Daniel Homa

Synthesis, cytotoxicity, and hydroxyapatite formation in 27-Tris-SBF for sol-gel based CaO-P2O5-SiO2-B2O3-ZnO bioactive glasses

CaO-P2O5-SiO2-B2O3-ZnO bioactive glasses were prepared via an optimized sol–gel method. The current investigation was focused on producing novel zinc based calcium phosphoborosilicate glasses and to evaluate their mechanical, rheological, and biocompatible properties. The morphology and composition of these glasses were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The particle size, mechanical and flexural strength was also determined. Furthermore, the zeta potential of all the glasses were determined to estimate their flocculation tendency. The thermal analysis and weight loss measurements were carried out using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) respectively. For assessing the in-vitro bioactive character of synthesized glasses, the ability for apatite formation on their surface upon their immersion in simulated body fluid (SBF) was checked using SEM and pH measurements. MTS assay cytotoxicity assay and live-dead cell viability test were conducted on J774A.1 cells murine macrophage cells for different glass concentrations.

Review and the state of the art: Sol–gel and melt quenched bioactive glasses for tissue engineering

Biomaterial development is currently the most active research area in the field of biomedical engineering. The bioglasses possess immense potential for being the ideal biomaterials due to their high adaptiveness to the biological environment as well as tunable properties. Bioglasses like 45S5 has shown great clinical success over the past 10 years. The bioglasses like 45S5 were prepared using melt-quenching techniques but recently porous bioactive glasses have been derived through sol-gel process. The synthesis route exhibits marked effect on the specific surface area, as well as degradability of the material. This article is an attempt to provide state of the art of the sol-gel and melt quenched bioactive bioglasses for tissue regeneration. Fabrication routes for bioglasses suitable for bone tissue engineering are highlighted and the effect of these fabrication techniques on the porosity, pore-volume, mechanical properties, cytocompatibilty and especially apatite layer formation on the surface of bioglasses is analyzed in detail. Drug delivery capability of bioglasses is addressed shortly along with the bioactivity of mesoporous glasses.

Sapphire-fiber-based distributed high-temperature sensing system

We present, for the first time to our knowledge, a sapphire-fiber-based distributed high-temperature sensing system based on a Raman distributed sensing technique. High peak power laser pulses at 532 nm were coupled into the sapphire fiber to generate the Raman signal. The returned Raman Stokes and anti-Stokes signals were measured in the time domain to determine the temperature distribution along the fiber. The sensor was demonstrated from room temperature up to 1200°C in which the average standard deviation is about 3.7°C and a spatial resolution of about 14 cm was achieved.

Magnetic Sensing with Ferrofluid and Fiber Optic Connectors

A simple, cost effective and sensitive fiber optic magnetic sensor fabricated with ferrofluid and commercially available fiber optic components is described in this paper. The system uses a ferrofluid infiltrated extrinsic Fabry-Perot interferometer (EFPI) interrogated with an infrared wavelength spectrometer to measure magnetic flux density. The entire sensing system was developed with commercially available components so it can be easily and economically reproduced in large quantities. The device was tested with two different ferrofluid types over a range of magnetic flux densities to verify performance. The sensors readily detected magnetic flux densities in the range of 0.5 mT to 12.0 mT with measurement sensitivities in the range of 0.3 to 2.3 nm/mT depending on ferrofluid type. Assuming a conservative wavelength resolution of 0.1 nm for state of the art EFPI detection abilities, the estimated achievable measurement resolution is on the order 0.04 mT. The inherent small size and basic structure complimented with the fabrication ease make it well-suited for a wide array of research, industrial, educational and military applications.

Modal reduction in single crystal sapphire optical fiber

Abstract. A type of single crystal sapphire optical fiber (SCSF) design is proposed to reduce the number of guided modes via a highly dispersive cladding with a periodic array of high- and low-index regions in the azimuthal direction. The structure retains a “core” region of pure single crystal (SC) sapphire in the center of the fiber and a “cladding” region of alternating layers of air and SC sapphire in the azimuthal direction that is uniform in the radial direction. The modal characteristics and confinement losses of the fundamental mode were analyzed via the finite element method by varying the effective core diameter and the dimensions of the “windmill”-shaped cladding. The simulation results showed that the number of guided modes was significantly reduced in the windmill fiber design, as the radial dimension of the air and SC sapphire cladding regions increase with corresponding decrease in the azimuthal dimension. It is anticipated that the windmill SCSF will readily improve the performance of current fiber optic sensors in the harsh environment and potentially enable those that were limited by the extremely large modal volume of unclad SCSF.

