1-km Hollow-Core Fiber With Loss at the Silica Rayleigh Limit in the Green Spectral Region

Abstract

In this letter, we report on the fabrication of an Inhibited-Coupling guiding fiber with a cladding amorphous lattice of nine tubes exhibiting record loss of 13.8 dB/km in the green spectral region. The fiber has been drawn over a length of 1 km with high stability during the drawing process (outer diameter variation of ± 0.2%). To our knowledge, this is the first time that loss figures as low as the fundamental Rayleigh scattering limit of silica are reported for a hollow-core optical fiber in the green spectral range. Also, this is the first report on a tubular fiber draw over such a long length. Additionally, this is the lowest loss figure ever demonstrated in any kind of optical fibers in this spectral region. Index Terms-Fiber optics, photonic crystal fiber, hollow-core fiber. I. INTRODUCTION EDUCING the loss of optical fibers has been a major preoccupation since their advent and, therefore, motivates intense research on both solid-and hollow-core optical fibers. In addition to the great attention given to the near-and mid-infrared ranges-whose efforts allowed to attain attenuation levels as low as 0.14 dB/km around 1550 nm for conventional solid-core fibers [1]-, improvements on the fiber optics technology in the visible spectral region are still required for addressing the needs of a wide set of growing application fields, since the loss of solid-core fibers in the visible are much higher than the ones obtained in the infrared due to the greater influence of the Rayleigh scattering for shorter wavelengths. For example, attenuation values in the green spectral range are around 30 dB/km for commercial single-mode fibers and around 20 dB/km for endlessy single-mode photonic crystal fibers [2-4] optimized for the visible range, which are higher than the limit, 13 dB/km, set be Rayleigh scattering in bulk silica. These improvements are particularly important for applications in the green spectral range (GSR) since, for instance, lasers emitting in the GSR are often used in the context of photovoltaic solar microprocessing for scribing and cutting in the solar cell fabrication process [5]. Moreover, lasers emitting in the visible spectral region are increasingly important for biological applications such as cytometry, DNA sequencing and confocal microscopy. Hence, improvements on the transmission capabilities of optical fibers in the visible range would bring ease of use, precision amelioration and cost effectiveness to these applications and, therefore, are highly desirable.

Hollow core optical fibres with comparable attenuation to silica fibres between 600 and 1100 nm

“…The four yellow circular markers indicate the typical loss of commercial solid core fibres between 600 and 1060 nm (C1: single-mode fibre at red visible wavelengths 47 ; C2: large-area single-mode photonic crystal fibre LMA-5 48 ; C3: highly multimode graded-index OM5 fibre for datacoms 49 ; C4 single mode high numerical aperture fibre for 980 nm pump delivery 50 ). The blue diamond markers represent the current state-of-the-art loss in hollow-core fibres -H1: Chafer et al 51 ; H2: Debord et al 52 ; H3: Debord et al 24 ; H4: Chafer et al 23 ; H5: Maurel et al 53 ; and H6: Gao et al 32 .…”

“…et al 23 , respectively) have all a 'tubular' single ring structure and loss in the 7-15 dB km −1 . Fibre H5 (Maurel et al 53 ) has a Kagome structure and a loss of 8.5 dB km −1 , while the two fibres in H6 (Gao et al 32 ) have a lower loss thanks to the addition of a nested membrane associated with the conjoined tubular structure.…”

Low-loss single-mode hybrid-lattice hollow-core photonic-crystal fibre

“…These principles provided conceptual tools to introduce the hypocycloid core contour (i.e., negative curvature) concept 8 , 9 , which enabled a dramatic enhancement in the light confinement of these fibres, as exemplified by IC-guiding hypocycloid core-contour Kagome lattice HCPCFs and single-ring tubular-lattice (SR-TL) HCPCFs 10 . Experimental illustrations of the negative curvature core-contour impact are the reduction in loss figures in Kagome HC-PCFs down to 8.5 dB/km at 1030 nm 11 , which is considerably lower than the dB/m loss level reported in the first Kagome fibre 12 , and the realisation of optimised SR-TL HCPCFs with a transmission loss as low as 7.7 dB/km at 780 nm 7 and 13.8 dB/km at 539 nm 13 . Among the noteworthy conclusions of this effort is the fact that for wavelengths shorter than ~1 µm, the transmission loss is no longer limited by the cladding design.…”

Hollow-Core Fibers with Specific Modal Operation and Low Loss in the Short-Wavelength Range

“…The microstructure of the SR-TL HC-PCFs encompasses a single ring of nontouching tubes which delimits a fiber core with a hypocycloid form and no connecting nodes. Noteworthy, these characteristics benefit IC guidance and allow the accomplishment of ultralow loss figures, e.g., the values of 7.7 dB/km at 780 nm, reported by Debord et al [3], and of 13.8 dB/km at 539 nm, described by Chafer et al [12]. At shorter wavelengths, the attenuation of SR-TL HC-PCFs has been accounted as 150 dB/km at 343 nm, 75 dB/km at 355 nm [12], and 100 dB/km at 218 nm [13].…”

“…Noteworthy, these characteristics benefit IC guidance and allow the accomplishment of ultralow loss figures, e.g., the values of 7.7 dB/km at 780 nm, reported by Debord et al [3], and of 13.8 dB/km at 539 nm, described by Chafer et al [12]. At shorter wavelengths, the attenuation of SR-TL HC-PCFs has been accounted as 150 dB/km at 343 nm, 75 dB/km at 355 nm [12], and 100 dB/km at 218 nm [13]. Indeed, as the loss of SR-TL HC-PCFs in the short wavelength range is limited by the surface scattering loss (SSL) [3], further decrease of the attenuation values in the visible and ultraviolet range should rely on the improvement of the core surface quality.…”