Emerging Low Detection Limit of Optically Activated Gas Sensors Based on 2D and Hybrid Nanostructures.

Gas sensing is essential for detecting and measuring gas concentrations across various environments, with applications in environmental monitoring, industrial safety, and healthcare. The integration of two-dimensional (2D) materials, organic materials, and metal oxides has significantly advanced gas sensor technology, enhancing its sensitivity, selectivity, and response times at room temperature. This review examines the progress in optically activated gas sensors, with emphasis on 2D materials, metal oxides, and organic materials, due to limited studies on their use in optically activated gas sensors, in contrast to other traditional gas-sensing technologies.

On-chip low-loss all-optical MoSe modulator.

Monolayer transition metal dichalcogenides (TMDCs), like MoS, MoSe, WS, and WSe, feature direct bandgaps, strong spin-orbit coupling, and exciton-polariton interactions at the atomic scale, which could be harnessed for efficient light emission, valleytronics, and polaritonic lasing, respectively. Nevertheless, to build next-generation photonic devices that make use of these features, it is first essential to model the all-optical control mechanisms in TMDCs. Herein, a simple model is proposed to quantify the performance of a 35-m-long SiN waveguide-integrated all-optical MoSe modulator.

Investigation of light-matter interaction in single vertical nanowires in ordered nanowire arrays.

Quasi one-dimensional semiconductor nanowires (NWs) in either arrays or single free-standing forms have shown unique optical properties (, light absorption and emission) differently from their thin film or bulk counterparts, presenting new opportunities for achieving enhanced performance and/or functionalities for optoelectronic device applications. However, there is still a lack of understanding of the absorption properties of vertically standing single NWs within an array environment with light coupling from neighboring NWs within certain distances, due to the challenges in fabrication of such devices. In this article, we present a new approach to fabricate single vertically standing NW photodetectors from ordered InP NW arrays using the focused ion beam technique, to allow direct measurements of optical and electrical properties of single NWs standing in an array.

Highly Efficient Near-Infrared Detector Based on Optically Resonant Dielectric Nanodisks.

Fast detection of near-infrared (NIR) photons with high responsivity remains a challenge for photodetectors. Germanium (Ge) photodetectors are widely used for near-infrared wavelengths but suffer from a trade-off between the speed of photodetection and quantum efficiency (or responsivity). To realize a high-speed detector with high quantum efficiency, a small-sized photodetector efficiently absorbing light is required.

Damage analysis of a perfect broadband absorber by a femtosecond laser.

Plasmonic metamaterial absorbers are particularly important in different applications such as photodetectors, microbolometers and solar cells. In this paper, we propose a tungsten boride (WB, a refractory ceramic) based broadband metamaterial absorber whose optical properties is numerically analyzed and experimentally characterized. We have also analyzed the damage characteristics of this absorber using a femtosecond laser and compared with an ordinary Au metamaterial absorber.

High Fluence Chromium and Tungsten Bowtie Nano-antennas.

Nano-antennas are replicas of antennas that operate at radio-frequencies, but with considerably smaller dimensions when compared with their radio frequency counterparts. Noble metals based nano-antennas have the ability to enhance photoinduced phenomena such as localized electric fields, therefore-they have been used in various applications ranging from optical sensing and imaging to performance improvement of solar cells. However, such nano-structures can be damaged in high power applications such as heat resisted magnetic recording, solar thermo-photovoltaics and nano-scale heat transfer systems.

Optoelectronic figure of merit of a metal nanoparticle-quantum dot (MNP-QD) hybrid molecule for assessing its suitability for sensing applications.

Recently, many have studied various configurations of metal nanoparticle-quantum dot (MNP-QD) hybrid molecules based on different metals and tunable parameters. In this paper, we aim to incite the interest in using MNP-QD nanohybrids, which possess sensing capabilities superior to those of the individual constituents, for sensing applications that rely on scattered light. When assessing whether a given MNP-QD configuration is suited for an application, sometimes it is hard to assess the pros and cons of a given configuration against other candidates.

Magnesium diboride (MgB) as a saturable absorber for a ytterbium-doped Q-switched fiber laser.

Magnesium diboride (MgB) is a well-known superconductor at temperatures below 39 K. At higher temperatures, it behaves as a lossy material. In this paper, we examine the performance of MgB nano-particles as saturable absorber in a ytterbium-doped fiber ring laser at room temperature: we show that the nano-particles can produce pulses between 200 and 1700 ns.

Integration of bow-tie plasmonic nano-antennas on tapered fibers.

In this article, a new and flexible approach to control the electric field enhancement of bow-tie nano-antennas by integrating them on the lateral of a tapered optical fiber is proposed. The device is driven by a Q-switched laser and the performance of a fabricated nano-antenna in a quartz slide is tested by a Surface Enhanced Raman Scattering (SERS) experiment. A refractive index sensing experiment is also performed and a sensitivity of (240 ± 30) nm/RIU is found in the 1.

Ytterbium-doped Q-switched fiber laser based upon manganese dioxide (MnO) saturable absorber.

Manganese dioxide (MnO) is an abundant material that is widely used in many devices, such as alkaline batteries. At infrared frequencies, MnO is lossy and strongly absorbs light. These characteristics make MnO a potential candidate as a low-cost saturable absorber in Q-switched lasers.

Absorption enhancement in graphene photonic crystal structures.

Graphene, a single layer of carbon atoms arranged in a honeycomb lattice, is attracting significant interest because of its potential applications in electronic and optoelectronic devices. Although graphene exhibits almost uniform absorption within a large wavelength range, its interaction with light is weak. In this paper, the enhancement of the optical absorption in graphene photonic crystal structures is studied: the structure is modified by introducing scatterers and mirrors.

