Hollow-core Negative Curvature Fiber Research Articles

Enhancing fiber atom interferometer by in-fiber laser cooling

We demonstrate an inertia sensitive atom interferometer optically guided inside a 22-cm-long negative curvature hollow-core photonic crystal fiber with an interferometer time of 20 ms. The result prolongs the previous fiber guided atom interferometer time by three orders of magnitude. The improvement arises from the realization of in-fiber {\Lambda}-enhanced gray molasses and delta-kick cooling to cool atoms from 32 {\mu}K to below 1 {\mu}K in 4 ms. The in-fiber cooling overcomes the inevitable heating during the atom loading process and allows a shallow guiding optical potential to minimize decoherence. Our results permit bringing atoms close to source fields for sensing and could lead to compact inertial quantum sensors with a sub-millimeter resolution.

Re-thinking the design of low-loss hollow-core fibers via optimal positioning of the nested elements.

Nested negative curvature hollow-core fibers (NCFs) represent state-of-art optical guidance in the near-infrared (near-IR) region. In this Letter, we propose a unique design approach for these types of fibers in order to further improve optical transmission via the optimal positioning of the nested elements. The nested elements in the proposed design are located at the center of the cladding tubes and are supported by bar-type structures. The topological optimization for the nested elements results in improved light guidance by two orders of magnitude with confinement losses as low as 0.003 dB/km within the targeted wavelength range of 1450 nm to 1600 nm. This bar-supported design features strong single-mode operation and low bending sensitivity in a wide range of bending radii.

Ultralow loss hollow-core negative curvature fibers with nested elliptical antiresonance tubes.

Hollow-core negative curvature fibers can confine light within air core and have small nonlinearity and dispersion and high damage threshold, thereby attracting a great deal of interest in the field of hollow core fibers. However, reducing the loss of hollow-core negative curvature fibers is a serious problem. On this basis, three new types of fibers with different nested tube structures are proposed in the near-infrared spectral regions and compared in detail with a previously proposed hollow-core negative curvature fiber. We used finite-element method for numerical simulation studies of their transmission loss, bending loss, and single-mode performance, and then the transmission performance of various structural fibers is compared. We found that the nested elliptical antiresonant fiber 1 has better transmission performance than that of the three other types of fibers in the spectral range of 0.72-1.6 µm. Results show that the confinement loss of the LP01 mode is as low as 6.45×10-6 dB/km at λ = 1.06 µm. To the best of our knowledge, the record low level of confinement loss of hollow-core antiresonant fibers with nested tube structures was created. In addition, the nested elliptical antiresonant fiber 1 has better bending resistance, and its bending loss was below 2.99×10-2 dB/km at 5 cm bending radius.

A self-verification temperature sensor based on surface plasmon resonance in a hollow core negative curvature fiber

We proposed and simulated a surface plasmon resonance (SPR) temperature sensor with two loss peaks in a hollow core negative curvature fiber (HC-NCF). Inner walls of the anti-resonant tubes in HC-NCF were plated with gold films to stimulate SPR, while the thermo-optic mixture of toluene and chloroform was filled in the air holes in HC-NCF to modulate the coupling between core modes and surface plasmon polaron modes (SPPMs). Simulation results showed that two SPPMs with opposite thermo-optic respond effects were excited at two separate wavelength bands due to their different dispersion characteristics. Temperature measurement sensitivities of −3.976 nm °C−1 and 1.071 nm °C−1 were obtained for the two SPPMs, while the sensitivity reached −5.047 nm °C−1 when detected the wavelength interval between the two SPPMs loss peaks. The two separate loss peaks could also be utilized in self-verification. The designed temperature sensor based on HC-NCF and SPR depicts high sensitivity and self-verification, which could be utilized for high precision and stable temperature monitoring.

Nested Partially Negative Curvature Hollow-Core Antiresonant Fiber

A nested partially Negative Curvature Antiresonant Hollow-Core Fiber (NC-AHCF) is numerically investigated. The fiber cladding has multiple reflective layers and no transverse nodes, which is aiming at reducing leakage losses. Moreover, the single mode operation with high purity can be obtained through the double resonant phase-matched coupling. The FOMs of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LP^{x}_{01}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LP^{y}_{01}$ </tex-math></inline-formula> mode can reach 2547 and 22596, respectively.

