Dual-core Fiber Research Articles

An Open-Cavity Gas Pressure Sensor Based on Vernier Effect of Twin-Hole and Dual-Core Fiber Fabry–Perot Interferometer

An Open-Cavity Gas Pressure Sensor Based on Vernier Effect of Twin-Hole and Dual-Core Fiber Fabry–Perot Interferometer

High-precision dynamic axial clearance measurement method based on an all-fiber heterodyne microwave-AMCW with an all-phase tracking algorithm

Rotor-stator axial clearance is critical to the safety and efficiency of major rotating machinery. However, factors such as high-speed rotation, narrow space, high temperature, and vibration present significant challenges for high-precision dynamic measurement of axial clearance. This paper proposes an axial clearance measurement method based on an all-fiber heterodyne microwave amplitude-modulated continuous wave (microwave-AMCW) system combined with an all-phase tracking algorithm, characterized by high precision, wide bandwidth, and a large measurement range. To mitigate environmental influences, a heterodyne all-fiber microwave-AMCW optical path structure is developed, and a compact dual-core fiber sensor probe is designed. The all-phase tracking algorithm is introduced to enhance dynamic precision and expand bandwidth. Additionally, what we believe to be a novel bandwidth test method based on time division multiplexing is proposed to evaluate the system's wide-bandwidth performance. The proposed system's performance is validated through simulations and experiments. The results demonstrate that the system exhibits excellent resistance to environmental interference, with a measurement range up to 24.5 mm and a static precision better than 4.5µm. Dynamic experiments further confirm the algorithm's effectiveness, achieving a precision better than 5.3µm at 100kHz bandwidth. Compared to other clearance measurement algorithms including the Hilbert transform and FFT, the proposed method reduces dynamic error by over 74%.

A novel dual-core fiber-optic gyroscope with independent rotation rate measurements in different cores of a dual-core optical fiber

A novel dual-core fiber-optic gyroscope with independent rotation rate measurements in different cores of a dual-core optical fiber

High-Sensitivity Microfluidic Mach-Zehnder Interferometric Salinity Sensor Based on C-Type Dual-Core Eccentric-Hole Fibers

High-Sensitivity Microfluidic Mach-Zehnder Interferometric Salinity Sensor Based on C-Type Dual-Core Eccentric-Hole Fibers

Temperature self-compensated dual core fiber-optic sensor integrated with moisture sensitive MIL-96(Al) film for breath detection

In this paper, a dual-core fiber optic sensor has been proposed for dynamic monitoring of temperature and humidity. The side core is polished into a D-type optical fiber, and a layer of nano-silver film and a layer of polydimethylsiloxane (PDMS) are deposited to construct a surface plasmon resonance (SPR) temperature compensator. The middle core is constructed as the long-period fiber grating (LPFG) sensing channel. The mode conversion of LPFG is achieved by TiO2 film, and its refractive index (RI) sensitivity is increased by about 4 times. Meanwhile, a layer of moisture sensitive MIL-96(Al) film is grown outside the TiO2 film. Due to the particular pore structure for water molecules, it is possible to change the effective RI of MIL-96(Al) film by absorbing water molecules. Research has shown that the LPFG sensor can achieve a relative humidity sensitivity of −0.411 nm/%RH. Finally, the sensor successfully achieved real-time dynamic monitoring of respiratory rate.

Dual-core fiber temperature sensor based on bending assist and spot pattern demodulation

A high sensitivity temperature sensor based on spot pattern demodulation of rare doped dual-core fiber (RDCF) is proposed. By utilizing the interference and scattering in RDCF, the related temperature variations can be captured by optical field. Furthermore, In order to improve the sensitivity, the RDCF is given a certain amount of bending. Due to the change of the spot mode caused by bending, the temperature changes more to the refractive index of the fiber core, so that the spot of the fiber changes more to facilitate the subsequent spot identification. In addition, considering the global and subtle nature of spot changes, a deep learning algorithm based on AlexNet transfer model is used to process image recognition at multiple temperatures. The experimental results show that the sensor can perceive different temperature in range of 30–199 °C, and the resolution is higher than 0.05 °C. These outstanding results indicate that the bending assisted temperature sensor based on spot pattern decoding of RDCF has potential applications in temperature quantitative sensing and artificial intelligence perception.

