Optical: systems and elements – Optical amplifier – Correction of deleterious effects
Reexamination Certificate
2001-02-28
2003-09-02
Black, Thomas G. (Department: 3663)
Optical: systems and elements
Optical amplifier
Correction of deleterious effects
C359S341410, C359S341420
Reexamination Certificate
active
06614587
ABSTRACT:
FIELD OF INVENTION
Invention relates to communications, particularly to controlling components in optical communications systems.
BACKGROUND OF INVENTION
The growing need for communications networks supporting high-speed transmission rates has contributed to the rising popularity of optical networks, particularly for applications such as backbone networks. The optical amplifier has increased the maximum span distance between expensive optical to electrical regenerators, making long haul optical networks more affordable. Metropolitan area networks (MANs) and access networks are new markets for the deployment of optical networks due to the high demand for bandwidth, especially by internet users. In long-haul networks, many optical amplifiers may be cascaded to traverse long distances creating concerns regarding the accumulation of channel power differences due to gain fluctuations and the accumulation of optical noise. For this application, the gain flatness requirements for each amplifier is typically very tight. For example, common gain flatness requirements may be in the range of +/−0.5 dB. The accumulation of optical noise in systems can be engineered by specifying the noise figure (NF) and gain of amplifiers. For typical MANs and access networks, the distances spanned by the optical network are much shorter than the distances spanned in long haul networks, so that the gain flatness and noise Figure requirements for amplifiers in the MAN can be relaxed compared to the requirements for a typical long haul network. Amplifiers with relaxed gain flatness and noise figure requirements typically used in MAN and access network applications are often less expensive than amplifiers with tight requirements.
Two common methods for amplifier control include automatic gain control (AGC) and automatic level control (ALC) techniques. AGC techniques are effective for maintaining the gain characteristics of an optical amplifier constant. However, the output power varies with the input power. In contrast, ALC techniques tend to be immune to variations of optical amplifier input power. However, when the number of optical channels changes, the ALC controlling microprocessor must be updated with the number of optical channels. For ALC-only controllers, the typical channel change update is done manually. In general, manual techniques tend to be time-consuming, inconvenient, error-prone and unacceptable to network administrators. To address these problems, expensive channel counters may be deployed to determine the number of channels when using ALC techniques. However, the added expense of a channel counter is typically unacceptable for use in low cost MANs and access networks.
What is needed is a stable, inexpensive and automated method for deploying, operating and maintaining optical amplifiers in a variety of optical networks under a wide range of conditions.
SUMMARY OF INVENTION
It is an object of the current invention to provide reliable and inexpensive methods for deploying, operating and maintaining optical amplifiers in a variety of optical networks under a wide range of conditions.
A preferred embodiment of the current invention may control one or more optical amplifiers or gain blocks operating in a variety of modes such as AGC mode, ALC mode and hybrid AGC/ALC mode without requiring the use of expensive channel counters. According to a preferred embodiment of the current invention, the number of channels may be estimated based on gain block input optical power readings and a channel reference table calculated using the initial number of channels served by the optical amplifier and an initial gain block input optical power.
Advantageously, the current invention enables the simple and inexpensive deployment, operation and maintenance of optical amplifiers or gain blocks in a wide variety of optical network such as MANs and WANs.
REFERENCES:
patent: 5491548 (1996-02-01), Bell et al.
patent: 5699081 (1997-12-01), Denkin et al.
patent: 5828486 (1998-10-01), Yoshida
patent: 6304347 (2001-10-01), Beine et al.
patent: 6366393 (2002-04-01), Feulner et al.
patent: 2002/0027706 (2002-03-01), Park et al.
patent: 2000 52684 (2000-09-01), None
Mao Charles
Xie Jin
Yu Jun
Avanex Corporation
Black Thomas G.
Hughes Deandra M.
Sawyer Law Group LLP
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