Hollow-core Fiber Research Articles

Tunable Fiber Gas Raman Laser of 6 W at 2.9 μm by Deuterium-Filled Hollow-Core Fiber

Tunable Fiber Gas Raman Laser of 6 W at 2.9 μm by Deuterium-Filled Hollow-Core Fiber

A Hollow-Core Fiber Based Stand-Alone Multimodal (2-Photon, 3-Photon, SHG, THG) Nonlinear Flexible Imaging Endoscope System

A Hollow-Core Fiber Based Stand-Alone Multimodal (2-Photon, 3-Photon, SHG, THG) Nonlinear Flexible Imaging Endoscope System

Fiber Gas Amplifier in CO2-Filled Hollow-Core Fiber and its Self-Absorption Phenomenon

Fiber Gas Amplifier in CO₂-Filled Hollow-Core Fiber and its Self-Absorption Phenomenon

Mid-Infrared Lasers and Supercontinuum Sources Based on Stimulated Raman Scattering in Gas-Filled Hollow-Core Fibers

Mid-Infrared Lasers and Supercontinuum Sources Based on Stimulated Raman Scattering in Gas-Filled Hollow-Core Fibers

Suppression of Optical Fringes in Gas Spectroscopy Inside Anti-Resonant Hollow-Core Fibers by Fiber Bending

Suppression of Optical Fringes in Gas Spectroscopy Inside Anti-Resonant Hollow-Core Fibers by Fiber Bending

Speed of Light in Hollow-Core Photonic Bandgap Fiber Approaching That in Vacuum.

A Fresnel mirror is introduced at a hollow-core photonic bandgap fiber end by fusion splicing a short single-mode fiber segment, to reflect the light backward to an optical frequency domain reflectometry. The backward Fresnel reflection is used as a probe light to achieve light speed measurement with a high resolution and a high signal-to-noise ratio. Thus, its group velocity is obtained with the round-trip time delay as well as the beat frequency at the reflection peak. Multiple Fresnel peaks are observed from 2180.00 Hz to 13,988.75 Hz, corresponding to fusion-spliced hollow-core fiber segments with different lengths from 0.2595 m to 1.6678 m, respectively. The speed of light in the air guidance is calculated at 2.9753 × 108 m/s, approaching that in vacuum, which is also in good agreement with 2.9672 × 108 m/s given by the numerical analysis with an uncertainty of 10-3. Our demonstration promises a key to hollow-core waveguide characterization for future wide-bandwidth and low-latency optical communication.

Multi-core hollow core fibre

Multi-core hollow core fibre

Optical Fiber HMS Ammonia Sensor with Cellular-like N-CQDs/MgxZn1-xO at Room Temperature.

This paper presents an optical fiber hollow malposition structure (HMS) elaborated with cellular-like N-CQDs/MgxZn1-xO for detecting ammonia (NH3) at room temperature. The gas detection was realized by combining the HMS to excite the surface evanescent field on the outer surface of the hollow core fiber (HCF) and the surface-coated cellular-like N-CQDs/MgxZn1-xO material for improving sensitivity. Experimental results demonstrate that the sensor coated with N-CQDs/Mg0.2Zn0.8O exhibits the highest sensitivity, reaching 8.9 pm/ppm, which is 11.6 times higher than that with Mg0.2Zn0.8O. Additionally, the NH3 sensor can determine a minimum concentration of 1 ppm and has response and recovery times of 6.2 and 7.1 s, respectively. Density functional theory (DFT) calculations confirm that N-CQDs reduces the bandgap of the composite material and increase the carrier concentration on its surface, thereby enhancing gas adsorption capacity. The intrinsic characteristics of the proposed sensor including small size, high sensitivity, and good stability reveal its promising prospects in detecting low concentrations of NH3.

