JPS624020B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical repeater, and more particularly to an optical repeater that allows optical signals to be transmitted through another optical fiber when an optical fiber fails.

Optical fiber is a low-loss, high-bandwidth transmission line.
It also has excellent transmission characteristics such as no crosstalk,
Furthermore, it is small in diameter, lightweight, and has many structural features, so it is widely used as a communication line. However, since the optical fiber is a narrow diameter line mainly made of glass, its tensile strength is weak and highly variable. Furthermore, transmission loss increases due to microbending during the installation stage.
Furthermore, when used for submarine cables, etc., during installation, tension may be applied to the cable due to the cable's own weight or pitching of the installation ship, which may cause the fiber to break or increase transmission loss. Therefore,
In order to deal with these failures and increase reliability against system interruptions, optical fiber switching methods are often adopted. The optical fiber switching method is a method in which a spare optical fiber is provided in a cable, and when the current optical fiber fails, the system is switched to the spare optical fiber for optical transmission, thereby improving system reliability. This method is a very advantageous method because the optical fiber has a small diameter, so even if a spare fiber is provided, it does not directly lead to an increase in the outer diameter of the cable.

A conventional optical repeater for switching the optical fibers described above is constructed as shown in FIG. That is, two optical fibers are connected to the optical directional coupler 1-1, and optical signals from either optical fiber can be received by the optical receiver 1-2. In some cases, two fibers are directly introduced into the light receiver 1-2 without providing the optical directional coupler 1-1. The photoreceiver 1-2 converts the incident light into an electrical signal, which is amplified by the equalization amplifier 1-3. Then, the gain control circuit 1-4 controls the optical receiver 1-2 so that the peak value of the output signal of the equalizing amplifier 1-3 becomes a constant value.
The amplification degree M of and the gain of equalization amplifiers 1-3 are controlled. Gain control is performed, for example, by controlling the bias current or the like based on the difference between the peak value of the output signal and the comparison value. The output signal of the amplifier 1-3 is discriminated and reproduced by the discrimination and reproduction circuit 1-5 and input to the laser diode drive circuit 1-6. A laser diode 1-7 is driven by a laser diode drive circuit 1-6 to emit light. Laser diode 1
-7 is selectively connected to optical fiber 2-1 or 2-2 by optical switch 1-9.
The optical switch 1-9 is driven by a switch control circuit 1-8, and the switch control circuit 1-8 is controlled by a remote control signal from a terminal station to perform the above selection switching. Conventional optical repeaters such as those described above require a remote control signal to be sent from the terminal station for switching the optical fiber in cases such as when loss increases in the optical fiber and falls below the minimum light receiving level, resulting in degraded error performance. Moreover, since it is necessary to add a control circuit for switching the optical switch to the optical repeater as described above, there is a drawback that the structure of the repeater becomes complicated. Furthermore, when switching for each relay section, a signal for selecting a repeater is also required. Also,
It is difficult for the terminal station to determine which relay section should be switched.

The purpose of the present invention is to solve the above-mentioned conventional drawbacks and
An object of the present invention is to provide an optical repeater capable of automatically switching over a faulty optical fiber with a simple configuration.

