In the research field of hollow-core optical fiber (HCF), one type of fiber geometry with a leaky mode nature has unexpectedly taken center stage over the last couple of years: the so-called ...hollow-core anti-resonant fiber (ARF). The guidance mechanism of this ARF has been elucidated explicitly, the optical performance of the fiber has improved significantly, and the range of potential fiber application areas has expanded steadily. This paper will review our continuous efforts to understand, design, and fabricate this hollow-core ARF with the aim of lower loss and wider bandwidth. We also explore the possibility of using an advanced form of ARF in communications applications. In the long journey of looking for optical fibers that provide better performance than conventional solid-core glass fibers, exploitation of the hidden potential of artificial photonic micro-structures will continue to advance.
Countering the optical network 'capacity crunch' calls for a radical development in optical fibres that could simultaneously minimize nonlinearity penalties, chromatic dispersion and maximize signal ...launch power. Hollow-core fibres (HCF) can break the nonlinear Shannon limit of solid-core fibre and fulfil all above requirements, but its optical performance need to be significantly upgraded before they can be considered for high-capacity telecommunication systems. Here, we report a new HCF with conjoined-tubes in the cladding and a negative-curvature core shape. It exhibits a minimum transmission loss of 2 dB km
at 1512 nm and a <16 dB km
bandwidth spanning across the O, E, S, C, L telecom bands (1302-1637 nm). The debut of this conjoined-tube HCF, with combined merits of ultralow loss, broad bandwidth, low bending loss, high mode quality and simple structure heralds a new opportunity to fully unleash the potential of HCF in telecommunication applications.
The performance of optical fiber communication, laser, and sensing systems is ultimately limited by the attenuation of optical fiber, which cannot be lower than the barrier set by Rayleigh scattering ...in bulk silica glass. In this work, the longstanding Rayleigh scattering limit is conquered by using a hollow‐core fiber (HCF). Two visible‐guiding hollow‐core conjoined‐tube anti‐resonant fibers are successfully fabricated and exhibit overall losses of 3.8 dB km−1 at 680 nm and 4.9 dB km−1 at 558 nm, respectively. The latter surpasses the Rayleigh scattering limit of silica glass fiber by 2 dB km−1 at the corresponding wavelength. Numerical simulations indicate that the loss level the authors achieve is still much higher than the ultimate loss limit caused by surface scattering of this HCF geometry, leaving plenty of room for further refinement.
The Rayleigh scattering loss of silica glass is believed to set the ultimate loss limit of silica fiber. Here, it is challenged by using a hollow‐core fiber (HCF) approach. A conjoined‐tube HCF with loss of 4.9 dB km−1 at 558 nm is achieved, surpassing silica glass fiber by at least 2 dB km−1 at this wavelength.
The optical performance characteristics of anti‐resonant hollow‐core fibers (known as AR‐HCFs or ARFs) are improving rapidly, but the polarization maintaining issue with these fibers remains ...unresolved. Although a regular nonbirefringent ARF can maintain high polarization purity under static conditions, it cannot resist mechanical disturbances. In this work, by designing a bi‐thickness semi‐tube ARF structure with fourfold rotational symmetry, the first ARF with a level of birefringence close to 10−4 is fabricated. The proposed ARF features a combination of phase birefringence of 9.1 × 10−5, a minimum loss of 185 dB km−1, a bandwidth of 133 nm, and single‐mode operation. Furthermore, the ARF shows high resistance to fiber bending and wide‐range temperature variations, thus confirming that this carefully designed ARF can serve as a practical workhorse in polarization‐related optical fiber applications.
An anti‐resonant hollow‐core fiber (ARF) with fourfold rotational‐symmetry and bi‐thickness semi‐tube structure is demonstrated, featuring a phase birefringence of almost 10−4, a minimum loss of 185 dB km−1, a bandwidth of 133 nm, and single‐mode operation. The high birefringence ensures great resistance to environmental perturbations, validating for the first time that ARF could be a practical workhorse in polarization‐related applications.
A route to supercontinuum generation in gas‐filled hollow‐core anti‐resonant fibers is demonstrated through the creation of a broad vibrational Raman frequency comb followed by continuous broadening ...and merging of the comb lines through either rotational Raman scattering or the optical Kerr effect. The demonstration experiments, utilizing a single pump pulse with 20 ps duration at 532 nm in a nitrogen‐filled fiber, produce a supercontinuum spanning from 440 to 1200 nm, with an additional deep ultraviolet continuum from 250 to 360 nm. Numerical results suggest that this approach can produce even broader supercontinuum spectra extending from the ultraviolet to mid‐infrared.
