Figure - available from: Nature Photonics
This content is subject to copyright. Terms and conditions apply.
Characterization of the 1-km-long NANF a, SEM image of the fibre cross-section. b, Measured and simulated propagation loss (left axis) and simulated chromatic dispersion (right axis). c, M² (beam quality) measurement at 1,064 nm. d, Near-field camera image of the NANF output beam at 1,064 nm (horizontal and vertical cross-sections through the beam centre are plotted with white lines).
Source publication
High-power laser delivery with near-diffraction-limited beam quality is typically limited to tens of metres distances by nonlinearity-induced spectral broadening inside the glass core of delivery fibres. Anti-resonant hollow-core fibres offer not only orders-of-magnitude lower nonlinearity but also loss and modal purity comparable to conventional b...
Citations
... We believe that the power limitation would primarily come from the SMF segment (with core diameter of ∼ 10 µm) as GRIN fibers typically have larger cores. Generally, average power tolerances for standard, commercial step-index SMF and length below 1 m can reach tens of kilowatts [25]. For pulsed signals, the answer is more complex, as it depends on factors such as pulse duration, repetition rate, and operating wavelength. ...
We propose a hollow-core fiber (HCF) end-cap that incorporates a short segment of a single-mode fiber (SMF) that serves as a modal filter. To adapt the end-cap input and output beam to the desired size, the SMF was fusion spliced with short segments of mode-field adapting graded index (GRIN) fibers on both sides. The end-cap is anti-reflective coated to minimize insertion loss and parasitic reflections. The presented proof-of-concept experiments show its ability to suppress coupling into HCFs' higher-order modes. For example, without any end-cap, the extinction ratio between the LP
$_{11}$
and the fundamental mode was found to be as low as 9 dB when coupling light from a free-space beam that was misaligned by as little as 1.1
$^{\circ }$
. This was improved to 23 dB when inserting the developed end-cap. Such small angle misalignment often exists when aligning the input beam with 3-axis (x,y,z) stages only (rather than 5-axis that also include pitch and yaw). Finally, we glued the end-cap with the HCF, providing hermetic sealing to the HCF input/output. This is of interest for stable operation in applications that use free-space light launch or require HCF output into free space.
... O VER the past few years, hollow-core anti-resonant fibers (HCARFs) have been a subject of intense interest and key innovation driver for many real-life applications, thanks to their distinctive light-guiding properties [1]- [3]. Unlike traditional solid-core fibers, state-of-the-art HCARFs exploit unprecedented optical properties including low-loss transmission [4]- [6], low optical non-linearity [7]- [9], low latency [10], low and anomalous dispersion [11], negligible corecladding power coupling [12]- [14], and resonant filtering of higher-order modes (HOMs) [15]. ...
... Unlike traditional solid-core fibers, state-of-the-art HCARFs exploit unprecedented optical properties including low-loss transmission [4]- [6], low optical non-linearity [7]- [9], low latency [10], low and anomalous dispersion [11], negligible corecladding power coupling [12]- [14], and resonant filtering of higher-order modes (HOMs) [15]. The exceptional optical characteristics of HCARFs find diverse applications such as high power laser delivery [1], [2], [16], sensing [17], [18], terahertz guidance [19], laser micro machining [20], quantum interferometer [21], gas-based nonlinear optics [11], [22]- [25], and so on. One of the unique features of HCARF is that most of the optical power (>99.99%) is guided inside the air-core Manuscript [12], while negligible power is coupled with silica cladding tubes, ensuring a high damage threshold. ...
Understanding the interplay between the core-guided modes and tube-modes of hollow-core anti-resonant fiber (HCARF) is essential to achieve low-loss and multi-mode guidance. In this paper, we thoroughly investigated the coupling between the core-guided modes and tube-modes of various HC ARFs using extensive analytical and finite-element modeling with the aim of achieving multi-mode guidance. We found that the coupling between the core-guided modes and tube-modes can significantly be enhanced by modifying and placing the cladding tubes of nested HCARFs. We proposed a modified nested HCARF that significantly enhances the inhibited-coupling (IC) between the core-guided modes and tube-modes compared to a regular and nested HCARF design. Due to the enhanced IC between the core-guided modes and tube-modes resulting from their phase mismatch, modified nested HCARF can support as high as 50 distinct spatial modes with propagation loss
$< $
10 dB/km and also demonstrate low-bend loss upon tight bending at 1064 nm. Our study will provide a better understanding of the coupling between the core-guided modes and tube-modes for designing multi-mode HCARFs. It is anticipated that the extraordinary optical properties of the proposed fiber can be beneficial for several applications including high power laser beam delivery, short-haul communication, and ultrafast nonlinear optics.
... Unlike conventional optical fibers, the hollow-core anti-resonant fiber (HC-ARF) comprises a ring of thin-walled capillaries enclosing an air core. This distinctive structural configuration confines light propagation within the air core, endowing HC-ARF with exceptional attributes such as low optical loss, wide transmission bandwidth, high mode purity, and high-power transmission [9][10][11][12][13][14][15], and fundamentally solves the limitations brought about by the material. It is also for this reason that silica fibers can break through their material limitations to expand their transmission wavelength to roughly 6 µm [16]. ...
