Two-core Fiber Research Articles

具有高阶耦合色散系数双芯非线性光纤耦合器开关的数值分析

具有高阶耦合色散系数双芯非线性光纤耦合器开关的数值分析

Effects of intrapulse stimulated Raman scattering on short pulse propagation in a nonlinear two-core fiber

The switching dynamics of short pulses propagating in a two-core optical fiber under the effects of intrapulse stimulated Raman scattering (ISRS) and intermodal dispersion is investigated theoretically. We find that, when the input pulses are short and intense enough, ISRS in general reduces the width of the pulses propagating in the launching core of the fiber and, at the same time, slows down the pulses. However, if the two-core fiber contains sufficient intermodal dispersion, the pulse-narrowing effect of ISRS can be weakened. Using typical fiber parameters, we demonstrate with numerical examples how the interaction of ISRS and intermodal dispersion affects the pulse shape.

In-fiber integrated Michelson interferometer

A novel fiber-optic in-fiber integrated Michelson interferometer has been proposed and demonstrated. It consists of a segment of two-core fiber with a mirrored fiber end. The sensing characteristics based on the two-core fiber bending, corresponding to the shift of the phase of the two-core in-fiber integrated Michelson interferometer, are investigated.

Independent core propagation in two-core photonic crystal fibers resulting from structural nonuniformities

Random nonuniformities in the photonic crystal lattice are shown to reduce the coupling length and the coupling efficiency of two-core photonic crystal fibers. These coupling properties are extremely sensitive to imperfections when the air holes are large; variations in the lattice of less than 1% are sufficient to cause essentially independent core propagation due to a drastic reduction in the efficiency of the core coupling. The observed sensitivity of two-core fibers to lattice imperfections is explained through a comparison with coupled mode theory.

Propagation of short pulses in an active nonlinear two-core optical fiber

The switching dynamics of short pulses in an active nonlinear two-core fiber coupler is investigated theoretically. The analysis takes into account the effects of coupling-coefficient dispersion, gain bandwidth, and gain saturation. In particular, we demonstrate that the pulse breakup effect due to coupling-coefficient dispersion can be suppressed by limiting the bandwidth of the linear gain, whether gain saturation is considered or not.

Effects of gain saturation on short pulse propagation in an erbium-doped nonlinear two-core fiber

Effects of gain saturation on short pulse propagation in an erbium-doped nonlinear two-core fiber

Effects of Intermodal Dispersion on Short Pulse Propagation in an Active Nonlinear Two-Core Fiber Coupler

The effects of intermodal dispersion in a passive two-core fiber coupler have been investigated. In this letter, we extend the study from the passive to the active two-core fiber coupler and investigate the effects of intermodal dispersion on the performance of the active coupler. In particular, we observe a new feature caused by the interaction between the intermodal dispersion and the gain bandwidth: The pulse breakup effect due to intermodal dispersion can be suppressed by the finite bandwidth of the linear gain.

Effects of gain saturation on short pulse propagation in an erbium-doped nonlinear two-core fiber

Propagation of short pulses in an erbium-doped nonlinear two-core fiber is studied by considering a general model that can include both gain saturation and intermodal dispersion, which has not been dealt with previously. In particular, we discuss the effects of gain saturation on the performance of the active nonlinear two-core fiber. We highlight the special temporal feature led by the interplay between intermodal dispersion and the finite bandwidth of the linear gain.

Two-core photonic crystal fibre for Doppler difference velocimetry

We present the first application of a two-core photonic crystal fibre for fringe projection for use as a Doppler difference velocimeter. The two-core fibre projects a series of fringes when both cores are simultaneously illuminated with 633 nm light. Light scattered from moving particles is coupled into a separate multi-mode collection fibre and detected using a silicon detector and amplifier. The scattered signal is processed in the frequency domain to obtain the particle velocity component perpendicular to the fringes.

Evaluation of intermodal dispersion in a two-core fiber with non-identical cores

It is known that the intermodal dispersion in a two-core fiber can affect seriously the propagation dynamics of short pulses and even cause pulse breakup. In this paper, we generalize the previous work on a two-core fiber with identical cores to one with non-identical cores. In particular, we present a general analytical formula for the calculation of the intermodal dispersion in a two-core fiber whose cores can have different radii and refractive indices. We highlight the effects due to the dissimilarity of the two cores on the intermodal dispersion and its wavelength dependence with numerical examples.

