Cailing Fu

Thin-Core-Fiber-Based Long-Period Fiber Grating for High-Sensitivity Refractive Index Measurement

We experimentally demonstrated the fabrication of asymmetric long-period fiber gratings (LPFGs) in thin core fiber by use of focused CO2 laser beam. The proposed device exhibits a high extinction ratio of over 25 dB at the resonant wavelength and a narrowed 3-dB bandwidth of only 8.7 nm, which is nearly one order of magnitude smaller than that of LPFGs in conventional single-mode fibers. It also exhibits a high polarization-dependent loss of over 20 dB at resonant wavelength. The temperature and external refractive index (RI) sensitivity of the proposed structure are measured to be 46 pm/°C, within a temperature range from 25 °C to 100 °C, and 1047.3 nm/RIU, within the RI range from 1.400 to 1.440, respectively. The temperature induced error is ~8% for RI measurement. Such long LPFGs may find potential applications of highly sensitive RI sensors in the fields of chemical and biomedical sensing.

Nano silica diaphragm in-fiber cavity for gas pressure measurement

We demonstrate an ultrahigh-sensitivity gas pressure sensor based on the Fabry-Perot interferometer employing a fiber-tip diaphragm-sealed cavity. The cavity is comprised of a silica capillary and ultrathin silica diaphragm with a thickness of 170 nm, with represents the thinnest silica diaphragm fabricated thus far by an electrical arc discharge technique. The resulting Fabry-Perot interferometer-based gas pressure sensor demonstrates a gas pressure sensitivity of about 12.22 nm/kPa, which is more than two orders of magnitude greater than that of a similarly configured fiber-tip air bubble sensor. Moreover, our gas pressure sensor has a low temperature cross-sensitivity of about 106 Pa/°C, and the sensor functions well up to a temperature of about 1000 °C. As such, the sensor can potentially be employed in high-temperature environments.

Sensing Characteristics of Tilted Long Period Fiber Gratings Inscribed by Infrared Femtosecond Laser

We propose a novel tilted long period fiber grating (TLPFG) design, inscribed using a line-by-line inscription technique and an infrared femtosecond (Fs) laser. The responses of this TLPFG to external refractive index, temperature, torsion, and strain were systematically investigated to determine its sensing characteristics. The external refractive index (RI) was measured to be −602.86 nm/RIU at an RI of ~1.432. The TLPFG was used to accurately measure temperatures up to 450 °C with a sensitivity of 103.8 pm/°C. The torsion and strain sensitivity of the device were 48.94 nm/(rad/mm) and −0.63 pm/µε, respectively. These results demonstrate that the proposed TLPFG could be used as sensors in a series of application fields including high temperatures and external environments.

Temperature Insensitivity Polarization-Controlled Orbital Angular Momentum Mode Converter Based on an LPFG Induced in Four-Mode Fiber

We propose a novel method for generating ±1-order orbital angular momentum (OAM) in long-period fiber gratings (LPFGs) by adjusting a polarization controller (PC). An LPFG, inscribed in a four-mode fiber (4MF) using a CO2 laser, was used to generate OAM±1 across a broad range of wavelengths from 1530 nm to 1630 nm. Additionally, the OAM vortex phase remained stable while the temperature increased from 23 °C to 50 °C. The LPFG, as a temperature sensor, and its temperature sensitivity was measured to be 38.6 ± 0.37 pm/°C at the resonant wavelength of 1625 nm. This design offers simple fabrication and several properties which are highly beneficial for all-fiber optical communications based on the OAM mode-division multiplexing technique.

Miniature Fabry-Perot interferometer strain sensor based on an elliptical air bubble

We demonstrated a high-robustness Fabry-Perot interferometer strain sensor based on an in-fiber elliptical bubble that was created by splicing together two sections of standard single mode fibers. Such a FPI could be used to develop a high-robustness strain sensor with a low cross-sensitivity between temperature and tensile stain. The sensitivity of this strain sensor was ∼2.4 pm/με, and exhibited low thermal sensitivity (less than 1.0 pm/°C) reducing the cross sensitivity between tensile strain and temperature. Moreover, such a strain sensor has a broad operation wavelength range ∼36 nm, fringe contrast ∼38dB, and super-high mechanical robustness. The robustness of the strain sensor based on the air mini-cavity is demonstrated up to 9800 με until the single mode fiber was fractured.

Refractive index sensing with long period grating in thin-core-fiber

Asymmetric long period grating in thin core fiber is proposed to measure refractive index of liquid with an averaged sensitivity of 1047.3 nm/RIU within the range from 1.400 to 1.440.

High-robustness strain sensor based on in-fiber Fabry-Perot interferometer with an elliptical cavity

An in-fiber Fabry-Perot interferometer based on an elliptical air-cavity was developed to a strain sensor with a high-robustness (up to 9800 μϵ ), and the detailed fracture analysis of the high-robustness strain sensor was made.