Single-Nanowire Thermo-Optic Modulator Based on a Varshni Shift

The rapid development of nanotechnology has spurred great efforts in improving thermo-optic (TO) modulators with higher performances for optical signal processing and interconnects, in which reducing the heating structure and increasing the heating efficiency is one of the most effective approaches to faster response and lower power consumption. Here we demonstrate a single-nanowire all-optical TO modulator based on a temperature-dependent Varshni shift of the band gap. A bottom-up grown single-crystal cadmium sulfide (CdS) nanowire, 170 nm in diameter and 13.5 mu m in length, is used as an optical waveguide to handle the signal and an ultracompact nanoheater simultaneously when the signal and the switch light are copropagated through the nanowire. The switch-light-induced temperature change causes a band gap shift of the nanowire, which in turn modulates the signal light propagated inside. By merging the two functionalities in a single nanowire, such an all-optical TO modulator shows the following advantages: faster response, ultrasmall footprint, high heating efficiency, and low power consumption. Using a switch light with 91 mu W of power and a 405 nm wavelength, a modulation depth of similar to 86% was achieved for a signal light with 287 mu W of power and a 515 nm wavelength, with a modulation time less than 20 mu s.