Dual-core Fiber Research Articles

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

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

Experimental study on temperature-insensitive curvature sensor based on reflective all-fiber structure

In the paper, a reflective all-fiber sensor for curvature measurement has been proposed, which is composed of Mach-Zehnder interferometer (MZI) and Fabry-Pérot interferometer (FPI). The MZI section acts as curvature sensing unit and is made by splicing a section of twin-hole and dual-core fiber (THDCF) between two sections of seven-core fiber (SCF). The FPI section is made by introducing an FPI cavity between two segments of single mode fibers inside a hollow core capillary through using UV-curable resins and used to reflect the energy. The reflection spectrum information tuned by MZI has respond to bending change. The experiment results show the reflective sensor exhibits a high curvature sensitivity and low temperature sensitivity of −1.19 nm/m−1 and −1 pm/°C in the range of 0–5.7778 m−1 and 30–100 °C, respectively. With the advantages of reflective structure, compact size, easy fabrication, and low temperature crosstalk, our sensor could be widely used in practical applications.

3D-printed terahertz subwavelength dual-core fibers with dense channel-integration

3D-printed terahertz subwavelength dual-core fibers with dense channel-integration

Analysis of high-contrast all-optical dual-wavelength switching in asymmetric dual-core fibers.

We systematically present experimental and theoretical results for the dual-wavelength switching of 1560 nm, 75 fs signal pulses (SPs) driven by 1030 nm, and 270 fs control pulses (CPs) in a dual-core fiber (DCF). We demonstrate a switching contrast of 31.9 dB, corresponding to a propagation distance of 14 mm, achieved by launching temporally synchronized SP-CP pairs into the fast core of the DCF with moderate inter-core asymmetry. Our analysis employs a system of three coupled propagation equations to identify the compensation of the asymmetry by nonlinearity as the physical mechanism behind the efficient switching performance.

Highly sensitive torsion sensor based on helical eccentric dual-core fiber Michelson interferometer

An optical fiber torsion sensor was academically put forward and experimentally demonstrated by applying a Michelson interferometer (MI) based on a helical eccentric dual core fiber (HEDCF). The sensor consists of an eccentric dual core fiber (EDCF), a taper, and a helical structure based on the EDCF. Since there is a large interval between a centric core and an eccentric core of the EDCF, the helical structure can greatly improve the torsion sensitivity of the sensor. When the twisting direction is consistent with the pre-twisting direction, the optical path difference (OPD) of MI negative increases during the twisting process, and the spectral resonance wavelength shifts blue. Experimental results show that the greater the degree of helical addition, the higher the torsional sensitivity. The torsion sensitivity can reach as high as −7.01 nm/(rad/m) in clockwise (CW) direction in the range of 0–9.595 rad/m. Moreover, the satisfactory sensitivity, stable structure and small temperature crosstalk, let it a valuable select in torsion sensing domain, and is promising to be useful for broad applications across engineering fields.

Double nested dual-core negative curvature fiber polarization beam splitter

In this paper, a polarization beam splitter（PBS） based on double nested dual-core negative-curvature fiber (DNHC-NCF) is designed. Two hollow cores are constructed by eight double nested cladding tubes arranged at certain angles. The influences of structural parameters on the performances of the DNHC-NCF PBS have been studied by using the finite element method (FEM). According to the simulation results, the structure of the proposed DNHC-NCF PBS is optimized. The final results indicate that the length of the proposed DNHC-NCF PBS is 1.38 cm and the extinction ratio (ER) is less than −20 dB in the wavelength range of 1.48–1.80 µm (320 nm, covers S + C + L + U bands). Besides, the higher order mode extinction ratio (HOMER) in the wavelength range of 1.3–1.71 µm is greater than 100, showing good single-mode characteristic as well. It is believed that the proposed double nested dual-core negative curvature fiber polarization beam splitter will have important applications in the fields of optical communication system.