In-Fiber Hybrid Structure Sensor Based on the Vernier Effect for Vector Curvature and Temperature Measurement

A vector curvature and temperature sensor based on an in-fiber hybrid microstructure is proposed and experimentally demonstrated. The proposed scheme enables the dimensions of the Fabry–Perot and Mach–Zehnder hybrid interferometer to be adjusted for the formation of the Vernier effect by simply changing the length of a single optical fiber. The sensor is fabricated using a fiber Bragg grating (FBG), multimode fiber (MMF), and a single-hole dual-core fiber (SHDCF). The sensor exhibits different curvature sensitivities in four vertical directions, enabling two-dimensional curvature sensing. The temperature and curvature sensitivities of the sensor were enhanced to 100 pm/°C and −25.55 nm/m−1, respectively, and the temperature crosstalk was minimal at −3.9 × 10−3 m−1/°C. This hybrid microstructure sensor technology can be applied to high-sensitivity two-dimensional vector curvature and temperature detection for structural health monitoring of buildings, bridge engineering, and other related fields.

Hybrid Si-Au plasmonic sensor on the end-facet of a dual-core optical fiber enhanced by hotspots: a theoretical study

We propose an efficient hybrid Si-Au sensor on the end-facet of a dual-core single-mode optical fiber. The design incorporates slanted Si grating couplers on the two cores, interconnected by a plasmonic waveguide bearing subwavelength corrugations. The corrugations enhance the surface sensitivity by creating regions of strongly enhanced fields - plasmonic hotspots. Unlike conventional Si waveguide grating couplers, we employ slanted slits for unidirectional coupling/decoupling between TM-polarized core light and surface plasmon polaritons. Our structure results in about 3% core-to-core (TM-to-TM) coupling efficiency, while also providing high bulk and surface sensitivities of about 1000 nm RIU−1 and 1.66 nm nm−1, respectively. The sensor can be interrogated remotely in a transmission arrangement. The sensing medium can be probed by dipping the fiber tip directly therein. Potential applications include remote sensing, brain studies, or in-vivo biosensing.

High Sensitivity Temperature Sensor Based on Directional Coupler in a Liquid-Filled Tapered Hollow Suspended Dual-Core Fiber

High Sensitivity Temperature Sensor Based on Directional Coupler in a Liquid-Filled Tapered Hollow Suspended Dual-Core Fiber

Refractive insensitive directional bend sensor based on specialty microstructure optical fiber with dumbbell shape core

With the development of information society, more and more special occasions are calling for a wide range of sensors with special properties. In this work, a refractive index insensitive directional bend sensor is proposed based on a specialty microstructure optical fiber with dumbbell shape core, which works as a dual core fiber (DCF). Firstly, this specialty microstructure optical fiber with dumbbell shape core has been fabricated with self-pressurised drawing technique. Then, it has been constructed as a Mach-Zehnder interferometer (MZI) sensor. Consequently, its bend sensing characteristics has been investigated from both theory and experiment. The response of the proposed sensor to the bending evidently displays the directional dependence. In the bending along x direction, the interference peak wavelength is almost insensitive to the curvature. But the transmission is sensitive, which almost obeys the exponential function. Correspondingly, in the bending along y direction the wavelength almost linearly varies with curvature, giving out an averaged sensitivity of 2.44 nm/m−1 in the curvature range of 0–3.79 m−1. But the peak transmission fluctuates without typical principle. In addition, the response of the proposed sensor to the refractive index variation has been checked. It is found that the peak wavelength is almost insensitive to the change of refractive index from 1.33 to 1.45, and the peak transmission fluctuates without clear principle. All these results demonstrate that the proposed sensor has great potential for future internet of things (IoT) applications.

Direct 3D-printed ring-resonator photonic circuit on a dual core fiber tip for remote sensing applications.

On-chip optical sensors using ring- and disk-resonators have many potential sensing applications, yet robust and efficient fiber-to-chip coupling and the differing form factor between the two pose deployment challenges. To resolve this, we 3D-printed a ring-resonator onto the tip of a dual-core fiber and demonstrate its use as a remote temperature sensor. The fiber-tip optical circuit is fabricated using direct laser writing (DLW) with two-photon absorption photopolymer material IP-Dip, forming micrometer-scale waveguide cores having a refractive index of 1.53 with a surrounding air cladding. We connect the two-fiber cores by a printed bus-waveguide, utilizing total internal reflection mirrors, allowing light launched into one core to be guided back to the other core. Furthermore, a DLW printed racetrack resonator evanescently coupled to the bus waveguide (Q ∼ 3000) imposes spectral dips on resonance wavelengths. Light sent down into one core is interrogated upon return from the second core, all from the distal end of the sensor. When the sensing end's temperature is varied, we find a sensitivity of 78 pm/K, due to the polymer's thermo-optic index variation. The ring-resonator could be functionalized for other sensing applications.