Highly Amplified Broadband Ultrasound in Antiresonant Hollow Core Fibers

High‐frequency broadband ultrasound in nested antiresonant hollow core fibers (NANFs) is investigated for the first time. NANFs have remarkable features enabling high‐resolution microscale optoacoustic imaging sensors and neurostimulators. Solid optical fibers have been successfully employed to measure and generate ultrasonic signals, however, they face issues concerning attenuation, limited frequency range, bandwidth, and spatial resolution. Herein, highly efficient ultrasonic propagation in NANFs from 10 to 100 MHz is numerically demonstrated. The induced pressures and sensing responsivity are evaluated in detail, and important parameters for the development of ultrasonic devices are reviewed. High pressures (up to 234 MPa) and sensing responsivities (up to −207 dB) are tuned over 90 MHz range by changing the diameters of two distinct NANF geometries. To the best of knowledge, this is the widest bandwidth reported using similar diameter fibers. The results are a significant advance for fiber‐based ultrasonic sensors and transmitters, contributing to improve their efficiency and microscale spatial resolution for the detection, diagnosis, and treatment of diseases in biomedical applications.

4.8-μm CO-filled hollow-core silica fiber light source

Mid-infrared (MIR) fiber lasers are important for a wide range of applications in sensing, spectroscopy, imaging, defense, and security. Some progress has been made in the research of MIR fiber lasers based on soft glass fibers, however, the emission range of rare-earth ions and the robustness of the host materials are still a major challenge for MIR fiber lasers. The large number of gases provide a variety of optical transitions in the MIR band. When combined with recent advances in low-loss hollow-core fiber (HCF), there is a great opportunity for gas-filled fiber lasers to further extend the radiation to the MIR region. Here, a 4.8-μm CO-filled silica-based HCF laser is reported for the first time. This is enabled by an in-house manufactured broadband low-loss HCF with a measured loss of 1.81 dB/m at 4.8 μm. A maximum MIR output power of 46 mW and a tuning range of 180 nm (from 4644 to 4824 nm) are obtained by using an advanced 2.33-μm narrow-linewidth fiber laser. This demonstration represents the longest-wavelength silica-based fiber laser to date, while the absorption loss of bulk silica at 4824 nm is up to 13, 000 dB/m. Further wavelength expansion could be achieved by changing the pump absorption line and optimizing the laser structure.

PDMS-assisted Mach–Zehnder interferometer for simultaneous sensing of strain and temperature based on hollow-core fibers

A PDMS-assisted Mach-Zehnder interferometric (MZI) fiber-optical sensor based on hollow-core fibers (HCF) is proposed and experimentally demonstrated for the simultaneous detection of strain and temperature. The transmission spectral evolution in response to the applied strain and temperature sensor are investigated. Experimental results suggest that our proposed sensor exhibits strain and temperature sensitivities up to −40.95 dB/N and 2.5 nm/°C for the sensing ranges of 0.01 N to 0.08 N and 35 °C to 42 °C, respectively. Moreover, crosstalk analyses were performed to discriminate the strain and temperature measurement. The proposed sensor possesses desirable advantages such as high sensitivity, easy-fabrication, and low-crosstalk, which paves new way toward developing photonic devices for strain/temperature dual-parameter sensing and related applications.

Optical absorption spectrum reveals gaseous chlorine in anti-resonant hollow core fibers

We have observed unexpected spectral attenuation of ultraviolet light in freshly drawn hollow core optical fibers. When the fiber ends are left open to atmosphere, this loss feature dissipates over time. The loss matches the absorption spectrum of gaseous (molecular) chlorine and, given enough time, the transmission spectrum of the fiber recovers to that expected from the morphological structure of the fiber. Our measurements indicate an initial chlorine concentration of 0.45 µmol/cm3 in the hollow core, equivalent to 1.1 mol% Cl2 at atmospheric pressure.

