Enhancement of thermal emission and control of its direction are important for applications in optoelectronics and energy conversion. A number of structures have been proposed as coherent emission sources, which exhibit a large emissivity peak within a narrow wavelength band and at well-defined directions. A commonly used structure is gratings, in which the excited surface polaritons or surface waves are coupled with propagating waves in air to produce coherent emission for p polarization. One-dimensional photonic crystals can also support surface waves but have not been applied as coherent emission sources. The present study demonstrates that coherent emission can be achieved by the use of a multilayer structure consisting of periodic layers (i.e., photonic crystal) coated with a polar material such as SiC. By excitation of surface waves at the interface between SiC and the photonic crystal, coherent emission is predicted for both p and s polarization. In addition to the excitation of surface waves, the emission from the proposed structure can be largely enhanced by the cavity resonance mode, which is very similar to that of Fabry-Perot etalon, as well as by the Brewster mode that occurs only for p polarization.
Surface waves and volume waves in a photonic crystal slab
