All-optical switching based on optical control of energy transfer between thin-film layers

The migration of electronic excitation energy between individual particles is a well-studied phenomenon. The ability to exert optical control over this transfer of energy is the subject of much recent research, and it forms the basis for a potential all-optical switching device. In detail, near-field energy transfer from an excited donor nanoparticle (following previous light absorption) to an acceptor particle can, under suitable conditions, be activated or deactivated by the input of a non-resonant laser beam, i.e. optical switching action occurs. It is envisaged that an all-optical device utilizing the described mechanism will involve nanoparticles contained within thin-film deposits on a pair of parallel substrates. Nanolithography is the technique offering the best prospects for the deposition and tailoring of nanoparticles within each optically active layer. This paper gives a theoretical analysis of the non-linear response mechanism, termed optically controlled resonance energy transfer (OCRET). The concept of transfer fidelity, signifying the accuracy of mapping input to designated output, is introduced and its key determinants are identified. Analysis shows that, at reasonable levels of laser intensity, cross-talk to unsought destinations can be effectively extinguished. The advantage of constructing these donor and acceptor thin-film layers around an ultra-thin spacer material (which is suitably transparent) is discussed, and potential applications beyond simple switching are outlined, including logic gates and optical buffers.