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This paper presents a 3-dimensional micro-optical system for improving the optical coupling efficiency in the external cavity tunable lasers. It is constructed by an optical fiber and a curved mirror; the former acts as a rod lens to transform the light in one direction while the latter converges the light in the other direction. Compared with the previous MEMS lasers that have no light focusing or only in one direction, this 3D micro-optical system allows for long external cavity length and high coupling efficiency, which are critical for wide tuning range. A prototype is fabricated on SOI wafer by DRIE with an etching depth of 75 µm. It obtains a coupling efficiency as high as 46.5% with a total external cavity length of 220 µm. In contrast, the coupling efficiency is only 13% when the fiber rod lens is absent, and is 1% when no light transformation is involved. Compared with conventional laser optical systems that employ external ball lenses and other optical components, this 3D micro-optical system possesses the advantages of simple packaging, large alignment tolerance and easy mass production.

This paper presents the design of a real pivot formed by a double-clamped beam for the rotational tuning structures in microelectromechanical systems (MEMS) tunable lasers. Micromechanical properties such as beam deformation, pivot position and pivot shift are investigated and compared with the virtual pivot formed by a cantilever beam. It is shown that the real pivot has negligible shift when subjected to load and fabrication error owing to its feature of structural symmetry, while the virtual pivot suffers from significant pivot shift, which would severely limit the wavelength tuning range. The two pivot designs are implemented into MEMS tuning structures that are fabricated by deep etching and released using a dry release approach. The real pivot measures a depth variation of 16% over the double-clamped beam but maintains the symmetry to the midpoint, and is still able to produce a rotation angle of 4.7 . In contrast, the virtual pivot has a depth reduction of 4% over the cantilever beam, but achieves only a 2.4 rotation due to the pull-in problem originated from the severe pivot shift. The real pivot design is more suitable for the MEMS tunable lasers as it is simple, symmetric, robust, and suitable for single-chip integration.[2006-0112]