Outer Cladding Layer Research Articles

Dispersion Engineering of Silicon Nitride Microresonators via Reconstructable SU-8 Polymer Cladding.

In this work, we propose a novel way to flexibly engineer the waveguide dispersion by patterning the cladding of waveguide microresonators. Experimentally, we demonstrate silicon nitride waveguides with air-, oxide-, and SU-8 polymer-cladding layers and compare the corresponding waveguide dispersion. By integrating SU-8 polymer as the outer cladding layer, the waveguide dispersion can be tuned from −143 to −257 ps/nm/km. Through the simple, conventional polymer stripping process, we reconstruct the waveguide dispersion back to that of the original air-cladded device without significantly impacting the quality factor of resonators. This work provides the potential to design the waveguide dispersion in normal and anomalous regimes within an integrated photonic circuit.

Bending Induced Temperature Increases in Double-Clad Fibers for High-Power Fiber Lasers

Rare-earth-doped optical fibers are one of the most promising solid-state lasers. In these fiber lasers, a cladding-pumping scheme using large-mode-area double-clad fibers (DCFs) is utilized to increase the overall conversion efficiency of pumping light and to overcome the restriction owing to the onset of stimulated Raman scattering. On the other hand, it is extremely challenging to increase the fiber core size while retaining the excellent beam quality because fibers with large core size allow propagation of several higher-order modes (HOMs), except for the fundamental mode (FM). In order to suppress HOMs, DCFs are bent with a relatively small bend radius. Failures at bends in an optical fiber are caused by light leaking from the core when the fiber is accidentally bent tightly with a high power input. For the DCFs with core radii of 10 and 20 mm, the relationship between the bending induced temperature increases and the bend losses in the bent DCFs was investigated theoretically by the explicit finite-difference method using the thermochemical SiO_x production model. The temperature at the boundary between the inner and outer cladding layers increased with increasing optical power <I>P</I> at 1.080 mm and was a large value higher than the softening temperature <I>T</I>_s of the silica glass when <I>P</I> = 5 kW was entered to the bent DCF with a bend radius <I>R</I> of 150 mm and a core radius of 10 mm. On the other hand, the temperature at the boundary was a small value lower than the <I>T</I>_s when <I>P</I> = 10 kW was entered to the bent DCF with a large <I>R</I> of 245-275 mm. Furthermore, it was found that the initiation of the fiber fuse was fairly easy under a certain conditions where the temperature at the boundary was higher than the <I>T</I>_s.

Design and Investigation of a High-Sensitivity PCF Sensor for the Detection of Sulfur Dioxide

A vertical photonic crystal fiber (V-PCF) and a horizontal PCF (H-PCF) are designed for the detection of sulfur dioxide (SO2) in this paper. A demanding numerical investigation is carried out in a wider range of wavelengths from 0.8 to 1 μm. SO2 is a major contributor to air pollution, which is responsible for asthma and cancer. The optical parameters are analyzed by using the finite element method (FEM) which consumes a completely circular isotropic perfectly matched layer (PML). The designed V-PCF sensor test is performed with different PML radius values, different elliptical constants for the inner cladding, the outer cladding layer, and the core. The higher relative sensitivity of 59.34% makes this proposed V-PCF a good design for SO2 detection.

Analysis of power confinement in Trench-Assisted Fiber for Sensing Applications

In this paper, we have the analysis on the effect of power confinement in trench assisted fiber. In single mode trench-assisted optical fibers at a certain value of trench width, all power propagates through the cladding. Single mode operation in the fiber is realized by the small diameter of the core and low mode field diameter gives tight confinement. The optimized design parameters are obtained by introducing trench between inner cladding and the outer cladding layer. The analysis shows that the relative refractive index difference in trench affects the properties of optical fiber for sensing applications.

