19.3 A MEMS-Based Dynamic Light Focusing System for Single-Cell Precision in optogenetics

Optogenetics is a technique that involves the use of light to excite or inhibit neurons that have been genetically modified to express light-sensitive ion channels (opsins). Implanted LEDs or optical fibers are the most common approaches in optogenetic stimulation systems, but their broad illumination and lack of beam steering capability make them insufficient for probing individual neurons. When a 3D scanning optical system is used to control the position of a laser spot, single-cell precision can be achieved in a volume of tissue containing millions of cells. Due to the sub-ms response time of modern opsins and a demand for high throughput neural stimulation [1], a random-access scanning system requires a kHz refresh rate, and the capability to dwell on a target depth for an arbitrary length of time. Existing lateral (XY) scanning tools are fast, however state-of-the-art axial (Z) scanning technologies such as electrically tunable lenses (ETLs) [2] and liquid crystal (LC) lenses [3] are limited to < 3ms settling times. Alternative axial scanning tools either lack dwelling capability [4] or have impractical actuator drive requirements [5].