Cladding Area Research Articles

High-sensitivity slot Bragg grating sensor based on chalcogenide glasses

In this study, the finite difference eigenmode approach was used to conduct a theoretical investigation and analysis of the chalcogenide slot waveguide. Maximum power confinement factors of 36.3 % and 56.7 % were found for the slot and cladding areas, respectively. The bidirectional eigenmode expansion approach was then used to develop the chalcogenide slot Bragg grating (SBG) sensor, which was manufactured by electron beam lithography and inductively coupled plasma etching. The chalcogenide SBG has a minimum feature size of 150 nm, which makes it easier to manufacture than silicon photonics Bragg grating devices. Measurement results show a high sensitivity of 325 nm/RIU compared to the conventional evanescent field waveguide sensor in the sensing experiment.

Design of high-birefringence photonic crystal fiber based on As2Se3

A photonic crystal fiber is designed with chalcogenide glass As2Se3 as the base material. As2Se3 has a high refractive index and a high nonlinear refractive index; as a result, it has a desired application for strengthening birefringence and nonlinearity. The outer layer of the fiber is a regular decagonal structure composed of four layers of circular air holes, and the inner cladding area is composed of four elliptical air holes arranged in a diamond pattern. The influence of the size of the circular air holes in the fiber cladding, the thickness between each layer, and the size and position of the elliptical air holes in the inner cladding area on the birefringence is analyzed and studied using the full vector finite element method. The results show that the birefringence value of the fundamental mode of the fibers is 0.108 at a wavelength of 1.55 μm, and at the same time, the nonlinear coefficients of the X and Y polarization states are 240 and 197 m − 1 · W − 1, respectively.

Simple hollow core photonic crystal fiber for monitoring carbon dioxide gas with very high accuracy

This paper presents a hollow core photonic crystal fiber (HC-PCF) based gas sensor for monitoring carbon dioxide (CO2). The HC-PCF based sensor is employed for monitoring the diverse liquids and gases with a higher relative sensitivity compared to solid core PCF and porous core PCF sensors. In this paper, the whole design and simulation works have been accomplished by COMSOL Multiphysics software through utilizing finite element method (FEM). Different geometrical parameters of this design such as air filling fraction (AFF), air-hole diameter of cladding and core area have been numerically investigated in order to optimize the design. This optimized design provides the relative sensitivity of 93.5% with a confinement loss of 0.004 dB/m at λ = 2.65 μm the absorption wavelength of CO2. Note that the lower effective area based HC-PCF gas sensor is capable to confine a substantial amount of light signal in the core and shows the better sensing performance. The outstanding outcomes make the proposed sensor being an appropriate candidate for monitoring CO2 gas in the atmosphere accurately.

Challenges in a Hybrid Fabrication Process to Generate Metallic Polarization Elements with Sub-Wavelength Dimensions.

We report on the challenges in a hybrid sub-micrometer fabrication process while using three dimensional femtosecond direct laser writing and electroplating. With this hybrid subtractive and additive fabrication process, it is possible to generate metallic polarization elements with sub-wavelength dimensions of less than 400 nm in the cladding area. We show approaches for improving the adhesion of freestanding photoresist pillars as well as of the metallic cladding area, and we also demonstrate the avoidance of an inhibition layer and sticking of the freestanding pillars. Three-dimensional direct laser writing in a positive tone photoresist is used as a subtractive process to fabricate free-standing non-metallic photoresist pillars with an area of about 850 nm × 1400 nm, a height of 3000 nm, and a distance between the pillars of less than 400 nm. In a subsequent additive fabrication process, these channels are filled with gold by electrochemical deposition up to a final height of 2200 nm. Finally, the polarization elements are characterized by measuring the degree of polarization in order to show their behavior as quarter- and half-wave plates.

Wear Resistance of Different Bionic Structure Manufactured by Laser Cladding on Ti6Al4V

In this study, the laser cladding system with an IPG YLS-6000 fiber laser was used, and the WC–Ti6Al4V powder reinforced composite coatings on Ti6Al4V titanium alloy with various bionic structures were innovatively fabricated. The microstructures and surface damage behavior of the coatings were characterized by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Additionally, the wear resistance of different bionic structures was evaluated, which had not been comprehensively explored in the published literature. The results indicated that the un-melted WC particles in the coatings act as a hard reinforcement, avoiding serious wear of the coating. In addition, the hard coatings exhibit excellent deformation resistance and the soft substrate cushion the shear stress. So when the “Ratio”, which refers to the laser cladding area to sample area, is between 0.25 and 0.3, the sample has the highest wear resistance. Furthermore, the “Dot + Line” bionic structure has the best wear resistance compared with other structures. The separated line units and the addition of dot units can improve the stress concentration state of bionic structure are conducive to release the stress to the substrate under the cladding layer.

