JPH0470718A - Optical amplification device equipped with gain control means - Google Patents

Abstract

PURPOSE:To use the device even for a network where a signal is present discontinuously on a transmission line, or a network which varies in signal modulating speed, etc., by providing a means which allows the gain control means to operate intermittently for an optical amplification part so that a held gain is renewed. CONSTITUTION:This device is equipped with the optical amplification part 2 such as a semiconductor laser amplifier and an optical fiber amplifier, a means 4 which photodetects part of the light output of the optical amplification part 2, means 6 and 7 which control the gain of the optical amplification part 2 by using the output of the photodetecting means 4, a means 6 which holds the state after the gain of the optical amplification part 2 is controlled, and the means 10 which allows the gain control means 6 to operate intermittently for the optical amplification part so that the held gain is renewed. Consequently, the AGC of the optical amplification part is performed intermittently by using a specific light signal at need and the gain state is normally held, so even the discontinuous signal and the signal which varies in modulating speed can be amplified stably and optically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is an optical communication network that transmits and exchanges optical signals, and is used to compensate for attenuation of optical signals.
The present invention relates to an optical amplification device incorporating means for obtaining ljl.

[Prior Art] In recent years, optical fiber transmission systems that use optical fibers as transmission paths have many advantages such as wide bandwidth, low loss, and electrically resistant FiB inductivity. Its introduction is progressing in the fields of systems and LANs.

Among these, in the field of optical LAN, the active type that electrically regenerates and relays optical signals at each node is popular, but research and development is also progressing on the passive type that can make better use of the characteristics of light. ing. However, in this passive optical LAN, the number of nodes connected to the system must be increased due to the attenuation of the optical signal.
difficult to do. For this reason, optical amplifiers that directly amplify light to compensate for optical signal attenuation are attracting attention. However, optical amplifiers generally suffer from changes in the environment and element characteristics over time. The gain will vary slightly. In order to suppress this fluctuation, the automatic gain side (hereinafter referred to as AGC) is generally used.
trol) is carried out. AGC of an optical amplifier is controlled so that the optical output output when an optical signal is input to the optical amplifier is a predetermined value.

FIG. 4 is a block diagram showing a conventional example of an optical amplification device that performs AGC of an optical amplifier. In this example, the optical amplification section is
A semiconductor laser amplifier is used in which a bias current is injected in a range below the oscillation threshold. In the same figure, 4
1-1.41-2 is an optical fiber, 42 is a semiconductor laser amplifier, 43 is an optical splitter, 44 is a light receiving circuit, and 49 is a drive circuit. The optical signal propagating through the optical fiber 41-1 is amplified by the semiconductor laser amplifier 42, and its output is branched by the optical splitter 43, so that part of the signal is sent to the light receiving circuit 44 and the rest is sent to the optical fiber 41-2. .

The optical signal incident on the light receiving circuit 44 is converted into an electrical signal,
It is appropriately processed and input to the drive circuit 49. The drive circuit operates a semiconductor laser according to this input electrical signal! '1
The bias current of the amplifier 42 is changed to drive the semiconductor laser amplifier 42 so that its optical output becomes constant.

[Problem H to be solved by the invention] However, in the conventional optical amplifying device, it is necessary that an optical signal is always input to the device for AGC, and
It was necessary to optimize the time constant according to the modulation speed of the optical signal on the fiber transmission path. This is because the AGC is always working, so if no optical signal is substantially input, the optical amplifier will have an enormous gain and malfunction.

Therefore, in trunk optical communication networks where optical signals with a constant modulation rate are always on the transmission path, such malfunctions do not occur and there is no problem.
It is difficult to apply the above-mentioned conventional example to a network in which there are discontinuous burst-like signals on a transmission path, such as et), or a network in which the modulation speed of an optical signal on a transmission path changes.

Therefore, in view of the above-mentioned problems, an object of the present invention is to provide an optical amplification device equipped with a gain control means that can be used even in a network where signals are discontinuously present on a transmission path or a network where the signal modulation rate changes. There is a particular thing.

[Means for Solving the Problems] The present invention that achieves the above object includes an optical amplifying section such as a semiconductor laser amplifier or an optical fiber amplifier, a means for receiving a part of the optical output of the optical amplifying section, and a light receiving means. means for controlling the gain of the optical amplification section using the output from the optical amplification section; means for maintaining the state after controlling the gain of the optical amplification section; Means is provided for causing the gain control means to act on the optical amplification section (for example, by intermittently activating the gain control means).

Furthermore, means may be provided for intermittently inputting a predetermined optical signal to the optical amplifying section in accordance with the operation of the optical amplifying section by the sum-1 gain control means.

As a result, AGC in the optical amplification section can be performed only intermittently using a predetermined optical signal if necessary, and since the gain state is normally maintained, discontinuous It becomes possible to stably amplify optical signals even when the signal or modulation speed changes.

[Embodiment] FIG. 1 is a block diagram showing a first embodiment of the optical amplification device of the present invention. In this embodiment, a semiconductor laser amplifier 2 is used as the optical amplification section, and a gain control means for controlling the gain of the optical amplification section and a means for maintaining the state after the control are constituted by digital circuits.