Low loss negative curvature hollow core fiber in visible red-light and near-infrared bands

Considering the low loss transmission and commercialization of hollow core fiber, negative curvature hollow core fiber (NC-HCF) has become a research hotspot in recent years. We report an innovative NC-HCF with an antiresonant layer inside the cladding tubes based on semi-ellipse and semi-circle structures. Based on the COMSOL simulation, it exhibits an ultralow loss from 0.6 to 1.6μm transmission band. On the one hand, as for semi-ellipse and semi-circle with antiresonant layer structure, the fiber lowest confinement loss (CL) of LP01 mode reaches a lowest value of 7.608 × 10 − 4 dB / km at 0.78 μm, and the high-order mode suppression ratio (HOMER) value can reach 4069. On the other hand, the semi-circle and semi-ellipse with antiresonant layer fiber structure shows the lowest CL of 1.675 × 10 − 4 dB / km at 0.79 μm, and the value of HOMER is 1776. Moreover, based on the fabrication tolerance analysis, the hollow core fibers proposed indicate better performance.

Analysis of Negative Curvature Hollow Core Fiber Coupled with Single Mode and Graded-Index Fibers

Analysis of Negative Curvature Hollow Core Fiber Coupled with Single Mode and Graded-Index Fibers

Mid-Infrared Negative Curvature Hollow-Core Fiber with Elliptically Nested Tubular Structure

Mid-Infrared Negative Curvature Hollow-Core Fiber with Elliptically Nested Tubular Structure

Single-polarization single-mode hollow-core negative curvature fiber with nested U-type cladding elements

Hollow-core negative curvature fibers (HC-NCFs) have become one of the research hotspots in the field of optical fiber because of their potential applications in the data and energy transmissions. In this work, a new kind of single-polarization single-mode HC-NCF with nested U-type cladding elements is proposed. To achieve the single-polarization single-mode transmission, we use two different silica tubes in thickness, which satisfy the resonance and anti-resonance conditions on the U-type cladding elements and the cladding tubes, respectively. Besides, the elliptical elements are introduced to achieve good single-mode performance. By studying the influences of the structure parameters on the propagation characteristics, the optimized structure parameters are obtained. The simulation results show that when the wavelength is fixed at 1550 nm, the single-polarization single-mode transmission is achieved, with the polarization extinction ratio of 25749 and minimum high-order mode extinction ratio of 174. Furthermore, the confinement loss is only 0.0015 dB/m.

Hollow core negative curvature fiber based refractive index sensor design and investigation for tuberculosis monitoring

A myriad of pensile but pertinent issues found in the optical fiber sensors can be sought resolution based on the antiresonant reflecting optical waveguide (ARROW) working principle. Due to its compact structure, the anti-resonance based sensor has several advantages such as high sensitivity response, low confinement loss, and high stability that make the sensor more effective for health monitoring. In this manuscript, an anti-resonance fiber sensor has been proposed for the detection of tuberculosis cells. An analytical structure has been explored to simulate the characteristics of the ARROW. For the suggested structure, the Finite Element Method (FEM) is used to conduct its numerical investigations. The proposed optical sensor working on the ARROW principle was implemented on the Comsol Multiphysics software. From the numerical analysis, it is noted that the designed sensor has reached around 99% sensitivity with negligible confinement loss and single modality due to the excellent light-guiding properties of the anti-resonance fiber. Besides, lots of optical parameters such as effective area, V-Parameter, spot-size along beam divergence have been calculated over the wide wavelength region. The achieved result indicates the various application’s suitability of Antiresonant Hollow-Core Fiber (ARHCF) as a tuberculosis sensor.

Exploration of hybrid cladding elements in chalcogenide hollow-core fibers for low-loss mid-infrared transmission

Optical losses of chalcogenide negative curvature hollow-core fibers with hybrid cladding elements were numerically investigated in this study. Microstructured cladding formed by the combination of tubular and elliptical elements was designed for low-loss operation in the mid-infrared spectrum. A confinement loss value of 0.287 dB/km was calculated for the proposed ellipse-nested tubular negative curvature fiber with optimized design parameters at 10.6 µm. Achieved confinement losses with the proposed design are several orders of magnitude lower than the tubular/elliptical negative curvature fibers in the targeted spectrum. The effect of the material absorption to the total fiber losses was also investigated along with the confinement losses. Suppression on the higher-order modes by the proposed fiber was numerically observed. The negative curvature fibers are promising for the low-loss guidance of CO2 lasers that are widely used for various applications spanning from material processing to surgery.

