Novel method for design of surface relief guided-mode resonant gratings at normal incidence

We demonstrate that the surface relief guided-mode resonant gratings with specified central wavelength and FWHM in the visible wavelength range can be designed by analyzing the complex poles of Reflectance and transmission coefficient matrix algorithm (RTCM), a variant of S-matrix propagation algorithm proposed for calculation of multilayer gratings. In addition, FWHM is computed with couple-mode (CM) theory of resonant gratings which is firstly extended by Norton et al. in calculation of waveguide grating. Furthermore, the side band reflections of the filter can be reduced to less than 5% in the visible wavelength with the antireflection (AR) design technique widely used in the thin-film field. (C) 2008 Elsevier B.V. All rights reserved.

Influence of Humidity on Fiber Bragg Grating Sensors

We demonstrate the influence of the relative humidity (RH) on the wavelength of fiber Bragg grating sensors (FBGS), performing tests with five FBGS at different humidity and temperature conditions. These tests were performed in a climate chamber whose RH changes according to a scheduled profile from 30% to 90%, in steps of 10%. These profiles were repeated for a wide range of temperatures from 10 degrees C to 70 degrees C, in steps of 10 degrees C. Two different types of instrumentation methods have been tested, spot welding and epoxy bonding, in two different materials, steel and carbon fiber reinforced polymer (CFRP). We discuss the results for each type of sensor and instrumentation method by analyzing the linearity of the Bragg wavelength with RH and temperature.

Análise Completa das Fibras de Bragg de Núcleo Oco.

A evolução nos sistemas digitais de comunicação está intrinsicamente relacionada ao desenvolvimento da tecnologia de fibras ópticas. Desde a sua criação, na década de 60, inúmeras pesquisas vem sendo realizadas com o intuito de aumentar a capacidade de informação transmitida, por meio da redução da atenuação, controle da dispersão cromática e eliminação das não-linearidades. Neste contexto, as Fibras de Bragg surgem como uma estrutura de grande potencialidade para se minimizar tais inconvenientes. As fibras de Bragg possuem um mecanismo de operação diferente em relação às fibras tradicionais de suportar os modos confinados. Nelas, o núcleo possui um baixo índice de refração, e a casca é constituída por anéis dielétricos de diferentes índices de refração, alocados alternadamente. Para uma fibra de Bragg com núcleo oco, como a considerada neste trabalho, há perdas decorrentes dos modos de fuga. Portanto, a análise da dispersão destas estruturas se situa no plano complexo, tornando-a muito difícil. Esta dissertação será fundamentada em uma estratégia imprescindível à análise dos modos transversais TE0m, TM0m e dos híbridos. Os resultados encontrados são validados confrontando-os com os obtidos na literatura. O trabalho discutirá as perdas e dispersões dos modos citados, e os resultados obtidos poderão nortear as pesquisas das fibras de Bragg.

System model for studying fibre grating dispersion compensators

A complete optical system model has been developed and used to assess chirped fibre Bragg grating dispersion compensators. Gratings suitable for dispersion compensation in both laser based and modulator based optical communications systems have been modelled. A grating 10 cm in length has been shown to permit virtually dispersion free transmission over 425 km, when used in an externally modulated system. Long haul dispersion compensation using several 2 cm gratings spaced at intervals along the fibre is also modelled, illustrating viable 10Gbit/s transmission over a distance in excess of 168 km.

Extending the transmission distance of a directly modulated laser source using Bragg grating dispersion compensators

Comprehensive computer modelling has been used to investigate the dependence of dispersion penalty on transmission length in an optical communications system employing a directly modulated 2.5Gbit/s DFB laser source and an optimised fibre grating dispersion compensator. Two grating apodization schemes, tanh and Gaussian, have been compared. The 2dB dispersion penalty transmission distance is shown to be approximately 520km along standard monomode fibre after compensation with a 5cm tanh grating. This represents a great improvement over the 150km range expected for a similar uncompensated system.

High coupling in novel 2D-lattice distributed reflector laser gratings

It is shown that 2D lattice gratings, despite being placed outside the waveguide region, exhibit sufficiently strong coupling coefficients that optical modes rapidly couple transversely into the etched grating region, yielding high coupling coefficients of 270cm-1. This performance allows mode-hop-free lasing operation in DBR structures.

Chiral gratings - A new class of polarization sensitive metamaterials

The first experimental demonstration of unique polarizatioon characteristics are reported. It is believed that the strong polarization effects reported result from the chirality imposed by the patterns of gammadions enhanced by plasmon effects due to the nanostructuring of the metal film in which they are cut. It is clear that such structures has the potential to yield many new and intriguing applications in optoelectronics and other areas.

改变离子束三维适形调强治疗中展宽Bragg峰宽度的装置

本实用新型涉及一种改变离子束三维适形调强治疗中展宽Ｂｒａｇｇ峰宽度的装置，包括扫描磁铁系统、束流监测系统、迷你型脊形过滤器、射程移位器、多叶准直器和患者体表补偿器，分别依序置于患者体表前，上述器件的中心与肿瘤靶区的中心处于束流轴线上，扫描磁铁系统由ｘ和ｙ方向两组相互垂直的二级磁铁组成，束流监测系统由电离室和位置灵敏探测器构成，以迷你型脊形过滤器中部垂直山脊的方向为轴，旋转迷你型脊形过滤器一个角度θ。本实用新型根据肿瘤靶区的大小，灵活改变展宽Ｂｒａｇｇ峰的宽度，来改变肿瘤靶区分层的厚度，达到节省照射治疗时间和提高照射治疗剂量的控制精度。这样提高了离子束治疗装置每天接受患者治疗的能力，可减少离子束治疗的费用。

Optical communication system performance using fibre Bragg grating dispersion compensators

Operating limits of a chirped fibre grating dispersion compensator are determined using a complete optical system model. A 10cm compensator extends the transmission range of an optimised 10Gbit/s MQW electroabsorption modulator from 80km to 425km.

Fast-switching phase gratings using in-plane addressed short-pitch polymer stabilized chiral nematic liquid crystals

We demonstrate a fast-switching (sub-millisecond) phase grating based upon a polymer stabilized short-pitch chiral nematic liquid crystal that is electrically addressed using in-plane electric fields. The combination of the short-pitch and the polymer stabilization enables the diffraction pattern to be switched “on” and “off” reversibly in 600 µs. Results are presented on the far-field diffraction pattern along with the intensity of the diffraction orders as a function of the applied electric field and the response times.