Design and study of trench-assisted long-period-waveguide-grating based gain flattening filter for erbium-doped waveguide amplifier

We propose a trench assisted long-period-waveguide-grating (LPWG) design for flattening the gain spectrum of erbium doped waveguide amplifier. The waveguide structure consists of a low index trench in the cladding region. The modes of the waveguide structure have been evaluated by the transfer matrix method and transmission characteristics of the long period grating have been simulated by using the coupled mode theory. The transmission spectrum of the long period waveguide grating has been utilized to equalize the gain spectrum of erbium doped waveguide amplifier in the desired wavelength range. Using the present structure we have achieved a gain of 18.5 ± 0.96 dB in 35 nm wide wavelength band (1526–1561 nm). We have numerically studied the effect of various waveguide and grating design parameters on transmission spectrum of the LPWG, in order to optimize gain flattening in the C-band of an erbium doped waveguide amplifier. © 2015, The Optical Society of India.