Hollow-core Fiber Research Articles

Design and fabrication of a tellurite hollow-core anti-resonant fiber for mid-infrared applications

The hollow core anti-resonant fibers (HC-ARFs) based on soft glass are in high demand for 3-6 µm laser delivery. A HC-ARF based on tellurite glass with 6 touching capillaries as cladding was designed and fabricated for the first time, to the best of our knowledge. A relatively low loss of 3.75 dB/m at 4.45 µm was realized in it. The effects of capillary number, core diameter, wall thickness of capillary, and material absorption loss on the loss of the HC-ARF were analyzed by the numerically simulation. The output beam quality was measured and the influence of bending on the fiber loss was discussed. The results of numerical simulation suggested that the theoretical loss of the prepared fiber can be reduced to 0.1 dB/m, indicating that tellurite HC-ARFs have great potential for mid-infrared laser applications.

Simulation of heat transport in textiles inspired by polar bear fur

The polar bear and several other Arctic mammals use fur composed of hollow-core fibers to survive in extremely cold environments. Here, we use finite element analysis to elucidate the role that the hollow core plays in regulating thermal transport. Specifically, we establish a three-dimensional model of a textile based on fibers with various core diameters and study transverse heat transport. First, these simulations revealed that textiles based on hollow-core fibers conduct significantly less heat than their solid-core counterparts with fibers with a core-to-fiber diameter ratio of 0.95, reducing thermal transport by 33%. In addition to this decrease in thermal transport, the mass per area of textiles is substantially reduced by making them hollow core. This led us to consider the performance of multi-layer textiles and to find that four-layer hollow-core textiles can exhibit a four-fold decrease in heat flux relative to single-layer solid-core textiles with the same mass per area. Taken together, these simulations show that hollow-core fibers are well suited for thermal insulation applications in which gravimetric thermal insulation is a priority.

Hollow-core fiber loading of nanoparticles into ultra-high vacuum

Many experiments in the field of optical levitation with nanoparticles today are limited by the available technologies for particle loading. Here, we introduce a particle loading method that solves the main challenges, namely deterministic positioning of the particles and clean delivery at ultra-high vacuum levels as required for quantum experiments. We demonstrate the efficient loading, positioning, and repositioning of nanoparticles in the range of 100–755 nm diameter into different lattice sites of a standing wave optical trap, as well as direct loading of 143–365 nm diameter particles into ultra-high vacuum, down to an unprecedented pressure below 10−9 mbar. Our method relies on the transport of nanoparticles within a hollow-core photonic crystal fiber using an optical conveyor belt, which can be precisely positioned with respect to the target trap. Our work opens the path for increasing nanoparticle numbers in the study of multiparticle dynamics and high turn-around times for exploiting the quantum regime of levitated solids in ultra-high vacuum.

Losses and orbital part of the Poynting vector of air-core modes in hollow-core fibers

Losses and orbital part of the Poynting vector of air-core modes in hollow-core fibers

Sub-two-cycle intense pulse generation based on two-stage hollow-core fiber compression using an ytterbium amplifier

We demonstrate the generation of sub-two-cycle intense laser pulses based on two-stage hollow-core fiber (HCF) compression in a compact setup (footprint of 0.65 m × 2.85 m) using a commercial Yb:KGW regenerative amplifier. Spectrally broadened laser pulses with an output power of 7.2 W from the second HCF stage are compressed down to 6.6 fs (1.9 cycles at 1030 nm) using a pair of chirp mirrors and a pair of wedges with an efficiency of 86%, leading to a compressed output of 6.2 W. A pulse-to-pulse energy stability of 0.17% is measured for 10 min.

Vector Magnetic Field Sensing Characteristics of the Magnetofluid-Encapsulated Polarization-Maintaining Fiber Single-End Offset Fusion Spliced Hollow-Core Fiber Structure

Vector Magnetic Field Sensing Characteristics of the Magnetofluid-Encapsulated Polarization-Maintaining Fiber Single-End Offset Fusion Spliced Hollow-Core Fiber Structure

In Situ All-Fiber Remote Gas Sensing Strategy Based on Anti-Resonant Hollow-Core Fiber and Middle-Hole Eccentric-Core Fiber

Laser absorption spectroscopy for gas sensing basically employs an air pump located at the gas cell probe to draw in ambient gases, and the on-site gas sample is subsequently delivered for laboratory non-real-time analysis. In this study, an in situ all-fiber remote gas sensing strategy is proposed. The anti-resonant hollow-core fiber (AR-HCF) is used as the sensing fiber, and a 20 m middle-hole eccentric-core fiber (MH-ECF) is used as the conducting fiber. The remote ambient gases can be inhaled into the AR-HCF as a result of the negative pressure transmitted through the MH-ECF when pumping gas at the interface of the MH-ECF. Since the real-time monitoring of greenhouse gas emissions in industrial processes holds immense significance in addressing global climate change, the detection of CO2 is achieved with the TDLAS-WMS method, and the gas sensing performance of an all-fiber remote gas sensing structure (RGS) is experimentally validated. The response time t90 under the pumping condition is about 456 s, which is about 30 times faster than that of free diffusion. Allan deviation results for more than one hour of continuous monitoring indicate that the lowest detection limit for the all-fiber RGS is 0.0373% when the integration time is 184 s. The all-fiber remote gas sensing strategy also possesses the benefits of being applicable to multiplex, hazardous gas environment passive monitoring.