Wideband and ultra-low confinement loss nested hollow-core anti-resonant fiber with double-single-layer structures

Wideband and ultra-low confinement loss nested hollow-core anti-resonant fiber with double-single-layer structures

MZI-based high intensity responsive sandwiched multi-layer fiber optic humidity sensor

This paper presents a multi-layer optical fiber humidity sensor based on dual-beam Mach-Zehnder interference (MZI) for optical intensity sensitivity. The sensor is fabricated using a large-scale axial offset fusion technique between a multimode fiber (MMF) and an offset hole two-core fiber (OHTC), making it suitable for agricultural and health monitoring applications. The 27 μm axial offset enables tilted light incidence, enhancing environmental sensitivity. With a single-cycle Graphene oxide (GO) coating of approximately 22 nm, the MMF-OHTC structure achieves high humidity sensitivity (0.39 dB/%RH) over the 25 %-80 % RH range with excellent linearity (R2≈0.99). The sensor exhibits stable, rapid response (2.52 s/0.46 s) and low temperature cross-sensitivity (0.06 %RH/°C). When combined with a hollow-core fiber Fabry-Perot interferometer (HCF-FPI), the system allows zero cross-talk simultaneous humidity and temperature measurements, expanding the potential applications of multi-layered structures in multifunctional detection systems.

Wavefront shaping and imaging through a multimode hollow-core fiber

Multimode fibers recently emerged as compact minimally-invasive probes for high-resolution deep-tissue imaging. However, the commonly used silica fibers have a relatively low numerical aperture (NA) limiting the spatial resolution of a probe. On top of that, light propagation within the solid core generates auto-fluorescence and Raman background, which interferes with imaging. Here we propose to use a hollow-core fiber to solve these problems. We experimentally demonstrate spatial wavefront shaping at the multimode hollow-core fiber output with tunable high-NA. We demonstrate raster-scan and speckle-based compressive imaging through a multimode hollow-core fiber.

Two-way 5G NR FSO-HCF-UWOC converged systems with R/G/B 3-wavelength and SLM-based beam-tracking scheme.

A two-way fifth-generation (5G) new radio (NR) free-space optical (FSO)-hollow-core fibre (HCF)-underwater wireless optical communication (UWOC) converged systems with a red/green/blue (R/G/B) 3-wavelengths and spatial light modulator (SLM)-based beam-tracking scheme is practically built. It is the first to practically build a two-way FSO-HCF-UWOC converged system with high-speed and long-distance optical wireless-wired-underwater wireless communication characteristics. It shows a 5G NR FSO-HCF-UWOC convergence from drone or buildings to undersea, using R/G/B 3-wavelengths and an SLM as a demonstration. The R/G/B 3-wavelengths are used to enhance the downstream and upstream aggregate transmission rates. An SLM with electrical comparator is used to adjust the laser beam and mitigate laser beam misalignment caused by drone movement or ocean flow. Over a hybrid of 1-km FSO, 10-m HCF, and 10.44-m ocean water-air-ocean water medium, downstream/upstream 5G-millimeter-wave (MMW) 9.1-Gb/s/24-GHz signals are transmitted with satisfactorily low bit error rates and error vector magnitudes, as well as distinct constellations. This demonstrated that the 5G NR FSO-HCF-UWOC converged system exhibits promising potential as it advances the scenario implemented by the 5G-MMW signals over FSO, HCF, and UWOC convergence, paving the way for high-speed and long-distance communications across diverse media.

Sensitivity-enhanced optical fiber sensor based on the Vernier effect for detection of ammonia in water

A sensitivity-enhanced optical fiber sensor for the detection of dissolved ammonia in water based on the Vernier effect is proposed and demonstrated. The sensor comprises a sensing Fabry-Perot interferometer (S-FPI) and a reference Fabry-Perot interferometer (R-FPI) in parallel. The S-FPI is an open cavity fabricated by the dislocation welding of single-mode fiber(SMF), which is filled with a mixture of ultraviolet-curable resin NOA 170 and Oxazine 170 perchlorate (O17). The R-FPI is a sealed cavity, which is constructed by fusion splicing of SMF and hollow core fiber (HCF). The proposed sensor is based on the chemical reaction between the dissolved ammonia and O17. This chemical reaction alters the refractive index (RI) of the S-FPI, resulting in a wavelength shift of the reflected spectrum. The two interferometers exhibit a nearly identical free spectral range (FSR), thereby enabling the generation of the Vernier effect, which markedly enhances the ammonia sensitivity of the sensor. Experimental results indicate that the sensor sensitivity is 0.34 nm/ppm in the dissolved ammonia range of 5-40 ppm, which is approximately 9.1 times that of the single S-FPI. The proposed sensor exhibits both good repeatability and a short response time, in addition to selectivity for the detection of ammonia.

