JPH0895096A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE: To provide an optical fiber amplifier of excellent efficiency and large gain even in the case of amplifying in both directions by making the transmission factor of the output signal light of a light branching/combining means larger than the transmission factor of an input signal light. CONSTITUTION: When a signal light input from the A-direction passes a light branching/combining part 8, the light is sent to an erbium dope optical fiber 1 by receiving deterioration of 6.9dB. The light is amplified to 17.5dBm by gain of 32.5dB by passing through the optical fiber 1, and sent to a light branching/combining part 9 on the output side. When this signal light passes through the light branching/combining part 9, it receives deterioration of 1dB, and it is supplied to a port 19 as a light having light output of 16.5dBm. A signal light input from the B-direction receives deterioration and amplification while passing through the light branching/combining part 9, an erbium dope optical fiber 11, and the light branching/combining part 8, and it is supplied to a port 18 as a light having light output of 16.5dBm. By this device, the light output is improved by 1.5dB compared with a customary device.

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 amplifying signal light using a rare earth element-doped optical fiber, and more particularly to an optical fiber amplifier for amplifying signal light input in both directions.

[0002]

2. Description of the Related Art In recent years, research and development of an optical fiber amplifier for directly amplifying an optical signal by introducing pumping light of an appropriate wavelength into an optical fiber doped with a rare earth element such as erbium (Er) have been actively conducted. ing. Compared to semiconductor amplifiers that use semiconductor lasers, for example, optical fiber amplifiers have features such as less polarization dependence, less coupling loss with optical fibers for transmission, excellent temperature characteristics, and wider wavelength range for amplification. Therefore, it is considered to be very useful in the future construction of optical communication systems. Active development and proposals have been made regarding applications of optical fiber amplifiers having these features.

Bidirectional optical amplification for bidirectional transmission in one optical fiber is one of them. This bidirectional amplification will be described with reference to FIG. In FIG. 4, 1,11
Is a rare earth element-doped optical fiber, 2, 3, 12, and 13 are optical isolators, 4,5, 14, and 15 are pumping semiconductor lasers, 6, 7, 16, and 17 are optical multiplexers, and 28 and 29 are optical branching couplings. It is a department. Usually, an optical component having a transmission ratio of input light and output light of 1: 1 is selected for the optical branching / coupling unit.

In the configuration of FIG. 4, when signal light is input from the directions indicated by arrows A and B, the input signal light is split at the above-described ratio in the optical branching / coupling unit 28 or 29. The branched light is sent to the rare-earth-doped optical fibers 1 and 11 that have been pumped by the pumping semiconductor lasers 4 and 15 in advance, and is amplified there.

The amplified signal light is sent to the optical branching / coupling unit 28 or 29, and the signal light input from the direction indicated by the arrow A is input from the optical branching / coupling unit 29 in the direction indicated by the arrow B. Are respectively output from the optical branching / coupling unit 28.

In this way, the signal light input from both directions is eventually subjected to some optical amplification. However, in the device shown in FIG. 4, the input / output section, that is, the optical branching / coupling section always causes optical loss. Especially in the optical output section,
Even the light that has been amplified will suffer the same optical loss as that generated in the optical input section.

For example, in the case of the light indicated by the arrow A in FIG. 4, the optical branching / coupling section 28 which is an optical input section receives a loss of 3 dB, and even if it is amplified, the optical branching / coupling section 29 which is an optical output section. It also suffers a loss of 3 dB, so a total of 6 dB
Will result in a loss of gain. As described above, the conventional optical fiber amplifying device that performs bidirectional amplification has a drawback that the gain is small and the efficiency is low.

[0008]

As described above, in the conventional optical fiber amplifying apparatus which performs bidirectional optical amplification, the gain is small and the amplification characteristic is sufficient as compared with the unidirectional optical amplification. There was a problem that was not obtained.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical fiber amplifier having excellent efficiency and large gain even in the case of bidirectional amplification as compared with the conventional one.

[0010]

In order to solve the above-mentioned problems, the present invention provides an optical fiber having an optical branching / coupling means for branching or coupling signal light in an optical input / output section of a rare earth element-doped optical fiber. In the amplifying device, the transmittance of the output signal light of the optical branching / coupling means is larger than the transmittance of the input signal light.

[0011]

In the above structure, the optical loss after being constructed is smaller than the optical loss before being amplified by the rare earth element-doped optical fiber. As a result, the loss amplified by the rare earth element-doped optical fiber becomes small, and efficient optical amplification becomes possible.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to FIGS. 1, 2 and 3. FIG. 1 is a diagram showing a schematic configuration of an optical fiber amplifier of the present invention, and the same parts as those in FIG. 4 are designated by the same reference numerals. The rare earth element-doped optical fibers 1 and 11 are erbium-doped optical fibers. Further, FIG. 2 is a graph showing the input / output characteristics when 150 mW of pumping light is incident on the erbium-doped optical fiber used in this example.

In FIG. 1, the point different from FIG. 4 is the signal light transmittance of the optical branching / coupling units 8 and 9, and in this embodiment,
The signal light transmittance is 21% for input signal light and 79% for output signal light.
%.

