Abstract: An optical switching apparatus comprises an optically resonant system (3, 12) and a pulse source configuration (1, 2) to direct first and second pulses (P1, P2) of optical radiation into the resonant system, the first pulse (P1) being configured to produce a coherent excitation of the resonant optical system so as to change its optical characteristics and the second pulse (P2) being of a phase to thereafter de-excite the coherent excitation produced by the first pulse. According to the invention, a device (13, 34) driveable externally of the resonant system such as an optical amplifier or a laser, maintains the coherence of the excitation produced by the first pulse until de-excited by the second pulse. The optically resonant system may comprise an optically responsive medium (3) which is capable of being switched into a state of coherent resonance or a resonant cavity.

Abstract: A photo-detector comprises a photo-absorptive region (1) which absorbs individual incident photons to produce corresponding electron-hole pairs. A bias (Vb) applied by an electrode (3) to the region 1 separates the oppositely charged electrons and holes such that the individual electrons apply a gate field to an electrometer (4) in the form of a single electron transistor which has a source-drain path (6) along which carrier charged transport is limited Coulomb blockade. The charge of the individual, photo-induced electrons (e) modulate charge carrier transport through the single electron transistor and the resulting current is detected by amplifier (A1) to produce an voltage output (Vout) so as to detect incident photons individually.

Abstract: An optical switching apparatus comprises an optically resonant system (3, 12) and a pulse source configuration (1, 2) to direct first and second pulses (P1, P2) of optical radiation into the resonant system, the first pulse (P1) being configured to produce a coherent excitation of the resonant optical system so as to change its optical characteristics and the second pulse (P2) being of a phase to thereafter de-excite the coherent excitation produced by the first pulse. According to the invention, a device (13, 34) driveable externally of the resonant system such as an optical amplifier or a laser, maintains the coherence of the excitation produced by the first pulse until de-excited by the second pulse. The optically resonant system may comprise an optically responsive medium (3) which is capable of being switched into a state of coherent resonance or a resonant cavity.