JP2000349718A - Optical fiber amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical fiber amplifier where constant gain control is attained independently of number of input channels and that employs a rear- earth group added optical fiber. SOLUTION: The optical fiber amplifier is provided with an optical switch 4, a natural emission amplification light level storage circuit 12 that stores output voltage from an output power measurement means 25 when the output power measurement means 25 receives only an ASE light with the optical switch 4 turned off, and a signal light output arithmetic circuit that subtracts a voltage stored in the natural emission amplification light level storage circuit 12 from the output voltage of the output power measurement means 25 when the output power measurement means 25 receives both a signal light and the ASE light with the optical switch 4 turned on and provides an output of the result to a gain constant control circuit.

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, and more particularly, to a method for making a gain uniform between input and output over each wavelength channel when used as a linear repeater in a wavelength division multiplexing type optical repeater transmission system. The present invention relates to an optical fiber amplifier using a rare earth-doped optical fiber.

[0002]

2. Description of the Related Art When an optical fiber amplifier is used as a linear repeater in an optical repeater transmission system of the wavelength division multiplex system, it is required that gain between input and output is uniform over each wavelength channel. Since the gain flatness of an optical fiber amplifier depends on the gain of an optical fiber doped with a rare earth as a gain medium, a control method that keeps the gain of the optical fiber amplifier constant to secure the gain flatness is used. There is a need to do.

In a conventional type optical fiber amplifier, as shown in FIG. 4, as a method of measuring a gain, a total power over a wavelength band of all channels is measured at an input portion, and a wavelength band of all channels is similarly measured at an output portion. The total power over the range is measured to determine the ratio between the two. By controlling the pumping light source to keep this ratio constant, it is possible to keep the gain of the optical fiber amplifier constant.

However, in this method, not only the total power of the signal light but also the total power including the spontaneous emission amplified light (ASE light) added by the optical fiber amplifier is measured. In a changing wavelength division multiplexing system, the ratio of the ASE optical power to the change in the number of input channels differs,
It was not possible to make the gain exactly constant for each number of input channels.

[0005] This operation will be described with reference to FIGS. 4 and 5. FIG. 5 shows, by way of example, the relationship between the optical spectrum of the input unit receiving light by the photodiode 2 and the optical spectrum of the output unit receiving light by the photodiode 10 when the number of input channels is reduced from a plurality of channels to one channel. When the number of input channels is reduced, as shown in FIG. 5, the input signal light level and the noise light level hardly change, and the received light power at the photodiode 2 is equal to the sum of the signal light and noise light channels. Become. In the case of the output light, if the signal light power is unchanged, the ASE light level hardly changes even if the number of channels changes.
Then, the sum of the amplified signal light power of each channel and the AS
The sum of the E light powers is monitored. When the ratio between the output monitor value and the input monitor value is calculated, it is determined that the smaller the number of channels, the greater the effect of ASE per channel and the gain is increased. 6 is controlled. As a result, when the number of channels decreases, the signal light gain per channel decreases as shown in FIG.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to add a rare-earth element capable of performing constant gain control independent of the number of input channels. To provide an optical fiber amplifier using an optical fiber.

[0007]

To achieve the above object, an optical fiber amplifier according to the present invention comprises: an optical switch for turning on / off an input to an optical fiber doped with rare earth; and an optical switch for turning off the optical switch. A spontaneous emission amplified light level holding circuit for storing the output voltage from the output power measuring means when the input to the output power measuring means is only ASE light; and turning on the optical switch to the output power measuring means. A signal light output operation circuit for subtracting the voltage stored in the spontaneous emission amplified light level holding circuit from the output voltage of the output power measuring means when both the signal light and the ASE light are input, and outputting the result to the constant gain control circuit And characterized in that: With this configuration, the optical switch is momentarily turned off to shut off the signal light input, and the ASE light power input to the photodiode while the light switch is off is stored in the spontaneous emission amplified light level holding circuit. If the time during which the optical switch is turned off is set sufficiently shorter than the life of the rare-earth ions (about several tens of μs), the input to the photodiode is almost the same as the ASE light level when a signal is being input. The ASE level at the time of signal light input can be measured. The output power measuring means monitors the sum of the amplified input signal light and the ASE added by the present optical fiber amplifier.
By removing the E level, it is possible to monitor the output power of only the amplified input signal light, and control the ratio of the output power to the input light monitor value so as to be constant.
Constant gain control that does not include a light component becomes possible.

In addition, an optical switch driving circuit for controlling ON / OFF of the optical switch and outputting the timing at which the optical switch is turned OFF to the spontaneous emission amplified light level holding circuit is added thereto. Switch is O
The operation can be facilitated by storing the ASE light power input to the output power measuring means while the FF is used.

