JP2001086066A - Wavelength equalizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a wavelength equalizer capable of realizing level equalization and level monitor of a wavelength multiplexed signal by using one optical multiplexer/demultiplexer. SOLUTION: Output level monitor is enabled, in addition to demultiplexing and multiplexing for wavelength equalization by one optical multiplexer/ demultiplexer 18 by inserting an optical branching device 19 into demultiplexed output of a reflection type wavelength equalizer formed by combining the optical multiplexer/demultiplexer 18, an optical reflector 17 and an optical circulator 15. Thus, a deviation of characteristics by using plural optical multiplexer/ demultiplexers is eliminated. In addition, since optical components except the optical multiplexer/demultiplexer 18 are realized by a simple structure, they are made into an array on the same substrate and the structure becomes one suitable for integration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength equalizer, and more particularly, to a wavelength equalizer for correcting a level deviation of a wavelength multiplex signal caused by a wavelength dependency of a gain of an optical amplifier in a wavelength multiplex transmission system.

[0002]

2. Description of the Related Art An optical transmission system using wavelength multiplexing is
A large amount of information can be transmitted by one optical fiber.

In particular, the practical use of a relay amplification technique using an optical fiber amplifier makes it possible to collectively amplify wavelength-division multiplexed signals, and system performance has been dramatically improved. Further, it is expected that a more flexible and advanced communication system can be constructed by using an Add / Drop device or a cross-connect device capable of switching a path for each wavelength.

In this wavelength division multiplexing transmission system, it is necessary to equalize the transmission quality of each wavelength. For this purpose, a wavelength equalization technique for flattening the signal light level of each wavelength is important. For example, in an optical amplifier, since the gain differs depending on the wavelength, the gain is flattened by inserting a wavelength equalizer having a loss characteristic to cancel the gain deviation.

However, in a long-distance transmission system in which optical amplifiers are connected in multiple stages, it is difficult to completely flatten the signal light level because a slight residual gain deviation is accumulated. Further, in a system using a cross-connect or the like, since separation and multiplexing are performed in units of wavelengths, the signal light level of each wavelength in a transmission line greatly fluctuates due to a loss error of each node or the like.

A wavelength equalizer shown in FIG. 2 has been proposed to suppress these signal light level deviations and level fluctuations.

FIG. 2 is a block diagram showing a conventional example of a wavelength equalizer.

An input wavelength-division multiplexed signal 1 is split by an input-side optical multiplexer / demultiplexer 2, and the split wavelengths (λ1, λ2,
.., Λn) for each of the variable optical attenuators 3 (3-1, 3-
,..., 3-n), and combine and output again by the optical multiplexer / demultiplexer 4 on the output side. A part of the output wavelength multiplexed signal 5 is split by an optical splitter 6, split by an optical multiplexer / demultiplexer 7, and separated by a photodetector 8 (8-1, 8-2,..., 8-n). Detect the wavelength level. The detected light level 9 of each wavelength (9-1, 9-2,..., 9-n) and the control circuit 1
The reference signal 11 (11-1, 11-2,
, 11-n) and the comparator 12 (12-1, 12-2,
.., 12-n) and the error signal 13 (13
The attenuation of each variable optical attenuator 3 is controlled so that (-1, 13-2,..., 13-n) becomes zero.

With such a control loop, the optical level of each wavelength output from the optical multiplexer / demultiplexer 4 becomes the same as that of the reference signal 11. The wavelength dependency of the level monitor circuit is corrected in advance, and the reference signal 11 is adjusted so that the light level of each wavelength becomes uniform.
Is set, the wavelength multiplexed signal 14 with the signal light level flattened is output.

Incidentally, a method of compensating for the loss of the optical multiplexer / demultiplexer by using a semiconductor optical amplifier having an amplifier function instead of the variable optical attenuator 3 is conceivable.

When this wavelength equalizer is applied to a high-density wavelength division multiplexing system, it is necessary to make the transmission wavelengths of the two optical multiplexers / demultiplexers 2 and 4 arranged at the input and output exactly coincide with each other. If the two wavelengths are shifted, a large insertion loss will result. As a method of reducing the insertion loss, a reflection-type wavelength equalizer shown in FIG. 3 has been proposed.

FIG. 3 is a block diagram showing another conventional example of a wavelength equalizer.

In this wavelength equalizer, an optical multiplexer / demultiplexer 16 is connected to a terminal B of an optical circulator 15 having a forward characteristic from a terminal A to a terminal B and from a terminal B to a terminal C. Is a light reflector 17 via the variable optical attenuator 3.
(17-1, 17-2,..., 17-n) are connected.

