Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
1998-12-02
2001-01-16
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
Optical fiber
15
Reexamination Certificate
active
06175444
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bi-directional optical amplifier optically amplifying a bi-directionally propagating signal light.
2. Description of the Related Art
A rare-earth element added optical fiber, made by adding a rare-earth element such as the Erbium(Er) to silica (SiO
2
) optical fiber, is well-known as an optical amplification element, which optically amplifies a damped bi-directional signal light and transmits it a long distance. In recent years, the optical amplifier with the optical amplification element has been used in place of the amplifier with a function of making a photoelectric conversion.
In the optical communication systems, a bi-directional optical communication or a bi-directional reception and transmission of a signal light are both made. In the bi-directional optical communication, in order to more efficiently use the optical transmission line, the bi-directional optical communication system is available where identical or different wave-lengths of signal lights are bi-directionally propagated along an optical fiber.
When an optical amplifier with the above optical amplification element is applied to the bi-directional optical communication system in order to amplify optically, a bi-directional optical amplifier is necessary. The conventional bi-directional optical amplifiers have incorporated a technology, for example, the one disclosed in “Japanese Patent Application Laid-open No. Hei-9-18417” or “Japanese Patent Application Laid-open No. Hei-4-62528”. The former (Japanese Patent Application Laid-open No. Hei-9-18417) is configured in such a way that EDFs (Erbium Doped Fibers) are connected to four ports in an optical circulator, respectively. On the other hand, the latter(Japanese Patent Application Laid-open No. Hei-4-62528) is configured in such a manner that an optical device, other than the rare-earth element added optical fibers, is connected to the input/output ports of an optical circulator.
However, both the above configurations need a reflection point upon which a signal light can be totally reflected. In addition, an optical filter is required in order to prevent a possible emission of spontaneous emission light at an optical input/output end. Accordingly, its configuration becomes complex, causing an increase of transmission losses.
SUMMARY OF THE INVENTION
Accordingly, the objective of a bi-directional optical amplifier according to the present invention is to decrease the noise factor, allowing an optical transmission of high quality.
A bi-directional optical amplifier according to the present invention is comprised of: an optical circulator with four ports; a first and a second optical amplification fiber; two pumping light sources, each outputting a pumping light; two optical couplers; and a wave-length selection/reflection filter.
The optical circulator according to the present invention comprises four ports of the first to fourth, each sending incoming light one after another to the adjacent port. The first to third optical amplification fibers are connected to the first to third ports of the optical circulator, respectively.
The first optical coupler, connected to the second port of the optical circulator, receives a first signal light(downward signal light) output from the second port. The first optical coupler has a feature to pass the first signal light. On the opposite side of the second port of first optical coupler, a first wave-length selection/reflection unit is prepared to selectively reflect the specific wave-lengths of the first signal light.
The first optical coupler synthesizes a pumping light output from the first pumping light source with the first signal light reflected on the first wave selection/reflection unit, outputting both the resulting first signal light and first pumping light to the second port. The first signal light and first pumping light received at the second port are both output from the third port. The first signal light enters a second optical amplification fiber connected to the third optical input terminal where the first signal light is optically amplified with the help of the first pumping light and then is output.
The second signal light(upward signal light) is also optically amplified with the help of the following units: the second optical coupler; the second pumping light source; the second wave-length selection/reflection unit; and the first optical amplification fiber, in the same manner that the first signal light is optically amplified.
The second optical coupler, connected to the fourth port of the optical circulator, receives the second signal light output from the fourth port. The second optical coupler has a feature to pass the second signal light. On the other side of the fourth port of the second optical coupler, a second wave-length selection/reflection unit is prepared to selectively reflect the specific wave-lengths of the second signal light.
The second optical coupler synthesizes the second pumping light emitted from the second pumping light source with the second signal light reflected on the second wave-length selection/reflection unit, outputting them to the fourth port. The second signal light and the second pumping light received by the fourth port are both output from the first port. The second signal light enters the first optical amplification optical fiber connected to the first light input terminal. It is then optically amplified with the help of the second pumping light. Utilizing the above operation, the first and second signal lights are both successfully, optically amplified.
It is noted that each of the first and second optical amplification fibers is a rare-earth element added optical fiber. The first and second wave-length selection/reflection units used in the optical amplifier according to the present invention are made from a dielectric multi-layered film filter or an optical fiber grating. An optical coupler including the dielectric multi-layered film filter or a fiber fusion-spliced optical coupler is used for the first and second optical couplers.
In the bi-directional optical amplifier according to the present invention with the above configuration, both the locations between the second port of the optical circulator and the first or second wave-length selection/reflection unit, and between the fourth port and the second wave-length selection/reflection unit, on which the first and second optical couplers are prepared, can be changed to other locations between the first port and the first optical amplification fiber, and between the third port and the second optical amplification fiber, respectively. In this case, it is noted that since the optical coupler is prepared on the main transmission line, the first and second signal lights have to be utilized in the same wave-length band.
Moreover, in the bi-directional optical amplifier, according to the present invention, the first and second optical couplers can be located either on the opposite side of both the first optical amplification fiber and the first port, or on the opposite side of the third port of the second optical amplification fiber. In this case, since the optical coupler is also located in the main transmission line, the first and second signal lights need to be utilized in the same wave-length band.
Furthermore, in the bi-directional optical amplifier, according to the present invention, the first and second pumping light sources can be connected to the opposite side of the second or fourth port of the first or second wave-length selection filter. In this configuration, the wave-length selection filters have a feature whereby they selectively reflect the specific wave-lengths of the first and second signal lights. They also pass the specific wave-lengths of the first and second pumping lights. In the above configuration, the first and second optical couplers are unnecessary, allowing it then to be a simple configuration.
REFERENCES:
patent: 5548438 (1996-08-01), Delavaux
patent: 5652675 (1997-07-01), Shibuya
patent: 5742416 (
Hellner Mark
McGinn & Gibb, P.C.
NEC Corporation
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