| dc.description.abstract | Infrared (IR) optics form the basis for many important applications, including thermal imaging, long-wave communications, chemical spectroscopy for pharmaceuticals, medical testing, environmental monitoring, automotives, and aerospace, to name a few. However, current state of the art IR devices are plagued by bulky components, low efficiency, and low robustness. In response, IR nanophotonics have garnered strong interest for next generation devices. The most promising approaches for IR nanophotonics involve coupling light to free carriers in metals and doped semiconductors (plasmon polaritons), or to lattice vibrations of polar crystals (phonon polaritons). Both of these polaritons enable shrinking the wavelength to much smaller scales than the free-space wavelength. From there, they diverge – plasmon polaritons offer broad tunability with low efficiency (resulting from short free carrier lifetimes), while phonon polaritons offer high efficiency (low losses from long phonon lifetimes) with low tunability (fixed to the region between the transverse and longitudinal optical phonons). The work presented here focuses on phonon polaritons in low symmetry crystals, which have been shown to offer remarkable control over the confinement and propagation of light at scales much smaller than the optical wavelengths. In particular, we study the phonon polaritons of uniaxial, biaxial, and monoclinic systems – demonstrating engineered polariton wavevector, ultrafast modulation, refractive polariton optics, tunable polariton beam-steering, and broken symmetry propagation in natural crystals. We also explore the design of optical phonon energies through atomic-scale structuring of superlattices – stacks of alternating crystal layers – and the use of these superlattices for engineered anisotropic nanophotonics. The results provide promising new paths for IR nanophotonic devices. | |