Design and analysis of large-core single-mode windmill single crystal sapphire optical fiber

Abstract. We present a large-core single-mode “windmill” single crystal sapphire optical fiber (SCSF) design, which exhibits single-mode operation by stripping off the higher-order modes (HOMs) while maintaining the fundamental mode. The “windmill” SCSF design was analyzed using the finite element analysis method, in which all the HOMs are leaky. The numerical simulation results show single-mode operation in the spectral range from 0.4 to 2  μm in the windmill SCSF, with an effective core diameter as large as 14  μm. Such fiber is expected to improve the performance of many of the current sapphire fiber optic sensor structures.

Attenuation measurements in single-crystal sapphire fiber via Raman scattering intensity

Performing attenuation measurements in unclad single crystal sapphire fiber has traditionally been accomplished through use the cutback method. Because single-crystal sapphire fibers do not cleave easily like silica fibers, this method requires repeated cutting and polishing of the sapphire fiber sample; which is very time consuming and introduces uncertainty in each loss measurement. In this paper, we present a new method to measure attenuation in sapphire or other single-crystal fibers based on distributed sapphire Raman optical time domain reflectometry (OTDR). This method is both nondestructive, significantly faster than the cutback method, and capable of measuring the local loss along the entire length of the fiber.

Fugitive methane leak detection using mid-infrared hollow-core photonic crystal fiber containing ultrafast laser drilled side-holes

The increase in domestic natural gas production has brought attention to the environmental impacts of persistent gas leakages. The desire to identify fugitive gas emission, specifically for methane, presents new sensing challenges within the production and distribution supply chain. A spectroscopic gas sensing solution would ideally combine a long optical path length for high sensitivity and distributed detection over large areas. Specialty micro-structured fiber with a hollow core can exhibit a relatively low attenuation at mid-infrared wavelengths where methane has strong absorption lines. Methane diffusion into the hollow core is enabled by machining side-holes along the fiber length through ultrafast laser drilling methods. The complete system provides hundreds of meters of optical path for routing along well pads and pipelines while being interrogated by a single laser and detector. This work will present transmission and methane detection capabilities of mid-infrared photonic crystal fibers. Side-hole drilling techniques for methane diffusion will be highlighted as a means to convert hollow-core fibers into applicable gas sensors.

