Laser direct-writing of Bragg gratings waveguides on porous silicon

In this work we present the realization through a laser oxidation process of a Bragg grating over a porous silicon (PSi) waveguide. In the last years, the possibility of patterning the Porous Silicon (PSi) with photolithographic processes has been investigated in silicon micromachining. Unfortunately, the masking process of PSi by using standard photoresist presents remarkable difficulties since the low resistance of the polymer to the electrochemical process. The PSi localized laser oxidation process is a good and cheaper alternative to the traditional photolithographic method to realize micropatterned structures. We exploited this technique to realize a Bragg grating. The morphological characteristic of the structure, constituted by 50 periods with a pitch of 10 mum, has been investigated by optical microscopy and profilometric technique. The transmission spectrum of the structure has been measured and compared with the calculated one by using the transfer matrix method and the slab waveguide modal calculation.