Two-core Fiber Research Articles

Optical equalisation with linearly tapered two-dissimilar-core fibre

A fibre with two dissimilar cores can be used as an all-optical equaliser to regenerate a signal degraded by chromatic dispersion in a long optical fibre link. For this, the two-core fibre has to be linearly tapered. The achievable dispersion of such a device is discussed, and a design example shown.

Two-core optical fibers: experiment

Two-core fibers are investigated experimentally. Low-loss birefringent single-mode two-core fibers, consisting of two cores and a pair of stress-inducing parts built in a cladding, were prepared. A power exchange of the order of a few millimeters occurs as a result of the coupling between the two cores. It was noted that the power-transfer efficiency shows a good wavelength selectivity because the fiber parameters, such as the core radius and refractive-index difference between the core and cladding of the two cores, are not identical. The Stokes beam of stimulated four-photon mixing, generated in a core by compensating for the material dispersion with the modal birefringence between the two orthogonally polarized fundamental modes, exclusively couples to the core, whereas the pump, first-order Raman Stokes, and anti-Stokes waves of the four-photon mixing remain uncoupled. This wavelength-selective coupling will be useful for various applications, such as in couplers in a wavelength-multiplexing optical system and in a fiber-optical amplifier.

Wavelength-selective coupling of two-core optical fiber: application and design

Wavelength-selective coupling characteristics of evanescent fields between nonidentical single-mode fibers are investigated theoretically. We study the application of two-core fiber, which has two adjacent cores embedded in a cladding, especially for fiber-optical amplifiers, using three-wave mixing or stimulated Raman scattering. The theory shows how to minimize the power-transfer efficiency between two cores either at the signal or at the pump wavelength, while maintaining 100% power transfer at the other wavelength. As a result, owing to the wavelength-selective coupling, a periodic interaction of the signal and pump lights is expected only in one of the two cores. This permits an efficient amplification of signal light. The attractive feature of the use of the two-core fiber is that various optics, such as lenses, beam splitters, and grating filters, can be eliminated from the setup.

Substrate-tube lithography for optical fibres

We describe the first use of substrate-tube lithography to build complex structures into MCVD fibre preforms. While the basic process is illustrated with high-birefringence fibres of 1.9 and 3 mm beat lengths and a two-core fibre, the technique is more general and may lead to a new class of integrated optical devices.

Coupling characteristics measurements between curved waveguides using a two-core fiber coupler

Coupling characteristics between two curved waveguides are studied using a two-core fiber. A tunable monochromatic light source is used to measure the wavelength dependence of the coupling efficiency. Measured values of the coupling efficiency agree well with theory. It is found that (1) the coupling efficiency can be changed from 0 to 1 by changing the radius of curvature, for example, from 100 mm to infinity in the measured coupler; and (2) when phase shift due to curvature sbeta/2R exceeds the coupling coefficient K, where s is the center-to-center core separation, beta the propagation constant, and R the radius of curvature, coupling between the curved cores does not occur, and there is only the phase shift between the cores.