Compact hollow waveguide mid-infrared gas sensor for simultaneous measurements of ambient CO2 and water vapor

A compact, sensitive and stable hollow waveguide (HWG) mid-infrared gas sensor, based on gas absorption lines using wavelength modulation spectroscopy with a second harmonic (WMS-2f) detection scheme, was developed for simultaneous measurements of ambient CO 2 and water vapor. Optimization of the laser modulation parameters and pressure parameter in the HWG are performed to improve the strength of the WMS-2f signal and hence the detection limit, where 14.5-time for CO 2 and 8.5-time for water vapor improvement in system detection limit is achieved compared to those working at 1 atm. The stability of the sensor has been improved significantly by optimizing environmental disturbances, incoupling alignment of the HWG and laser scanning frequency. An Allan variance analysis shows detection limit of the developed sensor of ~3 ppmv for CO 2 and 0.018% for water vapor, which correspond to an absorbance of 2.4 × 10 -5 and 2.7 × 10 -5 , with a stability time of 160 s, respectively. Ambient CO 2 and water vapor measurement have been performed in two days in winter and spring separately. The measurement precision is further improved by applying a Kalman adaptive filter. The HWG gas sensor demonstrates the ability in environmental monitoring and the potential to be used in other areas, such as industrial production and biomedical diagnosis

Investigation of a Side-polished Fiber MZI and Its Sensing Performance

A novel all-fiber Mach–Zehnder interferometer (MZI), which consists of lateral core fusion splicing of a short section of side-polished single mode fiber (SMF) between two SMFs was proposed and demonstrated. A simple fiber side-polished platform was built to control the side polished depth through a microscope. The sensitivity of the fiber MZI structure to the surrounding refractive index (RI) can be greatly improved with the increase of the side-polished depth, but has no effect on the temperature sensitivity. The sensor with a polished depth of 44.2 μm measured RI sensitivity up to -118.0 nm/RIU (RI unit) in the RI range from 1.333 to 1.387, which agrees well with simulation results by using the beam propagation method (BPM). In addition, the fiber MZI structure also can achieve simultaneous measurement of both RI and temperature. These results show its potential for use in-line fiber type sensing application

Novel Microfiber Sensor and Its Biosensing Application for Detection of hCG Based on a Singlemode-Tapered Hollow Core-Singlemode Fiber Structure

A novel microfiber sensor is proposed and demonstrated based on a singlemode-tapered hollow core -singlemode (STHS) fiber structure. Experimentally a STHS with taper waist diameter of 26.5 μm has been fabricated and RI sensitivity of 816, 1601.86, and 4775.5 nm/RIU has been achieved with RI ranges from 1.3335 to 1.3395 , from 1.369 to 1.378, and from 1.409 to 1.4175 respectively, which agrees very well with simulated RI sensitivity of 885, 1517, and 4540 nm/RIU at RI ranges from 1.3335 to 1.337, from 1.37 to 1.374, and from 1.41 to 1.414 . The taper waist diameter has impact on both temperature and strain sensitivity of the sensor structure: (1) the smaller the waist diameter, the higher the temperature sensitivity, and experimentally 26.82 pm/°C has been achieved with a taper waist diameter of 21.4 μm; (2) as waist diameter decrease, strain sensitivity increase and 7.62 pm/με has been achieved with a taper diameter of 20.3 μm. The developed sensor was then functionalized for human chorionic gonadotropin (hCG) detection as an example for biosensing application. Experimentally for hCG concentration of 5 mIU/ml, the sensor has 0.5 nm wavelength shift, equivalent to limit of detection (LOD) of 0.6 mIU/ml by defining 3 times of the wavelength variation (0.06 nm) as measurement limit. The biosensor demonstrated relatively good reproducibility and specificity, which has potential for real medical diagnostics and other applications

Rapid Detection of SARS-CoV-2 Nucleocapsid Protein by a Label-Free Biosensor Based on Optical Fiber Cylindrical Micro-Resonator

