L band amplifier with distributed filtering
First Claim
1. An optical amplifier for optical fiber telecommunications lines operating with an in-band transmission signal in a longer wavelength, tail region of a gain spectrum associated with the amplifier, said longer wavelength, tail region being between 1570 nm and 1620 nm, said amplifier comprising:
- a rare earth doped gain medium providing a first gain stage for the amplifier;
a source of pump power connected to the gain stage; and
a filter distributed over the gain medium wherein the filter attenuates light associated with amplified spontaneous emission (ASE) in the amplifier, such that the transmission signal in the longer wavelength region of the gain spectrum is amplified wherein the filter includes a continuous filter and the continuous filter comprises a doped waveguiding core that is unpumped so as to absorb the ASE light, and a doped waveguiding core that is pumped so as to amplify the transmission signal, further wherein the unpumped waveguiding core and the pumped waveguiding core exhibit waveguide dispersions such that coupling from the pumped core to the unpumped core occurs substantially only for light in the ASE gain spectrum.
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Abstract
An L-band optical amplifier has a rare earth doped gain medium including a filter distributed over a finite physical portion of the gain medium. The filter is distributed over between about 25% to substantially the entire length of the gain medium. The distributed filter substantially eliminates out-of-band light emission (C-band ASE, 1520 nm-1565 nm) and thus improves the performance of L-band amplification (1565 nm-1620 nm). Examples of distributed filters include discrete type filters such as long period gratings, or continuous type filters such as rare earth doped, twin core fibers, non-adiabatically tapered fibers and coaxial resonant ring fibers.
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Citations
22 Claims
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1. An optical amplifier for optical fiber telecommunications lines operating with an in-band transmission signal in a longer wavelength, tail region of a gain spectrum associated with the amplifier, said longer wavelength, tail region being between 1570 nm and 1620 nm, said amplifier comprising:
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a rare earth doped gain medium providing a first gain stage for the amplifier;
a source of pump power connected to the gain stage; and
a filter distributed over the gain medium wherein the filter attenuates light associated with amplified spontaneous emission (ASE) in the amplifier, such that the transmission signal in the longer wavelength region of the gain spectrum is amplified wherein the filter includes a continuous filter and the continuous filter comprises a doped waveguiding core that is unpumped so as to absorb the ASE light, and a doped waveguiding core that is pumped so as to amplify the transmission signal, further wherein the unpumped waveguiding core and the pumped waveguiding core exhibit waveguide dispersions such that coupling from the pumped core to the unpumped core occurs substantially only for light in the ASE gain spectrum. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. An erbium doped fiber amplifier having a known gain bandwidth for providing a signal amplification in a long wavelength region of the known gain bandwidth said long wavelength region being between 1570 and 1620 nm, said amplifier comprising:
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first gain stage comprising an erbium fiber exhibiting a first gain spectrum within the known gain bandwidth extending from about 1520 nm to 1565 nm;
a source of pump energy coupled to the first gain stage;
a second gain stage comprising an erbium fiber serially connected to the first gain stage exhibiting a useful gain spectrum within the known gain bandwidth between 1570 nm and 1620 nm, wherein the first gain stage further comprises a filter distributed along the first gain stage, said filter having a depth and a bandwidth sufficient to filter an out-of-band light emission having an emission spectrum substantially coincident with the first gain spectrum to the extent that any unfiltered out-of-band light emission in the first gain stage is insufficient to self-saturate the first gain stage, further wherein the useful gain spectrum exhibits a peak gain that is the peak gain of the known gain bandwidth wherein the filter comprises two erbium doped waveguiding cores in the erbium doped fiber of the first gain stage, further wherein no pumping energy is delivered to one of the doped cores such that said unpumped core attenuates the out-of-band light emission coupled into said unpumped core. - View Dependent Claims (17)
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18. A method of operating an optical amplifier for amplification of a signal in a longer wavelength tail region of a known gain bandwidth of the amplifier, said longer wavelength tail region being between 1570 nm and 1620 nm, said method comprising the steps of:
distributing a filter over a finite physical length portion of a phosphor-silicate based gain medium of a first gain stage of the amplifier wherein the filter has a depth and bandwidth sufficient to attenuate a wavelength spectrum associated with amplified spontaneous emission from the amplifier, wherein the step of distributing a filter over the medium of the amplifier comprises distributing continuous filter over the gain medium.
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19. A method of operating an optical amplifier for amplification of a signal in a longer wavelength tail region of a known gain bandwidth of the amplifier, amplifier, said longer wavelength tail region being between 1570 nm and 1620 nm, said method comprising the steps of:
distributing a filter over a gain stage of the amplifier said gain stage containing phosphor-silicate based fiber to attenuate an out-of-band light emission associated with amplified spontaneous emission from the amplifier such that an average inversion value associated with the amplifier is higher than the average inversion value associated with the amplifier without a distributed filter. - View Dependent Claims (20, 21, 22)
Specification