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.