That is, as shown in FIG. 3, the optical branching / coupling portions 8 and 9 use optical parts having characteristics of transmitting 79% of light and reflecting 21% of light. Therefore, the optical branching / coupling unit 8 is 21% of the signal light input from the direction indicated by the arrow A.
To guide the rare-earth element-doped light to the fiber 1.
Further, the optical branching / coupling unit 9 transmits 79% of the signal light that has passed through the optical isolator 3 and guides it to the port 19.

Similarly, for the signal light B input from the direction indicated by the arrow B, the optical branching / coupling unit 9 guides 21% of the signal light to the rare earth element-doped optical fiber 11, and the optical branching / coupling unit 8 79% of the signal light that has passed through the optical isolator 12 is guided to the port 18.

In the above structure, the operation when the optical input level is -8 dBm will be described below as an example.
In addition, for simplification of description, it is assumed that there is no loss in each optical component. Further, in order to clarify the effect of the present embodiment, description will be made by comparing the conventional configuration shown in FIG. 4 with the present embodiment.

First, in the conventional structure shown in FIG. 4, since the signal light input to the optical branching / coupling units 28 and 29 has a signal light transmittance of 50%, the optical input level is -8d.
In the case of Bm, each suffers deterioration of 3 dB. The light that has become −11 dBm due to this deterioration passes through each rare earth element-doped optical fiber 1 or 11 and is optically amplified to 18.0 dBm with a gain of 29.0 dB due to the optical amplification characteristics shown in FIG. Then, at the output side optical branching / coupling unit 8 or 9,
It suffers from dB degradation. As a result, the light output of the light supplied to each port is 15 dBm.

On the other hand, in the configuration of FIG. 1, the signal light input from the direction indicated by the arrow A is deteriorated by 6.9 dB when passing through the optical branching / coupling unit 8 having the transmittance of 21%. ,
An optical output of -14.9 dBm is sent to the erbium-doped optical fiber 1. By passing through the erbium-doped optical fiber 1, this signal light has a gain of 32.5 dB and a gain of 17.5 dBm due to the optical amplification characteristic shown in FIG.
The light is amplified to be sent to the optical branching / coupling unit 9 on the output side. Then, this signal light is deteriorated by 1 dB when passing through the optical branching / coupling portion 9 having a transmittance of 79%, and is supplied to the port 19 as light having an optical output of 16.5 dBm.

Similarly, the signal light input from the direction indicated by the arrow B undergoes a deterioration of 6.9 dB when passing through the optical branching / coupling portion 9, and is sent to the erbium-doped optical fiber 11. This signal light passes through the erbium-doped optical fiber 11 and has an optical amplification characteristic shown in FIG.
With a gain of 5 dB, it is optically amplified to 17.5 dBm and sent to the optical branching / coupling unit 8 on the output side. Then, this signal light is deteriorated by 1 dB when passing through the optical branching / coupling portion having a transmittance of 79%, and is supplied to the port 18 as light having an optical output of 16.5 dBm.

As described above, when the present embodiment is compared with the conventional example, the light output is improved by 1.5 dB. Although the embodiments of the present invention have been described with reference to the optical amplification characteristics of FIG. 2, when the fiber parameters of the doped fiber and the like change, different amplification characteristics are exhibited. The same effect can be realized by optimizing the light transmittance of the branching / coupling portion.

In the above embodiment, the input / output characteristics of the optical branching / coupling unit are 21% and 79%, respectively. However, the present invention is not limited to this, and the transmittance of the output signal light is the transmittance of the input signal light. If it is larger than the above, the same effect can be realized.

[0022]

As described above in detail, according to the optical fiber amplifier of the present invention, the optical output can be improved more than ever before.

[Brief description of drawings]

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

FIG. 2 is a diagram showing optical amplification characteristics of an erbium-doped optical fiber.

FIG. 3 is a diagram illustrating a flow of an optical branching / coupling unit.

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

[Explanation of symbols]

 1, 11 ... Rare earth element-doped optical fiber 8, 9, 28, 29 ... Optical branching coupling part 2, 3, 12, 13 ... Optical isolator 4,5, 14, 15 ... Excitation semiconductor laser 6, 7, 16, 17 … Optical multiplexer

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Claims (2)

[Claims] 1. An optical fiber amplifier having optical branching / coupling means for branching or coupling signal light into an input side and an output side of a rare earth element-doped optical fiber, wherein the optical fiber amplifier is provided on the output side of the rare earth element-doped optical fiber. An optical fiber amplifying device, wherein the signal light transmittance of the optical branching / coupling means is larger than the signal light transmittance of the optical branching / coupling means provided on the input side of the rare earth element-doped optical fiber. 2. The signal light transmittance of the optical branching / coupling means provided on the output side of the rare earth element-doped optical fiber is the signal light transmittance of the optical branching / coupling means provided on the input side of the rare earth element-doped optical fiber. 2. The optical fiber amplifying device according to claim 1, wherein the optical fiber amplifying device is at least twice as much.