arXiv subjects

Muhammad Fayyaz Kashif

Publications and source records attributed to Muhammad Fayyaz Kashif.

6 recordsLinked to original sources

arXiv2026

A Reflective Metasurface for High-Efficiency Terahertz Cross-Polarization Conversion

We demonstrate a reflective terahertz (THz) polarization conversion metasurface based on a double-ring aluminum resonator on a quartz substrate. Full-wave simulations are used to optimize the unit-cell geometry and investigate the polarization conversion mechanism through phase analysis, polarization ellipses, and surface-current distributions. The proposed metasurface exhibits a near-unity polarization conversion ratio (PCR) at resonance frequencies of 0.333 THz and 0.361 THz. Reflection-mode terahertz time-domain spectroscopy (THz-TDS) measurements show good agreement with the simulated results. The measured PCR exceeds 87% at both resonance frequencies, demonstrating efficient reflection-mode polarization conversion.

physics.optics↗

arXiv2025

Novel multifunctional plasmonic fiber probe: Enabling plasmonic heating and SERS sensing for biomedical applications

Optical fiber-based platforms are increasingly explored as compact, minimally invasive tools for integrated photonic functionalities in biomedical applications. Among these, the combination of plasmonic heating and optical sensing on a single fiber tip offers compelling opportunities for localized photothermal actuation and in situ molecular detection. In this work, we present a multifunctional plasmonic fiber probe (PFP) that enables spectral multiplexing of thermo-plasmonic heating and surface-enhanced Raman spectroscopy (SERS). This dual capability is achieved by integrating gold nanoislands (AuNIs) onto the flat facet of a multimode optical fiber using a solid-state dewetting process - a straightforward and scalable fabrication method that avoids the complexity of lithographic techniques. We characterize how the morphology of the AuNIs modulates optical extinction, photothermal response, and electromagnetic field enhancement across the visible and near-infrared spectrum. Specifically, we demonstrate efficient, wavelength-dependent heating under visible light and strong SERS signal enhancement under near-infrared excitation, both supported by electromagnetic and thermal simulations. The ability to decouple photothermal stimulation and Raman sensing in a single, fiber-integrated device addresses a current gap in lab-on-fiber technologies, where multifunctional operation is often constrained to a single wavelength.

physics.med-ph↗

arXiv2025

Deterministic Bottom-Up Fabrication of Plasmonic Nanostructures on Optical Nanofibers via Blurred Electron Beam Deposition

This study introduces a novel method for the deterministic fabrication of metallic nanostructures with controlled geometry and composition on suspended, single mode tapered optical nanofibers (TNFs) using a tailored Blurred Electron Beam Induced Deposition (BEBID) technique. TNFs, owing to their subwavelength diameters and intense evanescent fields, offer a unique platform for enhanced light matter interactions at the nanoscale. However, their mechanical fragility has thus far hindered the integration of plasmonic structures using conventional high energy deposition methods. BEBID addresses this limitation by deliberately defocusing the electron beam to reduce local mechanical stress, minimize vibration, and prevent fiber damage during deposition, thereby enabling the one-step growth of platinum nanopillars with sub 20 nm spatial precision and high structural fidelity directly on suspended TNFs. The fabricated structures were characterized using SEM, EDX, and their optical properties were investigated through broadband scattering spectra and polarization resolved measurements, showing strong agreement with Finite Difference Time Domain (FDTD) simulations. Numerical modeling further reveals that ordered arrays of nanopillars can shape and direct the scattered field along the fiber axis, enabling directional emission. This work establishes BEBID as a versatile bottom up nanofabrication approach for functional photonic architectures on fragile substrates, with direct applications in quantum photonics, nano optics, and on fiber plasmonic sensing.

physics.optics↗

arXiv2025

Direct Nucleation of Hierarchical Nanostructures on Plasmonic Fiber Optics Enables Enhanced SERS Performance

We present an innovative fabrication method to achieve bottom-up in situ surface-overstructured Au nanoislands (NIs) with tunable grades of surface coverage, elongation, and branching, directly on micro-optical fibers for sensing applications. These all-in-gold hierarchical nanostructures consist of NIs coated with surface protrusions of various morphologies. They are created in solution using a selective seeded growth approach, whereby additional gold growth is achieved over Au NIs formerly developed on the fiber facet by a solid-state dewetting approach. The morphology of nanosized surface-NI overstructuring can be adjusted from multi-dot-decorated Au NIs to multi-arm-decorated Au NIs. This engineering of optical fibers allows for improved remote surface-enhanced Raman spectroscopy (SERS) molecular detection. By combining solid-state dewetting and wet-chemical approaches, we achieve stable in-contact deposition of surface-overstructured NIs with the optical fiber solid substrate, alongside precise control over branching morphology and anisotropy extent. The fiber optic probes engineered by surface-overstructured NIs exhibit outstanding sensing performance in an instant and through-fiber detection scheme, achieving a remarkable detection limit at 10-7 M for the R6G aqueous solution. These engineered probes demonstrate an improved detection limit by one order of magnitude and enhanced peak prominence compared to devices solely decorated with pristine NIs.

physics.optics↗

arXiv2024

Tunable Nanoislands Decorated Tapered Optical Fibers Reveal Concurrent Contributions in Through-Fiber SERS Detection

Creating plasmonic nanoparticles on a tapered optical fiber tip enables a remote SERS sensing probe, ideal for challenging sampling scenarios like biological tissue, specific cells, on-site environmental monitoring, and deep brain structures. However, nanoparticle patterns fabricated from current bottom-up methods are mostly random, making geometry control difficult. Uneven statistical distribution, clustering, and multilayer deposition introduce uncertainty in correlating device performance with morphology. Here, we employ a tunable solid-state dewetting method to create densely packed monolayer Au nanoislands (NIs) with varied geometric parameters, directly contacting the silica TF surface. These patterns exhibit analyzable nanoparticle sizes, densities, and uniform distribution across the entire taper surface, enabling a systematic investigation of particle size, density, and analyte effects on the SERS performance of the through-fiber detection system. The study is focused on the SERS response of a widely employed benchmark Rhodamine 6G molecule and Serotonin, a neurotransmitter with high relevance for the neuroscience field. The numerical simulations and limit of detection (LOD) experiments on R6G show that the increase of the total near-field enhancement volume promotes the SERS sensitivity of the probe. However, for serotonin we observed a different behavior linked to its interaction with the nanoparticle's surface. The obtained LOD is as low as 10-7 M, a value not achieved so far in a through-fiber detection scheme. Therefore, we believe our work offers a strategy to design nanoparticle-based remote SERS sensing probes and provide new clues to discover and understand the intricate plasmonic-driven chemical reactions.

physics.optics↗

arXiv2019

Plasmonic sensing with FIB-milled 2D micro-arrays of truncated gold nano-pyramids

Plasmonic platforms are a promising solution for the next generation of low-cost, integrated biomedical sensors. However, fabricating these nanostructures often requires lengthy and challenging fabrication processes. Here we exploit the peculiar features of Focused Ion Beam milling to obtain single-step patterning of a plasmonic two-dimensional (2D) array of truncated gold nano-pyramids (TNP), with gaps as small as 17 nm. We describe the formation of plasmonic bandgaps in the arrangement of crossed tapered grooves that separate the nano-pyramids, and we demonstrate refractive index sensing via dark field imaging in patterned areas of 30 $μ$m $\times$ 30 $μ$m.

physics.app-ph↗