Influence of quasi-periodic cladding on single mode behavior in a leakage channel fiber: Towards the enhancement of modal discrimination and low bending loss of the LP01 mode

A silica quasi-periodic clad leakage channel fiber (LCF) is proposed to enhance the mode filtering characteristics with large effective mode area (Aeff). In this work, we explore the fiber characteristics, namely, bending loss (BL), Aeff and differential loss for different micro-structured cladding LCF designs. Of the various LCFs, an octagonal core-octagonal quasi-periodic clad LCF provides a large loss ratio (>103) between fundamental mode (LP01 mode) and most competitive higher order mode (LP11 mode). Further, it exhibits a high BL of 66.48 dB/m for LP11 mode by resonance mode filtering along with a bend induced modal discrimination at 1.05 μm wavelength. The detailed numerical results reveal that the differential loss ratio goes high when the effective index of the second ring of eight sectional elements in a quasi-periodic cladding is scaled up and the Aeff increases when it is scaled down. Thus, the proposed octagonal core-octagonal quasi-periodic clad LCF exhibits a large mode area of 1161 μm2, a low BL of 0.04 dB/m for the LP01 mode and a high differential loss ratio of 1624 between LP11 and LP01 modes at a critical bending radius of 15 cm with an air-filling ratio of 0.4. These interesting properties of the LCF could pave way for developing a compact high power fiber laser system.