Symmetrical dual-D and dual-core single-mode fiber surface plasmon resonance liquid sensor

A symmetrical dual-D and dual-core single-mode fiber surface plasmon resonance (SPR) liquid sensor is designed for biological detection. The dual-core design optimizes the transmission path, improves the momentum matching between free electrons and photons, and facilitates bidirectional coupling, consequently amplifying the SPR effect and enabling sensitive monitoring of the refractive index changes of biological solutions. In this structure, a gold wire is placed in the middle of the polished surface of the double-D-shaped single-mode fiber (SMF) to produce high-quality free electrons and promote the mode-coupling excitation of the SPR effect. The characteristics of the sensor are analyzed by the finite element method, and the important structural parameters are optimized systematically. The sensor can be operated in the near-infrared region for a refractive index (RI) range of 1.31–1.40 with a maximum wavelength sensitivity (WS) of 21,000 nm/RIU, amplitude sensitivity of 586.62RIU−1, as well as resolution of 4.76×10−6RIU. Small changes in the refractive index can be detected by the sensor and it can be produced easily by conventional manufacturing techniques. The sensor thus has wide application prospects in biomedical and chemical analysis and related applications.

Temperature self-compensated fiber-optic Pb(II) sensor with improved selectivity by Resorcylaldehyde post-modified organic metal framework

Post-modification of metal-organic framework (MOF) materials is an effective means to enhance their efficient and selective adsorption for heavy metal ions. In this article, we presented a reflection-type optical fiber surface plasmon resonance (SPR) sensor based on dual core fiber (DCF) coated with UiO-66-RSA (UiO-66-NH2 post-modified with resorcinol aldehyde) film for the specific detection of Pb(II) in aqueous media. The composite material UiO-66-RSA exhibits stronger affinity and specificity for Pb(II) than UiO-66-NH2. The adsorption of Pb(II) can change the equivalent refractive index (RI) of UiO-66-RSA film, causing a regular shift in SPR spectra. Experiments have shown that the limit of detection (LOD) of the SPR Pb(II) sensor can reach 0.1 nM. Meanwhile, research has found that the SPR sensor is accompanied by temperature crosstalk of 0.356 nm/°C. Therefore, we constructed a Michelson temperature interferometer using polymer micro tips on the end face of the fiber core to achieve temperature compensation. Based on the above two sensing channels, dual parameter demodulation of Pb(II) concentration and temperature can be achieved with an error rate of less than 0.5 %. This article has potential research value in exploring the application of post modification techniques of MOF in fiber optic lead ion detection.

A clock synchronization and trigger distribution scheme for China Spallation Neutron Source

China Spallation Neutron Source (CSNS) is a complex system engineering composed of particle accelerators, a target station, and neutron spectrometers with various equipment types and distribution. The collaborative operation of the equipment requires accurate clock synchronization and trigger distribution. Currently, to meet the requirements of different system devices, clock synchronization and trigger distribution in CSNS are implemented based on different methods, resulting in complex clock and trigger networks, demanding upgrades, and a lack of unified timestamps. This paper proposes a clock synchronization and trigger distribution scheme based on the field-programmable gate array (FPGA) and single-mode dual-core fiber link. The decoupling of clock phase synchronization and time base synchronization improves the frequency of phase compensation. Benefiting from the phase interpolator (PI) in the FPGA transceivers, high-precision phase compensation and phase deterministic control are realized, achieving picoseconds synchronization precision and stability in the four-level network. Based on the custom lightweight link layer protocol, by optimizing the routing method of data frames and adopting priority control, the transmission of multiple data is realized, and the hardware delay of the critical data, such as interlock, is guaranteed to be less than 1.5 μs in the four-level system. The scheme provides a general precise clock synchronization and distributed trigger method for CSNS devices, simplifies the system complexity, and is conducive to the system upgrade in the second stage.

Optical fractional solitonic structures to decoupled nonlinear Schrödinger equation arising in dual-core optical fibers

This paper explores a specific class of equations that model the propagation of optical pulses in dual-core optical fibers. The decoupled nonlinear Schrödinger equation with properties of M fractional derivatives is considered as the governing equation. The proposed model consists of group-velocity mismatch and dispersion, nonlinear refractive index and linear coupling coefficient. Different types of solutions, including mixed, dark, singular, bright-dark, bright, complex and combined solitons are extracted by using the integration methods known as fractional modified Sardar subequation method and modified F-expansion method. Optical soliton propagation in optical fibers is currently a subject of great interest due to the multiple prospects for ultrafast signal routing systems and short light pulses in communications. In nonlinear dispersive media, optical solitons are stretched electromagnetic waves that maintain their intensity due to a balance between the effects of dispersion and nonlinearity. Furthermore, hyperbolic, periodic and exponential solutions are generated. A fractional complex transformation is applied to reduce the governing model into the ordinary differential equation and then by the assistance of balance principle the methods are used, depending upon the balance number. Also, we plot the different graphs with the associated parameter values to visualize the solutions behaviours with different parameter values. The findings of this work will help to identify and clarify some novel soliton solutions and it is expected that the solutions obtained will play a vital role in the fields of physics and engineering.