Single-longitudinal-mode lasing based on enhanced scattering in eccentric-hole microstructured optical fiber resonators

In this paper, we propose a dual-core eccentric-hole fiber (DCEHF) microresonator to achieve single-longitudinal-mode (SLM) laser emission based on enhanced pump light field induced by scattering effect of the two fiber cores. The directional dependences of the scattered pump field distribution on incident angle as well as overlap integrals between scattered pump light fields and WGMs have been theoretical investigated, and the calculation results show that when the incident angle of the pump light is close to 180°, significant discrepancies would occur in the overlap integrals between WGMs and the scattered field. And consequently, specific mode having the largest overlap integral would outperform through the mode competition process to excite SLM lasing. We have experimentally obtained SLM lasing emission when the DCEHF-based microresonator is rotated by 206°, which is in good accordance with our calculation results. Additionally, experimental observation of the output laser spectrum shows that the proposed fiber microcavity supports highly stable SLM laser emission. The proposed microresonator based on DCEHFs possesses several desirable merits such as compact size, good laser stability, single-mode operation, and good compatibility with existent fiber-optic systems, which make it a good candidate for applications as functional photonic device in future micro-optics systems.

Impact of Zero-Dispersion Wavelength Fluctuations in a Coupled Dual-Core Fiber Optical Parametric Amplifier

We have studied the impact of zero dispersion wavelength (ZDW) fluctuations in coupled dual-core fiber optical parametric amplifiers (FOPAs) and compared it to the single-core single-pump FOPA. We have designed a Monte Carlo model, that simulates a multidimensional Ornstein-Uhlenbeck process, describing accurately ZDW fluctuations in single and multicore fibers. In order to validate our results we have developed an analytical model, based on Taylor expansion of the average gain and successfully compared both models, with experimental results published in the literature. We have found that a significant reduction of the impact of ZDW fluctuations can be obtained in dual-core FOPAs compared to single-core ones.

Dual-core-enhanced surface plasmon resonance for sensing high refractive index liquid based on photonic crystal fiber

A dual-core photonic crystal fiber sensor based on surface plasmon resonance is theoretically proposed for the high-sensitive detection of high refractive index liquid analytes. Dual-core construction can effectively enhance the coupling effect between the fiber-core mode and the surface plasmon polariton modes, leading to sharp loss peaks at the resonance wavelengths. As the refractive index of the targeted analyte varies, the resonance condition will change as well and cause a certain shift of loss peak. Numeric results show that this dual-core fiber sensor exhibits an average linear sensitivity 9538 nm/RIU and a maximum sensitivity is 11400 nm/RIU with a resolution 8.77 × 10−6 RIU. The detected range is broad and covers the high refractive index range from 1.45 to 1.58 with an average figure of merit 284.5 RIU−1. The dependence of structure parameters and the thickness of coated-metal thin-film on sensing performance is performed systemically and suggests different responses. The proposed sensor is highly promising in detecting high refractive index liquid analytes in the fields of biological detection, environmental monitoring and chemical analysis.

Simultaneous measurement of temperature and salinity based on a hole-assisted dual-core fiber.

An optical fiber sensor based on a hole-assisted dual-core fiber (HADCF) has been proposed and experimentally demonstrated for dual-parameter measurements. The dual-mode interferometer created uses the LP01 mode and LP11 mode in the suspended core of a specialist optical fiber, combined with a directional coupler formed by using the suspended core and the center core in a 16 mm long HADCF. Using this, the simultaneous measurement of salinity (due to the presence of NaCl) and temperature has been achieved through monitoring the interference dip and resonance dip. The sensitivities of the measurement of salinity and temperature are 190.7 pm/‰ and -188.2 pm/°C, respectively. The sensor developed has the advantages of simplicity of fabrication, a high level of integration and the potential for measurement of dual parameters, supporting its potential applications in marine environment measurements.

Dual-core fiber biosensor with graphene-MoS2 modification for dual-peak detection

A graphene-MoS2-based dual-core D-shaped biosensor is proposed. The sensor operates in the terahertz (THz) band and detects analytes with refractive indices from 1.33 to 1.38, encompassing most biomolecules. The accuracy of the measurement results is improved by dual-peak detection. Through optimization, the thickness of graphene is 4 times of single-layer graphene, the thickness of MoS2 is 10 µm, the thickness of the analyte is 22 µm, and the diameter of the small air hole is 52 µm. The main and secondary peaks of the sensor showed high sensitivity of 632.606 µm/RIU and 374.609 µm/RIU, respectively. Meanwhile, both the main and secondary peaks have very high figures of merit (FOM), with the highest value of 21,162.16 and 63,809.01, respectively, reflecting the sensor's excellent sensing performance. The proposed sensor provides a new idea for studying the graphene-MoS2-based dual-core biosensor.

Broadband 1.5-2.1 µm emission in gallo-germanate dual-core optical fiber co-doped with Er3+ and Yb3+/Tm3+/Ho3.

