PRIME: Fiber-Optic Fabrication Breakthrough Enables Advanced Neuroscience Exploration at WUSTL

To overcome this limitation, researchers at Washington University in St. Louis, including engineers and neuroscientists from the Hu and Kepecs labs, developed a single optical fiber capable of steering light in many directions simultaneously—effectively creating a controllable “disco ball” inside the brain.

Rather than relying on conventional tilted Fiber Bragg Gratings (FBGs) used in telecommunications, PRIME employs discrete, individually laser-written micro-gratings, each with its own orientation, depth, and position. These structures act as tiny, addressable out-couplers—directional mirrors embedded along the fiber—that redirect light into selected angles. Light targeting is achieved through spatial beam steering and timing rather than wavelength switching, allowing researchers to selectively activate individual nodes or illuminate all sites simultaneously for large-scale neural modulation.

In proof-of-concept experiments, a research team led by Shuo Yang successfully used PRIME to stimulate distinct subregions of the superior colliculus in freely moving animals, triggering specific behaviors such as freezing or escape. This capability provides an unprecedented window into the spatiotemporal dynamics of brain circuits and opens new possibilities for precision neuroscience.

High-precision XY scanning: Travel ranges from 50×50mm up to 300×300mm with 1 nanometer resolution.

• Frictionless direct-drive performance: Ironless linear motors enable speed up to 2m/s and acceleration up to 27.5 m/s², ideal for dynamic ultrafine alignment.
• Low-profile, cleanroom-ready design: The air-bearing system eliminates surface wear and friction-induced particle generation, reducing contamination—essential for delicate optical experiments.

Role in PRIME: The A-311 was used to inscribe micro-gratings into the PRIME fiber with nanometer-level positioning precision over a millimeter range, a capability crucial for mapping neural circuits spanning from microns to millimeters.

Vertical motion with nanometer precision: Offers 7mm of Z‑axis travel, 10nm incremental motion, and 25nm bidirectional repeatability.

• High dynamics: Voice-coil motor delivers speeds up to 200 mm/s, sub-nanometer encoder readbacks, and fast settling times—tailored for depth scanning.
• Counterbalance and closed-loop control: Built-in magnetic counterbalance supports heavy micro‑optics; remote control integration ensures stable and repeatable performance.

Role in PRIME: The V‑308 enables rapid and precise depth adjustment of laser focus, ensuring optimal machining precision for the grating elements.

By combining PI’s A‑311 air-bearing XY-stage for planar actuation with the V‑308 Z-stage for vertical nano-focusing, researchers gained full 3D-positioning control during the laser direct-writing process. This allowed:

• Dynamic targeting: The fiber can be scanned laterally and have its depth adjusted to flexibly target any of the 1,000+ grating sites.
• High‑fidelity stimulation: Nanometer-level motion ensures optical beams stay on‑target, enhancing specificity and reducing off‑target effects.
• Repeatable experiments: Closed‑loop systems ensure consistent beam delivery across repeated trials, a necessity for robust behavioral neuroscience experiments.