Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-06-19
2002-02-05
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S341200, C359S341440
Reexamination Certificate
active
06344915
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to communication systems having optical amplifiers. More particularly, the present invention relates to a system and method for shutting off an optical energy source in an optical communication system in order to protect service personnel repairing a system failure who might otherwise be exposed to harmful optical energy emissions. The present invention is particularly well suited for use in a wavelength division multiplexed (WDM) optical communication system having node distributed intelligence.
BACKGROUND OF THE INVENTION
Optical communication systems are a substantial and fast-growing constituent of communication networks. The expression “optical communication system,” as used herein, relates to any system which uses optical signals to convey information across an optical waveguide medium. Such optical communication systems include, for example, telecommunications systems, cable television systems, and local area networks (LANs).
Optical communication systems in all their forms are currently being challenged by dramatically increasing capacity demands. Current capacity, which is a function of existing waveguide media, is routinely exceeded by an ever increasing traffic of telephone, facsimile, computer Internet, and video data. In theory, this limited system capacity might be expanded by installing additional waveguide media. However, obtaining the necessary rights of way and installing the additional waveguide media are so costly that such expansion is impractical in many instances.
Thus, WDM optical communication systems are currently being incorporated into existing waveguide networks to increase capacity. In a WDM system, a plurality of optical communication signals are carried over a single waveguide, each signal being assigned a particular wavelength. U.S. Pat. Nos. 5,504,609; 5,532,864 and 5,557,439, the disclosures of which are incorporated herein by reference, teach several basic aspects of successful, contemporary WDM systems.
The use of optical amplifiers in WI)M systems to directly and simultaneously amplify a plurality of optical communication signals make WDM systems particularly useful in long distance optical networks. Optical amplifiers are commonly formed by the combination of a section of doped, or “active,” fiber and an optical energy source, typically a pump laser. The active fiber containing a fluorescent substance, generally a rare-earth dopant, accepts energy from the optical energy source, and transfers a portion of the optical energy to an information bearing optical communication signal, or a plurality of optical communication signals traversing the active fiber. The material composition and operation of active fiber amplifiers, is well documented; for example by Bjarklev,
Optical Fiber Amplifiers: Design and System Application
, (Artech House, Norwood, Mass.), c.1993 and
Erbium
-
Doped Fiber Amplifiers
, (John Wiley & Sons, Inc., N.Y.) c. 1994, the disclosures of which are incorporated herein by reference. As used in the context of the present invention, the term “active fiber amplifier,” is broadly construed to cover the entire class of devices, typically comprising a section of active fiber and an optical energy source, without regard to the particular composition of the active fiber or the exact structure and operating characteristics of the optical energy source. Furthermore, for the sake of simplicity throughout the subsequent description of the present invention, the entire, complex interaction between the optical energy source and the active fiber section, whereby optical energy is transferred from the optical energy source to the information bearing optical signal is referred to as the optical energy source “driving” the optical amplifier.
Unfortunately, the light wavelengths at which many conventional optical energy sources operate are hazardous to the human eye. This well known fact presents optical communication system designers with the challenge of incorporating a mechanism and/or a protocol for shutting off optical energy sources upon detection of a system fault. A “system fault,” as used in describing the present invention, is any mishap or condition which subsequently requires service personnel to intervene at a fiber level within the optical communication system. Typical system faults include a break or dislocation in the waveguide media, an optical amplifier failure, or other event requiring system element replacement.
Previous attempts to address the problem of shutting down the optical energy sources in an optical communication system following detection of a system fault have met with limited success. More importantly, these early attempts severely underperform when compared to what may be accomplished with increasing “intelligent” optical communication systems.
Referring to
FIG. 1
, a simplified optical communication system is shown comprising a West terminal
1
, an East terminal
2
, and intermediate optical line amplifiers
3
,
4
, and
5
, comprising amplifier nodes
3
E,
4
E, and
5
E arranged along an “East” running waveguide transmitting optical communication signals in a West-to-East direction, and amplifier
3
W,
4
W, and
5
W arranged along a “West” running waveguide transmitting optical communication signals in a East-to West direction. (As used in the present invention the terms “transmit,” and “transmission” are used to describe the processes of placing an optical signal in a waveguide, the physical movement of the optical signal via the waveguide, and/or the removal of the optical signal from the waveguide). Amplifiers
3
E and
3
W form intermediate amplifier
3
, amplifiers
4
E and
4
W form intermediate amplifier
4
, and amplifies
5
E and
5
W form intermediate amplifier
5
. If a break in the paired East/West waveguides is assumed between intermediate amplifiers
3
and
4
, the limitations of conventional safety shut down systems and methods are readily manifest.
Since each intermediate amplifier nominally includes paired amplifier nodes, such as (
3
E,
3
W) and (
4
E,
4
W) in
FIG. 1
, some early optical communication systems, upon directly detecting the loss of the East running optical communication signal at node
4
E, for example, would shut off the optical energy source in the
4
W amplifier node. With the resulting absence of an optical communication signal from
4
W,
3
W would shut off the optical energy source in
3
E. Thus, no potentially harmful emissions from amplifier nodes
3
E and
4
W would escape the waveguide break. While this system quickly resolved the safety hazard, it also placed the optical communication system in a undesirable state. For example, the operational status of intermediate node
5
could not be determined once the system was shut down at intermediate nodes
3
and
4
. Further, optical communication systems including such a shut down mechanism required node by node re-initiation of the system, since the intermediate amplifiers could not discriminate between the re-initiation of the optical communication signal and noise, such as a spontaneous optical amplifier emission.
Later attempts were made to remedy these problems, such as in U.S. Pat. No. 5,355,250 (the '250 patent). The '250 patent teaches a system which shuts off an optical energy source based on the detected magnitude of an optical communication signal at the input of an optical amplifier. Following detection, the sampled magnitude is compared to a predetermined reference value, and upon failing to meet this value the drive circuit for the optical energy source is turned off. In the system disclosed in '250 patent and similar systems, the entire bi-directional loop must be shut down node-by-node in cascade to secure portions of the optical communication system posing a safety threat. This result is explained in greater detail below.
In the system disclosed in the '250 patent, the entire bi-directional loop, between West terminal
1
and East terminal
2
, for the example shown in
FIG. 1
, would be shut down in a cascade of sign
Alexander Stephen B.
Corwin Robert M.
Litz Roy C.
Newman Donald T.
Shanton, III John L.
Ciena Corporation
Pascal Leslie
Sedighian M. R.
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