JPH11135863A - Fiber optic amplifier - Google Patents

Abstract

(57) [Problem] To provide an optical fiber amplifier having a constant amplification degree even if a wavelength signal is missing or added so as to be practical for wavelength multiplex transmission. The present invention is capable of amplifying a signal without increasing output fluctuation when optical fiber amplifiers are connected in multiple stages, and is also capable of preventing loss or addition of wavelength signal light which may occur during wavelength division multiplexed optical transmission. Since the amplification degree can be kept constant, an optical fiber amplifier suitable for stable wavelength multiplex transmission can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier for directly amplifying signal light using an optical fiber for optical amplification, and more particularly to an optical fiber amplifier suitable for wavelength division multiplex transmission, which is a communication system using a plurality of wavelengths.

[0002]

2. Description of the Related Art FIG. 4 shows a block diagram of a conventional optical fiber amplifier. Regarding the configuration of the conventional optical fiber amplifier, 30 is an optical splitter, 31 is an optical fiber for amplification (EDF), 32 is an optical splitter, 33 is an input light monitor, 34 is a semiconductor laser for excitation, 35 is a drive circuit, 3
6 is an output light monitor, 37 is a comparator, 38 is a fixed target value, and 39 is a switch. The input signal light is supplied to the drive circuit 35.
The pumping light is injected into the pumping optical fiber 31 together with the pumping light generated by the pumping semiconductor laser 34 driven by the laser, and is output as an output signal light amplified according to the optical power of the pumping light. Although the output of the optical fiber amplifier fluctuates due to a change in the pumping light of the pumping semiconductor laser 34 due to a temperature change or an aging change, control for keeping the output constant (constant output control) or keeping the signal amplification constant. Control (constant amplification degree control) is required. In order to perform the constant output control, the switch 39 is set to the constant output control so that the output light monitor signal is compared with a target value which is a fixed value, and the excitation semiconductor laser 34 is driven by the error signal to realize the control. Have been. Further, the switch 39 is set to control the amplification degree to a constant value, the signal of the input light monitor is set as a target value, the signal of the output light monitor is compared with the target value, and the excitation semiconductor laser 34 is driven by the error signal. Is realized.

[0003]

As described above, in the conventional optical fiber amplifier, the total power ratio of the input signal light and the output signal light is controlled to be constant in order to control the amplification degree to be constant. Was. Although it is also used for wavelength multiplexing transmission using multiple wavelengths, the input signal light is originally assumed to be a signal of one wavelength, which is the conventional communication method, and the target value is the input signal light, so the optical fiber amplifier However, there is a problem in that when a plurality of stages are connected in series and used, the amplification degree fluctuations are accumulated. That is, when the amplification degree fluctuation is ± 0.1 dB per one unit, the output fluctuation at the fifth unit is accumulated in the optical communication network in which five units are connected in series, and ± 5 dB.
0.5 dB. In the conventional output constant control, the target value is fixed, so that no matter how many units are connected in series, accumulation of power fluctuation does not occur. However, if a wavelength signal is dropped or added in the case of a wavelength division multiplexing communication system using multiple wavelengths, the output signal level of other wavelength signals will be affected in order to perform constant output control, and transmission will be performed. Was making an error. Therefore, the present invention solves such a problem, and even if a plurality of optical fiber amplifiers are connected in series, the output fluctuation is minimized without increasing the output fluctuation, and a wavelength that can be practically used for wavelength division multiplexing transmission. An object of the present invention is to provide an optical fiber amplifier having a constant amplification degree even when a signal is missing or added.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and an optical fiber amplifier for amplifying signal light by supplying pumping light from a pumping light supply means to an optical amplification optical fiber. An input light monitor for monitoring the previous input signal light, an output light monitor for monitoring the amplified output signal light, and an input immediately after the change when the input signal light detected by the input light monitor changes by a certain range or more. A sample-and-hold circuit that samples and holds the signal light, and a comparison unit for comparing the target value and the output signal light detected by the output light monitor with the sample data held by the sample-and-hold circuit as a target value. And the pump light supply means so as to reduce the difference between the output signal light and the target value compared by the comparison means. Providing an optical fiber amplifier for controlling et excitation light.

[0005]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an optical fiber amplifier according to an embodiment of the present invention, FIG. 2 is a detailed block diagram of a signal level detection circuit used in FIG. 1, and FIG. FIG. 3 is a diagram illustrating an operation when multiplexed signal light is used. In the optical fiber amplifier of the present invention shown in FIG. 1, 1 is an input signal light, 2 is an optical splitter, 3 is an optical amplification optical fiber (EDF), 4 is an optical multiplexer, 5 is an optical splitter, 6 is an output signal light, Reference numeral 7 denotes an input light monitor, 8 denotes a pumping semiconductor laser, 9 denotes an output light monitor, 10 denotes a laser drive circuit, 11 denotes a signal level detection circuit, 12 denotes a sample and hold circuit, and 13 denotes a comparator.

