Dual-core Fiber Research Articles

One-Pump Phase Sensitive Fiber Optical Parametric Amplifier With Dual-Core Fiber

The gain performance of one pump phase sensitive fiber optical parametric amplifier (PS-FOPA) in the dual-core fiber is numerically investigated without pump depleting. The effects of the core coupling coefficient(C), the pump wavelength and the initial signal phase on the gain of PS-FOPA are analyzed in detail. It shows that, the signal gain is greatly affected by different core coupling coefficients, and a flatter gain is achieved with suitable C value. Also, when the pump wavelength is greater than the zero-dispersion wavelength (ZDW), both the peak gain and gain bandwidth decrease with the increase of C, but the trend is opposite in case of the pump wavelength less than the ZDW. Additionally, the flatter and broader gain spectra are obtained by adjusting the initial signal phase in core 2. This simulation provides a detail analysis for the dual-core PS-FOPA, which is significant for the all optical fiber amplifier systems.

Random walks of trains of dissipative solitons

The propagation of light pulses in dual-core nonlinear optical fibers is studied using a model proposed by Sakaguchi and Malomed. The system consists of a supercritical complex Ginzburg-Landau equation coupled to a linear equation. Our analysis includes single standing and walking solitons as well as walking trains of 3, 5, 6, and 12 solitons. For the characterization of the different scenarios, we used ensemble-averaged square displacement of the soliton trajectories and time-averaged power spectrum of the background waves. Power law spectra, indicative of turbulence, were found to be associated with random walks. The number of solitons (or their separations) can trigger anomalous random walks or totally suppress the background waves.

Stimulated Brillouin scattering in a tapered dual-core As2Se3-PMMA fiber for simultaneous temperature and strain sensing.

Chalcogenide fibers are currently being used widely in nonlinear optical signal processing, as they exhibit ultrahigh nonlinearity. Here, we propose a sensor based on stimulated Brillouin scattering for simultaneous temperature and strain measurement in a dual-core tapered As2Se3-polymethyl methacrylate fiber using a Brillouin optical time-domain analysis system. Different Brillouin frequency responses under temperature and strain variations and the separation of Brillouin frequency shifts (BFSs) in two principal polarization axes are demonstrated experimentally over a 50-cm-long tapered dual-core hybrid microfiber. The temperature coefficients are -3.8272MHz/∘C and -3.3302MHz/∘C, and the strain coefficients are -0.06143MHz/µε and -0.03463MHz/µε. Due to the different temperature and strain dependences of Brillouin frequency peaks in two polarizations, temperature and strain resolutions of 1°C and 33µε are realized, respectively. Numerical simulations are also reported to account for the BFS difference in two polarization axes.

All-Pass and Add-Drop Microsphere Resonator in a Suspended Dual-Core Hollow Fiber

In this paper, we demonstrate an in-fiber all-pass and add-drop whispering gallery mode microsphere resonator. We fusion splice a section of single mode fiber (SMF) to a section of suspended dual-core hollow fiber (SDCHF), into which a microsphere is then embedded. Most of the input light from the SMF can be coupled into the cores of the SDCHF, with a maximum coupling efficiency obtained when maintaining a balance between the cone-apex angle and the core size of SDCHF in the conical region. The optical spectrum can be clarified by reducing coupling paths between the microsphere and the SDCHF. It is observed that the linewidth of the resonance peak is halved with halved coupling paths in the coupling model. When the microsphere with a suitable diameter is located at a critical position in the SDCHF, the coupler turns from an all-pass into an add-drop coupling structure. The device also demonstrates good stability as a refractive index (RI) sensor with a sensitivity of -386.12 dB/RIU when the RI of the surrounding medium ranges from 1.3333 to 1.3714. This in-fiber resonator device is inherently robust, compact, and has a great potential for sensing applications.

Broadband self-switching of femtosecond pulses in highly nonlinear high index contrast dual-core fibre

In this paper, we demonstrate a pulse energy-governed nonlinear self-switching of femtosecond pulses at wavelength of 1700 nm in a highly nonlinear high index contrast dual-core fibre. The fibre structure is composed of two microdimension cores and a solid cladding made of two thermally matched soft glasses developed in-house. A double switching behaviour under monotonic increase of the input pulse energy from 1 nJ to 3 nJ was observed at 35 mm fibre length in its anomalous dispersion region. A spatial intensity distribution measurement identified a switching contrast of 16.7 dB, and the registered spectra of the two output channels revealed a broadband switching behaviour within 150 nm. The obtained results indicate a novel type of solitonic switching and represent a significant progress in comparison to the previous experimental works and has a high application potential.

