Hollow-core Anti-resonant Fiber Research Articles

Numerical investigation of divided-pulse amplification assisted by a hollow core anti-resonant fiber

An all-fiber structure laser based on divided-pulse amplification technology and a hollow core anti-resonant fiber (HC-ARF) is proposed. We numerically investigate the process of divided-pulse amplification in the structure based on the vectorial nonlinear Schrödinger equations. By changing the splicing angle of the HC-ARF, a conventional soliton with 703 fs can be divided into two sub-pulses with orthogonal polarization states. After amplification and compression, the two sub-pulses are recombined into one pulse in an identical HC-ARF. The combining efficiency and limitations that originate from cross-phase modulation, self-phase modulation, fiber dispersion, and splicing angle are analyzed. Moreover, the number of sub-pulses can increase from two to eight to greatly suppress the accumulation of the nonlinear phase shifts, by using three segments HC-ARF with splicing angles of 45°. The simulation result indicates that the pulse peak power and average power can be greatly improved after amplifying and combining the eight sub-pulses. The work can provide what we believe to be a new method for achieving all-fiber high-peak and high-average power femtosecond lasers.

Mid-infrared pulsed fiber laser source at 4.3 µm based on a CO2-filled anti-resonant hollow-core silica fiber

Fiber lasers in the mid-infrared (mid-IR) band are of great interest due to their wide range of applications such as manufacturing, defense, spectroscopy, and free-space communication. Due to the immaturity of the soft glass fiber fabrication technology and the limitation of the type of doped rare earth, laser power scaling and wavelength expansion above 4 µm are greatly limited. Lasers based on gas-filled hollow-core fibers (HCFs) have proved to be an effective way of generating mid-IR lasers. We demonstrate a pulsed 4.3 µm laser source based on a CO2-filled HCF for the first time. The pulse energy characteristics and output spectrum of the mid-IR laser have been investigated. The maximum pulse energy of the mid-IR laser is 236 nJ. The maximum average power of the mid-IR laser is 297.8 mW with a slope efficiency of 17.3%. A step-tunable mid-IR output is achieved from 4293.718 nm to 4392.085 nm including 8 emission lines. Furthermore, the time-domain and frequency-domain properties of the mid-IR laser have been studied to understand laser operation better. This work has an important reference value for the development of pulsed mid-IR fiber gas laser sources.

Mid‐Infrared Sensing Using a Hollow–Core Fiber in a Nonlinear Interferometer

AbstractIncreasing the interaction path length is a well‐known method for enhancing the sensitivity of the optical detection system. Hollow–core fibers (HCFs) represent a viable alternative to the traditional multi‐path cells offering low optical losses and strong confinement of the optical field. Here, the incorporation of an Antiresonant Hollow–core Fiber (AR‐HCF) section into a nonlinear interferometer, where the AR‐HCF section serves as a gas‐sensing cell operating in the IR range is presented. By exploiting the effect of nonlinear interference, the detection is brought into the more operation‐friendly visible range. The detection of methane (CH4) gas at mid‐IR wavelengths within a half‐meter section of AR‐HCF, with an estimated concentration accuracy of 200 ppm·m is demonstrated. These results represent the combination of two research fields within a single instrument and pave the way for further advancement of quantum‐inspired gas sensing techniques.

High Fidelity Distribution of Telecom Polarization Entangled Photons through a 7.7 Km Antiresonant Hollow-Core Fiber

High Fidelity Distribution of Telecom Polarization Entangled Photons through a 7.7 Km Antiresonant Hollow-Core Fiber

Tunable diode laser absorption spectroscopy for gas detection with a negative curvature anti-resonant hollow-core fiber

In this study, an all-fiber gas sensing technology was proposed, which is based on tunable diode laser absorption spectroscopy in the near infrared. A negative curvature anti-resonant hollow-core fiber was used as the gas chamber and optical channel, and an opto-gas coupling miniature tee was used in the configuration. Down to ppb (parts-per-billion) level noise-equivalent concentration was achieved with a fast-response capability of less than 6 s. The results demonstrated strong long-term stability, with a relative standard deviation of approximately 2.1% over a 12-hour period. This approach demonstrates a simple, robust, fast response and compact sensor configuration that contributes to better management of greenhouse gas emissions and environmental pollution

Semi-Empirical Model for Calculating Birefringence and Confinement Loss in Bi-Thickness Fourfold Anti-Resonant Hollow-Core Fiber

Semi-Empirical Model for Calculating Birefringence and Confinement Loss in Bi-Thickness Fourfold Anti-Resonant Hollow-Core Fiber

Synthesizing gas-filled anti-resonant hollow-core fiber Raman lines enables access to the molecular fingerprint region

The synthesis of multiple narrow optical spectral lines, precisely and independently tuned across the near- to mid-infrared region, is a pivotal research area that enables selective and real-time detection of trace gas species within complex gas mixtures. However, existing methods for developing such light sources suffer from limited flexibility and very low pulse energy, particularly in the mid-infrared domain. Here, we introduce a concept that is based on the combination of an appropriate design of near-infrared fiber laser pump and cascaded configuration of gas-filled anti-resonant hollow-core fiber technology. This concept enables the synthesis of multiple independently tunable spectral lines, with >1 μJ high pulse energies and a few nanoseconds pulse width in the near- and mid-infrared regions. The number and wavelengths of the generated spectral lines can be dynamically reconfigured. A proof-of-concept laser beam synthesized of two narrow spectral lines at 3.99 µm and 4.25 µm wavelengths is demonstrated and combined with photoacoustic modality for real-time SO2 and CO2 detection. The proposed concept also constitutes a promising way for infrared multispectral microscopic imaging.