Magnetic and electronic materials in optical fibers

S heterostructures, such as nanowires, quantum dots and rings are, due to their unique properties, of potential interest for development of new nanodevices. For instance quantum dots in the strong quantum confinement regime exhibit size tunable bandgaps, large absorption cross sections, and multiple exciton generation, which can be exploited to improve photovoltaic conversion efficiency or detector selectivity. Optoelectrical properties of these nanostructures, their application in biochemical detectors, and processes important for detectors selectivity and sensitivity, interaction of light and nanostructures, and charge tunneling between nanostructures will be discussed. The effect of violation of symmetry of QD geometry on the tunneling is studied in details. We show that small violation of QD geometry drastically affects localization of electron and leads to relaxation of delocalized state of the system. Also considered will be the effect of electric field (applied to double QD system) as another factor that violates the QD symmetry. We show that electric field makes the same effect on “delocalized” electron wave function as the geometrical violation of the symmetry. We conclude that the symmetry violation in QDs reduces electron transport through the system, which may impact nanodevice performance. Additionally we consider double quantum rings (DQR) as a particular case of double quantum dot system. The anti-crossing of the levels as the mechanism of localizeddelocalized tunneling is clearlyan important element in QDR, which can be utilized to achieve stable quantum qubits states.Abstract: Over the last decade, optical whispering-gallery modes (WGMs) have been observed in solid micro-cavities of various geometries. WGMs supported by dielectric microspheres and toroids exhibit and optical field that is confined near to the surface. The interaction with chemical species may occur through the modification of the optical environment of the resonator if the internal field is exposed along the cavity-medium interface. For example, if interacting molecules exhibit optical absorption features at the operating wavelength, the lifetime of photons within the cavity is reduced. Silica resonators proved ultra-sensitive bio-chemical probes but were also studied as miniature systems to observe coupling and interaction phenomena between light and matter. Here, we propose to use liquid droplets as micro-resonators for sensing applications. The droplet itself serves as the sensor and the sample at the same time, where the internal optical field is directly used to probe dissolved analytes or nanoparticles. We free-space light excitation of whispering-gallery modes in vertically-suspended mm-size oil droplets and laser frequency locking on resonant modes for cavity lifetime measurements, recording Q-infrared and visible spectral regions. Appealing applications for spectroscopy, bio-sensing, material characterization and non-linear optics are envisaged.W present time-resolved studies of the thermalization and condensation process of a two-dimensional photon gas in an optical microcavity. In our experiment, a two-dimensional photon gas is confined in a high finesse microresonator containing a dye medium. If this system is operated in a regime in which reabsorption of cavity photons by the dye medium dominates over photon loss, e.g. by mirror transmission, a thermalization process of the photon gas to the temperature of the resonator (room temperature) takes place. In earlier work, we have experimentally observed both the thermalization process and, at sufficiently high photon densities, a condensation in the resonator ground mode. In recent experiments, we have studied the thermalization and condensation dynamics of the system after excitation with a short laser pulse. The timescale on which the photon gas becomes thermal (Bose-Einstein distribution) is found to be in the picosecond to nanosecond regime and is tunable by various system parameters e.g. by the dye concentration. Upon spatially displacing the pump spot from the optical axis, a transient laser-like oscillation of higher order cavity modes can be observed. These laser-like oscillations decay after several hundred picoseconds when the majority of photons have relaxed to the resonator ground state.S cancer cells are thought to play a key role in the initiation, growth, and relapse of malignant tumors. Recently, our group has shown that culturing melanoma cells in soft 3D Fibrin matrices can promote selection and growth of such tumorigenic cells. We defined these cells as tumor repopulating cells (TRCs). When injected in the tail vein, as few as 10 TRCs can generate metastatic tumors in the lungs of wild-type non-syngeneic mice. These cells express higher levels of Sox2, a self-renewal gene, whose down-regulation leads to differentiation of TRCs on 2D soft matrices. This paper studies the forceinduced epigenetic modification as a possible mechanism that links matrix-induced mechanical cues to Sox2 down regulation and differentiation of TRCs. Particularly, we focus on methylation of histone 3 lysine 9 (H3K9) and lysine 27 (H3K27). Using a H3K9 biosensor based on Forster Resonance Energy Transfer (FRET), we show that H3K9 methylation is lower in melanoma cells cultured in soft fibrin gels compared to control cells cultured on rigid plastic dish. Application of local forces via with an RGD-coated magnetic bead increase H3K9 methylation in control melanoma cells, but not in TRCs. Disruption of cytoskeletal filaments and inhibition of acto-myosin contractility blocks force induced H3K9 methylation. In contrast, H3K27 methylation does not depend on forces and remains unchanged both in control melanoma cells and TRCs. Silencing G9a or SUV39h1, a methyltransferase for H3K9, abolishes force-induced H3K9 methylation and elevates Sox2 expression in control melanoma cells.A efficient and robust method for series connection of photonic crystal micro cavities that are coupled to photonic crystal waveguides in the slow light transmission regime was experimentally demonstrated. It