Existence and extent of birefringence and polarisation-dependent loss in photonic lanterns

Ascertain the existence and quantify the extent of birefringence and polarisation-dependent loss within photonic lantern devices by measuring differences between orthogonal polarisations in reconstructed electric fields and determining the magnitude of polarisation-induced dispersion and loss across ports and wavelengths.

Background

The paper presents a coherent, spectro-polarimetric characterisation of a 19-port multicore-fibre-fed photonic lantern using digital off-axis holography, reconstructing complex electric fields across a 73 nm wavelength range and two linear polarisations. In comparing H and V polarisations, the authors observe subtle amplitude differences (up to ~10%) and near-uniform phase offsets, with port-dependent variation not attributable solely to centring or signal-strength effects.

These findings, together with measured differences in modal dispersion and departures from idealised simulation symmetries, motivate a broader investigation across devices to determine whether birefringence and polarisation-dependent loss are intrinsic properties of photonic lanterns, and to quantify their magnitudes. The authors note that upgrades to reduce system birefringence and experiments varying input polarisation could help resolve these questions.