Multisite silicon neural probes with integrated silicon nitride waveguides and gratings for optogenetic applications.

Optimal optogenetic perturbation of brain circuit activity often requires light delivery in a precise spatial pattern that cannot be achieved with conventional optical fibers. We demonstrate an implantable silicon-based probe with a compact light delivery system, consisting of silicon nitride waveguides and grating couplers for out-of-plane light emission with high spatial resolution. 473 nm light is coupled into and guided in cm-long waveguide and emitted at the output grating coupler. Using the direct cut-back and out-scattering measurement techniques, the propagation optical loss of the waveguide is measured to be below 3 dB/cm. The grating couplers provide collimated light emission with sufficient irradiance for neural stimulation. Finally, a probe with multisite light delivery with three output grating emitters from a single laser input is demonstrated

Modal analysis of semiconductor lasers with nonplanar mirrors

We present a formalism for analyzing laser resonators which possess nonplanar mirrors and lateral waveguiding [e.g., an unstable resonator semiconductor laser (URSL)]. The electric field is expanded in lateral modes of the complex-index waveguide and is required to reproduce itself after, one roundtrip of the cavity. We show how the waveguide modes, their gain and loss, and hence the criterion for truncation of the infinite set of modes can be derived from the Green's function of the one-dimensional eigenvalue equation for the waveguide. Examples are presented for three cases of interest - a purely gain-guided URSL, an index-guided URSL, and a gain-guided tilted-mirror resonator. We compare theoretical calculations to previous experiments