JPH11168255A - Optical fiber amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably output even a low-level light signal by connecting a light attentuator to the output terminal of an excitation light source. SOLUTION: An optical fiber amplifier 1 is provided with a light signal input optical fiber 2 and a light signal output optical fiber 8, first and second isolators 3 and 9, a rare earth element doped optical fiber 4, a branching filter 6, and an excitation light source 5. Also, it is provided with an optical attenuator 7 that is connected to the output terminal of the light source 5. The optical attenuator 7 in a configuration where, for example, excitation light is attenuated by an axis deviation fusion and an attenuation film with improved heat resistance is embedded is used. Then, by supplying excitation light that is outputted from the light source 5 by the optical attenuator 7 as needed and then supplying it to the branching filter 6, the level of a light signal that is emitted to the optical fiber 8 is changed, thus stably outputting a light signal with a small level that can normally be obtained by starting the light source 5 near a threshold.

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 used in an optical communication system or the like to directly amplify an optical signal.

[0002]

2. Description of the Related Art An optical fiber amplifier using an optical fiber doped with a rare earth element can amplify an optical signal without optical-electrical conversion, so that it is convenient and is an indispensable device for future optical communication. Development is underway. As an optical fiber doped with a rare earth element used for an optical fiber amplifier, a neodymium (Nd) -doped optical fiber for amplifying an optical signal in a 1.06 μm or 1.32 μm band, a praseodymium for amplifying an optical signal in a 1.3 μm band. (P
r) Doped optical fibers and the like can be mentioned. Among them, researches on optical fiber amplifiers using erbium (Er) doped optical fibers having a gain in the 1.55 μm band used for optical communication have been actively conducted.

A conventional optical fiber amplifier will be described with reference to FIG. In the conventional optical fiber amplifier 10, reference numeral 2 denotes an optical signal input optical fiber into which a received optical signal is input, and reference numerals 3 and 9 denote an isolator for transmitting an optical signal only in the direction of the arrow and blocking in the opposite direction, and reference numeral 4 denotes erbium. Rare earth element doped optical fiber doped with rare earth elements such as
Reference numeral 5 denotes an excitation light source such as a laser diode for supplying excitation light, and reference numeral 6 denotes an optical multiplexer / demultiplexer.

An optical signal input from the optical signal input optical fiber 2 passes through a first isolator 3, passes through an optical fiber 4 doped with a rare earth element such as erbium, and is supplied to an optical multiplexer / demultiplexer 6. On the other hand, the excitation light source 5 generates excitation light having a predetermined wavelength corresponding to the wavelength of the input optical signal, and supplies the excitation light to the optical multiplexer / demultiplexer 6. The optical multiplexer / demultiplexer 6 multiplexes the input optical signal and the pump light having different wavelengths from each other, and outputs the amplified amplified optical signal to the optical signal output optical fiber 8 via the second isolator 9.

Conventionally, gain control of the optical fiber amplifier 10 is generally performed by increasing or decreasing the intensity of the pumping light for generating the pumping light. For example, when a laser diode is used as an excitation light source, the starting current of the laser diode may be controlled. When the drive current of the laser diode is increased, the intensity of the excitation light increases,
The amplification gain of the optical signal will increase. Conversely, when a large-level optical signal is not required at the light emitting end of the optical fiber amplifier, the drive current of the laser diode is reduced to weaken the intensity of the excitation light.

However, in the conventional optical fiber amplifier, when the starting current of the laser diode is reduced to a value close to the threshold value, the wavelength of the pump light becomes unstable. As a result, the output of the pump light emitted from the optical multiplexer / demultiplexer is reduced. Will not be stable. In addition, although the temperature adjustment of the pump light source is usually performed only by cooling, the output of the optical fiber amplifier may not function effectively at low current drive due to the small amount of heat generated by the pump light source. There was a problem that it was not stable.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides an optical fiber amplifier capable of stably outputting a low-level optical signal.

