JPS63250228A - Optical repeater - Google Patents

Abstract

PURPOSE:To automatically adjust the amplitude of an input light signal by attenuating a light signal to pass through the light input passage of a light electric converting circuit in accordance with the amplitude of the light signal. CONSTITUTION:From the output electric signal of a light electric converting circuit 2, a control signal corresponding to the amplitude of an input light signal, especially, the peak signal amplitude is generated, and in accordance with the control signal, a variable light attenuator 12 is controlled. As the variable light attenuator 12 in this case, one side uses the element with a different transmission characteristic according to the position, changes mechanically the position with a control signal, and other side is composed of the light integrated circuit equipped with the dielectric waveguide and the electrode connected to the dielectric waveguide. By the control signal, a voltage impressed to the electrode is changed and the attenuating quantity of the light signal to pass through the dielectric waveguide is changed. Thus, a light electric converting circuit and a receiving circuit are not saturated and the amplitude of the input light signal can be automatically adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is applied to optical communications. The present invention is used as a regenerative repeater in a communication system that transmits digital optical signals through optical fibers. In particular, the present invention relates to an optical repeater that can expand the dynamic range for input optical signals with extremely large amplitudes.

[Conventional technology]

A conventional optical repeater has an optical fiber 1 as shown in FIG.
The propagated digital optical signal is converted into an electrical signal by an opto-electrical conversion circuit 2, and amplified and other processing is performed by a receiving circuit 3. A timing circuit 4 reproduces a timing signal from this output digital signal, and an identification circuit 5 identifies the digital signal for reproduction based on this timing number 48. The reproduced and identified digital signal is amplified by the drive circuit 6, drives the electro-optical conversion circuit 7, is converted into an optical signal again, and is transmitted to the optical fiber 8 of the next repeating section.

This circuit is equipped with an automatic gain control circuit 9 so that the input level of the identification circuit 5 is constant, and is configured to automatically control the gain of the receiving circuit 3.

In addition, in order to expand the dynamic range of this optical repeater by automatic gain control, a gain control signal is given to the opto-electric conversion circuit 2 as shown by the broken line in FIG. 6, and a bias current is given to the opto-electric conversion element. There is a method for changing the degree of anger of the photoelectric conversion circuit 2 by, for example, controlling.

[Problem that the invention seeks to solve]

However, in the actual usage of optical repeaters, there are topographical restrictions where transmission lines are placed, or optical fiber cables with extremely short intervals are used to harmonize with existing roads and buildings. It may be necessary to install an optical repeater.

In addition, in the submarine optical transmission system, which has fewer topographical restrictions, in order to minimize the number of optical repeaters used when initially setting up the transmission line, repeaters are installed at the maximum repeating interval allowed by the optical repeater. However, if a failure occurs in the relay transmission line after the facility is installed and the problem is repaired, it becomes necessary to add an optical fiber cable, and an additional optical repeater must be installed in that area. In this case, one optical repeater is inserted at an extremely short interval between optical fiber cables, and the output of the previous optical repeater is input to the input of that optical repeater with almost no attenuation, so the amplitude is extremely high. It will be a big level.

In such a case, the opto-electric conversion circuit and its output signal processing circuit may become saturated. This is a drawback that cannot be essentially addressed by the above-mentioned automatic gain control.

To solve this problem, it is possible to insert a fixed optical attenuator into the optical input circuit for repeaters that are inserted at a repeating interval of less than a predetermined value, but it is possible to Opening the package and inserting the optical attenuator is
This requires a lot of man-hours (in addition, it is not a desirable method in order to maintain high reliability.

The present invention improves on this by providing an optical repeater that can automatically adjust the amplitude of the input optical signal without saturating the circuit even when optical repeaters are arranged at extremely short repeating intervals. The purpose is to provide

[Means for solving problems]

The present invention is characterized in that variable optical attenuation means is provided for attenuating the optical signal passing through the optical input path of the opto-electric conversion circuit in accordance with the amplitude of the optical signal.

[Effect]

The simplest configuration is a photosensitive glass that darkens depending on the amplitude of the transmitted light, in the path of the input optical signal of the photoelectric conversion circuit.
For example, there is a method of inserting photochromic glass. The photosensitive glass used here is preferably a reversible glass that darkens depending on the intensity of the irradiated light and its transmittance decreases, and when the irradiated light disappears, it recovers and the transmittance returns to its original value.

