JPH06252486A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE:To make a bidirectional excitation method of a high performance possible at a low cost, by so controlling the outputs of first and second excitation lights based on the output of a monitoring part that the output or gain of an amplified light is kept constant, and by making the excitation lights highly reliable. CONSTITUTION:When the output of one of first or second excitation light is reduced, the controlling part of a means 6 for driving excitation light sources so controls the other excitation light that its output is increased. Thereby, since the outputs of third and fourth excitation lights are made constant, the excitation state of an amplifying optical fiber continues to be stable. Therefore, the output or gain of an amplified light is kept constant by virtue of the highly reliable excitation lights, and the long-term reliability of an optical fiber amplifier 1 can be improved. Also, since the third and fourth excitation lights branched by an optical mixing/branching device 4 have equal intensities to each other, even when the output of the first or second excitation light is varied, the states of the excitations applied to the amplifying optical fiber 1 from both its sides are balanced with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional pumping type optical fiber amplifier, and more particularly to high performance and high reliability of optical amplification.

[0002]

2. Description of the Related Art Conventionally, in an optical fiber amplifier, a plurality of pumping light sources are used in order to improve long-term reliability which is affected by a reduction or deterioration in output of pumping light generated from a semiconductor laser mainly used as a pumping light source. Has redundancy.

FIG. 2 is a block diagram showing an optical fiber amplifier of an optical switch system. Only one of the excitation lights generated from the excitation light sources 5a and 5b by the excitation light source driving device 6 is incident on the optical multiplexer 2 by the optical switch 8 and is incident on one end of the amplification optical fiber 1 by the optical multiplexer 2 to be amplified. The optical fiber 1 for excitation is excited. The signal light input from the input end passes through the optical isolator 3a, is multiplexed with the pumping light by the optical multiplexer 2, enters the amplification optical fiber 1, is amplified by the amplification optical fiber 1, and is amplified by the optical isolator 3b. And is output from the output end. When the output of the pumping light generated from one pumping light source entering the optical multiplexer 2 decreases, the optical switch 7 is switched by the control of the optical switch driving device 8, so that the pumping light generated from the other pumping light source is optically multiplexed. It can be switched to be incident on the vessel 2.

FIG. 3 is a block diagram showing a polarization combining type optical fiber amplifier. The pumping light generated from the pumping light sources 5a and 5b by the pumping light source driving device 6 retains polarization by the polarization-maintaining optical fibers 10a and 10b, and the polarization combiner 9 is used.
Incident on the optical multiplexer 2 and combined by the polarization combiner 9
To the one end of the amplification optical fiber 1 by the optical multiplexer 2 to excite the amplification optical fiber 1. The signal light input from the input end passes through the optical isolator 3a, is multiplexed with the pumping light by the optical multiplexer 2, enters the amplification optical fiber 1, is amplified by the amplification optical fiber 1, and is amplified by the optical isolator 3b. And is output from the output end.
When the output of the pumping light generated from one pumping light source decreases, the output of the pumping light generated from the other pumping light source can be increased by controlling the light source drive device 6.

FIG. 4 is a block diagram showing a conventional bidirectional pumping type optical fiber amplifier. The pumping light generated by the pumping light source driving device 6 from the pumping light sources 5a and 5b is incident on the optical multiplexers 2a and 2b, respectively, and is incident on one end and the other end of the amplification optical fiber 1 by the optical multiplexers 2a and 2b, respectively. The optical fiber 1 for amplification is excited bidirectionally. The signal light input from the input end passes through the optical isolator 3a, is multiplexed with the excitation light by the optical multiplexer 2a, is incident on the amplification optical fiber 1, and is amplified by the amplification optical fiber 1 to be combined with the optical multiplexer. It is output from the output end after passing through 2b and the optical isolator 3b. The bidirectional pumping type optical fiber amplifier is superior to the pumping type optical fiber amplifiers shown in FIGS. 2 and 3 in terms of good noise characteristics and high conversion efficiency.

The above-mentioned prior art is disclosed in Japanese Patent Laid-Open No. 4-16533.
No. 4 publication and "Paper WeP 2.7, p493.
~ 496, ECOC (1992) "and the like.

[0007]

However, in the above optical switch type optical fiber amplifier, the only optical switch with a small insertion loss is a type that mechanically switches pumping light, and the switching time has a lower limit of about 10 msec. Therefore, there is a problem that the pumping light is momentarily interrupted, and the reliability of the mechanical optical switch itself is low.

