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MPB Communications Inc.

Photonics Spectra
Jan 2003
Super Raman Fiber Laser

MPB Communications's Super Raman Fiber LaserThe Super Raman Fiber Laser from Montreal-based MPB Communications Inc. is a pump source that provides distributed Raman amplification in transmission spans of telecommunications systems via third-order cascaded Raman pumping. Third-order cascaded Raman amplification of C-band signals requires launching high power at 1276 nm, the third-order pump wavelength, and low seed powers at about 1356 and 1455 nm, the intermediate and final pump wavelengths.

The 1276-nm power produces high Raman gain for the 1356-nm seed radiation, leading to the generation of high power at 1356 nm. Similarly, the 1455-nm seed power is amplified by the Raman gain produced by the 1356-nm power. With each cascade, the peak power at the converted wavelength occurs farther out in the span; thus, cascaded pumping improves the amplifier noise figure.

At the heart of each Super Raman module is a Raman fiber laser that consists of an Yb-doped double-clad fiber laser and a phosphorous-doped-fiber Raman converter. The large phosphorous Raman shift allows the 1093-nm Yb laser output to be converted to the desired third-order Raman pump wavelength in a single conversion.

To provide seed powers at the intermediate and final wavelengths, high-reflectivity fiber gratings at 1356 and 1455 nm carry the 1276-nm pump power out of the span. The transmission fiber acts as a double-pass amplifier for the spontaneous Raman emission at each wavelength, with the feedback at the far end provided by a distributed Rayleigh scattering mirror.


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