Yuanlong Deng

High-Sensitivity Mach–Zehnder Interferometric Temperature Fiber Sensor Based on a Waist-Enlarged Fusion Bitaper

An all-fiber high-sensitivity temperature fiber sensor based on a Mach-Zehnder interferometer in standard single-mode fibers (SMFs) is described. The interferometer consists of two concatenated waist-enlarged fusion bitapers which are fabricated simply by cleaving and fusion splicing. It is demonstrated that such an all-fiber Mach-Zehnder interferometer incorporates intermodal interference between the LP01 mode and a high-order cladding mode of LP07 mode. Its response to temperature is investigated and a high sensitivity of 0.070 nm/°C is obtained by a 7.5 mm interferometer. This simple, low-cost and easy-to-fabricate core-cladding modal interferometer with entire SMF-based structure also has great potential in diverse sensing applications.

Some features of the photonic crystal fiber temperature sensor with liquid ethanol filling.

We introduce a novel photonic crystal fiber (PCF) temperature sensor that is based on intensity modulation and liquid ethanol filling of air holes with index-guiding PCF. The mode field, the effective refractive index and the confinement loss of PCF were all found to become highly temperature-dependent when the thermo-optic coefficient of the liquid ethanol used is higher than that of silicon dioxide and this temperature dependence is an increasing function of the d/Lambda ratio and the input wavelength. All the experiments and simulations are discussed in this paper and the temperature sensitivity of transmission power was experimentally determined to be 0.315 dB/ degrees C for a 10-cm long PCF.

Compact and Ultrasensitive Temperature Sensor With a Fully Liquid-Filled Photonic Crystal Fiber Mach–Zehnder Interferometer

We propose a compact and ultrasensitive all-fiber temperature sensor based on an in-line fully liquid-filled photonic crystal fiber (PCF) Mach-Zehnder interferometer (MZI). It consists of a small piece of index-guiding PCF fully infiltrated by fluid and two standard single-mode fibers offset spliced with PCF. Two core modes LP01 and LP11 are conveniently used as optical arms to form the in-line MZI-type interferometer. Experimental and theoretical investigations of its response to temperature confirm that high temperature sensitivity up to -1.83 nm/°C could be realized with such a compact interferometeric PCF temperature sensor.

Sensitivity-enhanced high-temperature sensing using all-solid photonic bandgap fiber modal interference

A wavelength-encoded interferometric high-temperature sensor based on an all-solid photonic bandgap fiber (AS-PBF) is reported. It consists of a small piece of AS-PBF spliced core offset with standard single-mode fibers. Two core modes LP(01) and LP(11) are conveniently utilized as optical arms to form Mach-Zehnder-type interference at both the first and the second photonic bandgaps, and the maximum extinction ratio exceeds 25 dB. Experimental and theoretical investigation of its response to temperature confirms that high temperatures up to 700 °C can be effectively sensed using such an AS-PBF interferometer, and benefiting from a large effective thermo-optic coefficient of fiber structure, the sensitivity can be significantly enhanced (71.5 pm/°C at 600 °C).

Mode-beating-enabled stopband narrowing in all-solid photonic bandgap fiber and sensing applications.

In this paper, core-cladding modal beating in a short piece of all-solid photonic bandgap fiber (AS-PBF) is observed in longitudinal propagation direction. It is demonstrated that at the stopband range of AS-PBF, the power could transfer back and forth between the fiber core and the first layer of high-index rods. Both experimental results and the theoretical analysis from transverse coupled mode theory confirm that the 3-dB width of the sharp stopband could be significantly narrowed by multicycles of such core-cladding modal couplings, which is of great benefit to the high-resolution sensing applications. Based on such a guiding regime, a high-temperature sensor head is also made and its response to temperature is tested to be of 59.9 pm/°C.