Further, in the above polarization synthesizing type optical fiber amplifier, since it is necessary to maintain the polarization from the pumping light source to the polarization synthesizing device to transmit the pumping light, the optical system is considered in consideration of the alignment of the polarization plane. However, there is a problem in that the assembling cost becomes high and that the polarization combiner itself requires expensive optical parts such as polarization prims.

Further, in the above-described conventional bidirectional pumping type optical fiber amplifier, when the output of the pumping light generated from the pumping light source is reduced or deteriorated, it becomes substantially forward pumping or backward pumping and noise characteristics and conversion. Since the characteristics change, there is a problem that it becomes difficult to keep the output or gain of the signal light constant or the noise performance.

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an optical fiber amplifier which realizes a high-performance bidirectional pumping system at a low cost with highly reliable pumping light. To aim.

[0011]

In order to achieve the above object, an optical fiber amplifier of the present invention comprises a first pumping light source for generating a first pumping light and a second pumping light for generating a second pumping light. Two
And an optical multiplexer / demultiplexer that multiplexes the first and second excitation lights and splits the third and fourth excitation lights.
A first optical multiplexer for multiplexing the signal light and the third pump light;
A second optical multiplexer for multiplexing the signal light and the fourth pump light,
Third pumping light that is incident in the same direction as the signal light from one end via the first optical multiplexer, and fourth pumping light that is incident in the opposite direction to the signal light from the other end via the second optical multiplexer. An optical fiber for amplification which is excited by and which amplifies the signal light incident from one end via the first optical multiplexer and emits the amplified light from the other end via the second optical multiplexer; A monitor unit that monitors the outputs of the first and second pumping lights, and a control that controls the outputs of the first and second pumping lights based on the output of the monitor unit so as to keep the output or gain of the amplified light constant. And a section.

The third and fourth excitation lights preferably have the same light intensity.

Further, it is preferable that the monitor section further monitors the output or gain of the amplified light.

[0014]

According to the present invention, the first and second pumping lights emitted from the first and second pumping light sources respectively enter the optical multiplexer / demultiplexer, are combined by the optical multiplexer / demultiplexer, and are further combined into the third and the third. It is split into four excitation lights. The third pump light is incident on the first optical multiplexer, and is incident on one end of the amplification optical fiber by the first optical multiplexer to excite the amplification optical fiber. On the other hand, the fourth pump light is incident on the second optical multiplexer, and is incident on the other end of the amplification optical fiber by the second optical multiplexer to excite the amplification optical fiber.
The signal light input from the input end is incident on the first optical multiplexer, is combined with the first pump light by the first optical multiplexer, and is incident on one end of the amplification optical fiber. This signal light is amplified by the amplification optical fiber, is incident on the second optical multiplexer as amplified light, is emitted in the opposite direction to the third pumping light by this second optical multiplexer, and is output from the optical fiber amplifier. It is output from the end. Here, the outputs of the first and second pumping lights are monitored by the monitor, and are controlled by the controller based on the output of the monitor, so that the output or gain of the amplified light is kept constant.

Therefore, when the output of one of the first and second pumping lights is lowered, the output or gain of the amplified light is lowered, so that the control unit controls the output of the other pumping light to rise. Therefore, the outputs of the third and fourth pumping lights are constant and the pumping state of the amplifying optical fiber by the pumping light is stable, so that the output or gain of the amplified light is held constant.

Further, according to the present invention, since the third and fourth pump lights are branched by the optical multiplexer / demultiplexer so as to have the same light intensity, the amplification optical fiber is equally excited in both directions. Therefore, even if the output of the first or second pumping light fluctuates, the intensities of the third and fourth pumping lights are always equal by the optical multiplexer / demultiplexer, so that the pumping states in both directions in the amplification optical fiber are balanced. Hold. Therefore, the noise characteristics of the amplified light are good and the conversion characteristics are high.

