Unique temperature dependence of selectively liquid-crystal-filled photonic crystal fibers

We demonstrate a unique temperature-dependent characteristic of the selectively liquid-crystal-filled photonic crystal fiber, which is realized by a selectively infiltrating liquid crystal into a single air hole located at the second ring near the core of the PCF. Three-resonance dips are observed in the transmission spectrum. Theoretical and experimental investigations reveal that the three-resonance dips all result from the coupling between the LP01 core mode and the rod modes, i.e., LP03 and LP51. Then, we find that the dip shift induced by temperature shows good agreements with the thermo-optic performance of the LC employed. Furthermore, the dips shift greatly with changes in temperature, providing a method to achieve temperature measurement in such a compact structure

Highly sensitive photonic crystal fiber salinity sensor based on Sagnac interferometer

For a sensor, high sensitivity, structural simplicity, and longevity are highly desired for measurement of salinity in seawater. This work proposed an ultrahigh sensitive photonic crystal fiber (PCF) salinity sensor based on the sagnac interferometer (SI). The propagation characteristics of the proposed PCF are analyzed by the finite element method (FEM). The achieved sensitivity reaches up to 37,500 nm/RIU and 7.5 nm/% in the salinity range from 0% to 100%. The maximum resolutions of 2.66 × 10−06 RIU and 1.33 × 10−02% are achieved with high linearity of 0.9924 for 2.20 cm length of the proposed PCF. Owing to such excellent results, this proposed sensor offers the potential to measure the salinity of seawater

Hybrid photonic-crystal fiber

This article offers an extensive survey of results obtained using hybrid photonic-crystal fibers (PCFs) which constitute one of the most active research fields in contemporary fiber optics. The ability to integrate novel and functional materials in solid-and hollow-core PCFs through various postprocessing methods has enabled new directions toward understanding fundamental linear and nonlinear phenomena as well as novel application aspects, within the fields of optoelectronics, material and laser science, remote sensing, and spectroscopy. Here the recent progress in the field of hybrid PCFs is reviewed from scientific and technological perspectives, focusing on how different fluids, solids, and gases can significantly extend the functionality of PCFs. The first part of this review discusses the efforts to develop tunable linear and nonlinear fiber-optic devices using PCFs infiltrated with various liquids, glasses, semiconductors, and metals. The second part concentrates on recent and state-of-the-art advances in the field of gas-filled hollow-core PCFs. Extreme ultrafast gas-based nonlinear optics toward light generation in the extreme wavelength regions of vacuum ultraviolet, pulse propagation, and compression dynamics in both atomic and molecular gases, and novel soliton-plasma interactions are reviewed. A discussion of future prospects and directions is also included

New Platform Designs for Enabling Atomic Interactions in Solid and Gaseous States

