Nortel Networks Corporation

Northern Telecom Limited

Bernard Villeneuve

Hyung B Kim

Douglas S Burbidge

An optical repeater is described which integrates an erbium doped optical fiber amplifier (EDFA) with a dispersion equalizer (DE) based on fiber gratings. The dispersion equalizer is based on parallel connection of a plurality of fiber gratings, or on parallel connection of a cascaded plurality of fiber grating branches, each branch carrying a plurality of gratings coupled in series. Each grating in each branch is chirped to provide selective reflection at one of the plurality of signal carrier wavelengths so that the total optical bandwidth of the dispersion equalizer is enhanced, i.e. the total bandwidth for a specific signal carrier wavelength is the combined optical bandwidths of the gratings which provide the reflection at the wavelength. The use of multiple gratings for each wavelength improves the optical bandwidth of the equalizer compared with single grating designs, enhancing the effective bandwidth. Further, the grating DE is disposed between two fiber amplifier lengths which share a single pump laser. Thus, this arrangement provides dispersion compensation and loss compensation in an optical repeater of lower cost, and smaller size, compared to a system of similar performance configured using discrete components.

Optical repeaters for single- and multi-wavelength operation with dispersion equalization

A compact wavelength monitoring and control assembly for a laser emission source is provided comprising a narrow bandpass, wavelength selective transmission filter element, of Fabry-Perot etalon structure, through which a non-collimated beam from the laser source is directed onto two closely spaced photodetectors. For wavelength stabilization, the differential output of the two photodetectors is used in a feedback loop to stabilize the wavelength of the laser source to a desired target wavelength. Through the angular dependence of the wavelength transmission of the Fabry-Perot etalon, a wavelength variation from the source is converted to a transmission loss, which is different for the two photodetectors, so that the wavelength change is detected as a differential power change. The device functions as an optical wavelength discriminator in which the detector converts optical energy to current for a feedback loop for controlling the light source. A lens may be used to control the divergence of the light incident on the filter element to optimize power transfer. Optionally, wavelength tunability is provided by changing the angle of inclination of the Fabry-Perot etalon relative to the laser source. The system is compact and may be co-packaged within the same package as a laser emission source, overcoming coupling, space and power dissipation problems common with known external semiconductor laser wavelength control units.

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Aylmer, Canada

Bernard Villeneuve