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Hybrid optical fibers have been widely investigated in different architectures to build integrated fiber photonic devices and achieve various applications. Here we proposed and fabricated hybrid microfiber waveguides with self-growing polymer nanofilms on the surfaces of microfibers triggered by evanescent field of light for the first time. We have demonstrated the polymer nanofilm of ∼50 nm can be grown on the microfiber with length up to 15 mm. In addition, the roughness of nanofilm can be optimized by controlling the triggering laser power and exposure duration, and the total transmission loss of the fabricated hybrid microfiber is less than 2 dB within a wide wavelength range. The hybrid polymer nanofilm microfiber waveguides have been characterized and their relative humidity (RH) responses have also been tested, indicating a potential for RH sensing. Our fabrication method may also be extended to construct the hybrid microfibers with different functional photopolymer materials.

Graphitic carbon nitride (g-CN) nanosheet is a potential material for sensing applications. The g-CN nanosheet films deposited on microfibers were first fabricated and employed for relative humidity (RH) optical sensing. The RH sensitivity of microfibers was significantly enhanced via g-CN nanosheet coating, the optical transmitted power of coated microfiber humidity sensor was changed ∼10.6 dB when the RH varied from 40% to 95%. In addition, fast response time of 0.43 s and recovery time of 0.87 s were demonstrated by monitoring human breathing. The g-CN nanosheet coated microfiber humidity sensor possesses excellent stability, repeatability, reversibility, and cost-effectivity. The experimental results validate that the microfiber combined with g-CN nanosheets is a promising platform for environmental and biological RH sensing applications.

The nanobore fiber (NBF) is a promising nanoscale optofluidic platform due to its long nanochannel and unique optical properties. However, so far, the applications of NBF have been based only on its original fiber geometry without any extra functionalities, in contrast with various telecom fiber devices, which may limit its wide applications. Here, we provide the first, to the best of our knowledge, demonstration of NBF-based fiber Bragg gratings (FBGs) introduced by either the femtosecond (fs) laser direct writing technique or the ultraviolet (UV) laser phase mask technique. Moreover, the FBG fabricated via the UV laser was optimized, achieving a high reflectivity of 96.89% and simultaneously preserving the open nanochannel. The NBF-based FBGs were characterized in terms of temperature variation and the infiltration of different liquids, and they showed high potential for nanofluidic applications.

Robust low-loss optical fiber joints are a prerequisite in all-fiber devices. Joining structurally dissimilar fibers, such as microstructured optical fibers, is a timely challenge, as they are beco...

The Fresnel reflection of a splice from the air–silica interface between a hollow-core fiber (HCF) and a solid-core conventional fiber will increase the splicing loss and also cause possible instability of transmission. Here, for the first time, we develop a novel approach to fusion splicing an antireflection-coated (AR-coated) conventional fiber and an antiresonant HCF, which was generally claimed to be impossible because of the heat-induced damage of the coating, and achieve state-of-the-art ultralow fusion splicing loss less than 0.3 dB and a low return loss less than −28 dB by optimizing the splicing procedures and parameters. Our new fusion splicing approach will benefit the wide application of HCFs in telecoms, laser technologies, gyroscopes, and fiber gas cells.

We propose a tapered optofluidic microstructured optical fiber with a subwavelength core, which can provide a promising low-loss subwavelength-scale optofluidic waveguide for various applications.

Bessel-like beams possess unique light intensity distribution and self-healing propagation property have been widely used in various fields such as imaging (Planchon et al in Nat. Methods 8:417–423, 2011 [1]), particle guiding (Arlt et al in Phys Rev A 63(6):063602, 2001 [2]), and microfabrication (Kumar et al Appl Phys A 123:698, 2017 [3]).

Fiber gas sensing techniques have been applied for a wide range of industrial applications. In this paper, the basic fiber gas sensing principles and the development of different fibers have been introduced. In various specialty fibers, hollow-core photonic crystal fibers (HC-PCFs) can overcome the fundamental limits of solid fibers and have attracted intense interest recently. Here, we focus on the review of HC-PCF gas sensing, including the light-guiding mechanisms of HC-PCFs, various sensing configurations, microfabrication approaches, and recent research advances including the mid-infrared gas sensors via hollow core anti-resonant fibers. This review gives a detailed and deep understanding of HC-PCF gas sensors and will promote more practical applications of HC-PCFs in the near future.

