JPH06268284A - Optical amplifier - Google Patents

Abstract

PURPOSE:To provide an optical amplifier which can maintain a stable performance for a long time even under moisture and hydrogen atmosphere. CONSTITUTION:In the title amplifier for amplifying signal light by allowing signal light and excitation light to enter an optical fiber 1 which is doped with an activated element and then amplifying signal light by the induction release light of the active element, the optical fiber 1 doped with the active element is placed inside a container 2 and is sealed with a sealing agent 3. Therefore, even if it is used under an atmosphere where it is exposed to moisture and hydrogen for a long time, amplification characteristics do not deteriorate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier forming a part of an optical communication system.

[0002]

2. Description of the Related Art In an optical communication system, amplification of an optical signal attenuated by long-distance transmission is conventionally carried out by converting an optical signal into an electric signal, electrically amplifying the electric signal, and then converting the electric signal again. Has been done. However, in such a method, there is a problem that the relay of the multiplex communication, which requires high speed, is naturally limited, and there is a problem that the system becomes complicated. Optical amplifiers that can amplify are being used. In the optical amplifier, the signal light passing through the optical fiber whose core portion is doped with an active element such as Er is directly emitted by the stimulated emission of the active element excited by the excitation light incident on the active element-doped optical fiber together with the signal light. It is amplified. An optical amplifier using an optical fiber doped with Er as an active element is suitable for optical amplification for 1.55 μm band optical communication and is already in practical use. For optical amplification for 1.3 μm band optical communication, Nd and Pr are used.
The optical fiber doped with is attracting attention.

The main components of an optical amplifier are, in addition to an optical fiber doped with an active element, a pumping light source for pumping the active element, a power supply circuit for driving the pumping light source, and pumping from the pumping light source. There are an optical multiplexer / demultiplexer for making light incident on the active element-doped fiber, an optical isolator for removing reflected light of pumping light or signal light, and the like. As the incident direction of the pumping light to the active element-doped fiber, the forward pumping pumped from the incident side to the active element-doped fiber of the signal light, the backward pumping pumped from the exit side,
There is bidirectional excitation that is excited from both the incident side and the output side,
Each of them can be used properly according to the purpose of use of the optical amplifier.

The active element-doped fiber used in the optical amplifier has a length which varies depending on the active element concentration in the core and the fiber structure, and various lengths from less than 10 m to more than 200 m are adopted, and the entire optical amplifier is compact. It is wrapped around a reel with a diameter of a few centimeters for the sake of simplicity.

[0005]

It is generally known that when an optical fiber is exposed to moisture or hydrogen for a long time, its performance is deteriorated and transmission loss is increased. The active element-doped fiber used in the optical amplifier also deteriorates in amplification characteristics when exposed to moisture or hydrogen for a long time. As a means to improve the hydrogen resistance, there is a method of coating the fiber with carbon.
In this case, a CV for applying a carbon coat to the drawing device
It required a major modification such as mounting a D device and a device for measuring the film thickness.

The present invention has been made to solve the above problems, and an object thereof is to provide an optical amplifier capable of maintaining stable performance for a long period of time even in an atmosphere of humidity or hydrogen.

[0007]

An optical amplifier according to the present invention for achieving this object, as shown in FIG. 1 corresponding to an embodiment, transmits signal light and pumping light to an optical fiber 1 doped with an active element. In an optical amplifier which is incident and amplifies the signal light by stimulated emission of the active element, an optical fiber 1 doped with the active element is put in a container 2 and sealed with a sealant 3.

[0008]

Since the optical fiber 1 doped with the active element is placed in the container 2 and sealed with the encapsulant 3, the amplification characteristic may deteriorate even when used in an environment exposed to moisture or hydrogen for a long time. Absent.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an embodiment of a 1.55 μm band optical amplifier to which the present invention is applied. The optical amplifier of the present invention shown in FIG.
It is inserted midway from the signal-side optical transmission fiber 11 on the incident side to the signal-optical transmission fiber 12 on the output side. A 1.55 μm band optical isolator 4 is connected to the signal light transmission fiber 11 on the incident side, and the active element-doped fiber 1 is further connected.
One end of is connected. The active element-doped fiber 1 is wound into a loop and placed in a stainless steel closed container 2. The closed container 2 is near the end of the active element-doped fiber 1.
Of the active element-doped fiber 1 through the hole formed in the wall of the
The inside of the closed container 2 in which is put is kept airtight. The other end of the active element-doped fiber 1 is connected to the input end of the optical multiplexer / demultiplexer 5. One of the ports branched to the signal light output side of the optical multiplexer / demultiplexer 5 is connected to the signal light transmission fiber 12 on the emission side via the isolator 7, and the pump light source 8 is connected to the other port via the isolator 6. It is connected.
The excitation light source 8 is connected to the drive power supply circuit 9.

