Measured group birefringence and group velocity dispersion of elliptical-core ZBLAN fibres for mid-infrared supercontinuum generation

Polarisation-maintaining ZBLAN optical fibres with small elliptical cores are attractive for nonlinear frequency conversion, for example in supercontinuum generation (SCG), and for dispersion management in ultrafast fibre laser systems operating in the mid-infrared (MIR) spectral region. Accurate characterisation of group birefringence and group velocity dispersion (GVD) is essential for modelling ultrafast pulse propagation in such fibres, yet experimental data remain scarce. Here, we present broadband measurements of group birefringence and GVD in four elliptical-core ZBLAN fibres, selected for their potential for low-noise MIR SCG, over the wavelength range 1.4 to 4.3 $\mu$m. Using polarisation-resolved white-light spectral interferometry, we quantify the dispersion characteristics of both fundamental modes in each fibre. Measurement uncertainties are evaluated using a standard deviation analysis to ensure reliability. This work aims to support the development of MIR supercontinuum sources and to facilitate the understanding of nonlinear optical phenomena in ZBLAN fibres.