Patent ID: 8135277

Claim:
A method of delayed optical switch using a nonlinear optical medium composing two closely spaced ground states such that a transition between the two said ground states is dipole forbidden, and an excited state such that two-photon transitions between said two ground states via said excited state are allowed, said method comprising following steps: a) applying to said nonlinear optical medium a first laser beam (P) as an input signal beam through an optical fiber, optical waveguide, surface plasmon, or free space at a first frequency corresponding to a first transition between a first ground state of said ground states and said excited state; b) applying a second laser beam (C 1 ) through an optical fiber, optical waveguide, surface plasmon, or free space at a second frequency corresponding to a second transition between a second ground state of said ground states and said excited state; c) applying a third laser beam (C 2 ) through an optical fiber, optical waveguide, surface plasmon, or free space at a third frequency corresponding to the second transition between the second ground state of said ground states and said excited state; d) adjusting an intensity of said second laser beam (C 1 ), to produce a slow light (S) from said first laser beam (P), where a pulse delay of the slow light (S) from the first laser beam (P) is controllable by the intensity of the second laser beam (C 1 ); e) adjusting an intensity of said third laser beam (C 2 ) to produce a nondegenerate four-wave mixing signal or a phase conjugate (D) via phase matching condition among said slow light (S) from said first laser beam (P), said second laser beam (C 1 ), and said third laser beam (C 2 ) in propagation vectors and wavelengths; and f) connecting said nondegenerate four-wave mixing signal (D) or said slow light (S) to free space or to optical fibers, in which said nondegenerate four-wave mixing signal (D) and said slow light (S) are physically separated in propagation directions.