Further, after the output unit, a second rare-earth-doped optical fiber and a second power for measuring the total power of all channels obtained by partially branching and photoelectrically converting the output signal light output from the optical fiber. Output power measuring means, a second pumping light source for pumping the optical fiber, and a subsequent stage based on the pumping light source based on the optical power output from the signal light output operation circuit and the output optical power of the second optical fiber. A second gain-constant control circuit for controlling the gain of only the section to be constant, and the second output when the optical switch is turned off so that the input to the output power measuring means is only ASE light. A second spontaneous emission amplified light level holding circuit for storing the output voltage from the power measuring means;
The voltage stored in the second spontaneous emission amplified light level holding circuit is subtracted from the output voltage of the second output power measuring means when both the signal light and the ASE light are input to the output power measuring means when N is set to N. Then, by adding a second signal light output operation circuit for outputting to the second constant gain control circuit, the method of the present invention can be used even when it is desired to use the method of the present invention as a two-stage configuration.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing the configuration of the first embodiment of the present invention, and FIG. 2 is an explanatory diagram of the operation of the first embodiment. As shown in FIG. 1, the optical fiber amplifier according to the present invention has a conventional optical fiber amplifier in which the input to the optical fiber 8 is O.
N / OFF optical switch 4 and optical switch 4 OFF
Then, the spontaneous emission amplified light level holding circuit 12 for storing the output voltage from the output power measuring means 25 when the input to the output power measuring means 25 is only ASE light, and the optical switch 4 are turned on. A constant gain control circuit is obtained by subtracting the voltage stored in the spontaneous emission amplified light level holding circuit 12 from the output voltage of the output power measuring means 25 when both the signal light and the ASE light are input to the output power measuring means 25. And a signal light output operation circuit 13 for outputting the signal light to the signal light output operation circuit 14. In the embodiment of the present invention, a photodiode and an I / V conversion circuit are used as output power measuring means, and an optical fiber doped with erbium is used as an optical fiber.
Further, an optical switch driving circuit 5 for controlling ON / OFF of the optical switch 4 and outputting a timing at which the optical switch 4 is turned OFF to the spontaneous emission amplified light level holding circuit 12 is added.
The optical switch of the spontaneous emission amplification light level holding circuit 12
ASE input to output power measuring means 25 while F
Light power was stored.

The optical fiber amplifier according to the present embodiment configured as described above operates as follows. A part of the wavelength division multiplexed signal light input to the optical fiber amplifier of the present invention is branched by the optical coupler 1 for monitoring.
FIG. 2A schematically shows a case where signal light of 2 ch is input as an example of an optical spectrum of a signal branched at the input unit. In the linear repeater, there is a noise light component generated in the preceding linear repeater in addition to the signal light component. This spectrum component is detected by the input monitor, is also optically amplified by the erbium-doped optical fiber, and is detected by the output power measuring means 25 as the sum of the ASE component generated by the erbium-doped optical fiber (see FIG. 2 (b)). (See when the switch is ON.)

When the gain is obtained by taking the ratio of the input monitor and the output monitor, the ASE component generated in the erbium-doped optical fiber becomes an error factor. Since the contribution of the ASE component increases as the number of input channels decreases, the gain changes as the number of channels changes. In the configuration of FIG. 1, the optical switch is momentarily (approximately several tens of μs) turned off when a system is constructed by mounting an optical fiber amplifier on the device, and the voltage from the output power measuring means 25 is synchronized with the timing signal. Is stored in the spontaneous emission amplification light level holding circuit 12, so that the power of the ASE component added by the erbium-doped optical fiber is measured and stored (see the optical switch OFF state in FIG. 2B).

Since the output power measuring means 25 monitors the sum of the amplified input light power and ASE light power, the power of the ASE component stored in the spontaneous emission amplified light level holding circuit 12 is removed therefrom. The output level obtained by multiplying the input power by a gain can be monitored. A true gain is obtained by comparing the output monitor value and the input monitor value, and a constant gain control is performed by controlling the current value of the pump light source 6 so that the gain becomes constant. Therefore, even in a wavelength division multiplexing system in which the number of input channels changes, constant gain control independent of the number of input channels can be realized.