Polymer Microbubble-Based Fabry–Perot Fiber Interferometer and Sensing Applications

A polymer microbubble-based Fabry-Perot fiber interferometer (FPI) for pressure and temperature measurement is proposed and demonstrated. By splicing a small segment of photonic bandgap fiber to a single-mode fiber and immersing such a fiber tip into an optical adhesive, a micro air bubble could be buried into the formed polymer diaphragm. Size of air bubble and polymer diaphragm thickness can be controlled by adjusting arc discharge intensity at the fiber splice point. In order to achieve the wide dynamic range and high-resolution measurement, a demodulation algorithm based on absolute phase analysis is adopted and present high sensitivity for simultaneous pressure and temperature sensing. This simple and reproducible fabrication method of such a sensor gives an alternative way to construct FPI-based biomedical and microfluidic sensors.

UV-Curable Polymer Microhemisphere-Based Fiber-Optic Fabry-Perot Interferometer for Simultaneous Measurement of Refractive Index and Temperature

A fiber-optic Fabry-Perot interferometer based on UV-curable polymer microhemisphere is proposed and demonstrated. The polymer microhemisphere is formed by adhering and solidifying a liquid microdroplet of UV-curable adhesive to the end face of a cleaved single-mode fiber. The height of polymer microhemisphere could be flexibly controlled by adjusting the diameter of a single-mode fiber. The theoretical and experimental results demonstrate that the refractive index (RI) and the temperature of external environment can be simultaneously measured by the fringe contrast variation and the wavelength shift of reflection spectra separately, alleviating the cross sensitivity effectively. The obtained temperature and RI sensitivities are about 0.19 nm/°C and 260 dB/RIU in the RI range of 1.38-1.42.

Core Mode-Cladding Supermode Modal Interferometer and High-Temperature Sensing Application Based on All-Solid Photonic Bandgap Fiber

A core-mode-cladding-supermode modal interferometer with all-solid photonic bandgap fiber (AS-PBF) is constructed, and a reflective Michelson-type high-temperature sensor is fabricated. Such a fiber sensor is constituted by a small segment of AS-PBF and a leading single-mode fiber. The splice region of the two fibers is weakly tapered to excite the cladding supermode. Both the interference spectra and the near-field infrared CCD images verify that the LP01 cladding supermode is effectively excited and interferes with the LP01 core mode, which agrees well with theoretical results. Benefiting from a large effective thermooptic coefficient between the two modes, temperature sensitivity up to 0.111 nm/°C at 500 °C is obtained in experiment. The proposed sensor is compact and easy to fabricate, which makes it very attractive for high-temperature sensing applications.

In-line flat-top comb filter based on a cascaded all-solid photonic bandgap fiber intermodal interferometer.

In this paper, an in-line comb filter with flat-top spectral response is proposed and constructed based on a cascaded all-solid photonic bandgap fiber modal interferometer. It consists of two short pieces of all-solid photonic bandgap fiber and two standard single-mode fibers as lead fibers with core-offset splices between them. The theoretical and experimental results demonstrated that by employing a cut and resplice process on the central position of all-solid photonic bandgap fiber, the interference spectra are well tailored and flat-top spectral profiles could be realized by the controllable offset amount of the resplice. The channel position also could be tuned by applying longitudinal torsion with up to 4 nm tuning range. Such a flat-top fiber comb filter is easy-to-fabricate and with a designable passband width and flat-top profile.

Safety monitoring of rail transit by fiber grating sensors

The subway is a representative form of the rail transit, and its catenary suspension system is a very important aspect to the safety of the whole system. The safety monitoring of the subway catenary suspension system is studied in this paper. A demonstrate model is set up in the laboratory, and some fiber Bragg grating (FBG) sensors including strain sensors and displacement sensors were utilized in the demonstrate system. It is shown that the used sensors could indicate the safety information of the system effectively. Especially, the designed displacement sensor that is packaged by athermal technique can abandon the influence of the environment temperature in a certain degree. Its engineering applicability is greatly improved.