Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-07-27
2001-04-10
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06215565
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to optical communications system operation and management, and more particularly to a method of and system for detecting and diagnosing faults in an optical communications system.
DESCRIPTION OF THE PRIOR ART
Optical fiber systems have become the physical transport medium of choice in long distance telephone and data communication networks. The original optical fiber systems included, in addition to a light transmitter and a light receiver connected by optical fiber, repeaters at various points along the optical fiber. Repeaters are optical-electrical devices that include a receiver and a transmitter in series with circuitry for reshaping and retiming the signal. The receiver part of the repeater converts the signal on the optical fiber from the optical domain to the electrical domain, and the transmitter converts the signal from the electrical domain back to the optical domain. The retiming and reshaping circuitry processes the signal in the electrical domain prior to retransmission.
Repeaters also include various fault detection circuitry. Whenever the fault detection circuitry of a repeater detects a loss of signal, which may be caused by a break in the fiber, the repeater generates an alarm indication signal (AIS), which is passed downstream from repeater to repeater to a controller. The controller can identify the repeater that originated the AIS and thereby determine the approximate location of the fiber break. Recently, optical network operators have proposed and have begun to introduce “all-optical” systems. An all-optical system does not include electro-optical repeaters. Rather, all-optical systems use optical amplifiers, such as rare earth-doped fiber amplifiers, to amplify the optical signals along the route.
In a communications network implemented with electro-optical equipment, failure detection and location is relatively easy to accomplish. In transit, the data-bearing signals are handled by numerous transmitters, receivers, amplifiers, multiplexers, and other equipment, any of which can readily recognize the absence of a valid signal and generate an alarm.
Some of the main advantages driving the implementation of all-optical networks are larger capacity links, path transparency regardless of bit rate and format, and more efficient switching of large bandwidth paths. In implementing an all-optical network, the detection and location of failure conditions is complicated because the data modulating the optical carrier is no longer readily available in the form of an electrical signal. To install equipment that transduces and decodes the high bit rate data stream defeats some of the principal advantages of an all-optical approach.
In patent application Ser. No. 08/582,845, filed Dec. 29, 1995 (Docket No. RIC-95-137), there is disclosed a technique for superimposing a low-level, low-frequency modulation onto the optical carrier along with the high bit rate data signal. An inexpensive photo detector can be used anywhere along the optical path to tap a small fraction of the optical carrier power and extract the low-level subcarrier without having to transduce and decode the high bit rate signal. This subcarrier can serve as a pilot tone to allow for a simple and reliable optical continuity indicator. However, the subcarrier technique alone cannot distinguish between the failure of an optical fiber, a transmitter, or a line amplifier. There has been proposed an optical performance monitor (OPM), which is a device that can monitor an optical line and measure such parameters as optical power, wavelength, and optical signal-to-noise ratio. However, the optical performance monitor cannot distinguish some types of failures.
SUMMARY OF THE INVENTION
The present invention provides a method monitoring performance of an optical communications system by measuring (i) sub-carrier signal-to-noise ratio, (ii) optical signal signal-to-noise ratio, and (iii) measuring optical signal bit error rate. The method diagnoses a system component failure based upon measured sub-carrier signal-to-noise ratio, optical signal signal-to-noise ratio, and optical signal bit error rate. Preferably, the method diagnoses a system component failure by consulting a component failure table.
According to the present invention, if the optical signal signal-to-noise ratio is degraded and both the subcarrier signal-to-noise ratio and the optical signal bit error rate are normal, then there is a failure of an optical signal signal-to-noise ratio test device. If the optical signal bit error rate is degraded and both the subcarrier signal-to-noise ratio and the optical signal signal-to-noise ratio are normal, then there is an optical signal failure at a receiver. If the subcarrier signal-to-noise ratio is normal and both the optical signal signal-to-noise ratio and the optical signal bit error rate are degraded, then the possible failures are a degraded amplifier pump laser, a presence of other carriers added to an amplified line, a robbing of amplifier power by the presence of mixing products, an optical cross-connect restoration, an increase in amplifier input isolator attenuation, a presence of stimulated Raman scattering, or a failure of a carrier in a common subcarrier technique.
If the subcarrier signal-to-noise ratio is degraded and both the optical signal signal-to-noise ratio and the optical signal bit error rate are normal, then there is either a faulty subcarrier transmitter, a faulty subcarrier receiver, or a non-linear element or saturable element in the system. If the optical signal bit error rate is normal and both the optical signal signal-to-noise ratio and the subcarrier signal-to-noise ratio are degraded, there is a combined subcarrier and optical signal signal-to-noise ratio test device failure. If the optical signal signal-to-noise ratio is normal and both the subcarrier signal-to-noise ratio and the optical signal bit error rate are degraded, there is a combined failure of both the optical signal receiver and the subcarrier receiver. If the subcarrier signal-to-noise ratio, the optical signal signal-to-noise ratio, and the optical signal bit error rate are all degraded, then there is either a reduction in transmitter laser power, a loss of signal at an amplifier input, or an operator error by pre-emphasizing a transmitter.
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Davis Gary B.
Fee John
Liu Shoa-Kai
MCI Communications Corporation
Pascal Leslie
Phan Hanh
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