Optical Filter Design and Analysis: A Signal Processing Approach
Optical Filter Design and Analysis: A Signal Processing Approach
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We present a novel optical beamformer based on Gires-Tournois fibre Bragg grating coupled cavities (GT-BF). This beamformer allows for independent control of both amplitude and phase of each antenna in an 8 elements array. It is designed to be used in radio-over-fibre (ROF) dense wavelength division multiplexed antenna remoting links with 25 GHz wavelength spacing, and allows for remote centralized array control. The GT-BF is optimized for 802.11a/g/n 5GHz signals with 20 MHz bandwidth, but we explore its performances up to 100 Mhz bandwidth. This is not a true time delay beamformer so the bandwidth is limited by the "beam squint" effect. The GT-BF is designed for the double sideband (DSB) optical modulation format, which is simple and allow for the use of low cost modulators. Finally, this beamformer can compensate for dispersion of the ROF link, which otherwise would cause DSB signal attenuation. The GT-BF is controlled by stretching or by adjusting the temperature of the Gires-Tournois fibre Bragg grating coupled cavities. The former method allows for faster adjustment of the array radiation diagram.