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We report a Nested Antiresonant Nodeless hollow-core Fiber (NANF) operating in the first antiresonant passband. The fiber has an ultrawide operational bandwidth of 700 nm, spanning the 1240–1940 nm wavelength range that includes the O-, S-, C- and L- telecoms bands. It has a minimum loss of 6.6 dB/km at 1550 nm, a loss ≤7 dB/km between 1465–1655 nm and ≤10 dB/km between 1297–1860 nm. By splicing together two structurally matched fibers and by adding single mode fiber (SMF) pigtails at both ends we have produced a ∼1 km long span. The concatenated and connectorized fiber has an insertion loss of approximately 10 dB all the way from 1300 nm to 1550 nm, and an effectively single mode behavior across the whole spectral range. To test its data transmission performance, we demonstrate 50-Gb/s OOK data transmission across the O-to L-bands without the need for optical amplification, with bit-error-rates (BERs) lower than the 7% forward error correction (FEC) limit. With the help of optical amplification, 100-Gb/s PAM4 transmission with BER lower than the KP4 FEC limit was also achieved in the O/E and C/L bands, with relatively uniform performance for all wavelengths. Our results confirm the excellent modal purity of the fabricated fiber across a broad spectral range, and highlight its potential for wideband, low nonlinearity, low latency data transmission.

We report an effectively single mode tubular antiresonant hollow core fiber with minimum loss of ~25 dB/km at ~1200 nm, and an extremely wide low loss transmission window (lower than 30 dB/km loss from 1000 nm to 1400 nm and 6 dB bandwidth exceeding 1000 nm). Despite the relatively large mode field diameter of 32 µm, the fiber can be interfaced to SMF28 to produce fully connectorized samples. Exploiting an excellent modal purity arising from large modal differential loss and low intermodal coupling, we demonstrate penalty-free 10G on-off keying data transmission through 100m of fiber, at wavelengths of 1065, 1565 and 1963nm.

The fabrication of hollow core microstructured fibers is significantly more complex than solid fibers due to the necessity to control the hollow microstructure with high precision during the draw. We present the first model that can recreate tubular anti-resonant hollow core fiber draws, and accurately predict the draw parameters and geometry of the fiber. The model was validated against two different experimental fiber draws and very good agreement was found. We identify a dynamic within the draw process that can lead to a premature and irreversible contact between neighboring capillaries inside the hot zone, and describe mitigating strategies. We then use the model to explore the tolerance of the draw process to unavoidable structural variations within the preform, and to study feasibility and limiting phenomena of increasing the produced yield. We discover that the aspect ratio of the capillaries used in the preform has a direct effect on the uniformity of drawn fibers. Starting from high precision preforms the model predicts that it could be possible to draw 100 km of fiber from a single meter of preform.

The low intrinsic nonlinearity and low signal latency characteristic of Hollow Core Photonic Bandgap Fibers (HC-PBGFs) have fueled strong interest for data transmission applications. Whereas most research to date has looked at improving the optical performance of HC-PBGFs (e.g., reducing the loss, increasing the transmission bandwidth and achieving well-tempered modal properties through the suppression of surface mode resonances). In this study, we address the challenging problem of scaling up the fabrication of these fibers to multi-kilometer lengths—an indispensable step to prove this fiber technology as viable. We report the fabrication of low loss, wide bandwidth HC-PBGFs operating both in the conventional telecoms window (1.55 μm) and in the predicted region of minimum loss (2 μm), in lengths that substantially exceed the state of the art. At 2 μm, we obtained a 3.85 km long fiber with ≈3 dB/km loss and >160 nm wide 3 dB bandwidth. Additionally, we report an HC-PBGF operating at 1.55 μm with a length of just over 11 km, transmission bandwidth in excess of 200 nm and a longitudinally uniform loss of ≈5 dB/km, measured via cutback and an integrated scattering method. We used the latter fiber to demonstrate error-free, low-latency, direct-detection 10 Gb/s transmission across the entire C-Band as well as 20 Gb/s quadrature phase shift keyed transmission. These represent the first demonstrations of data transmission over a length of HC-PBGF exceeding 10 km.

