Photoinitiator-free multi-photon fabrication of compact optical waveguides in polydimethylsiloxane

Abstract

Compact, low loss flexible optical waveguides are crucial in optofluidic and microfluidic devices for a dense integration of optical functionalities. We demonstrate the fabrication of compact optical waveguides in polydimethylsiloxane through multiphoton laser direct writing using phenylacetylene as the photosensitive monomer. Our fabrication technique employs photo-induced radical chain polymerization initiated by the monomer molecule itself without a photoinitiator. Because of the dense π-electrons in phenylacetylene, we achieved a high refractive index contrast (Δn ≥ 0.06) between the waveguide core and the PDMS cladding. This allowed for efficient waveguiding with a core size of 1.3-µm with a measured loss of 0.03 dB/cm in the spectral band of 650-700 nm.