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Proceedings Paper

PDMS surface modification in the application of waveguide claddings for evanescent field sensing
Author(s): Meng Wang; Sanna Uusitalo; Risto Myllylä; Leena Hakalahti; Markku Känsäkoski
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Paper Abstract

We fabricated SU-8 based slab waveguides on surface-modified poly(dimethyl siloxane) PDMS lower claddings for application in evanescent field sensing. In this application, higher sensitivity is obtained by generating stronger penetrating power above the waveguide into the analyte. This can be achieved by reducing the refractive index of the substrate. Compared with glass substrates that have a refractive index of 1.5, PDMS has a refractive index of 1.42 at 633 nm, thus serving as a better lower cladding material for high-sensitivity sensing with an evanescent field or as claddings in multilayer waveguide applications. In order to increase the adhesion of PDMS surfaces for successful SU-8 application we treated PDMS thin films in low-frequency (40 kHz) oxygen plasma for varied length of exposure time. The treatment process made PDMS hydrophilic and created nano-structures on the surfaces. The resultant surface topography with different exposure time was studied by an interferometric profiler on PDMS lower claddings and the later spin-coated SU-8 waveguides. Measurement results showed that longer plasma treatment on PDMS claddings significantly improved the uniformity and waviness of the waveguides. Light propagation tests performed with a prism coupler and an end-butt coupling setup proved that PDMS can be used as a proper material for SU-8 waveguides.

Paper Details

Date Published: 17 February 2010
PDF: 9 pages
Proc. SPIE 7593, Microfluidics, BioMEMS, and Medical Microsystems VIII, 759317 (17 February 2010); doi: 10.1117/12.841244
Show Author Affiliations
Meng Wang, Univ. of Oulu (Finland)
Sanna Uusitalo, VTT Technical Research Ctr. of Finland (Finland)
Risto Myllylä, Univ. of Oulu (Finland)
Leena Hakalahti, VTT Technical Research Ctr. of Finland (Finland)
Markku Känsäkoski, VTT Technical Research Ctr. of Finland (Finland)

Published in SPIE Proceedings Vol. 7593:
Microfluidics, BioMEMS, and Medical Microsystems VIII
Holger Becker; Wanjun Wang, Editor(s)

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