Hollow-core Optical Fiber Research Articles

Performance of silica single mode hollow-core optical fibers in optical communications

Performance of silica single mode hollow-core optical fibers in optical communications

Multicomponent trace gas detection with hollow-core fiber photothermal interferometry and time-division multiplexing

We report a multicomponent photothermal gas sensor with a conjoined-tube hollow-core optical fiber gas cell. With a common Fabry-Perot probe interferometer and a common gas cell, simultaneous detection of methane, acetylene and ammonia can be achieved by time-division multiplexing. Experiments with a 15-cm-long hollow-core fiber demonstrated noise-equivalent concentration of 24.2 parts-per-billion (ppb) for methane, 11.6 ppb for acetylene, and 46.1 ppb for ammonia. The dynamic range is measured to be around 5 orders of magnitude. The crosstalk issue is addressed by spectrum fitting. Assisted with an air pump and a compact gas chamber, the response time of less than 10 s is achieved.

Multi-parameter temperature prediction based on optical fiber filled with CsPbX3 QDs

To expand the range of application of quantum dots in the field of temperature sensing, this paper proposed three kinds of temperature sensors based on CsPbX3 (X = Br, Br/I, and I) quantum dots filling into hollow-core fibers. Based on the photoluminescence properties of quantum dots, quantum dots were prepared by the hydrothermal method and later filled in hollow-core optical fibers to fabricate three kinds of temperature sensors. In this paper, the temperature dependence of photoluminescence of quantum dot sensors has been studied. In detail, temperature variation characteristics of integrated photoluminescence, full width at half maximum, and central wavelength of the photoluminescence spectrum have been investigated. It is found that the integrated photoluminescence, full width at half maximum, and central wavelength all fluctuate regularly with temperature. In this paper, the support vector regression method is employed to determine the mathematical relation between integrated photoluminescence, full width at half maximum, central wavelength, and temperature. Later, the three parameters are used to achieve fast and accurate temperature measurement. The experimental results show that in the range of 30–100⁡°C, the precision of the optical fiber temperature sensors based on quantum dots is below 2⁡°C.

Near-Maximal Two-Photon Entanglement for Optical Quantum Communication at 2.1μm

The 2- to 2.5-$\ensuremath{\mu}$m waveband enjoys reduced solar background and low propagation losses in the atmosphere and hollow-core optical fibers. However, harnessing these advantages for optical quantum communications has proved challenging due to a lack of suitable quantum light sources and detectors. The authors demonstrate in this waveband a source of entangled photons that is suitable for generating secure keys for quantum key distribution, and provide device-independent certification of the entanglement. These results are promising for the future implementation of device-independent secure optical quantum communications in daylight.

Dissolved gas sensing using an anti-resonant hollow core optical fiber

Sensors that measure dissolved gases directly are needed for environmental, industrial, and biomedical applications. Here we present a hollow core fiber optic sensor capable of measuring dissolved methane gas in liquids using only nanoliters of sample gas. The sensor is based on an anti-resonant hollow core fiber combined with a permeable capillary membrane inlet that extracts gas from the liquid for analysis. Using a small capillary inlet for gas extraction is only possible due to the small amount of sample gas needed for analysis, and it presents new possibilities for dissolved gas analysis in a simple, robust, and compact sensor configuration. We demonstrate the sensing technique using wavelength modulation spectroscopy and measure methane dissolved in water with a 1σ lower detection limit of 230 ppb, a resolution of 45 ppb, and a response time of ∼8min.

An All-Optical Vector Magnetic Field Sensor Based on Magnetic Fluid and Side-Polished Hollow-Core Optical Fiber

We demonstrate an optical fiber vector magnetic field sensor based on Mach-Zehnder interferometer by splicing a section of side-polished hollow-core fiber between two sections of single-mode fiber. As a varied magnetic field is applied to the magnetic fluid encapsulated sandwiched structure, the transmission spectra of the sensor will vary with the intensity and the direction of the magnetic field. In our experiments, at the incident light wavelength around 1510 nm, the magnetic field orientation sensitivity and intensity sensitivity are 180 pm/° and 240 pm/mT, respectively. In addition, a high contrast of about 20 dB between the signal interference dip with the noise interference dip is obtained in our experiments. The proposed all-optical fiber magnetic field sensor has the advantages of simple structure, compact size, low cost and easy fabrication.