[0008]

According to the present invention, there is provided an optical fiber doped with a rare earth element and an excitation light source for supplying excitation light to the optical fiber, and an optical attenuator is provided at an output end of the excitation light source. Provide a connected fiber optic amplifier. Further, the present invention provides an optical fiber amplifier wherein the optical attenuator is configured to attenuate the excitation light by off-axis fusion welding.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to FIG. The optical fiber amplifier 1 shown in FIG. 1 has an optical signal input optical fiber 2 and an optical signal output optical fiber 8, a first isolator 3 and a second isolator 9, similarly to the configuration of the conventional optical fiber amplifier shown in FIG. And a rare earth element doped optical fiber 4, an optical multiplexer / demultiplexer 6, and an excitation light source 5. In addition, an optical attenuator 7 connected to an output terminal of the excitation light source 5 is provided.

In the optical fiber amplifier 1 of the present invention,
By attenuating the intensity of the pumping light output from the pumping light source 5 by the optical attenuator 7 as necessary and supplying the light to the optical multiplexer / demultiplexer 6, the level of the optical signal emitted to the optical signal output optical fiber is changed. Can be done. Therefore, even a small-level optical signal that could not be obtained unless the pumping light source was started near the threshold value can be stably output.

The optical attenuator 7 is composed of various commonly used optical elements such as a configuration in which excitation light is attenuated by off-axis fusion and a configuration in which an attenuation film having excellent heat resistance is embedded. be able to. Further, a plurality of optical attenuators may be combined.

The optical fiber amplifier 1 shown in FIG. 1 is of a backward pumping type in which pumping light is incident on the rare earth element-doped optical fiber 4 from the rear, but either forward pumping or dual pumping may be employed.

[0013]

(Conventional example) In the conventional optical fiber amplifier 10 having the configuration shown in FIG. 2, reference numeral 4 denotes an erbium-doped optical fiber, 5 denotes a pumping light wavelength of 1.48 μm, and a driving current of 500 m.
A is a laser diode having an excitation light output of 90 mW, and 6 is an optical multiplexer / demultiplexer equipped with a dielectric multilayer filter that reflects excitation light having a wavelength of 1.48 μm and transmits signal light having a wavelength of 1.55 μm. is there. In the optical fiber amplifier 10, the drive current of the pump light source 5 for obtaining an output of +3 dBm of output light is 85 mA, and the threshold value of the pump light source is 52 mA.
The output stability of this optical fiber amplifier is ± 0.3 dB / h
Met. In addition, since the heat generated by the laser diode is small, the cooling function for adjusting the temperature did not work well.

(Embodiment) FIG. 1 shows a configuration similar to that of the above-described conventional example except that an optical attenuator 7 having an off-axis fusion-adjusted configuration adjusted so as to have an attenuation of 3 dB is connected to the output end of an excitation light source 5. 1 is an optical fiber amplifier 1 according to the present invention. In the optical fiber amplifier 1, the driving power of the pumping light source 5 for obtaining the same output light +3 dBm as that of the conventional optical fiber amplifier 10 is 160 mA, and the output stability is ± 0.1 dB / h.
Met. In addition, the cooling function for temperature adjustment worked properly.

The optical fiber amplifier of the embodiment can be operated with a driving power of 160 mA, which is larger than the threshold value 52 mA of the pumping light source 5, in order to obtain +3 dBm of output light that is not stable with the conventional optical fiber amplifier. The pump light was stabilized, and stable output light could be obtained.

[0016]

According to the optical fiber amplifier of the present invention,
Since the optical attenuator is connected to the output terminal of the pump light source, a low-level optical signal can be stably output.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a configuration of an optical fiber amplifier according to the present invention.

FIG. 2 is an explanatory diagram illustrating a configuration of a conventional optical fiber amplifier.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical fiber amplifier of the present invention 2 optical signal input optical fiber 3 first isolator 4 rare earth element doped optical fiber 5 excitation light source 6 optical multiplexer / demultiplexer 7 optical attenuator 8 optical signal output optical fiber 9 first isolator 10 conventional Optical fiber amplifier

Claims (2)

[Claims] 1. An optical fiber amplifier comprising: an optical fiber doped with a rare earth element; an excitation light source for supplying excitation light to the optical fiber; and an optical attenuator connected to an output terminal of the excitation light source. 2. The optical fiber amplifier according to claim 1, wherein the optical attenuator has a configuration for attenuating the excitation light by off-axis fusion welding.