  Next-generation communication networks require > Tbit/s single-channel data
transfer and processing with sub-picosecond switches and routers at network
nodes. Materials enabling ultrafast all-optical switching have high potential
to solve the speed limitations of current optoelectronic circuits.
Chromoproteins have been shown to exhibit a fast light-controlled refractive
index change much larger than that induced by the optical Kerr effect due to a
purely electronic nonlinearity, alleviating the driving energy requirements for
optical switching. Here, we report femtosecond transient grating experiments
demonstrating the feasibility of < 200-fs all-optical switching by hydrated
thin films of photoactive yellow protein, for the first time, and compare the
results with those obtained using bacteriorhodopsin. Possibilities for the
practical utilization of the scheme in extremely high-speed optical modulation
and switching/routing with nominally infinite extinction contrast are
discussed.