2 W, 1.5 µm single-mode fiber methane Raman laser pumped by a Yb-doped fiber amplifier.

We report here, to the best of our knowledge, the first 1.5 µm methane-filled fiber Raman laser pumped by a fiber laser. Based on the narrow-linewidth pulsed Yb-doped fiber laser pump source and a 15 m hollow-core fiber filled with 2.5 bar methane, the maximum power of 2.06 W Stokes wave at 1543 nm is obtained. The output laser has a narrow linewidth of 2.3 GHz, and the pulse repetition frequency can be adjusted flexibly. The output shows excellent near-diffraction-limited beam quality with a M2 factor of ∼1.09. This work proves the advantage of the fiber laser pump source with modest peak power and flexible temporal characteristics in 1.5 µm fiber gas Raman laser emission, providing good guidance for generating pulsed fiber source with narrow linewidth and high beam quality.

Temperature–insensitive curvature sensor based on hollow-core fiber assisted microbubble Mach–Zehnder interferometer

Temperature–insensitive curvature sensor based on hollow-core fiber assisted microbubble Mach–Zehnder interferometer

Connecting Hollow-Core and Standard Single-Mode Fibers With Perfect Mode-Field Size Adaptation

Connecting Hollow-Core and Standard Single-Mode Fibers With Perfect Mode-Field Size Adaptation

Detection Method of Resonant Fiber Optic Gyroscope With Hollow-Core Photonic Crystal Fiber Based on Phase-Shift Keying Modulation

Detection Method of Resonant Fiber Optic Gyroscope With Hollow-Core Photonic Crystal Fiber Based on Phase-Shift Keying Modulation

Surface plasmon resonance temperature sensor based on the conjoined-tube hollow-core anti-resonant fiber with ultra-high temperature sensitivity

A surface plasmon resonance (SPR) temperature sensor based on the conjoined-tube hollow-core anti-resonant fiber (HC-ARF) is designed and analyzed. The conjoined-tube HC-ARF contains two connecting tubes with a cross arrangement in the cladding. The SPR temperature sensor is constructed by inserting a metal into one of the inner layer tubes and injecting a thermo-sensitive liquid into the hollow core of the HC-ARF to enhance the temperature sensitivity by exploiting the SPR effect. The effects of the structural parameters and thermo-sensitive media and metals on the sensing properties such as the temperature sensitivity, peak loss, resolution, amplitude sensitivity, and figure of merit (FOM) are analyzed systematically. Numerical analysis reveals ultra-high temperature sensitivity of 38.8 nm/°C and FOM of 673.84∘C−1, which are approximately 10 times higher than those of sensors described in the recent literature. In addition, the sensor is capable of detecting a wide temperature range from −5∘C to 60°C with good linearity. The SPR temperature sensor with high precision, a wide temperature detection range, a simple and easily modifiable structure, as well as good manufacturing tolerance has large potential in high-precision temperature monitoring in the petrochemical and biomedical industries.

A curvature fiber optic sensor with expandable measurement points based on anti-resonant hollow-core optical fiber

This work presents an expandable fiber optic curvature sensor. The sensor achieves multi-point curvature measurements by cascading different lengths of anti-resonant hollow-core fiber sensing units. The sensing unit is formed by connecting the anti-resonant hollow-core fiber between two single-mode fibers. The highest curvature sensitivity achieved by a single sensing unit is −11.86 nm/m−1, with a low temperature sensitivity of only 3 pm/°C. This sensing unit is readily manufacturable and exhibits good curvature sensitivity, temperature insensitivity, and stability. In contrast to traditional multi-point distributed sensors, this sensor can be flexibly installed at various positions, providing curvature sensing at desired locations. Moreover, it demonstrates the potential for multi-point curvature measurements, offering a promising solution for practical applications such as structural monitoring and robotic posture detection.

Non-Markovian Doppler Velocimetry of Optically Propelled Microparticles in Hollow-Core Photonic Crystal Fiber

Non-Markovian Doppler Velocimetry of Optically Propelled Microparticles in Hollow-Core Photonic Crystal Fiber

Azimuthal Fourier decomposition for loss analysis of hollow-core tube lattice fibers part I: Ideal fibers

This is the first part of two papers where we propose and apply a methodology for confinement loss analysis in tube lattice fibers (TLFs). The methodology is based on azimuthal Fourier decomposition (AFD) of the fiber’s cladding and core modes along the perimeters of the cladding tubes composing. This technique, combined with coupled mode theory, constitutes an effective approach to gain insight in the inhibited coupling waveguiding mechanism and design, along with fiber non-idealities impact on confinement loss. In this part I, we describe the approach and apply it to loss analysis of ideal TLFs. The approach is then applied to the analysis of the effects of tube thickness variation in part II.

