Fusion Splicing Research Articles

High power mid-infrared side-pump combiner with good thermal stability based on the point-by-point fusion splicing technique

High-power mid-infrared fiber lasers, featuring superior beam quality and good power-scaling ability, have a few important applications in material processing, medical surgery, and molecule spectroscopy. The high-power pump light combiner, as one of the key elements for constructing a mid-infrared fiber laser, is crucial for the laser performance. While some advanced side-pump combiners based on fluoride fiber have been reported in recent literatures, the thermal stability of the fluoride fiber combiner, which is closely-related to its power-scaling capability, is a long-living challenge. In this work, we demonstrate a high-power mid-infrared side-pump combiner with improved thermal stability, realized using the point-by-point fusion-splicing technique between a silica fiber taper and a piece of Er-doped fluoride gain fiber. The developed combiner exhibits a high coupling efficiency of ∼90%, supporting highly-stable operation at an incident pump power of up to 60 W. Using this combiner, we constructed a continuous-wave mid-infrared fiber laser which can deliver stably 4 W output power at 2.8 µm without using active cooling system. At this lasing power, the maximum input pump power is limited to 20 W to prevent fiber end-facet degradation, which can be further improved with the use of endcaps. This remarkable thermal stability renders the combiner great application potentials in constructing compact, robust, high-power fiber lasers at mid-infrared wavelengths.

Fiber-to-Chip Packaging With Robust Fiber Fusion Splicing for Low-Temperature Applications

Fiber-to-Chip Packaging With Robust Fiber Fusion Splicing for Low-Temperature Applications

Sensitivity-enhanced optical fiber sensor based on the Vernier effect for detection of ammonia in water

A sensitivity-enhanced optical fiber sensor for the detection of dissolved ammonia in water based on the Vernier effect is proposed and demonstrated. The sensor comprises a sensing Fabry-Perot interferometer (S-FPI) and a reference Fabry-Perot interferometer (R-FPI) in parallel. The S-FPI is an open cavity fabricated by the dislocation welding of single-mode fiber(SMF), which is filled with a mixture of ultraviolet-curable resin NOA 170 and Oxazine 170 perchlorate (O17). The R-FPI is a sealed cavity, which is constructed by fusion splicing of SMF and hollow core fiber (HCF). The proposed sensor is based on the chemical reaction between the dissolved ammonia and O17. This chemical reaction alters the refractive index (RI) of the S-FPI, resulting in a wavelength shift of the reflected spectrum. The two interferometers exhibit a nearly identical free spectral range (FSR), thereby enabling the generation of the Vernier effect, which markedly enhances the ammonia sensitivity of the sensor. Experimental results indicate that the sensor sensitivity is 0.34 nm/ppm in the dissolved ammonia range of 5-40 ppm, which is approximately 9.1 times that of the single S-FPI. The proposed sensor exhibits both good repeatability and a short response time, in addition to selectivity for the detection of ammonia.

Monolithic linear array fiber end cap for spectral beam combination

In this study, a fusion splicing system that facilitates the splicing of a monolithic linear array fiber end cap is constructed. The fusion splicing thermal field of the end cap irradiated by a CO2 laser is theoretically simulated using the finite element method. The experimental fusion splicing temperature agrees well with the simulation results. The splicing strength, misalignment, and high-power withstanding capacity of the fusion-spliced monolithic linear 3-fiber end cap are investigated. The use of the fabricated device in a dual-grating spectral beam combination (SBC) is also demonstrated with three-channel laser beams, achieving a combined beam with near-diffraction-limited beam quality M2=1.101. It shows that the development of the monolithic linear array fiber end cap is meaningful for achieving a compact high-brightness SBC system.

Transcriptomic Differences by RNA Sequencing for Evaluation of New Method for Long-Time In Vitro Culture of Cryopreserved Testicular Tissue for Oncologic Patients.

