Total internal reflection waveguide for depth-selective light delivery

Photostimulation with optical fiber implants delivers sufficient optical power deep in brain tissue but sacrifice spatial precision control and depth selectivity. We present a 3D-printed “staircase” waveguide containing total internal reflection micro mirrors that allow switchable light guiding to user-defined depths with minimal divergence. We demonstrated six discrete output depths in 220µm–1.5mm covering the cortical layers of rodent models, with transmission efficiency of 60% and each beam remained less than 150um in diameter after 1 mm propagation.