Resonant modes in triangular dielectric cavities
  The resonant optical modes of a high permittivity dielectric prism with an equilateral triangular cross section are discussed. Eigenmode solutions of the scalar Helmholtz equation with Dirichlet boundary conditions, appropriate to a conducting boundary, are applied for this purpose. The particular plane wave components present in these modes are analyzed for their total internal reflection behavior and implied mode confinement when the conducting boundary is replaced by a sharp dielectric mismatch. Improvement in TIR confinement by adjusting the longitudinal wavevector $k_z$ is also discussed. For two-dimensional electromagnetic solutions ($k_z=0$), TE polarization leads to longer lifetime than TM polarization, assuming that escape of evanescent boundary waves at the corners is the primary decay process. 
G. M. Wysin