A low-cost and portable optical chemical sensor based ammonia sensing system that is capable of detecting dissolved ammonia up to 5 ppm is presented. In the system, an optical chemical sensor is designed and fabricated for sensing dissolved ammonia concentrations. The sensor uses eosin as the fluorescence dye which is immobilized on the glass substrate by a gas-permeable protection layer. A compact module is developed to hold the optical components, and a battery powered micro-controller system is designed to read out and process the data measured. The system operates without the requirement of laboratory instruments that makes it cost effective and highly portable. Moreover, the calculated results in the system can be transmitted to a PC wirelessly, which allows the remote and real-time monitoring of dissolved ammonia.

We demonstrate a compact and high-resolution dual-polarization fiber laser accelerometer. A spring-mass like scheme is constructed by fixing a 10-gram proof mass on the laser cavity to transduce applied vibration into beat-frequency change. The loading is located at the intensity maximum of intracavity light to maximize the optical response. The detection limit reaches 107 ng/Hz1/2 at 200 Hz. The working bandwidth ranges from 60 Hz to 600 Hz.

A hybrid phase-sensitive optical time domain reflectometry (Φ-OTDR) and Brillouin optical time domain reflectometry (B-OTDR) system which can realize simultaneous measurement of both dynamic vibration and static strain is proposed. Because the Rayleigh scattering light and spontaneous Brilliouin scattering light are naturally frequency-multiplexed, the heterodyne asynchronous demodulation of frequency shift keying (FSK) in optical fiber communications is utilized, and the demodulations of the two scattering signals are synchronized. In addition, the forward Raman amplification is introduced to the system, which not only makes up for the deficiency of spontaneous Brilliouin scattering based distributed fiber sensor, but also has the merit of the single end measurement of B-OTDR. The designed Φ/B-OTDR hybrid system has the sensing range of 49 km with 10 m spatial resolution. The vibration and strain experiments show that this hybrid system has great potential for use in long-distance structural health monitoring.

Due to extremely effective advantages of the quantum cascade laser spectroscopy and technology for trace gas detection, this paper presents spectroscopy scanning, the characteristics of temperature tuning, system resolution, sensitivity, and system stability with the application of the presented gas sensor. Experimental results showed that the sensor resolution was ≤0.01cm–1 (equivalent to 0.06 nm), and the sensor sensitivity was at the level of 194 ppb with the application of H2CO measurement.

A time division multiplexing of 106 weak fibers Bragg gratings (FBGs) based on a ring resonant-cavity is demonstrated. A semiconductor optical amplifier is connected in the cavity to function as an amplifier as well as a switch. The 106 weak FBGs are written along a SMF-28 fiber in serial with peak reflectivity of about -30 dB and equal separations of 5 m. The crosstalk and spectral distortion are investigated through both theoretical analysis and experiments.

In this paper, we propose and simulate a pressure sensor based on two-dimensional photonic crystal with the high quality factor and sensitivity. The sensor is formed by the coupling of two photonic crystal based waveguides and one nanocavity. The photonic crystal with the triangular lattice is composed of GaAs rods. The detailed structures of the waveguides and nanocavity are optimized to achieve better quality factor and sensitivity of the sensor. For the optimized structures, the resonant wavelength of the sensor has a linear redshift as increasing the applied pressure in the range of 0 – 2 GPa, and the quality factor keeps unchanged nearly. The optimized quality factor is around 1500, and the sensitivity is up to 13.9 nm/GPa.

The key technology and main difficulty for optical fiber intrusion pre-warning systems (OFIPS) is the extraction of harmful-intrusion signals. After being processed by a phase-sensitive optical time-domain reflectometer (Φ-OTDR), vibration signals can be preliminarily extracted. Generally, these include noises and intrusions. Here, intrusions can be divided into harmful and harmless intrusions. With respect to the close study of signal characteristics, an effective extraction method of harmful intrusion is proposed in the paper. Firstly, in the part of the background reconstruction, all intrusion signals are first detected by a constant false alarm rate (CFAR). We then reconstruct the backgrounds by extracting two-part information of alarm points, time and amplitude. This ensures that the detection background consists of intrusion signals. Secondly, in the part of the two-dimensional Kolmogorov-Smirnov (K-S) test, in order to extract harmful ones from all extracted intrusions, we design a separation method. It is based on the signal characteristics of harmful intrusion, which are shorter time interval and higher amplitude. In the actual OFIPS, the detection method is used in some typical scenes, which includes a lot of harmless intrusions, for example construction sites and busy roads. Results show that we can effectively extract harmful intrusions.