Infrared soft glass hollow-core anti-resonant fibers (HC-ARF) with low loss, excellent mode purity, and robust high-power transmission capabilities have vast potential in mid-infrared high-power laser transmission and biomedical fields. Despite this, the fabrication of these fibers still faces formidable challenges, coupled with an incomplete understanding of the transmission characteristics, thereby amplifying the value of further exploration. In this paper, we fabricate a six-cell nodeless infrared HC-ARF originating from purified sulfide glass, synthesized using a meticulous “stack-and-draw” method and dual-gas-path pressure control method. Notably, we experimentally validate the theoretical performance expectations of this fiber. The fiber exhibits outstanding transmission capabilities and optical transmission quality, characterized by a recorded loss of 0.56 dB/m at 4.79 µm. This is already comparable to traditional step-index sulfide fibers, fully demonstrating its tremendous research value and application potential. Our work has successfully fabricated the lowest loss anti-resonant fiber on record in the mid-infrared field, propelling the development of sulfide HC-ARFs into a new phase and laying a solid foundation for the realization of fiber applications in laser transmission and the biomedical field.
... The measured output shown in Fig. 6 spectrum is very slightly broadened compared to incident spectrum. As implied in [18,42], self-phase modulation (SPM) and other nonlinear optical effects are likely to be negligible at such power level in an evacuated AR-HCF of 9.8 m length. We attribute the spectral broadening to the low resolution (0.47 nm) of spectrometer used for measurement. ...
... The measured output spectrum is very slightly broadened compared to incident spectrum. As implied in [18,42], SPM and other nonlinear optical effects are likely to be negligible at such power level in an evacuated AR-HCF of 9.8 m length. We attribute the spectral broadening to the low resolution (0.47 nm) of spectrometer used for measurement. ...
In this paper we explore the application of low-loss multimode anti-resonant hollow-core fiber (MM-AR-HCF) in the delivery of nanosecond laser pulses at 1 µm wavelength. MM-AR-HCF with large core offers a rich content of low-loss higher-order modes which plays a key role in the efficient coupling and transmission of high-power laser of low beam quality. In the experiment, laser pulses of an average pulse energy of 21.8 mJ with 14.6 ns pulse width (corresponding a peak power of 1.49 MW) are transmitted through MM-AR-HCF of 9.8 m length without damage. 85% transmission efficiency is achieved where the incident laser beam suffers a low beam quality with M²x and M²y of 2.18 and 1.99 respectively. Laser-induced damage threshold (LIDT) of MM-AR-HCF was measured to be 22.6 mJ for 85% transmission efficiency, which is 7 times higher than that for a multimode silica optical fiber with a large core of 200 µm.
... This structure reduces the confinement loss and allows most of the light to be transmitted in the air core. ARF has a wide range of applications, such as high-power lasers [6], photothermal spectroscopy [7,8], and high-precision sensors [1,9], due to 99.9% of the light propagating in the air core. This unique property also gives ARF weak Faraday effect strength (i.e., the actual measured uncorrected Verdet constant, defined in this paper as the effective Verdet constant), making it work well in a relatively strong magnetic field [10]. ...
Anti-resonant fiber (ARF) works well in a relatively strong magnetic field due to its weak Faraday effect, which results from the fundamental mode mainly transmitting in the air core. Accurately measuring the Faraday effect strength, i.e., the effective Verdet constant, of an ARF determines its applicable scenarios. However, the effective Verdet constant of ARF is ~3 orders of magnitude lower than that of a standard single-mode fiber, which is very difficult to measure. In this paper, we reveal that intermodal interference is the main obstacle to measuring the ultralow effective Verdet constant of ARF and propose using a narrow-band low-coherence light to suppress it. The measured effective Verdet constant of ARF is 0.423 ± 0.005 mrad/T/m at 1550 nm.
... As a new type of optical fiber, HC-PCFs provide an ideal transmission medium and experimental platform for laser-matter interaction and have received extensive attention and application in many fields, such as sensing, energy transmission, and communication [1][2][3][4][5]. Unlike traditional optical fibers, HC-PCFs have a hollow core, and the cladding is composed of periodically arranged microstructures with nanometer thickness. ...
