A New Hollow-Core Optical Fiber

The novel fibers’ latest advances have under­lined the technology’s potential for next generation optical inter­ferometric systems and sensors. Hollow-core optical fibers combine the free-space propa­gation perfor­mance of the most advanced inter­ferometers with the length scales of modern optical fibers by guiding light around bends in an air or vacuum filled core. Researchers are engaging with industry partners, colla­borating with the National Physical Labora­tory and exploi­ting a UK network in the Airguide Photonics programme as they further expand the impact of the discovery.

Illustration of the new antiresonant hollow-core optical fibers. (Source: U. Southampton)

Francesco Poletti, head of the hollow-core fiber group, says: “By eliminating the glass from the centre of the fiber, we have also eliminated the physical mechanisms by which the polari­zation purity of an input beam can be degraded. As a result, our fibers provide qualities that represent a paradigm shift toward a huge leap in perfor­mance. With an atte­nuation as low as 0.28 dB/km and the prospect of soon achieving levels poten­tially below the Rayleigh scattering limit of conven­tional fibres, such waveguiding structures could soon provide vacuum-like guidance purity and environmental insensi­tivity at bespoke wavelengths and over hundreds of kilo­meters for the next generation of photonics-enabled scientific instruments.”

Propagating light waves while preserving all of their essential attri­butes is a funda­mental concern for all appli­cations that use light to sense the environment or to transmit data and power. High-perfor­mance inter­ferometers, gyroscopes and frequency combs use the wavelength of light as a miniature ruler to measure distances, rotation speed and time with incredibly accurate precision. They all rely on the trans­mission of light beams with the highest possible spatial, spectral and polari­zation purity.

To achieve the best possible performance, scientists currently need to propagate light through free-space in a vacuum, such as, for example, in the four-kilometer arms of the Laser Inter­ferometer Gravi­tational-Wave Obser­vatory LIGO in the US. However, these advanced inter­ferometers are extremely expensive and often impractical at even much shorter length scales. Glass optical fibers offer a more pragmatic and portable alter­native in sensing technologies but degrade polari­zation purity and suffer from detri­mental nonlinear effects.

Hollow-core fibers overcome all of these challenges to enhance the potential of optical inter­ferometric systems and sensors, for example within optical gyroscopes that form the core of inertial navigation systems or for the flexible delivery and coherent combi­nation of intense polarized radiation for the next generation of MegaWatt lasers. This latest research – sponsored by the European Union funded LightPipe Project – builds upon a decades of work at the Zepler Institute’s renowned Opto­electronics Research Centre.

The center and its director Sir David Payne have played a leading role in the development of optical fiber tech­nology for appli­cations requiring control of the polari­zation states of light. Work in this area also led to the creation of spinout company Fibercore, which has established itself as a global market leader in the production of polarisation maintaining optical fibers. Payne said, “There are numerous appli­cations in optics that require strict polari­zation control, such as when two beams interfere to sense tiny changes caused by gravi­tational waves, or rotation sensing in fiber gyroscopes. The ideal way to transport light is in an optical fiber, but that normally leads to an uncertain, wandering polari­zation state and drift in the sensor. It is a great surprise to find that certain types of hollow-core fiber can preserve a stable polari­zation over long distances and this obser­vation will have a huge impact on next-gene­ration optical sensors. Hollow-core fibers continue to amaze us in ways that appear as if the fiber was not there – just like a vacuum with no diffrac­tion.” (Source: U. Southamptom)

Reference: A. Taranta et al.: Exceptional polarization purity in antiresonant hollow-core optical fibres, Nat. Phot., online 11 May 2020; DOI: 10.1038/s41566-020-0633-x

Link: Hollow Core Fiber Group, Optoelectronics Research Centre, University of Southampton, Southampton, UK

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