We demonstrate that ultrasound can be used to define and steer the trajectory of light within scattering media by exploiting local pressure differences created by acoustic waves that result in refractive index contrasts.

We introduce a radical approach to use ultrasonic waves to confine and steer light deep (a few millimeters) into the tissue without having to insert a physical light guide. Ultrasonic pressure waves launched from outside can propagate in the brain tissue with minimal loss and change the density of medium locally and interact with light to define and steer the trajectory of light.

Here we present the first non-invasive methodology for optical delivery and steering deep inside the brain through creating reconfigurable light paths by ultrasonic waves via modulating the refractive and diffractive properties of the medium.