Hollow-core photonic crystal fibers (HC-PCFs) provide an ideal transmission medium and experimental platform for laser–matter interaction. Here, we report a cascaded all-fiber gas Raman laser based on deuterium (D2)-filled HC-PCFs. D2 is sealed into a gas cavity formed by a 49 m-long HC-PCF and solid-core fibers, and two homemade fiber Bragg gratings (FBGs) with the Raman and pump wavelength, respectively, are further introduced. When pumped by a pulsed fiber amplifier at 1540 nm, the pure rotational stimulated Raman scattering of D2 occurs inside the cavity. The first-order Raman laser at 1645 nm can be obtained, realizing a maximum power of ~0.8 W. An all-fiber cascaded gas Raman laser oscillator is achieved by adding another 1645 nm high-reflectivity FBG at the output end of the cavity, reducing the peak power of the cascaded Raman threshold by 11.4%. The maximum cascaded Raman power of ~0.5 W is obtained when the pump source is at its maximum, and the corresponding conversion efficiency inside the cavity is 21.4%, which is 1.8 times that of the previous configuration. Moreover, the characteristics of the second-order Raman lasers at 1695 nm and 1730 nm are also studied thoroughly. This work provides a significant method for realizing all-fiber cascaded gas Raman lasers, which is beneficial for expanding the output wavelength of fiber gas lasers with a good stability and compactivity.
... As a well-known microstructure fiber, ARF is experiencing rapid innovation and shows fascinating characteristics [9,10]. 1) ARF almost eliminates the Kerr optical nonlinear effect in the traditional solid fiber that might cause a serious nonlinear noise in the all-fiber system [11]. 2) ARF enables the light to conduct in a near-vacuum latency with a group index of ∼1.0 [12]. ...
Controlling the output light-intensity and realizing the light-switch function in hollow-core anti-resonant fibers (HC-ARFs) is crucial for their applications in polarizers, lasers, and sensor systems. Here, we theoretically propose a hybrid light-intensity-tunable HC-ARF deposited with the sandwiched graphene/hexagonal boron nitride/graphene based on the typical six-circular-tube and the nested structures. Changing the external drive voltage from 12.3 to 31.8 V, the hybrid HC-ARF experiences a high–low alterative attenuation coefficient with a modulation depth 3.87 and 1.91 dB/cm for the six-circular-tube and nested structures respectively, serving as a well-performance light-switch at the optical communication wavelength of 1.55 µm. This response is attributed to the variation of the Fermi level of graphene and is obviously influenced by the core size, fiber length, and the number of graphene and hBN layers. Moreover, one attenuation dip of the modulation depth was found because of the epsilon-near-zero effect in graphene. Our design provides a feasible paradigm for integrating graphene with anti-resonant fibers and high-performance electro-optic modulators.
... The hollow channels in hollow core fiber allow infiltration of chemical samples, leading fiber based optofluidic and photocatalytic devices for photochemistry and particles sensing/trapping applications [14]- [17]. Due to the higher transmission speed of light in air-core optical fibers, they have been used for low latency and high power optical communications [18], [19]. ...
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.
... In addition dramatically improving the transmission capacity of optical fiber communications, HCFs are extremely advantageous for high-power transmission applications, such as passive optical networks [12] and power-over-fiber [13,14]. Several demonstration experiments on power transmissions that exceed 1 kW have been reported [15,16]. ...
Hollow-core photonic bandgap fibers exhibit nonlinear properties. In comparison with conventional silica-core optical fibers, we experimentally evaluate whether the hollow-core photonic bandgap fiber has extremely low nonlinearity compared with silica-core optical fibers in terms of stimulated Brillouin scattering and four-wave mixing. A low nonlinearity is useful for high-power optical transmission applications.
... ollow-core fibers have been widely investigated and fabricated in recent years due to their unique property of guiding light in the air core [1], which gives it many advantages over traditional solid-core fibers such as low nonlinearity, low latency, high threshold for material damage, ultralow Rayleigh scattering [2][3][4][5][6]. These characteristics greatly promote the application of hollow-core fibers in fields of data transmission [7,8], high-power laser [9,10], OAM mode transmission [11], and gas-based nonlinear optics [12][13][14]. ...
Hollow-core anti-resonant fibers (HC-ANF) have the advantages of low scattering loss, wide bandwidth and simplicity of preparation, but are sensitive to bend, which limits their practical applications. On the contrary, hollow-core photonic bandgap (HC-PBGF) fibers have lower confinement loss and more robust bending characteristic, but exhibit unavoidable high scattering loss, influence of surface modes and stricter manufacturing processes. In this paper, a novel hollow-core hybrid cladding fiber (HC-HBCF) which consists of anti-resonant circular tubes of inner cladding and periodically arranged air holes of outer cladding is proposed and investigated numerically. The results show that combining the claddings of antiresonance and photonic bandgap guidance mechanisms can effectively reduce the mode confinement loss by five and six orders of magnitude compared to the fibers with two claddings alone respectively. The proposed HC-HBCF exhibits similar excellent low scattering loss and spectral flatness as the single-tube anti-resonant fiber. Specifically, the proposed HC-HBCF exhibits the confinement loss of 5×10
<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sub>
dB/km at 1550 nm and a total loss of 0.1 dB/km from 1430 nm to 1770 nm. Meanwhile, the hybrid cladding fiber has an outstanding bending property with a bending loss of 0.16 dB/km at a small bending radius of 2 cm. The mode properties of HC-HBCF are also calculated and analyzed, indicating that the hybrid cladding fiber has a unique potential in controlling modal content.
