Fabrication of Grating-Fresnel lens by using PDMS based soft lithography

Fabrication of a new type hybrid plane optics, Grating-Fresnel (G-Fresnel) lens for miniature spectrometer is presented in this research. A polydimethylsiloxane (PDMS) based soft lithography technology is employed. In this method, the grating surface and Fresnel surface of the G-Fresnel lens are formed simultaneously by sandwiching the PDMS layer between a reverse Fresnel mold and a grating. Surface anti-adhesive treatment method has been proposed to solve the innate adhesion of PDMS layers. A fabrication system is constructed and a G-Fresnel with grating line spacing of 1.11 mu m (900 lines/mm)and Fresnel lens with a diameter of 25.4 mm and a focal length of 25 mm was successfully fabricated. Three-dimensional surface profilometry has been performed to examine the device quality. Measured results show that replicas remain high fidelity to its primary master mold. A miniature spectrometer system was constructed to evaluate the performances of this fabricated G-Fresnel lens. Experimental results show that the spectrometer can provide about 2 nm resolutions at wavelengths of 450nm, 532 nm, and 650 nm, which verified the effectiveness of this fabrication method.