Protein-based, high-speed photonic logical gates

The principle of all-optical logical operations utilizing the unique nonlinear optical properties of a protein was demonstrated by a logic gate constructed from an integrated optical Mach-Zehnder interferometer as a passive structure, covered by a bacteriorhodopsin film as the active element. The principle of logical operations is based on a reversible change of the refractive index of the bacteriorhodopsin film over either or both arms of the interferometer. Depending on the operating point of the interferometer, we could realize both binary and ternary logical modes of operation. Using an ultrafast transition of the bR photocycle (BR-K), we achieved high-speed (nanosecond) logical switching. This is the fastest operation of a protein-based integrated optical logic gate that has been demonstrated so far. The results are expected to have important implications for finding novel, alternative solutions in all-optical data processing research.