Earlier studies have established that culturing human ovarian tissue in a 3D system with a small amount of soluble Matrigel (a basement membrane protein) for 7 days in vitro increased gene fusion and alternative splicing events, cellular functions, and potentially impacted gene expression. However, this method was not suitable for in vitro culture of human testicular tissue. To test a new method for long-time in vitro culture of testicular fragments, thawed with two different regimes, with evaluation of transcriptomic differences by RNA sequencing. Testicular tissue samples were collected, cryopreserved (frozen and thawed), and evaluated immediately after thawing and following one week of in vitro culture. Before in vitro culture, tissue fragments were encapsulated in fibrin. Four experimental groups were formed. Group 1: tissue quickly thawed (in boiling water at 100 °C) and immediately evaluated. Group 2: tissue quickly thawed (in boiling water at 100 °C) and evaluated after one week of in vitro culture. Group 3: tissue slowly thawed (by a physiological temperature 37 °C) and immediately evaluated. Group 4: tissue slowly thawed (by a physiological temperature 37 °C) and evaluated after one week of in vitro culture. There are the fewest differentially expressed genes in the comparison between Group 2 and Group 4. In this comparison, significantly up-regulated genes included C4B_2, LOC107987373, and GJA4, while significantly down-regulated genes included SULT1A4, FBLN2, and CCN2. Differential genes in cells of Group 2 were mainly enriched in KEGG: regulation of actin cytoskeleton, lysosome, proteoglycans in cancer, TGF-beta signaling pathway, focal adhesion, and endocytosis. These Group 2- genes were mainly enriched in GO: spermatogenesis, cilium movement, collagen fibril organization, cell differentiation, meiotic cell cycle, and flagellated spermatozoa motility. Encapsulation of testicular tissue in fibrin and long-time in vitro culture with constant stirring in a large volume of culture medium can reduce the impact of thawing methods on cryopreserved testicular tissue.

Large measurement range curvature sensor based on all-fiber Mach-Zehnder interferometer using triple-ring-core few-mode fiber

This study experimentally demonstrates a large measurement range curvature sensor based on a Mach-Zehnder interferometer (MZI) in a triple-ring-core fiber (TRCF). The sensor is fabricated by fusion splicing a segment of TRCF between two pieces of single-mode fiber (SMF), forming the SMF-TRCF-SMF sandwich structure. Since the TRCF can support the propagation of a few guided modes, the fundamental mode interferes with high-order modes in the sensing part to produce a periodic interference spectrum. Bending causes the effective refractive index of the mode to change, which shifts the interference spectrum. The bending measurement is achieved by monitoring the wavelength variation of interference dips. The proposed sensors can realize curvature measurements up to 100 m-1, with a bending sensitivity of -225.9 pm/m-1. It is believed that the proposed MZI sensor may have potential applications in robot hand gesture recognition and control.

Mid-infrared all-fiber superfluorescent source in Er3+-doped fluoride fiber

We report, to the best of our knowledge, the first mid-infrared (MIR) all-fiber superfluorescent source based on a superfluorescent seed and a single-stage amplifier. A 7.8-m-long section of highly-Er3+-doped fluoride fiber is used in the superfluorescent seed and a 4.3-m-long section of lightly-Er3+-doped fluoride fiber acts as the amplifier. Two home-made MIR pump-signal combiners based on side-pumping technology are fabricated directly on two sections of gain fiber. By direct-low-loss fusion splicing of two kinds gain fiber, the power of MIR superfluoresescence main output is amplified to 0.35 W and the power of rear output is amplified to 0.2 W. The output spectrum under maximum power spans from 2680 nm to 2880 nm with 20 dB bandwidth of 60 nm. The measured time domain and output beam profile show that this superfluorescent source keeps relatively stable in microsecond time scale without self-pulsing effect occurrence and has near single-mode gaussian characteristic. This works provides a new way for MIR superfluorescent source, which is of practical interest in a range of applications.

Rapid Prototyping for Nanoparticle-Based Photonic Crystal Fiber Sensors.

