Opt Quant Electron (2008) 40:695–705 DOI 10.1007/s11082-008-9257-y Terahertz wave switch based on photonic crystal ring resonators A. R. Maleki Javan · N. Granpayeh Received: 4 May 2008 / Accepted: 17 November 2008 / Published online: 4 December 2008 © Springer Science+Business Media, LLC. 2008 Abstract In this paper, we have presented a compact and integrated terahertz wave switch design based on photonic crystal ring resonators. The photonic crystal structure with square lattice is investigated and applied for design of ring resonators. The switching mechanism of this novel switch is based on the variation of the resonant frequency of the ring resonator inserted between two parallel waveguides. The refractive index of the holes of the structure filled with polyaniline electrorheological fluids are varied by applied external electric field, the result of which is the variation of the ring resonant frequency. The proposed device is analyzed by using finite difference time domain method. Numerical simulation results show that this switch has high extinction ratio, small size, low voltage and advantages of selectivity of coupling THz wave to different output ports. Keywords Photonic crystals · Ring resonators · Terahertz wave switch · Electrorheological fluids 1 Introduction Terahertz frequency, with wavelength range of 30 μm to 3mm, has attracted the attentions of many researchers in the last decade. Many application potentials of the THz wave including medical diagnosis, security screening, military detection, radio astronomy, atmospheric stud- ies, high speed communication, chemical and biological sensing have been explored (Gang et al. 2004; Woolard et al. 2005; Shur 2005; Kurt and Citrin 2005). A. R. Maleki Javan (B ) · N. Granpayeh Faculty of Electrical Engineering, K. N. Toosi University of Technology, Tehran 1431714191, Iran e-mail: amalekijavan@eetd.kntu.ac.ir N. Granpayeh e-mail: granpayeh@kntu.ac.ir 123