Since the optical amplifier in this embodiment is for the 1.55 μm band, Er is used as the active element in the active element-doped fiber. The total length of the active element-doped fiber 1 is 30 m in this example. The signal light incident from the signal light transmission fiber 11 on the incident side enters the active element-doped fiber 1 via the isolator 4. On the other hand, in the active element-doped fiber 1, the pumping light from the pumping light source 8 is added to the optical multiplexer / demultiplexer 5.
It is incident due to the coupling function of. While passing through the active element-doped fiber 1, the signal light is amplified by the stimulated emission of the active element excited by the excitation light, passes through the optical multiplexer / demultiplexer 5, and passes through the isolator 7 to the signal light transmission fiber 12 on the emission side. It goes out to. In the above configuration, the pumping light is a so-called backward pumping optical amplifier in which the pumping light enters the active element-doped fiber 1 through the optical multiplexer / demultiplexer 5 in the direction opposite to the transmission direction of the signal light.

FIG. 2 shows another embodiment of the optical amplifier to which the present invention is applied. The optical amplifier of this embodiment has the same optical connection as that of the optical amplifier of the embodiment shown in FIG. 1, but is different in the structure for sealing the active element-doped fiber 1.
That is, the active element-doped fiber 1 is inserted into the aluminum seamless pipe that is the closed container 2, the end of the seamless pipe is sealed with the epoxy resin that is the sealant 3, and the inside of the container 2 is kept airtight. The seamless pipe containing the active element-doped fiber 1 is bent into a loop to keep the optical amplifier compact.

FIG. 3 shows another embodiment of the optical amplifier to which the present invention is applied. The optical amplifier of this embodiment is functionally the same as the optical amplifier of the embodiment shown in FIGS. 1 and 2, but has different optical connections, and is a so-called forward pump optical amplifier. Further, the structure for sealing the active element-doped fiber 1 is the same as that of the embodiment shown in FIG. 2, but the arrangement of each component is different. That is, the optical amplifier of the embodiment shown in FIG. 3 is as follows. The isolator 4 is connected to the signal light transmission fiber 11 on the incident side, and is connected to the first input port of the optical multiplexer / demultiplexer 5. A pumping light source 8 is connected to a second input port of the optical multiplexer / demultiplexer 5 via an isolator 6. The excitation light source 8 is a drive power circuit 9
It is connected to the. One end of the active element-doped fiber 1 is connected to the first output port of the optical multiplexer / demultiplexer 5. The active element-doped fiber 1 is inserted into an aluminum seamless pipe which is a hermetically sealed container 2, the end of the seamless pipe is sealed with an epoxy resin which is a sealant 3, and the interior of the container 2 is kept airtight. The other end of the active element-doped fiber 1 is connected to the signal light transmission fiber 12 on the emission side via the isolator 7. Active element doped fiber 1
The seamless pipe containing is bent into a loop,
Further, the isolator 4, the optical multiplexer / demultiplexer 5, the isolator 6, the pumping light source 8 and the drive power supply circuit 9 which are the necessary components described above are arranged inside the loop, and the optical amplifier is made more compact.

In the above embodiment, stainless steel and aluminum are used as the closed container 2, but aluminum alloy, titanium or its alloy, lead or its alloy, etc. can also be used. In particular, if a container made of lead or an alloy thereof is used, not only the moisture resistance and hydrogen resistance of the active element-doped fiber 1 but also the radiation resistance can be improved. In addition to metal, a ceramic container that is lightweight and has excellent corrosion resistance can be used. It is desirable to replace the inside of the container 2 with a dry inert gas.

Further, it can be used not only for the forward-pumping and backward-pumping optical amplifiers as in the above-described embodiment, but also for the bidirectional pumping optical amplifiers pumping from both the incident side and the outgoing side.

[0015]

As described above in detail, in the optical amplifier of the present invention, the active element-doped fiber is placed in a container and hermetically sealed so that the amplification function of the fiber does not deteriorate even in an atmosphere containing moisture or hydrogen. Therefore, stable performance can be maintained for a long time. It becomes an optical amplifier excellent in hydrogen resistance even without carbon coating as in the past.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of an optical amplifier to which the present invention is applied.

FIG. 2 is a perspective view of another embodiment of the optical amplifier to which the present invention is applied.

FIG. 3 is a perspective view of another embodiment of the optical amplifier to which the present invention is applied.

[Explanation of symbols]

1 is an active element doped fiber, 2 is a closed container, 3 is a sealant, 4/6 and 7 are optical isolators, 5 is an optical multiplexer / demultiplexer, and 8
Is a pumping light source, 9 is a drive power supply circuit, and 11 and 12 are signal light transmitting fibers.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01S 3/10 Z 8934-4M

Claims (1)

[Claims] 1. An optical amplifier for injecting signal light and excitation light into an optical fiber doped with an active element and amplifying the signal light by stimulated emission light of the active element, wherein the optical fiber doped with the active element is a container. An optical amplifier characterized by being placed in a container and sealed with a sealant.