Photonic crystal group delay device for optical code division multiple access

Abstract

We propose and demonstrate a photonic crystal optical group delay device, in which two dimensional photonic crystal line defect waveguide with chirped hole, induces sequential optical group delays for time-spreading/wavelength-hopping optical code division multiple access (O-CDMA). The photonic crystal line defect waveguide allows ultrasmall size of device due to its strong optical confinement by the photonic bandgap. And chirped photonic crystal waveguides, in which radius of holes are gradually changed so that the photonic bands are smoothly shifted to the higher frequency side. When a short pulse signal with a wide spectrum comes into this device, the guided light is localized at specific position depending on wavelength. This concept is suitable to realize a pulse waveform synthesizer and an en/decoder for time-spreading/wavelength-hopping O-CDMA. We have confirmed that this device has a chromatic temporal dispersion of ~ 33-fs/nm, corresponding to the repetition rate of ~ 1-ps for pulses with wavelength-interval of 30-nm, by two dimensional finite difference time domain simulation.