The advent of nanotechnology has motivated a revolution in the development of miniaturized sensors. Such sensors can be used for radiation detection, temperature sensing, radio-frequency sensing, strain sensing, and more. At the nanoscale, integrating the materials of interest into sensing platforms can be a common issue. One promising platform is photonic crystal fibers, which can draw in optically sensitive nanoparticles or have its optical properties changed by specialized nanomaterials. However, testing these sensors at scale is limited by the the need for specialized equipment to integrate these photonic crystal fibers into optical fiber systems. Having a method to enable rapid prototyping of new nanoparticle-based sensors in photonic crystal fibers would open up the field to a wider range of laboratories that could not have initially studied these materials in such a way before. This manuscript discusses the improved processes for cleaving, drawing, and rapidly integrating nanoparticle-based photonic crystal fibers into optical system setups. The method proposed in this manuscript achieved the following innovations: cleaving at a quality needed for nanoparticle integration could be done more reliably (≈100% acceptable cleaving yield versus ≈50% conventionally), nanoparticles could be drawn at scale through photonic crystal fibers in a safe manner (a method to draw multiple photonic crystal fibers at scale versus one fiber at a time), and the new photonic crystal fiber mount was able to be finely adjusted when increasing the optical coupling before inserting it into an optical system (before, expensive fusion splicing was the only other method).

High-sensitivity strain sensor based on an asymmetric tapered air microbubble Fabry-Pérot interferometer with an ultrathin wall

A Fabry-Pérot interferometer (FPI) with an asymmetric tapered structure and air microbubble with an ultrathin wall is designed for high-sensitivity strain measurement. The sensor contains an air microbubble formed by two single-mode fibers (SMF) prepared by fusion splicer arc discharge, and a taper is applied to one side of the air microbubble with a wall thickness of 3.6 µm. In this unique asymmetric structure, the microbubble is more easily deformed under stress, and the strain sensitivity of the sensor is up to 15.89 pm/µɛ as evidenced by experiments.The temperature sensitivity and cross-sensitivity of the sensor are 1.09 pm/°C and 0.069 µɛ/°C in the temperature range of 25-200°C, respectively, thus reducing the measurement error arising from temperature variations. The sensor has notable virtues such as high strain sensitivity, low-temperature sensitivity, low-temperature cross-sensitivity, simple and safe process preparation, and low cost. Experiments confirm that the sensor has good stability and repeatability, and it has high commercial potential, especially strain measurements in complex environments.

Dead Zone Fault Detection Optimization Method for Few-Mode Fiber Links Based on Unexcited Coupled Higher-Order Modes

Dead Zone Fault Detection Optimization Method for Few-Mode Fiber Links Based on Unexcited Coupled Higher-Order Modes

An in-fiber Mach–Zehnder strain sensor for studying multimode interference of light

Multimode interference of light is an optical interference phenomenon based on waveguides, which has broad applications in optical communication, lasers, and optical fiber sensing. Since optical fiber has become the most widely used optical waveguide in modern society, multimode interference in optical fibers is an ideal candidate for projects in university teaching laboratories. Here, we implement an in-fiber Mach–Zehnder strain sensor-based experiment to study multimode interference in optical fibers. The sensor is fabricated by fusion splicing a piece of thin core fiber between two single mode fibers. One end of the thin core fiber is spliced without a core offset, while the other end is spliced with a core offset. Due to the mode field diameter mismatch and core offset, cladding modes are excited and interfere with the core mode in thin core fiber. Students can observe the sensor fabrication demonstration and perform a strain test with an optical spectrum analyzer. The wavelength spectra captured by the optical spectrum analyzer under different strains are analyzed with the signal processing tools of fast Fourier transform and fast Fourier transform filter. Students then find characteristics of the multimode interference in the sensor from the analysis. The experiment extends undergraduates' knowledge of light interference and is an instructive exercise for them in modern coherence theory.

