Bacteriorhodopsin (bR) is a photochromic biological molecule that has promise for use in all-optical switches and other photonic components; however, bR is transparent in the all-important telecom band (1310-1550 nm), which seemingly eliminates it from contention as a base for optical telecom devices. But researchers at the Rowland Institute, Harvard University (Cambridge, MA) have created a bR-based optical switch that routes a near-IR (1311 nm) beam with the application of a low-power green (532 nm) pump.
A 300 µm silica microsphere is coated with bR, suspended between two optical fibers, and optically coupled to them. When 200 µW of pump light is applied through one of the fibers, the evanescent waves in the sphere’s whispering-gallery modes interact with the bR, causing a resonant-frequency shift in the cavity that switches the incoming near-IR probe light from one fiber port to another. Switching on is fast, but switching off is much slower (with a time constant of 11 s). Speedier switching is possible with other photochromic organic materials such as diarylethene. Contact Frank Vollmer at vollmer@rowland.harvard.edu.