The optical repeater of the present invention includes an optical receiver, a variable gain amplifier that amplifies the output electrical signal of the optical receiver, and a gain of the variable gain amplifier that is controlled so that the output signal of the variable gain amplifier becomes a constant value. an optical repeater which has a gain control circuit, converts an input optical signal into an electrical signal by the optical receiver, identifies and regenerates the output electrical signal of the variable gain amplifier, converts it into an optical signal, and sends it out; an optical switch that selectively selects one of the optical signals from the optical fibers and inputs it to the optical receiver; and an optical spring that outputs the output optical signal to the two optical fibers; The optical switch is characterized in that it is configured to be controlled by a control signal from the gain control circuit.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a block diagram showing one embodiment of the present invention. That is, optical fibers 2-1 and 2-
2 to optical switch 1-10, and
-10 selectively selects both of the above inputs and selects the receiver 1.
-Give to 2. The light receiving section 1-2 converts the input optical signal into an electrical signal and inputs it to the equalizing amplifier 1-3, and the gain control circuit 1-4 controls the output signal of the amplifier 1-3 so that the peak value of the output signal becomes a constant value. The bias current is outputted to the amplification degree M of the light receiving section 1-2 and the amplifier 1-3.
control the gain of. When the input to the optical receiver 1-2 decreases and the bias current for the above-mentioned gain control exceeds a predetermined value, the optical switch 1-2 is activated.
10 to switch. This switching determination value can be arbitrarily set by, for example, a transistor switching circuit. That is, the optical fiber 2-1
When the amount of light received from the optical fiber 2-2 falls below a certain value, the optical fiber 2-2 can be switched to receive the light.
This switching is performed using a bias current for gain control, etc., so it can be performed automatically when the amount of received light falls below a certain value, and a special switching control signal etc. is required for this purpose. does not require. In addition, since only the optical repeater that has decreased the amount of light received switches the optical fiber on the input side.
There is no need to judge the faulty section, and only the optical fiber in the faulty section can be switched.
The optical signal received by the normal optical fiber 2-2 is converted into an electrical signal through normal operation, amplified, and identified and regenerated by the identification and regeneration circuit 1-5. The laser diode 1-7 is driven by. Laser diode 1-7
The output optical signal is sent to optical fibers 2-1 and 2-2 via optical splitter 1-11. Therefore, the next optical repeater can receive light through a normal optical fiber in the same way as described above, and in the event of a failure, it can similarly switch to the other optical fiber to receive light. If both optical fibers 5-1 and 2-2 are in failure, the optical switch 1-10 repeats the switching operation alternately, and when one of the optical fibers recovers, it connects to that optical fiber.

As described above, in the present invention, the output optical signal is sent to two optical fibers, and the optical switch in the reception input section is configured to switch according to the control signal of the gain control circuit. When the input optical signal decreases due to increased loss in the optical fiber and the gain control signal becomes abnormally large, the control signal can be used to switch the optical switch and receive the signal through the normal optical fiber. Since this switching is performed automatically, there is no need to send a remote control signal for switching from the terminal station as in the conventional case, and there is no need for a switching control circuit for this purpose. Furthermore, since the optical fibers in the faulty section are automatically switched, it is possible to switch only the faulty section. Therefore, for example, in a certain section, the optical fiber 2-1 is a failure,
Another advantage is that even if the optical fiber 2-2 fails in other sections, the transmission path between the two end stations will not be affected. In such cases, with conventional optical repeaters, transmission between the two end stations is impossible unless selective switching is performed for each section.Selective switching for each section requires extremely difficult selection control and determination of faulty sections. Ta.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional optical fiber switching system and optical repeater, and FIG. 2 is a block diagram showing an embodiment of the present invention. In the figure, 1... optical repeater, 2... optical cable,
1-1... Optical directional coupler, 1-2... Light receiver, 1-
3... Equalization amplifier, 1-4... Gain control circuit, 1-5
...Identification reproducing circuit, 1-6...Laser diode drive circuit, 1-7...Laser diode, 1-8...Switch control circuit, 1-9, 1-10...Optical switch,
1-11... Optical splitter, 2-1, 2-2... Optical fiber.

Claims (1)

[Claims] 1 comprising a light receiver, a variable gain amplifier that amplifies the output electrical signal of the light receiver, and a gain control circuit that controls the gain of the variable gain amplifier so that the output signal of the variable gain amplifier becomes a constant value. , an optical repeater that converts an input optical signal into an electrical signal by the optical receiver, identifies and regenerates the output electrical signal of the variable gain amplifier, converts it into an optical signal, and transmits the optical signal from the two optical fibers; an optical switch that selectively selects one of them and inputs it to the optical receiver; and an optical splitter that outputs an output optical signal to two optical fibers, and the optical switch is connected to the gain control circuit. An optical repeater characterized in that it is configured to be controlled by a control signal.