal that generally exhibits the Faraday effect.
It is a structure sandwiched by two polarizers with the polarization direction of transmitted light deviated by 45 °. It has the property of transmitting light only in one direction and blocking light in the opposite direction. Therefore, light is transmitted from the semiconductor laser to the optical fiber. The reflected return light from the optical fiber can be removed by transmitting.

[0003]

However, the above-mentioned optical isolator which is the conventional reflection / return light compensation circuit is composed of a minimum of four components including a magneto-optical crystal including magnets and two polarizers. There are drawbacks that it requires a lot of man-hours for processing and assembling materials, is expensive, and lacks reliability and stability.

[0004] The present invention has been made in view of the above points,
An object of the present invention is to provide a reflected return light compensation circuit that can remove reflected return light from an optical fiber to a semiconductor laser without using an optical isolator.

[0005]

In order to achieve the above object, the present invention splits light from a light source into two lights, a first light and a second light, and at least the first light is directed to an optical fiber. The transmitted Y-branch coupler and the second light branched by the Y-branch coupler are incident, and the intensity and phase of the incident light are adjusted to adjust the Y-branch.
And a light reflection circuit for returning the light to the second optical branch output side of the branch coupler.

FIG. 1 is a block diagram showing the principle of a reflected return light compensation circuit according to the present invention. The output light power from the laser active layer 2 of the semiconductor laser 1 which is a light source is branched into two lights, a first light and a second light, by the Y-branching optical coupler 3, and the first light is transmitted by the optical fiber communication system 5. Incident on the optical fiber, second
Light is incident on the light reflection circuit 4. Therefore, the reflected return light 6 from the optical fiber of the optical fiber communication system 5 and the compensation light 7 from which the intensity and phase of the second light from the light reflection circuit 4 are adjusted are combined and interfered by the Y branch coupler 3. , To the semiconductor laser 1.

FIG. 2 shows a single mode Y used in the construction of the present invention.
The multiplexing / interference principle of the branch coupler is shown. Y for simplicity
The branching ratio of the optical power of the Y branch by the branching coupler 3 is set to 50.
% / 50% 3 dB coupler. Further, each branch and the input / output waveguide of this Y-branch optical coupler 3 are assumed to be single mode waveguides. The electric field amplitudes incident from the branches A and B are E _a and E _b , respectively.

As shown in FIG. 2 (a), when light with the same amplitude (E _a = E _b ) enters from the branches A and B in the same phase, even-mode guided light is excited at the branch point. Figure 2
When incident in the opposite phase as in (b), the odd-mode guided light is excited at the branch point. The even mode light is directly guided and output, whereas the odd mode light is radiated in the process of propagating in the Y-branched tapered waveguide and is not output as an output. That is, light having the same intensity and opposite phase to the light incident on the A branch of the Y branch coupler 3 is incident on the B branch of the Y branch coupler 3 so that they are combined by the combining / interference effect of the Y branch coupler 3. Since the odd symmetry mode is cut off, the optical power output at the output end becomes zero.

In the present invention, as shown in FIG. 1, the output light from the semiconductor laser is split by the Y branch coupler 3, one branch A is connected to the communication optical fiber of the comparison fiber communication system 5, and One branch B is connected to the light reflection circuit 4. In the ordinary optical fiber communication system 5, since the reflected return light from the optical connector or the like is generated, in this case, the reflected return light 6 having a certain intensity phase returns from the optical fiber to the branch A as shown in FIG. come.

At this time, the compensating light 7 having the same intensity and opposite phase as the reflected return light 6 returning to the branch A is input to the branch B of the Y-branch coupler 3 so that as a result of the combining / interference,
Since the total optical power of the reflected return light 6 is radiated to the outside of the Y branch coupler 3, as a result, the reflected return light is not incident on the semiconductor laser 1. That is, it becomes possible to eliminate the reflected return light 6 from the optical fiber and prevent it from re-incident on the semiconductor laser 1. The light reflection circuit 4 thus has a function of generating the compensating light 7 having the same intensity and the opposite phase as the reflected return light 6.

[0011]

Next, an embodiment of the present invention will be described. FIG. 3 shows a block diagram of the first embodiment of the present invention. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals. In this embodiment, as shown in FIG. 3, a semiconductor laser 1 is connected to an optical fiber communication system 5 via an A branch of a fiber type Y branch coupler 10 and a single mode fiber 11, while a fiber type Y branch is connected. Coupler 10
The B branch, the phase controller 12, the optical attenuator 13, and the compensation light reflecting mirror 14 are connected. Phase controller 1
2. The light attenuator 13 and the compensation light reflecting mirror 14 constitute the light reflecting circuit 4.

