Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1998-05-12
2001-05-22
Spyrou, Cassandra (Department: 2872)
Optical waveguides
With optical coupler
Plural
C372S006000, C359S341430
Reexamination Certificate
active
06236777
ABSTRACT:
The present invention relates to an improvement in the reliability of an optical communication system optically amplified comprising two optical fiber lines, as well as of an optical amplifying system, and a method for improving the reliability of an optical communication or an optical amplifying system.
In recent years, optical long distance communication system optically amplified has become increasingly common. In fact, in a long distance communication system, periodic optical amplifiers have become attractive alternatives to opto-electronic converters and electronic regenerators/repeaters to overcome signal attenuation. As a result, there is much interest in developing highly reliable yet low cost optical amplification systems.
Reliability is especially important when the communication system is not readily accessible, such as in undersea applications.
Rare earth doped optical amplifying fibers have been developed to provide high quality optical amplification at a relatively low cost. Among the doped amplifying fibers, excellent results have been achieved with Erbium doped fibers. Energy is provided to the doped optical amplifying fibers using a laser pump The doped amplifying fiber and the laser pump can be integrated into the optical fiber using a wavelength division multiplexer (WDM). The pump laser excites rare earth ions to a higher energy level to form an appropriate amplifying medium via inversion of the rare earth ions. The signal at the input of the Erbium doped amplifying fiber is thereby amplified by stimulated emission.
Since the laser pump is the only active component in the amplification system, it is the most likely to degrade or fail. Such failure would render the optical amplifier, and possibly the optical communication system inoperative. In order to overcome such a drawback, several techniques have been developed to design optical communication systems capable of limiting the impact of laser pump failure or degradation.
Redundancy has been suggested many times to obviate to optical amplifiers failures.
U.S. Pat. No. 5,173,957 issued to Bergano et al. relates laser pump redundancy for an optical fiber amplifier wherein at least two laser diodes are coupled via a 3 dB optical coupler to supply pump power to each of two one-stage optical fiber amplifiers simultaneously (
FIG. 8
attached hereto). If one of the laser diode pumps fails, the other laser diode pump provides power to each of the optical fiber amplifiers Thus, failure of one laser pump causes a 50% reduction in the pumping power of each of two one-stage optical fiber amplifiers.
U.S. Patent No. 5,241,414 issued to Giles et al. discloses a group of optical amplifiers wherein pump beams from an array of lasers are mixed together by means of a star coupler to form a plurality of composite pump beams. Each composite pump beam is distributed to the pump port of a particular optical amplifier of a group of optical amplifiers.
U.S. Patent No. 5,253,104 issued to Delavaux discloses a balanced doped fiber optical amplifier.
FIG. 7
shows an amplifier consisting of a preamplifier first stage and power booster second stage cascaded along a same optical fiber line. In this configurations pump signals are distributed and coupled between first and second stage so as to both share pump sources and provide a sparing arrangement.
Published UK Patent Application GB 2,272,202-A, discloses a diode-pumped optical fiber amplifier with its amplifying fiber divided into two parts so that there are two amplifier stages, both pumped by a laser diode. A second diode may be included for redundancy, its outputs being coupled via a pair of polarization beam splitter/combiner.
Published PCT Application WO 92/05642 discloses an optical fiber amplifier having one or more active fibers so coupled to an optical transmission line that each of the active fibers has at least one input for a pump signal. The optical fiber amplifier has an optical combination network with a plurality of inputs coupled to respective pump lasers. The outputs of the combination network are coupled to the pump signal inputs on the active fibers. The network is adapted to combine the optical energy added from the pump lasers so that the optical energy on each one of the outputs of the combination network originates from several pump lasers.
As a further improvement of the above mentioned solutions, in case of a two-stage optical amplifier reliability could be obtained by means of two laser pumps; each laser pump being connected with both stages of said optical amplifier. As shown in
FIG. 1
, the optical amplifier for optical fiber
402
comprises a first stage amplifying fiber
404
, a second stage amplifying fiber
406
, a first WDM
408
, a second WDM/
410
, a coupler
412
, and laser pumps
414
and
416
. Here, pumping signals from the laser pumps
414
and
416
are coupled by coupler
412
which distributes the coupled pumping signal to first and second stages
404
and
406
via WDMs
408
and
410
. The first WDM
408
interfaces optical fiber
402
with the pumping signal. In this manner, the first stage amplifying fiber
404
is pumped so that the signal received from the optical fiber
402
is amplified. Similarly, the second WDM
410
receives the pumping signal so that the second stage amplifying fiber
406
is pumped. Accordingly, the second stage amplifying fiber
406
amplifies the signal received from the first stage amplifying fiber
404
. However, in said amplifier failure of one laser pump would cause a 50% reduction in the pumping power.
The present invention aims to limit said 50% reduction of the pumping power in each optical fiber line of an optical communication system comprising two optic fiber lines without any additional cost, compared to a two lines optical communication system wherein each line is provided with a two-stage optical amplifier as shown in FIG.
1
.
More particularly, A is an object of this invention to provide an improvement in the reliability of an optical communication system comprising two optical fiber lines, a first transmitter for transmitting at least a signal in the first optical line, a second transmitter for transmitting at least a signal in the second optical line, at least one two-stage-amplifier in each of said first and second line, laser pumps providing pumping signals to said stages of the amplifiers, a first receiver for receiving the signal from the first optical line, and a second receiver for receiving the signal from the second optical line, wherein the reliability is improved in such a way that the possible failure of one laser pump causes less than 50% reduction in the pumping power in each optical fiber line.
It is a second object of this invention to provide an improvement in the reliability of an amplifying system comprising two optical fiber lines, at least one two-stage-amplifier in each line, laser pumps providing pumping signals to said stages of the amplifiers, wherein the reliability is improved in such a way that the possible failure of one laser pump causes less than 50% reduction in the pumping power in each optical fiber line.
It is a third object of this invention to provide an improvement in an amplifying system comprising two optical fiber lines, at least one two- stage-amplifier in each line, laser pumps providing pumping signals to said stages of the amplifiers, wherein the losses of gain and the increases of noise figure caused by failure of a laser pump are substantially limited.
It is a further object of this invention to provide an improvement in a method for providing a laser pump signal in an optical communication system comprising a first and a second optical fiber lines, wherein the possible failure of one laser pump causes less than 50% reduction in the pumping power in each optical fiber line.
These and other objects have been achieved by an optical communication system, an amplifying system and a method described herein below.
It has now been found that the above mentioned objects are achieved by providing a single laser pumping system that supplies a first p
Bentivoglio Ravasio Filippo
Ottolenghi Paolo
Boutsikaris Leo
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Pirelli Cavi E Sistemi S.p.A.
Spyrou Cassandra
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