3D-Printed Ultracompact Multicore Fiber-Tip Probes for Simultaneous Measurement of Nanoforce and Temperature.

Optical fiber force sensing has attracted considerable interest in biological, materials science, micromanipulation, and medical applications owing to its compact and cost-efficient configuration. However, the glass fiber has an intrinsic high Young's modulus, resulting in force sensors being generally less sensitive. While hyperelastic polymer materials can be utilized to enhance the force sensitivity, the thermodynamic properties of the polymer may weaken the sensing accuracy and reliability. Herein, we demonstrate ultracompact three-dimensional (3D)-printed multicore fiber (MCF) tip probes for simultaneous measurement of nanoforce and temperature with high sensitivity. The sensor is highly sensitive to force-induced deformation due to the special geometric features of the polymer microcantilever, and the high-temperature sensitivity can be implemented through the poly(dimethylsiloxane) (PDMS) microcavity on the same fiber facet. Moreover, the sensitivities of the fiber interferometers are remarkably enhanced by introducing the optical analogue of the Vernier effect. Such a device exhibits a force sensitivity of 56.35 nm/µN, which is more than 103 times that of all-silica fiber force sensors. The PDMS microcavity provides a temperature sensitivity of 1.447 nm/°C, measuring the local temperature of the probe and compensating for temperature crosstalk of the force detection. The proposed compact MCF-tip sensor can simultaneously measure nanoforce and temperature with high sensitivity, facilitating multiparameter sensing in a restricted space environment and showing the potential in miniaturized all-fiber multiparameter sensors.

Ultra-Bend-Resistant 4-Core Simplex Cable Used for Short-Reach Dense Spatial Division Multiplexing Optical Transmission.

We optimized and fabricated an ultra-bend-resistant 4-core simplex cable (SXC) employing 4-core multicore fiber (MCF) suitable for short-reach dense spatial division multiplexing (DSDM) optical transmission in the O-band. The characteristics of transmission loss, macro-bending and cross-talk (XT) between adjacent cores after cabling were firstly clarified. By introducing the trapezoid index and optimizing the cabling process, the maximum values of added XT of 1.17 dB/km due to 10 loops with a bending radius of 6 mm imposed over the 4-core SXC and a macro-bending loss of 0.37 dB/10 turns were, respectively, achieved.P Then, the optical transmission with low bit error rate (BER) was presented using a 100GBASE-LR4 transceiver over the 1.2 km long 4-core SXC. The excellent bending resistance of the 4-core SXC may pave the way for a reduction in space pressure and increase in access density on short-reach optical interconnect (OI) based on DSDM.

Fiber Bragg gratings inscribed in nanobore fibers.

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.

Ultralow-loss fusion splicing between antiresonant hollow-core fibers and antireflection-coated single-mode fibers with low return loss.

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.

Optical microfibers integrated with evanescent field triggered self-growing polymer nanofilms.

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.

Fabrication and Characterization of an Optimized Low-Loss Two-Mode Fiber for Optoacoustic Sensing.

An optimized multi-step index (MSI) 2-LP-mode fiber is proposed and fabricated with low propagation loss of 0.179 dB/km, low intermodal crosstalk and excellent bend resistance. We experimentally clarified the characteristics of backward Brillouin scattering (BBS) and forward Brillouin scattering (FBS) induced by radial acoustic modes (R0,m) in the fabricated MSI 2-LP-mode fiber, respectively. Via the use of this two-mode fiber, we demonstrated a novel discriminative measurement method of temperature and acoustic impedance based on BBS and FBS, achieving improved experimental measurement uncertainties of 0.2 °C and 0.019 kg/(s·mm2) for optoacoustic chemical sensing. The low propagation loss of the sensing fiber and the new measurement method based on both BBS and FBS may pave the way for long-distance and high spatial resolution distributed fiber sensors.

Low-loss fusion splicing between spacing-mismatched multicore fibers.

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.

High-efficient subwavelength-scale optofluidic waveguides with tapered microstructured optical fibers.

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.

Ultralow-loss fusion splicing between negative curvature hollow-core fibers and conventional SMFs with a reverse-tapering method.

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.

Fiber polarizer based on selectively silver-coated large-core suspended-core fiber.

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.

Continuous Passive Motion After Total Knee Arthroplasty: A Systematic Review and Meta-analysis of Associated Effects on Clinical Outcomes.

OBJECTIVE: To evaluate the efficacy of continuous passive motion (CPM) after total knee arthroplasty (TKA) and whether the use of CPM is related to improved clinical and functional outcomes. DATA SOURCES: A systematic MEDLINE search via Web of Science, Cochrane Library, and PubMed databases was conducted. STUDY SELECTION: English-language articles published between January 2000 and May 2018 reporting the related clinical outcomes of CPM after TKA were included. A total of 3334 titles and abstracts were preliminarily reviewed, of which 16 studies were included according to the eligibility criteria. DATA EXTRACTION: Two different reviewers were selected to perform the study extraction, independent of each other. If there were any disagreements regarding the final list of studies, the third reviewer reviewed the list as an arbitrator for completeness. DATA SYNTHESIS: A total of 16 trials with 1224 patients were included. The pooled results revealed that use of CPM did not show a statistically significant improvement of postoperative knee range of motion (ROM) except for middle-term passive knee extension and long-term active knee flexion ROM. Also, CPM therapy did not show a significant positive effect on the functional outcomes. No significant reduction in length of stay (LOS) and incidence of adverse events (AEs) was identified. CONCLUSION: Among patients undergoing TKA, neither the ROM nor the functional outcomes could be improved by CPM therapy. Moreover, the risk of AEs and LOS could not be reduced by application of CPM. The current available evidence suggested that this intervention was insufficient to be used routinely in clinical practice.

A new minimally invasive treatment for anal fistula.

In colorectal surgery, eradicating the fistula and maintaining continence are still complex challenges for a colorectal surgeon. A minimally invasive method using a novel device was performed to consecutively treat 14 patients with anal fistula from August 2008 to November 2009. After a follow-up period of 36 months, 13 patients achieved successful closure of their fistula tracts, and recurrence occurred only in one patient. Recurrence was due to the delay of dressing change. No patient had interference with continence, and no major intra- and postoperative complications were identified. Using the novel device with invasive methods can be a promising alternative for managing anal fistulas.