As demands on the performance of optical fibers continues to grow, fiber enthusiasts have attacked the problem through a combination of new materials and designs. In doing so, tremendous doors to useful and interesting optical phenomena have been opened. For example, photonic crystal fibers (PCFs), microstructured optical fibers (MOFs), and multi-material optical fibers (MMOFs) have proliferated and enable greatly strengthened or weakened optical nonlinearities, sensing, and lasing. However, enhanced performance comes at a cost, which is that the complexities of the structures require more laborious fabrication measures. And with greater effort comes greater opportunity for error. Given the wavelength of light, even small errors by human dimensions are performance-killers optically. Accordingly, means of precision characterization of structure and materials is critical to performance.
In the present work, the team used x-ray computed tomography (CT) for the first time to imagine the interior of several complex and multi-material preforms and fibers. A particular benefit of x-ray CT is that it is non-destructive and so these often-times expensive fibers do not have to be sacrificed in order for them to be analyzed. Additionally, CT can be used as a quality control tool so that one knows prior to fiber fabrication which regions of the preform will generate the best fibers (if any fiber at all) and so there are significant manufacturing efficiencies to be gained by this work.
Specifically analyzed were (1) the structural integrity and contamination of hollow core photonic bandgap fibers, (2) structural distortions upon fusion splicing said fibers, (3) structural and coating quality in multi-element fibers, and (4) structural integrity in metal-incorporated fibers. By comparison to scanning electron and optical microscopies, which are two-dimensional imaging techniques, the x-ray CT images can be reconstructed into a 3D image. And just as with x-ray imaging as employed in medical technologies, the absorption of x-rays is material-dependent and so spatial intensity profiles provide ways of discerning which materials are which. The result is a non-destructive, three-dimensional, material-dependent rendering with spatial resolutions down to 50 nm, possibly smaller. Such resolution is especially critical for these types of specialty optical fibers since small perturbations dramatically affect fiber loss.
In a clear and concise manner, this work of Sandoghchi et al. validates the use of x-ray CT as an novel and practical approach to pre- and post-analyze optical fibers in a truly non-destructive way. Its use might begin initially on high value specialty fibers but one can envision its on-line, real-time use in manufacturing as a quality assurance mode as well.
Anyone up for a kryptonite fiber?
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