| Optical fibre gratings have become very important enabling technology for the fibre-optic sensor and communication systems. Due to its wavelength selective property, fibre gratings, including fibre Bragg gratings (FBGs) and long-period gratings (LPGs), have become the key spectral or dispersion management devices in fibre communication systems.; In this work, we define structured fibre gratings as those fibre grating elements that comprise of two or more FBGs, or LPGs, or a combination of FBGs and LPGs. The main objective of this project is to analyze the mode-coupling mechanisms of structured fibre gratings, and develop new in-fibre grating devices for communication and sensing applications. Various structured fibre gratings, which are classified as structured long-period gratings, combined long-period and fibre Bragg gratings, structured fibre Bragg gratings, and sampled fibre Bragg gratings, were investigated theoretically and experimentally.; LPGs were initially developed for band-rejection filters, and are commonly used for gain-flattening of erbium-doped fibre amplifier (EDFA). We proposed a novel step-changed long-period grating as an effective gain-flattening device, in which the multi-path interference is suppressed but the spectral tailoring capability has been improved. Such grating devices have been fabricated, and demonstrated their flexible spectral tailoring capability.; By combining the mode coupling capability of LPG and FBG, a concatenated long-period and fibre Bragg grating has also been designed and fabricated. It was first demonstrated in this work that the light coupled out to the cladding mode by one of these gratings could be recoupled back to the guided mode by using a second grating.; In order to avoid the broadband loss introduced by LPGs and overcome the limitation of the 50% reflectivity, a novel Bragg grating pair, in which one Bragg grating is written in the fibre core whereas the other is written in the fibre cladding, was proposed. The novel device was analyzed by using coupled mode equations.; Finally, we investigated the spectral and dispersion characteristics of sampled fibre Bragg gratings. The couplings of multiple modes in conventional sampled FBGs, and the dispersion-slope managing capability of the chirped-sampled FBGs have also been investigated numerically by using the discretized fundamental matrix method. (Abstract shortened by UMI.)... |