Efficient high-power 1.9 µm picosecond Raman laser in H2-filled hollow-core fiber without generation of rotational lines

In this paper, an efficient high-power 1.9 µm picosecond Raman laser through pure vibrational stimulated Raman scattering (SRS) in H2-filled hollow-core fiber (HCF) is demonstrated. The maximum Raman conversion efficiency of 34 % and the Raman power of 7.3 W (36.5 µJ) is achieved within a 130 cm length of our in-house fabricated fiber. By controlling the H2 pressure, the high-order Stokes and rotational Stokes/anti-Stokes will not be generated, thereby enhancing the efficacy of the 1st Stokes conversion. In addition, the vibrational anti-Stokes are produced inevitably, which can be explained by the phase-matching of higher-order modes. Our results show SRS in H2-filled HCF to be a promising method for generating high-power 1.9 µm picosecond pulses, which are valuable in spectroscopy, defense, and efficient nonlinear conversion.

Extraction of Attenuation and Backscattering Coefficient along Hollow-Core Fiber Length Using Two-Way Optical Time Domain Backscattering.

Optical time domain reflectometry (OTDR) is a key technique to characterize fabricated and installed optical fibers. It is also widely used in distributed sensing. OTDR of emerging hollow-core fibers (HCFs) has been demonstrated only very recently, being almost 30 dB weaker than that in the glass-core optical fibers. However, it has been challenging to extract useful data from the OTDR traces of HCFs, as the longitudinal variation in the fiber's geometry, notably the core size or the longitudinal variations of the air pressure within the core, results in commensurate changes of the backscattering strength. This is, however, necessary for continuous improvement of HCF fabrication and subsequent improvement in their performance such as minimum achievable loss, potentially enabling the use of HCF in a significantly broader range of applications than used today. Here, we demonstrate, for the first time, that the distributed loss and backscattering coefficient in antiresonant HCFs can be separated, obtaining key data about fiber distributed loss and uniformity. This is enabled by using OTDR traces obtained from both ends of the HCF.

Single hollow-core microstructure fiber biosensor for pancreatic cancer diagnosis in terahertz regime

Abstract Pancreatic cancer is a kind of malignant tumor that is difficult to detect in its early stages, developing rapidly and with a 5-year survival rate of only 5% to 10%. Therefore early diagnosis and discovery of pancreatic cancer are very important for the successful treatment of the disease. Here, we report a single hollow-core microstructural fiber (SHC-MSF) biosensor based on a ZEONEX substrate, which has been optimized for the early detection of pancreatic cancer biomarkers. The proposed SHC-MSF biosensor adopts a single-aperture structure to increase the contact range with assay analytes to improve the detection sensitivity. Its biosensing performance was numerically analyzed using a finite element method with a perfect matching layer. Numerical results demonstrated that the proposed MSF-biosensor presented ultra-high sensitivity (bilirubin: 105.55%, glucose: 105.34%, creatinine: 105.67%) and negligible confinement loss (bilirubin: 5.52×10-14 cm-1, glucose: 1.65×10-14 cm-1, creatinine: 5.57×10-14 cm-1) in the range of 0.3~2.0 THz. Moreover, the SHC-MSF biosensor could selectively detect and distinguish cancer markers of different concentrations in the blood to achieve a more accurate diagnosis of pancreatic cancer. Finally, fabrication tolerance analysis of the proposed MSF-biosensor is provided to ensure the feasibility of rapid preparation.