We present a novel negative curvature antiresonant hollow core fibre design with the potential for low loss and very wide bandwidth. A low loss of 10.5 dB/km at 1550 nm is demonstrated, showing its potential for use in data transmission and high power beam delivery applications.

We demonstrate, to the best of our knowledge, the first optoelectronic oscillator that uses hollow-core photonic bandgap fiber (HC-PBGF) as a delay element of a sufficient length to allow for low-noise operation. We show experimentally that HC-PBGF can improve the temperature stability of the oscillator by a factor of more than 15, as compared to standard optical fiber. We also measured the oscillator's phase noise, allowing evaluation of the suitability of HC-PBGF for this application. Additionally, this Letter also provides, to the best of our knowledge, the first characterization of the temperature stability of a long length (>800 m in our Letter) of low-thermal sensitivity (2 ps/km/K) HC-PBGF wound on a spool.

We have demonstrated Raman frequency conversion and supercontinuum light generation in a hollow core Kagomé fiber filled with air at atmospheric pressure, and developed a numerical model able to explain the results with good accuracy. A solid-state disk laser was used to launch short pulses (~6ps) at 1030nm into an in-house fabricated hollow core Kagomé fiber with negative core curvature and both ends were open to the atmosphere. The fiber had a 150 THz wide transmission window and a record low loss of ~12 dB/km at the pump wavelength. By gradually increasing the pulse energy up to 250 µJ, we observed the onset of different Kerr and Raman based optical nonlinear processes, resulting in a supercontinuum spanning from 850 to 1600 nm at maximum input power. In order to study the pulse propagation dynamics of the experiment, we used a generalized nonlinear Schrödinger equation (GNLSE). Our simulations showed that the use of a conventional damping oscillator model for the time-dependent response of the rotational Raman component of air was not accurate enough at such high intensities and large pulse widths. Therefore, we adopted a semiquantum Raman model for air, which included the full rotational and vibrational response, and their temperature-induced broadening. With this, our GNLSE results matched well the experimental data, which allowed us to clearly identify the nonlinear phenomena involved in the process. Aside from the technological interest in the high spectral density of the supercontinuum demonstrated, the validated numerical model can provide a valuable optimization tool for gas based nonlinear processes in air-filled fibers.

Wide-bandwidth signal transmission with low latency is emerging as a key requirement in a number of applications, including the development of future exaflop-scale supercomputers, financial algorithmic trading and cloud computing. Optical fibres provide unsurpassed transmission bandwidth, but light propagates 31% slower in a silica glass fibre than in vacuum, thus compromising latency. Air guidance in hollow-core fibres can reduce fibre latency very significantly. However, state-of-the-art technology cannot achieve the combined values of loss, bandwidth and mode-coupling characteristics required for high-capacity data transmission. Here, we report a fundamentally improved hollow-core photonic-bandgap fibre that provides a record combination of low loss (3.5 dB km-1) and wide bandwidth (160 nm), and use it to transmit 373 x 40 Gbit s-1 channels at a 1.54 ms km-1 faster speed than in a conventional fibre. This represents the first experimental demonstration of fibre-based wavelength division multiplexed data transmission at close to (99.7%) the speed of light in vacuum