Interference fading suppression with fault-tolerant Kalman filter in phase-sensitive OTDR

A multi-sensor information fusion algorithm based on fault-tolerant Kalman filter is proposed in phase-sensitive optical time-domain reflectometer (Φ-OTDR) system, for achieving fading-free distributed vibration sensing. Firstly, a fault-tolerant dual-core complementary array model is designed. The Rayleigh scattering signal denoising, and vibration existence judgment of localization points are carried out to obtain the differentiated frequency demodulation results of the sensing points of the dual-core fiber array. Then a fault-tolerant control strategy is used to determine the sensor weight coefficients and vibration judgment coefficients during data fusion processing, and array data fusion is carried out based on time series data using Kalman filter to realize error value identification and filling. The advantage of this method is the combination of redundant data in a complementary way to improve the system stability. The frequency response ranges from 10 Hz to 2400 Hz and the localization accuracy is 98.33%. The influence of key parameters on the frequency demodulation performance of fault-tolerant Kalman filter is discussed, and a standard deviation of 14.6 Hz and an average error of 7.6 Hz are obtained. The demodulation frequency data matrix obtained by the classical demodulation method has a demodulation error probability of 89.18%, which proves the widespread existence of demodulation errors in vibration signals. The fusion error of demodulation frequency is reduced to 0.25 Hz, the frequency demodulation accuracy reaches 100%, and the demodulation error caused by interference attenuation can be completely eliminated. This system based on fault-tolerant Kalman filter has the characteristics of simple multiplexing structure, interference fading resistance and stable demodulation performance.

Enhancement of in-vitro cellular structure morphology imaging using multiwavelength confocal endoscopic scanner

Optical imaging is crucial for cell examination, but its instruments' bulky optics limit their flexibility, and a single wavelength provides limited sample information. This paper presents a fibre cantilever-based endoscopic scanner for multiwavelength reflectance confocal microscopy. The scanner utilises the dual-core fibre cantilever to produce Lissajous scans while accommodating two distinct wavelengths. Coloured surfaces were imaged at wavelengths of 520 nm, 635 nm and 850 nm, and verified with a colour chart and reflectance spectroscopy. Blue ink-stained plant stem cross-section samples were also imaged and compared. Furthermore, the scanner performed structure morphology imaging on cellular samples. The 520 nm and 635 nm wavelengths create low- and high-contrast images respectively, while the 850 nm wavelength delivers a sharper image while also capturing the surface profile of the target sample. The findings demonstrated the endoscopic scanner’s capability to extract information based on different wavelengths, providing a more diverse view of the sample and enhancing the surface profile. Using 635 nm and 850 nm, the reconstructed images have a contrast enhancement of 67.9% and 90.8% respectively from 520 nm. The smallest feature size measured on the cellular sample is 5 µm. The endoscopic scanner has the potential to study microfluidic and cell morphology.

Hosting exceptional point in all-lossy dual-core optical fiber and its exotic chiral light dynamics

Exploration of exceptional points (EPs) and associated unique features in gain-loss assisted optical systems to develop future all optical devices have been a great interest in recent years. However, incorporation and adjustment of gain distribution in a system is quite challenging. Here, we design a fabrication feasible dual-core optical fiber where only the customized transverse loss profile controls the interaction between two coupled modes and results in hosting an EP. Parametric encirclement of the identified EP and corresponding chirality-driven asymmetric mode conversion phenomenon between the supported modes have been reported. The proposed structure features ease of fabrication using state-of-the-art techniques with possible applications in all-optical components for communication and all fiber photonic devices.

High power ring spot adjustable fiber combiner based on (6 + 3) × 1 structure

Aiming at the problem that the ring beam mode adjustable signal combiner with a single center port structure limits the output power of the laser beam in the inner ring of the laser. A new all-fiber structure (6 + 3) × 1 signal combiner is designed, which can independently carry more than 3 kW of power at each input port, and the output fiber is a ring-shaped dual-core fiber. The tapered fiber bundle adopts the (6 + 3) × 1 structure, where the three input ports in the center form a tapered fiber bundle to transmit the laser beam to the inner core of the output fiber, and the remaining six ports in the outer ring transmit the beam to the outer core of the output fiber, and the beams of the inner and outer cores can be transmitted independently, which effectively increases the output power of the center port. Combiner using (6 + 3) × 1 structure of the fiber transmission efficiency of more than 98 %, the center of the M2 is 5.32, can withstand the role of the return light. The structure of the output beam energy is more uniform, can effectively prevent sputtering, so that it can be applied to ultra-precision welding and other fields. At the same time, the structure also provides a feasible new solution to increase the center M2 of the beam splitter.

Sensitivity analysis and propagation of optical solitons in dual-core fiber optics

Sensitivity analysis and propagation of optical solitons in dual-core fiber optics