The near-infrared emission in fabricated low-phonon energy, gallo-germanate glass, and double-core optical fiber has been investigated. Broadband amplified spontaneous emission (ASE) was obtained in optical fiber with cores doped with: 1st - 0.2Er2O3 and 2nd - 0.5Yb2O3/0.4Tm2O3/0.05Ho2O3 as a result of the superposition of emission bands from both cores corresponding to the Er3+:4I13/2→4I15/2 (1st core) and Tm3+:3F4 → 3H6/Ho3+:5I7 → 5I8 (2nd core) transitions. The effect of fiber length and pump wavelength on the near-infrared amplified spontaneous emission (ASE) properties has been analyzed for 1 m and 5 m optical fiber. The widest emission bandwidth (355 nm - 3 dB level) was obtained for a 5 m length optical fiber pumped by a 940 nm laser.

One-dimensional Townes solitons in dual-core systems with localized coupling.

The recent creation of Townes solitons (TSs) in binary Bose-Einstein condensates and experimental demonstration of spontaneous symmetry breaking (SSB) in solitons propagating in dual-core optical fibers has drawn renewed interest in the TS and SSB phenomenology in these and other settings. In particular, stabilization of TSs, which are always unstable in free space, is a relevant problem with various ramifications. We introduce a system which admits exact solutions for both TSs and SSB of solitons. It is based on a dual-core waveguide with quintic self-focusing and fused (localized) coupling between the cores. The respective system of coupled nonlinear Schrödinger equationsgives rise to exact solutions for full families of symmetric and asymmetric solitons, which are produced by the supercritical SSB bifurcation (i.e., the symmetry-breaking phase transition of the second kind). Stability boundaries of asymmetric solitons are identified by dint of numerical methods. Unstable solitons spontaneously transform into robust moderately asymmetric breathers or strongly asymmetric states with small intrinsic oscillations. The setup can be used in the design of photonic devices operating in coupling and switching regimes.

Highly-Sensitive Temperature Sensor Based on an All-in-Fiber Directional Coupler

A highly-sensitive all-in-fiber temperature sensor was designed and demonstrated based on a directional coupler by infiltrating self-made refractive index matching fluid (RIMF) into a single eccentric hole-assistant dual-core fiber (DCF). The beam propagation method was used to analyze the coupling characteristics of the single eccentric hole-assistant DCF, which demonstrated that the central core and the suspended core of the DCF would couple to form a directional coupler when the refractive index of the RIMF is between 1.452 and 1.453. Then, this in-fiber directional coupler was fabricated and used for temperature sensing. The experimental results showed that the temperature sensitivity of the sensor could be up to 52.194 nm/℃ in the temperature range from 7.207 ℃ to 10.920 ℃. In addition, the sensor had good stability, repeatability, and hysteresis. It is expected to have great potential in highly-sensitive sensing applications.

(Invited) Quiescent solitary waves in dual-core systems with separated Bragg grating and cubic–quintic nonlinearity

The existence and stability of zero-velocity solitons in a dual-core optical fiber, where one core possesses cubic–quintic nonlinearity and the other core is linear with a Bragg grating, are investigated. The frequency spectrum for the model consists of three bandgaps, of which only the central band gap is a genuine one. There are no soliton solutions in the central gap. On the other hand, the upper and lower gaps are filled with two distinct and disjoint families of soliton solutions, termed Type-1 and Type-2 solitons, that differ in their shapes and phase characteristics. When the relative group velocity in the linear core is zero, implicit analytical solutions for Type-1 and Type-2 quiescent solitons are found. For nonzero values of the relative group velocity, soliton solutions can only be found using numerical techniques. The stability of solitons has been analyzed systematically by means of numerical stability analysis. It is found that Type-2 solitons are always unstable. In the case of Type-1 solitons, stability regions are identified in the upper and lower bandgaps. The effects and interplay of the relative group velocity and the Bragg grating-induced linear coupling coefficient on the stability of the solitons are also analyzed.