The modal content of 7 and 19 cell Kagomé anti resonant hollow core fibers (K-ARF) with hypocycloid core surrounds is experimentally investigated through the spectral and spatial (Ssup2/sup) imaging technique. It is observed that the 7 and 19 cell K-ARF reported here, support 4 and 7 LP mode groups respectively, however the observation that K-ARF support few mode groups is likely to be ubiquitous to 7 and 19 cell K-ARFs. The transmission loss of the higher order modes (HOMs) was measured via Ssup2/supand a cutback method. In the 7 cell K-ARF it is found that the LPsub11/suband LPsub21/submodes have approximately 3.6 and 5.7 times the loss of the fundamental mode (FM), respectively. In the 19 cell it is found that the LPsub11/submode has approximately 2.57 times the loss of the FM, while the LPsub02/submode has approximately 2.62 times the loss of the FM. Additionally, bend loss in these fibers is studied for the first time using Ssup2/supto reveal the effect of bend on modal content. Our measurements demonstrate that K-ARFs support a few mode groups and indicate that the differential loss of the HOMs is not substantially higher than that of the FM, and that bending the fiber does not induce significant inter modal coupling. A study of three different input beam coupling configurations demonstrates increased HOM excitation at output and a non-Gaussian profile of the output beam if poor mode field matching is achieved.

We present the first detailed investigation of modal properties in hypocycloid Kagome fibers; even with an optimized input launch, higher order modes propagate over long fiber lengths, indicative that these modes have low attenuation.

While hollow core-photonic crystal fibres are now a well-established fibre technology, the majority of work on these speciality fibres has been on designs with a single core for optical guidance. In this paper we present the first dual hollow-core anti-resonant fibres (DHC-ARFs). The fibres have high structural uniformity and low loss (minimum loss of 0.5 dB/m in the low loss guidance window) and demonstrate regimes of both inter-core coupling and zero coupling, dependent on the wavelength of operation, input polarisation, core separation and bend radius. In a DHC-ARF with a core separation of 4.3 µm, we find that with an optimised input polarisation up to 65% of the light guided in the launch core can be coupled into the second core, opening up applications in power delivery, gas sensing and quantum optics.

We study in detail the macrobending effects in a wide transmission bandwidth (~200nm) 19 cell hollow-core photonic bandgap fiber operating at 1550nm. Our results indicate low bend sensitivity over a ~130nm wide interval within the transmission window, with negligible loss (

We discuss our recent progress in hollow core-photonic bandgap fiber fabrication for high capacity transmission, focusing on two key areas: longitudinal uniformity and length upscaling as well as reviewing highlight results in data transmission.

We report an effectively singlemode tubular antiresonant hollow core fiber with >1000nm bandwidth and record-low loss of 25dB/km, fully connectorizable with SMF28. We demonstrate penalty-free data transmission at wavelengths of 1065, 1565 and 1963nm.

We present a Kagome hollow core fiber with record low loss (12.3dB/km at 1010nm), a wide 3dB bandwidth (150nm), low bend sensitivity and large mode field diameter (~30µm), tailored for high power delivery applications.

We demonstrate the insertion of a micromirror into the core of a hollow core photonic crystal fiber (HC-PCF). The micromirror is formed from a single mode fiber that has been tapered to fit into the hollow core and fixed in place using a fusion splicer. A large range of reflectivities higher than 4% was also achieved by silver-coating the silica tapered-fiber end-face using thermal evaporation. The current micromirror provides two key advantages over using a full-sized fiber splice to create a reflective interface. First, the tapered fiber tip can be coated to increase the reflectivity without degradation due to heating during the splicing process. Second, increased efficiency of input and output coupling is possible because of improved mode-field overlap with the fundamental mode of the HC-PCF. We show potential applications of micromirrors for the formation of microcavities in hollow-core fibers and for gas saturated absorption spectroscopy.

A photonic integrated mode coupler based on silicon-on-insulator is employed for mode division multiplexing (MDM) over a 193 m 19-cell hollow-core photonic bandgap fibre (HC-PBGF) with a -3 dB bandwidth >120 nm. Robust MDM transmissions using LP01 and LP11 modes, and two degenerate LP11 modes (LP11a and LP11b) are both experimentally verified. © The Institution of Engineering and Technology 2014.

