ESE Seminar: “Nanophotonics: A High Bandwidth Optical Neural Interface”

Abstract
Light is a powerful tool for interrogating and manipulating biological systems, enabling targeted
stimulation, sensing, and imaging. Optical methods such as optogenetics have transformed the study of
neural circuits by making it possible to control neural activity using light. However, there remains a critical
demand in research and medicine for miniaturized high resolution optical tools that can be embedded
deep within biological systems like the brain. The brain poses particular challenges due to the sheer
number of densely packed interconnected neurons and the strong tissue scattering and absorption of
light. Nanophotonics, or chip-scale optical circuits, can enable unprecedented spatiotemporal resolution
by leveraging nanoscale coherent control of a large set of optical channels within subwavelength
waveguides with high speed reconfiguration capability, potential for integration with electronics, and low-
cost scalable manufacturability. This potential high bandwidth optical neural interface can be as thin as a
few neurons and have the ability to test spatial, temporal, and cell-type-specific aspects of neural
encoding from cellular to system level within the brain.

I will present the first implantable nanophotonic probe for optogenetic stimulation and recording of
neurons in live mice. To achieve this, we developed a reconfigurable visible nanophotonic platform based
on phase-controlled silicon nitride interferometric waveguide structures that can control cellular-sized
coherent emitters at blue wavelengths (peak of optogenetic actuators), far from traditional infrared
wavelengths. This enabled a neural interface that can generate and read multi-neuron spike patterns
deep within the brain with single-cell and sub-millisecond resolution, the highest resolution
neuromodulation shown with an implantable probe.

In addition, I will highlight two building blocks for future nanophotonic stimulation and sensing
devices that I developed using this platform: wide-angle chip-scale visible beam steering and multiplexing
within a single waveguide by utilizing the transverse spatial degree-of-freedom of light. I will show how
precise phase control and novel nanoscale photonic design of these building blocks has been applied to
emerging high bandwidth optical applications like portable display technology and quantum optical
systems. Finally, I will present a future outlook towards a new generation of implantable and wearable
biomedical devices based on nanophotonic 3D light projection and sensing techniques including high-
dimensional multiplexing, volumetric beam shaping, and quantum sensing.