Azimuthally asymmetric tubular lattice hollow-core optical fiber

A new, to the best of our knowledge, hollow-core optical fiber based on a tube lattice geometry is proposed. The fiber cross section is formed by eight tubes with five different thicknesses, and the guidance mechanism is based on the inhibited coupling phenomenon. As such, its transmittance spectrum displays low-loss windows intercalated with high-loss regions, each of the latter related to specific core-cladding modal couplings. The spectral behavior of the straight and bent waveguide is numerically analyzed. Simulations on different curvature radii and directions (angles) show the core mode displacement toward the outer side of the curvature and its impact on the spectral shift of the high-loss wavelengths. The different response of each tube resonance is investigated and discussed. The proposed structure identifies a new and promising path for the development of directional curvature sensors.

Hollow-core antiresonant terahertz fiber-based TOPAS extruded from a 3D printer using a metal 3D printed nozzle

We report the use of a terahertz (THz) transparent material, cyclic olefin copolymer (COC or TOPAS), for fabricating a hollow-core antiresonant fiber that provides an electromagnetic wave guidance in the THz regime. A novel fabrication technique to realize a hollow-core antiresonant polymer optical fiber (HC-ARPF) for THz guidance is proposed and demonstrated. The fiber is directly extruded in a single-step procedure using a conventional fused deposition modeling 3D printer. The fiber geometry is defined by a structured nozzle manufactured with a metal 3D printer, which allows tailoring of the nozzle design to the various geometries of microstructured optical fibers. The possibility to use the HC-ARPF made from TOPAS for guiding in the THz region is theoretically and experimentally assessed through the profile of mode simulation and time-frequency diagram (spectrogram) analysis.

Terahertz Hollow-Core Optical Fibers for Efficient Transmission of Orbital Angular Momentum Modes

Terahertz (THz) radiation has recently received a lot of interests in science and technology. The potential of orbital angular momentum (OAM) of light in the THz region is a novel idea for researchers with increasing applications in broadband communications. THz waveguides have rarely been reported to generate and guide OAM modes. In this paper, we propose for the first time hollow-core optical fibers consist of circular air-hole arrays for guiding THz OAM modes with the topological charge order up to l = 3. Using numerical simulations, two low-loss transmission windows over 0.47 - 0.65 THz (window1) and 0.95 - 1.20 THz (window2) are recognized to guide OAM modes. Results show that both windows of the THz fiber exhibit the flat near-zero dispersion as well as low confinement loss (~ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> dB/cm) with simultaneously high purity of the OAM modes (higher than 90%). Finally, two designs of THz optical fibers consist of one and two rings of air-hole arrays in their cladding are examined and it is shown that difference of the confinement loss and the modal purity between two designs are negligible. This implies that hollow-core optical fibers consist of one ring of air-hole array in their cladding are very promising for efficient transmission of OAM modes in the THz region.

Gas-induced differential refractive index enhanced guidance in hollow-core optical fibers

Hollow-core fibers (HCFs) are a potentially transformative fiber technology, where light is confined within a hollow core surrounded by a cladding composed of air holes defined by glass membranes. Dramatic reductions in the minimum losses achieved in a HCF are driving forward their application in low-latency data transmission and ultra-high-power delivery, and maximizing their performance is of increasing interest. Here, we demonstrate that introducing an extremely small gas-induced differential refractive index (GDRI) between the gas within the core and cladding regions of a HCF enables dramatic changes to a HCF’s optical properties, including loss, bend loss, and modality. Within this work, we focus on a tubular HCF and demonstrate through experiment and simulations that the confinement loss of this fiber can be reduced by a factor of 5 using a differential pressure of only 6.7 bar. Understanding GDRI is critical for applications where the gas content within the fiber is actively controlled. Moreover, GDRI provides a new means to control the optical properties of a HCF post-fabrication, opening up new areas of design space and providing a tool to tailor and enhance the optical performance of even state-of-the-art HCFs.