We describe a compact, all fiber, frequency stabilized diode laser system at 2051 nm using CO2 gas-filled Kagome Hollow Core Fiber (HCF), capable of tuning continuously over four transitions in12C16O2: R(24), R(26), R(28), and R(30). This laser system has been designed for use in future space-based atmospheric monitoring using differential absorption lidar (DIAL). The fully spliced Kagome HCF gas cell is filled to 2 kPa CO2 partial pressure and we compare the observed CO2 lineshape features with those calculated using HITRAN, to quantify the properties of the CO2-filled fiber cell. In this first demonstration of Kagome HCF used in a fully sealed gas cell configuration for spectroscopy at 2 µm, we characterize the frequency stability of the locked system by beat frequency comparison against a reference laser. Results are presented for the laser locked to the center of the12C16O2 R(30) transition, with frequency stability of ∼40 kHz or better at 1 s, and a frequency reproducibility at the 0.4-MHz level over a period of > 1 month. For DIAL applications, we also demonstrate two methods of stabilizing the laser frequency ∼3 GHz from this line. Furthermore, no pressure degradation was observed during the ∼15-month period in which frequency stability measurements were acquired.

Current optical reflectometric techniques used to characterize optical fibers have to trade-off longitudinal range with spatial resolution and therefore struggle to provide simultaneously wide dynamic range (>20dB) and high resolution (

We report a novel approach to reconstruct the cross-sectional profile of fabricated hollow-core photonic bandgap fibers from scanning electron microscope images. Finite element simulations on the reconstructed geometries achieve a remarkable match with the measured transmission window, surface mode position and attenuation. The agreement between estimated scattering loss from surface roughness and measured loss values indicates that structural distortions, in particular the uneven distribution of glass across the thin silica struts on the core boundary, have a strong impact on the loss. This provides insight into the differences between idealized models and fabricated fibers, which could be key to further fiber loss reduction.

We demonstrate a longitudinally resolved Optical Side Scattering Radiometry (OSSR) technique to measure discrete and distributed scattering loss with >60dB dynamic range and 5cm spatial resolution. We apply it to a record-length 11km hollow core photonic band-gap fibre.

We present for the first time the group velocity dispersion of multiple distinguishable modes propagating in 3, 7 and 19 cell hollow core photonic bandgap fibres. Measurements are made by direct phase extraction from spectral domain low coherence interferometry.

4×10Gbps WDM transmission over low loss HC-PBGF at 2μm wavelengths is demonstrated using a 2mm long QCSE based InP MZM with Vπ of 6V and ER>20dB. An OSNR of 25dB is required to achieve error free transmission.

An optical transmission loop experiment over hollow-core fiber is demonstrated with 1.25Gb/s OOK, 40G DP-QPSK, 100G DP-QPSK modulation schemes over distances of 31.0 km, 74.8 km, 55.8 km respectively, using two fiber spans with 2.7 km and 3.5 km length.

Various simple anti-resonant, single cladding layer, hollow core fiber structures are examined. We show that the spacing between core and jacket glass and the shape of the support struts can be used to optimize confinement loss. We demonstrate the detrimental effect on confinement loss of thick nodes at the strut intersections and present a fabricated hexagram fiber that mitigates this effect in both straight and bent condition by presenting thin and radially elongated nodes. This fiber has loss comparable to published results for a first generation, multi-cladding ring, Kagome fiber with negative core curvature and has tolerable bend loss for many practical applications.

The 2-µm wave band is emerging as a potential new window for optical telecommunications with several distinct advantages over the traditional 1.55 mu m region. First of all, the hollow-core photonic band gap fiber (HC-PBGF) is an emerging transmission fiber candidate with ultra-low nonlinearity and lowest latency (0.3% slower than light propagating in vacuum) that has its minimum loss within the 2-mu m wavelength band. Second, the thulium-doped fiber amplifier that operates in this spectral region provides significantly more bandwidth than the erbium-doped fiber amplifier. In this paper, we demonstrate a single-channel 2-mu m transmitter capable of delivering >52 Gbit/s data signals, which is twice the capacity previously demonstrated. To achieve this, we employ discrete multitone modulation via direct current modulation of a Fabry-Perot semiconductor laser. The 4.4-GHz modulation bandwidth of the laser is enhanced by optical injection locking, providing up to 11 GHz modulation bandwidth. Transmission over 500-m and 3.8-km samples of HC-PBGF is demonstrated.

