Zigeng Liu

Fiber Optic Liquid Level Sensor Based on Integration of Lever Principle and Optical Interferometry

We present a fiber-optic liquid level sensor that is conducted by a combination of optical interferometry and lever principle. The sensing unit is a Mach-Zehnder interferometer (MZI), which is formed by sandwiching a piece of photonic crystal fiber (PCF) between two single-mode fibers (SMFs). The measuring equipment is composed of a rotatable lever and a fixed link. The rotatable lever includes two different length arms, i.e., L1 and L2. Both ends of the MZI are glued on the tip of the L2 arm and the fixed link using ethoxyline, respectively. A hanging stick, which is dipped into a liquid tank, is directly mounted on the other end of the rotatable lever. The buoyancy will increase as the stick depth of immersion into the liquid increases. The tension the MZI subjected will increase according to the proportion of L1/L2 on account of the lever principle. The sensitivity of the sensor could be regulated with different ratios of lever arms. In our experiment, a maximum sensitivity of 111.27 pm/mm was obtained with a 1 : 7.8 ratio of two lever arms L1/L2. The demonstrated liquid level sensor has the advantages of simple structure, easy fabrication, low cost, and high sensitivity.

Refractive Index Sensor Based on Fiber Ring Laser

In this letter, we investigate a novel refractive index sensor based on a simple fiber ring laser incorporating a bent fiber filter. The bent fiber structure acted as a fiber filter and a sensing element. The bent fiber filter is made of a section of semicircular bare standard single-mode fiber with a selected bending radius. The gain medium (erbium-doped fiber) is pumped by a 980 nm wavelength laser. Laser emission around 1557.3 nm with a low pumping threshold is obtained when a bent fiber filter with 4.5 mm bending radius is used. The 3 dB bandwidth of the laser is less than 0.3 nm, which is beneficial to high precision sensing. The medium refractive index varied from 1.3259 to 1.3730, and the relationship between the lasing wavelength and the medium refractive index exhibited linear behavior, where good linearity of about 60 nm/RIU was obtained. Finally, we fabricated sensor prototypes with different bending radii. When a 4 mm bending radius was selected, the maximum sensitivity is 124 nm/RIU. The fabrication of the proposed refractive index sensor is simple and cost-effective, which makes it a good candidate for the potential sensing applications.

Microcapillary-Based High-Sensitivity and Wavelength-Tunable Optical Temperature Sensor

A high-sensitivity and wavelength-tunable temperature sensor based on a short piece of fused-silica microcapillary (FSC) spliced between two single mode fibers (FSCs) and immerged in ethonal solution is proposed and experimentally investigated. Using the thermo-optic effect of ethanol and high sensitivity to refractive index of the FSC modal interference, the temperature sensitivity of the sensor immerged in ethanol solutions is significantly increased over an FSC sensor in air. Besides, the sensitivity and the feature wavelength of the interferometer can be tuned by adjusting the concentration and refractive index of the filling ethonal solution, which is important for achieving the maximum measurement range.

Fiber Ring Laser-Based Displacement Sensor

We reported an erbium-doped fiber ring laser (FRL) displacement sensor based on a single-mode fiber (SMF) loop tied into the laser cavity. The proposed fiber loop structure acts as the sensing head as well as the filter of the FRL. A good linear relationship is obtained both in principle and in experiments between the displacement of one end of the loop and the central wavelength of the proposed FRL. The average sensitivity of this sensor reaches 227.5 pm/mm in the displacement range of 0–30 mm. High optical signal-to-noise ratio (

A Novel Low-Power-Consumption All-Fiber-Optic Anemometer with Simple System Design

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Determination of neutral temperature using fiber Bragg grating sensor in capacitively coupled argon plasmas

dB) and narrow 3-dB bandwidth (<0.7 nm) are also achieved due to the FRL structure. Moreover, the macrofiber loop, as the key sensor head of the proposed sensing system, is tied with simple SMF without removing the coating, which has obvious advantages of firm structure with a wide range of displacement measurement and easy fabrication with low-cost SMF.

