An optimal control approach is used to extend to the regime of pump depletion the idea of using spatially nonuniform nonlinear coefficients to tailor the shapes of optical pulses in a process of transient second-harmonic generation.
We investigate, both numerically and experimentally, the optical parametric generation (OPG) process in second-order nonlinear crystals driven by femtosecond pulses. We model the OPG process by solving the coupled second-order three-wave nonlinear propagation equations in the plane-wave limit, using noise fields to mimic the vacuum fluctuations. We focus on two parameters: (i) the temporal jitter between the OPG and the pump pulse; (ii) the carrier-envelope phase (CEP) relationship between the OPG and the pump pulse. Both numerical simulations and experiments support the following conclusions: (i) in the regime of low pump depletion the OPG pulse is synchronized with the pump, but its energy presents strong fluctuations; (ii) in the regime of high pump depletion, the energy of the OPG pulse stabilizes, but a temporal jitter with respect to the pump pulse is introduced; (iii) in both cases, the CEP relationship between pump and OPG pulses is completely random.
All optical processing of data on an integrated photonic chip requires all-optical switches as a fundamental element to actively modulate the transmission of the signal light by the control light. Traditional all-optical switches as a function of the intensities of the input fields can be classified into three categories as the regular, the optical limiting and the bistable switches. In this work, a whispering gallery mode resonator coupled to a waveguide with third-order nonlinearity in the pump depletion regime is investigated. The transmission spectra of the signal light are able to be controlled by adjusting the power-dependent frequency shifts. We find that the frequency shifts of the cavity modes depend not only on the nonlinear processes of self- and cross-phase modulation but also on the coupling between the pump and the signal lights in the pump depletion regime. When the pump light is increased to milliwatts, the transmission coefficient of the nonresonant signal light has a critical point corresponding to the complete destructive interference from the combing effects of pump depletion, self- and cross-phase modulation. The results show that the output power of the signal light responds to the input power of the pump light with V-shaped curves. These input–output power curves can be utilized to construct a V-type all-optical switch for applications in automatic protection and monitoring the light intensity in optical communication network. Significantly, the V-type all-optical switch can also be constructed in system with both second- and third-order nonlinearities involved.