Fabrication of high performance microlenses for an integrated capillary channel electrochromatograph with fluorescence detection

We describe the microfabrication of an extremely compact optical system as a key element in an integrated capillary channel electrochromatograph with fluorescence detection. The optical system consists of a vertical cavity su rface-emitting laser (VCSEL), two high performance microlenses, and a comme rcial photodetector. The microlenses are multilevel diffractive optics patt erned by electron beam lithography and etched by reactive ion etching in fu sed silica. The design uses substrate-mode propagation within the fused sil ica substrate. Two generations of optical subsystems are described. The fir st generation design has a 6 mm optical length and is integrated directly o nto the capillary channel-containing substrate. The second generation desig n separates the optical system onto its own substrate module and the optica l path length is further compressed to 3.5 mm. The first generation design has been tested using direct fluorescence detection with a 750 nm VCSEL pum ping a 10(-4) M solution of CY-7 dye. The observed signal-to-noise ratio of better than 100:1 demonstrates that the background signal from scattered p ump light is low despite the compact size of the optical system and is adeq uate for system sensitivity requirements. (C) 1999 American Vacuum Society. [S0734-211X(99)09706-1].