A submicrometer integrated optical sensor based on Bragg gratings in silicon-on-insulator technology is theoretically proposed in this paper. The grating analysis is performed using a mixed numerical ...approach based on the finite-element method and coupled mode theory. The possibility to use third-order instead of first-order grating is discussed and performances compared, thus overcoming fabrication problems associated to submicrometer scale features. A detection limit of approximately 10 -4 refractive index unit has been calculated for a 173-mum-long grating. Strategies to further improve this value have been discussed too. Finally, fabrication tolerances influence on optimized gratings has been investigated.
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