Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
1999-12-14
2001-10-23
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
Optical fiber
C359S341410
Reexamination Certificate
active
06307670
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical amplifier having an optical fiber and, more particularly, to a gain-controllable optical fiber amplifier and method of controlling the amplifier pump power.
2. Technical Background
Data communication systems increasingly are employing optical fibers as the transmission paths for information. The use of optical fiber generally allows for the transmission of large amounts of data at high speeds for long distance transmission. Optical fiber, although to a lesser extent than other transmission mediums such as wire, usually is susceptible to some signal loss such that signals transmitted therewith are attenuated as the transmission path becomes longer. As a consequence, one or more optical amplifiers are often employed in the communication path to amplify the optical signals.
Various types of optical amplifiers have been developed and are used to amplify optical signals. In particular, the erbium-doped fiber amplifier (EDFA) is one example of an optical fiber amplifier that is widely known for use in amplifying optical signals. The erbium-doped fiber amplifier is a rare earth element-doped optical fiber amplifier containing erbium, as the rare earth substance, injected into the optical fiber and raised to an excited state by pump light that is input separately from the signal light so that the signal light is amplified by the pump energy. Accordingly, the amplifier generally requires one or more pump light sources coupled to the optical fiber.
In recent years, the amount of information transmitted on optical fibers has increased significantly. Typically, to increase the capacity of the optical transmission path, several light signals at different wavelengths (i.e., channels) are multiplexed for transmission through a single optical transmission. In a multiple-wavelength multiplexed transmission system, a plurality of channels are made available for transmission by an optical fiber. However, the total number of active channels that are used may fluctuate as channels are added or dropped depending on the demand, or in the event that channels fail. In order to maintain a constant per-channel gain, the gain of a fiber amplifier used in the systems generally must be controlled in response to changes in the number of active channels. Accordingly, the greater the number of channels that are multiplexed on an optical fiber, generally the greater the amount of pump energy that becomes necessary to maintain a constant per-channel gain, and vice versa.
While the source of pump light may be controlled in conventional optical amplifiers to provide a substantially constant overall gain, a number of drawbacks exist. Conventional constant gain amplifiers do not completely compensate for changes in the number of channels. In conventional amplifiers, changes in the number of channels generally leads to noise figure degradation and per channel power variations. In particular, multiple-pump rare earth element-doped fiber amplifiers commonly have an internal element, such as a dispersion compensation filter, that is generally sensitive to high per-channel signal powers. Gain or power control achieved by varying the pump power of the rare earth element-doped fiber may present noise figure degradation, especially when the total input power becomes comparable to backward amplified spontaneous emission (ASE) at the input of the amplifier coil. For this reason and others, it is desirable to provide a gain controllable fiber amplifier that minimizes the amount of noise introduced by the amplifier.
SUMMARY OF THE INVENTION
The present invention provides a gain-controllable optical fiber amplifier and method of controlling gain that minimizes noise introduced into the optical signal and minimizes excursions in the per channel power internal to the amplifier. To achieve this and other advantages, and in accordance with the purpose of the present invention as embodied and described herein, the present invention provides a gain-controllable optical fiber amplifier having an input for receiving an optical signal and an output for providing an amplified optical signal. A first gain stage is coupled between the input and output and includes a first optical fiber and a first pump. According to a further aspect of the present invention, a second gain stage is coupled in series with the first gain stage and includes a second optical fiber and a second pump. The amplifier includes a pump controller for controlling the amount of power output from each of the pumps to maintain a substantially constant overall gain. The controller decreases the power output from each of the pumps as a function of a minimum value of the corresponding pump to minimize the noise level sufficient to support amplified spontaneous emission. Accordingly, the present invention advantageously controls the gain applied in an optical fiber amplifier in a manner that minimizes the amount of noise that may otherwise be introduced into the optical signal.
Additional features and advantages of the invention will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description or recognized by practicing the invention as described in the description which follows together with the claims and appended drawings.
It is to be understood that the foregoing description is exemplary of the invention only and is intended to provide an overview for the understanding of the nature and character of the invention as it is defined by the claims. The accompanying drawings are included to provide a further understanding of the invention and are incorporated and constitute part of this specification. The drawings illustrate various features and embodiments of the invention which, together with their description, serve to explain the principals and operation of the invention.
REFERENCES:
patent: 5117196 (1992-05-01), Epworth et al.
patent: 5245690 (1993-09-01), Aida et al.
patent: 5506724 (1996-04-01), Shimizu et al.
patent: 5563732 (1996-10-01), Erdogan et al.
patent: 5706124 (1998-01-01), Imoto et al.
patent: 5710660 (1998-01-01), Yamamoto et al.
patent: 5812710 (1998-09-01), Sugaya
patent: 5835259 (1998-11-01), Kakui et al.
patent: 5900968 (1999-05-01), Srivastava et al.
patent: 5903385 (1999-05-01), Sugaya et al.
patent: 5907429 (1999-05-01), Sugata
patent: 5912761 (1999-06-01), Jander et al.
patent: 5923463 (1999-07-01), Hamada
patent: 6094298 (2000-07-01), Luo et al.
patent: 0871302 (1998-10-01), None
patent: 2334397 (1999-08-01), None
“Accurate Control of Output Power Level in Gain-Flattened EDFA with Low Noise Figure,” S. Y. Park et al., ECOC 97—Eleventh International Conference on Integrated Optics and Optical Fibre Communications 23rd European Conference on Optical Communications IOOC-ECOC 97 (Conf. Publ. No. 448), Sep. 22-25, 1997, pp. 43-46.
Corning Incorporated
Hellner Mark
Price Heneveld Cooper DeWitt & Litton
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