The current global outbreak of coronavirus (COVID-19) continues to be a severe threat to human health. Rapid, low-cost, and accurate antigen detection methods are very important for disease diagnosis. The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) nucleocapsid protein (N-Protein) is often used as the diagnostic and screening for coronavirus detection. To this end, we propose and experimentally validate a highly sensitive whispering gallery mode (WGM) optical cylindrical micro-resonator (CMR) for bio immunoassay detection. To study the biokinetic process of immunoassay, the surface of the WGM micro-resonator is functionalized with N-Protein monoclonal antibody (N-Protein-m Ab), which led to the specific detection of N-Proteins. The spectral characteristics of the WGM resonance dip were investigated, and it is found that the transmission spectrum of WGM shows a monotonically increasing red-shift as a function of recording time. The WGM red-shift is due to the antibody-antigen reaction and can be used for the analysis of the immunoassay process. The wavelength shift is shown to be proportional to the concentration of N-Protein, which ranges between 0.1 and 100 μg /mL. Finally, different types of samples (concentration of 10 μg /mL of N-Protein) were prepared and tested to simulate the specificity of the sensor in the practical application environment. This method has the merits of a rapid assay, lower expense, easy preparation, and miniaturization, which makes the sensor have the potential for broad applications in the field of biochemistry and biomedical detection

Fiber Ring Laser Based on Side-Polished Fiber MZI for Enhancing Refractive Index and Torsion Measurement

A fiber ring laser based on a side-polish fiber Mach-Zehnder interferometer (MZI) for effective improving refractive index (RI) and torsion sensing is proposed and investigated. The side-polished fiber MZI sensor can not only enhance the evanescent wave but also break circular symmetry of optical fiber face section, so it can be used for the surrounding RI and torsion sensing. A spectrum 3 dB bandwidth of less than 0.15 nm has been achieved which makes the fiber ring laser torsion sensing system to have higher measurement resolution. Experiment results show that the RI and torsion sensitivity of proposed sensor is dependent on the polish depth: the thicker the polish depth, the higher the sensitivity. For a sensor with side polish depth of 47 μ m, the measured RI sensitivity reaches-81.36 nm/RIU, the torsion sensitivity is as high as-0.019nm/O, the sensitivity converted to torsional rate is-0.267 nm/(rad. m-1)

Wearable optical fiber sensor based on a bend singlemode-multimode-singlemode fiber structure for respiration monitoring

Respiration rate (RR) is an important information related to human physiological health. A wearable optical fiber sensor for respiration monitoring based on a bend singlemode-multimodesinglemode (SMS) fiber structure, which is highly sensitive to bend, is firstly proposed and experimentally demonstrated. The sensor fastened by an elastic belt on the abdomen of a person will acquire the respiration signal when the person breaths, which will introduce front and back movement of the abdomen, and thus bend of SMS fiber structure. Short-time Fourier transform (STFT) method is employed for signal processing to extract characteristic information of both the time and frequency domain of the measured waveform, which provides accurate RR measurement. Six different SMS fiber sensors have been tested by six individuals and the experimental results demonstrated that the RR signals can be effectively monitored among different individuals, where an average Pearson Correlation Coefficient of 0.88 of the respiration signal has been achieved, which agrees very well with that of commercial belt respiration sensor. The proposed technique can provide a new wearable and portable solution for monitoring of respiratory with advantage of easy fabrication and robust to environment

Long-Period Fiber Grating Based on Side-Polished Optical Fiber and Its Sensing Application

A novel side-polished long-period fiber grating (LPFG) sensor was proposed and experimentally validated. Side-polished can provide a stronger evanescent field than traditional grating and bring superior sensitivity. The greater the side-polished depth, the higher the refractive index (RI) sensitivity. When d = 44,μm , the RI sensitivity reached 466.85 nm/RIU in the range of 1.3330-1.3580, which is fourfold higher than the LPFG prepared by the electric-arc discharge (EAD) method. A graphene oxide (GO) nano-film is coated on the LPFG to make it realize high sensitivity relative humidity (RH) sensing. Humidity sensitivity reached -0.193 nm/%RH in the range of 40%-80% RH. In addition, side-polished breaks the symmetry of the distribution of the cross-sectional light field, which determines the ability to achieve vector curvature measurement. It shows good sensing performance in the same/opposite bending direction as the side polished surface. When the input light polarization is 90°, the average sensitivity reaches 5.03 and -5.9 nmm-1 in the range of 0-19.67 m-1 , respectively. This strongly indicates that the fabricated sensors show high sensitivity, low-cost materials, and robust performance and break the limitations of the EDA method to prepare gratings, which have good application potential for biomedicine and the field of construction

