Hollow-core Photonic Bandgap Fiber Research Articles

Multi-kilometer Long, Longitudinally Uniform Hollow Core Photonic Bandgap Fibers for Broadband Low Latency Data Transmission

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.

Accurate modelling of fabricated hollow-core photonic bandgap fibers.

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.

Experimental Demonstration of Improved Equalization Algorithm for IM/DD Fast OFDM

We experimentally investigate the fast orthogonal frequency division multiplexing (OFDM) scheme with improved performance in compensating asymmetric channel impulse response using single-tap equalizers. We demonstrate for the first time 18 Gb/s intensity modulation and direct detection optical fast OFDM over both 80 km standard single-mode fiber at $1.55~ \mu \text{m}$ and 1.15 km hollow-core photonic bandgap fiber at $2~\mu \text{m}$ . The results show that the proposed algorithm has better performance and lower complexity than the previous schemes under asymmetric channel impulse responses. In addition, the results validate that the emerging 2 $\mu \text{m}$ fiber-optic system can achieve the performance close to that of the 1.55 $\mu \text{m}$ system.

High-speed detection at two micrometres with monolithic silicon photodiodes

With continued steep growth in the volume of data transmitted over optical networks there is a widely recognized need for more sophisticated photonics technologies to forestall a ‘capacity crunch’[1]. A promising solution is to open new spectral regions at wavelengths near 2µm and to exploit the long-wavelength transmission and amplification capabilities of hollowcore photonic-bandgap fibres[2,3] and the recently available thulium-doped fibre amplifiers[4]. To date, photodetector devices for this window have largely relied on III-V materials[5] or, where the benefits of integration with silicon photonics are sought, GeSn alloys, which have been demonstrated thus far with only limited utility[6-9]. Here, we describe a silicon photodiode operating at 20 Gb/s in this wavelength region. The detector is compatible with standard silicon processing and is integrated directly with silicon-on-insulator waveguides, which suggests future utility in silicon-based mid-infrared integrated optics for applications in communications.

Broadband supercontinuum generation using a hollow optical fiber filled with copper-ion-modified DNA.

We experimentally demonstrated supercontinuum generation through a hollow core photonic bandgap fiber (HC-PBGF) filled with DNA nanocrystals modified by copper ions in a solution. Both double-crossover nano DNA structure and copper-ion-modified structure provided a sufficiently high optical nonlinearity within a short length of hollow optical fiber. Adding a higher concentration of copper ion into the DNA nanocrystals, the bandwidth of supercontinuum output was monotonically increased. Finally, we achieved the bandwidth expansion of about 1000 nm to be sufficient for broadband multi-spectrum applications.

Design, Simulation, and Optimization of Acetylene Gas Sensor Using Hollow-Core Photonic Bandgap Fiber

Design, Simulation, and Optimization of Acetylene Gas Sensor Using Hollow-Core Photonic Bandgap Fiber

Fabrication and Characterization of Long-Period Gratings in Hollow Core Fibers by Electric Arc Discharge

Recently, the fabrication of long-period gratings (LPGs) in hollow-core air-silica photonic bandgap fibers by means of pressure assisted electrode arc discharge (EAD) technique have been presented. The EAD procedure properly combined with air pressure inside fiber holes enables the localized modification of hole size and shape in both core and cladding region avoiding holes collapsing. LPGs are fabricated with a step-by-step approach by periodically repeated EAD treatment. In this paper, the role of pressure inside the fiber holes as well as the effect of the grating pitch on the transmitted spectra have been experimentally investigated to achieve the design criteria of novel hollow core devices. An appropriate perturbation of fiber structure (core and/or cladding) may change the field profile of the fiber modes and cause light coupling from the fundamental mode to higher order modes. Here, the experimental demonstration of LPG prototypes with different features exhibiting attenuation bands with depth up to 12 dB are reported. Finally, the resonant wavelength dependence on local temperature and strain changes are experimentally investigated. We believe that the fabrication of LPGs-based devices in hollow core optical fibers enable new functionalities hitherto not possible.

Ultra-sensitive all-fibre photothermal spectroscopy with large dynamic range.

Photothermal interferometry is an ultra-sensitive spectroscopic means for trace chemical detection in gas- and liquid-phase materials. Previous photothermal interferometry systems used free-space optics and have limitations in efficiency of light–matter interaction, size and optical alignment, and integration into photonic circuits. Here we exploit photothermal-induced phase change in a gas-filled hollow-core photonic bandgap fibre, and demonstrate an all-fibre acetylene gas sensor with a noise equivalent concentration of 2 p.p.b. (2.3 × 10−9 cm−1 in absorption coefficient) and an unprecedented dynamic range of nearly six orders of magnitude. The realization of photothermal interferometry with low-cost near infrared semiconductor lasers and fibre-based technology allows a class of optical sensors with compact size, ultra sensitivity and selectivity, applicability to harsh environment, and capability for remote and multiplexed multi-point detection and distributed sensing.