Numerical Study of Solid Core Photonic Crystal Fibres with Endlessly Single Mode

In this work, a solid core photonic crystal fibre (SC-PCF) has been designed with endlessly single mode of which both centerd core and holes in the cladding are organized by circles. The designed SC-PCF has a single solid centerd core which is ringed by a six rings hexagonal cladding. The computation of SC-PCF is achieved by using the finite element method (FEM) with perfectly matched layer (PML) boundary condition. All the designed factors like dimensions and distance of both core and cladding areas have varied with an optimized structure. After ending the numerical calculation, the results shows that there are a link between the air hols in the cladding , and the different normalized air hole size.

Design and Analyze the Refractive Index Sensor Having the Discontinuity between Sensing Region and Cladding Area by Large Core Diameter

We present the design and analysis of the Refractive Index sensor having the discontinuity between sensing region and cladding area by large core diameter. If sensing region is placed in different refractive index medium then the cladding, the modal field distribution changes. The overlap of modal fields in the cladded region and the sensing region gives an estimate of fractional power transfer from the input end to output end. This fractional power transfer gives us the refractive index of the medium.

Experimental Study on the Shaft Laser Cladding Bending and the Establishment of the Empirical Formula

In order to study the influence of the layer of the laser cladding to the bending degree, obtain the mathematical formulation in shaft laser cladding bending and derive the empirical formula, the laser cladding test for shaft was designed. The laser cladding test had been proceeded at the same cladding area and different layer of cladding. The results of the experiment show that the shaft is bended facing the laser beam. The bending degree and the layer of laser cladding are at the direct proportion. At the same time mathematical formulation in shaft laser cladding bending has been established and the parameter which is used to measure the degree of the bending has been obtained. Empirical formula between bending degree and the layer of laser cladding has been established. The circular run-out formula along the shaft length has been derived. The calculated value and the measured value are of the goodness fit. The maximal error is 0.035mm, and the average error is 0.017mm. It illustrates that the mathematic formulation is correct and the empirical formula has high accuracy.

Thermally tunable lithium-niobate long-period waveguide grating filter fabricated by reactive ion etching

We fabricate a long-period grating band-rejection filter with a lithium niobate (LiNbO(3)) channel waveguide, where the grating is formed on the waveguide surface by plasma reactive ion etching. The filter shows three distinct thermal tuning regimes. Below approximately 55 degrees C, the center wavelength of the rejection band decreases linearly with an increase in the temperature at a high sensitivity (-1.4 nm/ degrees C). The temperature sensitivity drops abruptly to a negligible value at approximately 55 degrees C and stays low up to approximately 70 degrees C, above which it jumps abruptly to a large positive value (1.6 nm/ degrees C). We attribute these peculiar tuning characteristics to the formation of different crystal phases in the core and cladding areas of the LiNbO(3) waveguide and the abrupt transitions of the thermo-optic coefficients of some crystal phases. The grating could be developed into various kinds of integrated-optic filters and switches for application in optical signal processing.

Thermomechanical Properties of High-Power and High-Energy Yb-Doped Silica Fiber Lasers

The thermomechanical properties of both single-core and multicore Yb-doped fiber lasers for both continuous wave and Q-switched operations are studied using finite element method. It was found that the maximum stress of multicore fiber lasers is 10%-20% lower than that of single-core fiber lasers with the same effective core and cladding areas at the same operating power level. For Q-switched operation, the stress in a multicore fiber laser relaxes much faster than that in a single-core fiber laser, and the peak stress is found to be proportional to the pulse energy.