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

Enhanced Inhibited Mode-Coupling: Multi-Mode Hollow-Core Anti-Resonant Fiber Designs

Enhanced Inhibited Mode-Coupling: Multi-Mode Hollow-Core Anti-Resonant Fiber Designs

Accurate Loss Prediction of Realistic Hollow-Core Anti-Resonant Fibers Using Machine Learning

Accurate Loss Prediction of Realistic Hollow-Core Anti-Resonant Fibers Using Machine Learning

Spectral Bandwidth Tuning of Photoionization-Induced Blue-Shifted Solitons in gas-Filled Hollow-Core Anti-Resonant Fibers

Spectral Bandwidth Tuning of Photoionization-Induced Blue-Shifted Solitons in gas-Filled Hollow-Core Anti-Resonant Fibers

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.

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

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.

Low-latency 100 Gb/s PAM-4 PON with a 42.5 dB power budget over the 20 km anti-resonant hollow-core fiber.

The surging growth in data traffic has necessitated the development of higher-speed, lower-latency intensity modulation and direct detection (IM/DD) passive optical networks (PONs) with higher power budgets. To address the inherent limitations of traditional silica-based solid-core fibers, anti-resonant hollow-core fibers have garnered significant attention from both academia and industry. In this Letter, we present an experimental demonstration of 100 Gb/s PAM-4 IM/DD PON transmission over a 20 km anti-resonant hollow-core fiber in the C band, utilizing low-complexity digital signal processing (DSP). The result achieves a record high power budget of 42.5 dB, facilitated by a 3-tap weighted lookup table (LUT) at the optical line terminal (OLT) side and a semiconductor optical amplifier used as a preamplifier at the optical network unit (ONU) side. This represents the highest power budget reported for IM/DD PON to date, to the best of our knowledge,and offers a promising alternative for the future evolution of PON systems.

Glass capillary systems for micro-volume fluorometry

Capillary-based fluorometry can be considered a promising alternative to cuvette-based methods, enabling low-volume measurements while reducing analyte consumption and waste generation. In this work, we compared the performance of three types of glass container systems, i.e., anti-resonant hollow core fibers, capillaries, and standard cuvettes, using green fluorescent protein (GFP) as a reference analyte. Among these, when the volume of the analyte and the fluorescence intensity are assessed, a capillary accommodating 2.9 μL was found as an optimal choice. The capillary-based interrogation setup was further optimized to enhance sensitivity by adjusting the florescence-exciting laser beam position and optimizing the capillary’s shape. The obtained capillary-based setup achieved a noteworthy 85 % reduction in sample volume compared to previous studies utilizing capillary-based fluorometry, highlighting its significant contribution to material conservation. The system achieved a limit of detection as low as 26 μg/mL (1.01 nM) GFP concentration and a resolution of 3.5 μg/mL. With its low cost and potential for reusability, capillary-based fluorometry presents a compelling alternative to traditional cuvette-based fluorometry, offering a promising solution for micro-volume analysis.

Narrowband stimulated Raman scattering and molecular modulation in anti-resonant hollow-core fibres

Raman scattering is the inelastic process where photons bounce off molecules, losing energy and becoming red-shifted. This weak effect is unique to each molecular species, making it an essential tool in, e.g., spectroscopy and label-free microscopy. The invention of the laser enabled a regime of stimulated Raman scattering (SRS), where the efficiency is greatly increased by inducing coherent molecular oscillations. However, this phenomenon required high intensities due to the limited interaction volumes, and this limitation was overcome by the emergence of anti-resonant fibres (ARFs) guiding light in a small hollow channel over long distances. Based on their unique properties, this Perspective reviews the transformative impact of ARFs on modern SRS-based applications ranging from development of light sources and convertors for spectroscopy and materials science, to quantum technologies for the future quantum networks, providing insights into future trends and the expanding horizons of the field.

Optimization of low-loss, high birefringence parameters of a hollow-core anti-resonant fiber with back-propagation neural network assisted hyperplane segmentation algorithm

In engineering, optimizing parameters often involves computationally expensive tasks, especially when dealing with multi-dimensional variables and multiple performance metrics. This falls under the category of multi-objective black-box optimization. To address this, we propose two optimization algorithms for low and medium-dimensional spaces, incorporating relaxation conditions for hyperplane segmentation. For the specific parameter optimization of HC-ARF, we employed a two-stage approach. It combines a BP neural network as a surrogate model with a hyperplane separation optimization algorithm. This method efficiently optimizes both confinement loss (CL) and birefringence, using a weighted sum approach to identify their Pareto sets. We validate the effectiveness and stability of the surrogate model by comparing it with traditional optimization algorithms. Exhaustive experiments confirm the superiority of this algorithm and the results show that our optimized structure achieves impressive performance metrics, including a loss of 0.8 dB/m, a birefringence of 2.2×10−4, and a critical bending radius of 0.5 cm under optimal parameters.

Design of hollow-core anti-resonant optical fiber based on bragg elements with low-loss and wide bandwidth

A type of anti-resonant hollow-core optical fiber consisting of Bragg elements is proposed. The confinement and bending losses are numerically simulated using the finite element method. It is found that the introduction of concentric rings to form anti-resonant structure can reduce the mode transmission loss by 2 ∼ 4 orders of magnitude compared with the anti-resonant element composed of only one dielectric layer, therefore it can achieve ultra-low loss optical transmission. The influence of the structural parameters on the confinement loss was investigated. Furthermore, it is demonstrated that each dielectric layer independently contributes to the confinement of the core modes. It is also found that the Bragg reflection structure can effectively suppress the coupling between core and cladding modes, and achieve broadband low-loss optical transmission under small bending radius. In particular, it can achieve a low transmission loss of less than 0.1 dB km−1 over a wide wavelength range of 600 nm at the bending radius of 3 cm.