A team of researchers from the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland has demonstrated a new technique for fabricating compact, low-loss optical waveguides in a polydimethylsiloxane (PDMS) slab.
The method uses a femtosecond writing laser to initiate two-photon absorption in light-reactive monomers embedded in the PDMS. Two-photon absorption creates enough energy in the monomer molecules to trigger a chain polymerization reaction without the use of potentially toxic photoinitiator compounds. The resulting polymerized waveguides have a higher refractive index (RI) than the surrounding PDMS, making them efficient at confining light, and have a simpler chemical structure than photoinitiator-fabricated waveguides, making them potentially useful in biomedical applications.
The EPFL team used a host–guest system and optimized multiphoton laser direct writing to fabricate its optical waveguides. The researchers chose PDMS as the “host” because the elastomer is transparent over a wide spectral range and has outstanding chemical and thermal stability.