Search

Light propagating through random media produces characteristic speckle patterns, directly related to the large multitude of scattering events. These complex dynamics remarkably display robustness to perturbation of the incoming light parameters, maintaining correlation in the scattered wavefront. This behavior is known as the optical memory effect. Here we unveil the properties of the nonlinear optical memory effect, which occurs when an optothermal nonlinearity perturbs the random material. The effect is characterized through a series of pump and probe experiments in silica aerogel, in the visible range. This additional degree of freedom further generalizes the memory effect, opening the road to applications based on the nonlinear response of random media.

We propose and demonstrate the concept of a contra-directional coupler between a W1 and a slotted photonic crystal waveguide. The bandwidth and operating wavelength of such a coupler can be controlled via its geometrical parameters, and power transfer is not periodic unlike in the more familiar codirectional case. Light of specific wavelengths can be extracted from the W1 mode into air slot modes using this design, with W1/slot coupling efficiencies of up to 99±1%, and waveguide extracted coupling efficiencies of up to 51±12% demonstrated experimentally. Combining several of these couplers in series, we demonstrate the spectral filtering functionality on-chip. The device therefore combines the well-known sensing function of the slotted waveguide geometry with the spectrometer function, thus uniting two essential biosensor functions in a monolithic device.

The speckle pattern arising from a thin random, disordered scatterer may be used to detect the transversal mode of an incident beam. On the other hand, speckle patterns originating from meter-long multimode fibers can be used to detect different wavelengths. Combining these approaches, we develop a method that uses a thin random scattering medium to measure the wavelength of a near-infrared laser beam with picometer resolution. The method is based on the application of principal component analysis, which is used for pattern recognition and is applied here to the case of speckle pattern categorization.

We analyze phase matching with reference to frequency doubling in nanosized quadratic waveguides encompassing form birefringence and supporting cross-polarized fundamental and second-harmonic modes. In an AlGaAs rod with an air void, we show that phase-matched second-harmonic generation could be achieved in a wide spectral range employing state-of-the-art nanotechnology.

By numerically integrating the three-dimensional Maxwell equations in the time domain with reference to a dispersive quadratically nonlinear material, we study second-harmonic generation in planar photonic crystal microresonators. The proposed scheme allows efficient coupling of the pump radiation to the defect resonant mode. The outcoupled generated second harmonic is maximized by impedance matching the photonic crystal cavity to the output waveguide.

Using a three-dimensional fully vectorial nonlinear time-domain analysis, we numerically investigate generation of terahertz radiation by pumping a photonic crystal microcavity out of resonance. High quality factors and a quadratic susceptibility lead to few-cycle terahertz pulses via optical rectification. Material dispersion as well as linear and nonlinear anisotropy is fully accounted for.

Using three-dimensional time-domain numerical simulations of the nonlinear dispersive Maxwell equations for a defect microcavity in a photonic crystal wire, we show that the transmission through the bandgap can be all-optically modulated via the generation of transient states associated with the nonlinear splitting of the defect mode. Analytical results based on time-domain coupled-mode theory are derived as well.

With second-harmonic generation in surface and buried planar waveguides achieved by direct and reverse proton exchange in lithium niobate, we demonstrate a novel kind of quadratic spatial simulton:?The transverse-electric fundamental input and the transverse-magnetic second-harmonic waves nonlinearly couple two superimposed planar waveguides, permitting transverse localization of light at room temperature and at excitations as low as 340 nJ in 20-ps pulses.