Microphotonic devices fabricated by silicon micromachining techniques

Silicon micromachining is an attractive technique for batch production of a wide class of miniaturised components and systems. In particular, micromachined components can be combined with semiconductor lasers, micro-lenses etc. to develop a class of Microsystems based on photonics (Microphotonics). This class of Microsystems founds applications in modern photonics, such as infra-cavity switches for q-switched lasers, and modulators for free-space optical interconnects. We have designed and fabricated several optical Microsystems based on surface and bulk micromachining techniques. Our process makes use of 100 nm thick Silicon Nitride membranes, which are patterned by electron beam (e-beam) lithography and removed after pattern metallization by reactive ion etching. The first of the fabricated devices is a nickel fine pitch grating driven electrically by the force which develops by the flow currents in two parallel conductors. This force results in a motion which alters the grating pitch and therefore the optical modulation of the device. The second device is a nickel micro-mirror which can be rotated around an axis by the same principle of the previous micro-grating. It is worthwhile to point out that the mirror curvature can be adjusted from convex to concave by controlling the residual stress of the electroplated nickel film; this gives to the optical designer an additional degree of freedom to perform even more sophisticated functions.