Miniaturized 3×3 optical fiber array for optogenetics with integrated 460 nm light sources and flexible electrical interconnection

We report on the design, fabrication, assembly, as well as optical and thermal characterization of a novel MEMS-based optical probe array for optogenetic research. The system allows the optical stimulation of neural brain tissue at 3×3 independently controllable spots. It comprises nine high-efficiency light emitting diodes (LED) integrated in a micromachined silicon (Si) housing that ensures the mechanical stability and precise alignment of 5-mm-long optical glass fibers with a diameter of 125 μm. The fibers transmit the light emitted by the LEDs (center wavelength 456 nm) into the brain tissue. A highly flexible polyimide (PI) ribbon cable provides the electrical interconnection of the LEDs to a control unit. The compact housing (volume less than 2.2 mm³) is beneficial for chronic system implantations in rodents. Furthermore, the electrical-only interconnection of this array represents a distinct advantage over conventional systems using external light sources interfaced by optical fibers. The optical characterization of the array reveals an optical output power of up to 1.28 mW/mm² at a drive current and duty cycle of 30 mA and 10%, respectively. The corresponding temperature increase of the silicon housing is 2.2 K only.