Ultracompact 1x4 TM-polarized beam splitter based on photonic crystal surface mode

We provide an improved surface-mode photonic crystal (PhC) T-junction waveguide, combine it with an improved PhC bandgap T-junction waveguide, and then provide an ultracompact 1 x 4 TM-polarized beam splitter. The energy is split equally into the four output waveguides. The maximal transmission ratio of each output waveguide branch equals 24.7%, and the corresponding total transmission ratio of the ultracompact 1 x 4 beam splitter equals 98.8%. The normalized frequency of maximal transmission ratio is 0.397(2 pi c/a), and the bandwidth of the ultracompact 1 x 4 TM-polarized beam splitter is 0.0106 (2 pi c/a). To the best of our knowledge, this is the first time such a high-efficiency 1 x 4 beam splitter exploiting the nonradiative surface mode as a guided mode has been proposed. Although we only employed a 1 x 4 beam splitter, our design can easily be extended to other 1 x n beam splitters. (c) 2012 Optical Society of America