Supercontinuum generation in holey microstructure fibers by femtosecond laser pulses

It Is reported that the supercontinuum spectrum can be generated in holey microstructure fibers by femtosecond laser pulses with a 800nm center wavelength. Broadband continua extending from 440 to 890nm are generated in holey microstructure fibers. Based on the theory of scalar approximation, the effective refractive index of the cladding and effective area for the fundamental space-filling mode and chromatic dispersion of fibers are calculated. It is found that the holey microstructure fibers have specifically the ability of controlling dispersion and waveguide property.The mechanism of supercontinuum generation in holey microstructure fibers is explicated preliminarily. The theoretic analysis is in good accodance with the experimental result.It is considered that supercontinuum broadband spectrum can be generated in holey microstructure fibers even if their cladding constitutes of random gas-line.

High-power and tunable operation of erbium-ytterbium co-doped cladding-pumped fiber lasers

We describe erbium-ytterbium co-doped fiber lasers in different free-running and tunable configurations. The lasers were cladding-pumped by high-power multimode diode sources. We compare pumping at 915 and 980 nm. With a free-running laser, we obtained slope efficiencies of up to 50% with 915-nm pumping and 38% with 980-nm pumping, with respect to absorbed pump power. We reached a double-ended output power of 16.8 W from the free-running laser. Thanks to a high rare-earth concentration and a small inner cladding area (possible with the high-brightness pump sources we used), the operating pump absorption of the fiber reached 8 dB/m. With such high absorption, short fibers with high nonlinear thresholds are possible even with cladding pumping. The tunable fiber laser had a tuning range from 1533 to 1600 nm and emitted 6.7 W of output power at 1550nm in a high-brightness, single-polarization, narrow linewidth beam.

Efficiency optimization of high-power, Er^3+–Yb^3+-codoped fiber amplifiers for wavelength-division-multiplexing applications

A rate-equations model that takes into account the energy transfer between Er3+ and Yb3+, as well as Er3+ clustering, is employed to analyze the power conversion efficiency (PCE) of high-power, gain-flattened, Er3+–Yb3+-codoped fiber amplifiers (EYDFA). Numerical results for C-band EYDFA and L-band EYDFA show that the PCE strongly depends on the excess pump losses and on the pump-band amplified spontaneous emission (ASE). It is found that the L-band EYDFA is more efficient in the limit of strong injected signal powers and large cladding areas. It is also shown that the PCE significantly improves on increasing the Yb3+ concentration in the C-band EYDFA, whereas in the L-band EYDFA it mainly depends on the pump wavelength. The effect of Er3+ clusters on the PCE is discussed.

Jacketed air-clad cladding pumped ytterbium-doped fibre laser with wide tuning range

A tunable cladding-pumped ytterbium-doped fibre laser is presented. An air-clad inner cladding supported by a micro-structured silica mesh inside a silica jacket is used. A measured inner-cladding NA of 0.4 to 0.5 enables efficient pump launch into a 36 µm-diameter inner cladding. The small inner cladding area enables tuning from 1010 to 1120 nm.

Iodine stress corrosion cracking of Zircaloy reactor cladding: iodine chemistry (a review)

This review covers chemical aspects of the iodine stress corrosion cracking (ISCC) pellet-cladding interaction (PCI) failures which have occurred in some reactors with UO 2 fuel in unlined Zircaloy tubes. The cracking mechanism is discussed in relation to chemical factors. Cesium and iodine are released as fission products and form CsI but its dissociation iodine pressure p(I) is many orders of magnitude greater than chemical thermodynamic calculations predict, due to radiolysis. This enhanced p(I) can form ZrI 4 in regions where Zr is exposed (not protected by surface scale) and a van Arkel vapour transport reaction then causes rapid Zr transport from localised cladding areas, i.e. pitting, which later becomes a crack site. Requirements are a critical strain rate (which cracks protective scale), iodine pressure and time, i.e. a power ramp. Factors include that a stress caused by a power ramp may relax before the required gap chemistry is achieved and that a ramp also releases short-lived I and Cs fission products which add to the iodine pressure available.

Fundamental influences on the ultrasonic inspection at cladded nuclear components

The ultrasonic inspection at cladded nuclear components is limited by random fluctuations of the sensitivity, by a reduced signal-to-noise ratio and by disturbing phantom indications of different provenience. The influences of the cladding on the ultrasonic inspectability of the near cladding area and of the ferritic base material can be characterized by typical ultrasonic parameters like V-transfer echo and its random fluctuations and by the signal-to-noise ratio for the detection of near cladding reference reflectors. The complex physical mechanism influencing the propagation of ultrasound in claddings cannot sufficiently be described by theoretical models. Therefore simple but characteristic measurements on test blocks have been proposed in this contribution.