Acoustic Pressure Sensing with Hollow-Core Photonic Bandgap Fibers

Recently, photonic crystal fibers (PCFs) have attracted many researchers because of their special characteristics, and design flexibility that cannot be realized by conventional fibers. One of the important areas of research is the optical fiber hydrophones. In this paper, the finite element solver COMSOL multiphysics (FES) is used to study and compare the phase sensitivity to acoustic pressure of a hollow-core photonic band gap fiber (HC-PBF), and a conventional single-mode fiber (SMF) for various acoustic pressures in the frequency range from 10 kHz to 50 kHz. Simulation results of the investigated optical fibers show that the normalized responsivity (NR) to acoustic pressure of the investigated HC-PBF, and SMF are-344 dB, and-366 dB, respectively.

Phase Sensitivity to Acoustic Pressure of Microstrustured Optical Fibers: A Comparison Study

Recently, photonic crystal fibers (PCFs) have attracted many researchers because of their unique properties, and design flexibility that can’t be realized by conventional fibers. One of the fruitful areas of research is the optical fiber hydrophone. In this paper, the finite element solver (FES), COMSOL multiphysics, is used to study and compare the response to acoustic pressure of a hollow-core photonic band gap fiber (HC-PBF), a solid-core photonic crystal fiber (SC-PCF), and a conventional single-mode fiber (SMF) for different acoustic pressures in the frequency range from 10 kHz to 50 kHz. The key structural factors affect the sensitivity to acoustic pressure (S) of the microstructured fibers are studied and a mathematical formula describes the relation of S and the dominant structural factor is proposed. Simulation results of the investigated optical fibers show that the normalized responsivity (NR) of the HC-1550, LMA-5, and SMF are -344 dB, -367.5 dB, and -366 dB, respectively. The proposed simulation results are in good agreement with published theoretical and experimentally measured results. The proposed results indicate the significance of the HC-PBFs in the future hydrophone systems and are useful for the design of microstrustured optical fibers for sensing applications.

Gas-filling dynamics of a hollow-core photonic bandgap fiber for nonvacuum conditions

This paper introduces an analytical model for the pressure-driven delivery of gas mixtures consisting of multiple components of gases with varied viscosity to hollow-core photonic bandgap fibers. Photonic bandgap fibers have been used for all-fiber spectroscopy configurations for gases like methane and acetylene that are relevant to the development of all-fiber chemical sensors. The unique structure of these fibers permits the formation of a gas cell with micrometer-scaled volumes to promote strong interaction with the guided optical field supported by increased interaction lengths and low optical losses. The influence of the effective viscosity of the delivered gas is significant to the fiber-filling process and is emphasized in this discussion. Unlike previous work, this investigation is not limited to closed-loop configurations with low gas flows, single-gas delivery systems, or vacuum conditions. The findings of this study are relevant to applications employing spectroscopy principles including manufacturing process monitoring for integrated fibers possessing metal–oxide junctions, antiresonant fibers, and suspended-core-type fiber evanescent-field Raman spectroscopy applications. The experimental results agree with the predictions for the case of hydrodynamic flow under nonvacuum conditions. The dynamics of the gas delivery to the perforated optical fiber were predicted and demonstrated for a 0.365 m fiber length with a 12.5 μm core. This core region was occupied by a preliminary gas, which affected the filling rates. The effective viscosities for the pure gas (acetylene) produced filling rates of 6 s (at 10 psi) and 11 s (at 5 psi). However, mixed gases (acetylene balance nitrogen) presented viscosity-dependent delays of 0.3 and 0.5 s.

100 Gbit/s WDM transmission at 2 µm: transmission studies in both low-loss hollow core photonic bandgap fiber and solid core fiber.

We show for the first time 100 Gbit/s total capacity at 2 µm waveband, using 4 × 9.3 Gbit/s 4-ASK Fast-OFDM direct modulation and 4 × 15.7 Gbit/s NRZ-OOK external modulation, spanning a 36.3 nm wide wavelength range. WDM transmission was successfully demonstrated over 1.15 km of low-loss hollow core photonic bandgap fiber (HC-PBGF) and over 1 km of solid core fiber (SCF). We conclude that the OSNR penalty associated with the SCF is minimal, while a ~1-2 dB penalty was observed after the HC-PBGF probably due to mode coupling to higher-order modes.

High-Capacity Directly Modulated Optical Transmitter for 2-μm Spectral Region

The 2-μm wave band is emerging as a potential new window for optical telecommunications with several distinct advantages over the traditional 1.55 μm 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-μm 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-μm 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.

