Chunying Guan

Twin-core fiber optical tweezers

We present an abruptly tapered twin-core fiber optical tweezers, which is fabricated by fusing and drawing the twin-core fiber. In the twin-core fiber, the two beams are guided by the tapered fiber. At the end of the fiber tip, a larger converge angle between the two beams are made due to the abrupt tapered shape, which is formed a fast divergent optical field. The microscopic particle trapping performance of this special designed tapered twin-core fiber tip is investigated. The functionality of the proposed novel twin-core fiber optical tweezers is extended since an in-fiber integrated Mach-Zehnder interferometer has been used to control orientation of the trapped particle. The distribution of the optical field emerging from the tapered fiber tip is simulated based on the beam propagation method (BPM). By using this two-beam combination technique, a strong enough gradient forces well is obtained for microscopic particles trapping in three dimensions. The abruptly tapered twin-core fiber optical tweezers is rigid and easy to handle, especially useful for building up a multi-tweezers system for trapping and manipulating micro-scale particles.

Fiber-tip high-temperature sensor based on multimode interference

A fiber-tip high-temperature sensor based on multimode interference is demonstrated both theoretically and experimentally. The temperature sensor presented can measure a broad temperature interval ranging from room temperature to 1089 °C. An average sensitivity of 11.4 pm/°C is achieved experimentally.

Bitapered fiber coupling characteristics between single-mode single-core fiber and single-mode multicore fiber

By splicing and tapering at the fusion point of one-core single-mode fiber and three- or four-core single-mode fiber, an effective bitapered fiber coupling technique is implemented. Based on the beam propagation method, the bitapered coupling characteristics between the one-core fiber and the multicore single-mode fiber are simulated and analyzed. The theoretical prediction is confirmed by the experimental results, and the difference between the simulation and the experimental results is also discussed.

Optically controlled background-free terahertz switching in chiral metamaterial

We demonstrate a multiband background-free terahertz (THz) switch in photoactive chiral metamaterial using polarization conversion. Orthogonal arrangement of two asymmetrical split-ring apertures allows a high polarization conversion efficiency and low copolarization transmission. The chiral metamaterial embedded with photoactive silicon promises a dynamic control on cross-polarization transmission and thus enables an efficient background-free THz switch. The on/off state of THz metamaterial switching can be efficiently controlled by an optical pump. The realization of a cross-polarization THz switch provides a new mechanism of mode switching to control THz wave propagation and will be a promising candidate for polarization devices.

Highly-dispersive electromagnetic induced transparency in planar symmetric metamaterials

We propose, design and experimentally demonstrate highly-dispersive electromagnetically induced transparency (EIT) in planar symmetric metamaterials actively switched and controlled by angles of incidence. Full-wave simulation and measurement results show EIT phenomena, trapped-mode excitations and the associated local field enhancement of two symmetric metamaterials consisting of symmetrically split rings (SSR) and a fishscale (FS) metamaterial pattern, respectively, strongly depend on angles of incidence. The FS metamaterial shows much broader spectral splitting than the SSR metamaterial due to the surface current distribution variation.

Packaged, high-Q, microsphere-resonator-based add-drop filter.

In this Letter a packaged add-drop filter composed of a silica microsphere resonator and two fiber tapers is demonstrated theoretically and experimentally. A two-step fabrication process using an UV curable polymer is shown to stabilize the microsphere resonator with a diameter of 153 μm coupled to two tapered microfibers with diameters of 1.5 μm which are used as add and drop ports. A high loaded quality factor (Q-factor) of 0.9×10(5) and a free spectral range (FSR) of about 104 pm are obtained at around 1550 nm from the microsphere for the parallel coupling tapered fibers in the add-drop configuration. This device has a range of advantages, such as ease of fabrication, low-cost, and compatibility with traditional and commercial fiber systems.

Polarization splitter based on interference effects in all-solid photonic crystal fibers

We propose a novel kind of polarization splitter in all-solid photonic crystal fibers based on the mode interference effects. Both the full-vector finite-element method and the semi-vector three-dimensional beam propagation method are employed to design and analyze the characteristics of the splitter. Numerical simulations show that x-polarized and y-polarized modes are split entirely along with 6.8 mm long propagation. An extinction ratio of more than 20 dB and a crosstalk of less than -20 dB are obtained within the wavelength range of 1.541-1.556 microm. The extinction ratio and the crosstalk at 1.55 microm are 28.9 and -29.0 dB for x polarization, while the extinction ratio and the crosstalk at 1.55 microm are 29.9 and -29.8 dB for y polarization, respectively.

Asymmetrical Twin-Core Fiber Based Michelson Interferometer for Refractive Index Sensing

An asymmetrical twin-core fiber based Michelson interferometer is reported as a refractive index sensor. One core of the twin-core fiber locates at the fiber center and the other core is 26 μ m away from the central core. Part of the cladding of the twin-core fiber over a small length is removed by chemical etching to make the effective refractive index of the fundamental mode of the side core is sensitive to the ambient refractive index. Therefore, the interference spectrum between the central core and the side core shifts with the variation of the ambient refractive index. The sensitivity of such a Michelson interferometer is ~ 270 nm/RIU in the range of 1.34-1.38.

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.

Low-temperature sensitivity periodically tapered photonic crystal-fiber-based refractometer

In this Letter, an all-fiber refractometer with a simple configuration of periodical tapers on a photonic crystal fiber (PCF) is proposed and investigated experimentally. The proposed fiber refractive index (RI) sensor consists of a PCF sandwiched between two standard single-mode fibers, with tapers periodically fabricated along the PCF using a CO(2) laser beam focused by a ZnSe cylindrical lens. The proposed fiber sensor can be used for RI sensing by measuring the wavelength shift of the multimode interference dip over the transmission spectrum. An average sensitivity of 222 nm/RIU has been experimentally achieved over a RI range from 1.33 to 1.38. The proposed refractometer is also significantly less sensitive to temperature, and an experimental demonstration of this reduced sensitivity is presented. The proposed RI sensor benefits from simplicity and low-cost and achieves a competitive sensitivity compared with other existing fiber-optic sensors.