Design and Simulation of a New Coaxial Probe for Near Field Scanning Optical Microscopy

Design of the new photonic devices having attractive optical properties such as subwavelength confinement of light has a numerous applications in developing nanoscale sensors, photonic integrated circuits, solar cells and etc. Abbe’s diffraction limit restricts the use of subwavelength scale photonic elements due to their size and therefore new approaches are required in order to achieve desirable nanometer scale properties of these devices. Delivering light energy to nanometer scale regions can be achieved by surface plasmon polariton (SPP) waves that propagate in metal-dielectric interface. The paper presents results in FDTD (finite-difference time domain) simulation of a new coaxial probe of nanometer-scale size.Based on FDTD simulations of the coaxial probe field localization and enhancement in the region around the tip of coaxial probe has been obtained. Configuration of the probe consists of the truncated Au cone as a core, truncated dielectric (SiO2) cone in the middle and outer metallic cladding. Simulations of the probe revealed that increasing the radius of Au core structure could lead to the enhanced field around the tip. Additionally, increasing radius of outer cladding layer doesn’t affect field enhancement around the tip. Different configurations of the probe have been analyzed in the range of visible spectrum of the source and as a result the most promising configuration has been selected

Five-Axis Ultrasonic Additive Manufacturing for Nuclear Component Manufacture

Ultrasonic additive manufacturing (UAM) is a three-dimensional metal printing technology which uses high-frequency vibrations to scrub and weld together both similar and dissimilar metal foils. There is no melting in the process and no special atmosphere requirements are needed. Consequently, dissimilar metals can be joined with little to no intermetallic compound formation, and large components can be manufactured. These attributes have the potential to transform manufacturing of nuclear reactor core components such as control elements for the High Flux Isotope Reactor at Oak Ridge National Laboratory. These components are hybrid structures consisting of an outer cladding layer in contact with the coolant with neutron-absorbing materials inside, such as neutron poisons for reactor control purposes. UAM systems are built into a computer numerical control (CNC) framework to utilize intermittent subtractive processes. These subtractive processes are used to introduce internal features as the component is being built and for net shaping. The CNC framework is also used for controlling the motion of the welding operation. It is demonstrated here that curved components with embedded features can be produced using a five-axis code for the welder for the first time.

Experimental characterizations of laser cladding of iron- and nickel-based alloy powders on carbon steel 1045 for remanufacturing

The purpose of this investigation is to test the laser cladding of different alloy powders onto 1045 medium-carbon steel substrates for parts remanufacturing. The types of alloy powder, laser output powers, and scanning speeds are selected as influencing factors to conduct laser cladding experiments with orthogonal design on the carbon steel 1045 substrate. Bonding shear strength and microhardness of the cladding layer and the substrate are tested and analyzed. The high resolution scanning electron microscopy and energy dispersive X-ray spectroscopy are also used to analyze cladding layers, microstructures, and elements. The experimental results show that a good metallurgical bond is formed between the cladding layer and the substrate without porous cracks and other defects. Shear stress intensity of nickel-based powder is two to three times higher than that of substrate material, while iron-based powder is five times higher than the substrate material. The type of the powder is the most significant factor and laser power is the least. The hardness of outer cladding layer is higher than that of bonding section and inner section. In the heat-affected zone, hardness is higher than that of the substrate material.

Preparation of Plasma Cladding Gradient Wear-Resistant Layer and Study on Its Impact Fatigue Properties

Plasma cladding technology is used to prepare plasma cladding gradient wear-resistant specimens, and the performance of these specimens is analyzed and compared with those of single cladding specimens. The results indicate that plasma cladding gradient wear-resistant layers implement the gradient changes in microstructure and hardness from the surface of the outer cladding layer to the fusion line and that the outer and inner cladding layers are well combined, the inner cladding layer can improve rapid decreases in hardness of single wear-resistant samples from the cladding layer to the matrix, changes in hardness from the outer to inner cladding layer are buffered, and the inner cladding layer performs important functions in the transition between the outer cladding layer and substrate. The highest hardness of the outer layer, which reaches 735 HV0.1, is approximately 3.9 times that of the matrix. The impact fatigue resistance performance of the plasma gradient cladding specimens is superior to that of single cladding specimens, and fatigue cracks begin to form only after 1 × 105 cyclical impacts.

