JPH04340933A - Optical amplifier - Google Patents

Abstract

PURPOSE:To obtain the optical amplifier which does not oscillate itself and has a high amplification degree. CONSTITUTION:An amplifier 12 generates natural emission light containing components with the same wavelength with input signal light and this natural emission light is inputted to a trailing-stage amplifier 13 having a high amplification degree at all times. Therefore, the amplifier 2 does not oscillate itself even when the signal light is not inputted to an input fiber 1.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier used in a post-amplifier for an optical transmitter, an optical repeater, a pre-amplifier for an optical receiver, etc. in optical communication technology.

0002

2. Description of the Related Art Conventionally, an optical amplifier using a specific optical fiber (for example, an Er-doped fiber) is known as one of the optical amplifiers for directly amplifying signal light.

FIG. 2 is a block diagram showing an example of this type of optical amplifier (IEICE Optical Communication System Study Group Material OCS89-3, May 1989, P. 13-20). In FIG. 2, signal light (1.55 μm band) input from an input fiber 21 is converted into a parallel light beam by a lens 22a, passes through a filter 23, and is converged onto the end face of an Er doped fiber 25 by a lens 22b. On the other hand, pump L
The light (1.48 μm band) emitted from D24 is sent to lens 2.
2c, it is converted into a parallel beam of light, reflected by a filter 23,
It is focused onto the end face of the Er doped fiber 25 by the lens 22b. As a result, the signal light (1.55 μm band)
is amplified in the Er-doped fiber and extracted from the output fiber 26.

[0004] In order to prevent self-oscillation of the optical amplifier, an optical isolator may be inserted midway between the input fiber 21 and the output fiber 26.

[0005]

However, the optical amplifier having the above structure has a problem in that when the amplification degree is increased, self-oscillation occurs when the input signal light disappears.

In some cases, this self-oscillation cannot be prevented even if an optical isolator is inserted between the input fiber 21 and the output fiber 26.

The present invention has been made in order to solve the above problems, and an object thereof is to provide an optical amplifier that does not self-oscillate even when there is no input signal light and has a high amplification degree. do.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a first
a polarization-independent isolator connected to the output side of the first fiber amplifier, and a second fiber amplifier with high amplification connected to the output side of the isolator. It is.

[0009]

[Operation] The first fiber amplifier generates spontaneous emission light containing a component of the same wavelength as the input signal light, and this spontaneous emission light is input to the second fiber amplifier at the subsequent stage. Therefore, even when there is no input signal light, the second fiber amplifier does not self-oscillate. As a result, an optical amplifier that does not cause self-oscillation and has a high amplification degree can be obtained.

0010

Embodiment FIG. 1 is a block diagram showing an embodiment of the present invention. In this embodiment, two amplifiers 12 and 13 are connected in series, and the amplifier 12 has an input fiber 1 and a lens 2 (
3), filter 3, pump LD4 that emits pump light (1.48 μm band), E doped with erbium element
r Consisting of a doped fiber 5 and a polarization-independent isolator 6, the amplifier 13 includes three lenses, a filter 7, and a pump LD that emits pump light (1.48 μm band).
8. This is a fiber amplifier consisting of an Er doped fiber 9 doped with erbium element, a polarization independent isolator 10, and an output fiber 11. Both amplifiers 12 and 13 have substantially the same configuration as the conventional optical amplifier shown in FIG. 2, and therefore operate in the same manner. However, the amplification degree of the amplifier 12 is set low so as not to cause self-oscillation even when there is no input signal light, and the amplifier 13
has such a high amplification that it self-oscillates when there is no input light.

Next, the operation of this embodiment will be explained.

When signal light (1.55 μm band) is input to input fiber 1, this signal light is sequentially amplified by amplifier 12 and amplifier 13 and output from output fiber 11.

Next, when no signal light is input to the input fiber 1, the amplifier 12 naturally does not output any signal light. However, the pump light emitted from pump LD4 is E
Since the light is input to the r doped fiber 5, low power spontaneous emission light in the 1.55 μm band is always outputted from the Er doped fiber 5, and the amplifier 12 outputs this spontaneous emission light. The amplifier 13 amplifies and outputs the spontaneous emission light in the same way as normal input signal light. That is, the amplifier 13 would cause self-oscillation if there was no input signal light, but since the spontaneous emission light (1.55 μm band) is input from the amplifier 12, the amplification state is maintained without causing self-oscillation. Here, in order for the amplifier 13 to not cause self-oscillation, it is generally necessary to input spontaneous emission light of about -10 dBm, but this level of spontaneous emission light power can be easily obtained by the amplifier 12 in the previous stage. It can be output.

The isolator 6 inserted on the output side of the amplifier 12 is configured so that the Er-doped fibers 5 and 9 mutually amplify the spontaneous emission light from the other Er-doped fiber, and oscillate by multiplexing and reciprocating. It also works to prevent

[0015]

As described above in detail, according to the present invention, a low amplification that does not cause self-oscillation is provided before the second fiber amplifier that has a high amplification that is likely to cause self-oscillation. Since the first fiber amplifier is provided and the spontaneous emission light generated by the first fiber amplifier is input to the second fiber amplifier, even if the input signal light is cut off, the second fiber amplifier will not oscillate. I won't wake you up. Therefore, by cascading the first fiber amplifier and the second fiber amplifier,
It is possible to obtain an optical amplifier with high amplification that does not cause self-oscillation.

[Brief explanation of the drawing]

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

FIG. 2 is a configuration diagram of a conventional optical amplifier.

[Explanation of symbols]

1 Input fiber 2 Lens 3, 7 Filter 4, 8 Pump LD 5, 9 Er Doped fiber 6, 10
Isolator 11 Output fiber

Claims (1)

[Claims] 1. A first fiber amplifier having a low amplification that does not cause self-oscillation, and a polarization-independent isolator connected to the output side of the first fiber amplifier.
and a second fiber amplifier with a high amplification power connected to the output side of the isolator.