JPH1187823A - Light amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve excitation efficiency. SOLUTION: To one end of a light amplification fiber 10 to which a rare earth element is added, a wavelength division multiplex(WDM) photocoupler 14 for multiplexing excitation light (wavelength λp) from an excitation light source 12 to signal light to be light amplified, and for supplying it to the light amplification fiber 10, is connected. To the other end of the light amplification fiber 10, an optical fiber grating 16 for selectively reflecting the wavelength λp of the excitation light for 100% or almost 100%, and for transmitting the signal light almost without loss, is connected. At the input part of the signal light to be light amplified, an optical isolator 18 for interrupting light propagated in the opposite direction of the signal light is arranged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical amplifier for amplifying an optical signal as light.

[0002]

2. Description of the Related Art As such an optical amplifier, 1.4 is applied to an optical amplification fiber doped with rare earth represented by erbium.
It is widely known that an excitation laser beam of 8 μm or 0.98 μm is incident by a wavelength division multiplexing (WDM) optical coupler.

[0003] The WDM optical coupler is arranged on the incident side of the signal light to be optically amplified, is arranged on the emission side of the amplified signal light, and is arranged on both the incidence side and the emission side. The configuration is known.

[0004]

In the conventional example, of the pump light incident on the optical amplification fiber, the light not absorbed by the optical amplification fiber is discarded as it is, and the excitation light rate is low.

In a unidirectional pump configuration in which the pump light is incident on the optical amplification fiber only from one of the incident side and the output side of the signal light, the pump light is absorbed in the optical amplification fiber, so that the optical amplification is performed. There is a problem that the gain gradually decreases in the axial direction of the optical amplification fiber, and the gain efficiency is poor. In a bidirectional pump configuration in which pump light is incident from both sides of the optical amplification fiber,
Although such problems are mitigated, a plurality of example light sources must be prepared, and if one of the pump light sources fails for some reason, the problem of poor gain efficiency of the unidirectional pump configuration will occur. Surface.

An object of the present invention is to provide an optical amplifier capable of obtaining a higher pumping light rate.

It is another object of the present invention to provide an optical amplifier which can achieve the same gain efficiency as bidirectional pumping even with a single pumping light source.

[0008]

According to the present invention, a first reflecting member which selectively reflects the excitation light from the optical amplifying medium but transmits the light to be amplified is provided on one side of the optical amplifying medium. Is provided. As a result, the excitation light having a sufficient intensity is still returned to the optical amplification medium, and the excitation light can be used effectively. That is, the excitation light rate is improved. Since the power distribution of the pump light is made uniform in the axial direction in the optical amplifying medium, the gain efficiency is improved.

Further, by providing a similar reflecting member, that is, a second reflecting member on the other side of the optical amplifying medium, the excitation light is substantially confined in the optical amplifying medium.
The pumping light rate and gain efficiency are improved.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention.

Reference numeral 10 denotes an optical amplification fiber doped with a rare earth element. At one end, an excitation light (wavelength λp) from an excitation light source 12 is multiplexed to a signal light to be optically amplified, and the resulting signal is applied to the optical amplification fiber 10. A wavelength division multiplexing (WDM) optical coupler 14 to be supplied is connected, and a wavelength lambda p of the pump light is selectively 100% or almost 100% at the other end of the optical amplification fiber 10.
An optical fiber grating 16 that transmits the signal light with almost no loss while connecting the signal light is connected.

[0013] The input section of the signal light to be optically amplified includes:
An optical isolator 18 that blocks light propagating in the opposite direction to the signal light is provided.

The operation of this embodiment will be described. The signal light to be optically amplified passes through the optical isolator 18 and the optical coupler 14
Incident on. The excitation light of wavelength λp is also applied to the optical coupler 14 from the excitation light source 12. Excitation light wavelength λp
Are, for example, the 1.48 μm band and the 0.98 μm band. The optical coupler 14 multiplexes the signal light with the pump light from the pump light source 12 and supplies the signal light to the optical amplification fiber 10.

The optical amplification fiber 10 is excited by the excitation light to optically amplify the signal light. In the process of propagating through the optical amplifying fiber 10, the pump light is attenuated as shown by a symbol A in FIG. FIG. 2 shows the change in the pump light power in the axial direction in this embodiment. The vertical axis is the normalized pump light power,
The horizontal axis indicates the standardized fiber distance of the optical amplification fiber 10. In this embodiment, the length of the optical fiber 10 is set to a length at which the excitation light is attenuated by 3 dB.

