Light Propagation in Photonic Crystal Superprisms

摘要

The superprism is known as a highly dispersive phenomenon in photonic crystals, which is expected to realize a narrow band filter, beam deflector, dispersion compensator, etc. Thus far, its large angular dispersion has been theoretically discussed worldwide through the dispersion surface analysis. In general, however, incidence of a finite width beam to a photonic crystal excites a wide angular spectrum of Bloch waves, which leads to a significant beam divergence. The dispersion surface analysis including such a property indicates that a large angular dispersion and a high quality beam propagation are achieved simultaneously under some limited conditions for incident angles, beam widths and wavelength range. A high resolution will be possible, but the length of the photonic crystal required is of cm to 10 cm order and beam width of 100 micron order. To solve these problems, we proposed a k-vector super-prism, which utilizes a large angular dispersion of k-vector and an angled output end of the photonic crystal. In this prism, the length of the PC is significantly shortened to 100 micron order with maintaining a high resolution. In addition, latitudes for the beam width and wavelength range are greatly expanded, so the butt-joint of a singlemode fiber and operation over C- to L bands will be possible. The FDTD simulation demonstrates the light propagation, which agrees with these expectations, but also showed some peculiar light diffraction, which should be cared in designing a high efficiency filter.