Design of S-Band Erbium-Doped Concentric Dual-Core Photonic Crystal Fiber Amplifiers With ASE Suppression

In this paper, we theoretically design and numerically demonstrate a large mode area and single-mode erbium-doped photonic crystal fiber (PCF) amplifier operating in the S-band with a complete suppression of amplified spontaneous emission (ASE) and very low Raman gain coefficient at 980-nm pump. The proposed fiber design is based on a dual-concentric core refractive index profile and is solved through full-vectorial finite-element method. Numerical simulations reveal that more than 50 dB of gain can be achieved with a mean gain value of 27 dB over 70-nm bandwidth in a 7.2-m-long fiber. The effect of bending on the amplification characteristics has been noted. It has been shown that by a proper choice of the PCF profile parameters, the fiber amplifier can be made bend-insensitive for a bending radius as small as 5 cm. Further, our design guidelines should be useful to achieve a functional bend-insensitive fiber amplifier, where rack space is a premium and tight bending radius becomes inevitable.