Thermo-optic instabilities in asymmetric dual-core amplifiers

Dynamical thermo-optic instabilities in asymmetric dual-core fiber amplifiers are investigated by numerical simulations. A coupled-mode model capable of describing the asymmetric dual-core structure is derived, and structures with various levels of refractive-index asymmetry from 10 − 6 to 10 − 4 are studied. The most viable route to avoid thermally induced power signal field fluctuations is found to be core decoupling via large separation and strong refractive-index asymmetry. A design criterion for this strategy to be effective is suggested based on the numerical results.

Snakelike similaritons in combined harmonic-lattice potentials with a varying source

We study the dynamics of snakelike similaritons to the nonlinear Schrodinger equation in combined harmonic-lattice potentials with a varying source term. Using the self-similar and Mobius transformations, we construct a large number of analytical solutions which generate many types of novel snakelike similaritons under some constraint conditions, such as the W- and bell-shaped breathing similaritons and the elliptic function solutions. Then, four specific examples of physical interest are considered in details to show the dynamical behaviors of the similaritons. Especially, the compression effect of snakelike similaritons is demonstrated in dispersion-decreasing media with Bessel modulated nonlinearity. We find that the structures of snakelike similaritons can be controlled by tuning the coefficient parameters, the combined harmonic-lattice potentials, and the source term. The stability of the solutions has also been performed by numerical simulations. Our results may have potential applications in the dual-core fiber waveguides and Bose–Einstein condensates in the presence of an inhomogeneous source.

Applicable ultrafast all-optical switching by soliton self-trapping in high index contrast dual-core fibre

The improvement potential of ultrafast all-optical switching by soliton self-trapping, using all-solid dual-core fibres with high index contrast, was analyzed numerically. The study of the femtosecond nonlinear propagation was performed based on coupled generalised nonlinear Schrödinger equations considering three fibre architectures: homogeneous cladding all-solid, photonic crystal air-glass, and photonic crystal all-solid. The structural geometries of all three architectures were optimised in order to support high-contrast switching performance in the C-band, considering pulse widths at the 100 fs level. Comparing the three structural alternatives, the lowest switching energies at common excitation parameters (1700 nm and 70 fs pulses) were predicted for the homogeneous cladding dual-core structure. Further optimization of the excitation wavelength and pulse width resulted in lower switching energies and simultaneous improvement of the switching contrasts at the combination of 1500 nm, 75 fs pulses and a fibre length of 43 mm. The spectral aspect in this optimised case expresses a broadband and uniform switching character with a span of over 200 nm and a contrast exceeding 30 dB at more frequency channels.

Design and coupling characteristics of terahertz dual-core anti-resonant fiber

The THz wave has good photonic and electronic properties, and has high penetration for non-polar materials, but its own photon energy is low. In addition, the THz wave also has characteristics such as wide bandwidth and large communication capacity, thereby making the THz wave possess important academic value and wide application prospects in the fields of non-destructive testing, biomedical imaging and communication. The development of THz technology requires not only high-performance THz waveguide technology for efficient transmission of THz waves, but also important optical devices such as optical switches, modulators, and couplers that are suitable for THz bands. With the in-depth study of THz waveguide technology, researchers have proposed many high-performance THz waveguide structures, such as metal hollow core tube waveguide, parallel metal plate waveguide, photonic crystal fiber and microstructure hollow core fibers, among which hollow-core photonic crystal fibers and hollow-core anti-resonant fibers (HC-ARF) have developed rapidly in recent years. So far, THz single-mode single-polarization fiber and high-birefringence fiber have been widely studied, but the researches on the fiber structure and devices that realize THz wave directional coupling are relatively rare. In this paper, we study the influences of the arrangement and distribution of the inner and outer claddings of HC-ARF on transmission characteristics, and thus design a new type of THz dual-core anti-resonant fiber. Compared with ordinary quartz fiber couplers and dual-core photonic crystal fibers, it can utilize a relatively simple structure and achieve directional coupling above 2 THz. Using the finite element analysis method to theoretically analyze the loss characteristics and coupling characteristics of the fiber, it is found that HC-ARF changes the periodic arrangement and distribution of the inner cladding tube within a certain range, which can achieve mode leakage without affecting the fiber transmission characteristics. So the THz dual-core anti-resonant fiber can be designed by using the mode leakage coupling mechanism. By changing the core distance and core gap size, the directional coupling with a coupling length of 0.72 m is realized at a transmission frequency of 2.5 THz. This terahertz dual-core anti-resonance fiber will have an important application value in terahertz optical devices such as terahertz optical switches, modulators and couplers.