Formation of Gd2O3:Nd3+ nanocrystals in silica microcapillary preforms and hollow-core anti-resonant optical fibers

A silica microcapillary preform and a hollow-core anti-resonant optical fiber doped with small-size (<50 nm) Gd2O3:Nd3+ nanocrystals are fabricated by the liquid polymer-salt method for the first time, to our knowledge. Aqueous solutions of gadolinium nitrate and neodymium chloride and a soluble organic polymer (polyvinylpyrrolidone) are used to form Gd2O3:Nd3+ nanocrystals inside the air channels of a preform followed by drawing of an optical fiber. Characterization of microcapillary preforms and optical fibers doped with Gd2O3:Nd3+ nanocrystals is performed with XRD, SEM, optical microscopy and photoluminescence analysis. Basic technological factors affecting structural and luminescent properties of the fabricated materials are considered. Particularly, it is found out that microcapillary preforms and hollow-core anti-resonant optical fibers doped with Gd2O3:Nd3+ nanocrystals demonstrate photoluminescence (emission spectra and luminescence lifetimes) characteristic to Nd3+ ions in metal sesquioxides. In addition, it is revealed that luminescence kinetics in optical fibers is described by two exponential dependences with decay times τ1 = 12 µs and τ2 = 233 µs that can be attributed to the feature of a cubic crystal structure of Gd2O3.

Hollow-core optical fiber with eight-pointed star cladding structure for low-loss transmission in telecom bands

Hollow-core optical fiber with eight-pointed star cladding structure for low-loss transmission in telecom bands

Finesse Limits in Hollow Core Fiber based Fabry-Perot interferometers

Due to their low sensitivity to changes to the external environment, low optical nonlinearity, low chromatic dispersion, and compatibility with fiber systems, hollow-core optical fibers (HCFs) represent an ideal medium for fiber Fabry-Perot interferometers (FPs). Many applications can benefit from the availability of FPs with high finesse or high finesse-length product. However, the mechanisms that limit the performance of HCF-based FPs are yet to be fully elucidated to the best of our knowledge. In this paper, we present a comprehensive analysis of several factors that impact HCF-FP performance and limit their finesse, e. g., mirror tilt, the distance between the HCF end-face and mirror, HCF cleave angle and HCF attenuation. In a sequence of experiments, we built and characterized five HCF-FPs with lengths ranging from 0.65 m to 9.25 m. By fitting the experimental data with derived analytical expressions, we found the mirror-assisted coupling loss to be below -0.0028 dB (corresponding to a coupling efficiency of 99.94%), which should allow finesse values greater than 5000 to be achieved. Experimentally, we demonstrate here a value of 2400, limited by the parameters of the mirrors available to us presently. We then show that the low coupling loss and high repeatability of mirror alignment and HCF cleave quality allows the effective use of such high-finesse FP for reliable measurements of HCF attenuation, even with short fiber length samples (10 m in our demonstration).

Microstructured optical fibers sensor modified by deep eutectic solvent: Liquid-phase microextraction and detection in one analytical device

A sensitive optical sensor based on hollow core microstructure optical fibers modified with deep eutectic solvent was produced for the first time. An easy procedure for the modification of hollow-core microstructure optical fibers with deep eutectic solvent was developed. Deep eutectic solvents based on natural monoterpenoids and fatty acids were investigated for glass surface modification. The sensor was used for the determination of non-steroidal anti-inflammatory drugs (mefenamic acid, diclofenac, flurbiprofen and ketoprofen) in human urine samples. The mechanism of the sensor response was investigated and discussed. Liquid-phase microextraction of non-steroidal anti-inflammatory drugs was implemented in deep eutectic solvent phase supported in the inner surface of hollow-core microstructure optical fibers followed by transmission spectra measurement in one analytical device. The preconcentration step performed directly in the analytical device allowed to obtain high sensitivity and selectivity. The limits of detection calculated from the calibration plots based on 3σ were 3 μg L−1 for all target analytes.