Efficient blue luminescence from colloidal CdSe quantum-dot quantum-well nanocrystals

ABSTRACTCdS/CdSe/ZnS quantum dot quantum well (QDQW) nanocrystals were synthesized using the successive ion layer adsorption and reaction technique. CdSe QWs with a well width of 1.05 nm emitted blue light at 467 nm with a spectral full-width-at-half-maximum of ∼30 nm. It was found that a 3-monolayer ZnS outer cladding layer can effectively passivate the QDQW structures, leading to a ∼35% quantum yield (QY) of the QW photoluminescence. QDQW light-emitting diodes (LEDs) with blue QW electroluminescence (EL) were fabricated. The devices with an emitting layer comprising QDQWs embedded in a poly(N-vinylcarbazole) host were five times brighter than LEDs based on closely-packed QDQWs. However, the overall EL of the devices was dominated by interface state emission due to poor charge injection into the QDQWs.

Modified Smooth Transition Method for Determination of Complex Modes in Multilayer Waveguide Structures

The smooth transition method for determination of complex leaky modes in multilayer waveguides is revisited. The mapping between the mode solutions of the initial close waveguide and that of the final open waveguide is discussed and established. It is suggested that a more suitable initial guess should be the real guided modes and the imaginary evanescent modes in a close waveguide with perfect reflecting boundary conditions. Further, the artificial boundary should be positioned right at the two farthest interfaces of the multilayer stacks adjacent to the outer cladding layers. The accuracy, efficiency, and robustness of the new algorithm are validated through calculating the leaky modes in a multilayer waveguide structure and three-layer slab waveguide structures.

Parabolic pulse generation in a dispersion-decreasing solid-core photonic bandgap Bragg fiber

We analyze the interplay of nonlinearity and dispersion in a dispersion-decreasing photonic bandgap Bragg fiber as a new platform for generating parabolic pulses. A suitably designed linearly tapered, low-index-contrast, solid-core Bragg fiber – amenable to fabrication by conventional modified chemical vapor deposition technology – is shown to yield stable parabolic pulses. The fiber design was optimized through a simple and accurate transfer-matrix formalism and pulse evolution was studied by the well-known split-step Fourier method. Our study revealed feasibility of generating parabolic pulses in such a dispersion-decreasing Bragg fiber of length as short as 1 m. We have also studied the effect of third order dispersion on generated parabolic pulse, which is an important deteriorating factor in such applications. The effective single-mode operation of the proposed device is achieved through appropriate tailoring of the outer cladding layers.

The Development of Double Clad Fiber and Double Clad Fiber Coupler for Fiber Based Biomedical Imaging Systems

We report the fabrication of double clad fiber (DCF) and DCF coupler, suitable for fiber based imaging systems requiring the dual-channel transmission. Unlike the conventional DCF which uses silica for both cladding layers, the proposed DCF uses a low-index polymer for its outer-cladding layer coated over the conventional silica inner-cladding layer. The DCF is drawn with a conventional SMF preform but a low-index polymer coating is used for both jacket and outercladding of the fiber. To achieve the cladding mode coupling, a DCF coupler is fabricated by simply twisting two pieces of the proposed DCF after removing the polymer-coating at contacting regions. A cladding mode coupling ratio of 30% was achieved with a contact length of 16 cm. The proposed DCF and DCF coupler were employed in a composite optical coherence tomography (OCT) and fluorescence spectroscopy (FS) system, and both OCT images and FS signal from a plant tissue are measured simultaneously.

Design Considerations for 1.3 $\mu$m GaNAsSb–GaAs High Speed and High Quantum Efficiency Waveguide Photodetectors

The electrical and optical characteristics of a 1.3 mum GaNAsSb-GaAs p-i-n waveguide photodetector (WGPD), consisting of GaAs inner and Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> As outer cladding layers, were simulated using a lumped-element model and finite difference beam propagation method (BPM). The effect of multiple cladding layers' thicknesses and aluminum composition on the quantum efficiency was investigated to provide design guide and deduce the range of parameters needed for achieving quantum efficiency higher than 89%. The simulation shows that a p-i-n waveguide structure with 10 mum length, 4 mum ridge width, 2.4 mum ridge height and 0.4 mum GaN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.033</sub> As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.887</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.08</sub> core layer thickness can exhibit a theoretical cut-off frequency limit of over 80 GHz. Maximum quantum efficiency of 91.5% can be obtained for this structure with cladding layer thickness of 0.5 mum for GaAs and 0.5 mum for Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> As.

