Abstract
This paper demonstrates multiphoton excited fluorescence imaging through a polarisation maintaining multicore fiber (PM-MCF) while the fiber is dynamically deformed using all-proximal detection. Single-shot proximal measurement of the relative optical path lengths of all the cores of the PM-MCF in double pass is achieved using a Mach-Zehnder interferometer read out by a scientific CMOS camera operating at 416 Hz. A non-linear least squares fitting procedure is then employed to determine the deformation-induced lateral shift of the excitation spot at the distal tip of the PM-MCF. An experimental validation of this approach is presented that compares the proximally measured deformation-induced lateral shift in focal spot position to an independent distally measured ground truth. The proximal measurement of deformation-induced shift in focal spot position is applied to correct for deformation-induced shifts in focal spot position during raster-scanning multiphoton excited fluorescence imaging.
Highlights
The development of ultra-compact optical fiber endoscopes employing spatially coherent radiation that do not require distal optical elements is a rapidly growing field
In order to achieve a real-time readout of deformation-induced changes in the optical path lengths of the cores of the polarisation maintaining multicore fiber (PM-multicore optical fiber (MCF)), the interferogram on Camera 2 was recorded at 100 frames per second as the optical fiber was deformed by a sinusoidally oscillating loudspeaker cone operated at 1 Hz
Camera 1 was configured so that its acquisition was exactly synchronised to Camera 2 to provide an independent measurement of the actual shift in focal position induced by deforming the fiber
Summary
The development of ultra-compact optical fiber endoscopes employing spatially coherent radiation that do not require distal optical elements is a rapidly growing field. By removing the need for distal optical elements, the diameter of the endoscope is limited only by the size of the optical fiber and there is no need to develop miniaturised optical components Such approaches can be categorised into two groups: those utilising higher order modes in a single multimode optical fiber to convey image information and those using a single optical fiber with multiple single mode cores. An early experimental demonstration for transmitting an image through a single multimode optical fiber in single pass was demonstrated in 1991 using optical phase conjugation in a photorefractive crystal [1] and from 2012 it was realised using a range of different experimental configurations [2,3,4,5] This approach is compact, does not require specialised multicore optical fibers and is well suited to imaging fluorescence using singlephoton excitation [2, 5]. Modal dispersion in multimode fiber makes it challenging to transmit the ultrashort pulses required for multiphoton excitation, we note that progress is being made in this area by restricting the modes used to a small subset with similar optical path lengths [6]
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