JPH10117031A - Optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate adverse effects on a signal beam by a laser beam oscillated in a resonator by generating stable inverted distributing condition in an optical amplifier of an optical resonator with a laser beam and then extracting the amplified signal beam with an optical isolator in such a direction that the laser beam does not leak within the optical resonator. SOLUTION: A first and a second wavelength multiplex optical isolators 8, 12 are provided. An optical amplifying fiber 1 is an erbium-doped fiber(EDF). When a signal beam is input to an optical fiber 10b, this signal beam is transmitted in the direction of arrow mark a within an optical resonator 2. Adequate amplification is executed, not depending on an input intensity in the EDF 1 where the inverted distributing condition is fixed and an output is provided from an optical fiber 10d via the second wavelength multiplex optical isolator 12. In the second wavelength multiplex optical isolator 12 from which the amplified signal beam can be extracted, the laser beam in the optical resonator in different running direction from the signal beam is hardly isolated, and therefore a laser beam which causes noise, etc., does not enter the signal beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier for amplifying an optical signal, and more particularly, to an optical amplifier suitable for use in wavelength division multiplexed optical communication.

[0002]

2. Description of the Related Art In an optical fiber communication system, a regenerative repeater that converts signal light into an electric signal, amplifies the signal, and outputs the signal again as a signal light is used. Optical fiber amplifiers, particularly those called erbium-doped optical fiber optical amplifiers (EDFAs), have been rapidly commercialized. The application range of the EDFA is expanding, and it also extends to wavelength division multiplexing optical communication (WDM), which has attracted attention as high-capacity optical communication. Wavelength multiplexing optical communication uses light of multiple different wavelengths,
Information is carried on each light, and these are combined by a wavelength division multiplexer and transmitted to an optical fiber. The communication per fiber compared to the conventional optical communication using only one light The capacity can be greatly increased.

The EDFA can amplify a WDM wavelength-multiplexed optical signal at a time.
In systems, expectations are growing as simple linear repeaters that replace conventional regenerative repeaters.
There are also problems to be solved for use in the M system.
The EDFA excites erbium ions in the EDF by passing excitation light of a predetermined wavelength through an erbium-doped fiber (EDF) to create a population inversion state of electrons in the EDF,
The signal light is passed through the EDF in the inverted distribution state, and the light having the same wavelength as the signal light is stimulated to be emitted, thereby amplifying the passed signal light. In this case, the gain characteristic of each wavelength (channel) causes a gain deviation between the channels due to the EDF absorption coefficient, the stimulated emission coefficient, the inversion distribution state, and the like, and also due to the change in the inversion distribution state due to the change in the intensity of the input signal light. Since a gain deviation occurs between the channels, even if the wavelength-multiplexed signal light is input to the EDFA with the average intensity between the channels being equivalent, a difference in the intensity of the signal light output from the EDFA may occur.
That is, the gain of the EDFA has wavelength dependence. Therefore E
When a DFA is connected in multiple stages as a linear repeater, the gain difference between wavelengths is accumulated and increased, which causes a greater problem, and limits the transmission characteristics of the system.

In order to solve such a problem, an EDFA
A method of fixing the gain of each channel by forming an optical resonator therein to cause laser oscillation and fixing the population inversion by the laser oscillation has been proposed. FIG. 4 shows an example of an EDFA adopting this method. The EDF and the fiber gratings B provided at both ends of the EDF constitute a Fabry-Perot optical resonator C. When excitation light is incident on the EDF via E, a 1520 nm laser is oscillated in the optical resonator C, and this stable laser creates a population inversion state fixed in the EDF to fix its gain. The signal light input from the input port (Signal in) through the optical isolator F is amplified by the EDF having a fixed gain, and then is output through the optical isolator G and the rejection filter H to the output port (Signal out). ) Is output.

[0005]

The EDFA shown in FIG.
Since the laser light oscillated in the Fabry-Perot type optical resonator C for stabilizing the gain is output together with the signal light from the signal light output port (Signal out), the laser light adversely affects the signal light. There is a fear. In the optical amplifier, a rejection filter H is used to prevent laser light oscillated in the optical resonator C from being output to the output side of the signal light.
However, it is difficult to completely eliminate the laser beam even with the rejection filter H, and this solution has been desired.