Finite-difference time-domain methods to analyze ytterbium-doped Q-switched fiber lasers.

Q-switched lasers are widely used in material processing, laser ranging, medicine, and nonlinear optics--in particular, Q-switched lasers in optical fibers are important since they cannot only generate high peak powers but can also concentrate high peak powers in small areas. In this paper, we present new finite-difference time-domain methods that analyze the dynamics of Q-switched fiber lasers, which are more flexible and robust than previous methods. We extend the method to analyze fiber ring lasers and compare the results with our experiments.

Thick multilayered (silica/gold) dipole nano-antenna.

Nano-antennas are the optical equivalent of antennas that are used to transmit and receive information at radio frequencies. These antennas have been used in different applications in photonics such as optical imaging, particle manipulation, bio-sensing, and improvement of the performance of solar cells. In this article we study composite nano-antennas made of alternating layers of silica and gold.

Polarizer based upon a plasmonic resonant thin layer on a squeezed photonic crystal fiber.

In this article, a polarizer based on surface plasmon resonance in a squeezed rectangular lattice is analyzed through a full-vector finite-element method solver. The device allows one state of polarization (e.g.

Offset semi-parabolic nanoantenna made of a photonic crystal parabolic mirror and a plasmonic bow-tie antenna.

In a parabolic mirror, light coming parallel to the antenna passes through its focal point. In this work, a waveguide feeds a semi-parabolic photonic crystal mirror and the emerging beam feeds a bow-tie antenna placed at the mirror's focal point-it is shown that the antenna system can not only feed a bow-tie antenna (producing a localized moderately high electric field) but also produces a directional radiation beam. The semi-parabolic mirror is also modified to reduce reflection back to the feeding waveguide.

Composite chromium and graphene oxide as saturable absorber in ytterbium-doped Q-switched fiber lasers.

In recent years, graphene and its compounds (e.g., oxides) have been used as saturable absorbers in passive Q-switched and mode-locked lasers, leading to the fabrication of compact pulsed fiber lasers.

Arrays of recycled power TM polarized nano-antennas.

In recent years, plasmonic nano-antennas have been used in a wide range of applications in sensing, particle detection, imaging and Surface Enhanced Raman Scattering (SERS) detection. Also, arrays of nano-antennas have been recently developed to produce more directional radiation beams or to operate over a wide range of wavelengths. In this article, it is shown that small arrays of nano-antennas can be created by recycling the power that flows through their antenna gaps.

Analysis of interference between two optical beams in a quasi-zero electric permittivity photonic crystal superlattice.

A quasi-zero-average-index photonic crystal structure has been recently demonstrated by using the concept of complementary media. It consists of dielectric photonic crystal superlattices with alternating layers of negative index photonic crystals and positive index dielectric media. This photonic crystal structure has unique optical properties, such as phase-invariant field and self-collimation of light.

Driving plasmonic nanoantennas with triangular lasers and slot waveguides.

Plasmonic nanoantennas can generate high-intensity electric fields in a very small area. However, being passive devices, they need to be excited by external laser sources. The excitation of nanoantennas by semiconductor lasers can be inefficient and a significant amount of light may return back to the laser source after being scattered by the nanoantenna.

Improved transmission model for metal-dielectric-metal plasmonic waveguides with stub structure.

We present an improved analytical model describing transmittance of a metal-dielectric-metal (MDM) waveguide coupled to an arbitrary number of stubs. The model is built on the well-known analogy between MDM waveguides and microwave transmission lines. This analogy allows one to establish equivalent networks for different MDM-waveguide geometries and to calculate their optical transmission spectra using standard analytical tools of transmission-line theory.

Unified perfectly matched layer for finite-difference time-domain modeling of dispersive optical materials.

Finite-difference time-domain (FDTD) simulations of any electromagnetic problem require truncation of an often-unbounded physical region by an electromagnetically bounded region by deploying an artificial construct known as the perfectly matched layer (PML). As it is not possible to construct a universal PML that is non-reflective for different materials, PMLs that are tailored to a specific problem are required. For example, depending on the number of dispersive materials being truncated at the boundaries of a simulation region, an FDTD code may contain multiple sets of update equations for PML implementations.

Coupling of light from microdisk lasers into plasmonic nano-antennas.

An optical dipole nano-antenna can be constructed by placing a sub-wavelength dielectric (e.g., air) gap between two metallic regions.

Analysis of optically pumped equilateral triangular microlasers with three mode-selective trenches.

Semiconductor laser devices based on triangular resonators can provide cheap, compact, and high performance optical sources for optical communications, computing, defense, and biological applications. I modify the original structure by introducing three trenches and analyze their effects on the electromagnetic modes propagating in the triangular cavity. I also analyze the coupling of light into single-mode waveguides.

Analysis of distributed-feedback lasers with fractionally organized gratings.

We analyze the performance of distributed-feedback lasers with special grating structures. These grating structures consist of subgratings with different lengths (that are integer multiples of a reference length) and/or different phase shifts (that are also integer multiples of a reference phase shift). These grating structures can provide transmission peaks with high quality factors, which may be useful for distributed-feedback lasers.

Analysis of strategies to improve the directionality of square lattice band-edge photonic crystal structures.

Recently, photonic crystal band-edge structures have been analyzed in the literature. However, most devices that have been presented so far emit light in different directions. We present a modal analysis (no gain included) of a few schemes to improve the directionality of these devices, i.