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 0-20 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.

We have experimentally demonstrated the flat supercontinuum (SC) generation using a 10-m-long ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fluoride fiber pumped by an erbium-doped mode-locked fiber laser incorporating carbon-nanotube-based saturable absorbers. In order to improve the spectral flatness of SC, the standardized single-mode fiber with different lengths is connected to the output of the mode-locked fiber laser before the pulse amplification. The generated SC with ZBLAN fiber exhibits the best spectral flatness with fluctuation less than 1.29 dB over the wavelength of 1571.8 nm - 1803.1 nm, showing potential applications in optical sensing.

An improved glucose sensitive membrane (GSM) is prepared by immobilizing glucose oxidase (GOD) onto a mixture of silica mesocellular foams (SiMCFs) and SiO2 nanoparticles (SiNPs) and then trapping it in a polyvinyl alcohol (PVA) gel. The membrane is coated onto a gold-glass sheet to create a surface plasmon resonance (SPR) sensor. A series of experiments are conducted to determine the optimized parameters of the proposed GSM. For a GSM with a component ratio of SiMCFs : SiNPs = 7 : 3 (mass rate), the resonance angle of the sensor decreases from 68.57° to 63.36°, and the average sensitivity is 0.026°/(mg/dL) in a glucose concentration range of 0 mg/dL-200 mg/dL. For a GSM with a component ratio of SiMCFs : SiNPs = 5 : 5 (mass rate), the resonance angle of the sensor decreases from 67.93° to 63.50°, and the sensitivity is 0.028°/(mg/dL) in a glucose concentration range of 0 mg/dL - 160 mg/dL. These data suggest that the sensor proposed in this study is more sensitive and has a broader measurement range compared with those reported in the literature to date.

Atomically thin two-dimensional semiconductor nanomaterials have attained considerable attention currently. We here theoretically investigate the phenomena of slow and superluminal light based on the MoS2 resonator system driven by two-tone fields. Superluminal and ultraslow probe light without absorption can be obtained via manipulating the pump laser on- and off-resonant with the exciton frequency under different parameters regimes, respectively, of which the magnitude is larger than that in a carbon nanotube resonator. The bandwidth of the probe spectrum determined by the quality factor Q of MoS2 resonator is also presented. Furthermore, we also demonstrate the phenomenon of phonon induced transparency and show an optical transistor in the system. The all-optical device based on MoS2 resonator may indicate potential chip-scale applications in quantum information with the currently popular pump-probe technology.

The detection of crack on materials is an important issue in industry. On the contrary to conventional methods, such as manual inspection, sensor detection, and image processing techniques, a new simple method to detect the crack is proposed with optical voice recorder based on digital holography in this paper. Holograms obtained with sound waves passing through the materials are recorded by using the digital holography technique. Temporal behavior of the sound wave passing through the material, which is obtained from these holograms, gives image of crack. In this article, cracks in various materials are determined by the proposed new method, and crack images obtained with this new system are presented.

A finite-difference-time-domain (FDTD) approach is undertaken to investigate the extraordinary optical transmission (EOT) phenomenon of Au circular aperture arrays deposited on a Bragg fiber facet for refractive index (RI) sensing. Investigation shows that the choice of effective indices and modal loss of the Bragg fiber core modes will affect the sensitivity enhancement by using a mode analysis approach. The critical parameters of Bragg fiber including the middle dielectric RI, as well as its gap between dielectric layers, which affect the EOT and RI sensitivity for the sensor, are discussed and optimized. It is demonstrated that a better sensitivity of 156 ± 5 nm per refractive index unit (RIU) and an averaged figure of merit exceeding 3.5 RIU-1 are achieved when RI is 1.5 and gap is 0.02 μm in this structure.

To obtain a good interference fringe contrast and high fidelity, an automated beam iterative alignment is achieved in scanning beam interference lithography (SBIL). To solve the problem of alignment failure caused by a large beam angle (or position) overshoot exceeding the detector range while also speeding up the convergence, a weighted iterative algorithm using a weight parameter that is changed linearly piecewise is proposed. The changes in the beam angle and position deviation during the alignment process based on different iterative algorithms are compared by experiment and simulation. The results show that the proposed iterative algorithm can be used to suppress the beam angle (or position) overshoot, avoiding alignment failure caused by over-ranging. In addition, the convergence speed can be effectively increased. The algorithm proposed can optimize the beam alignment process in SBIL.

An all-organic Mach-Zehnder waveguide device for volatile solvent sensing is presented. Optical waveguide devices offer a great potential for various applications in sensing and communications due to multiple advantageous properties such as immunity to electromagnetic interference, high efficiency, and low cost and size. One of the most promising areas for applications of photonic systems would be real-time monitoring of various hazardous organic vapor concentrations harmful to human being. The optical waveguide volatile solvent sensor presented here comprises a novel organic material applied as a cladding on an SU-8 waveguide core and can be used for sensing of different vapors such as isopropanol, acetone, and water. It is shown that the reason for the chemical sensing in device is the absorption of vapor into the waveguide cladding which in turn changes the waveguide effective refractive index. The presented waveguide device has small footprint and high sensitivity of the mentioned solvent vapor, particularly that of water. The preparation steps of the device as well as the sensing characteristics are presented and discussed.

Glass has been widely used as an important component in structures such as reflection glass curtainwalls, high speed trains, and landscape glass bridges with advantages of transparent and easy to clean, which are exposed to extreme weather conditions and external loads. Over time, these factors can lead to a damage of glass. So the health status of glass structure is critical, which should be routinely monitored to improve safety and provide reliable maintenance strategy. In this paper, fiber Bragg grating (FBG) sensors are used to monitor glass damage based on the fact that the main components of both the optical fiber and the glass are silica, which hints that both optical fiber and glass have the similar mechanical properties. Furthermore, the diameter of FBG installed on the glass structure is small, which has little effect on the beauty of glass. In order to validate the feasibility of the damage monitoring method, one common glass panel model with two-side fixations is loaded impact and static loads respectively, on the upper and lower surfaces of which four FBG sensors and two resistance strain gages are installed. A comparison study among the measured strains from the FBG sensors, those from the resistance strain gages, and those calculated from finite element model (FEM) analysis is conducted and the result obtained with experiments agrees with the element result. Test results show that the FBG sensors can effectively measure the glass deformation or damage under the impact and static load.

Multi-component and multi-point trace gas sensing in the wavelength modulation spectroscopy is demonstrated based on the frequency-division multiplexing and time-division multiplexing technology. A reference photodetector is connected in series with a reference gas cell with the constant concentration to measure the second-harmonics peak of the components for wavelength stabilization in real time. The central wavelengths of the distributed feedback lasers are locked to the target gas absorption centers by the reference second-harmonics signal using a digital proportional-integral-derivative controller. The distributed feedback lasers with different wavelengths and modulation frequencies are injected into the gas cell to achieve multi-components gas measurement by the frequency-division multiplexing technology. In addition, multi-point trace gas sensing is achieved by the time-division multiplexing technology using a photoswitch and a relay unit. We use this scheme to detect methane (CH4) at 1650.9 nm and water vapor (H2O) at 1368.597 nm as a proof of principle with the gas cell path length of 10 cm. The minimum detection limits achieved for H2O and CH4 are 1.13 ppm and 11.85 ppm respectively, with three-point gas cell measurement; thus 10.5-fold and 10.1-fold improvements are achieved in comparison with the traditional wavelength modulation spectroscopy. Meanwhile, their excellent R-square values reach 0.9983 and 0.99564 for the concentration ranges of 500 ppm to 2000 ppm and 800 ppm to 2700 ppm, respectively.