Polaritonics

In this regime, signals are carried by an admixture of electromagnetic and lattice vibrational waves known as phonon-polaritons, rather than currents or photons.

Since phonon-polaritons propagate with frequencies in the range of hundreds of gigahertz to several terahertz, polaritonics bridges the gap between electronics and photonics.

A compelling motivation for polaritonics is the demand for high speed signal processing and linear and nonlinear terahertz spectroscopy.

Polaritonics, like electronics and photonics, requires three elements: robust waveform generation, detection, and guidance and control.

A full treatment of the Cherenkov-radiation-like terahertz wave response reveals that in general, there is also a forward propagation component that must be considered in many cases.

It was the first time that electromagnetic waves were imaged directly, appearing much like ripples in a pond when a rock plummets through the water's surface (see Fig.

For example, patterned materials with feature sizes on the order of a few tens of micrometres cause parasitic scattering of the imaging light.

In fact, the only etchant known to be even marginally successful is hydrofluoric acid (HF), which etches slowly and predominantly in the direction of the crystal optic axis.

Figure 1 : Polaritonics may resolve the incongruence between electronics, which suffers technological and physical barriers to increased speed, and photonics, which requires lossy integration of light source and guiding structures. Other quasiparticles /collective excitations such as magnon -polaritons and exciton -polaritons, their location identified above, may be exploitable in the same way that phonon-polaritons have been for polaritonics.
Figure 2 : Fanciful depiction of a polaritonic circuit illustrating fully integrated terahertz wave generation, guidance, manipulation, and readout in a single patterned material. Phonon-polaritons are generated in the upper left and lower right hand corners by focusing femtosecond optical excitation pulses into the crystal near waveguide entrances. Phonon-polaritons propagate laterally away from the excitation region and into the waveguides. Signal processing and circuit functionality is facilitated by resonant cavities, reflectors, focusing elements, coupled waveguides, splitters, combiners, interferometers , and photonic bandgap structures created by milling channels that fully extend throughout the thickness of the crystal.
Figure 3 : Frames from a phonon-polariton movie of broadband phonon-polariton generation and propagation in lithium niobate taken with real-space imaging. The first frame shows the initial phonon-polaritons at the time of generation. Immediately afterwards, wavepackets travel away from the excitation region in both directions. The second frame, taken 30 ps after generation, shows two phonon-polaritons traveling to the right. The first (left) is the reflection of the initial left-going wavepacket and the other was initially traveling to the right.