In my last blog, I highlighted some theoretical research done by Francesco Poletti of the Optoelectronics Research Centre (ORC) at the University of Southampton (Southampton, England), who showed that a type of single-mode hollow-core antiresonant fiber (HC-ARF) could potentially transmit light at a loss lower than even that for the best solid silica fibers; in the new fiber, almost all the light is channeled in its hollow core.
I have since received a very informative email from Walter Belardi of the ORC, who notes that the hollow-core "nested-ring" design that I discussed in my last blog had originally been proposed by Belardi and Jonathan Knight at the beginning of 2014, both doing their research at the University of Bath (Bath, England).1, 2 In addition, Belardi and Knight already fabricated prototypes of the fiber and presented the results at this year's OFC, although "no improvement over the current 'single ring' technology has been shown to date due to the not-yet-mature fabrication technique," says Belardi.
What Poletti presented, and what I was using as source for my blog, was a very complete analysis of this same structure, including an estimation of the possible scattering losses.
Reducing leakage loss
Belardi also points out that the advantage of using the nested-ring design over other hollow-core anti-resonant fibers is not related to fiber breakdown due to scattering at high optical power levels. "The fraction of optical power in glass does not consistently change when you pass from a single ring to a nested-ring design," says Belardi. In fact, single-ring designs as well show a fraction of power in glass of less than 0.01%;2, 3 this was demonstrated by a group at Heriot-Watt University (Edinburgh, Scotland).4
The great advantage of the nested-ring design, explains Belardi, is that it reduces confinement (leakage) losses. "What is interesting here is that with this design we will be able to use this kind of optical fiber even at much shorter wavelengths: the visible, and maybe the UV," he says.
More info can be found at Belardi's website: www.walterbelardi.com.
REFERENCES:
1. W. Belardi and J. C. Knight, "Negative curvature fibers with reduced leakage loss," OFC 2014, San Francisco 9-13 March 2014.
2. W. Belardi and J. C. Knight, "Hollow antiresonant fibers with reduced attenuation," Optics Letters 39, 1853-1856 (2014).
3. W. Belardi and J. C. Knight, "Effect of core boundary curvature on the confinement losses of hollow antiresonant fibers," Optics Express, Vol. 21(19), pp. 21912-21917 (2013).
4. P. Jaworski et al., "Picosecond and nanosecond pulse delivery through a hollow-core Negative Curvature Fiber for micro-machining applications," Optics Express 21, 22742-22753 (2013).