We present a novel method for validating the relative power value (MPI) of the Spatial and Spectral (S2) imaging technique. By applying corrections for spectral leakage and sampling errors we found the MPI determinations to be accurate within 1dB.

Optical injection locking is used to increase the modulation bandwidth and suppress chirp in a single-channel, single-polarization discrete multi-tone bit-loading-optimized transmitter. Transmission through a hollow-core photonic bandgap fiber with negligible signal degradation and distortion is demonstrated.

We report the fabrication of a record 11km length of photonic bandgap fiber supporting >200nm bandwidth with longitudinally uniform loss of ≈5dB/km at 1560nm and demonstrate error-free, low-latency, direct-detection 10Gbit/s transmission across the entire C-Band.

Specialty optical fibers, in particular microstructured and multi-material optical fibers, have complex geometry in terms of structure and/or material composition. Their fabrication, although rapidly developing, is still at a very early stage of development compared with conventional optical fibers. Structural characterization of these fibers during every step of their multi-stage fabrication process is paramount to optimize the fiber-drawing process. The complexity of these fibers restricts the use of conventional refractometry and microscopy techniques to determine their structural and material composition. Here we present, to the best of our knowledge, the first nondestructive structural and material investigation of specialty optical fibers using X-ray computed tomography (CT) methods, not achievable using other techniques. Recent advances in X-ray CT techniques allow the examination of optical fibers and their preforms with sub-micron resolution while preserving the specimen for onward processing and use. In this work, we study some of the most challenging specialty optical fibers and their preforms. We analyze a hollow core photonic band gap fiber and its preforms, and bond quality at the joint between two fusion-spliced hollow core fibers. Additionally, we studied a multi-element optical fiber and a metal incorporated dual suspended-core optical fiber. The application of X-ray CT can be extended to almost all optical fiber types, preforms and devices.

We report a novel OFDM-transmitter operating in the emerging 2µm waveband. Sub-FEC limit transmission of a 32QAM signal over 500m of both solid and hollow-core fiber was achieved and the generation of 30Gbits 64QAM demonstrated.

This paper presents WDM transmission at 2µm over 1.15km of HC-PBGF with wavelength channels selected to span a 36.3nm waveband. A total capacity of 81Gbit/s was achieved using 4 x 12.5Gbit/s NRZ-OOK external modulation and 4 x 7.7Gbit/s 4-ASK Fast-OFDM direct modulation signals.

X-ray computational tomography is demonstrated as a powerful non-destructive tool to image the internal structure of a hollow core photonic band-gap fibre and its preforms. The technique is applied to measure the deformation within a splice with unprecedented detail.

We present a new S2-based technique with potential for near real-time (1s) characterization of the modal-content of multimode fibers. We also demonstrate the identification and removal of measurement artifacts originating from reflections from optical components.

We describe low loss (50dB/km at 3.3µm) and low bend sensitivity mid-IR hollow core-photonic bandgap fiber. Gas sensing applications are highlighted by a methane spectrum recorded in our fiber.

Hollow-core photonic-bandgap fiber, fabricated from high-purity synthetic silica, with a wide operating bandwidth between 3.1 and 3.7µm, is reported. A minimum attenuation of 0.13dB/m is achieved through a 19-cell core design with a thin core wall surround. The loss is reduced further to 0.05dB/m following a purging process to remove hydrogen chloride gas from the fiber - representing more than an order of magnitude loss reduction as compared to previously reported bandgap-guiding fibers operating in the mid-infrared. The fiber also offers a low bend sensitivity of

To improve yield in fabricated HC-PBGFs we have studied morphology and longitudinal evolution of occasional, undesired defects causing localized loss. The short spatial and temporal duration of the defects seems indicative of residual preform contaminations.