Generates a control signal corresponding to the amplitude of the input/destination signal and the peak signal amplitude from the output electrical signal of the opto-electric conversion circuit,
A configuration can be adopted in which the variable optical attenuator is controlled according to this control signal.

One type of variable optical attenuator in this case uses an element whose transmission characteristics differ depending on its position, and its position is mechanically changed by the control signal. The other type is composed of an optical integrated circuit equipped with a dielectric waveguide and an electrode connected to the dielectric waveguide. This changes the amount of attenuation of the optical signal passing through the optical waveguide.

In either case, as an optical repeater, some kind of device must be inserted into the input circuit of the opto-electric conversion circuit, so even if the optical signal is extremely weak, a slight loss will occur, causing the amplitude In a small range, the signal-to-noise ratio deteriorates and the dynamic range is reduced. Therefore, the present invention can be implemented in a small number of optical repeaters for short distance use, and these short distance repeaters can be used when the repeater interval is extremely small or when the repeater interval is relatively small. It is better to keep it as is.

〔Example〕

FIG. 1 is a block diagram of an apparatus according to a first embodiment of the present invention. The optical signal propagated through the optical fiber 1 is input to the opto-electrical conversion circuit 2 and converted into an electrical signal.

This electrical signal is amplified and processed by the receiving circuit 3.

The output signal of this receiving circuit 3 is manually input to a timing circuit 4 to reproduce a timing signal. Using this timing signal, the identification circuit 5 identifies and reproduces the digital signal from the output of the receiving circuit 3.

The output of the identification circuit 5 is input to a drive circuit 6, amplified, given to an electro-optical conversion circuit 7, converted into an optical signal again, and sent to an optical fiber 8 in the next repeating section. The input signal level of the identification circuit 5 is detected by an automatic gain control circuit 9, and the amplification gain of the receiving circuit 3 is controlled so that this level is constant.

The feature of this device is that a variable optical attenuation means 11 is provided in the input circuit of the photoelectric conversion circuit 2.

In this first embodiment, the variable light attenuation means 11 is a photochromic glass plate. Photochromic glass has a reversible property: when an optical signal is input, the glass darkens and its transmittance decreases, and when the optical signal is no longer present, the transmittance returns to its original value. Since photochromic glass is a crystallized glass, it can maintain stable characteristics for a long period of time. Photochromic glass is used in things such as sunglasses.

However, since photochromic glass has a slow response to the level of light irradiated with it, it may reach saturation immediately after startup when the amplitude of the input optical signal is large, but it gradually darkens and reaches a very low level under normal usage conditions. It is possible to suppress the amplitude of a high input optical signal to an appropriate level.

For detailed information on the composition and properties of photochromic glass, please refer to "Glass Handbook" published by Asakura Shoten.
There is a detailed description.

FIG. 2 is a block diagram of an apparatus according to a second embodiment of the present invention. In this example, the variable light attenuation means are elements numbered 12-16 in the drawing. That is, this variable optical attenuation means
a peak detection circuit 13 that branches an electrical signal from the output signal of the signal and detects the peak level of the signal; a comparison circuit 14 that compares the output of the peak detection circuit 13 with a reference level input to the terminal 16; It includes a control circuit 15 that generates a control signal based on the comparison output of the comparison circuit 14, and a variable optical attenuator 12 that changes the amount of optical attenuation based on this control signal.

The other configuration in FIG. 2 is the same as that of the first embodiment device explained in FIG. 1 above.

FIG. 3 is a diagram showing an example of the configuration of the variable optical attenuator 12. This example includes a transmission element 22 through which an optical signal passes and whose transmittance varies depending on its position, an electromechanical conversion means 21 that applies mechanical displacement according to a control signal, and this electromechanical conversion means 2.
and a mechanical means for displacing the position of the transmitting element 22 according to the mechanical displacement of the transmissive element 22. That is, the output of the control circuit 15 is given to an electromechanical conversion means 21 constituted by a pulse motor, and a transmission element 22 whose light transmittance varies depending on the rotation angle is attached to this rotation shaft. By changing and controlling the rotation angle of the transmission element 22 using a control signal, the intensity of the transmitted light indicated by the arrow can be variably attenuated.

