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Register a new userTMDC Resonators for Second Harmonic Signal Enhancement
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Added by
Sebastian Busschaert
Publication date
2020
fields
Physics
and research's language is
English
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In addition to their strong nonlinear optical response, transition metal dichalcogenides (TMDCs) possess a high refractive index in the visible and infrared regime. Therefore, by patterning those TMDCs into dielectric nanoresonators, one can generate highly confined electromagnetic modes. Controlled fabrication of TMDC nanoresonators does not only enhance the materials intrinsic nonlinear response, but also allows for spatially shaping the emission via nanoresonator arrays. Here we fabricate patterned WS2 disks that support a high internal resonant electric field and show strong enhancement of second harmonic (SH) generation in the visible regime. In addition, we assemble the WS2 disks in arrays to spatially direct the coherent SH emission, in analogy to phased array antennas. Finally, we investigate and discuss drastic differences in the areal emission origin and intensity of the measured SH signals, which we find to depend on material variations of the used bulk WS2.
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We investigate the generation of ultraviolet (UV) second-harmonic radiation on the boundary of a UV transparent crystal, which is derived from the automatic partial phase matching of the incident wave and the total internal reflection. By adhering to another UV non-transparency crystal with larger second-order nonlinear coefficient chi^{(2)}, an nonlinear interface with large disparity in chi^{(2)} is formed and the enhancement of UV second-harmonic radiation is observed experimentally. The intensity of enhanced second harmonic wave generated at the nonlinear interface was up to 11.6 times at the crystal boundary. As a tunable phase-matching method, it may suggest potential applications in the UV, even vacuum-UV, spectral region.
Plasmonic enhancement of nonlinear optical processes confront severe limitations arising from the strong dispersion of metal susceptibilities and small interaction volumes that hamper desirable phase-matching-like conditions. Maximizing nonlinear interactions in nanoscale systems require simultaneous excitation of resonant modes that spatially and constructively overlap at all wavelengths involved in the process. Here, we present a hybrid rectangular patch antenna design for optimal second harmonic generation (SHG) that is characterized by a non-centrosymmetric dielectric/ferroelectric material at the plasmonic hot spot. The optimization of the rectangular patch allows for the independent tuning of various modes of resonances that can be used to enhance the SHG process. We explore the angular dependence of SHG in these hybrid structures and highlight conditions necessary for maximal SHG efficiency. Furthermore, we propose a novel configuration with a periodically-poled ferroelectric layer for orders-of-magnitude enhanced SHG at normal incidence. Such a platform may enable the development of integrated nanoscale light sources and on-chip frequency converters.
Lithium niobate (LN), dubbed by many as the silicon of photonics, has recently risen to the forefront of chip-scale nonlinear optics research since its demonstration as an ultralow-loss integrated photonics platform. Due to its significant quadratic nonlinearity ($chi^{(2)}$), LN inspires many important applications such as second-harmonic generation (SHG), spontaneous parametric down-conversion, and optical parametric oscillation. Here, we demonstrate high-efficiency SHG in dual-resonant, periodically poled z-cut LN microrings, where quasi-phase matching is realized by field-assisted domain engineering. Meanwhile, dual-band operation is accessed by optimizing the coupling conditions in fundamental and second-harmonic bands via a single pulley waveguide. As a result, when pumping a periodically poled LN microring in the low power regime at around 1617nm, an on-chip SHG efficiency of 250,000%/W is achieved, a state-of-the-art value reported among current integrated photonics platforms. An absolute conversion efficiency of 15% is recorded with a low pump power of 115$mu$W in the waveguide. Such periodically poled LN microrings also present a versatile platform for other cavity-enhanced quasi-phase matched $chi^{(2)}$ nonlinear optical processes.
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