Collective responses of localized surface plasmon resonances, known as surface lattice resonances (SLRs) in metal nanoparticle arrays, can lead to high quality factors (∼100), large local-field enhancements and strong light-matter interactions. SLRs have found many applications in linear optics, but little work of the influence of SLRs on nonlinear optics has been reported. Here we show how SLRs could be utilized to enhance nonlinear optical interactions. We devote special attention to the sum-frequency, difference-frequency, and third-harmonic generation processes because of their potential for the realization of novel sources of light. We also demonstrate how such arrays could be engineered to enhance higher-order nonlinear optical interactions through cascaded nonlinear processes. In particular, we demonstrate how the efficiency of third-harmonic generation could be engineered via cascaded second-order responses.

Using finite element method, we investigated a hybrid palsmonic terahertz waveguide with an additional stripe with a frequency of about f = 3 THz. The structure consisted of a semiconductor stripe located at the center of the gap between a five-layer graphene and a high-index dielectric ridge which were all placed on a low-index dielectric substrate. A properlysized stripe helps the power ratio inside the gap to considerably increase, and the normalized mode area to improve greatly as well. A power confinement ratio of 0.65 and a normalized mode area of 0.03 were obtained. This shows respective improvements of 30% and 72% in comparison to conventional waveguides. This structure also provides a good propagation length of about 820 µm.

In this study, a reciprocal broadband four‐way spatial divider/combiner with coaxial probes entering a rectangular cavity is simulated, experimentally fabricated and tested. A combination of circuit model and full electromagnetic wave methods is used to simplify the design procedure by increasing the role of the circuit model and, in contrast, reducing the amount of full wave optimisation. The presented structure is compact and easy to fabricate. Keeping its return loss greater than 10 dB, the constructed combiner operates with a 100% bandwidth from 5 to 15 GHz. A through scenario is also analysed whereas both measured and simulated results indicate a negligible loss. The measurements are in good agreement with the simulations done by high frequency structural simulator software.

We theoretically investigate the propagation of broadband single-cycle terahertz (THz) pulses through a medium with a nonlinear optical response. Our model takes into account non-paraxial effects, self-focusing and diffraction, as well as dispersion, in both the linear and nonlinear optical regimes. We investigate the contribution of non-instantaneous Kerr-type nonlinearity to the overall instantaneous and delayed Kerr effect at the THz frequencies. We show how increasing the nonlinear relaxation time and its dispersion modifies the THz pulse after the propagation through a transparent medium. We also discuss the effect of linear dispersion on self-action during the pulse propagation.

Nonlinear absorption can limit the efficiency of nonlinear optical devices. However, it can also be exploited for optical limiting or switching applications. Thus, characterization of nonlinear absorption in photonic devices is imperative for designing useful devices. This work uses the nonlinear transmittance technique to measure the two-photon absorption coefficients ( α 2 ) of AlGaAs waveguides in strip-loaded, nanowire, and half-core geometries in the wavelength range from 1480 to 1560 nm. The highest α 2 values of 2.4, 2.3, and 1.1 c m / G W were measured at 1480 nm for 0.8-µm-wide half-core, 0.6-µm-wide nanowire, and 0.9-µm-wide strip-loaded waveguides, respectively, with α 2 decreasing with increasing wavelength. The free-carrier absorption cross section was also estimated from the nonlinear transmittance data to be around 2.2 × 10 − 16 c m 2 for all three geometries. Our results contribute to a better understanding of the nonlinear absorption in heterostructure waveguides of different cross-sectional geometries. We discuss how the electric field distribution in the different layers of a heterostructure can lead to geometry-dependent effective two-photon absorption coefficients. More specifically, we pinpoint the third-order nonlinear confinement factor as a design parameter to estimate the strength of the effective nonlinear absorption, in addition to tailoring the bandgap energy by varying the material composition.