Tunable narrowband spectral filters with high throughput and wide dynamic range are in high demand for many applications, however, a cost is usually associated with the filter narrowing either in the dynamic range, in the throughput or the manufacturability. Here it is shown for the first time that using the coupling between waveguide and lossy modes (LMs) in lossy ultrathin films through thin film coupling layer it is possible to obtain a reflection peak with controllable width (sub-Angstroms till tens of nm) and tunability over wide spectral range (>500nm in the visible and near infrared). The excitation of broadband LM is enabled using an ultrathin absorptive layer with high imaginary to real part ratio of the dielectric constant (i.e 6nm of Cr). The wider dynamic range and higher contrast are observed more with TE polarization than TM. The tuning is achieved by incidence angle scan of few degrees or by modulating the waveguide layer from the visible till the near infrared and in principle it can be designed to operate in any spectral range. Such a thin waveguide layer can allow tuning at ultrahigh speed using conventional electrooptic, magnetooptic, piezoelectric or thermooptic materials using relatively low external fields. The tuning sensitivity and range depend strongly on the waveguide layer thickness and the refractive index mismatch between the waveguide and the coupling layer. Under small index mismatch new peaks are seen via Rabi type splitting with gaps as high as 700nm or more, thus exhibiting ultrahigh tuning with negative sensitivity.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics