Simultaneously phase-matched enhanced second and third harmonic generation

Hybrid nanowires for phase-matching of third-harmonic generation in hyperbolic metamaterial

We propose a phase-matching technique for third-harmonic generation, called hyperbolic phase matching, that possibly can be achieved by optimal designing and engineering dispersion of hybrid-nanowire hyperbolic metamaterial. We demonstrate phase-matched conditions for two different third-harmonic interacting configurations, which can be created at two optimal incident angles of the pump field. Moreover, each composed hybrid nanowire can enhance third-harmonic generation by using strong field confinement along the metal/dielectric interface due to plasmonic resonance. Finally, conversion efficiencies of transmitted and reflected third-harmonic pulses as a function of incident angle and input pulse intensity are examined by numerical integration of nonlinear birefringent coupled-mode equations. The numerical results validate the idea that, using a combination of phase-matched conditions and pump field confinement, we can achieve a dramatic enhancement of conversion efficiencies of third-harmonic generation.

Efficient higher-order nonlinear optical effects in CdSe nanowaveguides

Stimulating higher-order nonlinear optical (HO-NLO) response from individual semiconductor nanostructures is challenging due to the low nonlinear coefficients and the small number of molecules within the nanostructures. In this work, we demonstrate efficient third harmonic generation and multi-photon luminescence in CdSe nanowaveguides by means of evanescent wave coupling technique. Under appropriate conditions, a coupling efficiency of 70% can be achieved from an optical microfiber to a single CdSe nanowaveguide, leading to the enhanced HO-NLO effects. Provided a high signal-to-noise ratio, we thus observe a fourth order excitation power dependence of 3-photon luminescence, and we attribute it to surface defect mechanism based on the recombination of free carriers. This work provides an alternative for efficient excitation for HO-NLO, which also makes these hard-to-produce signals more feasible in the applications of nonlinear optical devices.

Second- and third-harmonic generation and hyper-Rayleigh scattering in porous-silicon-based photonic microcavities

Optical second-harmonic (SH) generation in porous-silicon-based photonic microcavities is observed in the form of hyper-Rayleigh scattering (HRS), with the SH radiation being diffuse and depolarized. Infiltration of sodium nitrite into the pores essentially suppresses HRS and results in generation of specular and partially polarized SH. Dissimilarly, the third-harmonic (TH) radiation from both unfilled and infiltrated samples is specular and polarized. These results indicate different spatial localization of the SH and TH sources.

Gap solitons in a nonlinear quadratic negative-index cavity

We predict the existence of gap solitons in a nonlinear, quadratic Fabry-Pérot negative index cavity. A peculiarity of a single negative index layer is that if magnetic and electric plasma frequencies are different it forms a photonic band structure similar to that of a multilayer stack composed of ordinary, positive index materials. This similarity also results in comparable field localization and enhancement properties that under appropriate conditions may be used to either dynamically shift the band edge, or for efficient energy conversion. We thus report that an intense, fundamental pump pulse is able to shift the band edge of a negative index cavity, and make it possible for a weak second harmonic pulse initially tuned inside the gap to be transmitted, giving rise to a gap soliton. The process is due to cascading, a well-known phenomenon that occurs far from phase matching conditions that limits energy conversion rates, it resembles a nonlinear third-order process, and causes pulse compression due to self-phase modulation. The symmetry of the equations of motion under the action of either an electric or a magnetic nonlinearity suggests that both nonlinear polarization and magnetization, or a combination of both, can lead to solitonlike pulses. More specifically, the antisymmetric localization properties of the electric and magnetic fields cause a nonlinear polarization to generate a dark soliton, while a nonlinear magnetization spawns a bright soliton.