FIG. 4 is a diagram showing another example of the configuration of the variable optical attenuator 12. This example is an optical integrated circuit in which a dielectric waveguide 24 and an electrode 25 connected to the dielectric waveguide 24 are formed on a substrate 26. This optical integrated circuit is an application of a structure known as an optical switch that is controlled by electrical signals. The input light is branched on the dielectric waveguide made of lithium niobate, and the dielectric waveguide 2 is divided by the voltage applied to the electrode 25.
Apply electric fields in opposite directions to 4 to change the refractive index,
The two paths change the phase of the light passing through it. By recombining the light from the two paths, it is possible to substantially adjust the amount of light passing through. In other words, if the light passing through the two paths has exactly opposite phases to each other, the output light is zero, and if they are exactly in phase with each other, the output light is 1, and by adjusting the phase between them, arbitrary attenuation can be given. can.

FIG. 5 is a diagram showing still another example of the configuration of the variable optical attenuator 12. This example is also an optical integrated circuit in which a dielectric waveguide 27 and an electrode 25 connected to the dielectric waveguide 27 are formed on a substrate 26. In this example, by applying an electric field to the dielectric waveguide 27 from the electrode 25, the dielectric waveguide 27 is
A portion of the light passing through the dielectric waveguide 24 is refracted and emitted from the waveguide, thereby substantially controlling the amount of attenuation of the light passing through the dielectric waveguide 24.

〔Effect of the invention〕

As explained above, according to the present invention, even when optical repeaters are arranged at extremely short repeating intervals, the opto-electric conversion circuit and the receiving circuit do not become saturated, and moreover, the amplitude of the input optical signal is automatically adjusted. It is possible to provide an optical repeater that can adjust the

By implementing the present invention, it is possible to arrange repeaters to a state where the repeater interval is almost zero, so that the constraints on repeater installation are relaxed and the degree of freedom in designing a transmission path is improved. Furthermore, when applied to submarine optical cables, it is possible to appropriately cope with the need to add optical cables due to repairs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus according to a first embodiment of the present invention. FIG. 2 is a block diagram of an apparatus according to a second embodiment of the present invention. FIG. 3 is a diagram showing a configuration example of a variable optical attenuator using electromechanical conversion means. FIG. 4 and FIG. 5 are diagrams showing an example of the configuration of a variable optical attenuator using an optical integrated circuit. FIG. 6 is a block diagram of a conventional device. DESCRIPTION OF SYMBOLS 1... Optical fiber on the input side, 2... Optoelectric conversion circuit, 3... Receiving circuit, 4... Timing circuit, 5...
- Identification circuit, 6... Drive circuit, 7... Electro-optical conversion circuit, 8... Output side optical fiber, 9... Automatic gain control circuit, 11... Variable optical attenuation means, 12. ...Variable optical attenuator, 13...Peak detection circuit, 14...Comparison circuit, 15...Control circuit, 21...Electromechanical conversion means (pulse motor), 22...Transmission element. ? ψ5-Kaijiiwo11? 1i11 Figure Shoulder 2■ Shoulder 5 Figure

Claims (5)

[Claims] (1) An opto-electrical conversion circuit that receives an optical signal propagated through an optical fiber and converts it into an electrical signal, a timing regeneration circuit that regenerates a timing signal from the output of this opto-electrical conversion circuit, and an output timing of this timing regeneration circuit. An optical relay comprising an identification circuit that identifies the output signal of the opto-electric conversion circuit based on a signal, a drive circuit that amplifies the output of this identification circuit, and an electro-optic conversion circuit that generates an optical signal based on the output of this drive circuit. What is claimed is: 1. An optical repeater comprising: a variable optical attenuation means for attenuating an optical signal passing through the optical input path of the opto-electric conversion circuit according to the amplitude of the optical signal. (2) The optical repeater according to claim 1, wherein the variable optical attenuation means that attenuates the optical signal according to the amplitude of the optical signal includes a photosensitive glass that darkens according to the amplitude of the transmitted light. (3) The variable optical attenuation means for attenuating according to the amplitude of the optical signal includes means for extracting a control signal corresponding to the amplitude of the input optical signal from the output electrical signal of the opto-electric conversion circuit, and attenuation according to this control signal. The optical repeater according to claim 1, further comprising a variable optical attenuator that provides transmitted light with a variable optical attenuator. (4) A variable optical attenuator consists of a transmission element through which an optical signal passes and whose transmittance varies depending on its position, an electromechanical transducer that applies mechanical displacement according to a control signal, and a mechanical displacement of the electromechanical transducer. and mechanical means for displacing the position of the transmissive element according to the invention. (5) The optical repeater according to claim (3), wherein the variable optical attenuator includes an optical integrated circuit including a dielectric waveguide and an electrode connected to the dielectric waveguide.