Realizing low loss air core photonic crystal fibers by exploiting an antiresonant core surround

Abstract

The modal properties of an air core photonic crystal fiber which incorporates an anti-resonant feature within the region that marks the transition between the air core and the crystal cladding are numerically calculated. The field intensity at the glass/air interfaces is shown to be reduced by a factor of approximately three compared to a fiber with more conventional core surround geometry. The reduced interface field intensity comes at the expense of an increased number of unwanted core interface modes within the band gap. When the interface field intensity is associated with modal propagation loss, the findings are in accord with recent measurements on fabricated fibers which incorporate a similar antiresonant feature.

Models for guidance in kagome-structured hollow-core photonic crystal fibres

“…To minimise loss it is therefore important to ensure that the structure comprises struts of a uniform width, including those struts surrounding the core. We note that this is a different requirement for low loss than that in bandgap-guiding hollow-core fibres [15].…”

Design of low-loss and highly birefringent hollow-core photonic crystal fiber

“…The incorporation of elliptical features introduces more anti-crossing events within the band gap range, but for the 7-cell core size, low-loss propagation is still possible over a wavelength range extending over nearly 200nm centered on 1550nm. The number of unwanted anti-crossing events associated with the elliptical antiresonant coresurround inclusions is generically found to be fewer than is introduced by a continuously thick antiresonant core-surround ring such as the one considered in [16].…”

“…Low-loss guidance can be facilitated by the incorporation of antiresonant features within the core-surround. A non-birefringent antiresonant core-surround design, which is just a glass ring of appropriately chosen thickness, has been shown to substantially decrease the field intensity at the glass / air interfaces and therefore the loss [15,16]. A fabricated fiber which incorporates a coresurround which is a close approximation to this geometry has shown losses as low as 1.2dB/km [15,17].…”

Hollow-core photonic bandgap fibers: technology and applications

“…Here the core surround thickness is made to be as close as possible to the antiresonant condition, 2 /( 4 -1 ), T n =λ i.e., comparatively thicker than the struts in the photonic crystal cladding ( 3 T S տ ). The combination of a thick core surround with the reduction in field intensity at the core boundary resulting from enlarging the core from 7 to 19 missing cells led to the lowest properly documented loss in a HC-PBGF to date of 1.7 dB/km at a wavelength of 1560 nm [51,58] ( Figure 5E), with mention of losses as low as 1.2 dB/km at slightly longer wavelength in a similarly structured fibre made in a further article [56]. In parallel, alternative designs incorporating antiresonant nodes in a thin core surround were also investigated and shown to provide loss improvements [59,60] although the small 7c core employed in these works did not allow any further improvements in terms of setting a new record loss.…”