Modal Gain Controllable 2-LP-Mode Fiber Amplifier Using PLC Type Coupler and Long-Period Grating

We propose a 2-LP-mode erbium-doped fiber amplifier (EDFA) with a planar lightwave circuit (PLC) type coupler and a long-period grating (LPG) for controlling mode dependent gain (MDG). We successfully fabricated a PLC that combines C-band light and 980-nm pump light with a low insertion loss of less than 1.8 dB for a signal over the C-band, and less than 1.5 dB for a 980-nm pump light. Finally, we realized experimentally an adaptive MDG control from -1.5 to +1.4 dB within the C-band by pump mode conversion using an LPG without affecting the crosstalk and noise figure characteristics of the EDFA.