September 2014
Spotlight Summary by Oliver Friedrich
Highly birefringent 98-core fiber
Clinical endoscopy and preclinical imaging has seen challenging expectations to image performance regarding resolution, imaging speed, specificity and a drive towards being able to scan smaller and smaller body parts either through natural orifices or penetration channels. In particular for the latter demand, a shift from larger diameter trocars to cannulas and puncture needles requires ongoing miniaturization of fibre optics as well as scanning mirrors, electronics or camera chips. Endoscopy in medicine has changed little over 50 years in using white light imaging through as many as possible uncoupled cores assembled into an optical fibre with proximal or distal scanning. An increase in cell and tissue contrast has been realized for clinical endoscopy by use of confocal endomicroscopy systems using a single optical fibre (replacing the need for a confocal pinhole) or uncoupled fibre bundles in conjunction with either proximal or distal miniaturized scanner mirrors or actuators. Although such systems may increase signal-to-noise ratio and desired specificity, they may require applying external labels, i.e. dyes or fluorescently labelled antibodies, to the specimen before scanning. Label-free multicore endomicroscopy is believed by many to be the next generation endoscopy application that circumvents some of the problems associated with external labels. Multiphoton excitation of biological targets, i.e. myosin, collagen and tubulin, may well be suited to detect or monitor disease progression or early diagnosis of chronical inflammatory organ remodelling patterns, while multiphoton CARS spectroscopy may also be used for tumour diagnostics with cellular accuracy. In particular, multicore fibres are of growing interest as each single core itself acts as a light guide representing an image pixel. This revokes the need for scanning units, the miniaturization of which sets size limits. All individual cores build up to a phased array and in particular for multi-mode fibres, the diameter of each core can even be further reduced to exploit multiple modes being sent via the same fibre. In view of future applications to use for label-free imaging modalities in endoscopic devices, preservation of polarization is mandatory since non-linear optical effects, e.g. second harmonic generation (SHG) to visualize myosin or collagen, are strongly polarization dependent. And lastly, with long multicore fibres, pulse broadening through dispersion, eventually changing with bending of fibres in different spatial angle elements, can introduce severe image distortions.
In their present work, Stone and colleagues have successfully overcome some of the constraints towards the optical properties of previous multicore fibres that would prevent or at least narrow down application for multiphoton endomicroscopy. They succeeded to produce a highly birefringent multicore fibre consisting of ninety eight cores with a core diameter of ~2 µm to be used for single mode imaging at 800 nm, a wavelength typically used for SHG imaging of tissues. Although the fibre length is reported as 3.6 m (generously suitable for endoscopy), there was no significant coupling between cores at 800 nm, the birefringence was comparably high to the one of commercial single core fibres and most importantly, polarization in each individual core was maintained. This is achieved through their interesting design including stress applying parts as boron-doped silica inclusions flanking individual cores. Those apply mechanical stresses to introduce anisotropy to the cores. With this approach, their multicore fibre with 98 single cores by far outnumbers a previous five-core fibre where polarization already has been shown to be maintained in fs-pulse applications. Therefore, the 98-core fibre presented here is expected to yield higher resolutions and versatility in multiphoton endomicroscopy which will reflect a major boost to that field. Reproducible fabrication of such multicore fibres using the stack and draw technique is a very delicate process in optical engineering that requires much experience and ‘trial and error’ stoicism and the work by Stone et al. is commended to successfully have managed to produce such a fibre.
It will be of great interest to see upcoming work implementing the fibre to endoscopic imaging systems. The relatively small outer diameter of ~230 µm might also bring the vision of including such fibres into standard injection needles for ‘optical needle imaging biopsy’ closer to reality.
You must log in to add comments.
In their present work, Stone and colleagues have successfully overcome some of the constraints towards the optical properties of previous multicore fibres that would prevent or at least narrow down application for multiphoton endomicroscopy. They succeeded to produce a highly birefringent multicore fibre consisting of ninety eight cores with a core diameter of ~2 µm to be used for single mode imaging at 800 nm, a wavelength typically used for SHG imaging of tissues. Although the fibre length is reported as 3.6 m (generously suitable for endoscopy), there was no significant coupling between cores at 800 nm, the birefringence was comparably high to the one of commercial single core fibres and most importantly, polarization in each individual core was maintained. This is achieved through their interesting design including stress applying parts as boron-doped silica inclusions flanking individual cores. Those apply mechanical stresses to introduce anisotropy to the cores. With this approach, their multicore fibre with 98 single cores by far outnumbers a previous five-core fibre where polarization already has been shown to be maintained in fs-pulse applications. Therefore, the 98-core fibre presented here is expected to yield higher resolutions and versatility in multiphoton endomicroscopy which will reflect a major boost to that field. Reproducible fabrication of such multicore fibres using the stack and draw technique is a very delicate process in optical engineering that requires much experience and ‘trial and error’ stoicism and the work by Stone et al. is commended to successfully have managed to produce such a fibre.
It will be of great interest to see upcoming work implementing the fibre to endoscopic imaging systems. The relatively small outer diameter of ~230 µm might also bring the vision of including such fibres into standard injection needles for ‘optical needle imaging biopsy’ closer to reality.
Add Comment
You must log in to add comments.
Article Information
Highly birefringent 98-core fiber
J. M. Stone, F. Yu, and J. C. Knight
Opt. Lett. 39(15) 4568-4570 (2014) View: Abstract | HTML | PDF