Chromatic dispersion effect in a microwave photonic filter using superstructured fiber Bragg grating and dispersive fiber

In this paper a microwave photonic filter using superstructured fiber Bragg grating and dispersive fiber is investigated. A theoretical model to describe the transfer function of the filter taking into consideration the spectral width of light source is established. Experiments are carried out to verify the theoretical analysis. Both theoretical and experimental results indicate that due to chromatic dispersion the source spectral width introduces an additional power penalty to the microwave photonic response of the filter.

High rate growth of nanocrystalline diamond films using high microwave power and pure nitrogen/methane/hydrogen plasma

In this work, we investigate the impact of minute amounts of pure nitrogen addition into conventional methane/hydrogen mixtures on the growth characteristics of nanocrystalline diamond (NCD) films by microwave plasma assisted chemical vapour deposition (MPCVD), under high power conditions. The NCD films were produced from a gas mixture of 4% CH4/H2 with two different concentrations of N2 additive and microwave power ranging from 3.0 kW to 4.0 kW, while keeping all the other operating parameters constant. The morphology, grain size, microstructure and texture of the resulting NCD films were characterized by using scanning electron microscope (SEM), micro-Raman spectroscopy and X-ray diffraction (XRD) techniques. N2 addition was found to be the main parameter responsible for the formation and for the key change in the growth characteristics of NCD films under the employed conditions. Growth rates ranging from 5.4 μm/h up to 9.6 μm/h were achieved for the NCD films, much higher than those usually reported in the literature. The enhancing factor of nitrogen addition on NCD growth rate was obtained by comparing with the growth rate of large-grained microcrystalline diamond films grown without nitrogen and discussed by comparing with that of single crystal diamond through theoretical work in the literature. This achievement on NCD growth rate makes the technology interesting for industrial applications where fast coating of large substrates is highly desirable.

High frequency sensing interrogation system using fiber Bragg grating based microwave photonic filtering

A high frequency sensing interrogation system by using fiber Bragg grating based microwave photonic filtering is proposed, in which the wavelength measurement sensitivity is proportional to the RF modulation frequency applied to the optical signal.

A novel all fiber microwave transversal filter with complementary outputs

A novel all-fiber bipolar delay line filter is realized in a single-line cascaded high birefringence fiber structure. Optically coherent operation is achieved with suppression of interference noise. Complementary filter outputs give simultaneous lowpass and highpass responses.

Femtosecond laser writing of buried waveguides in erbium III-Doped oxyfluoride glasses and nano-glass-ceramics

Femtosecond-pulsed laser writing of waveguides, a few mm long, is demonstrated; waveguides were written orthogonally to the writing beam inside the bulk of ErIII-doped oxyfluoride glasses at a depth of 160 mum. The writing beam was 795 nm wavelength, 54 fs pulse duration and 11 MHz repetition rate. Tracks were written at pulse energies of 13.1 nJ to 26.1 nJ and sample translational velocity of 10 mmmiddot.s-1 to 28 mmmiddots-1. The influence of translational velocity and pulse energy on the cross-sectional shape and integrity of the written tracks is reported. Tracks tend to be narrower as the pulse energy is lowered or translational velocity decreased. Above 22.9 nJ, pulse energy, tracks tend to crack. The estimated refractive index profile of one track has a maximum increase of refractive index of 0.003 at the centre. These glasses normally form nano-glass-ceramics on heat treatment just above the glass transformation temperature (Tg). Here, a post-fs-writing heat-treatment just above Tg causes nano-ceramming of the glass sample and removes a light-guiding peripheral region of the fs-written tracks suggesting that this region may have been fs-modified by stress alone. Waveguiding at 651 nm and 973 nm wavelengths, and upconversion, are demonstrated in optimally written tracks.

Investigation of an optically reconfigurable plasma for silicon based microwave applications

This paper investigates the use of photoconductive plasmas for controlling microwave circuits and antennas on semiconductor substrates. Initial experiments show that significant changes in the reflection coefficient characteristics can be obtained by varying the length of a photo-illuminated plasma region from 0 to 2mm. The resulting structure forms the basis for further experiments involving tuneable microwave devices. © 2013 European Microwave Association.

Fracture toughness of SIC, Si3N4, and sialon ceramics using controlled surface flaws

Knoop and Vickers indentation cracks have frequently been used as model 'precracks' in ceramic bend specimens for fracture toughness (K1c) determination. Indentation residual stress reduces the measured K1c but can be removed or accounted for by grinding, annealing, or modelling. Values of K1c are obtained for four materials using Vickers indentations and an improved stress intensity factor. Methods for residual stress removal or incorporation are compared, and the most reliable stress removal alternative is identified for each material. © 1996 The Institute of Materials.