The wavelength-division multiplexed signal 1 input from the terminal A of the optical circulator 15 is input to the optical multiplexer / demultiplexer 16 via the terminal B, where it is demultiplexed, and the variable optical attenuator 3 (3-1, 3-
2,..., 3-n), the light is reflected by the light reflector 17 and passes through the same path to the optical multiplexer / demultiplexer 1.
The wavelength-division multiplexed signal 5 is multiplexed by the optical circulator 6 and output at the terminal C of the optical circulator 15. A part of the wavelength multiplexed signal 5 is split by the optical splitter 6 and controlled by the same procedure as that of the wavelength equalizer shown in FIG. 2 to output the wavelength multiplexed signal 14 having the signal light level flattened. Can be done.

With such a configuration, demultiplexing and multiplexing can be performed by one optical multiplexer / demultiplexer 16, so that wavelength adjustment of the optical multiplexer / demultiplexer on the demultiplexing side and the multiplexing side becomes unnecessary. . Further, the number of expensive optical multiplexer / demultiplexers can be reduced. As a result, downsizing, cost reduction, and improvement in reliability can be achieved.

[0016]

However, even in a wavelength equalizer of a reflection type, an optical multiplexer / demultiplexer for monitoring the level deviation between wavelengths must be provided separately.
There is a problem that it is necessary to match the wavelength characteristics of the two optical multiplexer / demultiplexers.

An object of the present invention is to provide a wavelength equalizer capable of solving the above-mentioned problems and realizing level equalization of a wavelength division multiplexed signal and level monitoring using one optical multiplexer / demultiplexer. It is in.

[0018]

In order to achieve the above object, a wavelength equalizer according to the present invention splits a wavelength-multiplexed optical signal and flattens the optical level for each individual wavelength. In the wavelength equalizer that combines and outputs the signals again, the common input terminal of the optical multiplexer / demultiplexer is connected to the terminal B of the optical circulator having the forward characteristic from the terminal A to the terminal B and from the terminal B to the terminal C, One output terminal of an optical splitter that splits a part of signal light is connected to each individual input / output terminal of the optical multiplexer / demultiplexer, and an optical reflector is connected to an input terminal of the optical splitter via a variable optical attenuator. Are connected to the other output terminals of the optical splitter, photodetectors are respectively connected, the output terminal of the photodetector is connected to one input terminal of a comparison circuit, and the output terminal of the comparison circuit is The control input terminal of the attenuator is connected, and the other input terminal of the comparison circuit is In which the control circuit is connected to control the attenuation of the variable optical attenuator based on the signal light level to be detected more.

In addition to the above configuration, in the wavelength equalizer of the present invention, the variable optical attenuator may be a semiconductor optical amplifier capable of adjusting an input light level by a control signal.

In addition to the above configuration, in the wavelength equalizer of the present invention, the optical multiplexer / demultiplexer may be an integrated optical multiplexer / demultiplexer using an arrayed waveguide type grating formed on a substrate.

In addition to the above structure, the wavelength equalizer according to the present invention is characterized in that two or more optical elements among optical elements such as an optical circulator, an optical splitter, an optical reflector, a photodetector, and a variable optical attenuator are on the same substrate. It may be an integrated optical component formed thereon.

According to the present invention, one optical splitter is inserted into the demultiplexing output of the reflection type wavelength equalizer in which the optical multiplexer / demultiplexer, the optical reflector, and the optical circulator are combined. The optical multiplexer / demultiplexer enables output level monitoring in addition to demultiplexing and multiplexing for wavelength equalization. For this reason, the characteristic deviation due to the use of a plurality of optical multiplexer / demultiplexers is eliminated.
Further, since optical components other than the optical multiplexer / demultiplexer can be realized with a simple structure, it is easy to form an array on the same substrate, and the structure is suitable for integration.

[0023]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing one embodiment of the wavelength equalizer of the present invention. Note that common members are used for members similar to those in the conventional example.

This wavelength equalizer is connected to a terminal B of an optical circulator 15 having a forward characteristic from a terminal A to a terminal B and from a terminal B to a terminal C by a common input / output terminal Pc of the optical multiplexer / demultiplexer 18.
Are connected, and each individual input / output terminal Pio of the optical multiplexer / demultiplexer 18 is connected.
The optical splitter 19 (19-1, 1-1) for splitting a part of the signal light into
9-2,..., 19-n) are connected,
The variable optical attenuator 3 (3-1, 3) is connected to the input terminal of the optical branching device 19.
,..., 3-n) through the light reflector 17 (17-1,.
17-2,..., 17-n), and the photodetector 8 (8-1, 8-2,..., 8-n) is connected to the output terminal of the optical splitter 19.
Are connected to each other, and the comparator 1 is connected to the output terminal of the photodetector 8.
2 (12-1, 12-2,..., 12-n) are connected to one another, the control circuit 10 is connected to the other input terminal of the comparator 12, and the variable light is connected to the output terminal of the comparator 12. The control input terminal of the attenuator 3 is connected. The variable optical attenuator 3 can adjust the amount of attenuation by a control signal.

