Abstract
Hollow-core fibers (HCFs) are a potentially transformative fiber technology, where light is confined within a hollow core surrounded by a cladding composed of air holes defined by glass membranes. Dramatic reductions in the minimum losses achieved in a HCF are driving forward their application in low-latency data transmission and ultra-high-power delivery, and maximizing their performance is of increasing interest. Here, we demonstrate that introducing an extremely small gas-induced differential refractive index (GDRI) between the gas within the core and cladding regions of a HCF enables dramatic changes to a HCF’s optical properties, including loss, bend loss, and modality. Within this work, we focus on a tubular HCF and demonstrate through experiment and simulations that the confinement loss of this fiber can be reduced by a factor of 5 using a differential pressure of only 6.7 bar. Understanding GDRI is critical for applications where the gas content within the fiber is actively controlled. Moreover, GDRI provides a new means to control the optical properties of a HCF post-fabrication, opening up new areas of design space and providing a tool to tailor and enhance the optical performance of even state-of-the-art HCFs.
Highlights
Hollow-core guidance reduces nonlinearity, increases bandwidth, and offers a route to ultra-low loss in optical fibers [1,2,3]
We have demonstrated that a very small refractive index change induced by different refractive indices between the gases in the core and cladding regions of a hollow core antiresonant fiber (HC-ARF) can significantly affect the fiber’s confinement loss, bend loss, and modality
For the fiber considered here, experimental results and simulations show that raising the gas pressure in the fiber core by 7 bars with respect to the cladding reduces confinement loss fivefold
Summary
Hollow-core guidance reduces nonlinearity, increases bandwidth, and offers a route to ultra-low loss in optical fibers [1,2,3]. To optimize a HCF’s attenuation, bend loss, and modality [11,12,13], several structural parameters, including the cladding tube number and size, can be modified during the fiber’s design and fabrication These geometry modifications are limited by performance trade-offs in fiber design and fabrication constraints [14,15], and an alternative approach for modifying a HCF’s optical properties is of great interest. For the first time to our knowledge, we explore a new regime whereby the gas content within the core of a HCF is controlled independently from that in the cladding holes to create a gas-induced differential refractive index (GDRI) between the core and cladding holes This can be achieved experimentally by filling these regions with gases of differing pressures and/or compositions.
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