was shown that group index taper engineering provides excellent optical impedance matching between the input and output strip waveguides and the photonic crystal waveguide, a nearly flat transmission over the entire guided mode spectrum and clear multi-resonance peaks corresponding to individual micro cavities that are connected in series. Series connected photonic crystal micro cavities are further multiplexed in parallel using cascaded multimode interference power splitters to generate a high density silicon nano photonic microarray comprising 64 photonic crystal micro cavity sensors, all of which are interrogated simultaneously at the same instant of time. The devices were fabricated on a SOI wafer with 250 nm silicon layer and 3μm buried oxide (BOX) layer. All components including PCWs, PC micro cavities, group index tapers and strip waveguides are patterned on SOI chip simultaneously. PCW devices with and without PC tapers were fabricated on the same chip. Light is coupled into and out of the devices using sub wavelength grating couplers via polarization maintaining single mode fiber on the input side and standard single mode fiber on the output side respectively. Optical spectrum analyzer (OSA) is used to analyze the transmitted light. All the transmission spectra of PC devices with and without PC tapers were normalized to the spectrum from a reference waveguide comprising two grating couplers and one single strip waveguide. All spectra are measured in water with the objective to implement biosensing.T surface solitons propagation dynamics at the interface of nonlinear media with periodic refractive-index has become a considerate topic in nonlinear optics for their potential important applications in optical sensing, switching and exploration of intrinsic and extrinsic surface characteristics. At present, many fantastic optical surface solitons have been a subject of intense study in these nonlinear media with Kerr nonlinearity and saturable nonlinearity via Pockels effect. Spatial solitons in centrosymmeric photorefractive media due to quadratic electro-optic effect require a smaller nonlinearity. Here, we have got a deep understanding on the band structure of several types of optical lattices in centrosymmetric photorefractive crystals and have predicted theoretically several types of surface solitons, i.e., gap solitons, defect solitons, superlattice solitons and surface solitons driven by diffusive effect media in centrosymmetric photorefractive crystals. Moreover, we systematically studied the factors affected these surface solitons in centrosymmetric photorefractive crystals, five physical factors, i.e., the external bias electric field, lattice depth, profile of signal beam, saturation parameter and diffusion process, were considered. The quantitative relationship between the factors and the conditions, characteristics, stability and existence of surface solitons was established. For saturation parameter being strong temperature-dependent, we could adjust the crystal temperature to change surface soliton properties. This is a new optical control scheme for these surface solitons.T development of ultra-compact integrated nanophotonic structures for communications, sensing, and signal processing has been of great interest lately. Recent progress in the development of miniaturized high-Q microresonators has resulted in orders of magnitude reduction in the size of functional integrated photonic structures. The possibility of low-power tuning of the resonance features in these structures has made the formation of reconfigurable photonic structures possible. Among existing CMOS-compatible substrates, silicon (Si) and silicon nitride (SiN) have been used the most. Despite impressing progress in Si-based and SiN-based integrated photonics, neither substrate alone can be used for practical applications. Si (despite its good reconfigurability) suffers from strong nonlinear effects (especially at high light intensities) and relatively large free-carrier loss while SiN (with one order of magnitude lower loss and lower nonlinearity compared to Si) is very hard to tune. Thus, a reliable material system that combines ultra-loss-loss and high power handling with efficient and fast reconfigurability is of high demand in integrated nanophotonics. In this talk, the author will first demonstrate the recent achievements in the development and optimization of hybrid multi-layer CMOS-compatible material systems (e.g., SiN/Si, multi-layer Si/SiO2, etc.) to address all the practical requirements of ultra-fast and ultra-compact integrated photonic structures. Using these hybrid material systems, the author will demonstrate a series of ultra-compact and high-performance reconfigurable photonic devices and subsystems that are formed by using high Q resonators. The use of these devices and subsystems for realization of densely-integrated reconfigurable photonic chips for signal processing applications will be discussed.H boron nitride (hBN) possesses extra ordinary physical properties including high temperature stability, dielectric strength, optical absorption, negative electron affinity, neutron capture cross section, and corrosion resistance. Its energy band gap is comparable to AlN (Eg ~ 6 eV). Due to its similar in-plane lattice constant to graphene and chemical inertness and resistance to oxidation, hBN is also considered as the ideal template and gate dielectric layer in graphene electronics. The synthesis of wafer-scale hBN epilayers by MOCVD has been demonstrated. It was observed that the band edge emission of hBN is more than two orders of magnitude higher than that of high quality AlN and the emission with the electric field perpendicular to the c-axis is about 1.7 times stronger than the component along the c-axis. The exciton emission in hBN exhibits two-dimensional features. Based on the graphene optical absorption concept, the estimated band-edge absorption coefficient of hBN is about 7x105cm-1, which is 3 times larger than that of AlN. The hBN epilayer based photodetectors exhibit a sharp cut-off wavelength around 230 nm, which coincides with the band-edge