A novel single tapered fiber optical tweezers is proposed and fabricated by heating and drawing technology. The microscopic particle tapping performance of this special designed tapered fiber probe ...is demonstrated and investigated. The distribution of the optical field emerging from the tapered fiber tip is numerically calculated based on the beam propagation method. The trapping force FDTD analysis results, both axial and transverse, are also given.
A two-axis bending sensor based on cascaded eccentric core fiber Bragg gratings (ECFBGs) is presented and demonstrated. The sensor is fabricated by independently writing two FBGs in two ECFs, which ...are spliced with orthogonal core-offset directions. Each ECFBG is most sensitive at the core-offset direction and insensitive at the perpendicular direction. When one ECFBG is in the state of most insensitive to bend, the other ECFBG must be in the most sensitive state. Therefore, the cascaded ECFBG structure can easily realize 2-D bending measurement. The sensor's spectral responses to the curvature at different bending directions are experimentally investigated. The maximum curvature sensitivities of the two ECFBGs are 37 and 39 pm/m -1 , respectively, within the curvature range from 0 to 8.18 m -1 .
We experimentally demonstrate a temperature compensated highly sensitive refractometer based on integrated parallel Fabry-Pérot interferometers (FPIs). The sensor is constructed by splicing a ...fraction of hollow-core fiber between a seven-core fiber and a single-mode fiber, which simultaneously forms an open cavity and a sealed cavity. The two FPIs are mutually independent. The opening cavity provides entire interaction between filled liquid/gas and guided light with a high sensitivity of 1096.9 nm/RIU, but that of the closed one is on the contrary, i.e., insensitive to the external refractive index (RI) because of the sealed resonant cavity. The temperature sensitivities of the parallel FPIs in deionized water are -137.6 and 2.25 pm/°C, respectively. Therefore, such a refractometer could eliminate the temperature cross sensitivity, with ultra-compact size, low cost, and prompt access to liquid samples for direct RI measurement.
A Mach-Zehnder interferometer based on double off-axis twisted deformation on single mode fiber (SMF) is proposed and experimentally demonstrated for gas pressure measurements. The off-axis twisted ...deformation is achieved by twisting a SMF under continuous arc discharging. An open air-gap was created on the cladding of the SMF between the two off-axis deformation points by using a femtosecond laser. The cladding modes transmit through the air-gap whose refractive index is directly determined by the air pressure. The interferometer is applied for high-sensitive pressure sensing with a sensitivity of -5.183 nm/MPa and temperature cross-sensitivity of 13.3 kPa/°C. Consequently, the open air-gap added MZI structure can therefore be considered an excellent candidate as a gas pressure sensor in harsh environments due to its low cost, compact size, ease of fabrication, and all-fiber configuration.
This paper presents a graphene-Au coated photonic crystal fiber (PCF) sensor in the visible regime. Designing a side-polish D-shaped plane over the PCF's defect of the periodic air holes can ...effectively enhance the evanescent field. Graphene on gold can enhance the sensor's sensitivity because it can stably adsorb biomolecules and increase the propagation constant of the surface plasmon polariton (SPP). Using the finite element method (FEM), we demonstrated that the sensing performance is greatly improved by optimizing the PCF's geometric structural parameter. The proposed PCF sensor exhibited high performance with a maximum wavelength sensitivity of 4200 nm/RIU, maximum amplitude sensitivity of 450 RIU
, and refractive index resolution of 2.3 × 10
RIU in the sensing range 1.32-1.41. This research provides a potential application for the design a new generation of highly sensitive biosensors.