In such a configuration, when the wavelength division multiplexed signal light 1 is input from the terminal A of the optical circulator 15, the signal light 1 is split by the optical multiplexer / demultiplexer 18 via the terminal B, Each individual demultiplexed signal is output from the input terminal of the optical splitter 19 through the branch side terminal of the optical splitter 19, further reflected by the optical reflector 17 via the variable optical attenuator 3, and again passes through the same path. The signal is output from the terminal B of the optical circulator 15 to the terminal C. At this time, part of the signal light reflected by the light reflector 17 and passing through the variable optical attenuator 3 is:
The light is output from the other branch output terminal of the optical splitter 19, is input to the photodetector, and its light level is detected.

The control circuit 10 compares the detected signal light level with the reference signal, and adjusts the attenuation of the variable optical attenuator 3 so that the error signal becomes zero. As a result, the signal light level becomes the same as the level set by the reference signal. If there is a deviation in the loss between the wavelengths of the optical multiplexer / demultiplexer 18 in advance, the signal light levels of all the wavelengths can be made equal by setting a reference signal level in which the loss deviation is corrected.

That is, demultiplexing and multiplexing for wavelength equalization,
Further, demultiplexing for output level monitoring can be realized by one optical multiplexer / demultiplexer. For this reason, there is no signal degradation due to wavelength characteristic shift due to the use of a plurality of optical multiplexer / demultiplexers. Further, reliability is improved, and cost reduction and downsizing are possible.

Further, since optical components other than the optical multiplexer / demultiplexer that require more precise wavelength control can be realized with a simple structure, it is easy to form an array on the same substrate, and the wavelength equalizer is used. The structure is suitable for integration.

As described above, according to the present invention, the reflection type configuration using one optical multiplexer / demultiplexer does not cause characteristic deterioration due to a shift in the wavelength characteristic of the optical multiplexer / demultiplexer, and is highly reliable, small-sized, and low-cost. Since a wavelength equalizer can be provided, the signal quality of an optical signal transmission system in which a path is changed in wavelength units using a high-density wavelength multiplexed signal can be stabilized. That is,
A large-capacity and flexible wavelength division multiplexing transmission system can be realized.

[0031]

In summary, according to the present invention, the following excellent effects are exhibited.

Using one optical multiplexer / demultiplexer, it is possible to provide a wavelength equalizer capable of realizing level equalization of a wavelength multiplexed signal and level monitoring.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a wavelength equalizer of the present invention.

FIG. 2 is a block diagram showing a conventional example of a wavelength equalizer.

FIG. 3 is a block diagram showing another conventional example of a wavelength equalizer.

[Explanation of symbols]

 3 (3-1, 3-2, ..., 3-n) Variable optical attenuator 8 (8-1, 8-2, ..., 8-n) Photodetector 10 Control circuit 12 (12-1, 12- 2, ..., 12-n) Comparator 15 Optical circulator 17 (17-1, 17-2, ..., 17-n) Optical reflector 19 (19-1, 19-2, ..., 19-n) Optical branching vessel

Claims (4)

[Claims] 1. A wavelength equalizer for demultiplexing a wavelength-multiplexed optical signal, flattening an optical level for each individual wavelength, and multiplexing and outputting again. A common input terminal of an optical multiplexer / demultiplexer is connected to a terminal B of an optical circulator having a forward characteristic from B to a terminal C, and a part of the signal light is branched to each individual input / output terminal of the optical multiplexer / demultiplexer. One output terminal of the optical splitter is connected, an optical reflector is connected to the input terminal of the optical splitter via a variable optical attenuator,
A photodetector is connected to the other output terminal of the optical splitter, an output terminal of the photodetector is connected to one input terminal of a comparison circuit, and an output terminal of the comparison circuit is connected to the output terminal of the variable light. A control input terminal of the attenuator is connected, and a control circuit for controlling the amount of attenuation of the variable optical attenuator based on the signal light level detected by the photodetector is connected to the other input terminal of the comparison circuit. A wavelength equalizer, characterized in that: 2. The wavelength equalizer according to claim 1, wherein said variable optical attenuator is a semiconductor optical amplifier capable of adjusting an input light level by a control signal. 3. The wavelength equalizer according to claim 1, wherein the optical multiplexer / demultiplexer is an integrated optical multiplexer / demultiplexer using an arrayed waveguide type grating formed on a substrate. 4. The optical circulator, the optical splitter,
4. The integrated optical component according to claim 1, wherein two or more optical elements among the optical elements such as the optical reflector, the optical detector, and the variable optical attenuator are formed on the same substrate. The wavelength equalizer as described.