The operation will be described with reference to FIGS. The pumping light from the pumping semiconductor laser 8 is supplied to the optical amplification optical fiber (EDF) 3, and the input signal light 1 input to the optical amplification optical fiber 3 is amplified. It has an input light monitor 7 for monitoring the input signal light 1 of the optical fiber for amplification 3 before amplification, and an output light monitor 9 for monitoring the output signal light 6 after amplification. The input signal light 1 is a signal level detection circuit 1
When a change exceeding the range set in 1 is detected, a sample pulse is output from the signal level detection circuit 11, and the data of the input signal light 1 immediately after this change is sampled and held in the sample hold circuit 12.

Further, the sampled and held value is input to a comparator 13 as a new target value, compared with an output signal light 6 detected by an output light monitor 9, and an excitation semiconductor laser is generated by an error signal based on the comparison result. 8 is controlled. The signal level detection circuit 11 and the sample hold circuit 12 always operate, and the target value is updated when a change in the input signal level is detected, so that the output signal light 6 changes stepwise according to the input signal light 1. It has a changing configuration. In the sample-and-hold state, the output signal light 6 becomes constant regardless of the state of the input signal 1, and the output fluctuation does not accumulate regardless of how many units are connected in series.

In the signal level detection circuit 11 shown in FIG.
20 is an input light monitor signal, 21 is a window comparator, 22 is a sample and hold circuit, 23 is a sample and hold signal, 24 is a variable resistor (VR1), and 25 is a variable resistor (VR2). The operation will be described with reference to FIG.

The window comparator 21 has an input light change detection range set therein.
Is exceeded, a sample pulse is output. The sample hold circuit 22 samples and holds the input optical monitor signal 20 according to the sample pulse. Since the change detection range of the window comparator 21 is created from the sample hold signal 23, the change detection range is updated every time the sample hold signal 23 is updated. The change detection range is set to VR1 (24), VR2 (2
Perform using 5).

FIG. 3 is a diagram for explaining the operation of the signal level detection circuit when wavelength multiplexed signal light is used. An example in which one wavelength light is missing from the four wavelength signal light and the wavelength becomes three wavelengths will be described. The input monitor output at the time of inputting four wavelengths is larger than that at the time of inputting three wavelengths. By monitoring the input monitor output, the loss of one wavelength can be detected. The input monitor output signal is compared by the window comparator 21 shown in FIG. 2. When a loss of one wavelength signal is detected, a sample pulse is output to sample and hold the input signal light, and a sample hold signal is generated.

For example, when the input monitor output is ± 0.5 dB
Even if there is a degree of fluctuation, the sample-and-hold signal is a signal without fluctuation. This sample hold signal is used as the target value of the comparator 13 described with reference to FIG.

[0012]

As described above, according to the present invention, when optical fiber amplifiers are connected in multiple stages, signal amplification can be performed without increasing output fluctuations. Therefore, since the degree of amplification can be kept constant, an optical fiber amplifier suitable for stable wavelength division multiplexing transmission can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical fiber amplifier according to an embodiment of the present invention.

FIG. 2 is a detailed block diagram of a signal level detection circuit used in FIG.

FIG. 3 is a diagram illustrating an operation when a wavelength multiplexed signal light is used in the optical fiber amplifier of the present invention.

FIG. 4 is a block diagram of a conventional optical fiber amplifier.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 input signal light 2 optical splitter 3 optical amplification optical fiber (EDF) 4 optical multiplexer 5 optical splitter 6 output signal light 7 input optical monitor 8 excitation semiconductor laser 9 output optical monitor 10 laser drive circuit 11 signal level detection circuit 12 Sample hold circuit 13 Comparator

Claims (3)

[Claims] 1. An optical fiber amplifier for amplifying signal light by supplying pumping light from a pumping light supply means to an optical fiber for optical amplification, an input light monitor for monitoring input signal light before amplification, and an output signal light after amplification. An output light monitor that monitors the input signal light, a sample and hold circuit that samples and holds the input signal light immediately after the change when the input signal light detected by the input light monitor changes beyond a certain range, and that is held by the sample and hold circuit. A comparison unit for comparing the target value with the output signal light detected by the output light monitor, using the sample data as a target value, and comparing the output signal light and the target value compared by the comparison unit. An optical fiber amplifier which controls excitation light from the excitation light supply means so as to reduce the difference. 2. The input signal light has a wavelength multiplexed optical transmission signal characteristic, and when a change in signal light power with respect to loss or addition of one wavelength signal light or a plurality of wavelength signal lights is detected by an input light monitor, The optical fiber amplifier according to claim 1, wherein the target value is updated by holding sample data to obtain the target value. 3. The optical fiber amplifier according to claim 1, wherein said target value is updated by holding sample data based on an external control command.