Dual core photonic crystal fiber-based intrinsically gain flattened EDFA

We investigate the inherent gain flattening characteristics of an EDFA based on a highly asymmetric dual-core photonic crystal fiber for operation in the C-band. The gain flattening was achieved by exploiting the strong optical power coupling between the two cores like that in a directional coupler at the phase matching wavelength (lambda(P)), which is designed to be around 1533 nm. The inner core is partially doped with erbium. The fiber refractive index profile parameters were so tailored such that a large fraction of the composite guided power flips from the un-doped outer core to the inner erbium-doped core at wavelengths greater than lambda(P). Thus the guided power at relatively longer wavelengths gets amplified more as compared to that at shorter wavelengths in the C-band. This phenomenon resulted in an effective flattening of the gain spectrum. Optimization of the design has led to an estimated median gain of similar to 21.2 dB with gain excursion within +/- 1.25 dB within the C-band (1532-1562 nm). Results of this work should be of importance for realizing relatively inexpensive (due to cost saving on gain flattening filter head) and efficient EDFAs suitable for potential deployment in transparent wide area and metro networks.