Further, according to the present invention, since the monitor section directly monitors the output or gain of the amplified light in addition to the outputs of the first and second pumping lights, the control section is based on the output of this monitor section. Controls the outputs of the first and second excitation lights. Therefore, the output or gain of the amplified light is more accurately kept constant.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and operation of one embodiment of the present invention will be described below with reference to FIG. 1 of the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a bidirectional pumping type optical fiber amplifier according to the present invention.
The pumping light sources 5a and 5b are semiconductor lasers that generate pumping light having a wavelength of 1.48 μm, and are provided with a PD (photodiode) for monitoring a light output thereof. The pumping light source driving device 6 drives the two pumping light sources 5a and 5b respectively, a monitor unit that monitors the output current of the optical output monitor PD provided in each pumping light source 5a and 5b, and the output of the monitor unit. And a control unit for controlling the drive circuit based on the above. The optical multiplexer / demultiplexer 4 has an insertion loss of 3d.
The coupler B is composed of a melt-stretching type fiber coupler that combines the pumping lights from the pumping light sources 5a and 5b and branches them into two pumping lights having the same intensity. Optical multiplexer 2a,
2b is a WDM (wavelength division multiplexing) coupler having a wavelength of 1.
It is composed of a melt-stretching type fiber coupler that combines the excitation light of 48 μm and the signal light of wavelength 1.55 μm. The amplification optical fiber 1 is an Er-doped quartz fiber that amplifies signal light having a wavelength of 1.55 μm by stimulated emission of Er excited by excitation light having a wavelength of 1.48 μm. The optical isolators 3a and 3b are polarization independent optical isolators that remove reflected return light, and are arranged between the incident end and the optical multiplexer 5a, and between the optical multiplexer 5b and the output end.

Next, the operation of the embodiment shown in FIG. 1 will be described. First, the control unit of the excitation light source driving device 6 controls the drive circuit to turn on only one of the excitation light sources 5a and 5b, for example, the excitation light source 5a. The monitor unit of the excitation light source drive device 6 monitors the output current from the optical output monitor PD of the excitation light source 5a, and the control unit controls the drive current of the excitation light source 5a so that this becomes a predetermined value. .
The other pumping light source 5b remains in the OFF state. Hereinafter, this is referred to as a first initial state.

Wavelength 1.48μ generated from excitation light source 5a
The pumping light of m is incident on the optical multiplexer / demultiplexer 4, is branched into pumping light of the same intensity, and is incident on the optical multiplexers 2a and 2b, respectively. The excitation light emitted from the optical multiplexer 2a enters the left end of the amplification optical fiber 1 and excites the rare earth element Er. On the other hand, the excitation light emitted from the optical multiplexer 2b is incident on the right end of the optical fiber amplifier 1 to excite the rare earth element Er. In this state, the signal light having a wavelength of 1.55 μm input from the input end passes through the optical isolator 3a and passes through the optical multiplexer 3a.
And is combined with excitation light having a wavelength of 1.48 μm. The signal light emitted from the optical multiplexer 2a enters the left end of the amplification optical fiber 1 and is amplified by stimulated emission of excited Er. Wavelength of 1.55 μm emitted from amplification optical fiber 1
The amplified light is incident on the optical multiplexer 2b and has a wavelength of 1.48 μm.
Is emitted in the direction opposite to the excitation light of. The amplified light emitted from the optical multiplexer 2b passes through the optical isolator 3b and is output from the output end.

In the first initial state, when the output of the pumping light from the pumping light source 5a decreases with respect to the driving current within the rated value, the monitor unit of the pumping light source driving device 6 causes the optical output monitor of the pumping light source 5a. The decrease of the output current from the PD for use in the vehicle is detected.
The control unit of the pumping light source driving device 6 determines that the pumping light source 5a has deteriorated due to the output of the monitor unit, and controls the driving circuit to turn the pumping light source 5a off and the pumping light source 5b on. The monitor unit of the pumping light source driving device 6 monitors the output current from the optical output monitoring PD of the pumping light source 5b, and the control unit controls the driving current of the pumping light source 5b so that this becomes a predetermined value. . Therefore, the pumped state of the amplification optical fiber 1 becomes stable regardless of the output deterioration of the pumping light source 5a, and the gain of the amplified light is held constant.

The initial state may be different from the above. The control unit of the excitation light source driving device 6 controls the driving circuit,
Both the excitation light sources 5a and 5b are turned on. The monitor unit of the pumping light source driving device 6 monitors the output currents from the optical output monitoring PDs of the pumping light sources 5a and 5b so that this becomes a predetermined value corresponding to an output that is ½ or less of the maximum output of the pumping light. In addition, the control unit controls the drive current of the excitation light sources 5a and 5b. Hereinafter, this is referred to as a second initial state.

Wavelengths generated from the excitation light sources 5a and 5b 1.
The excitation light of 48 μm is incident on the optical multiplexer / demultiplexer 4 to be multiplexed, is branched into excitation light of the same intensity, and is incident on the optical multiplexers 2a and 2b, respectively. Other operations are the first
The same as in the initial state of.