Gaseous Oxygen Detection Using Hollow-Core Fiber-Based Linear Cavity Ring-Down Spectroscopy

We demonstrate a method for the calibration-free and quantitative analysis of small volumes of gaseous samples. A 10 m hollow-core photonic bandgap fiber is used as the sample cell (volume = 0.44 $\mu$ L) and is placed inside a linear resonator setup. The application of cavity ring-down spectroscopy and in consideration of rather small coupling losses, this leads to an increased effective optical path length of up to 70 m. This implies a volume per optical interaction path length of 6.3 nL $\cdot$ m $^{-1}$ . We used tunable diode laser spectroscopy at 760 nm and scanned the absorption for oxygen sensing. The optical loss due to sample absorption is obtained by measuring the ring-down time of light propagating inside the cavity. The resultant absorption coefficient shows a discrepancy of only 5.1% comparing to the HITRAN database. This approach is applicable for sensitive measurements if only submicroliter sample volumes are available.

MicroStructure Element Method (MSEM): viscous flow model for the virtual draw of microstructured optical fibers.

We propose a new method to accurately model the structural evolution of a microstructured fiber (MOF) during its drawing process, given its initial preform structure and draw conditions. The method, applicable to a broad range of MOFs with high air-filling fraction and thin glass membranes, is an extension of the Discrete Element Method; it determines forces on the nodes in the microstructure to progressively update their position along the neck-down region, until the fiber reaches a final frozen state. The model is validated through simulation of 6 Hollow Core Photonic Band Gap Fibers (HC-PBGFs) and is shown to predict accurately the final fiber dimensions and cross-sectional distortions. The model is vastly more capable than other state of the art models and allows fast exploration of wide drawing parameter spaces, eliminating the need for expensive and time-consuming empirical parameter scans.

Investigation on the Effect of Underwater Acoustic Pressure on the Fundamental Mode of Hollow-Core Photonic Bandgap Fibers

Recently, microstructured optical fibers have become the subject of extensive research as they can be employed in many civilian and military applications. One of the recent areas of research is to enhance the normalized responsivity (NR) to acoustic pressure of the optical fiber hydrophones by replacing the conventional single mode fibers (SMFs) with hollow-core photonic bandgap fibers (HC-PBFs). However, this needs further investigation. In order to fully understand the feasibility of using HC-PBFs as acoustic pressure sensors and in underwater communication systems, it is important to study their modal properties in this environment. In this paper, the finite element solver (FES) COMSOL Multiphysics is used to study the effect of underwater acoustic pressure on the effective refractive indexneffof the fundamental mode and discuss its contribution to NR. Besides, we investigate, for the first time to our knowledge, the effect of underwater acoustic pressure on the effective areaAeffand the numerical aperture (NA) of the HC-PBF.

谐振式光子带隙光纤陀螺一体化方案

谐振式光子带隙光纤陀螺一体化方案

空芯光子带隙光纤散射损耗特性及结构优化研究

空芯光子带隙光纤散射损耗特性及结构优化研究

InP-Based Active and Passive Components for Communication Systems at 2 μm

Progress on advanced active and passive photonic components that are required for high-speed optical communications over hollow-core photonic bandgap fiber at wavelengths around 2 μm is described in this paper. Single-frequency lasers capable of operating at 10 Gb/s and covering a wide spectral range are realized. A comparison is made between waveguide and surface normal photodiodes with the latter showing good sensitivity up to 15 Gb/s. Passive waveguides, 90° optical hybrids, and arrayed waveguide grating with 100-GHz channel spacing are demonstrated on a large spot-size waveguide platform. Finally, a strong electro-optic effect using the quantum confined Stark effect in strain-balanced multiple quantum wells is demonstrated and used in a Mach-Zehnder modulator capable of operating at 10 Gb/s.

Splice Loss Optimization of a Photonic Bandgap Fiber via a High V-Number Fiber

We report on a low-loss fusion splice between a hollow-core photonic bandgap fiber (NKT's HC-1550-02) and a conventional single mode fiber (Corning's SMF28) using a high V-number intermediate fiber. Compared to the commonly used fiber postprocessing techniques, the intermediate fiber method offers a new adjusting degree of freedom of V-numbers, enabling the reduction of coupling loss to 0.35 dB. Experimentally, a low fusion splice loss of 0.63 dB has been achieved between Nufern's SM1950 (V =2.836) and HC-1550-02 fiber, resulting in an overall insertion loss of 0.73 dB from SMF28 to HC-1550-02 fiber. We believe this is the lowest splice loss value reported for HC-1550-02 fiber using an arc splicer, on the aspect of both using a step-index solid-core fiber (0.63 dB) and a SMF28 fiber (0.73 dB).