Three-dimensional fabrication of sub-micron optical waveguides in PDMS and other polymer materials

Optical waveguides are one of the most important photonic components. They are indispensable tools in many of todayâ s technologies because of their capacity of guiding light. In particular, compact, low loss, flexible polymer optical waveguides are crucial in optofluidic and microfluidic devices for a dense integration of optical functionalities. The sought after suitable materials and innovative fabrication techniques to achieve low loss long polymer optical waveguides and interconnects has proven to be challenging. In a fiber optic endoscope, thousands of single-mode (SM) optical fibers acting as single pixels are closely packed together, delivering the local information to a camera chip. Biocompatible polymer-based waveguides increasingly became valid alternatives to silica fibers to deliver and collect light for optical diagnosis, therapy and surgery. In particular, polydimethylsiloxane (PDMS) is well known to be a suitable polymer for biomedical implantation devices, thanks to its excellent physical and chemical properties. In this thesis, I demonstrate the fabrication of compact optical waveguides in PDMS through multiphoton laser direct writing (MP-LDW). The core of this research consists of the investigation of suitable combinations of monomer and PI capable of efficient photopolymerization in a cured PDMS matrix. We achieved, for the first time, the photoinitiator-free fabrication of optical waveguides employing phenylacetylene as the photosensitive monomer via multi-photon absorption. Because of the dense Ï -electrons in phenylacetylene, we achieved a high refractive index contrast (Î n â ¥ 0.06) between the waveguide core and the PDMS cladding. This allowed for efficient waveguiding at a core size of 1.3-µm with a measured loss of 0.03 dB/cm in the spectral band of 650-700 nm. Motivated by the need of minimizing self-focusing, we investigated alternative chemical schemes and demonstrated the fabrication of submicron optical waveguides in PDMS using divinylbenzene (DVB) as the monomer through two-photon polymerization (2PP). We show that the commercial oxime ester photoinitiator Irgacure OXE02 is suitable for triggering the DVB polymerization, resulting in a stable and controllable fabrication process for the fabrication of defect-free, 5-cm long waveguides. Moreover, I present the methodologies we have developed for the fabrication of polymer rectangular step-index (STIN) optical waveguides using a commercial 3D printing system (Photonic Professional GT, Nanoscribe GmbH), using the proprietary IP-dip resist. We performed a full calibration and implemented a printing strategy for the fabrication of a 720 ÎŒm long SM-fiber bundle. We characterized it in terms of refractive index, transmission loss and imaging capabilities. We further demonstrate how a convolutional neural network (CNN) can reconstruct the original images from a scrambled output from the waveguide bundle due to crosstalk. To achieve this, we have constructed a CNN