We appear opaque because our tissues scatter light very strongly. Traditionally, focusing of light in biological tissues is confounded by the extreme scattering nature of tissues. Interestingly, optical scattering is time-symmetric and we can exploit optical phase conjugation methods to null out scattering effects. We have demonstrated a time-reversed ultrasound-encoded (TRUE) optical focusing strategy based on the use of digital optical phase conjugation to flexibly and controllably deliver high optical power in ex vivo tissues. Our ability to meaningfully focus light in such turbidity is enabled by the successful use of the time-reversal symmetry of optical scattering. As a focusing method, we expect that the use of the digital TRUE focusing technique would enable the extension of optogenetic techniques to the deep brain for non-invasive, spatially specific, excitation/inhibition. Moving forward, the method can also potentially allow deep tissue optical imaging at unprecedented depth.

Professor Yang's research efforts are in the areas of novel microscopy development and time-reversal based optical focusing. Prof. Yang joined the California Institute of Technology in 2003. He is the Thomas G. Myers professor in the areas of Electrical Engineering, Bioengineering and Medical Engineering. He has received the NSF Career Award, the Coulter Foundation Early Career Phase I and II Awards, and the NIH Director's New Innovator Award.  He is a fellow of the Coulter foundation, AIMBE, OSA and SPIE.