In Fig. 1, the arrows in the figure indicate the transmission direction of optical signals, and 1-1, -2 are optical fibers which are transmission lines,
2 is a semiconductor laser amplifier that amplifies the optical signal; 3 is an optical branching device that distributes the optical output from the semiconductor laser amplifier 2; 4 is a light receiving circuit that receives the optical signal and converts it into an electrical signal; 5;
6 is an A/D converter that converts the electrical signal from an analog signal to a digital signal, and 6 is an operation that outputs a digital signal that controls the gain of the semiconductor laser amplifier 2 based on the digital signal from the A/D converter 5. circuit; 7 is a storage circuit that stores data necessary for gain control; 8 is a D/A converter that converts the digital signal from the arithmetic circuit 6 into an analog signal;
9 is a drive circuit that adjusts the gain based on the analog signal from the D/A converter 8 and drives the semiconductor laser amplifier 2;
10 is a communication control circuit that controls communication and the like.

The gain of the semiconductor laser amplifier 2 is determined by the bias current injected into the active region by the drive circuit 9 through the electrodes of the semiconductor laser amplifier 2, while the bias current output from the drive circuit 9 is determined by the bias current that is driven from the D/A converter. It is controlled by the magnitude of the input signal input to the circuit 9. Memory circuit 7
Stores therein the output data (hereinafter referred to as Do) of the A/D converter 5 when the optical output of the semiconductor laser amplifier 2 reaches a predetermined value. This data D0 may be rewritten as appropriate.

The operation of this embodiment will be explained based on the above configuration. The operation when setting the gain of the optical amplifier is performed as follows.

First, when the arithmetic circuit 6 receives a gain setting command from the communication control circuit 10, it sets the gain using the following series of steps. This command may be set to be issued at regular intervals, may be issued in response to a signal from some kind of detector (for example, one that detects environmental conditions such as temperature), or may be issued from an external device. It may be issued by manual operation by a person, and there are five different modes.

At this time, a predetermined optical signal having the same duty ratio as a signal used for communication is input to the semiconductor laser amplifier 2. This optical signal is set to be sent out from a light source such as an optical node using an optical amplification device or a system management device of an optical communication system. In any case, it is necessary to input the signal to the amplifier 2 as a predetermined signal at least at the time of gain control.

When the above command is input, the arithmetic circuit 6 monitors the optical output of the semiconductor laser amplifier 2 based on the output of the A/D converter 5 regarding the above predetermined signal. As a result of the comparison, the output data from the A/D converter 5 is equal to the value preset in the storage circuit 7. If it is found that there is a deviation from the laser diode, the arithmetic circuit 6 determines the amount and direction of the deviation, controls the drive circuit 10 through the D/A converter 8, and adjusts the gain of the semiconductor laser amplifier 2. Adjust its light output. This adjustment is performed so that the output data of the A/D converter 5 becomes equal to the value D0 preset in the storage circuit 7. When this adjustment is completed, the arithmetic circuit 6 sends a signal to the D/A converter 8 to hold the output of the D/A converter 8 at the value at the end of this adjustment, and the gain setting is completed. This is notified to the communication control circuit 10.

In this way, the output of the D/A converter 8 continues to be held until the next gain setting command is output from the communication control circuit 10. When gain setting commands are issued at predetermined intervals and this embodiment is used in an optical communication network system, the time interval between one setting and the next setting is sufficiently longer than the transmission time of discontinuous signals such as packet communication. Communication may be performed within this time interval.

In the first embodiment, the light receiving circuit 4 corresponds to light receiving means,
The arithmetic circuit 6 includes gain control means and gain holding means, forms part of the storage circuit 7 gain control means, and the communication control circuit 10
includes means for intermittently activating the gain control for the optical amplification section.

FIG. 2 is a block diagram showing a second embodiment.

In this embodiment, a semiconductor laser amplifier 2 is used as the optical amplification section, and the control means for controlling the gain of the optical amplification section and the means for maintaining the state after the control are configured by a hybrid of a digital circuit and an analog circuit. There is.

In FIG. 2, elements having the same functions as those in FIG. 1 are numbered the same as in FIG. First example and second example
The difference between the embodiments is that a comparator 11. which compares the output of the light receiving circuit 4 with a reference voltage. A reference voltage source 12 that provides a reference voltage to the comparator 11 and a counter 13 that provides a digital signal to the D/A converter 8 are provided to convert a part of the circuit into an analog version.

In the second embodiment, the communication control circuit 10 includes a comparator 11, a counter 13, a D/A converter 8, in addition to the functions of the first embodiment.
It has a function of controlling the gain of the optical amplifier 2 by controlling the gain of the optical amplifier 2.

