Single Optical Fiber Probe for Fluorescence Detection and Optogenetic Stimulation

We have developed a fiber-optic-based probe for precise delivery of stimulation/excitation light pulses and detection of faint fluorescence signals for applications in neuroscience and optogenetics. In this design, a thin multimode fiber serves as the head of the probe to be inserted into the brain. This fiber is used to deliver light to the region of interest and guide a sample of the emission signal back to detectors. The major tradeoff in the design of such a system is to decrease the size of the fiber and intensity of input light to minimize physical damage and to avoid photobleaching/phototoxicity but to keep the signal-to-noise ratio (S/N) reasonably high. Here, the excitation light and the associated emission signal are frequency modulated. Then, the output of the detector is passed through a time lens which compresses the distributed energy of the emission signal and maximizes the instantaneous S/N. By measuring the statistics of the noise, the structure of the time lens is designed to achieve the global optimum of S/N. We have also designed side-firing fibers and a micromechanical assembly for distributed light delivery and fluorescence detection.

I. Introduction

A single optical fiber probe is designed for precise delivery of light pulses to regions of interest within the brain tissue and detection of fain fluorescence signal with specific applications in optogenetics. In this section, we review the biology, potentials of the technique, and the requirements for a new instrumentation. Details of the design and experimental results are discussed in the following sections.