This dissertation is composed of two projects that explored two new platforms for measuring atomic interactions using simpler designs than in the literature. The first project of this dissertation designed a platform that enables the measurement of Lennard-Jones interaction between two solid surfaces in the form of Atomic Force Microscope (AFM) probe, using different techniques from Micro electrical Mechanical Systems (MEMS). MEMS by definition implies a mechanical and electrical parts of a system. There are many defects and imperfections that emerges on both sides of the system. On the mechanical side, one of the most common imperfections is residual stress, where most fabrication recipes are designed to eliminate it. Residual stress on films causes curvature (manifested as buckling, bending, etc.) for structures that are meant to be straight. On the electrical side, fringing field is considered very complicated to model, and too small to experimentally detect and separate from the main direct electrostatic field; hence, mostly it gets ignored in modelling. This project will try to make a benefit of these two unwanted phenomena combined (residual stress and fringing field) to make a new design for an Atomic Force Microscope (AFM) probe (tip). The tip behavior is first analyzed and modeled statically using COMSOL software, then dynamically using Mathematica software. Both models were combined and compared with the experimental results obtained by an optical profilometer, scanning electron microscope, and a vibrometer. It was found that the model gave good predictions of the experimental behaviors, except with higher displacement amplitude of the model than that of experiment. The reason is due to the purposeful curvature of the probe (cantilever) induced by residual stress, which caused some parts of the probe not to be on the same level with the electrode; hence, weakened its actual response experimentally. Since use of correction factors to account for fringing field is nothing new, a correction reduction factor was introduced to lower the model response to match that of the experiment. The results show that the structure of the actuator (parallel plate or a single comb finger) is not of importance in modeling fringing field, as we have applied literature force modeled for non-curved parallel plate capacitors for our curved comb-finger structure and got identical response to our comb-finger derived new force with a matter of just a correction factor (i.e. free parameter). We have also shown that the curvature equation is unnecessary in the model, and the behavior of the curved probe can be modeled as a straight one. The second project of this dissertation is another simple design for enhancing light-matter interaction between a single laser beam and an atomic gas (cesium) in what is known as cavity Quantum Electrodynamics (QED). Increasing the interaction between light and matter is inspired by the desire to unravel more understanding about the nature of both interacting entities: light and matter. This can be enabled by engineering necessary platforms where such maximally interacting light and matter can be realized. Usually there are two ways to increase such interaction: 1) increase transverse confinement, and 2) increase the interaction time (in addition to increasing the number of atoms). Each of these two ways is done in a separate platform design. This second project proposes a new platform that can have both ways: increasing both transverse confinement and interaction time by using the hollow core of photonic crystal fiber as the interaction host (hence blocking light from propagating transversally by the photonic bandgap effect), while the light will be bounced back and forth against the atomic gas, not by the conventional Fabry-Perot cavity, but instead by inscribing a Bragg grating mirror on the walls of the hollow core (hence, increase interaction time). The unblocked hollow core will allow easier atomic gas insertion. Different mirror inscription methods were studied, and the best method was employed using a photoresist-assisted layer, instead of direction inscription on the core silicon wall. Initial numerical modeling was done using Lumerical software that gave the Bragg parameters corresponding to the best Bragg mirror reflection which was up to 99.99% reflectivity from only about 300 Bragg periods (shorter mirror) corresponding to only ~100 µm penetration depth. Moreover, since the hollow core photonic crystal fiber is of a high cost, an injection port was designed and built to enable low fiber material loss caused by conventional injection

A Novel Gold Film-coated V-shape Dual-core Photonic Crystal Fiber Polarization Beam Splitter Covering the E+S+C+L+U Band

In this paper, a novel gold film-coated V-shape dual-core photonic crystal fiber (V-DC-PCF) polarization beam splitter (PBS) based on surface plasmon resonance effect is proposed. The coupling lengths of the X-polarization (X-pol) and Y polarization (Y-pol) and the corresponding coupling length ratio of the proposed V-DC-PCF PBS without gold film and with gold film are compared. The fiber structure parameters and thickness of the gold film are optimized through investigating their effects on the coupling lengths and coupling length ratio. As the propagation length increases, the normalized output powers of the X-pol and Y-pol of the proposed V-DC-PCF PBS at the three wavelengths 1.610, 1.631, and 1.650 µm are demonstrated. The relationships between the extinction ratio (ER), insertion loss (IL) and wavelength for the three splitting lengths (SLs) 188, 185, and 182 µm are investigated. Finally, it is demonstrated that for the proposed V-DC-PCF PBS, the optimal SL is 188 µm, the ILs of the X-pol and Y pol are less than 0.22 dB, and the splitting bandwidth (SB) can cover the E + S + C + L + U band. The proposed V-DC-PCF PBS has the ultra-short SL, ultra-wide SB, and ultra-low IL, so it is expected to have important applications in the laser, sensing, and dense wavelength division multiplexing systems

Novel Specialty Optical Fibers and Applications

Novel Specialty Optical Fibers and Applications focuses on the latest developments in specialty fiber technology and its applications. The aim of this reprint is to provide an overview of specialty optical fibers in terms of their technological developments and applications. Contributions include:1. Specialty fibers composed of special materials for new functionalities and applications in new spectral windows.2. Hollow-core fiber-based applications.3. Functionalized fibers.4. Structurally engineered fibers.5. Specialty fibers for distributed fiber sensors.6. Specialty fibers for communications

Nano-structure-based optical sensors fabrication and validation to gas sensing applications

