Coherent light generators – Particular pumping means – Pumping with optical or radiant energy
Reexamination Certificate
1998-11-24
2001-03-27
Font, Frank G. (Department: 2877)
Coherent light generators
Particular pumping means
Pumping with optical or radiant energy
C372S072000, C372S006000, C385S027000, C385S045000, C385S048000
Reexamination Certificate
active
06208678
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a laser pump source and method of operation thereof, and more particularly to a laser pump source which provides a plurality of single mode laser pump outputs.
BACKGROUND OF THE INVENTION
One of the main areas of use of the laser pump source is in the optical pumping of fibre amplifiers for use in optical telecommunications systems.
Common optical amplifiers include rare earth doped fibre amplifier such as Erbium doped amplifiers. Such amplifiers demonstrate high gain and low noise. These devices also operate to amplify signals in the wavelength range 1.5 to 1.6 microns and as such cover the 1.54 microns window in silica optical fibres used in telecommunications.
Such amplifiers require pumping in one of their absorption bands at the 807 nm, 918 nm or 1480 nm. Multi-mode pumping may be used to pump fibre amplifiers using a method known as cladding pumping in which specially designed Erbium doped fibres are pumped by a multi-mode pump laser via the cladding of the Erbium doped fibre. However, this is a complex process requiring a special fibre design and is not suitable for most amplifiers. Also, this system can not be retrofitted to pump presently deployed amplifiers that do not include such fibres.
Single mode pumping may also be used. In this case a relatively low power single mode pump may be used to pump a single Erbium fibre amplifier or the output from a higher power, normally 980 manometer, single mode pump laser may be split to pump a plurality of fibres. In this case, passive fibre splitting would be used to provide the plurality of outputs. This method has its drawbacks in that single mode pumps are expensive in comparison to multi-mode pumps and the reliability of high power 980 manometer single mode pumps decreases super linearly (approximately cubicly) with output power. Hence, there will be reliability issues if a high power single mode pump is used to pump a plurality of Erbium doped fibre amplifiers.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a plurality of sources of single mode pump light for pumping a plurality of individual laser amplifiers.
It is a further object of the present invention to provide an inexpensive laser pump source suitable for pumping a plurality of fibre amplifiers.
It is a still further object of the present invention to provide a plurality of sources of single mode pump light for use in a metro communications system.
It is a still further object of the present invention to provide a method of provision of a plurality of single mode optical pump sources.
It is a still further object of the present invention to provide an optical fibre coupler for use with a laser pump source and method of operation thereof.
FIELD OF THE INVENTION
The first three above referenced objects of the invention are attained utilising a laser pump source comprising
a multi-mode pump laser having an output,
an optical fibre coupler having a first section and a second section, the first section of the optical fibre coupler comprising a multi-mode fibre which is optically coupled to the pump laser output, the second section of the fibre coupler comprising a plurality of single mode optical fibres each of which has an input which is optically coupled to the multi-mode fibre, and
a pump drive which is controllable to dither the optical centre frequency of the light produced by the pump laser so as to scramble modal power distribution at the inputs of the single mode optical fibres.
Preferably, the second section of the fibre coupler is a fused tapered single mode fibre bundle.
Preferably, the fused tapered single mode fibre bundle is matched to the core diameter and numerical aperture of the multi-mode fibre.
Preferably, the fibre bundle comprises a plurality of optical fibres, so arranged as to present a substantially circular cross-sectional profile.
In one embodiment the fibre bundle comprises 7 single mode fibres.
In another embodiment the fibre bundle comprises 19 single mode fibres.
Preferably, the pump drive is controllable to scramble modal power distribution by producing optical frequency dither in the pump laser.
Preferably, the frequency of the optical frequency dither is greater than approximately 10 kHz.
Preferably, the first and second sections of the fibre coupler are physically fused together.
Alternatively, the first and second sections of the fibre coupler are optically coupled through an expanded beam connector.
Preferably, the multi-mode fibre is approximately 1 m long.
The fourth of the above referenced objects of the invention is attained utilising a method of providing a plurality of single mode optical pump sources, comprising the steps of:
providing a laser pump source comprising a multi-mode pump laser having an output, providing an optical fibre coupler having a first section and a second section, the first section of the optical fibre coupler comprising a multi-mode fibre, the second section of the fibre coupler comprising a plurality of single mode optical fibres each of which has an input, optically coupling the multi-mode fibre to the pump laser output, optically coupling each of said single mode optical fibres to the multimode fibre and providing a pump drive which is controllable to dither the optical centre frequency of the light produced by the pump laser so as to scramble modal power distribution at the inputs of the single mode optical fibres.
Preferably, the step of providing said second section of the fibre coupler comprises providing a fused tapered single mode fibre bundle.
Preferably, the step of providing said fused tapered single mode fibre bundle comprises the step of matching the core diameter and numerical aperture of the bundle to that of the multi-mode fibre.
Preferably, the step of providing said fused tapered single mode fibre bundle comprises the step of providing a bundle comprising a plurality of optical fibres, so arranged as to present a substantially circular cross-sectional profile.
Preferably, the step of controlling the pump drive so as to scramble modal power distribution comprises producing optical frequency dither in the pump laser.
Preferably, the frequency of the optical frequency dither is greater than approximately 10 kHz.
Preferably, the step of optically coupling each of said single mode optical fibres to the first section of the optical fibre coupler, comprises the step of physically fusing together the first and second sections of the fibre coupler.
Alternatively, the step of optically coupling each of said single mode optical fibres to the first section of the optical fibre coupler, comprises the step of optically coupling the first and second sections of the optical coupler through an expanded beam connector.
The final above referenced object of the invention is attained utilising a laser pump source comprising:
a multi-mode pump laser having an output, and a pump drive which is controllable to dither the optical centre frequency of the light produced by the pump laser so as to scramble modal power distribution;
the optical fibre coupler having a first section and a second section, the first section of the optical fibre coupler comprising a multi-mode fibre which is optically couplable to the pump laser output, the second section of the fibre coupler comprising a plurality of single mode optical fibres each of which is optically coupled to the first section of the optical fibre coupler.
Preferably, the second section is a fused tapered single mode fibre bundle.
Preferably, the fused tapered single mode fibre bundle is matched to the core diameter and numerical aperture of the multi-mode fibre.
Preferably, the fibre bundle comprises a plurality of optical fibres, so arranged as to present a substantially circular cross-sectional profile.
In one embodiment the fibre bundle comprises 7 single mode fibres.
In another embodiment the fibre bundle comprises 19 single mode fibres.
Preferably, the first and second sections of the fibre coupler are physically fused together.
Preferably, the first and second sectio
Flores Ruiz Delma R.
Font Frank G.
Lee Mann Smith McWilliams Sweeney & Ohlson
Nortel Networks Limited
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