Influence of the coherence of spectral domain interference of Fano resonance on the degree of polarization of light

We show an intriguing connection between the coherence of spectral domain interference of two electromagnetic modes in Fano resonance and the resulting degree of polarization of light. A theoretical treatment is developed by combining a general electromagnetic model of partially coherent interference of a spectrally narrow and a broad continuum mode leading to Fano resonance and the cross-spectral density matrix of the interfering polarized fields of light. The model suggests a characteristic variation of the degree of polarization across the region of spectral dip and the peak of Fano resonance as an exclusive signature of the connection between the degree of polarization and the coherence of the interfering modes. The predictions of the model is experimentally verified in the partially polarized Fano resonance spectra from metal Chalcogenides systems, which emerged due to the interference of a narrow excitonic mode with the background continuum of scattered light in the reflectance spectra from the system. The demonstrated connection between polarization and coherence in the spectral domain Fano-type interference of electromagnetic modes is fundamentally important in the context of a broad variety of non-trivial wave phenomena that originate from fine interference effects, which may also have useful practical implications.