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The thickness-dependent multimodal nature of three-dimensional (3D) coupled photonic crystal waveguides is investigated with the aim of realizing a medium for controlled optical gap soliton formation in the slow light regime. In the linear case, spectral properties of the modes (dispersion diagrams), location of the gap regions versus the thickness of the 3D photonic crystal, and the near-field distributions at frequencies in the slow light region are analyzed using a full-wave electromagnetic solver. In the nonlinear regime (Kerr-type nonlinearity), we infer an existence of crystal-thickness-dependent temporal solitons with stable pulse envelope and use the solitonic pulses for driving quantum transitions in localized quantum systems within the photonic crystal waveguide. The results may be useful for applications in optical communications, multiplexing systems, nonlinear physics, and ultrafast spectroscopy.

Spintronic THz emitters (STEs) rely on spin current acceleration or decay, resulting in a burst of broadband THz emission, offering a new route to THz optics. Here, we demonstrate novel metastructures of STEs for molding the vectorial focal distribution of the emitted THz radiations. The metastructures also allow controlling the characteristics of local fields. Performing combined micromagnetic-electromagnetic simulations, we demonstrate the generation of broadband THz fields with designed vectorial, chiral, magnetic, or topological features and discuss the potential of these fields for studying magnetic, multiferroic, and chiral structures. The STEs metastructure is shown to produce higher-order electric and magnetic multipoles as well as localized, longitudinal, broadband magnetoelectric THz pulses. Furthermore, subwavelength features of the near fields at a distance less than 10 μm can be tuned by steering the magnetization of the metastructure. The results point to a new type of engineered STEs for the generation of structured broadband THz fields, with potential applications in the fields of optoelectronics, optics, and ultrafast magnetism.