Low-loss single-mode modified conjoined tube hollow-core fiber.

We explain the effects of cladding geometries on conjoined tube hollow-core negative curvature fibers and offer a modified conjoined tube negative curvature fiber with appropriate positioning of an additional negative curvature D-shaped layer joining the flat bar to reveal attractive performances over existing recent related fibers. The proposed fiber ensures the least loss of 0.003 dB/km at 1.43 µm, a ∼0.04dB/km loss covering the wide bandwidth of approximately 300 nm, the lowest surface scattering loss of ∼0.02dB/km, and the lowest microbending loss of ∼0.04dB/km, thus providing a propagation loss of 0.10 dB/km at the 1.55 µm wavelength and also offering excellent bend loss performance (∼0.015dB/km loss at a 7 cm bend radius). The fiber, with a core diameter of 30.50 µm, also shows a higher-order mode extinction ratio of ∼1600 and maintains greater than 100 over most of the telecom bands; hence, it effectively provides single-mode operation. We show the potential of conjoined tube hollow-core negative curvature fibers in optical communications systems.

Ultralow-loss fusion splicing between negative curvature hollow-core fibers and conventional SMFs with a reverse-tapering method.

Negative curvature hollow-core fibers (NC-HCFs) can boost the excellent performance of HCFs in terms of propagation loss, nonlinearity, and latency, while retaining large core and delicate cladding structures, which makes them distinctly different from conventional fibers. Construction of low-loss all-fiber NC-HCF architecture with conventional single-mode fibers (SMFs) is important for various applications. Here we demonstrate an efficient and reliable fusion splicing method to achieve low-loss connection between a NC-HCF and a conventional SMF. By controlling the mode-field profile of the SMF with a two-step reverse-tapering method, we realize a record-low insertion loss of 0.88 dB for a SMF/NC-HCF/SMF chain at 1310 nm. Our method is simple, effective, and reliable, compared with those methods that rely on intermediate bridging elements, such as graded-index fibers, and can greatly facilitate the integration of NC-HCFs and promote more advanced applications with such fibers.

Nested compound negative curvature hollow-core fiber for single-mode operation in the infrared region

In this study, a novel tubular hollow-core fiber design with extended cladding structures aiming low transmission losses and dominant single-mode guidance in the infrared region is proposed. The fiber parameters are optimized to achieve low-loss operation at the target wavelength of 2μm, at which the emission spectrum of thulium-doped fiber lasers are centered. The confinement loss of the fundamental mode is found to be less than 0.02 dB/km in the near- and mid-infrared region, which makes the proposed design a strong alternative for conventional step-index silica optical fibers. Strong suppression of the higher order modes, and low bending sensitivity are also observed in the proposed design. The proposed fiber shows promising results to achieve low-loss transmission in the infrared spectrum.

Highly sensitive temperature sensor based on surface plasmon resonance in a liquid-filled hollow-core negative-curvature fiber

We numerically investigated a novel temperature sensor, which utilized a liquid-filled and Au-coated hollow-core negative-curvature fiber. All the air holes in the fiber were filled with a temperature-sensitive liquid, while two cladding tubes were coated with Au films. As the temperature increased, the coupling wavelength between the core mode and surface plasmon polariton mode supported by the Au layer shifted. The temperature sensitivity was 2.860 nm/°C in the range of 20–40 °C, and the inner wall of double-sided cladding tubes were deposited with a 30 nm Au layer. The designed sensor shows a high sensitivity, which is suitable for temperature detection in industrial and biomedical applications.

Refractive Index Sensors Based on Long-Period Grating in a Negative Curvature Hollow-Core Fiber.

