Slow Light in Subwavelength Grating Waveguides

Structural slow light is the dispersion engineering process by which the group velocity of light can be drastically reduced in a periodic waveguide structure. Enabling large group delay and enhancing the light-matter interaction on a subwavelength scale, on-chip slow light is of great interest in a vast array of fields such as non-linear optic, sensing, laser physics, telecommunication and computing. In this work, we experimentally demonstrate, for the first time, slow light in subwavelength grating waveguides on the silicon-on-insulator platform. We present a comprehensive numerical study in analytical modelling and 3-D FDTD. Multiple waveguides variations were fabricated using an electron-beam lithography process. Figures of merit such as group index, bandwidth and loss-per-delay are examined in both theory and experiment. A maximum measured group index of 47.74 with a loss-per-delay of 103.37 dB/ns has been achieved near the wavelength of 1550 nm. A broad bandwidth of 8.82 nm was measured, in which the group index remains larger than 10. We also show that the region of slow light operation can be shifted over a large wavelength span by controlling a single design parameter.