Design of weakly-coupled ultra-flattened dispersion few-mode photonic crystal fiber

In this paper, a novel design of weakly-coupled few-mode photonic crystal fiber (FM-PCF) supporting 6 vector modes (HE11a, HE11b, TM01, HE21a, HE21b, TE01) with ultra-flattened chromatic dispersion is proposed. We investigate the impact of fiber parameters on chromatic dispersion, minimum effective refractive index difference (minΔneff), confinement loss, effective mode area, bending loss and nonlinear coefficient. To achieve ultra-flattened chromatic dispersion and large minΔneff, an extra small elliptical defected hole is introduced in the fiber core. The circular holes in the first ring are replaced by elliptical holes to further obtain flattened-chromatic dispersion. The simulation results show that the chromatic dispersion slope (< 2.1 × 10–5 ns/km/nm2) and large minΔneff (> 6 × 10–4) are obtained for the optimized fiber structure. And the proposed FM-PCF has low confinement loss (< 10−4 dB/km) and good bending resistance. The proposed fiber can achieve an ultra-flattened chromatic dispersion (< 0.032 ns/nm/km) of 6 vector modes around C-band, and has the potential applications for large-capacity mode division multiplexing communication systems.