Graphitic carbon nitride nanosheets deposited on microfibers for relative humidity sensing is first demonstrated with high sensitivity. Fast response time of 0.43 s and recovery time of 0.87 s are characterized. © 2020 The Author(s)

Multicore fibers (MCFs) offer a fascinating solution to the need to increase the fiber density and thus meet the exponentially growing demand for capacity in optical communication networks. Despite overwhelming research into MCFs, the desire for a general fusion splicing scheme between dissimilar MCFs remains unanswered. Here, we propose a tapering technique to reshape MCFs that includes both reverse-tapering and down-tapering schemes and can be exploited to tailor the core-to-core spacing and modify the modal property of MCFs. By matching both the spacing and the mode field diameter, we demonstrated a low-loss (0.18 ± 0.10 dB) and low-crosstalk (–68 ± 3 dB) fusion splice between two spacing-mismatched MCFs with a spacing difference of up to 26 μm. The proposed novel schemes are also suitable for splicing between MCFs with slightly different spacings and can provide a unique perspective for fabricating MCF devices and boosting various MCF applications.

Microstructured optical fibers (MOFs) have attracted intensive research interest in fiber-based optofluidics owing to their ability to have high-efficient light-microfluid interactions over a long distance. However, there lacks an exquisite design guidance for the utilization of MOFs in subwavelength-scale optofluidics. Here we propose a tapered hollow-core MOF structure with both light and fluid confined inside the central hole and investigate its optofluidic guiding properties by varying the diameter using the full vector finite element method. The basic optical modal properties, the effective sensitivity, and the nonlinearity characteristics are studied. Our miniature optofluidic waveguide achieves a maximum fraction of power inside the core at 99.7%, an ultra-small effective mode area of 0.38 µm2, an ultra-low confinement loss, and a controllable group velocity dispersion. It can serve as a promising platform in the subwavelength-scale optical devices for optical sensing and nonlinear optics.

International audience; Negative curvature hollow-core fibers (NC-HCFs) can boost the excellent performance of HCFs in terms of propagation loss, nonlinearity, and latency, while retaining large core and delicate cladding structures, which makes them distinctly different from conventional fibers. Construction of low-loss all-fiber NC-HCF architecture with conventional single-mode fibers (SMFs) is important for various applications. Here we demonstrate an efficient and reliable fusion splicing method to achieve low-loss connection between a NC-HCF and a conventional SMF. By controlling the mode-field profile of the SMF with a two-step reverse-tapering method, we realize a record-low insertion loss of 0.88 dB for a SMF/NC-HCF/SMF chain at 1310 nm. Our method is simple, effective, and reliable, compared with those methods that rely on intermediate bridging elements, such as graded-index fibers, and can greatly facilitate the integration of NC-HCFs and promote more advanced applications with such fibers.

A tunable fiber polarizer based on the selectively silver-coated large-core suspended-core fiber (LSCF) was proposed. A thin silver layer was coated on the inner surface of two opposite air holes of the LSCF by the chemical liquid-phase deposition method. The y -polarized light (parallel to the two silver-coated air holes) will excite surface plasmon resonance and experience large transmission loss, while the x -polarized light does not, resulting in a fiber polarizer. By varying the liquid filled in the microchannels of the LSCF, the operating wavelength can be tuned in the visible and near infrared region along with the surface plasmon resonance wavelength. The dependence of the polarization characteristics on the fiber length was experimentally investigated. The maximum polarization extinction ratio (PER) of 20.1 dB, 19.6 dB, and 18.3 dB and insertion loss (IL) of 2.24 dB, 2.56 dB, and 2.08 dB are achieved with the optimal fiber length of 16 cm at the operating wavelengths of 565.4 nm, 626.7 nm, and 739.7 nm, respectively. Compared with the multimode fiber-based polarizers reported previously, the proposed selectively silver-coated LSCF polarizer exhibits higher PER and lower IL.

We present a novel and efficient approach to generating Bessel-like beams through fabricating self-growing polymer microtips at the facet of single-mode fibers. To produce these beams, the length and shape of microtips were precisely optimized. Specifically, the convex droplet height and its photopolymerization parameters feature prominently in Bessel-like beams via microtips. A wide conversion bandwidth of the microtips and self-healing properties of the produced Bessel-like beam were also investigated in detail. Our microtips provide an effective, low-cost, and ultra-compact way for Bessel-like beams generation.