High sensitivity humidity sensor based on gelatin coated side-polished in-fiber directional coupler

We demonstrate the first experimental realization of in-fiber directional coupler-based relative humidity (RH) sensor. A segment of single eccentric hole-assistant dual-core fiber (SEHADCF) is directly spliced between two single mode fibers (SMFs) to realize an in-fiber directional coupler (IFDC), and the suspended core of the SEHADCF is exposed to the external environment by using the side-polishing process. Gelatin is covered on the exposed suspended core to form the cladding of the suspended core and acts as a humidity sensitive material. Compared to the previous literatures, we report the highest sensitivity of the RH sensor to our best knowledge. In the RH range of 70 %–90 %, the average and maximum RH sensitivities are −7.005 nm/%RH and −18.94 nm/%RH, respectively. In addition, the temperature response and stability of the IFDC is also experimentally measured. Due to the super-high sensitivity and low temperature crosstalk, the proposed sensor will be expected to be a promising candidate for highly sensitive RH sensing applications in high humidity environment.

10 kHz-34 MHz ultrasound detection based on a dual-core hybrid taper

We propose and demonstrate an approach for 10 kHz to 34 MHz ultrasound detection based on a dual-core As2Se3-PMMA taper. We fabricate dual-core As2Se3-PMMA tapers with a Young’s modulus 24 times smaller than that of silica fibers, which enhances the acoustic response. Dual-core As2Se3-PMMA fiber tapers show high sensitivities to both shear and longitudinal waves due to the dual-core structure, low Young’s modulus, submicrometer dimension of the core, and the high-contrast interference pattern by the even and odd modes. A dual-core As2Se3-PMMA taper with a core diameter of 0.6 µm detects acoustic waves in the frequency range from 10 kHz to 34 MHz, which are excited by three piezoelectric transducers with optimal operating frequencies of 100 kHz, 3.65 MHz, and 6.8 MHz, respectively.

High sensitivity temperature sensor based on liquid filled hole-assisted dual-core fiber

A high sensitivity temperature sensor is numerically and experimentally investigated in liquid filled eccentric hole-assisted dual-core fiber (EHADCF). The sensor is constructed by cascading two single mode fibers (SMFs) with an intermediate liquid filled EHADCF segment. The light couples periodically between the center and suspended cores due to small core distance. Refractive index (RI) matching liquid with high thermo-optic coefficient is filled into the air-hole of the EHADCF as the cladding of the suspended core. The dispersion curves of the center and suspended cores of the EHADCF change with the temperature, leading to the shift of the resonance peak. The measured temperature sensitivity of the sensor is −562.4 pm/°C. In addition, the stability of the sensor is also measured. Due to high sensitivity, good stability, compact size and large temperature range, the proposed sensor shows promising potentials for temperature sensing in environment monitoring.

Low-temperature crosstalk and surrounding refractive index insensitive vector bending sensor based on hole-assistant dual-core fiber.

A low-temperature crosstalk and surrounding refractive index insensitive vector bending sensor based on resonance coupling is proposed and experimentally demonstrated. The sensor is constructed by directly sandwich-splicing asegment of single eccentric hole-assisted dual-core fiber between two single-mode fibers. The transmission characteristicsof the sensor are theoretically analyzed by combining coupled-mode theory and full-vector finite-element method. The bending responses of the sensor are experimentally measured in the curvature range of0-3.6651 m-1. The bending sensitivities are -15.95 nm/m-1 and 14.87 nm/m-1 at 0° and 180° bending orientation, respectively, which are higher than that of most long-period fiber-grating-based and interferometer-based vector bending sensors. Moreover, the temperature and surrounding refractive index responses of the sensor are investigated. The measured results show that the proposed sensor has a low temperature sensitivity of 21.7pm/°C in the range of 15°C-55°C and is insensitive to the surrounding refractive index in the range of 1.335-1.425, which reduces the cross-sensitivity from temperature and surrounding refractive index.

Bending sensor with parallel fiber Michelson interferometers based on Vernier-like effect

A highly sensitive bending sensor based on two parallel fiber Michelson interferometers (MIs) with a Vernier-like effect is proposed and demonstrated. The interferometric structure consists of a dual-core fiber (DCF) spliced with a short section of dual-side-hole fiber (DSHF). The centric core of the DCF is aligned with one air-hole of the DSHF to form a reflective interface. The centric core of the DCF is connected to the core of the DSHF with a little lateral offset to make the light in the centric core couple to both the core and cladding of the DSHF. The light beams reflected by the end of the DSHF and the DCF interfere with each other, forming two parallel MIs. The free spectral range (FSR) difference between the two MIs is very small due to the tiny difference in refractive index (RI) between the core and cladding of the DSHF, which results in a Vernier-like effect. The most novel feature of the mentioned structure is that both MIs are sensitive to bending with the same sensitive direction. Experimental results indicate that the bending sensitivity of the sensor can reach 38.53 nm/m−1. This kind of sensor has far-reaching significance in the research of structural safety monitoring.

