Figure 1. Conceptual drawing of the stimulation/recording setup and layout of the multi-electrode-optrode array (MEOA) chip.

(a) The light is introduced into the system at the input array region, which is located at the edge of the chip. There is a grating coupler at each location (indicated with a triangle) that couples light into a particular waveguide when a light source is placed above it. The light is then carried by the corresponding waveguide into one of the optrodes (output grating coupler). (b) The MEOA is composed by an array of eight by eight optrodes and TiN electrodes. There are two types of optrodes for two different wavelengths (450 nm, corresponding to blue, and 590 nm, corresponding to amber), which are vertically interlaced. The electrode diameter is 60 μm and the optrodes are 6 × 23 μm² and 6 × 30 μm² for blue and amber, respectively. The pitch is 100 μm in both directions for the electrodes and 200 μm vertically by 100 μm horizontally for each type of optrode.