Optical protection switch employing an interference filter

Details Optical protection switch employing an interference filter Optical protection switch employing an interference filter

1997-12-19

2001-07-24

Pascal, Leslie (Department: 2733)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200

Reexamination Certificate

active

06266168

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to optical switching and more particularly relates to a path protection feature for an optical switch.
BACKGROUND OF THE INVENTION
It is well-known that a provider/operator of a communications network strives to increase the level of “survivability” of the network whenever a fault occurs, e.g., a loss of signal is detected over a communications path. The operator typically increases the level of survivability by employing a protection-switching architecture to recover from a loss of signal condition. Protection switching, as it is commonly referred to, involves establishing preassigned backup resources, e.g., a duplicated/standby communications path, which may be switched into service when a loss of signal occurs.
The detection of a loss of a signal is usually done simply by comparing the level of an optical signal received via a communications path with a predetermined threshold. If the level of the received optical signal is continuously below the threshold for a predetermined period of time, then protection switching may be requested for that communications path.
It appears, however, that the presence of one or more optical amplifiers in a communication path complicates the detection of a Loss Of Signal (LOS), since the amplifiers may not immediately reduce their output power when an LOS occurs. As a result, the level of the received signal may not change until each optical amplifier in the path has been instructed by a local controller to reduce its laser pump power and thus its output power. Disadvantageously, user data may be lost, since a substantial amount of time, e.g., 700 milliseconds, may be exhausted before the LOS is detected.
Moreover, the detection of a LOS is further complicated if the optical signal is composed of a plurality of optical signals of different wavelengths &lgr;I.
SUMMARY OF THE INVENTION
We deal with the foregoing amplifier problem, in accordance with an aspect of the invention, by employing an interference filter to generate a number of different signals, e.g., main and complementary signals. These signals are then processed such that if either their sum or difference is below a respective threshold, indicating that only a noise signal is present, then a Loss Of Signal (LOS) is declared, and the system is switched to the protection line if that line is found to be available for service.
Advantageously, in this way protection switching may be invoked rapidly, typically within, for example, 3 milliseconds from the detection of a LOS, all in accordance with the principles of the invention.
These and other aspects of the invention, will become apparent from the following detailed description and accompanying drawing.


REFERENCES:
patent: 5680235 (1997-10-01), Johansson
patent: WO 97/01907 (1997-01-01), None

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