7.7 dB/km transmission loss at 750 nm inhibited-coupling guiding hollowcore photonic crystal fibers

The last few years have seen the emergence of a new class of hollow-core photonic crystal fibers (HC-PCF) no longer relying on photonic bandgap guidance but on inhibited-coupling (IC) mechanism. The first specie of this fiber family took the form of Kagome-lattice [1]. The guiding rule for enhancement of such a guidance (minimizing the coupling between the core mode and cladding mode, i.e (φclad |Δn2| φcore) → 0) led to the introduction in 2010 of hypocycloidal (or negative curvature) core contour [2] in Kagome HC-PCFs where record loss values (8.5 dB/km at 1 μm [3]) have been demonstrated. Thanks to this design, three reasons explain the reduction of such a criterion: i) the HE11 mode field spatial overlap with silica is reduced to the tangent sections of the inner cups of the hypocycloid contour, ii) the larger perimeter of the hypocycloid contour results in a higher azimuthal-like number in the silica core-surround modes and hence, stronger transverse phase-mismatch with the core mode. iii) the spatial overlap between the core-mode with connecting nodes supporting low azimuthal number modes is strongly reduced. Recently, another hollow-core fiber design has been proposed that fully fulfils the mentioned features for IC guidance, relying on a tubular lattice with a one ring of isolated (with no connecting nodes) thin glass tubes [4]. Here, we report on the fabrication and characterization of ultra-low loss single-ring tubular lattice HC-PCFs (SR HC-PCF) guiding m the UV-VIS-NIR with absolute record loss value for HC-PCF at 750 nm with 7.7 dB/km, supplanting bandgap fiber performances in this spectral range.