S-Band Gain-Flattened Double-Pass Discrete Fibre Raman Amplifiers Using Mechanically Induced Long-Period Fibre Gratings

We experimentally demonstrate an S-band double-pass (DP) discrete fibre Raman amplifier (FRA) gain-flattened by using a mechanically induced long-period fibre grating (LPFG). Due to a photo-elastic effect in the fibre and its peak loss, the wavelength and depth of the mechanically induced LPFG are continuously regulated by varying the pressures, the angle of the fibre on the graphite rods which are used to produce the periodical pressures along the fibre, the number and the diameter of the graphite rods. Using this gain flattening filter, the gain profile of the DP-FRA is flattened to within ±0.8dB in the wavelength range from 1485nm to 1525nm.