Femtosecond laser fabrication of nanograting-based distributed fiber sensors for extreme environmental applications

The femtosecond laser has emerged as a powerful tool for micro-and nanoscale device fabrication. Through nonlinear ionization processes, nanometer-sized material modifications can be inscribed in transparent materials for device fabrication. This paper describes femtosecond precision inscription of nanograting in silica fiber cores to form both distributed and point fiber sensors for sensing applications in extreme environmental conditions. Through the use of scanning electron microscope imaging and laser processing optimization,high-temperature stable, Type II femtosecond laser modifications were continuously inscribed,point by point, with only an insertion loss at 1 d B m~(-1) or 0.001 d B per point sensor device.High-temperature performance of fiber sensors was tested at 1000℃, which showed a temperature fluctuation of ±5.5℃ over 5 days. The low laser-induced insertion loss in optical fibers enabled the fabrication of a 1.4 m, radiation-resilient distributed fiber sensor. The in-pile testing of the distributed fiber sensor further showed that fiber sensors can execute stable and distributed temperature measurements in extreme radiation environments. Overall, this paper demonstrates that femtosecond-laser-fabricated fiber sensors are suitable measurement devices for applications in extreme environments.

Pressure Sensor Based on the Fiber-Optic Extrinsic Fabry-Perot Interferometer

Pressure sensors based on fiber-optic extrinsic Fabry-Perot interferometer(EFPI)have been extensively applied in various industrial and biomedical fields.In this paper,some key improvements of EFPI-based pressure sensors such as the controlled thermal bonding technique,diaphragm-based EFPI sensors,and white light interference technology have been reviewed.Recent progress on signal demodulation method and applications of EFPI-based pressure sensors has been introduced.Signal demodulation algorithms based on the cross correlation and mean square error(MSE)estimation have been proposed for retrieving the cavity length of EFPI.Absolute measurement with a resolution of 0.08 nm over large dynamic range has been carried out.For downhole monitoring,an EFPI and a fiber Bragg grating(FBG)cascade multiplexing fiber-optic sensor system has been developed,which can operate in temperature 300℃with a good long-term stability and extremely low temperature cross-sensitivity.Diaphragm-based EFPI pressure sensors have been successfully used for low pressure and acoustic wave detection.Experimental results show that a sensitivity of 31 mV/Pa in the frequency range of 100 Hz to 12.7 kHz for aeroacoustic wave detection has been obtained.

Design and experiment of a six-row air-blowing centralized precision seed-metering device for Panax notoginseng

Panax notoginseng is grown mainly in Yunnan Province.Under the present high-density planting patterns for the plant,to solve the problems of a high rate of seed damage and the inability to use a traditional single air-blowing metering device,this paper designs a six-row air-blowing centralized precision seed-metering device for P.notoginseng to realize mechanized precision seeding of this species.This paper describes the working principle of the seed-metering device,and the main structural parameters are determined by combining theoretical calculations with simulation analysis.A mechanics model of the seed filling,cleaning and pressing processes of the seed-metering device was constructed.The seeds of P.notoginseng in Yunnan Province were selected as experimental subjects.An experimental study on the seed-metering performance of the seed-metering device was carried out using the quadratic rotation orthogonal combination test method.The outlet pressure of the air nozzle,forward velocity and cone angle of the hole were selected as test factors.Mathematical models of the grain spacing qualified index,miss index,multiple index and the coefficient of variation of the row displacement consistency were established to analyze the order of factors affecting indicators.Through parameter optimization,the optimum combination of parameters was determined as follows:the cone angle of the hole is 50°,the forward velocity is less than 0.73 m/s,and the outlet pressure of the air nozzle is 0.32-0.52 kPa.The qualified index of grain spacing is higher than 94%,the miss index is less than 3%,the multiple index is less than 5%,and the coefficient of variation of the row displacement consistency is less than 5%.The test results are essentially consistent with the optimization results.The metering device meets the requirements of precision seeding of P.notoginseng.This study provides a basis for the design of a six-row air-blowing centralized precision seed-metering device for P.notoginseng.

Trace Ammonia Detection Based on Near-Infrared Fiber-Optic Cantilever-Enhanced Photoacoustic Spectroscopy

A trace ammonia(NH3)detection system based on the near-infrared fiber-optic cantilever-enhanced photoacoustic spectroscopy(CEPAS)is proposed.A fiber-optic extrinsic Fabry-Perot interferometer(EFPI)based cantilever microphone has been designed to detect the photoacoustic pressure signal.The microphone has many advantages,such as small size and high sensitivity.A near-infrared tunable erbium-doped fiber laser(EDFL)amplified by an erbium-doped fiber amplifier(EDFA)is used as a photoacoustic excitation light source.To improve the sensitivity,the photoacoustic signal is enhanced by a photoacoustic cell with a resonant frequency of 1624 Hz.When the wavelength modulation spectroscopy(WMS)technique is applied,the weak photoacoustic signal is detected by the second-harmonic detection technique.Trace NH3 measurement experiments demonstrate that the designed fiber-optic CEPAS system has a linear response to concentrations in the range of 0 ppm‒20 ppm at the wavelength of 1522.448 nm.Moreover,the detection limit is estimated to be 3.2 ppb for a lock-in integration time of 30 s.