Theoretic Study of Cascaded Fiber Bragg Grating

The purpose of this chapter is to simulate and analyze the spectral characteristics of the fiber Bragg grating (FBG) to obtain narrow bandwidth and minimization side lobes in reflectivity. Fiber Bragg grating has made a big revolution in telecommunication systems. The existence of fiber Bragg grating is needed when an optical fiber amplifier and filter are used. They can be used as band reject filter or band pass filter for optical devices. The model equations of the cascaded uniform fiber Bragg grating and different cascaded apodization functions such as, Hamming apodized fiber Bragg grating, Barthan apodized fiber Bragg grating, Nuttall apodized fiber Bragg grating, Sinc apodized fiber Bragg grating and Proposed apodized fiber Bragg grating are numerically handled and processed via specially cast software to achieve maximum reflectivity, narrow bandwidth without side lobes

Quadratic behavior of fiber Bragg grating temperature coefficients

We describe the characterization of the temperature and strain responses of fiber Bragg grating sensors by use of an interferometric interrogation technique to provide an absolute measurement of the grating wavelength. The fiber Bragg grating temperature response was found to be nonlinear over the temperature range -70 degreesC to 80 degreesC. The nonlinearity was observed to be a quadratic function of temperature, arising from the linear dependence on temperature of the thermo-optic coefficient of silica glass over this range, and is in good agreement with a theoretical model. (C) 2004 Optical Society of America

Acousto-optic effect in microstructured polymer fiber bragg gratings:simulation and experimental overview

A fine control of the microstructured polymer fiber Bragg grating spectrum properties, such as maximum reflected power and 3-dB bandwidth, through acousto-optic modulation is presented. For simulation purposes, the device is modelled as a single structure, comprising a silica horn and a fiber Bragg grating. For similar sized structures a good correlation between the numerical results and the experimental data is obtained, allowing the strain field to be completely characterized along the whole structure. It is also shown that the microstructured polymer fiber Bragg grating requires less effort from the piezoelectric actuator to produce modification in the grating spectrum when compared with a silica fiber Bragg grating. This technique has potential to be applied on tunable optical filters and tunable cavities for photonic applications

Strain Transfer and Test Research of Stick-up Fiber Bragg Grating Sensors

Because of the flaws of fiber Bragg grating, needs to set up protective layer between the structure and fiber layer to protect the fiber grating. Firstly the strain transferring rules of the FBG sensors is analyzed, carefully analyze the main factors influencing the fiber Bragg grating strain sensor transfer, and analyze concretely effect of each factor, the fiber Bragg grating sensors embedded angle deviation is analyzed and influence on the measured results. Finally, by a series of repeated, coherent, dynamic and fatigue characteristic test, it is proved that the FBG sensor has applied valu

Optical fiber temperature sensor based on fiber bragg grating

It is important to study optical fiber temperature sensor based on fiber Bragg Grating. The Fiber Bragg grating sensors can offer highly sensitive, cost effective solutions for optical sensing. While fiber Bragg gratings have been implemented in various sensing applications over the past few decades, recent efforts explore the limits of reflected and transmitted for FBG sensors. The FBG temperature sensor, is essential to establish the smallest distance of single mode fibre in order to reduce optical losses of the FBG system. One of the most generally used deployed optical sensors is the fiber Bragg grating, with optical circulator, ASE source and OSA, the FBG which reflects a wavelength of light that shifts in response to variations in temperature. The advantage of reflection that its can easily detect the Bragg reflected signal. The FBG is very sensitive to variations in temperature degrees over a temperature range of (30–60) °C. The variation of wavelength of an fiber Bragg grating is caused by the temperature. Moreover, change in temperature affect both the effective refractive and grating period of an FBG, which result in a shift in the reflected wavelength. Moreover, most of the existing FBG sensors systems on the market provide a limited wavelength resolution Therefore, it is the purpose of this thesis to enhance the grating sensors sensitivity to temperature. In addition, the purpose to make a small comparison between the transmitted and reflected spectrum. It is apparent that any shift in the Bragg wavelength is influenced by the temperature. Moreover, the sensitivity was calculated equal to 17.1pm°C with SNR equal to 13.7 dB based on the reflection spectrum

External-fiber-grating vertical-cavity surface-emitting lasers

A Bragg grating in graded-index multimode fiber was coupled to a 0.8-/spl mu/m VCSEL. By using a fiber Bragg grating, the spectral width of the VCSEL decreased to 1/2-1/3 of the initial value, depending on the temperature of the fiber Bragg grating. The minimum spectral width was less than 0.1 nm FWHM. Data transmission using 1-km graded-index multimode fiber was investigated at 700 Mb/s. The power penalty decreased by using the fiber Bragg grating. The decrease was 2 dB for the optimum grating temperature at a bit error rate of 10/sup -9/

Efficient large-scale multiplexing of fiber Bragg grating and fiber Fabry-Perot sensors for structural health monitoring applications

Fiber Bragg gratings have been demonstrated as a versatile sensor for structural health monitoring. We present an efficient and cost effective multiplexing method for fiber Bragg grating and fiber Fabry-Perot sensors based on a broadband mode-locked fiber laser source and interferometric interrogation. The broadband, pulsed laser source permits time and wavelength division multiplexing to be employed to achieve very high sensor counts. Interferometric interrogation also permits high strain resolutions over large frequency ranges to be achieved. The proposed system has the capability to interrogate several hundred fiber Bragg gratings or fiber Fabry-Perot sensors on a single fiber, whilst achieving sub-microstrain resolution over bandwidths greater than 100 kHz. Strain resolutions of 30n epsilon/Hz(1/2) and 2 n epsilon/Hz(1/2) are demonstrated with the fiber Bragg grating and fiber Fabry-Perot sensor respectively. The fiber Fabry-Perot sensor provides an increase in the strain resolution over the fiber Bragg grating sensor of greater than a factor of 10. The fiber Bragg gratings are low reflectivity and could be fabricated during the fiber draw process providing a cost effective method for array fabrication. This system would find applications in several health monitoring applications where large sensor counts are necessary, in particular acoustic emission

Rapid characterization of the ultraviolet induced fiber Bragg grating complex coupling coefficient as a function of irradiance and exposure time

We report the application of optical frequency domain reflectometry and a discrete-layer-peeling inverse scattering algorithm to the spatial characterization of the UV induced complex coupling coefficient during fiber Bragg grating growth. The fiber grating is rapidly characterized using this technique to give irradiance dependent growth as a function of exposure time, thereby providing the complete characterization of the coupling coefficient in the form of a "growth surface," which is related to the fiber's photosensitivity. We compare measurements of fiber Bragg grating growth in SMF-28 when exposed to continuous wave 244 nm irradiation from 0 to 90 W cm(-2) for exposure times up to 3230 s with a selection of other fibers including high germanium concentration fiber and erbium doped fiber. (c) 2007 Optical Society of America

Optical strain gauge with high spatial resolution

A technique to enhance the spatial resolution of typical fiber Bragg grating–based strain gauges has been experimentally verified in this study. Just analyzing the intensity of the reflection spectrum of a sampled fiber Bragg grating, its inner deformation profile has been obtained with a spatial resolution of Formula L<1mm. The proposed method employs a synthesis algorithm to retrieve the longitudinal axis strain profile of a sampled fiber Bragg grating glued to an asymmetric plate. The achieved experimental results have been compared to the mechanical simulations of the employed plate, exhibiting a good response even without compensating the residual stress provoked during the installation process.This study was supported by the project TEC2010-20224-C02-02 and grant AP2009-1403