Next, the operation of the second embodiment will be explained. The optical signal enters the semiconductor laser amplifier 2 via the optical fiber 1-1,
A part of the light output is sent to the light receiving circuit 4 by the optical splitter 3,
The remainder is sent out to optical fiber 1-2. The optical signal input to the light receiving circuit 4 is converted into an electrical signal and input to the comparator 11. A comparator 11 connects the output of the light receiving circuit 4 and the reference voltage source 1.
Compare the voltages of 2 and check the results (amount of deviation, direction of deviation, etc.)
is input to the communication control circuit 10. The communication control circuit lO inputs the counter 3 and the D/A converter 8 based on the output of the comparator 11.
The digital output of the counter 13 is sent to the D/A converter 8.
is man-powered. The output voltage of the reference voltage source 12 is set equal to the output voltage of the light receiving circuit 4 when the optical output of the semiconductor laser amplifier 2 reaches a predetermined value when the predetermined optical signal is input.

Gain setting of the semiconductor laser amplifier 2 is performed by the following procedure. At this time, 2 First, as in the first embodiment, a predetermined optical signal is input to the semiconductor laser amplifier 2.5 The communication control circuit 10 starts operating the counter 13, and while monitoring the pressure of the comparator 11, As the output current of the drive circuit 9 is gradually increased or decreased via the D/A converter 8, the output voltage of the light receiving circuit 4 increases (or decreases).
When the voltage exceeds or falls below the voltage of the reference voltage source 12, the output of the comparator 11 is turned on. At this time, the communication control circuit 10 stops the counter 13 and holds the output of the D/A converter 8 at the value at that time. In this way, as in the first embodiment, the gain of the semiconductor amplifier 2 is adjusted and the optical output is adjusted.

The other points are substantially the same as the first embodiment. In the second embodiment, the light receiving circuit 4 corresponds to the light receiving means, and the comparators 11. The reference voltage source 12 and the counter 13 form part of the gain control means, and the communication control circuit 10 forms part of the gain control means, the gain holding means, and the gain control means is intermittently activated for the optical amplification section. including the means to

FIG. 3 is a block diagram showing a third embodiment of the present invention.

In this embodiment, an optical fiber amplifier 14 is used as the optical amplification section, and the control means for controlling the gain of the optical amplification section and the means for maintaining the state after the control are constituted by digital circuits. In FIG. 3, blocks having the same functions as those in FIG. 1 are numbered the same as in FIG. A light emitting circuit 15 including a light source for exciting and driving the amplifier 14 and an optical combiner 16 for joining the output light from the light emitting circuit 5 to the optical fiber amplifier 14 are provided. be. The gain of the optical fiber amplifier 14 is controlled by the output light of the light emitting circuit 15, and this gain control procedure is performed in the same manner as described in the first embodiment of the present invention.

By the way, the above embodiment is just an example, and f! Various changes are possible.

If the control means for controlling the gain of the optical amplifier using the output from the light receiving means and the means for maintaining the state after controlling the gain of the optical amplifier have the same function as in the above embodiment, Any configuration consisting of a digital circuit, an analog circuit, or a hybrid thereof may be used. In addition, the application of optical amplification equipment is not limited to optical communication networks, but also in other optical transmission systems, where it is effective when there are discontinuous optical signals on the optical transmission path or when the modulation speed of the optical signal changes. Can be used for

[Effects of the Invention] As explained above, according to the present invention, an optical amplifier used in an optical communication network etc. includes a gain control means for controlling the gain of the optical amplifier based on the output from the light receiving means;
means for maintaining the gain of the optical amplifier in the controlled state;
Since a means is provided for causing the gain control means to act on the optical amplifier intermittently so as to intermittently update this maintained gain state, intermittent AGC of the optical amplifier becomes possible, and the transmission line An optical amplification device with stable optical output that can be used even in networks where signals are discontinuously distributed or where the signal modulation speed changes is realized.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the first embodiment of the present invention, Fig. 2 is a block diagram of the second embodiment, Fig. 3 is a block diagram of the third embodiment, and Fig. 4 is a block diagram of the conventional example. . 1-1.1-2...Optical fiber, 2...
Semiconductor laser amplifier, 3... Optical splitter, 4...
...Light receiving circuit, 5...A/D converter, 6...
・Arithmetic circuit, 7...Memory circuit, 8...D/
A converter, 9... Drive circuit, 10... Communication control circuit, 11... Comparator, 12... Reference voltage source 13... Counter, 14... Optical fiber amplifier, 15... Light emitting circuit, 16... Optical combiner

Claims (1)

[Scope of Claims] 1. An optical amplifying section, means for receiving a part of the optical output of the optical amplifying section, and means for controlling the gain of the optical amplifying section based on the output from the light receiving means; means for maintaining the state after controlling the gain of the optical amplifying section; and means for causing the gain control means to act on the optical amplifying section intermittently so as to intermittently update the maintained gain. An optical amplification device comprising: 2. The optical amplifying device according to claim 1, further comprising means for intermittently inputting a predetermined optical signal to the optical amplifying section in accordance with the operation of the optical amplifying section by the gain control means. 3. The optical amplification device according to claim 1, wherein the gain control means and the gain holding means are constituted by digital circuits. 4. The optical amplification device according to claim 1, wherein the gain control means and the gain holding means are constructed by a hybrid of digital and analog circuits.