Patent ID: 7136218

Claim:
A Raman optical amplifier comprising: a first amplifier for Raman-amplifying an input optical signal to form a primarily-amplified optical signal; a second amplifier for outputting a Raman pumping light of a predetermined wavelength to Raman-pump the first amplifier, while amplifying the primarily-amplified optical signal to form a secondarily-amplified optical signal; a circulator having first through third ports, the circulator being configured to receive the primarily-amplified optical signal at the first port, to output the received primarily-amplified optical signal to the second port, to receive the Raman pumping light and the secondarily-amplified optical signal at the second port, to output the received Raman pumping light and secondarily-amplified optical signal to the third port, to re-receive the Raman pumping light at the third port, and to output the re-received Raman pumping light to the first port; and a filtering device connected to said third port, the filtering device being configured to reflect the Raman pumping light received from said third port while passing the secondarily-amplified optical signal received from said third port. wherein the filtering device comprises an optical fiber connected to the third port of the circulator, a Bragg grating being formed on the optical fiber, the Bragg grating having a predetermined grating period to reflect the Raman pumping light received from the third port of the circulator.