November 2015
Spotlight Summary by Paul Steinvurzel
Optical side scattering radiometry for high resolution, wide dynamic range longitudinal assessment of optical fibers
An old technique has been adapted to achieve unprecedented dynamic range and spatial resolution in measuring transmission loss of km-length photonic bandgap fibers. In side scatter radiometry, one end of an optical fiber is illuminated and the remaining length is spooled through an integrating sphere to continuously measure light scattered through the cladding. It was first demonstrated in the early days of optical fiber development over 40 years ago, but has since mostly fallen into disuse in favor optical time domain reflectometry (OTDR). OTDR measures weak backscatter, and only requires access to the fiber input (so, for example, it can measure fibers already in the ground). It is optimized for measuring standard single mode fibers, but inadequate for characterizing hollow core photonic bandgap fibers, which have higher transmission loss, and a greater variety of loss mechanisms. Bandgap fibers guide light based on antiresonances in the cladding, and so may not necessarily guide at 1310 or 1550 nm, which are typically the only wavelengths available in commercial OTDRs. Researchers at the University of Southampton have revived side scatter radiometry to non-destructively measure transmission loss in km-scale bandgap fibers. This technique works at any frequency which can be detected by the integrating sphere, demonstrated here in the 1.5 and 2 μm wavelength bands. The authors achieve 60 dB dynamic range in power (necessary if the fiber loss is several dB/km or more) and < 10 cm spatial resolution, which allows them to distinguish between losses due to structural defects and losses due to contamination of the glass. This sort of information is crucial for improving loss and manufacturing yield of hollow core bandgap fibers, and represents an important step forward if the promise of using such fibers for low nonlinearity, low latency optical communications is to become a reality.
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Article Information
Optical side scattering radiometry for high resolution, wide dynamic range longitudinal assessment of optical fibers
S. R. Sandoghchi, M. Petrovich, D. R. Gray, Y. Chen, N. V. Wheeler, T. D. Bradley, N. H. L. Wong, G. T. Jasion, J. Hayes, E. Numkam Fokoua, M. B. Alonso, S. M. Mousavi, D. J. Richardson, and F. Poletti
Opt. Express 23(21) 27960-27974 (2015) View: Abstract | HTML | PDF