Yiping Xu

Low-Cost Multipoint Liquid-Level Sensor With Plastic Optical Fiber

A simple and low-cost discrete liquid-level measurement system is present in this letter. It consists of a group of plastic optical fiber segments, which are aligned coaxially and spaced equally. When the spacing between every two adjacent fiber segments is filled with liquid, the light power will be easier to couple from one segment to the next as compared with the situation that the fibers are exposed in air. Based on this point, we design this intensity-based sensor and investigate its working properties theoretically by using the ray-tracing method. The performance of this sensor is demonstrated in detail where different liquids are utilized as specimens.

Superconductivities of n‐type Nd1.85Ce0.15CuO4−y prepared under high pressure

In this work we provide the report on the preparation of a bulk n‐type NdCeCuO superconductor using a high‐pressure high‐temperature sintering procedure. The superconductor was obtained by sintering as‐prepared material at 4.0 GPa at 530 °C for 20 min and required no additional reducing treating. The sample shows a higher onset temperature Tcon (32 K), a higher zero resistance temperature Tc0 (22 K), and a much lower resistivity than a standard bulk sample. Indeed the room‐temperature resistivity and the quasimetallic resistivity in the normal state for our polycrystalline sample are similar to those of single crystals. This high‐pressure sintering procedure reduces weak link effects and opens the possibility of preparing high‐quality bulk n‐type superconductors.

Superconductivities of n -type Nd sub 1. 85 Ce sub 0. 15 CuO sub 4 minus y prepared under high pressure

In this work we provide the report on the preparation of a bulk n‐type NdCeCuO superconductor using a high‐pressure high‐temperature sintering procedure. The superconductor was obtained by sintering as‐prepared material at 4.0 GPa at 530 °C for 20 min and required no additional reducing treating. The sample shows a higher onset temperature Tcon (32 K), a higher zero resistance temperature Tc0 (22 K), and a much lower resistivity than a standard bulk sample. Indeed the room‐temperature resistivity and the quasimetallic resistivity in the normal state for our polycrystalline sample are similar to those of single crystals. This high‐pressure sintering procedure reduces weak link effects and opens the possibility of preparing high‐quality bulk n‐type superconductors.

Slow-light element for tunable time delay based on optical microcoil resonator

We propose a simple and compact slow-light element by use of an optical microcoil resonator (OMR) constituted by two microfiber coils. Based on the matrix exponential method, we solve the coupled-wave equations of the OMR with n turns of microfiber coils and obtain a general solution. Simulations indicate that a tunable slow-light propagation can be obtained by controlling the coupling coefficient between the two adjacent microfiber coils by means of regulating the voltage applied to the ferroelectric crystal. A slow-light time delay up to 62 ps with a bandwidth of 0.4 nm is performed at the wavelength around 1.5 μm.

All-optical control of microfiber resonator by graphene's photothermal effect

We demonstrate an efficient all-optical control of microfiber resonator assisted by graphenes photothermal effect. Wrapping graphene onto a microfiber resonator, the light-graphene interaction can be strongly enhanced via the resonantly circulating light, which enables a significant modulation of the resonance with a resonant wavelength shift rate of 71 pm/mW when pumped by a 1540 nm laser. The optically controlled resonator enables the implementation of low threshold optical bistability and switching with an extinction ratio exceeding 13 dB. The thin and compact structure promises a fast response speed of the control, with a rise (fall) time of 294.7 μs (212.2 μs) following the 10%–90% rule. The proposed device, with the advantages of compact structure, all-optical control, and low power acquirement, offers great potential in the miniaturization of active in-fiber photonic devices.

Design and fabrication of tapered microfiber waveguide with good optical and mechanical performance

In this paper, the inherent dependence of optical and mechanical characteristics of tapered microfiber waveguide on its contour profile is studied. Both theoretical analysis and experimental investigation are given. In theory, the optimal profile parameters of the tapered microfiber are proposed to improve the microfiber performance, where it is better to make the tapered microfiber keep two longer than 5-mm-long transition regions which have a decaying exponential profile. And the uniform waist diameter of the tapered microfiber should be more than 600 nm and less than 1 μm. In this case, the microfiber indicates several favorable advantages, such as low loss, strong evanescent field and relatively shorter transition region. In experiment, according to the profile parameters we proposed, we successfully fabricated a tapered microfiber with a low loss of 0.05 dB in air and 0.8 dB on a MgF2 substrate at the wavelength of 1550 nm, and it has low surface roughness.

Online fabrication scheme of helical long-period fiber grating for liquid-level sensing

We present a novel online fabrication scheme of helical long-period fiber gratings (H-LPFGs) by directly twisting a standard single-mode fiber (SMF) in a microheater. This is done by taking advantage of the inherent core-cladding eccentricity in SMF. We adopt a fiber optic rotary joint to eliminate the accompanying twisting spiral for real-time spectral monitoring and a stepping mechanical system to accurately control the twisting length in fabrication. As a consequence, low-cost and high-quality H-LPFGs can be readily fabricated. Meanwhile, by using this kind of H-LPFG, we design a simple and low-cost wavelength-interrogated liquid-level sensor with a high sensitivity of 0.1 nm/mm.

Evaluation of effective mass transport coefficients through comparison of solidification on the ground and on board a satellite

Mass transport caused by buoyancy convection in front of the solid–liquid interface was evaluated in terms of measurements of primary dendritic spacing combining with separation of the effective (or integral) mass transport coefficient DL. It was shown that DL in normal gravity (1g) condition was 1.64 times as high as that in microgravity (μg) condition at the cooling rate (v) of 0.056 K/s for Pd40Ni40P20 alloy. The higher DL value is due to the contribution of buoyancy convection on the ground.

Wideband slow light in microfiber double-knot resonator with a parallel structure

The characteristics of slow light in the microfiber double-knot resonator with a parallel structure are investigated both theoretically and experimentally. It is predicted that a wide bandwidth of about 20 GHz and flat-top group delay of about 70 ps can be generated in this resonator by changing the coupling coefficient. In the experiment, such a resonator was fabricated and the slow-light effect was demonstrated. As a result, when a pulse with a bandwidth of 3.35 GHz (equivalent to the temporal width of 299 ps) was launched into the resonator, a large group delay, whose average value was about 69.4 ps with a flat-top wavelength bandwidth of about 190 pm, was achieved

Theoretical and experimental study of structural slow light in a microfiber coil resonator

In this paper, a compact slow-light microfiber coil resonator (MCR) is fabricated and the slow-light properties of it are analyzed and tested. Based on coupled-wave theory, a theoretical model for describing the slow-light propagation in the MCR is established. Experimentally, the MCR slow-light element is fabricated and its relative slow-light time delay is measured. The group velocity of the light pulse in the MCR slow-light element can be reduced to about 0.47c (c is the speed of light in vacuum) and the shape of the light pulse passing through the MCR is well preserved.