Focus scanning with feedback-control for fiber-optic nonlinear endomicroscopy

Biomed Opt Express. 2017 Apr 17;8(5):2519-2527. doi: 10.1364/BOE.8.002519. eCollection 2017 May 1.

Focus scanning with feedback-control for fiber-optic nonlinear endomicroscopy.


Fiber-optic endomicroscopes open new avenues for the application of non-linear optics to novel in vivo applications. To achieve focus scanning in vivo, shape memory alloy (SMA) wires have been used to move optical elements in miniature endomicroscopes. However, this method has various limitations, making it difficult to achieve accurate and reliable depth scanning. Here we present a feedback-controlled SMA depth scanner. With a Hall effect sensor, contraction of the SMA wire can be tracked in real time, rendering accurate and robust control of motion. The SMA depth scanner can achieve up to 490 µm travel and with open-loop operation, it can move more than 350 µm within one second. With the feedback loop engaged, submicron positioning accuracy was achieved along with superior positioning stability. The high-precision positioning capability of the SMA depth scanner was verified by depth-resolved nonlinear endomicroscopic imaging of mouse brain samples.


1 Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland.

2 Solomon H. Snyder Department of Neuroscience, Johns Hopkins University Medical School, Baltimore, Maryland.