SUMMARY OF THE INVENTION An object of the present invention is to provide a wavelength multiplexing optical communication which does not cause a deviation between channels and which can also eliminate an adverse effect on signal light due to laser light oscillated in a resonator. An object of the present invention is to provide an optical amplifier suitable for multiplex communication.

[0007]

The optical amplifier according to the first aspect of the present invention has the following features as shown in FIGS. 1 (a) and 2 (a).
An optical amplifying fiber 1, a wavelength selecting means, a traveling direction restricting means, a pumping light is injected into an optical resonator 2 configured in a ring shape, and laser oscillation of a wavelength selected by the wavelength selecting means is performed; The laser light is propagated in only one direction by the traveling direction restricting means, and the laser light
A stable inversion distribution state is created in the optical amplification fiber 1 inside, and the signal light to be amplified is combined with the optical resonator 2 and passed through the optical amplification fiber 1, and the signal light amplified by the optical amplification fiber 1 is subjected to optical resonance. The laser beam in the vessel 2 is split and extracted in a direction in which it does not leak.

[0008] The optical amplifier according to claim 2 of the present invention comprises:
The signal light incident on the optical resonator 2 is split by the optical splitter 12 from the optical resonator 2, and the propagation direction of the laser light in the optical resonator 2, which is directed by the traveling direction restricting means, is: The direction is determined depending on the demultiplexing characteristics of the optical demultiplexer 12 so that the leakage of the laser light from the optical demultiplexer 12 is reduced.

An optical amplifier according to a third aspect of the present invention comprises:
The wavelength selecting means is the optical filter 3 provided in the optical resonator 2, and the traveling direction restricting means is the optical isolator 4 provided in the optical resonator 2.

The optical amplifier according to claim 4 of the present invention comprises:
An optical splitter or splitter 8 for splitting and outputting laser light is provided in the optical resonator 2 to partially output the laser light in the optical resonator 2.

As shown in FIG. 2A, the optical amplifier according to claim 5 of the present invention comprises a directional coupler 5 in an optical resonator 2.
Is provided to regulate the traveling direction of the pumping light in the optical resonator 2, and the pumping light in the unrestricted direction is outputted once and made incident on the fiber grating 6 to reflect only the desired wavelength light. By sending the reflected excitation light through the directional coupler 5 in the direction in which the optical resonator 2 is not restricted, a laser beam traveling in one direction in the optical resonator 2 is generated. Things.

[0012]

First Embodiment FIG. 1A shows a first embodiment of an optical amplifier according to the present invention. This optical amplifier includes an optical resonator 2 formed in a ring shape using an optical fiber 10a. On the optical resonator 2, a first optical amplifier fiber 1 and a second optical resonator 2 are arranged in the direction of the arrow b in FIG. 1, a wavelength division multiplexer 11, a first wavelength division multiplexing optical demultiplexer (optical splitter or optical demultiplexer) 8, an optical isolator 4, an optical filter 3, a second
Wavelength division multiplexer 12 and second wavelength division multiplexer 13
Is attached. An excitation light source 14 is connected to the second wavelength division multiplexing optical multiplexer 13 via an optical fiber 10e, and an optical fiber 10b for inputting signal light to the first wavelength division multiplexing optical multiplexer 11, Wavelength division multiplexing optical demultiplexer 8
Is connected to an optical fiber 10c for outputting unnecessary laser light in the optical resonator 2, and an optical fiber 10d for outputting amplified signal light to the second wavelength division multiplexing optical demultiplexer 12. I have.

The wavelength division multiplexing optical multiplexer 1 shown in FIG.
1. Each of the wavelength division multiplexing optical demultiplexers 8 and 12 has directionality.
b is multiplexed into the optical resonator 2 in the direction of the arrow a in the figure, and the first wavelength division multiplexing optical demultiplexer 8 moves the optical resonator 2 to the arrow b.
The light (laser light) traveling in the direction is demultiplexed into the optical fiber 1
0c, and the second wavelength division multiplexing optical splitter 12 splits the light traveling through the optical resonator 2 in the direction of arrow a to split the light into
d.