Role of lateral Core-Offset in the sensitivity enhancement of single Mode-No core-Single mode fiber cascaded structure

In this study, an extensive examination of the influence of core-offset on different sensitivities of a single-mode-no-core-single-mode (SNS) fiber sensor probe in a variety of external disturbances, including refractive index changes, strain, and temperature, has been presented and thoroughly investigated. To achieve this, a consistent sensing length of 5 cm no-core fiber (NCF) was utilized between two single-mode fibers (SMFs) with different offset values, facilitated by the built-in options of a fusion splicer. The theoretical and experimental principles of sensitivity are discussed in detail. Key aspects such as spectral analysis and fast Fourier transform of the disclosed transmission spectrum underwent meticulous scrutiny. The outcome of the experiment indicates that the SNS fiber sensor exhibits an increasing sensitivity to refractive index (RI) over the 1.333–1.398 range when the offset value increases, with a maximum of 201.221 nm/RIU sensitivity. On the other hand, the RI sensitivity decreases with increasing offset value in the range of 1.402–1.441; the highest sensitivity attained is 656.641 nm/RIU. The strain sensitivity shows a decreasing trend with increasing offset, with the maximum sensitivity reaching −1.59 pm/µε in a wide range of 0 to 2000 µε. For temperature sensing, the sensitivity remains unaffected with a core offset; consistently, the achieved sensitivity is approximately 11.51 pm/°C over a broad range of temperature of 30 °C to 120 °C Compared with RI, it is found that the reliance of core-offset on strain sensitivity is very low whereas on temperature sensing almost insensitive, provided that the sensing length and diameter remain constant. These results provide insightful direction for the creation of extremely sensitive sensors for a variety of applications.

Widely tunable S-band ring-cavity Tm3+-doped fluorotellurite fiber laser.

Tm3+-doped fluorotellurite fibers (TDFTFs) are fabricated by using a rod-in-tube method. A 2.1 m long TDFTF is used as the gain medium, in which both ends of the TDFTF are connected to a short piece of a silica fiber by direct fusion splicing. By inserting the above TDFTF and a tunable optical bandpass filter into a ring cavity and employing a 1400/1570 nm dual-wavelength pumping technique, tunable lasing from 1460 to 1526 nm is obtained, which almost covers the whole S-band. To the best of our knowledge, this is the first report of tunable Tm3+-doped fiber laser with a tunable range almost covering the whole S-band. Furthermore, by removing the tunable optical bandpass filter from the ring cavity, free-running multi-wavelength lasers at 1500 and 1901 nm are achieved. Our results show that TDFTFs are promising gain media for constructing S-band fiber lasers.

Vernier effect based on cascading two Mach–Zehnder interferometers for selectable comb filter and saturable absorber applications in erbium-doped fiber laser

We present the applications of a Vernier effect based on cascading two Mach–Zehnder interferometers (MZIs) as a selectable comb filter and saturable absorber (SA) in an erbium-doped fiber laser (EDFL).Each MZI is composed of bi-tapered polarization-maintaining fibers (PMFs) constructed by fusion splicing between two single-mode fibers (SMFs), which are then connected in series to produce the Vernier effect. The first tapered MZI (called MZI-1) acted as a comb filter to providea larger free spectral range (FSR). The second MZI (MZI-2) based comb filter has a smaller FSR. The combination of these two filters forms an envelope structure on the comb-like spectrum. In this work, the first implementation of the comb filterbased onthe Vernier effectwas used as a wavelength-selectable filter. Through the adjustment of the polarization controller (PC1) and (PC2) inside the cavity, the FSR of the envelope can be varied, thereby switchable and adjustable multiwavelength was achieved. The second implementation uses a graphene nanoparticle (G-Nps)/polymer composite deposited onto the MZI-1 comb filter to act as an SA. At the 80 mW pump threshold, stable Q-switching EDFL operation was successfully activated at 1560.8 nm. The shortest pulse width of 2.89 μs at a 85.91 kHz repetition rate was achieved at 330 mA (180 mW) pump power. The proposed Vernier effect based on cascading two tapered MZIs configuration can find potential applications in the fields of advancedmultiwavelength fiber lasers and short pulse generation.

Composite membrane of graphene oxide and gold nanoparticles functionalized S fiber taper aptasensor for highly sensitive bisphenol A detection.