We present a method to reconstruct the cross-sectional profile of fabricated hollow-core photonic bandgap fibers from SEM images. For the first time, numerical simulations show a good agreement with measured loss and surface mode position.

First experimental wavelength scaling in 19-cell core HC-PBGF indicates that the minimum loss waveband occurs at longer wavelengths than previously predicted. Record low loss (2.5dB/km) fibers operating around 2µm and gas-purging experiments are also reported.

We review the capacity records achieved using mode-division multiplexing in few-mode fiber and hollow-core photonic bandgap fibers. Currently the MDM-capacity record for both fiber types is 73.7 Tb/s, whereas per wavelength 960 Gb/s is achieved.

The longest coherent transmission distance of 0.95km, and highest distance×bandwidth product 19cell hollow-core photonic bandgap fiber (HC-PBGF) are demonstrated, indicating the potential for longer distance HC-PBGF high capacity coherent transmission applications.

Hollow-Core Photonic-Bandgap Fibres (HC-PBGFs) offer several distinct advantages over conventional fibres, such as low latency and radiation hardness; properties that make HC-PBGFs interesting for the high energy physics community. This contribution presents the results from a gamma irradiation test carried out using a new type of HC-PBGF that combines sufficiently low attenuation over distances that are compatible with high energy physics applications together with a transmission bandwidth that covers the 1550nm region. The radiation induced attenuation of the HC-PBGF was two orders of magnitude lower than that of a conventional fibre during a 67.5 hour exposure to gamma-rays, resulting in a radiation-induced attenuation of only 2.1dB/km at an accumulated dose of 940kGy.

The first demonstration of a hollow core photonic bandgap fiber (HC-PBGF) suitable for high-rate data transmission in the 2 µm waveband is presented. The fiber has a record low loss for this wavelength region (4.5 dB/km at 1980 nm) and a >150 nm wide surface-mode-free transmission window at the center of the bandgap. Detailed analysis of the optical modes and their propagation along the fiber, carried out using a time-of-flight technique in conjunction with spatially and spectrally resolved (S2) imaging, provides clear evidence that the HC-PBGF can be operated as quasi-single mode even though it supports up to four mode groups. Through the use of a custom built Thulium doped fiber amplifier with gain bandwidth closely matched to the fiber's low loss window, error-free 8 Gbit/s transmission in an optically amplified data channel at 2008nm over 290m of 19 cell HC-PBGF is reported.

International audience; Gas-filled hollow optical fiber references based on the P(13) transition of the ν1+ν3 band of C122H2 promise portability with moderate accuracy and stability. Previous realizations are corrected (

We formulate a simple model based on mass conservation to accurately predict the structural parameters of hollow-core photonic bandgap fibers from knowledge of the second stage preforms from which they are drawn. We show that combining this model with precalculated property maps can allow real-time prediction of the optical properties of manufactured fibers.

We report fabrication of the first low-loss, broadband 37-cell photonic bandgap fiber. Exploiting absence of surface modes and low cross-talk in the fiber we demonstrate mode division multiplexing over three modes with record transmission capacity.

Hollow core-photonic bandgap fiber, operating in the spectral region between 3 and 4 µm, is reported. Order of magnitude loss reduction is demonstrated (0.13dB/m) compared to previously reported fibers, combined with very low bend sensitivity.

We review our recent progress in the fabrication, characterization, modeling and splicing of wide transmission bandwidth hollow core photonic bandgap fibers and discuss their modal properties and potential for data transmission.

Photonic bandgap fibers (PBGF) potentially offer a very substantial increase of capacity per fiber over solid core fibers. We review transmission experiments using PBGF and their viability for next-generation transmissions systems.