Extended Data Fig. 2: Light switching tree and optical characterization.

a. Schematic of switching tree architecture, which distributes light from a single input grating coupler to one of fourteen waveguides on the shank. A network of 15 thermo-optic switches is controlled by four digital-to-analog converters (DACs), allowing light to be routed to each emitter, or to reference sites used for calibration. Each probe contains a separate switching tree for blue and red light. b. Maximal intensity projections of the 3D distribution of light emitted by a red emitter, when the probe was immersed in water. Contours show intensity levels at 1, 5, and 10 mW/mm². c. Same, when the probe was immersed in an optical phantom (1% milk) whose estimated reduced scattering coefficient \({\mu }_{s}^{{\prime} }\) (23 cm⁻¹) is in the range measured in rodent gray matter (20–30 cm⁻¹, see Methods). d, e. Same as b, c, for a blue emitter.