Abstract
Controlling light propagation through a step-index multimode optical fiber (MMF) has several important applications, including biological imaging. However, little consideration has been given to the coupling of fiber and tissue optics. In this Letter, we characterized the effects of tissue-induced light distortions, in particular those arising from a mismatch in the refractive index of the pre-imaging calibration and biological media. By performing the calibration in a medium matching the refractive index of the brain, optimal focusing ability was achieved, as well as a gain in focus uniformity within the field-of-view. These changes in illumination resulted in a 30% improvement in spatial resolution and intensity in fluorescence images of beads and live brain tissue. Beyond refractive index matching, our results demonstrate that sample-induced aberrations can severely deteriorate images from MMF-based systems.
Highlights
Controlling light propagation through a step-index multimode optical fiber (MMF) has several important applications, including for biological imaging
The wavefront shaping unit was composed of a liquid-crystal spatial light modulator (LC-SLM, Meadowlark Optics, HSPDM512), the MMF (Thorlabs, FG050UGA, core diameter 50 μm, numerical aperture (NA) 0.22), and relay optics
The LC-SLM was conjugated to an iris letting through the onaxis first-order diffraction beam for wavefront shaping [8]
Summary
Controlling light propagation through a step-index multimode optical fiber (MMF) has several important applications, including for biological imaging. In this Letter, we characterise the effects of a refractive index mismatch between the biological and calibration media on focus formation in the context of brain imaging using one-photon fluorescence point-scanning microscopy through MMF.
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