We propose a high-birefringence twin-core hollow optical fiber, which is composed of two rectangular Ge-doped cores, annular silica cladding, and a large central air hole. The rectangular cores are weakly coupled with the air hole and arranged in the same silica cladding. The mode birefringence in single-mode operation of 1.55 μm reaches 2.48 × 10 − 4, which is comparable with traditional panda polarization maintaining fiber. By introducing an extra stress zone, the mode birefringence can be improved further by two times. The high birefringence of the twin-core hollow fiber is induced by strong asymmetry of the waveguide structure. The characteristics of the guiding mode, birefringence, and evanescent field are analyzed numerically by full-vector finite-element method. The effect of geometric and material parameters is discussed. The proposed scheme of twin-core hollow fiber can overcome the polarization fading effect and signal cross talk occurring in traditional multicore fibers and is much desirable for improving the performance of in-fiber integrated interferometers and biochemical sensors.
We propose a novel embedded-core hollow optical fiber composed of a central circular air hole and a semi-elliptical core
embedded in an annular cladding. Both the phase birefringence and group birefringence are investigated based on the
finite element method (FEM). The embedded-core hollow optical fiber has polarization-preserving properties. The
birefringence magnitude of the proposed fibers is the same order as that of the side-hole optical fiber. The theoretical
results reveal that the birefringence of embedded-core hollow optical fibers can reach the order of 10<sup>-4</sup>. The group
birefringence of the fiber is obtained by using the wavelength scanning technique and can reach 4.7×10<sup>-5</sup>. The
measurement results are basically consistent with the theoretical simulations.
Optical fibres play more and more important roles in astronomy, for example, to transfer light from the focus point of
telescopes to spectrometers. In this paper, a novel designed, a fibre-brush-shape converter was designed to transfer circle
input of a fibre to a line-shape output. The brush-shape converter consists of several bare fibres at one end, one fibre at
the other end and a taper between them. The light propagating from the bare fibres to the single fibre will be coupled.
According to the theoretical and calculated results, the power of the light could be confined in the core of the fibre if the
parameters of the taper are appropriate.
We design and fabricate a two elliptical cores hollow optical fiber, which has an about 60μm diameter hollow air hole
centrally, a 125μm diameter cladding, two 8μm/4μm (major axis/minor axis) elliptical cores, and a 2μm thickness silica
cladding between core layer and air hole. Its mode birefringence is consisted of geometry birefringence and self-stress
birefringence. Based on the finite element method the birefringence characteristics are analyzed numerically at 200nm-
1800nm wavelength. We expect that the two elliptical cores hollow fiber has some potential applications in in-fiber
interferometers with polarization maintaining, poling fiber and Bio-sensor based on evanescent wave field.
We propose a novel embedded two elliptical cores fiber with a hollow air hole, and demonstrate the fabrication of
the embedded two elliptical cores hollow fiber (EECHF). By using a suspended core-in-tube technique, the fibers are
drawn from the preform utilizing a fiber drawing system with a pressure controller. The fiber have a 60μm diameter hollow air hole centrally, a 125μm diameter cladding, two 7.2μm /3.0μm (major axis/minor axis) elliptical cores, and a 3μm thickness silica cladding between core layer and air hole. The EECHF has a great potential for PMFs, high sensitivity in-fiber interferometers, poling fiber and Bio-sensor based on evanescent wave field. The fabrication technology is simple and versatile, and can be easily utilized to fabricate multi-core fiber with any desired aspect ratio elliptical core.
Based on the specialty designed linear-core-array fiber, a laser beam shape convertor has been
proposed and demonstrated. The experimental and theoretical results shown that a multi beam with the peak
power distributed in a linear array have been obtained at the end of the linear-core-array fiber and the output
beam shape depend on the coupling condition and the supermodes propagation distance along the
linear-core-array fiber. This device transfers the laser shape from a Gaussian beam to a controlled linear array
beam. It could be used in industry for manufacturing or medicine applications.
The mode field characteristics of eccentric optical fibers are investigated theoretically. The eccentric optical fiber is
converted to be a concentric three-layered optical fiber through the conformal representation and the corresponding field
distribution is given by solving eigenvalue equation of a general three-layered optical fiber waveguide. The method
should be proved a simple solution for optimizing the configurations of special optical fibers.
We propose and fabricate a twin-half hollow elliptical core polarization maintaining fiber. The shape of the core in the
polarization maintaining fiber is designed to be elliptical for generating a geometry birefringence. In the cladding, two
half-hollows are symmetrically distributed with respect to the elliptical core for producing a stress birefringence.
Therefore, the birefringence in such a polarization maintaining fiber is the mixed effect of the geometry and stress
birefringence. The birefringence generating mechanism is analyzed in detail and a theoretical formula depicting the
birefringence is built up. The simulation results for the twin-half hollow elliptical core fiber at different structural
parameters are obtained by using finite element method. Through adjusting the structural parameters of the fiber, the
relationships between the birefringence and the core diameter as well as the width of the core bridge are discussed.
A fiber optic bending sensing system that uses twin-core fiber as the sensing element has been proposed and
demonstrated. The twin-core fiber act as a two-beam interferometer in which phase differences is a function of the
curvature, and it can be demodulated by the shift of the unique identification spectrum. By way of FFT analysis of the
white light interferometric spectrum, the variation of bending can be measured. The relationship between the bending
curvature and the shift of the unique identification spectrum has been given and the experimental results were also
By using spherical designed three-core fiber, a micro structured light pattern generator for sensing of 3-D object shapes
has been demonstrated. The square or hexagon grid interferometric fringe pattern formed by the fiber optic
interferometric grid generator is projected on an object's surface. The deformed grid pattern containing information of
the object's surface topography is captured by a CCD camera and is analyzed using a 2-D Fourier transforming
profilometry. The use of fiber optic grid interferogram technique greatly simplifies the holographic interferometry system
and the carrier grid interferogram can be conveniently generated without the use of excessive auxiliary components or
sophisticated experimental devices, and moreover, the three-core fiber can be used in very narrow places due to its small
size. Finally, the square or hexagon grid interferometric fringe pattern provides a data fusion ability, which could further
improve the accuracy of the 3-D shape sensing results.