Two types of carbon nanotubes [single walled nanotubes (SWCNTs) and multi walled carbon nanotubes (MWCNTs)] are deposited on porous silicon by the drop casting technique. Upon exposure to test gas mixing ratio 3% NO2, the sensitivity response results show that the SWCNTs’ sensitivity reaches to 79.8%, where MWCNTs’ is 59.6%. The study shows that sensitivity response of the films increases with an increase in the operating temperature up to 200 ℃ and 150 ℃ for MWCNTs and SWCNTs. The response and recovery time is about 19 s and 54 s at 200℃ for MWCNTs, respectively, and 20 s and 56 s at 150℃ for SWCNTs.

Endpoint detection (EPD) is very important undertaking on the side of getting a good understanding and figuring out if a plasma etching process is done on the right way. It is truly a crucial part of supplying repeatable effects in every single wafer. When the film to be etched has been completely erased, the endpoint is reached. In order to ensure the desired device performance on the produced integrated circuit, many sensors are used to detect the endpoint, such as the optical, electrical, acoustical/vibrational, thermal, and frictional. But, except the optical sensor, the other ones show their weaknesses due to the environmental conditions which affect the exactness of reaching endpoint. Unfortunately, some exposed area to the film to be etched is very low (<0.5%), reflecting low signal and showing the incapacity of the traditional endpoint detection method to determine the wind-up of the etch process. This work has provided a means to improve the endpoint detection sensitivity by collecting a huge numbers of full spectral data containing 1201 spectra for each run, then a new unsophisticated algorithm is proposed to select the important endpoint traces named shift endpoint trace selection (SETS). Then, a sensitivity analysis of linear methods named principal component analysis (PCA) and factor analysis (FA), and the nonlinear method called wavelet analysis (WA) for both approximation and details will be studied to compare performances of the methods mentioned above. The signal to noise ratio (SNR) is not only computed based on the main etch (ME) period but also the over etch (OE) period. Moreover, a new unused statistic for EPD, coefficient of variation (CV), is proposed to reach the endpoint in plasma etches process.

A phase shift demodulation technique based on subtraction capable of measuring 0.03 phase degree limit between sinusoidal signals is presented in this paper. A self-gain module and a practical subtracter act the kernel parts of the phase shift demodulation system. Electric signals in different phases are used to verify the performance of the system. In addition, a new designed optical source, laser fiber differential source (LFDS), capable of generating mini phase is used to further verify the system reliability. R-square of 0.99997 in electric signals and R-square of 0.99877 in LFDS are achieved, and 0.03 degree measurement limit is realized in experiments. Furthermore, the phase shift demodulation system is applied to the fluorescence phase based oxygen sensors to realize the fundamental function. The experimental results reveal that a good repetition and better than 0.02% oxygen concentration measurement accuracy are realized. In addition, the phase shift demodulation system can be easily integrated to other applications.

Pavement roughness is one of the most important factors for appraising highway construction. In this paper, we choose the laser triangulation to measure pavement roughness. The principle and configuration of laser triangulation are introduced. Based on this technology, the pavement roughness of a road surface is measured. The measurement results are given in this paper. The measurement range of this system is 50 μm. The measurement error of this technology is analyzed. This technology has an important significance to appraise the quality of highway after completion of the workload.

In the present study, we have theoretically modelled a surface plasmon resonance (SPR) based sensing chip utilizing a prism made up of gallium phosphidee. It has been found in the study that a large range of refractive index starting from the gaseous medium to highly concentrated liquids can be sensed by using a single chip in the visible region of the spectrum. The variation of the sensitivity as well as detection accuracy with sensing region refractive index has been analyzed in detail. The large value of the sensitivity along with the large dynamic range is the advantageous feature of the present sensing probe.

In this paper, the response of fiber Bragg gratings (FBGs) subjected to the ultrasonic wave has been theoretically and experimentally investigated. Although FBG sensors have been widely used in the ultrasonic detection for practical structural health monitoring, the relationship between the grating length and ultrasonic frequency is not yet to be obtained. To address this problem, an ultrasound detection system based on FBGs is designed and the response sensitivity of different lengths gratings are detected. Experimental results indicate that the grating with 3 mm length has a higher sensitivity when detecting high frequency ultrasonic wave, and the amplitude can be up to 0.6 mV. The 10 mm length grating has better detection sensitivity for low frequency ultrasonic wave and the amplitude is 0.8 mV. The results of this analysis provide useful tools for high sensitivity ultrasound detection in damage detection systems.

A multichannel heterodyne fiber optic vibrometer is demonstrated which can be operated at ranges in excess of 50 m. The system is designed to measure periodic signals, impacts, rotation, 3D strain, and vibration mapping. The displacement resolution of each channel exceeds 1 nm. The outputs from all channels are simultaneous, and the number of channels can be increased by using optical switches.