A DMD-enabled multimode fiber wavefront shaping interface for spatially addressable optogenetic stimulation

Spatially confined and rapidly addressable light delivery is important for optogenetic stimulation when optical access to the target plane is limited. Digital micromirror device (DMD) has shown its potential for rapid optical control and wavefront shaping through scattering media and multimode fiber (MMF). Despite previous works, an unresolved practical question is how the optical trade-offs of a direct binary-amplitude modulation-enabled MMF implementation translate into functional performance for cell-scale optogenetic stimulation when the relevant optical and biological requirements are evaluated together. We report a DMD-MMF wavefront shaping platform for spatially addressable stimulation beyond the distal fiber facet and evaluate coupled optical and optogenetic functional requirements. The system combines high-speed binary amplitude modulation with 40-s binary transmission matrix calibration to generate user-defined foci through a 1 m MMF. It produced foci with a diameter of approximately 2.5 μm and a peak-to-background ratio of approximately 35, and switched between target positions within 44 μs to support single-spot, multi-spot, and scan-based excitation. We characterized focusing under controlled fiber perturbations, during 30 min of operation, over an axial refocusing range of up to approximately 1 mm, and after propagation through fixed mouse brain-slice samples with thicknesses of 50 to 200 μm. We then relate these optical characteristics to functional experiments in cultured neurons, in which wavefront-shaped stimulation supports spatially targeted activation and inhibition and produces stronger calcium responses or suppression than unshaped speckle illumination under matched stimulation conditions. To relate these optical characteristics to functional experiments for optogenetics, scan-based wavefront-shaped stimulation elicited targeted optogenetic activation and inhibition in cultured neurons at the cell scale. Compared with unshaped speckle illumination, wavefront-shaped stimulation produced stronger calcium responses at lower illumination power density. These results establish an experimentally validated operating envelope linking the optical characteristics of direct binary-amplitude modulation enabled MMF platform to bidirectional cell-scale optogenetic modulation under controlled in vitro conditions.