Optical communications – Diagnostic testing – Fault detection
Reexamination Certificate
2000-02-10
2003-09-30
Pascal, Leslie (Department: 2733)
Optical communications
Diagnostic testing
Fault detection
C014S038000, C370S228000
Reexamination Certificate
active
06626587
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to optical systems, and in particularly to optical telecommunication systems and to methods of increasing the safety of their use.
BACKGROUND OF THE INVENTION
Laser safety standards (IEC) in telecommunication systems require appropriate safety measures, and especially in case of a fiber break. Such safety measures might include Automatic Power Reduction (to be referred to hereinafter as “APR”) or Automatic Laser Shutdown (to be referred to hereinafter as “ALS”).
Continuously operating lasers have been employed in a variety of applications. Using means for interrupting the laser beam is a normal practice in such applications to avoid hazardous emissions. U.S. Pat. No. 4,663,520 describes such a fail-safe laser apparatus in which a shutter may intercept or attenuate the laser beam avoiding undesired emission of the laser beam once a predefined radiation threshold is breached.
Another approach to the problem is described in U.S. Pat. No. 5,229,593. The system disclosed by this patent, includes a microprocessor to control the laser output beam to a safety level when the input bean indicates that the output beam is not being received at the remotely positioned terminal.
The laser safety issue in optical transport telecommunication systems has been addressed among others, in ITU-T Recommendation G.664, based on the IEC 60825 laser safety standard. In accordance with this recommendation, a complete optical transport system can be regarded as a Class 1 (low hazard) laser product, since under normal operating conditions the emissions are completely enclosed and no light should be emitting outside the enclosure.
However, when the fiber breaks or an optical connector is unplugged, there exists a risk of a potentially hazardous exposure, assuming the internal emitters are of high enough power.
In accordance with IEC 60825, the hazard level of equipment is defined as one that should not exceed level
3
A (+17 dBm in the 1550 nm region) in restricted locations and level
3
B (+27 dBm in the 1550 nm region) in controlled locations.
Although in some cases the threshold of the allowed hazard level will not be exceeded, still, in order to provide appropriate shutdown operation of inserted stand-alone boosters and pre-amplifiers in optical transport systems, it might be useful to provide shut down features also at lower hazard levels.
One of the main disadvantages associated with the prior art solutions described, is, that once a failure occurs in one channel out of a plurality of channels, the traffic transmission in all the remaining channels is stopped. However, in a system that comprises a large number of channels, it may happen from time to time that the communication in at least one channel fails due to reasons other than the breaking of the fiber (e.g. laser malfunctioning, etc.). In such a case it would obviously be undesirable that the communication in all channels is automatically blocked.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical system that allows continued operation of non-failing channels, when a failure occurs in some channels of that system.
It is yet another object of the present invention to provide a system that further comprises protection means that allow diversion of traffic from failing channel to a protection channel.
It is still another object of the present invention to provide method for allowing continued operation of non-failing channels when some of the system's channels are not functioning, with or without using a protection channel in the system.
Other objects of the invention will become apparent as the description of the invention proceeds.
In accordance with the present invention there is provided an optical transmission system comprising a plurality of telecommunication channels, characterized in that when a failure occurs in one or more of said telecommunication channels, a continuous operation of the non-failing telecommunication channels is enabled, provided that the overall transmitted energy in said non-failing telecommunication channels exceeds a pre-defined threshold.
According to an embodiment of the invention, the optical transmission system comprises:
a plurality of optical transmitters;
a wave division multiplexer receiving outputs from said plurality of optical transmitters over a plurality of optical channels;
an optical link;
a wave division demultiplexer receiving an input from said division multiplexer over said optical link;
a plurality of optical receivers, each receiving an input from said wave division demultiplexer;
a determination means for determining whether the energy of the input received from said division multiplexer exceeds a pre-defined threshold; and
a blocking means controlled by said determination means and operative to intercept all laser beams leaving said wave division multiplexer.
According to still a another embodiment of the invention, the optical transmission system further comprises:
at least one optical splitter;
a detector receiving input from said at least one optical splitter;
wherein the wave division demultiplexer receiving an input from said division multiplexer over said optical link and providing outputs to the at least one optical splitter. Preferably, the optical transmission system comprises a plurality of optical splitters, each of which is operative to split the input received thereby so that a part of the input is transmitted to the detector and the remaining of the input is transmitted to a corresponding one of the plurality of optical receivers. Based on the input received at the detector, the determination means are operative to determine whether the energy of the input thus received exceeds a pre-defined threshold.
By another embodiment of the invention the blocking means comprises a switching mechanism. Such a mechanism may comprise an optical switch, or alternatively, a shutter movable between open and closed positions, adapted for completely intercepting all laser beams incident thereon in its closed position.
In yet another embodiment of the present invention, there is provided an optical transmission system comprising a plurality of telecommunication channels extending between a first and a second locations, wherein a plurality of channels are operative for carrying traffic in normal operating mode from the first location to the second location and at least one channel is adapted to operate as a protection channel, characterized in that when a failure occurs in one or more of said telecommunication channels, a continuous operation of the non-failing telecommunication channels is enabled, provided that the overall transmitted energy in said non-failing telecommunication channels exceeds a pre-defined threshold. Thus, when a failure occurs in one or more of the telecommunication channels carrying traffic in normal operating mode, the traffic of at least one of the failing channels is transmitted via the at least one protection channel.
According to still another embodiment of the present invention, the protection channel is a non-active redundant channel that may be activated upon detection of LOS in a forward channel.
In accordance with another embodiment of the invention in the optical transmission system provided, at least one of a plurality of channels operative for carrying traffic in normal operating mode is assigned a higher priority than at least one other channel of the plurality of channels operative for carrying traffic in normal operating mode, and in the event that a failure occurs in the higher priority channel, the system is adapted to divert the traffic from the failing channel to said lower priority channel.
By a preferred embodiment of the invention there is provided an optical transmission system comprising:
a plurality of optical transmitters;
a wave division multiplexer receiving outputs from said plurality of optical transmitters over a plurality of optical channels;
an optical link;
a wave division demultiplexer receiving an input from said division mu
Browdy and Neimark , P.L.L.C.
ECI Telecom Ltd.
Pascal Leslie
Payne David C.
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