Next, the operation of another embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a configuration diagram showing the configuration of the second embodiment of the present invention. This example is a configuration example in which the optical fiber amplifier has a two-stage configuration of a front stage and a rear stage. In the optical fiber amplifier having the configuration of the first embodiment of the present invention in the front stage, the second stage is also provided in the rear stage. A second output power measuring means 26 for measuring the total power of all the channels obtained by partially splitting and photoelectrically converting the output signal light output from the optical fiber at the preceding stage, Second excitation light source 15 for exciting an optical fiber
And controlling the pumping light source such that the gain of only the rear part becomes constant based on the optical power output from the signal light output operation circuit 13 of the former part and the output light power of the second optical fiber. Gain constant control circuit 23 and optical switch 4
Is turned off to store the output voltage from the second output power measuring means 26 when the input to the second output power measuring means 26 is only ASE light. The holding circuit 21 and the optical switch 4
N to the second output power measuring means 26
The voltage stored in the second spontaneously amplified light level holding circuit 21 is subtracted from the output voltage of the second output power measuring means 26 when both of the E light are input, and the second gain is obtained. A second signal light output operation circuit 22 for outputting to the constant control circuit 23 is added. By using the configuration of the present invention as in the present embodiment, the present invention can be applied even when it is desired to use a two-stage configuration.

[0015]

The optical fiber amplifier according to the present invention includes an optical switch, a spontaneous emission amplified light level holding circuit, and a signal light output operation circuit, and measures an ASE component generated in the optical fiber portion at the time of initial introduction. By removing the ASE component which is stored and superimposed by calculation, it is possible to control the gain to be constant even when the number of channels changes. Also, by providing an optical switch drive circuit,
The ON / OFF timing of the optical switch can be controlled in accordance with the spontaneous emission amplification light level holding circuit. Further, after the output section, a second rare-earth-doped optical fiber and a second output power measurement for measuring the total power of all channels obtained by partially branching and photoelectrically converting the output signal light output from the optical fiber Means, a second constant gain control circuit, a second pumping light source, a second spontaneous emission amplified light level holding circuit, and a second signal light output operation circuit, thereby making the method of the present invention possible. It can also be used when it is desired to use a two-stage configuration.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram of an operation of the first embodiment of the present invention.

FIG. 3 is a configuration diagram illustrating a configuration of an optical fiber amplifier according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram showing a configuration of a conventional optical fiber amplifier.

FIG. 5 is an explanatory diagram of an operation of a conventional optical fiber amplifier.

[Explanation of symbols]

1. Optical coupler 1 2. Photodiode 1 3. 3. I / V conversion circuit 1 Optical switch 5. Optical switch drive circuit 6. Excitation light source 7. WDM coupler 8. 8. Erbium-doped optical fiber Optical coupler 2 10. Photodiode 2 11. I / V conversion circuit 2 12. 12. Spontaneous emission amplification light level holding circuit 13. Signal light output operation circuit Constant gain control circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/04

Claims (3)

[Claims] 1. An optical fiber for amplifying an input signal light by adding a rare earth element, and an input power measuring means for measuring a total power of all channels by partially branching and photoelectrically converting an input signal light input to the optical fiber. Output power measuring means for measuring the total power of all channels by partially splitting and photoelectrically converting the output signal light output from the optical fiber, an excitation light source for exciting the optical fiber, and the excitation light source An optical fiber amplifier comprising: a gain constant control circuit for controlling a gain to be constant based on an input optical power and an output optical power of an optical fiber, wherein an optical switch for turning on / off an input to the optical fiber; A spontaneous emission amplified light level holding circuit for storing an output voltage of the output power measuring means when the optical switch is turned off; A signal light output arithmetic circuit for subtracting the voltage stored in the spontaneous emission amplified light level holding circuit from the output voltage of the output power measuring means when the light recording switch is turned on and outputting the result to the constant gain control circuit. An optical fiber amplifier, comprising: 2. An optical fiber amplifier according to claim 1, wherein said optical switch drive circuit controls ON / OFF of said optical switch and outputs a timing at which said optical switch is turned OFF to said spontaneous emission amplified light level holding circuit. Prepared,
The optical fiber amplifier, wherein the spontaneous emission amplified light level holding circuit stores an output voltage of the output power measuring means during the time. 3. The optical fiber amplifier according to claim 1, wherein a second optical fiber doped with a rare earth element and a signal light output from the optical fiber are partially branched after the output section. Second output power measuring means for measuring the total power of all channels obtained by photoelectric conversion, a second excitation light source for exciting the optical fiber,
A second gain constant control circuit for controlling the pump light source so that the gain is constant based on the optical power output from the signal light output operation circuit and the output optical power of the second optical fiber; A second memory for storing an output voltage from the second output power measuring means when the switch is turned off.
Spontaneous emission amplified light level holding circuit and optical switch ON
The second signal output from the second spontaneous emission amplified light level holding circuit by subtracting the voltage stored in the second spontaneous emission amplified light level holding circuit from the output voltage of the second output power measuring means at the time of An optical fiber amplifier comprising an optical output operation circuit.