In the second initial state, one of the pumping light sources 5a and 5b, for example, the pumping light source 5a, for a drive current within the rated value.
When the output of the pumping light from the pump light source decreases, the monitor unit of the pumping light source driving device 6 detects the decrease in the output current from the optical output monitoring PD of the pumping light source 5a. The control unit of the excitation light source driving device 6 determines that the excitation light source 5a has deteriorated due to the output of the monitor unit, and controls the drive circuit to increase the output of the excitation light from the excitation light source 5b. The monitor unit of the pumping light source driving device 6 monitors the output current from the optical output monitoring PD of the pumping light source 5b so that it matches a predetermined value corresponding to a constant total output of the pumping light from the pumping light sources 5a and 5b. In addition, the control unit controls the drive current of the excitation light source 5b according to a preset algorithm. Therefore, the pumped state of the amplification optical fiber 1 becomes stable regardless of the output deterioration of the pumping light source 5a, and the gain of the amplified light is held constant.

In the above embodiment, the monitor section of the pumping light source driving device 6 monitors only the output current of the PD for monitoring the optical output of the pumping light source 5, but the output terminal P for monitoring the optical output is monitored.
By installing D and monitoring the output current by the monitor unit, the output or gain of the amplified light can be more accurately kept constant.

Further, in the above embodiment, the optical multiplexer / demultiplexer 4 multiplexes the two incident pumping lights and splits them into two pumping lights of the same intensity, but the optimum pumping of the amplification optical fiber 1 is performed. In order to correspond to the state, the combined pumping light may be split into pumping lights of different intensities.

The present invention is not limited to the above embodiment, but various modifications can be made.

For example, in the above-mentioned embodiment, the optical multiplexer 2 and the optical multiplexer / demultiplexer 4 are constructed by using the melt-stretching fiber coupler. However, even if they are constructed by using an optical filter, the same operational effect can be obtained. To be

In the above embodiment, the upper limit of the output power of the pumping light emitted from the pumping light source is set to 1/2 of the maximum output in the second initial state, but the upper limit of the output may be an appropriate value.

[0031]

As described above, when the output of one of the first and second pumping lights is lowered, the control unit controls the other pumping light so that the output of the other pumping light is raised.
Since the output of the fourth pumping light is constant, the pumping state of the amplification optical fiber remains stable. Therefore, the output or gain of the amplified light is kept constant by the highly reliable pumping light, and the long-term reliability of the optical fiber amplifier can be improved. Further, since the optical multiplexer / demultiplexer splits the third and fourth pumping lights with the same intensity, even when the output of the first or second pumping light fluctuates, the pumping state in both directions in the amplification optical fiber is changed. Holds equilibrium. Since this optical multiplexer / demultiplexer is composed of relatively inexpensive optical components, high-performance bidirectional pumping with excellent noise characteristics and conversion characteristics can be performed on the amplification optical fiber at low cost.

Therefore, it is possible to provide a high-performance bidirectional pumping type optical fiber amplifier which outputs highly reliable pumping light from a low-cost optical multiplexer / demultiplexer.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram showing an optical fiber amplifier of an optical switch system.

FIG. 3 is a configuration diagram showing a polarization combining type optical fiber amplifier.

FIG. 4 is a configuration diagram showing a conventional bidirectional pumping type optical fiber amplifier.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical fiber for amplification, 2 ... Optical multiplexer, 3 ... Optical isolator, 4 ... Optical multiplexer / demultiplexer, 5 ... Excitation light source, 6 ... Excitation light source drive device, 7 ... Optical switch, 8 ... Optical switch drive circuit, 9
... polarization combiner, 10 ... polarization-maintaining optical fiber.

Claims (3)

[Claims] 1. A first pumping light source that generates a first pumping light, a second pumping light source that generates a second pumping light, and the first and second pumping lights are multiplexed. An optical multiplexer / demultiplexer for branching into third and fourth pumping lights, the signal light and the third light
Via the first optical multiplexer, the second optical multiplexer that combines the signal light and the fourth excitation light, and one end through the first optical multiplexer. Is excited by the third pumping light that has entered in the same direction as the signal light and the fourth pumping light that has entered in the opposite direction from the signal light from the other end via the second optical multiplexer. And an amplification optical fiber that amplifies the signal light incident from the one end via the first optical multiplexer and emits amplified light from the other end via the second optical multiplexer, A monitor unit for monitoring the outputs of the first and second pumping lights, and the first unit based on the output of the monitor unit so as to keep the output or gain of the amplified light constant.
And a control unit for controlling the output of the second pumping light. 2. The optical fiber amplifier according to claim 1, wherein the third and fourth pump lights have the same light intensity. 3. The optical fiber amplifier according to claim 1, wherein the monitor section further monitors the output or gain of the amplified light.