Optical-induced spectral tuning in grating-assisted nonlinear couplers

The spectral (wavelength) properties of the grating-assisted nonlinear coupler are investigated theoretically. The interaction of linear and nonlinear wavelength-dependent phase detuning leads to a rich display of new and useful characteristics. Among these are bandpass tuning and spectral shaping. The grating frequency is viewed as a `free design parameter´ which may be judiciously chosen to bring about an optimum behavior for a given application. As a wavelength processing element, the coupler behaves as an extended and continuously tunable wavelength filter, with tuning proportional to the input power. As an an-optical switch, a broadened and virtually transparent passband is easily achieved, which has desirable consequences for ultra-fast (large bandwidth) switching. The coupler may be operated in two complimentary modes: The active mode, where the power level of an input pulse or signal interacts in a nonlinear fashion with the passband of the coupler; and the passive mode, where a separate idler input is used to bias the device for a desired response to a smaller injected signal