Grating writing in structured optical fibers is reviewed. Various laser sources have been used including UV and near IR nanosecond and femtosecond lasers, each enabling different material processing regimes. The issue of scattering is modeled through simulation and compared with experiment. Good agreement has been established.

We report on the simulation and characterisation of compound phase-shifted fiber Bragg structures for use as novel in-fiber magneto-optical point sensors. Through simulation we show that the Faraday rotation spectra of phase-shifted gratings can be tailored by tuning the ratio of substructure lengths. A design process for tailoring the magneto-optical spectrum is illustrated, and it is shown that a general optimum structure exists for producing a region of total reflection incorporating magneto-optical Faraday rotation that is enhanced both in strength and spectral width. A practical optical fiber system that exploits the proposed distributed feedback (DFB) structures to enable novel all-fiber sensors for the dual measurement of magnetic field strength and temperature is described in detail, and the sensor response is simulated. The study is supported by laboratory fabrication of the proposed fiber DFB structures which demonstrates the principle of enhancement in terms of tailored group delay spectra and highlights practical issues for sensor packaging.

Magneto-optical activity giving rise to circular birefringence and Faraday rotation is not usually an appropriate basis for point measurement of magnetic field strength, acting as it must over extended lengths. In this paper we report on investigations into the dispersion characteristics of structured fibre Bragg gratings for the purposes of implementing novel polarimetric point sensors. Phase-shifts inscribed along the grating profile introduce windows in transmission that correspond to highly resonant wavelengths undergoing large group delay. We demonstrate through fabrication of structured gratings that their dispersion characteristics can be tailored, producing regions of spectrally co-located reflection and large group delay. Importantly, it is shown how a number of such regions can contribute to a single enhanced group delay in reflection. Through simulation we discuss the potential for implementing polarimetric magnetic field sensors which operate in reflection.

BACKGROUND:Sperm DNA damage shows great promise as a biomarker of infertility. The study aim is to determine the usefulness of DNA fragmentation (DF), including modified bases (MB), to predict assisted reproduction treatment (ART) outcomes.METHODS:DF in 360 couples (230 IVF and 130 ICSI) was measured by the alkaline Comet assay in semen and in sperm following density gradient centrifugation (DGC) and compared with fertilization rate (FR), embryo cumulative scores (ECS(1)) for the total number of embryos/treatment, embryos transferred (ECS(2)), clinical pregnancy (CP) and spontaneous pregnancy loss. MB were also measured using formamidopyrimidine DNA glycosylase to convert them into strand breaks.RESULTS:In IVF, FR and ECS decreased as DF increased in both semen and DGC sperm, and couples who failed to achieve a CP had higher DF than successful couples (+12.2% semen, P = 0.004; +9.9% DGC sperm, P = 0.010). When MB were added to existing strand breaks, total DF was markedly higher (+17.1% semen, P = 0.009 and +13.8% DGC sperm, P = 0.045). DF was not associated with FR, ECS or CP in either semen or DGC sperm following ISCI. In contrast, by including MB, there was significantly more DNA damage (+16.8% semen, P = 0.008 and +15.5% DGC sperm, P = 0.024) in the group who did not achieve CP.CONCLUSIONS:DF can predict ART outcome for IVF. Converting MB into further DNA strand breaks increased the test sensitivity, giving negative correlations between DF and CP for ICSI as well as IVF.

This paper details an investigation of the response spectra of an FBG sensor embedded in a cylindrical hollow composite beam which is subjected to pure torsion and torsion - bending combined loading. The spectra of embedded FBG sensors under torsional and combined loading were obtained and post processed in order to investigate the performances of FBG sensors in torsional strain measurements. Further, the spectra of the embedded FBGs located at the vicinity of the points of damage inside the tube were also investigated to identify the spectral changes due to the damage. A detailed finite element mesh was created for the hollow beam specimen and static analysis was performed for comparison. It has been found that the FEA results are in good agreement with the experimental results. Further, it has been observed that the reflected spectrums of FBG sensors were chirped due to a possible warping of the FBG sensor due to torsional loading.