The S fiber taper (SFT) aptasensor with a composite sensitive membrane of graphene oxide and gold nanoparticles was proposed for the rapid and highly sensitive detection of bisphenol A (BPA). The SFT was obtained using a fusion splicer; subsequently, the composite film was deposited on its surface, and the specific aptamer was covalently bonded to the surface of gold nanoparticles. The detection mechanism relies on monitoring changes in the external refractive index induced by the specific binding of BPA to the aptamer. The developed SFT aptasensor exhibited a remarkable sensitivity of 15.5 nm/nM and a limit of detection as low as 0.01 nM for BPA. These findings highlight the aptasensor's potential for diverse monitoring applications.

Enhancing sensitivity of trace copper detection based on coupled optoelectronic oscillator

We propose to employ coupled optoelectronic oscillator (COEO) for trace copper detection to achieve an enhanced sensitivity and stability. By replacing the optical source of the traditional OEO with an optical feedback loop, the oscillation frequency is determined by the cavity loop length in conjunction with the laser output wavelength. The sensing head, which is fabricated by inserting a fusion spliced fiber with large lateral offset fusion splicing in a Sagnac loop, act as a wavelength selection component in the laser loop. Hence, the oscillation frequency changes with the varying solution concentration. Benefitting from the matching of the laser loop and the OEO loop, the final oscillation mode is more stable. By comparing the performance of the COEO-based, single-loop and dual-loop OEO-based sensors, the highest sensitivity of 41.1 Hz/(uMol/L) is obtained by the COEO-based sensor. Since the positive feedback of two loops, the single mode oscillation can be implemented without additional devices.

Interferometric fiber sensor for lead ion detection based on MoS2 hydrogel coating

A fiber optic sensor coated with molybdenum disulfide (MoS2) hydrogel is firstly proposed for the detection of lead ion (Pb2+). By splicing a dispersion-compensating fiber (DCF) between two single-mode fibers (SMFs) to form a Mach-Zehnder interferometer (MZI), and using a fusion splicer to discharge the SMF input and output to form a thick waist cone to act as a coupler. A portion of the DCF cladding is etched to excite higher order cladding patterns and a hydrogel sensing film is applied to the etched area, the sulfur atoms in the sensing film form coordination bonds with Pb2+ and change the refractive index (RI) of the sensing film, which further leads to the wavelength shift of the resonant dip. The production process is simple and environmentally friendly. By monitoring the wavelength shift, the adsorption of Pb2+ is continuously monitored, and the sensor has a sensitivity of 3.25 × 108 nm/(mol/L) in the range of 0–1.1 × 10−8 mol/L Pb2+ in aqueous solution. The theoretical detection limit of Pb2+ concentration is 6.15 × 10−11 mol/L at a spectrometer resolution of 0.02 nm. In addition, the experimental results show that the sensor has good repeatability, selectivity and stability, and has a broad application prospect in the field of Pb2+ detection in industry and agriculture.

Fiber Optic Splicing Training with Mechanical Splicers and Fusion Splicers for Computer and Network Engineering Vocational School Students

Fiber Optic Splicing Training with Mechanical Splicers and Fusion Splicers for Computer and Network Engineering Vocational School Students

An Intensity-Demodulated Fiber-Optic Magnetometer Based on Nanostructured Magnetic Fluid-Filled Fluidic Photonic Crystal Fibers.

An intensity-demodulated fiber-optic magnetometer is proposed and experimentally investigated, which is fabricated via fusion splicing a segment of photonic crystal fiber (PCF) between single-mode fibers (SMFs), with the cladding air holes of PCF filled with magnetic fluid. Using the magneto-optical properties of the magnetic fluid, the transmission spectrum is changed with an external magnetic field. Based on the intensity variations in the transmission spectrum, the magnetic field is detected, and a sensitivity of 0.238 dB/mT is obtained at 1550.03 nm with the length of PCF 5.5 cm. By converting light signals into electrical signals, a sensitivity of 0.003 V/mT is achieved. The fiber-optic magnetometer possesses the advantages of simple fabrication, compact/robust structure, and low cost.

Differentiated Focal Plane Assisted Multi-core Fiber Fusion Splice Loss Evaluation

Differentiated Focal Plane Assisted Multi-core Fiber Fusion Splice Loss Evaluation