Performance of a new optical fibre amplifier with reduced pump power for 1310 nm

Fibre amplifiers play an important part in modern lightwave communication systems, In this paper experimental and simulation results of praseodymium doped fibre amplifiers (PDFA) for the 1300 nm wavelength region are presented. A mathematical model based on rate equations of a PDFA is given and the optical output power spectrum, including amplifier gain and amplified spontaneous emission (ASE) noise, are derived, An experimental set up of a PDFA is described, measured and simulated results are compared: Fibre net gain over input power, wavelength and pump power are presented together with noise figures, Various configurations of fibre amplifiers are investigated and a new structure is presented, where the optical signal at the end of the amplifier is reflected back thus travels twice through the doped fibre, With a pump power of 300 mW a 35 dB gain is abtained which is about 10 dB higher than for the conventional codirectionally pumped amplifier, It is also shown that the new structure allows for reduction of the pump power by a factor 2 without loss of amplifier gain, This is a major advantage because PDFAs require in principle significantly higher pump power than erbium doped fibre amplifiers (EDFA), which operate at a wavelength of about 1550 nm, Figures for SNR and bit-error probability for a communication link including PDFAs are presented which show that attenuation of the fibre is no longer a hard limiting factor for optical digital transmission at 1310 nm with very high bit rates.