Parylene Photonic Neural Probes
In this project, we are developing high-density flexible optoelectrical neural probes capable of electrophysiology recording and optical stimulation with high spatiotemporal resolution. These neural probes consists of an electrical layer with high density of passive recording electrodes and a photonic layer. The photonic layer has an array of compact polymer waveguides.
We have shown, for the first time, that Parylene C, which is a polymer widely used in biomedical implants can be used to form photonic waveguides to guide light. In our design, Parylene C is used as the waveguide core with Polydimethylsiloxane (PDMS) as the cladding. The large refractive index contrast between Parylene C (n = 1.64) and PDMS (1.4) enables us to realize very compact photonic waveguides that can tightly confine light.
A very unique feature of these waveguides is that 45-degree mirrors can be integrated at the input and output of the waveguides to enable vertical broadband input coupling of light and out of plane illumination at the output. The out of plane illumination is very important for neural probe design since it enables co-localization of optical stimulation volume with the recording volume and it can potentially reduce the photoelectric artifact significantly.
We have implemented a dense array of these flexible waveguides with integrated laser diodes in the backend using a flip-chip bonding process to realize a fully-packaged stand-alone photonic neural interface.
We are now working on the design of a dense-array of these waveguides in the detection mode to realize a flat and ultracompact endoscopic imager.
J. W. Reddy and M. Chamanzar, “Parylene Photonic Waveguide Arrays: A Platform for Implantable Optical Neural Implants” CLEO (2018).