High-Quality Factor Suspended-Wire 1D Photonic Crystal Micro-cavity in Silicon-on-Insulator

We present a comparison of high Q-factor tapered membrane-type onedimensional photonic crystal micro-cavities embedded in photonic wire waveguides based on silicon-on-insulator (SOI). Q-factor values as large as 24,000 have been measured, together with normalized transmission of 67%: an improvement in the Q-factor value in comparison with previous results obtained on structures with silicon cores supported by a silica buffer layer. Simulation using a 3D FDTD approach shows close agreement with measurements. Introduction High quality factor waveguide micro-cavity structures have been a topic of research interest for several years. Hole-based one-dimensional photonic crystal (PhC) microcavities embedded in photonic wire waveguides, with a Q-factor value of around 500, were described in [1]. We now report achievement of an experimental Q-factor value as large as 24,000 in an air-suspended photonic-wire waveguide micro-cavity structure a value that is, to our knowledge, the highest achieved in this particular format. High Q-factor values have been reported for several different device designs [2,3], but the requirement of achieving high Q-factor values, together with large optical transmission and small modal volumes, has become increasingly important [4]. Recent work based on photonic-wires combined with 1D PhC micro-cavities having silicon waveguide cores supported by a silica buffer layer has achieved Q-factor values in excess of 100,000. Air-suspended membrane-type photonic crystal structures [5], including micro-cavities, have been successfully fabricated and have demonstrated very high cavity Q-factor values, but there are still issues of mechanical stability, robustness and fabrication complexity. The motivation of our work on designing and producing suspended-membrane PhC/PhW waveguide microcavities has been to investigate the impact of increased optical confinement within the waveguides, as well as the effect of possible reductions in the propagation losses. Design considerations and FDTD simulation approach Planar one-dimensional photonic crystal micro-cavities embedded in 500 nm wide photonic wire waveguides have been realized recently with Q-factor values of approximately 18,500 and normalized transmission of nearly 85% [4]. This performance combination was achieved in structures in which the silicon guiding layer was supported by a silica lower cladding or buffer layer. The devices produced are useful for telecommunications applications such as dense wavelength division multiplexing (DWDM) and optical signal processing more generally. Detailed descriptions of the devices can be found in reference [4]. Figure 1 shows an SEM image Eindhoven, The Netherlands, June 11-13, 2008 FrPD3