Flexible Polymer Optical Waveguides for Integrated Optogenetic Brain Implants

Fabrication and Characterization of PDMS Waveguides for Flexible Optrodes

“…Hence, flexible silicone waveguides with mean losses of −4.4 dB cm −1 ± 2.4 dB cm −1 and −4.8 dB cm −1 ± 1.3 dB cm −1 for wavelengths of 632 and 473 nm, respectively, were successfully fabricated with the electrochemical etching approach. Another entirely PDMS‐based manufacturing approach that relies on a sophisticated cleanroom process obtained a loss of −4.7 dB cm −1 at 1550 nm with a 50 µm waveguide core, [ 18 ] whereas a method that uses PDMS as core material and the surrounding medium as cladding had a fraction of 31% ± 10% of input light at the fiber tip. [ 31 ] PDMS‐based waveguides have also been successfully integrated into lab‐on‐chip devices achieving reported losses of −3.1 dB cm −1 at 532 nm and −2.9 dB cm −1 at 633 nm, [ 32 ] whereas a different approach even reached down to −0.40 dB cm −1 at 460 nm.…”

“…Due to these properties and handling capabilities, PDMS was recently introduced as material for implantable waveguides (Figure 1B). [18][19][20] Nevertheless, PDMS waveguides must prove that they transmit sufficient light to activate opsins in electrically excitable cells. Prerequisites are that they maintain their light transmission properties over time without getting opaque and no drastic refractive index changes occur, so that the core refractive index (n core ) remains larger than the cladding refractive index (n cladding ).…”