A Broadband Optical Fiber Coupler Based on Dual-Hollow Core Fiber

Hollow fiber has become a research hotspot in the field of special fibers for its excellent characteristics, such as low loss, low delay, low dispersion, and low nonlinear coefficient. Due to the lack of fiber coupler matching hollow core fiber, the application development of hollow core fiber in the all-fiber integrated system is greatly hindered. Dual-core fiber is widely used in the development of fiber couplers because it can choose optical power, wavelength, and polarization state by the coupling between the two cores. For the urgent need for hollow core fiber coupler, the design and research of wideband fiber coupler based on dual-hollow core fiber are carried out in this paper. Based on the coupled mode theory, the theoretical correlation between the structural parameters and the coupling length in the dual-hollow core anti-resonant fiber was analyzed by using the COMSOL simulation software system. On this basis, a 50:50 wideband fiber coupler was designed by adjusting the structural parameters to reduce the coupling length and introducing the sleeve into the cladding pipe to reduce the loss. The bandwidth of the coupler is up to 150 nm and the transmission loss is on the order of 10−2 dB/m.

Plasmonic Biosensor on the End-Facet of a Dual-Core Single-Mode Optical Fiber.

Optical biosensors target widespread applications, such as drug discovery, medical diagnostics, food quality control, and environmental monitoring. Here, we propose a novel plasmonic biosensor on the end-facet of a dual-core single-mode optical fiber. The concept uses slanted metal gratings on each core, interconnected by a metal stripe biosensing waveguide to couple the cores via the propagation of surface plasmons along the end facet. The scheme enables operation in transmission (core-to-core), thereby eliminating the need to separate the reflected light from the incident light. Importantly, this simplifies and reduces the cost of the interrogation setup because a broadband polarization-maintaining optical fiber coupler or circulator is not required. The proposed biosensor enables remote sensing because the interrogation optoelectronics can be located remotely. In vivo biosensing and brain studies are also enabled because the end-facet can be inserted into a living body, once properly packaged. It can also be dipped into a vial, precluding the need for microfluidic channels or pumps. Bulk sensitivities of 880 nm/RIU and surface sensitivities of 1 nm/nm are predicted under spectral interrogation using cross-correlation analysis. The configuration is embodied by robust and experimentally realizable designs that can be fabricated, e.g., using metal evaporation and focused ion beam milling.

Highly Sensitive Dual-Core Microstructured Fiber Sensor Operating Near the Dispersion Turning Point

In this paper, a highly sensitive dual-core microstructured fiber (DC-MSF) sensor is proposed. Because of the adjustable dispersion characteristic of the DC-MSF, the group refractive index (RI) difference between the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> -polarization odd and even supermodes could achieve the zero value at the dispersion turning point, which makes the DC-MSF sensor have a high sensitivity. The simulation results show that the sensitivity can be up to 52875 nm/RIU around the RI of 1.4, the operating bandwidth of sensitivity over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> nm/RIU is 625 nm, and the operating bandwidth of sensitivity over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> nm/RIU is 100 nm. Moreover, the DC-MSF can also be used as a temperature sensor by coating the polydimethylsiloxane on the surface, and the sensitivity can be up to 23.12 nm/°C around 22 °C. The detectable RI and temperature ranges of the proposed DC-MSF sensor are 1.375-1.425 and -15-95 °C, respectively.

Parametric amplification in coupled nonlinear waveguides: The role of coupling dispersion

We present the theory of parametric amplification in coupled nonlinear waveguides considering the frequency dependency of the coupling strength. We show that coupling dispersion can indeed compensate for the uncoupled individual waveguides dispersion enabling a substantial tailoring of the gain spectrum. Our theory describes both phase-sensitive and phase-insensitive operational modes, it can be straightforwardly generalized to include arbitrary higher-order waveguide and coupling dispersion and its predictions agree very well with numerical simulations both in the presence and in the absence of waveguide losses. It provides a tool for the design of novel versatile parametric amplifiers based both on coupled integrated waveguides and dual-core fibers too.

Parametric amplification based on intermodal four-wave mixing between different supermodes in coupled-core fibers.

Parametric amplifiers relying on the nonlinear four-wave mixing process are known for their signature symmetric gain spectrum, where signal and idler sidebands are generated on both sides of a powerful pump wave frequency. In this article we show analytically and numerically that parametric amplification in two identically coupled nonlinear waveguides can be designed in such a way that signals and idlers are naturally separated into two different supermodes, hence providing idler-free amplification for the supermode carrying signals. This phenomenon is based on the coupled-core fibers analogue of intermodal four wave-mixing occurring in a multimode fiber. The control parameter is the pump power asymmetry between the two waveguides, which leverages the frequency dependency of the coupling strength. Our findings pave the way for a novel class of parametric amplifiers and wavelength converters, based on coupled waveguides and dual-core fibers.