An optical amplification fiber 1 shown in FIG. 1A is an erbium-doped fiber (EDF), an optical filter 3 is a filter that transmits light having a wavelength of 1532 nm, and an optical isolator 4 is such that the light transmission direction is one direction. It regulates. The pumping light source 14 is a semiconductor diode that oscillates a 1480 nm laser, and the laser light is multiplexed to the optical resonator 2 via the second wavelength division multiplexing optical multiplexer 13 and propagated.

Excitation light output from the excitation light source 14 and propagated to the optical resonator 2 excites the EDF 1 of the optical resonator 2, and the wavelength selected by the optical filter 3 in the optical resonator 2 and the optical isolator 4 Causes the laser beam to oscillate in the direction selected (the direction of the arrow b), thereby creating a population inversion state fixed (stabilized) to the EDF 1 in the optical resonator 2. FIG. 1B shows a laser oscillation portion in the optical resonator 2 of the optical amplifier. A part of the laser light oscillated by the optical resonator 2 is the first wavelength division multiplexed optical demultiplexing. The light is branched by the device 8 and output to the optical fiber 10c.

In the optical amplifier shown in FIG.
When the signal light is input to 0b, the signal light propagates through the optical resonator 2 in the direction of the arrow a and passes through the EDF 1, and is appropriately amplified by the EDF 1 in which the population distribution is fixed regardless of the input intensity. The light is output from the optical fiber 10d via the second wavelength division multiplexing optical splitter 12. In the second wavelength division multiplexing optical demultiplexer 12 from which the amplified signal light is taken out, the laser light in the optical resonator 2 having a different traveling direction from the signal light is hardly branched. Laser light does not enter, and is suitable for high-quality communication.

[0017]

Embodiment 2 FIG. 2 (a) shows a second embodiment of the optical amplifier according to the present invention, which is formed in a ring shape using an optical fiber 10a in the same manner as in the above embodiment. An optical resonator 2 is provided. However, on the optical resonator 2,
Starting from the optical amplification fiber 1 and along the direction of the arrow b in the figure, the first wavelength-multiplexed wave coupler 11 and the directional coupler 5 are sequentially arranged.
, A first wavelength division multiplexing optical demultiplexer 12, and a second wavelength division multiplexing optical multiplexer 13.

The directional coupler 5 has three ports. The light input to the port can be output to the port, and the light input to the port can be output to the port. Is not output to The port of the directional coupler 5 is connected to the optical resonator 2
Is connected, and a fiber grating 6 is connected to a port. Also, as in the first embodiment, an excitation light source 14 is connected to the second wavelength division multiplexing optical multiplexer 13 via an optical fiber 10e, and light for inputting signal light is input to the first wavelength division multiplexing optical multiplexer 11. An optical fiber 10d for outputting an amplified signal light is connected to the fiber 10a and the first wavelength division multiplexing optical demultiplexer 12.

The wavelength multiplexing optical multiplexer 11 and the wavelength multiplexing optical demultiplexer 12 each have a directionality as shown in FIG. 2A, and the wavelength multiplexing optical multiplexer 11 is an optical fiber 10.
The signal light of b is multiplexed into the optical resonator 2 in the direction of arrow a in the figure, and the first wavelength division multiplexing optical demultiplexer 12 demultiplexes the light traveling through the optical resonator 2 in the direction of arrow a. be able to.

The optical amplification fiber 1 is an erbium-doped fiber (EDF), the optical fiber grating 6 reflects light having a wavelength of 1532 nm and transmits the other light, and the directional coupler 5 controls the light transmission direction. Is regulated in one direction. The excitation light source 14 is 1480 n
m is a semiconductor diode that oscillates a laser of m.
And propagated.