The pump light is attenuated by 3 dB at the stage where the pump light has propagated through the optical amplification fiber 10 in the same direction as the signal light, specifically, at the position of the optical fiber grating 16, but is reflected by the optical fiber grating 16. This time, it propagates in the opposite direction to the signal light. Also at this time, the excitation light excites the rare earth element of the optical amplification fiber. In other words, it is as if the pump light was also incident from the output side of the optical amplification fiber 10. The signal light is also amplified by the pump light traveling in the opposite direction to the signal light.

The pump light traveling in the opposite direction to the signal light is shown in FIG.
At the signal light input end of the optical amplification fiber 10, the power is 25% of the initial power.
The pump light is incident on the optical coupler 14 in the opposite direction, a part of the pump light is directed to the pump light source 12, and the rest propagates to the input part of the signal light. However, the pump light component propagating toward the input part of the signal light is blocked by the optical isolator 18. Therefore, the pump light is transmitted to the optical fiber grating 16.
And does not impair the optical processing system in the preceding stage even if the light is propagated in the opposite direction to the signal light.

After all, the sum of the power of the pump light propagating in the same direction as the signal light and the power of the pump light reflected by the optical fiber grating 16 and propagating in the opposite direction to the signal light contributes to the gain of the optical amplification fiber. That is, in the axial direction of the optical amplification fiber 10, the characteristic shown by the symbol C in FIG. 2 is obtained.
The characteristic indicated by symbol A in FIG. 2 corresponds to the case of conventional unidirectional excitation. As is clear from the comparison between the characteristic indicated by reference character A and the characteristic indicated by reference character C in FIG. 2, the present embodiment has a smaller change in the pumping light power in the axial direction of the optical amplification fiber 10,
Therefore, the gain can be made uniform in the axial direction.

In this embodiment, since the pump light which has been conventionally discarded is reflected by the optical fiber grating 16 and reused, a high pump light rate can be achieved. This means that if the gain is the same, the output light intensity of the pump light source 12 can be reduced.

In the above embodiment, the optical fiber grating 16 for reflecting the excitation light is disposed only on the output side of the optical amplification fiber 10, but as shown in FIG. 3, between the optical isolator 18 and the optical coupler 14. An optical fiber that selectively reflects 100% or almost 100% of the wavelength λp of the excitation light.
The grating 20 may be arranged. That is, the optical fiber gratings 16 and 20 that reflect the excitation light are arranged on both the input side and the output side of the optical amplification fiber 10. In this case, the pump light introduced into the optical amplification fiber 10 by the optical coupler 14 makes a round trip between the optical fiber gratings 16 and 20, and the pump light can be utilized without waste. Since the optical fiber grating 20 is a reflection element for selecting the wavelength λp of the pump light, the signal light is transmitted to the optical fiber grating 2.
0 can be transmitted with almost no loss.

The present embodiment can be used for, for example, an optical communication system in a 1.3 μm band or a 1.5 μm band. 1.5μ
When amplifying the signal light of m, the optical amplification fiber 10 has E
The wavelength of the excitation light source 12 is 1.48 μm band or 0.98 μm band. When amplifying the 1.3 μm signal light, Pr is added to the optical amplification fiber 10, and the wavelength of the excitation light source 12 is in the 1.02 μm band.

[0022]

As can be easily understood from the above description, according to the present invention, a high pumping light rate and a high gain efficiency can be realized with a very simple configuration. Therefore, an inexpensive and highly reliable optical amplifier can be provided, which can contribute to improvement of the reliability of the optical fiber communication system.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an embodiment of the present invention.

FIG. 2 is a characteristic diagram of the present embodiment.

FIG. 3 is a modified example of the present embodiment.

[Explanation of symbols]

 10: Optical amplification fiber 12: Pump light source 14: WDM optical coupler 16: Optical fiber grating 18: Optical isolator 20: Optical fiber grating

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Toshio Tani 2-3-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo International Telephone & Telephone Corporation

Claims (2)

[Claims] 1. An optical amplification medium, an excitation light source for generating excitation light, excitation light supply means for supplying excitation light generated by the excitation light source to the optical amplification medium, and disposed on one side of the optical amplification medium And a first reflecting member that selectively reflects the excitation light from the optical amplification medium but transmits the light to be amplified. And a second reflection member disposed on the other side of the optical amplifying medium for selectively reflecting the excitation light from the optical amplifying medium but transmitting the target light for optical amplification. The optical amplifier according to claim 1, wherein: