Splicing Point Research Articles

BOTDA-Based Technique for Measuring Maximum Loss and Crosstalk at Splice Point in Few-Mode Fibers

BOTDA-Based Technique for Measuring Maximum Loss and Crosstalk at Splice Point in Few-Mode Fibers

Fiber-optic Michelson interferometer for detecting coolant level and refractive index

Abstract This paper presents an interferometer based on a single-mode fiber-multimode fiber-thin-core fiber (SMF–MMF–TCF) Michelson interference structure that can be used for the measurements of coolant level and refractive index. Because of the different diameters of the cores of the individual fibers, optical excitation and coupling occur at the splicing points of the fibers. The multimode fibers are the couplers in the sensing structure, which allow the exciting light to enter the cladding of the thin-core fibers. The end face of the thin-core fiber is coated with a silver film to enhance the reflectivity of the light. The results show that the interference intensity first increases and then decreases with the length of TCF. When TCF is 4 cm, the interference light intensity is the strongest. The sensitivity of the sensor is 138.091 nm/RIU with the linearity of 0.977 over the refractive index of the coolant in the range of 1.3605–1.3880, and the temperature and time effects on the sensor are small. The proposed sensor has the advantages of simple fabrication, high repeatability, and good stability and it can be applied to the measurements of coolant level and refractive index in automotive engines.

High-coupling efficiency and robust fusion splicing between fluorotellurite and chalcogenide fibers

We demonstrate a low-loss and high-robustness fusion splicing point between fluorotellurite fiber and arsenic sulfide-based chalcogenide fiber (As2S3) by using an asymmetric fiber splicing technology. The splicing loss of point is less than 0.55 dB at the wavelength of 1.55 μm, and the monitored tension is 129 g by tuning the distance of the fusion splicing head offset in the fusion splicing process. Using an all-fiber testing system, the fusion splicing point loss between the 1.55 μm testing light source tail fiber (silica fiber) and the fluorotellurite fiber is 0.503 dB. The output power from the As2S3 fiber is 0.91 W with a testing light source of 2 W, and the temperature of the splicing joint shows no evident increase. This finding indicates that the fusion splicing point offers excellent beam quality. This work lays a solid foundation for building an all-fiber cascaded system generating mid-infrared supercontinuum with high-coupling efficiency between mid-infrared soft-glass fibers.

Harmonic mode-locked fiber laser based on microfiber-assisted nonlinear multimode interference

A novel harmonic mode-locked fiber laser based on nonlinear multimode interference (NL-MMI) in a microfiber-assisted ultrafast optical switch is proposed in this Letter. The microfiber-assisted ultrafast optical switch can be obtained by tapering the splicing point of the graded-index multimode fiber (GIMF) and single-mode fiber, which not only helps to shorten the self-imaging period in GIMF to relax the strict requirement of NL-MMI on the length of multimode fiber, but also improves the harmonic order. In the experiment, with the waist diameter of ∼15 µm, the repetition rates of the fiber laser can be stably locked at 285 MHz, corresponding to the 16th-order harmonic mode-locking, with the pulse duration of 1.52 ps. Our results provide novel insight into the design of a high-repetition-rate laser and the application of microfibers in the mode-locking device.

Brillouin optical time domain reflectometry for estimating loss and crosstalk at the splice point in few-mode fibers

We propose a technique using Brillouin optical time domain reflectometry for estimating the loss and crosstalk at a splice point in few-mode fibers. The technique measures the splice loss of a fundamental mode using a feature where the Brillouin gain spectrum differs depending on the mode. Then, the splice loss of the higher-order mode and the modal crosstalk at the splice point are estimated from the measured loss of the fundamental mode. We reveal the feasibility of our technique in a comparison of the experimental results with the numerically calculated ones. The fiber under test we used was two mode fibers with a graded-index profile. We found that the splice loss of the LP01 mode can be yielded by measuring the splice loss under the condition that the scattered light of the LP01 mode becomes larger than that of other modes. Moreover, we determined that the loss and crosstalk of the LP11 mode could be yielded using the measured loss of the LP01 mode and the approximate expression of the mode coupling coefficient at the splice point.

The influence of axial offset of fusion splicing on a large mode area fiber based oscillator

Fiber oscillators have the potential for achieving high power, high beam quality lasers with simple and compact structure, of which the fusion splicing point is an important aspect to the laser output characteristics. A model taking into account the axial offset of the splicing point and spatial mode competition has been proposed to analyze the mode interaction of a large mode area fiber based oscillator. The calculated results show that the axial offset of the output side fusion point has the main influence on the laser output beam quality, but the axial offset would not obviously reduce the optical efficiency, especially when the value is smaller than 2 μm. The influence of cavity parameters on the laser output characteristics under the existence of splicing point with axial offset has also been discussed. This model can provide a method for analyzing the mode dynamic that may be helpful for understanding the mode interactions in fiber oscillators.

Double F-P Interference Optical Fiber High Temperature Gas Pressure Sensor Based on Suspended Core Fiber

A compact and simple double F-P interference optical fiber optic gas pressure sensor based on suspended core structure is proposed and demonstrated. The sensor is formed by splicing a Section of thin-walled grapefruit photonic crystal fiber (G-PCF) with single-mode fiber (SMF). By adjusting the special fusion parameters, a short air-cavity region is formed in the G-PCF next to the splicing point with the SMF segment, and the other end of the G-PCF segment is open to the atmosphere. The output interference spectrum of the sensor comprises of two spectral parameters that have different sensitivities to temperature and gas pressure. One of them is the wideband envelope that is associated with the air-cavity and it is only sensitive to the gas pressure but insensitive to the change of ambient temperature. This property is particularly useful for addressing the complex temperature-pressure cross sensitivity of both spectral parameters. The research findings indicate that the sensor can perform an accurate measurement for gas pressure in dynamic range of 0-1.0 MPa under the high temperature condition up to 500 °C.

Compact strain fiber sensor based on Fabry-Perot microstructural air cavity

A Fabry-Perot air chamber was prepared at the splicing point of two single-mode fibers by the heating-expansion of liquid glycerin. The morphology of the Fabry-Perot air chamber was optimized by the splicing parameters (drawing process, discharging location, time and intensity) and the fibers’ end-face (plane or arc). The in-line Fabry-Perot interferometer was employed to determine the tensile strain from 0 to 1.2 N. A sensitivity of 3.628 nm/N and the resolution of ∼0.005 N were experimentally demonstrated. The reported Fabry-Perot strain sensor is easy to fabricate, low cost, and flexible to connect with other fibers.

Multiplexed Weak Waist-Enlarged Fiber Taper Curvature Sensor and Its Rapid Inline Fabrication.

This study proposes a multiplexed weak waist-enlarged fiber taper (WWFT) curvature sensor and its rapid fabrication method. Compared with other types of fiber taper, the proposed WWFT has no difference in appearance with the single mode fiber and has ultralow insertion loss. The fabrication of WWFT also does not need the repeated cleaving and splicing process, and thereby could be rapidly embedded into the inline sensing fiber without splicing point, which greatly enhances the sensor solidity. Owing to the ultralow insertion loss (as low as 0.15 dB), the WWFT-based interferometer is further used for multiplexed curvature sensing. The results show that the different curvatures can be individually detected by the multiplexed interferometers. Furthermore, it also shows that diverse responses for the curvature changes exist in two orthogonal directions, and the corresponding sensitivities are determined to be 79.1°/m−1 and –48.0°/m−1 respectively. This feature can be potentially applied for vector curvature sensing.

Seven-core fiber torsion sensor with microcavity structure based on intensity measurement

A seven-core fiber torsion sensor with microcavity structure based on intensity measurement is proposed. It is composed of a seven-core fiber (SCF) and two multi-mode fibers (MMF). The first end of the SCF has a microcavity structure. Because the mode fields between the MMF and SCF do not match at the splicing point, the phenomenon of mode interference will be formed between cladding modes and core modes. Experimental results show that in a clockwise situation, the intensity of transmission spectrum increases in the torsion range of 0∼70°, the torsion sensitivity is 0.098 dB/∘. And in a counterclockwise situation, the intensity of transmission spectrum decreases, the torsion sensitivity is 0.103 dB/∘. The sensor has a simple structure and easy to fabricate, so it has wide application prospects in the field of torsion sensing.

Novel Intensity-demodulated Fiber-optic Refractive Index Sensor Based on Splicing Point Tapered Fiber

Novel Intensity-demodulated Fiber-optic Refractive Index Sensor Based on Splicing Point Tapered Fiber

Compact all-fiber thermo-optic modulator based on a Michelson interferometer coated with NaNdF4 nanoparticles.

We propose and investigate an all-fiber thermo-optic modulator based on a side-polished twin-core fiber (TCF) Michelson interferometer (MI) coated with NaNdF4 nanoparticles. The MI was fabricated by tapering the splicing point between the TCF and a single mode fiber (SMF). A short suspended core fiber (SCF) is spliced to one core of the TCF to introduce a fixed optical phase difference (OPD). The side-polished core is coated with photo-thermal material NaNdF4. Owing to the ohmic heating of NaNdF4 nanoparticles under 808 nm pump laser, the effective refractive index of the polished core is changed, resulting in a phase shift of the MI. The MI has a significant modulation phase shift with 2.9 π near the wavelength of 1260 nm and can obtain an optical switching with a rise (fall) time of 152 (50) ms. The proposed device will have a great application potential in optical modulators due to compact structure and strong robustness.

Fault detection sensitivity enhancement based on high-order spatial mode trend filtering for few-mode fiber link.

In this paper, we propose and experimentally verify a method for optimizing the fault detection sensitivity of few mode fiber (FMF) link based on high-order spatial mode trend filtering. The employment of high-order mode trend filtering as a signal processing tool identifies meaningful level shifts from FMF optical time-domain reflectometer (FMF-OTDR) profile, which is associated with the problem of the minimization of the intrinsic random noise and modal crosstalk impact on the acquired data. A FMF link fault detection system is built, and the proposed method is utilized to detect the fault loss characteristics of 7.2 km 6-mode fiber with three fusion splice points with different fusion quality, and the detection results of each mode are compared with the results obtained by FMF-OTDR. The experimental results show that our proposed method can effectively improve the low fault detection sensitivity of high-order spatial mode caused by random noise and mode crosstalk.

Walsh Hadamard Code and Wavelength Division Multiplexing Designed and Implemented Using Array FBGs

Array fiber Bragg grating (AFBGs) was produced using an advanced fabrication technique to write many fibers Bragg gratings (FBGs) in a single strand of optical fiber without any splicing points. AFBG was used to assign a unique signature code for each user in a multiple access technique such as spectral amplitude encoding, optical code division, and multiple access (SAE-OCDMA). A number of bits have been assigned to the signature code including zero bits or one bits. Thus, by using FBG, the zeros bits can be achieved. Then, Walsh Hadamard (WH) code represents one of the smart encoding techniques that can be implemented by AFBGs. In addition, AFBG was applied to isolate the accompanying wavelength of the multiplexed signal. Likewise, AFBG was used to implement wavelength division multiplexing (WDM). Therefore, SAE can be improved by using AFBG. As a result, the code words (1 0 1 0), (1 1 0 0) and (1 0 0 1) for users 1, 2 and 3, respectively, are assigned by using AFBGs. The proposed experimental results are presented using a super luminescent diode (SLD), coupler, AFBGs, optical circulator, and fiber Bragg grating analyzer (FBGA). The proposed simulation results are presented using commercial software OptiGrating version 4.2 and OptiSystemTM version 7.0 from Optiwave.

Realization of in Situ Fiber-Core Temperature Measurement in a Kilowatt-Level Fiber Laser Oscillator: Design and Optimization of the Method Based on OFDR

High-power fiber lasers have been widely used in various industrial manufacturing and military defense applications. During the development of fiber lasers in the past decades, the thermal effect has always been one of the biggest obstacles. It is crucial to study the temperature characteristics and overcome the thermal restrictions for a better output performance. With the systematic design and optimization in this article, optical frequency domain reflectometry (OFDR) can achieve in situ distributed temperature measurement of the fiber core in high-power fiber lasers. This allows a better study of the temperature characteristics and thermal effects. The fiber-core distributed temperature of a kilowatt-level fiber oscillator is first demonstrated based on this method here. The splicing point between the high reflectivity fiber Bragg grating (HR-FBG) and gain fiber withstands the highest temperature, reaching 101.6 °C at a 1.47 kW output. In addition, the temperature of the gain fiber gradually decreases from 92 °C to 30 °C along the pumping direction. The internal temperatures of the combiner and HR-FBG are also measured to evaluate their performances in the high-power regime. The temperature distributions in the experiment agree well with the theoretical simulation.

Exploration of Low-Energy Earth-Moon Transfer Orbit Based on Crossing Orbit of Double Three-Body System

The design of low energy lunar transfer orbit and orbit optimization method based on crossing orbit is studied in this paper. The four-body problem of Sun-Earth-Moon-satellite is decoupled into two three-body problems of Sun-Earth-satellite and Earth-Moon-satellite. Low-energy lunar exploration orbit is designed by changing orbit at a certain intersection field through manifold of two Halo orbit of three-body system. A serial optimization design method for global initial value search and local gradient optimization are designed. When a motion state variable is partially modified, the differential correction method combined with adaptive regression algorithm is adopted. For the splicing points of manifolds of different systems, the velocity vector is modified to make the spacecraft get into the target berthing track, and to obtain the splicing points that can form crossing track of the two three-body systems. An example of orbit design is given to show that the Earth-Moon transfer orbit based on invariant manifold splicing has the characteristics of energy saving and long-time consumption, which can be used for the tasks with large loads and low time requirements. This research provides a method for the design of low energy lunar transfer orbit. It will benefit the energy consuming, material design of spacecraft, and so on.

Bias twisting in side-tapered PMF Sagnac loop interferometer for simultaneous measurement of directional torsion and temperature.

The polarization-maintaining fiber-based Sagnac loop interferometer (PSLI) is frequently applied in directional torsion measurement, but may suffer from a large temperature cross talk. In this study, a novel method was proposed for fabrication of side-tapered PSLI by a two-step arc-discharge technique at the splicing point. The energy distribution of the taper region was characterized, and comprehensive tests were performed in terms of torsion and temperature. The experimental results showed that, through bias twisting, the measuring areas were effectively gapped and highly sensitive torsion and temperature responses were gained simultaneously. With a small wavelength shift, the torsion sensitivity reached 13.54 dB/rad in the range from -30 to 30 rad/m. Moreover, the temperature sensitivity was found to be -1.579nm/∘C, with a near-zero intensity fluctuation. Therefore, the sensor fabricated herein successfully achieves simultaneous measurement of directional torsion and temperature with high sensitivity and ultralow cross talk. The proposed scheme has the merits of practicality, low cost, and ease of operation, and is very promising for multiparameter engineering monitoring.

Ultra-low fusion splicing loss between silica and ZBLAN fiber for all-fiber structured high-power mid-infrared supercontinuum generation

The improvement of mid-infrared supercontinuum (MIR-SC) power, spectrum width, and flatness had been drastically limited by the coupling inefficiency between silica and soft-glass fibers. In this work, the achievement of a fusion splicing between single-mode silica and ZBLAN fiber with ultra-high coupling efficiency, high robustness, and low thermal instability has been explored and demonstrated by using the asymmetric fiber splicing technology. By tuning power and splicing offset finely, a high-quality fusion-splicing point is achieved with the splicing loss of less than 0.1 dB. In addition, a long-term stable 5.89 W MIR-SC with spectral bandwidth covering from 2 μm to 3.8 μm, which shows that the stability and robustness of this splicing point are high enough for any practical applications, is demonstrated for experimental verification. This work will lay a solid foundation for the further development of high-quality all-fiber structured MIR-SC.

Regulation and Function of RNA Pseudouridylation in Human Cells.

Recent advances in pseudouridine detection reveal a complex pseudouridine landscape that includes messenger RNA and diverse classes of noncoding RNA in human cells. The known molecular functions of pseudouridine, which include stabilizing RNA conformations and destabilizing interactions with varied RNA-binding proteins, suggest that RNA pseudouridylation could have widespread effects on RNA metabolism and gene expression. Here, we emphasize how much remains to be learned about the RNA targets of human pseudouridine synthases, their basis for recognizing distinct RNA sequences, and the mechanisms responsible for regulated RNA pseudouridylation. We also examine the roles of noncoding RNA pseudouridylation in splicing and translation and point out the potential effects of mRNA pseudouridylation on protein production, including in the context of therapeutic mRNAs.

Switchable and tunable multi-wavelength fiber ring laser employing a cascaded fiber filter

• We propose a novel cascaded hybrid fiber filter. • A switchable and tunable multi-wavelength fiber laser. • This laser has excellent robustness because of no core-offset splicing point. • This laser operates more stably compare to the previous similar works. A switchable and tunable multi-wavelength fiber laser based on cascaded hybrid fiber filter (CHFF) is proposed and demonstrated. The CHFF is composed of a single ellipsoid hybrid structure optical fiber filter (SE-HSOFF) and a Sagnac loop interferometer. Here the SE-HSOFF consists of single mode fiber (SMF)-few mode fiber (FMF)-SMF, and there is an ellipsoidal structure fabricated by SMF-FMF. It has the function of realizing the switchability of fiber laser. The Sagnac loop interferometer incorporated with a segment of polarization maintaining fiber (PMF) is used as a tuning component. By adjusting the state of polarization controller (PC), the laser can operate in single-, dual-, triple- and quadruple-wavelength laser states, and the lasing wavelength can be tuned by about 10 nm when it operates in dual-wavelength state. The optical signal to noise ratio (OSNR) is larger than 30.0 dB. This laser has excellent robustness because there is no core-offset splicing point and operates very stably in every output state at room temperature.