Direct milling and casting of polymer-based optical waveguides for improved transparency in the visible range

Polymer waveguides fabricated from photoresist have an inherent high propagation loss in the short visible wavelength range caused by absorption due to the added photosensitizers. We have addressed this problem by development of two novel methods for the fabrication of microfluidic systems with integrated optical waveguides. Polymethylmethacrylate (PMMA) is dissolved in anisole and 'doped' with styrene-arcylonitrile copolymer to vary the refractive index. The doped PMMA with a higher refractive index is then spin coated onto a PMMA substrate with a lower refractive index to provide waveguide properties. Direct micromilling enabled us to fabricate 100 µm wide optical waveguides. Propagation losses of less than 1 dB cm−1 could be achieved throughout the entire visual range down to a wavelength of 400 nm. A casting process amenable to high number production of such devices was furthermore developed.