Silica remains the key optoelectronic and photonic medium, the essence of nearly all modern optical transport systems. Engineering of silica in its various forms ranges from 1 to 3-dimensional waveguide and periodic structures, including recent interest in 3-D photonic crystals. Most of the processing methods involve complex vapour deposition and various co-dopants, which have an advantage of overcoming the lack of finesse involved with general formation of glass structure through high temperature processing and quenching. Nevertheless, to obtain micron or sub-micron precision over the processing of glass for device purposes, invariably post processing methods are commonly used, ranging from etching of systems with dopants, often through patterned masks, to laser processing using UV to mid IR lasers. Concrete examples of micron scale laser processing of glass include direct written waveguides, Bragg gratings in waveguides and optical fibres and photonic crystals. The drawback with these post-processing techniques is that they often produce glass that is structurally less stable than the starting phase. For many applications the thermal stability of laser induced glass changes determines the limits in which they can operate – an excellent example which will form the basis for this chapter, is the optical fibre Bragg grating. Fibre Bragg gratings are used in many industrial and technological applications. Within standard telecommunications applications, for example, type I fibre Bragg gratings that can operate to 80°C for 25 years are required – such gratings can in principle operate for lengthy periods up to 300°C. Gratings that can operate at temperatures well above standard telecommunication requirements are critical to the success of many real time sensing applications. In the oil and gas industries, an alternative application, although standard oil bores are typically quoted as having an environment no more than ~(180-250)°C [Schroeder et al. 1999; Kersey 2000], variations can occur and the increasing depth of the next generation bores suggest sensors that can operate to 400°C or more are desirable for long term or permanent operation. In industries involving high temperature furnaces, such as aluminium smelting or coal based power stations, it would be of interest to be able to monitor temperatures in excess of 1000°C. Similar temperature requirements span many

The thermal stability of Type I gratings is increased by postthermal tuning of the grating. Optimization of the procedure leads to gratings that can withstand temperatures as high as 600 degrees C. Aging tests lead to lifetime predictions as high as 25 years with <3 dB reduction at 400 degrees C. Single exponential relaxation is observed. Above 800 degrees C regeneration is obtained.

The fabrication and use of fiber Bragg grating (FBG) sensors, which operates in near infrared region (Bragg wavelength λB = 830 nm) to monitor the damage accumulation in composite is reported. The spectra ∼830 nm of the embedded FBG sensor in 0°/90° woven cloth/vinyl ester composite were distorted and broadened due to fatigue loading, as expected. These distortions in FBG spectra indicate asymmetric and nonuniform strain distributions along the grating length of the FBG sensors due to the accumulation of damage during fatigue loading regimes. This information is useful for formulating a fundamental relationship between FBG spectral changes and the damage accumulation of composite structures. The results demonstrate that the sensitivity and durability of the embedded FBG sensors fabricated by conventional writing techniques at 830 nm range and monitored using inexpensive Si-based source and arrays were excellent for health monitoring of composite structures.

The thermal stability of type 1 gratings is increased by post thermal tuning of the grating, leading to gratings that can withstand temperatures up to 600 °C, lifetime predictions suggests <3dB reduction after 25 years at 400 °C.

The sensitivity to transversal pressure of both silica and polymer microstructured fibres is studied. Transversal loads ranging from 100-1600 g are applied over a 5 mm long region of the fibres. Transversal pressure deforms the fibre structure proportionally to the applied load causing light to leak out, hence one can estimate structural changes by measuring the output of the fibre. The polymer fibre experiences higher deformations and consequently higher loss. Both fibres present linear behaviour within the studied load range and no hysteresis is observed.