PL emission peak. Diode behavior in the p-n structures of p-hBN/n-AlxGa1-xN (x∼0.62) has been demonstrated. These results represent a major step towards the realization of hBN based practical photonic and optoelectronic devices.The rays of light carry energy as well as linear and angular momentum. The latter properties are exploited in solar sails, optical tweezers, and micro/nano opto-mechanical motors and actuators. A fundamental characteristic of photons, their momentum in the presence of material media, has been the subject of debate and controversy for more than a century. The socalled Abraham-Minkowski controversy involves theoretical arguments in conjunction with experimental tests to determine whether the vacuum photon momentum must be divided or multiplied by the refractive index of the host medium. Also, momentum conservation is intimately tied to the force law that specifies the rate of exchange of electromagnetic and mechanical momentum between light and matter. In this presentation the author will discuss the foundational postulates of the MaxwellLorentz theory of electrodynamics that clarify the prevailing ambiguities and resolve the reigning controversies.A simple, fracture-based, layer transfer process has been developed and successfully applied to a number of different semiconductor substrate materials. The process is called Controlled Spalling and works by depositing a tensile stressor layer on the surface of a substrate, introducing a crack near the edge of the substrate, and mechanically guiding the crack as a single fracture front across the surface. The entire process is performed at room-temperature using only common laboratory equipment and can even be applied to completed devices. Recently, this process has been used to separate InGaN/GaN multiquantum well (MQW) light emitting diode (LED) structures that were grown on sapphire substrates. By controlling the stress and thickness of the surface stressor layer, the fracture depth, and thus the layer thickness, can be controlled. Separation of the epitaxial device layers has been made to occur within the n-GaN region, as well as at the GaN/sapphire growth interface. We have also demonstrated successful layer transfer from bulk GaN as well thereby allowing potential reuse of this expensive substrate material.T ease and efficiency of coherent optical control of fundamental charge and spin states in semiconductor quantum dots (QDs) makes these materials promising for realizing the building blocks of a solid state quantum computer. Optimal quantum control techniques may be used to tailor the QD-light coupling, providing a direction for optimizing the speed and fidelity of elementary quantum gates as well as the pursuit of complex-instruction-set quantum computing. This potential was recently illustrated through the application of femtosecond pulse shaping to the theoretical optimization of a C-ROT gate in a single QD, and the experimental demonstration of a parallel single qubit gate involving two qubits in distant quantum dots. Here we report the demonstration of adiabatic rapid passage (ARP) on a single semiconductor QD. Through the application of femtosecond pulse shaping techniques to broad-bandwidth control pulses, we achieve a 20-fold reduction in the gate time for ARP in comparison to previous work. Our experiments also explore a new regime of strong and rapidly-varying Rabi energies, which we exploit to gain new insight into electron-phonon coupling. Our experiments show that the exciton inversion efficiency depends on the sign of the pulse chirp, with a suppression of resonant coupling to acoustic phonons for positive pulse chirp at low temperatures.I recent years, there has been an enormous amount of research into the development of mid-IR lasers. The uses of these lasers are numerous and varied: Trace gas detection, battery powered spectroscopy, free-space communication, and remote sensing are a few examples currently being studied. Quantum Cascade Lasers (QCLs) are capable of reaching Watt level output power at room temperature, cw operation but are limited to the spectral region of above 3.5 microns. Recently, Shterengas et al fabricated type-I quantum well cascade diodes that emit below 3 microns with output power near 590 mW and improved conversion efficiency compared to single-stage type-I diodes. This novel advance in cascade laser technology makes it possible, for the first time, to produce a sub 3.0 micron laser beam at multi-Watt power levels via type-I quantum wells with a cascade pumping scheme. GaSb-based type-I quantum well heterostructures exhibit strong electron/hole confinement (minimizes thermal issues), large refractive index contrast (maximizes optical confinement), and minimized threshold carrier concentration (minimizes Auger recombination). In this study, a careful characterization of the properties of these new cascade lasers was conducted. Current, voltage, and output power were measured up to room temperature in multiple lasers. Spectral characteristics were measured both below and above the laser threshold point under a variety of conditions. A detailed discussion of the temperature and bias dependent characteristics as well as a thorough description of the new type-I quantum well heterostructure will be given in the presentation.

Optical, mechanical and TEM assessment of titania-doped Bi2V1−xTixO5⋅5−δ bismuth vanadate oxides

Optical, mechanical and structural behaviors have been studied for titania-doped Bi2V1−xTixO5⋅5−δ which are used as electrolytes for intermediate temperature fuel cells. Parameters like band gap (Eg), Urbach energy (Eu), refractive index, hardness (H) and fracture strength (K) have been calculated as a function of dopant concentration, i.e. 0⋅05 ≤ x ≤ 0⋅2. Furthermore, analysis of transmission electron microscopy (TEM) images for all the oxides was conducted along with line spectra of planes. Results are discussed in light of correlation of these optical and mechanical parameters to their structural properties. Band gap has also been correlated to the conductivity of these oxides. Good correlation has been obtained between them.