Optogenetics is known as a technique that genetically targets specific neurons to express light sensitive channel proteins and provides the capability to stimulate the central nervous system with millisecond precision: Compared to deep brain stimulation, which affects bigger regions of the brain and thereby making it impossible to precisely stimulate individual cells, optogenetics offers the possibility of targeted neuron stimulation without affecting surrounding neurons. Numerous optogenetic devices have been developed for light delivery and simultaneous electrophysiological recordings. Most of them consist of an optical fiber and separate micro electrodes attached to the optical fiber. Even such small electrodes can induce tissue damage. In order to reduce the tissue damage, we present a fiber-based optogenetic light-delivery device with microelectrodes coated on the surface of the optical fiber. Our work uses metalized optical fiber, in order to deliver the light and simultaneously record the induced modulation (electrophysiological signals) with minimum tissue damage. Light delivery is done from the optical fiber tip, while microelectrodes are fabricated from the metal thin-film. These coating serves as the microelectrodes are used for the recording of electrophysiological signals. In this work, we present the details of electrode micro-structuring on the optical fiber using sputtering process. We also present and comment on the results of resistance measurements of the sputtered electrodes. Currently, we use copper for electrode fabrication, later we foresee to utilize gold as a biocompatible electrode material.
A detailed study of the tuning characteristic of a novel MEMS-based tunable optical filter is presented together with supporting characterization results. The device is based on a Fabry-Perot interferometer employing a solid-state silicon resonator and silicon-based distributed Bragg reflectors (DBR). It is fabricated as a free-standing membrane, which is suspended through micro-machined arms. Tuning is achieved by thermal modulation of the resonator’s optical thickness. The tuning behavior of thin film interference filters differs significantly from filters based on an etalon structure. An analytical approach is presented to include effects caused by the Bragg reflectors. Based on this model different material systems are investigated in order to improve the achievable tuning range. A maximum reflectance of 99.8 % and a stop band width of 783 nm are achieved. A minimum spectral width of 1.19 nm and an insertion loss of 1.7 dB have been measured in transmission measurements for filter membranes, consisting out of a λ/2 layer of amorphous silicon and Bragg reflectors each with 12 λ/4 layer-pairs of silicon nitride and silicon dioxide. Using external heating the filter shows a tuning efficiency of 51.7 pm K-1, as predicted through the proposed effective resonator length model.
A novel MEMS-based tunable optical filter, an essential component for monitoring and reconfiguration of optical wavelength-division multiplexing networks, is presented. The device is based on a Fabry-Perot interferometer employing multiple solid-state silicon cavities and silicon-based dielectric Bragg mirrors. Tuning is achieved through thermal modulation of the resonator's optical thickness. It is fabricated as a free-standing membrane using silicon MEMS technology. The filter membrane is fixed by micromachined suspension arms, which thermally isolates it against the substrate. The present concept features low power consumption and fast thermal modulation. Light coupling to the filter array is realized by positioning of fibers and the filter chip in a micro-optical bench setup.