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, 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) and liquid crystal (LC) lenses are limited to <; 3ms settling times. Alternative axial scanning tools either lack dwelling capability or have impractical actuator drive requirements. We propose an axial focusing device comprised of an ASIC and phase modulating piston-motion MEMS mirrors with settling times <;100ps [6] enabling a 10kHz refresh rate. The driver ASIC is capable of addressing MEMS process variations that impact voltage-to-2 displacement behavior by employing a nonlinear, reconfigurable 6-bit DAC to achieve a f2linear input code-to-displacement response. We combine the driver with a 23,852-element MEMS array wired as 32 independently addressable rings to demonstrate high-speed axial (Z) focusing capability. The ASIC also has a 200x200 pixel array with a pad openings that can drive 40,000 independent MEMS mirrors at a 10kHz refresh rate 'to serve as a development platform for a MEMS mirror-based spatial light modulator (SLM), which would unify all three axes of scanning in a single, integrated device and rz would enable high-speed 3D optogenetic control of up to thousands of neurons