Long-period optical fiber gratings (LPGs) are one of the widely used concepts for the sensing of refractive index (RI) changes. Negative curvature hollow-core fibers (NCHCFs), with their relatively large internal diameters that are easy to fill with liquids, appear as a very interesting medium to combine with the idea of LPGs and use for RI sensing. However, to date, there has been no investigation of the RI sensing capabilities of the NCHCF-based LPGs. The results presented in the paper do not only address this matter, but also compare the RI sensitivities of the NCHCFs alone and the gratings. By modeling two revolver-type fibers, with their internal diameters reflecting the results of the possible LPG-inscription process, the authors show that the fibers’ transmission windows shift in response to the RI change, resulting in changes in RI sensitivities as high as −4411 nm/RIU. On the contrary, the shift in the transmission dip of the NCHCF-based LPGs corresponds to a sensitivity of −658 nm/RIU. A general confirmation of these results was ensured by comparing the analytical formulas describing the sensitivities of the NCHCFs and the NCHCF-based LPGs.

Negative curvature hollow core fiber sensor for the measurement of strain and temperature.

Three different types of strain and temperature sensors based on negative curvature hollow core fiber (NCHCF) are proposed. Each sensor is produced by splicing a small section of the NCHCF between two sections of single mode fiber. Different types of interferometers are obtained simply by changing the splicing conditions. The first sensor consists on a single Fabry-Perot interferometer (FPI). The remaining two configurations are attained with the same sensing structure, depending on its position in relation to the interrogation setup. Thus, a double FPI or a hybrid sensor, the latter being composed by an FPI and a Michelson interferometer, are formed. The inline sensors are of submillimeter size, thus enabling nearly punctual measurements.

Mid-infrared hollow core fiber drawn from a 3D printed chalcogenide glass preform

We report the fabrication of a microstructured optical fiber drawn from a soft glass 3D printed preform. For this proof of concept, a chalcogenide glass that is well known for its capability to be shaped at low temperature and its mid-infrared transmission was selected: Te20As30Se50. The obtained negative curvature hollow core fiber shows several transmission bands in the 2–12 µm range that are reproduced numerically using finite element-based simulations and coupled mode theory.

Ethane detection with mid-infrared hollow-core fiber photothermal spectroscopy.

We report a compact mid-infrared (MIR) photothermal spectroscopic ethane (C2H6) sensor with a hollow-core negative-curvature-fiber (HC-NCF) gas cell. The HC-NCF supports low-loss transmission of an MIR pump (3.348 µm) and a near-infrared (NIR) probe (1.55 µm). The pump and probe laser beams are launched into the gas cell from the opposite ends of the HC-NCF, allowing independent MIR pump delivery and NIR fiber-optic probe circuitry. The use of Fabry-Perot as the probe interferometer simplifies the sensor design and suppresses the common-mode noise in the lead in/out single-mode fiber. With a 14-cm-long HC-NCF, an ethane sensor system with the limit of detection (LOD) of 13 parts-per-billion (ppb) is achieved with 1 s lock-in time constant. The LOD goes down to 2.6 ppb with 410 s average time, which corresponds to noise equivalent absorption (NEA) of 2.0×10-6 and is a record for the hollow-core fiber MIR gas sensors. The system instability is 2.2% over a period of 8 hours.

Hollow-Core Negative Curvature Fiber with High Birefringence for Low Refractive Index Sensing Based on Surface Plasmon Resonance Effect.

In this paper, a hollow-core negative curvature fiber (HC-NCF) with high birefringence is proposed for low refractive index (RI) sensing based on surface plasmon resonance effect. In the design, the cladding region of the HC-NCF is composed of only one ring of eight silica tubes, and two of them are selectively filled with the gold wires. The influences of the gold wires-filled HC-NCF structure parameters on the propagation characteristic are investigated by the finite element method. Moreover, the sensing performances in the low RI range of 1.20–1.34 are evaluated by the traditional confinement loss method and novel birefringence analysis method, respectively. The simulation results show that for the confinement loss method, the obtained maximum sensitivity, resolution, and figure of merit of the gold wires-filled HC-NCF-based sensor are −5700 nm/RIU, 2.63 × 10−5 RIU, and 317 RIU−1, respectively. For the birefringence analysis method, the obtained maximum sensitivity, resolution, and birefringence of the gold wires-filled HC-NCF-based sensor are −6100 nm/RIU, 2.56 × 10−5 RIU, and 1.72 × 10−3, respectively. It is believed that the proposed gold wires-filled HC-NCF-based low RI sensor has important applications in the fields of biochemistry and medicine.