Self-Reference Surface Plasmon Resonance Biosensor Based on Multiple-Beam Interference

A compact and low-power consuming fiber-optic anemometer based on single-walled carbon nanotubes (SWCNTs) coated tilted fiber Bragg grating (TFBG) is presented. TFBG as a near infrared in-fiber sensing element is able to excite a number of cladding modes and radiation modes in the fiber and effectively couple light in the core to interact with the fiber surrounding mediums. It is an ideal in-fiber device used in a fiber hot-wire anemometer (HWA) as both coupling and sensing elements to simplify the sensing head structure. The fabricated TFBG was immobilized with an SWCNT film on the fiber surface. SWCNTs, a kind of innovative nanomaterial, were utilized as light-heat conversion medium instead of traditional metallic materials, due to its excellent infrared light absorption ability and competitive thermal conductivity. When the SWCNT film strongly absorbs the light in the fiber, the sensor head can be heated and form a “hot wire”. As the sensor is put into wind field, the wind will take away the heat on the sensor resulting in a temperature variation that is then accurately measured by the TFBG. Benefited from the high coupling and absorption efficiency, the heating and sensing light source was shared with only one broadband light source (BBS) without any extra pumping laser complicating the system. This not only significantly reduces power consumption, but also simplifies the whole sensing system with lower cost. In experiments, the key parameters of the sensor, such as the film thickness and the inherent angle of the TFBG, were fully investigated. It was demonstrated that, under a very low BBS input power of 9.87 mW, a 0.100 nm wavelength response can still be detected as the wind speed changed from 0 to 2 m/s. In addition, the sensitivity was found to be −0.0346 nm/(m/s) under the wind speed of 1 m/s. The proposed simple and low-power-consumption wind speed sensing system exhibits promising potential for future long-term remote monitoring and on-chip sensing in practical applications.

Simple method for self-referenced and lable-free biosensing by using a capillary sensing element

Neutral temperature Tg in capacitively coupled argon plasmas was measured by using a fiber Bragg grating sensor. The measurement of Tg is based on the thermal equilibrium process between the sensor and neutral gases, which is found to become fast upon increasing pressure, due to enhanced heat conduction. Additionally, Tg was found to increase with increasing high frequency power due to enhancive collisions with charged particles. It is also observed that Tg exhibits a significant gradient in space, ranging from 10 to 120 °C higher than room temperature for the conditions investigated. In addition, the spatial profiles of Tg at different pressures generally resemble those of the Ar+ density ni, measured with a floating double probe. The neutral gas is mainly heated via elastic collisions with ions in the sheath region followed by heat conduction among neutrals.

Fiber-optic anemometer based on single-walled carbon nanotube coated tilted fiber Bragg grating

We demonstrated a novel self-reference surface plasmon resonance (SPR) fiber biosensor, which provided a multiple-beam interference referencing signal for refractive index (RI) compensating. The sensor was fabricated by splicing a capillary to a multimode fiber (MMF) coated with a gold film. The gilded MMF acts as the measuring channel while the capillary is used as referencing channel. The experiment result showed that the measuring signal has an irreversible change corresponding specific binding and referencing signal has reversible change. It indicated that the measuring signal can inspect biomolecular interactions in real time and the referencing signal can be used to compensate for interference effects due to bulk RI changes. The sensor provides a high sensitivity of 1470.291 nm/RIU and a resolution about 3.536 × 10-5 RIU. In addition, this self-reference SPR biosensor we proposed is low cost, simple, and reproduction, which can be applied in biochemical sensing field.

Fiber Bragg grating-based temperature sensor for neutral gas in capacitively coupled plasmas

We demonstrated a simple method for self-reference and label free biosensing based on a capillary sensing element and common optoelectronic devices. The capillary sensing element is illuminated by a light-emitting diode (LED) light source and detected by a webcam. Part of gold film that deposited on the tubing wall is functionalized to carry on the biological information in the excited SPR modes. The end face of the capillary was monitored and separate regions of interest (ROIs) were selected as the measurement channel and the reference channel. In the ROIs, the biological information can be accurately extracted from the image by simple image processing. Moreover, temperature fluctuation, bulk RI fluctuation, light source fluctuation and other factors can be effectively compensated during detection. Our biosensing device has a sensitivity of 1145%/RIU and a resolution better than 5.287 × 10-4 RIU, considering a 0.79% noise level. We apply it for concanavalin A (Con A) biological measurement, which has an approximately linear response to the specific analyte concentration. This simple method provides a new approach for multichannel SPR sensing and reference-compensated calibration of SPR signal for label-free detection.