Multimode fiber

To measure the optical transmittance of the elastomer material, the elastomer was cured in a 1-cm quartz cuvette. The transmittance was measured by using an Evolution 300 spectrophotometer (Thermo Scientific, Waltham, MA, USA). To quantify propagation loss, we coupled light into the elastomer waveguide by using a multimode fiber with a numerical aperture of 0.22 (Thorlabs, Newton, NJ, USA). The fiber was coupled to a diode-pumped solid-state laser delivering light at 445 nm (Civil Laser, Hangzhou, China). The fiber was stripped of the acrylate coating, and 2 to 3 mm of the bare fiber was inserted into the center of one end of an elastomer waveguide. To measure the propagation loss of the waveguides, the cut-back method was used. The transmitted power through the waveguide was measured while the waveguide was suspended in air, or placed on top of strips of scleral tissue dissected from fresh porcine eyeballs. The transmitted power through the waveguide was measured with a double-integrating sphere (IS200-4; Thorlabs) at waveguide lengths of 60, 45, 30, and 15 mm. The experiment was repeated with at least three waveguides for each thickness (0.8, 1.0, and 1.4 mm). The data were adjusted to compensate for material absorption and fit to an exponential decay model (see theory below) to extract the scattering loss coefficients to air and scleral tissue.

We used a laser system with two wavelengths for optogenetic stimulation (473 nm, blue laser) or control (594 nm, yellow laser). Laser light was delivered to cortex through a 100 μm or a 200 μm diameter multimode fiber (Thorlabs). Fiber endings were placed just above the cortical surface in area 21a. The intensity and waveform of the laser were controlled via a custom circuit in TDT, and timing was controlled by the visual stimulus computer using Psychtoolbox-3, a toolbox in MATLAB (MathWorks)^{108 (link)}.