Single laser to multiple optical fiber device for optogenetics-based epidural spinal cord stimulation

This paper reports on the design and optical characterization of a single laser to multiple optical fiber (SLMOF) device for optogenetics research. Output end of SLMOF is an optical fiber bundle made by 210 optical fibers arranged into a 7×30 matrix. Single laser beam produced by laser diode (LD) is delicately steered on optical table to be coupled into target optical fiber. By controlling the power of the LD and quickly switching among fibers, this device allows for high flexibility when designing spatiotemporal light patterns. We tested the optical characterization of the device both in vitro and in vivo. Light was emitted from the end of the fiber at a power of 275.4 mW/mm2 when a drive current of 80 mA was used. The transmission fraction was 18.6% after penetrating 0.2 mm of spinal cord slice, and 1.3% after 1 mm. Coupling with 50 ms of repetitive stimulation at 10 Hz produced an only 0.348 K temperature increase at the spinal cord surface. The capacity of the system for optogenetics research was also demonstrated by epidural spinal cord stimulation induced hindlimb motion in paralyzed rats expressing channelrhodopsin-2 (ChR2).