LiNbO3-Based Synaptic Sensors via Microring Resonator Modulators

The precise measurement of action potentials with high sensitivity and broad bandwidth (BW) is crucial in neuroscience research. However, current electrode-based methods are limited by BW, sensitivity to biological noise, and tissue damage caused by measurement byproducts. To address these challenges, we propose a novel optrode that leverages the electrooptic (EO) effect of lithium niobate to detect electric fields generated by voltage differences in the extracellular medium. This new approach combines the EO effect with a ring resonator and coherent balance detector, enabling highly sensitive and precise action potential measurements. We demonstrate the feasibility of this optrode by carrying the signal with modulation and beating it through coherent detection to detect weak signals. The array configuration of the sensor offers multiplexed sensing capabilities, enabling simultaneous detection of neural activity from multiple locations within the brain. Also, since light is used for measurements, the optrode does not generate heat or produce toxic byproducts, preventing tissue damage. The designed EO ring resonator exhibits a quality factor of approximately 104, allowing for the sensing of action potentials as small as
$15~\mu $
V. Hence, the proposed method has the capability to overcome the limitations of current electrode-based methods, facilitating more accurate measurements of action potentials and advancing the understanding of neuronal activity in the brain.