  We developed planar multilayered photonic-plasmonic structures, which support
topologically protected optical states on the interface between metal and
dielectric materials, known as optical Tamm states. Coupling of incident light
to the Tamm states can result in perfect absorption within one of several
narrow frequency bands, which is accompanied by a singular behavior of the
phase of electromagnetic field. In the case of near-perfect absorptance, very
fast local variation of the phase can still be engineered. In this work, we
theoretically and experimentally demonstrate how these drastic phase changes
can improve sensitivity of optical sensors. A planar Tamm absorber was
fabricated and used to demonstrate remote near-singular-phase temperature
sensing with an over an order of magnitude improvement in sensor sensitivity
and over two orders of magnitude improvement in the figure of merit over the
standard approach of measuring shifts of resonant features in the reflectance
spectra of the same absorber. Our experimentally demonstrated
phase-to-amplitude detection sensitivity improvement nearly doubles that of
state-of-the-art nano-patterned plasmonic singular-phase detectors, with
further improvements possible via more precise fabrication. Tamm perfect
absorbers form the basis for robust planar sensing platforms with tunable
spectral characteristics, which do not rely on low-throughput nano-patterning
techniques.