Objective: To determine the effects of sildenafil citrate, a cyclic monophosphate-specific type 5 phosphodiesterase inhibitor known to affect sperm function, on fertilization and early embryo cleavage.Design: This acute mammal study included male and female mice assigned randomly, the females sacrificed after mating and their oocytes/embryos evaluated at four time periods after treatment. Setting: Academic research environment.Animal(s): Male and female CBAB(6) Mice.Intervention(s): Female mice were injected intraperitoneally with 5 IU gonadotropin (hCG) to stimulate follicular growth and induce ovulation. They were each caged with a male that had been gavaged with sildenafil citrate (0.06 mg/0.05 mL) and allowed to mate. After 12, 36, 60, and 84 h, females were killed, their oviducts were dissected out, and retrieved embryos were assessed for blastomere number and quality.Main Outcome Measure(s): Fertilization rates and numbers of embryos were evaluated after treatment.Result(s): Fertilization rates (day 1) were markedly reduced (-33%) in matings where the male had taken sildenafil citrate. Over days 2-4, the numbers of embryos developing in the treated group were significantly fewer than in the control group. There was also a trend for impaired cleavage rates within those embryos, although this did not reach significance.Conclusion(s): The impairments to fertility caused by sildenafil citrate have important implications for infertility centers and for couples who are using this drug precoitally while attempting to conceive. (Fertil Steril (R) 2009; 91:893-9. (c) 2009 by American Society for Reproductive Medicine.)

We report some of our recent progress in the area of Bragg grating writing in photonic crystal fibres (PCFs). The various challenges that PCFs present are discussed and the methods used to overcome these challenges are presented. The fabrication of highly-durable type-IIa gratings in highly nonlinear photonic crystal fibre is demonstrated, the rotational variance of grating inscription is also investigated through both experiments and numerical modeling. In other experiments we fabricate a narrow-linewidth distributed feedback (DFB) laser in erbium-doped PCF, achieving stable, single-mode and CW operation. The potential of such a DFB PCF in sensing applications is assessed by accurately measuring an absorption line of acetylene gas.

Strong regenerated gratings with a maximum grating strength exceeding (40-50) dB are fabricated inside an optical fibre by bulk macro thermal processing similar to 900 degrees C using a UV-laser seeded Bragg grating. Further annealing between 1000 degrees C and 1100 degrees C leads to a stabilised grating similar to 18 dB in strength. This suffers no further degradation at 1100 degrees C for the period monitored, over 4 hours. The potential resolution of this process is demonstrated by regenerating two complex profiles. Phase information is retained between seed and regenerated structures. This opens the way for nano-engineering of materials using thermal processing and seed templates. [DOI: 10.2971/jeos.2009.09052]

objectives: To describe the patterns of computer use during patient visits to family doctors and to determine whether doctors alter their pattern of computer use in consultations which have significant psychological content.Design: Observational, non-randomised cluster trial with data being collected from videotaped consultations.Setting: Three inner-city Family Practice offices involved in physician training in Belfast, Northern Ireland. Participants: Ten family doctors, who declared using computers during their consultations and consecutive consenting adult patients attending these doctors.Results: One hundred consultations were videotaped (59% patient participation rate). The average consultation time was 9 min 48 s, and number of problems per consultation was 1.9. Three broad styles of computer use were defined: (1) "endusers" who only used the computer at the end of a consultation to summarise the consultation, (2) "continuous users", who interacted with the computer throughout the consultation, and (3) "minimal users", who only ever used the computer at the end of the consultation mostly to issue prescriptions. Of the 100 consultations videoed 37% were of a psychological nature. Consultations with psychological content were on average longer (11 min 47 s vs. 8 min 39 s) and the average percentage time doctors spent on the computer was about half that of non-psychological consultations (11% vs. 23% and p < 0.001).Conclusion: The doctors were found to adopt one of three broad styles of computer use during their consultations. In consultations with observable significant psychological content doctors significantly reduce the proportion of time at the computer suggesting an ability to appropriately tailor their use of the computer during consultations. (C) 2007 Elsevier Ireland Ltd. All rights reserved.

The measurement of the tuning speed in fiber Bragg gratings is an increasingly important parameter for characterizing the dynamics of tunable devices. Optical spectrum analyzers and wavelength meters are not suitable due to their slow response for measuring the wavelength shift in time. In this paper we report on a technique for estimating the tuning speed of a fiber Bragg grating which is based on accessing the wavelength shift through a calibration curve and measuring the time in which the shift occurs with the help of a fast photo-detector.