Letter 1 Polarization-dependent fluoride fiber coupler and application to pulsed laser triggering

We present the first ZBLAN-based polarization-dependent optical fiber coupler (OFC). The polarization extinction ratio (PER) reaches 2.5 dB/4.0 dB at the through-port/cross-port of the single-mode OFC. With an unpolarized light input, the OFC provides a coupling ratio of 73.5%/26.5% at the through-port/cross-port, with an excess loss of 1.47 dB at a wavelength of 1.918 μm. The OFC is used as the polarization-dependent element combined with nonlinear polarization evolution that triggers the pulsation of a mode-locked fiber laser. This approach generates fundamental solitons with a duration of 1.83 ps at a wavelength of 1.918 μm. The soft-glass OFC supports a power of at least 320 mW without damage. The polarization-dependent ZBLAN OFC is expected to play an important role in mid-infrared (MIR) fiber optics.