Field propagation study in ultra-small core photonic crystal fiber beyond the fundamental mode cut-off

We present the study of the behavior of the electromagnetic field propagating in the ultra-small core photonic crystal fiber (PCF) beyond its fundamental mode cut-off. We first use plane waves expansion (PWE) method to find necessary parameters and then involve finite-difference time-domain (FDTD) method accelerated with graphic processing unit (GPU) for long-range light propagation simulation. The confinement losses beyond $\lambda = 1200 nm$ achieves tens of dB/cm which can be lowered significantly by increasing the number of cladding rings.