Fast response multi-segment anti-resonant hollow-core fiber methane sensor at 1687 nm

Typically, hollow-core fiber (HCF)-based laser gas sensing systems use a single monolithic fiber as a gas cell. This results in a tradeoff between sensitivity which requires long optical fiber and sensor’s response time, that grows with the fiber length. Here we present a simple approach to solve this issue with new all-fiber modular gas cell design. The setup uses modified fiber mating sleeves to connect multiple HCFs in series, with optical loss of typically from 2 to 3 dB per connection. By injecting the sample gas at every second HCF-to-HCF connection, all HCF segments are filled simultaneously. We demonstrated the setups with two and four HCF segments, each with a length of 1.35 m. Laser absorption spectroscopy of methane near 1687 nm is used for setup characterization. Using the inlet pressure of 2 bar, the gas filling time is reduced over 13 times, from 77.9 s for a monolithic fiber, to only 5.9 s for the four-segment design (total HCF length of 5.4 m). With the pressure increased to 3 bar, the response time is further decreased to 3.6 s. Pressure buildup and drawdown times in the HCF were also examined.

Wide-bandwidth mode converter based on a dual-hollow-core anti-resonant fiber

This paper proposes a broadband mode converter utilizing a dual-hollow-core anti-resonant fiber (DHC-ARF) for the first time, in which the mode index matching between LP01 and LP11 modes is achieved by adjusting the core diameter size of the hollow-core anti-resonant fiber (HC-ARF). Notably, the air gap can become the main channel for the energy exchange between the two cores by adjusting the air gap size between the two cores of the DHC-ARF. The coupling length of the mode converter is greatly reduced, and a compact and broadband mode converter is realized. Simulation results demonstrate that the proposed mode converter achieves a coupling efficiency (CE) of 92.79 % at a wavelength of 1.55 μm at a length of 10.7 mm. The bandwidth of 330 nm at a CE greater than 90 % covers the E + S + C + L + U bands. The proposed mode converter exhibits a large core diameter compatible with hollow-core fiber communication and is expected to be applied for high-speed and high-capacity hollow-core mode-division-multiplexing fiber-optic communication. The device design methodology presented in this paper can also provide technical references for developing higher-order mode converters, such as LP01 mode to LP02 mode and LP01 mode to LP21 mode, based on DHC-ARF.

Mid-infrared optical frequency comb spectroscopy using an all-silica antiresonant hollow-core fiber.

We present the first mid-infrared optical frequency comb spectrometer employing an absorption cell based on self-fabricated, all-silica antiresonant hollow-core fiber (ARHCF). The spectrometer is capable of measuring sub-mL sample volumes with 26 m interaction length and noise equivalent absorption sensitivity of 8.3 × 10-8 cm-1 Hz-1/2 per spectral element in the range of 2900 cm-1 to 3100 cm-1. Compared to a commercially available multipass cell, the ARHCF offers a similar interaction length in a 1000 times lower gas sample volume and a 2.8 dB lower transmission loss, resulting in better absorption sensitivity. The broad transmission windows of ARHCFs, in combination with a tunable optical frequency comb, make them ideal for multispecies detection, while the prospect of measuring samples in small volumes makes them a competitive technique to photoacoustic spectroscopy along with the robustness and prospect of coiling the ARHCFs open doors for miniaturization and out-of-laboratory applications.

Wavelength conversion through stimulated Raman scattering in an oxygen-filled fiber for multi-band LiDAR.

Wavelength conversion afforded by stimulated Raman scattering within a hollow core fiber is potentially useful for multispectral light detection and ranging (LiDAR). Herein, we make use of the ideal 1550 cm-1 vibrational Raman shift of an antiresonant fiber filled with gaseous oxygen so that the first and second Raman orders as well as the transmitted pump are all located in separate atmospheric transmission windows. To the best of our knowledge, this is the first report of stimulated Raman scattering in an oxygen-filled fiber. The host of closely spaced rotational stimulated Raman scattering (SRS) lines (12 cm-1) accompanying the transmitted pump and vibrational Raman orders form continuum bands allowing for much greater spectral coverage of the atmospheric transmission windows. The temporal profiles of the Raman orders can be separated without the use of a grating to potentially achieve a multi-band LiDAR.

Hollow core optical fiber enabled by epsilon-near-zero material

Abstract Hollow core optical fibers of numerous guiding mechanisms have been studied in the past decades for their advantages on guiding light in air core. This work demonstrates a new hollow core optical fiber based on a different guiding mechanism, which confines light with a cladding made of epsilon-near-zero (ENZ) material through total internal reflection. We show that the addition of a layer of ENZ material coating (e.g. indium tin oxide layer) significantly reduces the loss of the waveguide compared to the structure without the ENZ layer. We also show that the propagation loss of the ENZ hollow core fiber can be further improved by integrating ENZ materials with lower loss. This study presents a novel type of hollow core fiber, and can find advanced in-fiber photonic applications such as laser surgery/spectroscopy, novel gas-filled/discharge laser, in-fiber molecular/gas sensing, and low-latency optical fiber communication.