Surface and subsurface Vickers indentation cracks in SiC, Si3N4, and sialon ceramics

The nature of subsurface cracks formed under and around Vickers hardness indentations is often assumed rather than identified. Subsurface cracks in four engineering ceramics are revealed using a penetrant technique, and flaw dimensions are recorded. The resulting data are used to investigate several aspects of indentation cracking, such as crack shape, functional relationships between indentation load and flaw dimensions, and the performance of indentation fracture toughness equations. An R curve is constructed for each of the materials. © 1995 The Institute of Materials.

Etching and microstructure of engineering ceramics

Engineering ceramics are often difficult to prepare metallographically because of their hardness, wear resistance and chemical inertness. Two silicon carbides, a silicon nitride and a sialon, are prepared and etched using several different techniques. The most efficient methods are identified. © 1995.

Corrosion of silicon carbide ceramics using conventional and electrochemical methods

Silicon carbide ceramics are candidate materials for use in aggressive environments, including those where aqueous acids are present. Standard corrosion testing methods such as immersion testing are not always sufficiently sensitive for these ceramics owing to the very low, almost unobservable, corrosion rates encountered. Using electrochemical methods the corrosion processes can be assisted, leading to higher rates and thus the elucidation of reaction mechanisms. The behaviour of a sintered and a reaction bonded silicon carbide has been investigated in aqueous HCl, HF, HNO3, and H2SO4, using standard immersion and new electrochemical methods. Both materials were passive in HCl, HNO3, and H2SO4 because of the formation of a surface silica film, and were active in HF. In HF, corrosion of sintered silicon carbide was slight and the residual silicon was removed from reaction bonded specimens.

Chemical reactions of double bonds in activated carbon:microwave and bromination methods

The reaction of localised C=C bonds on the surface of activated carbons has been shown to be an effective method of chemical modification especially using microwave-assisted reactions.

Microwave decontamination of eyelid warming devices for the treatment of meibomian gland dysfunction

PURPOSE: The role of bacteria in meibomian gland dysfunction is unclear, yet contamination of compresses used as treatment may exacerbate this condition. This study therefore determined the effect of heating on bacteria on two forms of compress. METHODS: Cotton flannels and MGDRx EyeBags (eyebags) were inoculated by adding experimental inoculum (Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeruginosa; one species for each set of 3 eyebags and flannels). One of each were then randomised in to 3 groups: no heating (control); therapeutic (47.4±0.7°C); or sanitisation (68±1.1°C). After treatment, bacteria cell numbers were calculated. The experiment was repeated in triplicate. RESULTS: There was a statistically significant difference between each treatment with the eyebag for S. aureus (control=7.15±0.11logC/ml, therapeutic heating=5.24±0.59logC/ml, sanitisation heating=3.48±1.43logC/ml; P<0.001) and S. pyogenes (7.36±0.13, 5.73±0.26, 4.75±0.54; P<0.001). P. aeruginosa also showed a significant reduction (P<0.001) from control (6.39±0.34) to therapeutic (0.33±0.26) and sanitisation (0.33±0.21), but the latter were similar (P=1.000). For the flannels, there was significant difference between each treatment for S. aureus (6.89±0.46, 3.96±1.76, 0.42±0.90; P<0.001). For S. pyogenes, there was a significant reduction (P<0.001) from control (7.51±0.10) to therapeutic (5.91±0.62) and sanitisation (5.18±0.8), but the latter were similar (P=0.07). For P. aeruginosa, there was a significant difference (P<0.001) from control (7.15±0.36) to sanitisation (5.83±0.44); but not to therapeutic (6.84±0.31) temperatures (P=0.07). CONCLUSIONS: Therapeutic heating produces a significant reduction in bacteria on the eyebags, but only sanitisation heating appears effective for flannels. However, patients should be advised to heat the eyebag to sanitisation temperatures on initial use.

High performance microwave photonic response of superstructured fibre Bragg grating with designed apodisation function

The microwave photonic responses based on the superstructure fibre Bragg gratings with designed apodisation profile are investigated. The rejection level of more than 60 dB for a bandpass filtering response is demonstrated.

Microwave photonic filtering using Gaussian-profiled superstructured fibre Bragg grating and dispersive fibre

Microwave photonic filtering is realised using a superstructured fibre Bragg grating. The time delay of the optical taps is precisely controlled by the grating characteristics and fibre dispersion. A bandpass response with a rejection level of >45 dB is achieved.