(3-Aminopropyl) Triethoxysilane-Based Immobilization of Pt/WO3 on a Microfiber Sensor for High Sensitivity Hydrogen Sensing

A novel high stability hydrogen sensor based on a Pt/WO3 coated single-mode tapered-no-core single-mode (STNCS) fiber interferometer is proposed and experimentally studied. The STNCS structure is treated by (3-Aminopropyl) triethoxysilane (APTES) and then coated with Pt/WO3 nanorods. Compared to the traditional method of using poly (dimethylsiloxane) (PDMS) to adhere Pt/WO3 nanorods on the fiber surface, the APTES modified fiber forms strong covalent bonds with Pt/WO3 with stronger adhesion to the fiber surface, resulting in improved long-term stability. Experimental results show that the sensitivity of the sensor varies from -31.05 nm/% to -4.30 nm/% as the hydrogen concentration increases from 0 to 1.04%. The sensor also demonstrates good reproducibility, longer term stability and repeatability

Quantitative detection of multi-frequency disturbance signal by ϕ-OTDR system

Recently, the combination of pattern recognition technology and distributed fiber sensing systems has become increasingly common, so whether the disturbance signal can be well recovered has become increasingly important. To verify the recovery and linear response of a distributed fiber optic sensing system to multi-frequency disturbance signals, a heterodyne coherent detection system for phase-sensitive optical time-domain reflectometry is developed. The output beat signal is extracted using the digital in-phase/quadrature demodulation algorithm. The signal can be precisely located on a 7 km length range, and the disturbance signal can be restored well through the phase information. Not only the superposition signal composed of the same signal but also that composed of different kinds of signals can be successfully restored. A fast Fourier transform algorithm is used to obtain the frequency information of the superimposed signal. Combined with the use of a finite impulse response filter, the superposed signal is decomposed according to its frequency components, which perfectly restores the two signals before they are superimposed. In addition, their amplitude is highly linear with the driving voltage of the piezoelectric transducer. The system can fully retain the details of each frequency component in the recovery of multi-frequency disturbance signals. More importantly, in field experiments, the disturbance behavior is well recovered, which has broad prospects in the application of perimeter security

Singlemode-Multimode-Singlemode Optical Fiber Sensor for Accurate Blood Pressure Monitoring

A dual-channel single-mode-multi-mode-single-mode (SMS) fiber optic sensor encapsulated by polydimethylsiloxane (PDMS) was proposed for the first time, for the simultaneous monitoring of the brachial and radial arteries for accurate blood pressure prediction. With the help of the machine learning algorithm Support Vector Regression (SVR), the SMS fiber sensor can continuously and accurately monitor the systolic and diastolic blood pressure. Commercial sphygmomanometers are used to calibrate the accuracy of blood pressure measurement. Compared with the single-channel system, this system can extract more pulse wave features for blood pressure prediction, such as radial artery transit time (RPTT), brachial artery transit time (BPTT), and the transit time difference between the radial artery and the brachial artery (DBRPTT). The results show that the performance of dual-channel blood pressure monitoring is more accurate than that of single-channel blood pressure monitoring in terms of the absolute value of the correlation coefficient (R) and the average value of the difference between SBP and DBP. In addition, both the single-channel and dual-channel blood pressure monitoring are in line with the Association for the Advancement of Medical Devices (AAMI), but the average deviation (DM, 0.06 mmHg) and standard deviation (SD, 1.54 mmHg) of dual-channel blood pressure monitoring are more accurate. The blood pressure monitoring system has the characteristics of low cost, high sensitivity, non-invasive and capability for remote real time monitoring, which can provide effective solution for intelligent health monitoring in the era of artificial intelligence in the future