We present three different nano-resonant structures (nanoposts, nanoholes etc.) fabricated on either bulk substrate or micron size tip of optical fiber and one graphene oxide coated glass substrate for gas detection in visible or mid-infrared region of electromagnetic spectrum. Nanostructures provide an efficient way to control and manipulate light at nanoscale paving the way for the development of reliable, sensitive, selective and miniaturized gas sensing technologies. Moreover, the inherent light guiding property of optical fiber over long distances, their microscopic cross-section, their efficient integration capabilities with gas absorption coatings and mechanical flexibility make them suitable for remote sensing applications. The three nanostructure-based gas sensing techniques are based on the detection of surface plasmon resonance (SPR) wavelength shifts, guided mode resonance (GMR) wavelength shifts, and Rayleigh anomaly (RA) mode intensity variations. The SPR and GMR based sensors operate in the visible region of light spectrum. Later, we also integrate a heater with the GMR-based fiber-tip sensor to realize a reusable gas sensor having tunable sensor recovery time. The RA-based sensor is realized by solvent-casting of chalcogenide glass to work as mid-infrared optical resonator. Further, we utilize the dynamic variations in infrared values of graphene oxide in response to gas to realize a gas sensor. First, we present a high-sensitivity gas sensor based on plasmonic crystal incorporating a thin layer of graphene oxide. The presented plasmonic crystal is formed by an array of polymeric nanoposts with gold disks at the top and perforated nanoholes in a gold thin film at the bottom. The thin coating of graphene oxide assembled on the top surface of mushroom plasmonic nanostructures works as the gas absorbent material for the sensor. The optical response of the plasmonic nanostructure is altered due to different concentrations of gas absorbed in the graphene oxide coating. By coating the surface of multiple identical plasmonic crystals with different thicknesses of graphene oxide layer, the effective refractive index of the graphene oxide layer on each plasmonic crystal will be differently modulated when responding to a specific gas. This allows identifying various gas species using the principal component analysis-based pattern recognition algorithm. The present plasmonic nanostructure offers a promising approach to detect various volatile organic compounds. Second, we report a simple yet efficient method of transferring nanopatterns to optical fiber tip. We have also demonstrated a TiO2 coated GMR structure which is sensitive to changes in surrounding refractive index and provides shifts in its resonant wavelength. The GMR sensor at the fiber tip is also demonstrated to work as a gas sensor by coating it with a thin layer of graphene oxide. This simplified and rapid nanostructuring at fiber tip can contribute to remote sensing applications through the insertion of the nanopatterned fiber tips into aqueous and gaseous analytes in regions otherwise inaccessible. Third, we present the first heater integrated nanostructured optical fiber of 200 ïÿým diameter to realize a high-sensitivity and reusable fiber-optic gas sensor. In our GMR-enabled fiber-optic gas sensor, resonance shifts upon the adsorption of the analytes on the graphene oxide (GO) coated sensor surface. For repeated use of this sensor, a regeneration of the sensor surface is required by a complete desorption of the analyte molecules from the GO layer. In our presented design, this has been achieved by the integration of a controllable heater at the fiber tip. Fourth, we present a straightforward analysis based on the maximum and minimum envelopes of the reflection spectra to dynamically investigate the changes in complex refractive index of graphene oxide in response to gases. The performance of graphene oxide -based gas sensors is strongly influenced by the variations in optical properties of graphene oxide when exposed to gas. The presented method does not require any complex dispersion model as compared to ellipsometry. Accordingly, the technique we employ can be leveraged to reliably evaluate the optical performance of any graphene oxide-based gas sensors in a simpler manner, when compared to ellipsometry. Furthermore, the accuracy of the derived values of complex refractive index of the graphene oxide layer has been confirmed by comparing with literature. Finally, we report the development of a first of a kind planar resonant structure that enhances the mid-IR absorption by the analyte adsorbed on its surface, enabling highly sensitive and selective label-free detection of gas and/or biomarkers. Chalcogenide glasses (As2S3) are promising for infrared photonics owing to their transparency in visible to far infrared, where various biomolecules and gases have their characteristic absorption lines, arising from rotational-vibrational transitions. Here we present the proposed design of a nanoscale tunable planar mid-IR optical resonator, realized by solvent-casting of As2S3. Our technique of preparing nanostructure having resonance at mid-IR enables the realization of mid-IR bio as well as gas sensors