By driving the vibrational response of light molecules confined inside a micro‐structured hollow‐core fiber with picosecond duration laser pulses, a discrete frequency comb of spectral lines is initially created. Upon further propagation through the fiber the lines broaden and merge to form a smooth and continuous optical spectrum spanning from the ultraviolet to mid‐infrared: an ultra‐broadband white‐light supercontinuum.
We demonstrate a 2.8 μm gas Raman laser in a methane-filled hollow-core negative-curvature fiber with average power of 113 mW, pulse energy of 113 μJ and estimated peak power of 9.5 MW. Raman quantum ...efficiency of 40% has been reached from the pump source at 1.064 μm to the 2nd order vibrational Stokes at 2.812 μm using 1.8 MPa methane gas. To our knowledge, this is the first high peak power fiber-based gas Raman laser in mid-infrared region and a range of applications in supercontinuum generation, laser surgery, molecular tracing and gas detection are in prospect.
We report high performance nodeless hollow-core anti-resonant fibers (HARFs) with broadband guidance from 850 nm to >1700 nm and transmission attenuation of ~100 dB/km. We systematically investigate ...their bending loss behaviors using both theoretical and experimental approaches. While a low bending loss value of 0.2 dB/m at 5 cm bending radius is attained in the long wavelength side (LWS) of the spectrum, in this paper, we pursue light guidance in the short wavelength side (SWS) under tight bending, which is yet to be explored. We analytically predict and experimentally verify a sub transmission band in the SWS with a broad bandwidth of 110 THz and an acceptable loss of 4.5 dB/m at 2 cm bending radius, indicating that light can be simultaneously guided in LWS and SWS even under tight bending condition. This provides an unprecedented degree of freedom to tailor the transmission spectrum under a tight bending state and opens new opportunities for HARFs to march into practical applications where broadband guidance under small bending radius is a prerequisite.
Cyclopamine is a teratogenic steroidal alkaloid, which inhibits the Hedgehog (Hh) signaling pathway by targeting the Smoothened (Smo) receptor. Suppression of Hh signaling with synthetic small ...molecules has been pursued as a therapeutic approach for the treatment of cancer. We report herein the asymmetric synthesis of cyclopamine based on a two-stage relay strategy.
: total synthesis of veratramine through a convergent approach, wherein a crucial photoinduced excited-state Nazarov reaction was applied to construct the basic 6-6-5-6 skeleton of C-
-D-
-steroid.
: conversion of veratramine to cyclopamine was achieved through a sequence of
selective redox manipulations.
Aim
Novel long‐acting drugs for type 2 diabetes mellitus may optimize patient compliance and glycaemic control. Exendin‐4‐IgG4‐Fc (E4F4) is a long‐acting glucagon‐like peptide‐1 receptor agonist. ...This first‐in‐human study investigated the safety, tolerability, pharmacokinetic, pharmacodynamic and immunogenicity profiles of a single subcutaneous injection of E4F4 in healthy subjects.
Methods
This single‐centre, randomized, double‐blind, placebo‐controlled phase 1 clinical trial included 96 subjects in 10 sequential cohorts that were provided successively higher doses of E4F4 (0.45, 0.9, 1.8, 3.15, 4.5, 6.3, 8.1, 10.35, 12.6 and 14.85 mg) or placebo (ChinaDrugTrials.org.cn: ChiCTR2100049732). The primary endpoint was safety and tolerability of E4F4. Secondary endpoints were pharmacokinetic, pharmacodynamic and immunogenicity profiles of E4F4. Safety data to day 15 after the final subject in a cohort had been dosed were reviewed before commencing the next dose level.
Results
E4F4 was safe and well tolerated among healthy Chinese participants in this study. There was no obvious dose‐dependent relationship between frequency, severity or causality of treatment‐emergent adverse events. Cmax and area under the curve of E4F4 were dose proportional over the 0.45‐14.85 mg dose range. Median Tmax and t1/2 ranged from 146 to 210 h and 199 to 252 h, respectively, across E4F4 doses, with no dose‐dependent trends. For the intravenous glucose tolerance test, area under the curve of glucose in plasma from time 0 to 180 min showed a dose‐response relationship in the 1.8‐10.35 mg dose range, with an increased response at the higher doses.
Conclusion
E4F4 exhibited an acceptable safety profile and linear pharmacokinetics in healthy subjects. The recommended phase 2 dose is 4.5‐10.35 mg once every 2 weeks.
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