In this article, we propose and demonstrate a probe-type multi-core fiber (MCF) sensor for the multi-parameter measurement of seawater. The sensor comprises an MCF and two capillary optical fibers ...(COFs) with distinct inner diameters, in which a 45° symmetric core reflection (SCR) structure and a step-like inner diameter capillary (SIDC) structure filled with polydimethylsiloxane (PDMS) are fabricated at the fiber end. The sensor is equipped with three channels for different measurements. The surface plasmon resonance (SPR) channel (CH
) based on the side-polished MCF is utilized for salinity measurement. The fiber end air cavity, forming the Fabry-Pérot interference (FPI) channel (CH
), is utilized for pressure and temperature measurement. Additionally, the fiber Bragg grating (FBG) channel (CH
), which is inscribed in the central core, serves as temperature compensation for the measurement results. By combining three sensing principles with space division multiplexing (SDM) technology, the sensor overcomes the common challenges faced by multi-parameter sensors, such as channel crosstalk and signal demodulation difficulties. The experimental results indicate that the sensor has sensitivities of 0.36 nm/‱, -10.62 nm/MPa, and -0.19 nm/°C for salinity, pressure, and temperature, respectively. As a highly integrated and easily demodulated probe-type optical fiber sensor, it can serve as a valuable reference for the development of multi-parameter fiber optic sensors.
A relative humidity (RH) sensor based on an integrated Mach-Zehnder interferometer (MZI) consisting of two off-axis twisted deformation points and an air channel passing through the core of a ...single-mode fiber (SMF) is proposed and experimentally demonstrated. The off-axis deformations are achieved by twisting the SMF under continuous arc discharge. The air channel is created between the two off-axis deformation points by femtosecond laser machining. Because the air channel is exposed to the environment, its refractive index is directly determined by the RH, which affects the optical path difference of the MZI and, in turn, leads to the shifts in the resonance wavelength. A prototype MZI demonstrates an RH sensitivity of approximately -0.144 nm/%RH without the use of any hygroscopic materials. More prominently, an ultrafast response time of about 68 ms is achieved. The proposed MZI structure is therefore demonstrated to be an excellent RH sensor candidate due to its compact size, outstanding performance, ease of fabrication, and all-fiber configuration.
A high sensitive bending sensor based on eccentric core fiber (ECF) Mach-Zehnder modal interferometer (MZI) with direction recognition ability is proposed and demonstrated. The MZI-based bending ...sensor is fabricated by fusion splicing a piece of ECF in between two standard single mode fibers with a small lateral core-offset. Due to the eccentric location of the core of the ECF, a bend applied on the ECF-based MZI can cause an elongation or shortening of the eccentric core, which makes the ECF-based MZI suitable for directional bending measurement. The bending characteristics are investigated experimentally within the curvature range of 0-1.11 m -1 . The bending sensitivities of the sensor are 13.49 nm/m -1 at the bending direction of 0° and -18.4 nm/m -1 at the direction of 180° corresponding to the interference dip at the wavelength of 1553.22 nm.
A novel fiber-optic flow velocity sensor based on a twin-core fiber Michelson interferometer has been proposed and demonstrated. The sensor only is a segment of twin-core fiber acting as cylinder ...cantilever beam. The force exerted on the cylinder by the slow flow speeds of order mm/s of the fluid with unknown velocity bends the fiber, which corresponds to the shift of the phase of the twin-core in-fiber integrated Michelson interferometer.
We proposed a novel temperature-compensated multi-point strain sensing system based on cascaded FBG and optical FMCW interferometry. The former is used for simultaneous sensing of temperature and ...strain, and the latter is used for position information reading and multiplexing. In the experiment, a narrow linewidth laser with continuous frequency-sweeping was used as the light source. After demodulating the beat-frequency signal, the link information of the 16 m fiber was obtained, and the measured result was identical to the actual position. The measurement accuracy reached 50.15 mm, and the dynamic range was up to 22.68 dB. Meanwhile, we completed the sensing experiments for temperature range from 20 °C to 90 °C and strain range from 0 με to 7000 με. The sensitivity of the sensing system to temperature was 10.21 pm/°C, the sensitivity and accuracy to strain were as high as 1.163 pm/με and 10 με, respectively. Finally, the measured strain and temperature values were obtained using the sensing matrix. The sensing system has important practical significance in the field of quasi-distributed strain measurement.
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