Spectral diagnostics of an optical discharge propagating along a hollow-core optical fibre

The results of spectral diagnostics of an optical discharge (OD) plasma propagating through a hollow-core revolver fibre under the action of repetitively pulsed laser radiation are presented. The revolver fibre is made of silica glass, with a diameter of the hollow core being 20 μm. The peak values of the laser radiation intensity reach 1012 W cm−2at an average Nd : YAG laser power of about 2 W. The time-averaged spectrum of the OD plasma in the visible range has the form of a continuum and is close to the blackbody spectrum with a temperature of 13.3 – 17 kK. The form of the spectrum does not depend on the gas filling of the fibre core (air or argon). In the UV part of the spectrum, lines of neutral silicon are observed, which are indicative of the partial evaporation of the reflecting cladding of the fibre.

Carbon Dioxide Detection with High Sensitivity Based on Photo-Thermal Spectroscopy in Hollow-Core Optical Fiber

Carbon Dioxide Detection with High Sensitivity Based on Photo-Thermal Spectroscopy in Hollow-Core Optical Fiber

Polarization-Maintaining Anti-Resonant Hollow-Core Optical Fibers

Polarization-Maintaining Anti-Resonant Hollow-Core Optical Fibers

Polarization Effects on Thermally Stable Latency in Hollow-Core Photonic Bandgap Fibers

Conveyance of light in air endows hollow-core optical fibers with remarkably low sensitivity of the propagation delay to temperature changes. This sensitivity was demonstrated to be further reduced and even made negative (crossing zero) in photonic bandgap type of hollow core fibers. When operating long lengths of this fiber close to the zero sensitivity wavelength, it was observed experimentally that there is a small residual variation in propagation delay which had no apparent correlation to imposed temperature changes. In this article, we analyze the polarization effects that give rise to this variation, showing that the highest level of practically achievable thermal stability of the latency is limited by polarization mode dispersion. We show measurements of differential group delay between polarization modes in long lengths of photonic bandgap fiber at various temperatures and focus on spectral regions where thermally stable latency is predicted and measured. Our experimental observations, corroborated by numerical simulations, indicate the presence of strong polarization mode coupling in the fibers in addition to birefringence. The detailed understanding gained through this study allows us to propose practically achievable (i.e., manufacturable) fiber designs with up to three orders of magnitude lower polarization mode dispersion at wavelengths where the latency is insensitive to thermal fluctuations. This paves the way to fibers with polarization independent and thermally stable latency to serve a multitude of applications.

Polymer-salt synthesis of Gd2O3:Nd3+ nanophosphors

The paper describes aspects of Gd2O3:Nd3+ phosphors synthesis by the liquid polymer-salt method. The double role of polyvinylpyrrolidone as an organic solvent was revealed in the process of highly-luminescent cubic nanocrystals formation. The developed technique was applied for modification of a hollow-core anti-resonant optical fiber by thin films based on the synthesized material without any structural and phase transformations of Gd2O3 nanocrystals after the fiber drawing process.

Hollow core optical fibres with comparable attenuation to silica fibres between 600 and 1100\u2009nm

For over 50 years, pure or doped silica glass optical fibres have been an unrivalled platform for the transmission of laser light and optical data at wavelengths from the visible to the near infra-red. Rayleigh scattering, arising from frozen-in density fluctuations in the glass, fundamentally limits the minimum attenuation of these fibres and hence restricts their application, especially at shorter wavelengths. Guiding light in hollow (air) core fibres offers a potential way to overcome this insurmountable attenuation limit set by the glass’s scattering, but requires reduction of all the other loss-inducing mechanisms. Here we report hollow core fibres, of nested antiresonant design, with losses comparable or lower than achievable in solid glass fibres around technologically relevant wavelengths of 660, 850, and 1060 nm. Their lower than Rayleigh scattering loss in an air-guiding structure offers the potential for advances in quantum communications, data transmission, and laser power delivery.