The 2x2 Assisted Fiber-optic Rotary Joint is a two-channel device with a motion sensor and motorized rotation assistance that connects optical fibers on its stationary side with their counterparts on the rotating side. It detects torsion in fiber-optic tether to a moving animal, turns the rotor accordingly, and lets the animal move without discomfort.

The optical channels follow separate paths and have low loss,  low signal variations during rotation, and no crosstalk. Its fixed side has FC receptacles, while the rotating side has M3 receptacles. The optical system uses achromatic doublet lenses and a fiber optic 0.22 NA with consistent performance for a low NA laser light over the entire visible range from 450 to 650 nm.

These assisted rotary joints are intended for optogenetics experiments involving independent activation or silencing of two different brain sites/regions of the tethered behaving animals regardless of their size.