Ultra-slow light with high normalized delay–bandwidth product and refractive-index sensing in photonic crystal coupled-cavity waveguide

Ultra-slow light can enhance light–matter interactions and effectively realize all-optical buffering and modulation. In this paper, we present an efficient design for a two-dimensional square-lattice photonic crystal coupled-cavity waveguide, which can realize multi-frequency band slow-light transmission in the near-infrared band (1500–1640 nm).Through adjusting intercavity spacing N and structural parameters of elliptical air holes, high group index ng (202.46) within the bandwidth of 5.04 nm and improved normalized delay–bandwidth​ product of 0.6583 can be obtained at the wavelength of 1550.05 nm. Moreover, the designed devices can effectively function as a slow light sensor with the wavelength sensitivity of 585 nm/RIU. Multiple functions can be achieved synchronously in only one structure, which is essential in complex optical integrated circuits.