Generalized coupled nonlinear equations for the analysis of asymmetric two-core fiber coupler

Studies have shown that 1st order coupling coefficient dispersion can cause significant effects on the propagation of short pulses in a twincore coupler. In this paper, we have extended the study to the case of nonidentical cores and investigated the effect of 2nd order dispersive coupling coefficient on switching dynamics. A pair of new coupled nonlinear equations have been presented and analyzed.

Channel-dropping filter based on a grating-frustrated two-core fiber

We present experimental results on the operation of a dissimilar two-core fiber segment as a channel dropping filter based on the principle of grating-frustrated coupling. The restoration of 100% coupling by ultraviolet (UV)-tuning of the fiber is demonstrated over a bandwidth in excess of 20 nm. It is also shown that a grating can be inscribed in one of the cores while maintaining perfect coupling conditions between the cores.

Experimental demonstration of intermodal dispersion in a two-core optical fibre

The recent prediction that intermodal dispersion could affect the propagation of short pulses in a two-core optical fibre was confirmed experimentally. A picosecond pulse at 1.548 μm launched into one core of a meters-long two-core fibre was found to come out of either core of the fibre as two temporally separate pulses. By measuring the time delay between these two pulses, the intermodal dispersion in the fibre was estimated to be 1.13 ps/m, in good agreement with theory.

Optical bandpass filter from a curved segment of a detuned two-core fiber

We present the use of a dual-core fiber as a bandpass filter. Our device is based on the fact that intrinsic detuning between the propagation constants of the two cores can be compensated for in a controlled manner by use of a loop. This compensation is made to occur for a specific frequency band, so that the resulting device acts as a bandpass filter.

Vector normal modes on two-core optical fibers. I. The normal mode solutions

A vector theory based on the circular harmonics expansion method combined with the finite-element method is formulated to solve the guided normal modes on the two-core fiber with radially inhomogeneous core index profiles. Numerical examples are given for the two-identical-core cases with power-law core index profiles. Polarization patterns for the vector modes on the strongly guiding two-core fiber structure, such as that of a fused coupler made with biconical tapering technology under weakly fusing condition, are presented.

Vector normal modes on two-core optical fibers. II. The modal cutoffs

For pt.I see ibid., vol.15, no.7, p.1213-24 (1997). A vector theory based on generalization of the circular harmonics expansion method combined with the finite-element method is formulated to determine cutoff values for higher-order normal modes on the two-core fiber with radially inhomogeneous core index profiles. The method is developed under the transverse magnetic field formulation in order to avoid the spurious solutions. Numerical examples are given for the two-identical-core cases with power-law core index profiles.

Analysis of modal cutoffs of radially inhomogeneous two-core optical fibers by circular harmonics expansion method

A scalar theory based on generalization of the circular harmonics expansion method combined with the finite element method is formulated to determine cutoff values for higher order normal modes on the two-core fiber with radially inhomogeneous core index profiles under the weakly guiding approximation. The validity of the field expansion expression in the derived generalized circular harmonics expansion method is proved rigorously by expanding the Green's function for the Laplace equation in a surface integral equation into generalized circular harmonics. Numerical examples are given for the two identical-core cases with power-law core index profiles. Our method is shown to be able to provide exact cutoff values for the touching-core case.

Intermodal dispersion in two-core optical fibers

The switching characteristics of a two-core optical fiber can be described by the beating of the even and odd modes of the composite two-core structure. It is shown that the group-delay difference between these two modes can be as large as 10 ps/m. This intermodal dispersion sets a limit on the shortest duration of the optical pulse that can be switched effectively in devices that use long lengths of two-core fibers, such as wavelength-division multiplexers, polarization splitters, and nonlinear directional couplers.

Long-distance soliton transmission with a nonlinear twin-core fiber

We numerically demonstrate soliton transmission over long distances in a new regime in which the soliton evolves in a two-core fiber over many dispersion lengths between successive amplifications. Shorter pulses than those transmitted in the average soliton dynamics regime are predicted, while a significant drift of the soliton mean frequency owing to the soliton self-frequency shift is observed and controlled by appropriate gain and loss parameters.

Nonlinear refractive index in erbium doped optical fiber: Theory and experiment

An intensity-dependent refractive index in erbium doped optical fiber has been observed for the first time. The effect has been observed by an interferometric technique using a two-core fiber. The effect is analyzed theoretically, and the important nonlinear parameters for thin material have been determined and are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>