The pumping light output from the pumping light source 14 and propagated to the optical resonator 2 excites the EDF 1 of the optical resonator 2 and, in this case, the wavelength and the directional coupling selected by the fiber grating 6. As a result, only the stabilized laser light in the direction (the direction of the arrow b) selected by the cavity 5 is oscillated, and the EDF 1 in the optical resonator 2 is oscillated.
To create a population inversion state fixed (stabilized) to

FIG. 3 (a) shows the result of an experiment using the optical amplifier of FIG. 2 (a), and shows the output spectrum of the optical fiber 10d in a state where the signal light for amplification is not input to the optical fiber 10b. It is shown. EDFA1
The spontaneous emission light amplified in step (1) has a spectrum with a concave portion near 1530 nm due to the characteristics of the wavelength division multiplexing optical demultiplexer 12, and the laser light at 1532.2 nm in the optical resonator 2 is suppressed to -44.0 dBm. You can see that 4B, the port of the directional coupler 5 in FIG. 2A is reversed so that the laser travels in the optical resonator 2 in the direction of arrow a as shown in FIG. 2B. It is an output spectrum when there is no input signal light. In this case, the laser beam in the optical resonator 2 is 1532.2.
The light intensity in nm is as high as -6.23 dBm, and it can be seen that the laser light leaks out to the optical fiber 10d which is the output port of the signal light. This comparative example also confirms that the laser light generated in the optical resonator 2 does not leak to the output side in the optical amplifier of the present invention.

[0023]

By using the optical amplifier of the present invention, it is possible to prevent or suppress the laser light oscillated in the optical resonator from being output to the output port of the amplified signal light. High-quality optical communication with reduced generation is possible.
This is particularly effective in a system in which optical amplifiers are connected in cascade in many stages.

[Brief description of the drawings]

FIG. 1A is a schematic diagram showing a first embodiment of an optical amplifier of the present invention, and FIG. 1B is a schematic diagram of a one-way traveling ring resonator laser portion in the amplifier.

FIG. 2A is a schematic diagram showing a second embodiment of the optical amplifier of the present invention, and FIG. 2B is a schematic diagram showing an example of a configuration in which laser light and signal light travel in the same direction in the amplifier. FIG.

3A is an explanatory diagram showing an output light spectrum in a no signal light state in the optical amplifier of FIG. 2A, and FIG. 3B is a view showing a no signal light state in the optical amplifier of FIG. 2B; FIG. 4 is an explanatory diagram showing an output spectrum of FIG.

FIG. 4 is a schematic diagram showing an example of a conventional optical amplifier.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical amplification fiber 2 Optical resonator 3 Optical filter 4 Optical isolator 5 Directional coupler 6 Fiber grating 8 Optical splitter 12 Optical splitter

Claims (5)

[Claims] 1. An optical amplifying fiber (1), a wavelength selecting means, a traveling direction restricting means, and pump light is injected into a ring-shaped optical resonator (2) to be selected by said wavelength selecting means. A laser beam having a wavelength is emitted, and the laser beam is propagated in only one direction by the traveling direction restricting means. This laser beam causes a stable inversion distribution state in the optical amplification fiber (1) in the optical resonator (2). The signal light to be amplified is multiplexed into the optical resonator (2) and passed through the optical amplifier fiber (1), and the signal light amplified by the optical amplifier fiber (1) is output from the optical resonator (2). An optical amplifier, wherein a laser beam is split in a direction in which laser light does not leak out. 2. The optical demultiplexer (12) demultiplexes the signal light incident on the optical resonator (2) from the optical resonator (2) and directs the signal light by the traveling direction restricting means. Tableware (2)
The propagation direction of the laser light inside the optical splitter (12) depends on the demultiplexing characteristics of the optical demultiplexer (12), and is determined so as to reduce the leakage of the laser light from the optical demultiplexer (12). The optical amplifier according to claim 1, wherein: 3. The wavelength selecting means is an optical filter (3) provided in an optical resonator (2), and the traveling direction restricting means is an optical isolator (4) provided in the optical resonator (2). 3. The optical amplifier according to claim 1, wherein: 4. An optical splitter or splitter (8) for splitting and outputting a laser beam in the optical resonator (2) and partially outputting the laser beam in the optical resonator (2). The optical amplifier according to any one of claims 1 to 3, wherein: 5. A directional coupler (5) is provided in the optical resonator (2) to regulate the traveling direction of the pump light in the optical resonator (2), and to excite the light in an unregulated direction. The light is output once and made incident on the fiber grating (6) to reflect only the desired wavelength light, and the reflected excitation light is transmitted through the directional coupler (5) to the optical resonator (2). By feeding in unregulated directions,
3. The optical amplifier according to claim 1, wherein a laser beam traveling in one direction in the optical resonator is generated.