The power branching ratio of the fiber type Y branching coupler 10 is such that it is divided into A branch on the optical fiber side and B branch on the reflecting circuit side at a ratio of 100: 1. The phase and intensity of the light incident on the fiber type Y-branch coupler 10 can be controlled by using the phase controller 12 and the optical attenuator 13. Compensation light reflector 1
4 is an optical fiber type having a reflectance of 98% (an optical fiber end face having gold vapor-deposited thereon, for example, HP-made 8
156 option 203) is used. Further, as the optical attenuator 13, a commercially available one (for example, MPCA1300 manufactured by Applied Optoelectronics) is used.

Next, the operation of this embodiment will be described. The laser light emitted from the laser active layer 2 of the semiconductor laser 1 is branched into two by a fiber type Y-branch coupler 10, one of which is used by being incident on an optical fiber communication system 5 through a single mode fiber 11 and used. Reflected return light from the connector etc. is generated. The reflected return light 6 is incident on the A branch of the fiber type Y branch coupler 10 through the single mode fiber 11.

On the other hand, the other light split into two by the fiber type Y branch coupler 10 is made incident on the compensation light reflecting mirror 14 through the phase controller 12 and the optical attenuator 13 and reflected. The reflected light is adjusted to have the same intensity as the amplitude of the reflected return light 6 by the optical attenuator 13, and is further converted into the compensation light 15 having a phase opposite to that of the reflected return light 6 by the phase controller 12, and then the fiber type Y branch coupler. It is incident on the A branch of 10.

Compensation light 15 having the same intensity and opposite phase as the reflected return light 6 incident on the A branch of the fiber type Y branch coupler 10.
Is incident on the B-branch of the Y-branch coupler 10, the reflected return light 6 is canceled by the compensating light 15 due to the multiplexing / interference effect of the Y-branch coupler 10, and the optical power output to the output end is zero. Becomes Thus, according to this embodiment, the reflected light returning to the semiconductor laser 1 can be eliminated without using an optical isolator.

FIG. 4 shows a block diagram of the second embodiment of the present invention. 3, the same components as those of FIG. 3 are denoted by the same reference numerals, and the description thereof will be omitted. The second embodiment shown in FIG. 4 is characterized in that an integrated optical component 20 in which the laser active layer 2 and the Y branch coupler are integrated is used. This embodiment also operates similarly to the first embodiment and has the same features as the first embodiment.

The present invention is not limited to the above embodiment, and for example, the connection order of the optical attenuator 13 and the phase controller 12 may be the reverse of that shown in FIGS.

[0018]

As described above, according to the present invention,
The light reflection circuit generates compensation light having the same intensity and opposite phase as the reflected return light from the optical fiber and returning it to the branch output side of the Y branch coupler to the light reflection circuit. By utilizing the interference characteristics, it is possible to eliminate the reflected return light from the optical fiber communication system to the semiconductor laser without using an optical isolator, and to realize stable operation of the semiconductor laser.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a diagram illustrating the principle of the present invention.

FIG. 3 is a configuration diagram of a first embodiment of the present invention.

FIG. 4 is a configuration diagram of a second embodiment of the present invention.

[Explanation of symbols]

 1 semiconductor laser 2 laser active layer 3 Y branch coupler 4 optical reflection circuit 5 optical fiber communication system 6 reflected return light 10 fiber type Y branch coupler 11 single-mode fiber 12 phase controller 13 optical attenuator 14 compensation optical reflector 15 compensation light 20 Semiconductor laser / Y-branch coupler integrated optical component

Claims (2)

[Claims] 1. Light from a light source is divided into first light and second light.
Y-branch coupler that splits at least the first light into an optical fiber and second light that is branched by the Y-branch coupler are incident, and the intensity and phase of the incident light are adjusted to control the Y-branch. And a light reflection circuit for returning the light to the second optical branch output side of the branch coupler. 2. The light reflecting circuit includes a reflecting mirror that reflects the second light, an optical attenuator that adjusts the intensity of the reflected light from the reflecting mirror, and a phase controller that adjusts the phase of the reflected light. The reflected return light compensating circuit according to claim 1, further comprising a light intensity and phase control adjusting circuit.