Optical Properties of Single Infrared Resonant Circular Microcavities for Surface Phonon Polaritons

Abstract

Plasmonic antennas are crucial components for nano-optics and have been extensively used to enhance sensing, spectroscopy, light emission, photodetection, and others. Recently, there is a trend to search for new plasmonic materials with low intrinsic loss at new plasmon frequencies. As an alternative to metals, polar crystals have a negative real part of permittivity in the Reststrahlen band and support surface phonon polaritons (SPhPs) with weak damping. Here, we experimentally demonstrate the resonance of single circular microcavities in a thin gold film deposited on a silicon carbide (SiC) substrate in the mid-infrared range. Specifically, the negative permittivity of SiC leads to a well-defined, size-tunable SPhP resonance with a Q factor of around 60 which is much higher than those in surface plasmon polariton (SPP) resonators with similar structures. These infrared resonant microcavities provide new possibilities for widespread applications such as enhanced spectroscopy, sensing, coherent thermal emission, and infrared photodetectors among others throughout the infrared frequency range.

Low-loss, infrared and terahertz nanophotonics using surface phonon polaritons

“…For the spectral range where localized modes can be supported in 4H-SiC and Ag, it is clear that the former exhibits values for Im(ε) that are significantly lower, in some cases reduced by more than an order of magnitude. Achieving such low values of Im(ε), where optical losses are lowest, is key to achieving the extremely narrow line-widths and high quality factors that were recently reported for SiC- [23,64,91] and hBN-based [53] localized SPhP nanoscale resonators. As will be discussed in Sections 3 and 5, the reduced Im(ε) has direct, positive implications for SPhP-based nano-optics.…”

“…Similar to the case of SPPs, there exists a momentum mismatch between the incident photons and the SPhP modes (illustrated for the 4H-SiC/ air interface in Figure 2B along with the well-known bulk phonon polariton branches). This mismatch can be overcome using the coupling of the incident field to surface modes through a diffraction grating [92], high index prism [58,93,94], scattering from a nearby sub-wavelength particle such as an SNOM tip [20,36,38,64] or via nanostructuring of the SPhP material into sub-wavelength particles [23,53,91]. By doing so, an overlap between the light line, k = ω/c and the SPhP dispersion curve, can be realized.…”

“…In these materials, the mechanisms governing optical loss are derived from the scattering of optical phonons, which typically occurs on time-scales in excess of a picosecond [60,63]. This results in a drastic reduction in the optical losses of the SPhP modes [20,23,64] in comparison to their plasmonic counterparts [41][42][43]. With the recent advances in ultra high quality and/or purity materials such as SiC, III-V and III-nitride semiconductors, further reductions are anticipated.…”

Second harmonic generation spectroscopy in the Reststrahl band of SiC using an infrared free-electron laser

“…In recent years, there has been considerable interest in the mid-infrared Reststrahl 1 spectral region of Silicon Carbide (SiC), [2][3][4][5][6] since it holds much promise for a novel approach to low-loss, mid-infrared (IR) nanophotonic applications based on surface phonon polaritons (SPhPs). 4,5 Similarly to surface plasmon polaritons in metals, these surface phonon waves in the Reststrahl band of polar dielectrics can be tailored using resonant optical nano-antennas 4,5 as the fundamental building block of future nanophotonic devices.…”

“…4,5 Similarly to surface plasmon polaritons in metals, these surface phonon waves in the Reststrahl band of polar dielectrics can be tailored using resonant optical nano-antennas 4,5 as the fundamental building block of future nanophotonic devices. 7,8 Most importantly, nanophotonics based on SPhPs could solve the intrinsic optical loss-problem of plasmonics, 9 making use of the much smaller damping rates of phonons as compared to plasmons.…”