Temperature and Refractive Index-Independent Mode Converter Based on Tapered Hole-Assisted Dual-Core Fiber

A compact mode converter (MC) has been demonstrated based on tapered hole-assisted dual-core fiber (HADCF). The MC is fabricated by splicing single mode fiber (SMF) and a piece of HADCF that is composed of a central single mode core (SMC), an eccentric few mode core (FMC), and a large eccentric air hole. The HADCF is tapered in a controllable manner and the fundamental mode LP 01 of the central core is coupled to the high-order LP 11 mode of the eccentric core as two modes satisfy the phase matching condition. The high-order LP 11 mode can be converted effectively across the range from O-band to C-band by only changing the tapered length. With the decreasing taper ratio, the mode conversion wavelength has a blue shift. The measured purity of the LP 11 modes in the range from 1310 to 1550 nm are always higher than 95%. In addition, the tapered HADCF-MC is insensitive to the change of the temperature and external refractive index.