Fengjun Tian

Optical fiber modulator derivates from hollow optical fiber with suspended core

A fiber optic integrated modulation-depth-tunable modulator based on a type of hollow optical fiber with suspended core is proposed and investigated. We synthesized magnetic fluid containing superparamagnetic Fe(3)O(4) nanoparticles and encapsulated it in the hollow optical fiber as the cladding layer of the suspended core by fusing the hollow optical fiber with the multimode optical fibers. The light with a wavelength of 632.8 nm is coupled in and out of the modulating element by a tapering technique. Experimental results show that the light attenuation in the system can be greatly influenced by only 2.0×10(-2) μL of the magnetic fluid under different magnetic field strengths. The saturated modulation depth is 43% when the magnetic field strength is 489 Oe. The response time of the system is <120 ms. Significantly, this work presents information for the development of all-fiber modulators, including other integrated electro-optic devices, such as optical switch, optical fiber filter, and magnetic sensors utilizing the special structure of this hollow optical fiber with suspended core and superparamagnetic magnetic fluid.

Three-core fiber-based shape-sensing application

By using specially designed three-core fiber, a microstructured light-pattern generator for sensing 3-D shapes has been demonstrated. The square or hexagon grid-interferometric fringe pattern formed by the fiber-optic interferometric grid generator is projected onto an objects surface. The deformed grid pattern containing information of the objects surface topography is captured by a CCD camera and is analyzed using 2-D Fourier transforming profilometry. The use of the 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; moreover, the three-core fiber can be used in very narrow places, owing to its small size. Finally, the square or hexagon grid-interferometric fringe pattern provides a data-fusion ability that could further improve the accuracy of the 3-D shape-sensing results.

Optical refractometer based on an asymmetrical twin-core fiber Michelson interferometer

We report and demonstrate an optical refractometer based on a compact fiber Michelson interferometer. The Michelson interferometer is composed of an asymmetrical twin-core fiber containing a central core and a side core. By chemically etching a segment of the twin-core fiber until the side core is exposed, the effective index of the side core in the etched region is sensitive to the environmental refractive index, which leads to a shift of the transmission spectrum of the Michelson interferometer. The experimental results show that such a device has a refractive index resolution of more than 800 nm/refractive index unit in the range of 1.34-1.37.

Integrated fiber Michelson interferometer based on poled hollow twin-core fiber

We propose an integrated fiber Michelson interferometer based on a poled hollow twin-core fiber. The Michelson interferometer can be used as an electro-optic modulator by thermal poling one core of the twin-core fiber and introducing second-order nonlinearity in the fiber. The proposed fiber Michelson interferometer is experimentally demonstrated under driving voltages at the frequency range of 149 to 1000 Hz. The half-wave voltage of the poled fiber is 135 V, and the effective second-order nonlinear coefficient χ² is 1.23 pm/V.

Characteristics of Near-Surface-Core Optical Fibers

A near-surface-core optical fiber is proposed that consists of a cladding and a circular or an elliptical core close to the surface of the cladding. The finite element method (FEM) is utilized to analyze characteristics of the near-surface-core optical fiber, including the mode characteristic, birefringence, and evanescent field. The results reveal that the near-surface-core optical fiber has polarization- preserving properties and a non-zero cut-off frequency for the fundamental mode. The near-surface-core optical fiber has a strong evanescent field due to a small distance between the core and the ambient medium and is a promising candidate for evanescent wave sensors. The near-surface-core optical fiber has an interesting phenomenon of surface-enhanced optical effect, which is similar to that of the nanofiber.

Characteristics of embedded-core hollow optical fiber

We propose a novel embedded-core hollow optical fiber composed of a central air hole, a semi-elliptical core, and an annular cladding. The fiber characteristics are investigated based on the finite element method (FEM), including mode properties, birefringence, confinement loss, evanescent field and bending loss. The results reveal that the embedded-core hollow optical fiber has a non-zero cut-off frequency for the fundamental mode. The birefringence of the hollow optical fiber is insensitive to the size of the central air hole and ultra-sensitive to the thickness of the cladding between the core and the air hole. Both thin cladding between the core and the air hole and small core ellipticity lead to high birefringence. An ultra-low birefringence fiber can be achieved by selecting a proper ellipticity of the core. The embedded-core hollow optical fiber holds a strong evanescent field due to special structure of thin cladding and therefore it is of importance for potential applications such as gas and biochemical sensors. The bending losses are measured experimentally. The bending loss strongly depends on bending orientations of the fiber. The proposed fiber can be used as polarization interference devices if the orientation angle of the fiber core is neither 0° nor 90°.

Experimental and Theoretical Investigations of Bending Loss and Birefringence in Embedded-Core Hollow Fiber

The bending loss and birefringence in an embedded-core hollow fiber are investigated numerically and experimentally. The bending losses of the fiber for two polarized lights are measured for different bending orientations and bending radii. Both the simulated and measured results show that the bending loss of the embedded-core hollow fiber has a strong directional dependence. The bending loss is larger and more sensitive to bending radius when the fiber is bent toward the core direction. In the opposite bending direction, the fiber has the antibending capacity. Because the core of the fiber sample is a nonstrict elliptical, a critical orientation angle exists during the bending of the optical fiber. Away from the critical angle, the bending losses are not sensitive to the bending orientation regardless of antibending direction or bending sensitive direction. The group birefringence of the optical fiber is also measured.

Supermodes Analysis for Linear-Core-Array Microstructured Fiber

Linear-core-array microstructured fibers are fabricated using the modified chemical-vapor deposition (MCVD) for preparing each core performs, and two D-shape large-scale silica rods are also used in the linear-core-array fiber perform stacking. The supermodes in optical fibers with linearly distributed 23 cores are presented by using coupled-mode theory. The coupling coefficients between two adjacent cores are estimated based on the weak guidance approximation. The near- and far-field distributions of supermodes supported by the multicore fiber (MCF) are presented. A Talbot cavity is exploited to select wanted supermodes. The calculated results show that the in-phase supermode can dominate the output. The coupling field propagation characteristics of the optical fibers are also analyzed.

Capillary optical fiber linking approach for biosensors

A method for linking a single mode fiber and a capillary fiber is proposed based on splicing and tapering at the fusion point between the two fibers. It can be used in bio-sensing system.

Linear-core-array microstructured fiber

Linear-core-array microstructured fibers are fabricated using the modified chemical-vapor desposition and etching method for preparing each core performs, and two D-shape large-scale silica rods are also used in the linear-core-array fiber perform stacking. The supermodes in optical fibers with linearly distributed 23 cores are investigated by using the coupled-mode theory. The coupling field propagation characteristics of the optical fibers are analyzed. The linear-core-array fiber could be used in improving the high-power fiber laser-beam shape, enhancing its quality.