A Simple and Effective Method for Calculating the Bending Loss and Phase Enhancement of a Bent Planar Waveguide

A simple and effective method is introduced to calculate the bending loss and phase enhancement of a bent planar waveguide. The wave field is represented in terms of Airy functions and an eigenvalue equation is derived by matching the boundary conditions and the radiation condition in the outer cladding layer. The complex propagation constant is obtained by solving the eigenvalue equation with the Newton–Raphson method, and the imaginary part of the propagation constant gives directly the bending loss of the bent waveguide. The results are compared with the previous experimental and numerical results and are shown to be highly accurate and effective. The phase enhancement due to the bending is also studied.

A Series of Double Well Semiconductor Quantum Dots

Five-layered nanocrystals have been prepared that consist of a CdS core covered by a shell of HgS followed by several monolayers of CdS that are covered by again a shell of HgS and an outer cladding layer of CdS. The resulting quantum dots, thus, contain a double well electronic structure. Both HgS wells are either as thick as a monolayer or as two monolayers. The wells are separated by a wall of two to three monolayers of CdS giving rise to a family of double well semiconductor quantum dots. Absorption spectra of eight members of this family are presented together with some first results from TEM measurements.

A novel all-optic tunable long-period grating using a unique double-cladding layer

In this paper, a novel all-optic tunable filter based on long-period grating (LPG) with a unique double-cladding layer structure is implemented. The LPG that has an ultra-thin silica inner cladding layer and a dye-doped liquid crystal outer cladding layer is tuned by photochemical driving liquid-crystal molecular reorientation. The unique feature of this tunable filter is that there is no contact electrodes required, which may make the fabrication of tunable filter easier.

A highly sensitive long period grating based tunable filter using a unique double-cladding layer structure

In this paper, we present a highly sensitive long period grating (LPG) with a unique double-cladding layer structure including an ultra-thin inner silica cladding layer and a low refractive index liquid crystal outer cladding layer. By using an ultra-thin cladding layer (28 μm in diameter) reduced by chemical etching, the LPG has a single resonant band over a wide range of wavelength and higher sensitivity to the environmental refractive index change. In addition, the high thermal-optic effect of liquid crystal makes it very easy to tune the resonant wavelength by controlling the temperature of the liquid crystal. Thus, a highly sensitive tunable filter can be made. The experimental results show that a tuning efficiency of 2.1 nm/°C is achieved. To the best of our knowledge, this is the highest tuning efficiency ever reported.

Building cladding air pressure equalisation investigations—comparison between field results and a numerical model

Experimental measurements of the air pressure differentials across the outer cladding layers on four buildings have been made, to assess the likely weathertightness performance of the cladding systems due to the mechanism of pressure equalisation. Results for two of these four buildings verify the pressure equalisation percentages predicted through the use of the numerical model PERAM.

Edge-emitting quantum well laser with Bragg reflectors

We have fabricated edge-emitting GaAs/AlGaAs quantum well lasers in which the outer cladding layers have been replaced by multilayer Bragg reflectors. The reflectance peak spans the intrinsic spontaneous emission spectrum of the wells and there are no allowed vertical cavity modes within this spectrum. Compared with an equivalent alloy structure the threshold current of these lasers is reduced by 25%. This is due to a reduction in the spontaneous recombination current rather than an increase in internal efficiency. Studies of spontaneous emission normal to the sample surface show that the emission intensity is significantly reduced. We suggest that the threshold current is reduced by reduction in the spontaneous recombination rate due to a combination of inhibition of the emission and photon recycling.

Polarization splitter based on antiresonant reflecting optical waveguides

We propose the first polarization splitter based on antiresonant optical waveguides (ARROW's). The three air core structure is built up of two moveable outer cladding layers and two fixed inner cladding layers. The moveability of both outer cladding layers makes micromechanical switching of the polarized light between two output channels possible. The polarization discrimination is realized through thin metal films deposited on the outermost surfaces of the outer cladding layers. The extinction ratios of channels 1 and 3 as a function of the thickness of all cladding layers are calculated. We found that for extinction ratios below -20 dB thickness fluctuations smaller than /spl plusmn/15 mm are allowed. >