We demonstrate the use of cost-effective tapered telecommunication fiber in refractive index-based sensing when operated in the visible range of wavelength. To fabricate the tapered fiber, a two-step chemical-etching method is adopted. The two-step etching method is quintessential in overcoming issues such as the uncontrollable etching of Ge-doped silica fibers by hydrofluoric acid. The work details the optimization of the etching process. The tapered fiber is then chemically treated to immobilize gold nanoparticles on it. Finally, the performance of the proposed Au-immobilized tapered fiber sensor probe is studied when excited with visible light. Different concentrations of sucrose are used to detect the refractive index sensitivity. Performance parameters such as sensitivity, full-width half maximum, the figure of merit, and quality factor are determined for the sensor probe.
Silicon nitride (SiN) has emerged as a promising platform for the development of photonic integrated circuits (PICs) covering a wide range of application areas from the visible to the infrared regime. Optical microcavity has evolved to be a highly versatile component in PICs, enabling the development of various disciplines, including lasers, filters, sensors, tele/data communication, and quantum technologies. SiN microring resonators are particularly compatible with already established micro or nanofabrication protocols and display useful properties, such as ultra-compactness, low loss, and planar nature. In this work, we have demonstrated the hybrid nanophotonic chip modeling, nanofabrication, two-dimensional semiconductor (TMDC) integration, and chip testing of high-Q ultra-compact SiN microring resonators supporting the Terahertz (THz) free spectral range (FSR) cavity modes at the visible wavelength. Counterpart, the monolithic integration of solid-state color centers with photonic elements of the same material is a promising approach to overcome the constraints of fabrication complexity and coupling losses in traditional hybrid integration approaches. We have engineered a novel
Atomically thin two-dimensional transition metal dichalcogenides have garnered tremendous attention from researchers owing to their distinct electrical and optical properties. Improving the photoluminescence of these two-dimensional atomic semiconductors is imperative for their seamless integration into photonic and optoelectronic devices. Concurrently, the advent of two-dimensional materials such as graphene and transition metal dichalcogenides has ushered in opportunities within the realm of valleytronics. Valleytronics endeavors to exploit valley degrees of freedom for information processing, mirroring the principles of spin-based spintronics and charge-based electronics. Notably, these materials demonstrate a unique spin-valley locking mechanism, thereby enabling modulation of the electronic valley degree of freedom through light. In the present study, we fabricated cost-effective nanocone structures via colloidal lithography and subsequently integrated them with a monolayer of WSe2. Through this methodology, we amplified both the photoluminescence and valley polarization enhancement of the WSe2 monolayer by harnessing plasmonic hotspots.
Radiative losses in nanophotonic devices are a fundamental challenge in their miniaturization. Plasmonic metals overcome the radiation losses, but high ohmic losses hinder the optical performance. Supercavity modes, also known as quasi-bound states in the continuum (BIC), help circumvent this problem. In this work, we propose a low refractive index 2D-periodic array of slotted disk that supports symmetry protected BIC and accidental BIC at off-gamma point. This BIC point is very fascinating to study the exciton-cavity interaction. To study the exciton-cavity, TMDCs have the great potential to generate the exciton. This exciton is coupled with BIC mode to generate the polariton state in a strong coupling region.
The presence of a vertical component to the transition dipole moment in interlayer excitons, which suppresses electron-hole overlap, results in longer radiative lifetimes as compared to intralayer excitons. Such tightly bound interlayer excitons well-suited candidates for valley-based quantum information processing applications. Their optical accessibility is, however, limited due to their out-of-plane transition dipole moment. We first design a system to strengthen the coupling of interlayer excitons in two-dimensional (2D) material heterostructures with Purcell enhanced out-of-plane resonant modes of a Whispering Gallery Mode (WGM) resonator at room temperature. The high quantum confinement of light in a small modal volume and high Q-factor allow a much stronger coupling of these excitons to the electromagnetic field. We then discuss how to engineer an asymmetric transmission of light from these excitons, which facilitates readout from such systems. We also present our attempts to experimentally demonstrate the valley selective separation and routing of interlayer excitons in the MoSe2/WSe2 heterobilayer stack of TMDCs material by integrating on a planar silicon nitride (SiN) bus-waveguide coupled with a microring resonator (MRR).
Atomically thin two-dimensional transition metal dichalcogenides have fascinated researchers due to their unique electronic and optical properties. The control of exciton-trion dynamics in two-dimensional semiconductors is critical for their application in optoelectronic devices. One way to engineer the exciton-trion dynamics is by applying strain in the monolayers of these two-dimensional materials using nanostructured substrates. Here we demonstrate a versatile route to engineering the exciton-trion dynamics in monolayer WSe2 by applying biaxial strain. A polytetrafluoroethylene (PTFE) nanocone array decorated by thin gold film and fabricated via colloidal lithography is used to create the strain in the superposed monolayer. To distinguish the effect of strain and plasmonics, we compare our results on the nanocone surface with the one for monolayer WSe2 on a plane gold film.
Large-area nano-patterned surfaces invoking hydrophobicity hold great significance for Surface Enhanced RamanSpectroscopy or SERS substrates. Conventionally, these structures are fabricated using state-of-the-art litho-graphic techniques. These techniques while being efficient, are complex and are cost-ineffective. Here, we report a low-cost, facile and scalable solution for fabrication of periodic array of metallic nanocones using colloidal lithography and reactive ion etching process. Nanocone array coated with gold thin film serves as a hydrophobicsurface with plasmonic properties. Hydrophobicity on the cones helps to keep the analyte molecule localized near the tip of nanocones where, due to plasmonic behavior of metal thin film i.e. field enhancement by the metal gives rise to significant SERS. We validate this concept through our fabricated substrate via detection ofRhodamine 6G molecules using Raman spectroscopy and report the limit of detection upto 1 nM.
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