The recent progresses of fiber sensor fabrication in our group are reviewed.Novel inline fiber Mach-Zehnder interferometer(MZI) sensors with various structures are proposed and manufactured by femtosecond laser fabrication and fusion splicing for high-quality sensing of refractivity-sensitive parameters such as temperature,concentration,humidity,pressure,stress and strain: a) for an MZI sensor with a trench on a single-mode fiber,the refractive index(RI) sensitivity of acetone vapor is about 104 nm/RIU(refractive index unit) and the temperature sensitivity is 51.5 pm/℃ from 200 to 875 ℃;b) For an MZI consisting of two micro-air-cavities,the sensitivity is 501.5 nm/RIU and the detection limit is 1.994×10-6 RIU at the refractive index of 1.4;c) to reduce the fabrication cost,a new fusion-splicing based method is proposed to fabricate MZI sensors;the sensitivity is 664.57 nm/RIU with a detection limit of 1.5×10-6 RIU and its cost is tens of times cheaper than those of commercialized long period fiber Gratings;Also,5×10-5 acetone vapors are successfully detected by the MZI sensors coated with zeolite thin films.
Wang SumeiJiang LanLi BenyeZhao LongjiangYang JinpengWang MengmengXiao HaiLu YongfengHai-Lung Tsai
The sensitivities of betavoltaic batteries and photovoltaic batteries to series and parallel resistance are studied.Based on the study,an electrode pattern design principle of GaAs betavoltaic batteries is proposed.GaAs PIN junctions with and without the proposed electrode pattern are fabricated and measured under the illumination of ^（63）Ni.Results show that the proposed electrode can reduce the backscattering and shadowing for the beta particles from ^（63）Ni to increase the GaAs betavoltaic battery short circuit currents effectively but has little impact on the fill factors and ideal factors.
A fiber inline interferometric refractive index （RI） sensor consisting of a microchannel and a fiber taper is proposed in this letter. The microchannel is fabricated by combining femtosecond laser micromachining and arc fusion splicing. No subsequent chemical etching process is needed. Three sensors with microchannel widths of 4, 8, and 10 μm are prepared. The sensitivity in the RI range from 1.33 to 1.35 is up to -361.29 nm/RIU at the microchannel width of 8 μm. The sensitivity is -20 times greater than that of the paired taper-based MZI sensors and long period fiber grating pair MZI sensors.
Isotope source energy deposition along the thickness direction of a semiconductor is calculated,based upon which an ideal short current is evaluated for betavoltaic batteries.Electron-hole pair recombination and drifting length in a PN junction built-in electric field are extracted by comparing the measured short currents with the ideal short currents.A built-in electric field thickness design principle is proposed for betavoltaic batteries：after measuring the energy deposition depth and the carrier drift length,the shorter one should then be chosen as the built-in electric field thickness.If the energy deposition depth is much larger than the carrier drift length,a multi-junction is preferred in betavoltaic batteries and the number of the junctions should be the value of the deposition depth divided by the drift length.
In this study we experimentally reveal that the phase change mechanism can be selectively triggered by shaping femtosecond pulse trains based on electron dynamics control （EDC）, including manipulation of excitations, ionizations, densities, and temperatures of electrons. By designing the pulse energy distribution to adjust the absorptions, excitations, ionizations, and recombinations of electrons, the dominant phase change mechanism experiences transition from nonthermal to thermal process. This phenomenon is observed in quadruple, triple, and double pulses per train ablation of fused silica separately. This opens up possibilities for controlling phase change mechanisms by EDC, which is of great significance in laser processing of dielectrics and fabrication of integrated nano- and micro-optical devices.
A high temperature sensor based on an ultra-abrupt tapered fiber Michelson interferometer fabricated by the fusion-splicing method is proposed. The sensor consists of a single abrupt taper and the cleaved surface is used as the reflection mirror. The thermal characteristic is investigated at 25 to 1000 ℃. The sensitivity of the sensor is observed to vary with the temperature, that is, 25 and 78 pm/℃ at 25 300 and 300 1 000 ℃, respectively. The Michelson interferometer sensors have the advantages of simple structure, cost effectiveness, compactness, and simple fabrication process.
An approach to the simultaneous optical ring resonators is proposed measurement of refractive-index （RI） and theoretically demonstrated. With and temperature changes using a liquid-core silica ring resonator as an example, two different-order whispering gallery modes （WGMs） might differ in not only RI but also temperature sensitivities. Thus, a second-order sensing matrix should be defined based on these WGMs to determine RI and temperature changes simultaneously. The analysis shows that the RI and temperature detection limits can be achieved on the order of 10.7 RI unit and 10-3 K at a wavelength of approximately 780 nm.
The manipulation of the subpulse number, pulse delay, and pulse energy distribution of an ultrafast laser enables electron dynamics control by changing absorptions, excitations, ionizations, and recombinations of electrons, which can result in smaller, cleaner, and more controllable structures. This letter experimentally reveals that ablation sizes and recasts can be controlled by shaping femtosecond pulse trains to adjust transient localized electron dynamics, material properties, and corresponding phase change mechanisms.
This study proposes a new hybrid Mach-Zehnder interferometric （MZI） sensor based on two core-offset attenuators and an abrupt taper in a single-mode fiber fabricated by a fiber-taper machine and electric arc discharge. When the distance between the two core-offset attenuators is stretched to 4500 Bm, significant interference signals are detected with a prominent attenuation peak of -28 dB. The proposed MZI can be used to measure temperature due to its low refractive index （RI） and strain cross-sensitivity. The temperature sensitivity is 34.95-0.04 and 106.70-0.04 pm/℃ in the temperature ranges of 14-250 and 250-1000 ℃, respectively.
