High-speed gate-tunable terahertz coherent perfect absorption using a split-ring graphene

We exploit split-ring graphene to realize coherent perfect absorption (CPA) in the terahertz (THz) regime. By controlling the relative phase of two counter-propagating coherent beams, the coherent absorption at resonant frequency of 2.91 THz can be tuned continuously from 99.7% to less than 2.1 x 10(-4)%, which gives a modulation contrast of 56.7 dB. Moreover, the coherent absorption also can be tuned by varying the gate-controlled Fermi energy based on the electro-absorption effect of graphene, giving a modulation contrast of 19 dB. Center frequency tunable CPA is also achieved using gate-tunable split-ring graphene. We discuss the tolerance of the geometric parameters (radii of the inner and outer circles, gap aperture) and study the device performance dependence on the relative intensities of two input beams and the angle between two input beams. Additionally, the response time of the device is analyzed to be similar to 36 ps, which indicates possible high-speed gate-tunable THz CPA operations. (C) 2015 Optical Society of America