Outage Probability Due to Intercore Crosstalk in Dual-Core Fiber Links With Direct-Detection

The outage probability (OP) in short-haul direct-detection (DD) optical links supported by weakly-coupled multicore fiber (MCF) impaired by intercore crosstalk (ICXT) and using ON–OFF keying signaling is assessed theoretically and through simulation. A closed-form expression for the OP is proposed for a single interfering core. This expression is useful to provide fast and reliable performance estimates in preliminary studies of weakly-coupled MCF-based systems where the ICXT is highly correlated along the signal bandwidth, i.e., when the skew-bit rate product is small. Particularly, the results for a 20-km-long link at 10 Gbit/s and walk-off below 1 ps/km are detailed. For high skew-bit rate products, i.e., when the ICXT is decorrelated along the signal bandwidth, the simulation results show that for a typical OP of 10−4, the tolerance to ICXT increases above 4 dB, when compared with low skew-bit rate products. It is also shown that the DD links with finite extinction ratio are more robust to outage induced by the ICXT than those with an ideal extinction ratio.

3D electrohydrodynamic printing of highly aligned dual-core graphene composite matrices

The aim of this study was to develop an EHD printing method to fabricate graphene-loaded polycaprolactone (PCL)/polyethylene oxide (PEO) dual-core matrices. Graphene was incorporated in shell PCL components, while gelatin and dopamine hydrochloride (DAH) were encapsulated in two PEO cores to enhance biocompatibility of graphene-loaded matrices. Furthermore, the effect of PEO concentration on dual-core fiber formation was evaluated. The influence of process parameters (applied voltage, inner flow rate, outer flow rate and X-Y-Z collector stage speed) on dual-core fiber morphology was evaluated. Our findings show graphene-loaded structures to possess two inner cores and increasing graphene content yields matrices with smoother surfaces, causing a slight reduction in their contact angle behavior. Furthermore, the addition of graphene to matrices results in reduced elasticity. DAH release from matrices comprising various graphene concentrations showed no significant difference and drug release mechanism was diffusion based. In vitro biological tests indicate resulting graphene-loaded dual-core matrices exhibit good biocompatibility and also improve PC12 cell migration. The findings suggest matrices to have potential applications in nerve restoration and regeneration.

Optical solitons in dual core fibers under various nonlinearities

This paper retrieves different types of soliton solutions for coupled nonlinear Schrödinger equation (NLSE). We use extended F-expansion method to find bright, dark and other trigonometric solutions with Kerr law and anti-cubic law. We also find Gausson soliton for coupled NLSE under log law nonlinearity.

2 × 2 microparticles curvilinear transport channel based on dual self-accelerating beams

We propose and demonstrate a 2 × 2 microparticles curvilinear transport channel based on a dual self-accelerating beam generator. The device is composed of a dual-core fiber, a hollow capillary fiber, and a coreless silica fiber. The dual self-accelerating beams produced by the device propagate along the curvilinear trajectory due to the transverse accelerating property and then cross at the front of the fiber probe. The experimental results show that the yeast cell is transported along the curvilinear trajectory. By adjusting the optical power ratio of dual beams, we may control and ensure the yeast cell steers at the cross point. The proposed 2 × 2 curvilinear microparticles transport channel based on dual self-accelerating beams can realize microparticles sorting and obstacle avoidance, which means that it would be a useful tool in biology and colloidal science.

An Ultrashort Wavelength Multi/Demultiplexer via Rectangular Liquid-Infiltrated Dual-Core Polymer Optical Fiber.

We propose a rectangular liquid-infiltrated dual-core polymer optical fiber (POF) for short-range communication systems by the beam propagation method (BPM). The POF multi/demultiplexer (MUX/DEMUX) at the wavelengths of 0.52/0.65-μm, 0.57/0.65-μm, and 0.52/0.57-μm are devised. The simulation results demonstrate that the ultrashort length of three ultrashort POF couplers are 183.6 μm, 288 μm, and 799.5 μm. Compared with the conventional optical fiber couplers, these results could have significant applications in the miniaturization of optical devices for visible light communication.

New exact solutions to the dual-core optical fibers

In this article, new exact solutions of the dual-core optical fibers model are determined by using the Riccati–Bernoulli sub-ODE method. As a result, rational, trigonometric, hyperbolic and exponential functions and a variety of special solutions like kink-shaped, bell-type soliton solutions are established. We also consider the linear stability analysis for the dual-core optical fibers model. We also plot the 3D graphs for some selected solutions with the aid of the MATLAB software. We finally compare our results with the other methods and show that the Riccati–Bernoulli sub-ODE method is superior to other methods.