Broadband Raman pre-amplifier for wavelength division multiplexed optical communication systems

A WDM optical transmission system, comprising:

• a transmitter and a receiver;
• an optical fiber transmission path coupling said transmitter to said receiver;
• an optical amplifier arrangement disposed at an intermediate point along said transmission path, said optical amplifier arrangement including:
• a splitter for dividing a multiplexed optical signal having a prescribed bandwidth into a plurality of distinct sub-bands;
• a plurality of output paths for respectively receiving said plurality of distinct sub-bands;
• a plurality of optical amplifiers disposed in said output paths, said optical amplifiers each having a prescribed gain shape across the bandwidth of its respective sub-band;
• a coupler for recombining said distinct sub-bands and coupling said recombined distinct sub-bands onto said optical fiber transmission path;
• an optical preamplifier coupled to an input of the splitter, said optical preamplifier being a Raman amplifier having a bandwidth substantially encompassing said prescribed bandwidth of the multiplexed optical signal.

A method for amplifying a multiplexed optical signal traveling in an optical fiber transmission path of a WDM optical communication system, said method comprising the steps of:

• imparting Raman gain to a multiplexed optical signal at an intermediate point along the transmission path, said multiplexed optical signal having a prescribed bandwidth;
• demultiplexing the optical signal into a plurality of distinct sub-bands after Raman gain is imparted thereto;
• directing said plurality of sub-bands onto respective ones of a plurality of optical paths;
• amplifying a plurality of said sub-bands propagating on said optical paths;
• recombining said distinct sub-bands and directing said recombined distinct sub-bands onto said optical fiber transmission path.