Chunsheng Yan

Detection Of Gas Concentration By Correlation Spectroscopy Using A Multi-Wavelength Fiber Laser

A correlation spectroscopy (COSPEC) based on a multi-wavelength fiber laser is first proposed for the detection of gas concentration. The lasing wavelengths are selected to match several characteristic absorption peaks of the gas under test, and the gas concentration is easily measured by correlating it with the reference gas. The present method is immune from the instability of the light source and the influence of other gases. The concentration measurement of C2H2 is demonstrated in the experiment in its near-infrared dominant absorption region. The technique has prospects for simultaneous detection of multiple gases, and the measurement of mixed gases of C2H2 and CO2 is also analyzed.

Interrogation technique for a fiber Bragg grating sensing array based on a Sagnac interferometer and an acousto-optic modulator

We propose and experimentally demonstrate a novel real-time interrogation technique for a fiber Bragg grating (FBG) sensing system that is based on a frequency-shifted asymmetric Sagnac interferometer. FBG sensors are connected to the Sagnac loop by an optical coupler, and an acousto-optic modulator (AOM) is asymmetrically placed in the Sagnac loop. By linearly sweeping the driving frequency of the AOM, the environmental variation around each FBG sensor can be determined by measuring the spectrum of the interference signals of the two counterpropagating light beams reflected by the corresponding FBG. The system has the advantages of low cost and real-time sensing.

Modeling and implementation of a fiber-based quartz-enhanced photoacoustic spectroscopy system

A compact fiber-based quartz-enhanced photoacoustic spectroscopy system requiring no extra optical lens has been developed for the detection of acetylene. The system is based on a common fiber or an axicon fiber to conduct the light. Experimental results show comparable detection sensitivity to that of tapered fiber-based photoacoustic spectroscopy systems. The system is easy to adjust and has low insertion loss and is thus well suited for small portable sensor applications in the future. A numerical model based on actual beam profiles was furthermore developed as part of the study to investigate the optimal positions of the fibers and to verify the experimental results.

Fast two-dimensional fluorescence correlation spectroscopy technique for tea quality detection.

A fast two-dimensional fluorescence correlation spectroscopy technique based on light emitting diodes is developed, which uses light intensity and excitation wavelength as quickly changeable and easily controllable external perturbations. A compact and automatic system is set up to detect tea quality. A partial least square regression method is used to create predictive models for tea grades. Compared to the traditional fluorescence spectroscopy method, this convenient two-dimensional correlation spectroscopy technique is more accurate according to our experimental results and is promising for practical applications.

Gas-self-filter-based erbium-doped fiber loop laser for gas detection

An erbium-doped fiber (EDF) loop laser, based on a gas-self-filter (GSF), is developed with single or multiple wavelength emission. The GSF is a type of Mach-Zehnder interferometer with a gas cell in one arm. By matching the destructive wavelength of the interferometer with the gas absorption line, the self-filtering function is achieved. A GSF-based multi-wavelength laser with a side-mode suppression ratio of ~50u2009u2009dB is performed. As an example, C₂H₂ gas is detected using a single-wavelength GSF-based laser with correlation spectroscopy, and a good linearity of the measurement is obtained. The present laser has the potential advantage for multiple gas detection, e.g., being free of wavelength calibration.

Low Coherent Optical Frequency Domain Reflectometry Interrogates Fiber Bragg Grating Sensors

A novel fiber optical reflectometry is proposed for long distance measurements and sensing applications. The reflectrometric information is included in the phase difference of two interfering light beams reflected at the same scattering point on the fiber under test (FUT). The reflection position and local information can be determined by modulating the frequency difference and analyzing the reflecting signal in frequency domain. Theoretical analysis and experimental demonstration are presented. Two adjacent reflection points 50 km away from the reflectometry with a gap of 11 meters between each other is distinguished. It is estimated that the operating range could be over 500 km theoretically by employing a light source with 0.3 nm bandwidth. This novel reflectometry is applied as a fiber Bragg grating interrogation solution as an example.

Methane detection using scattering material as the gas cell

A compact methane (CH4) detection system is presented and developed by using an alumina ceramic scattering material as its gas cell. Due to the materials high scattering performance, the optical path length of the gas cell at 1653.7 nm can reach 15.96 cm although its physical length along the light transmission direction is only 0.50 cm. The wavelength modulation spectroscopy technique is employed to enhance the detection sensitivity, and the second harmonic gas absorption signal with low noise is detected and processed. The long-term stability of the system is investigated by the Allan deviation analysis method. Detection limits of 4.5 and 2.6 ppm are achieved at averaging times of 20 s and 200 s, respectively. The dynamic gas exchange performance is also experimentally studied. The experimental results indicate that our system is a good choice for practical applications owing to its small volume, high sensitivity, and stability.

Classification evaluation of tobaccos using LED-induced fluorescence spectroscopy

Tobacco is one of the most important economic crops in the world, assessment of its quality has a very important business significance. A compact, low-cost, and maneuverable optical sensor system for classification evaluation of different tobaccos was described in this paper using light-emitting-diodes (LEDs)-induced fluorescence. The principal components analysis (PCA) method is used to extract the dominant features of the tobaccos for identifying the classification of tobaccos. The technique is suitable for practical identification due to the use of a straightforward data evaluation method and compact system.

Real-time monitoring of sulfur dioxide using ultraviolet light-emitting diode

A compact and low-cost light-emitting diode (LED) with center wavelength of 295 nm and high light density was used measure the concentration of sulfur dioxide, which has a strong structured absorption band in the ultraviolet region 300 nm. Differential optical absorption spectroscopy (DOAS) was used to determine the concentration of sulfur dioxide using reference absorption spectrum due to 1000 ppm SO2. A sensitivity of about 1.5 ppm was achieved with a gas cell in 1-s integration time, enabling real-time monitoring of sulfur dioxide.

Quasi-distributed sensing network based on coherence multiplexing and spatial division multiplexing for coal mine security monitoring

A low-cost fiber Bragg grating (FBG) sensing system for coal-mine security monitoring is proposed in this paper. Based on the coherence multiplexing (CM) and spatial division multiplexing (SDM) techniques, this hybrid sensing network can support more than 40 sensors for quasi-distributed detection. It is demonstrated experimentally that the multiplexed sensing signal of each sensor can be clearly distinguished by an optical low-coherence reflectometry (OLCR). Methane concentration is detected with maximum sensitivities of an intensity variation of 10.92% and a concentration variation of 1%, using a well-designed sensor structure. Strain and temperature are also detected by this system, which also exhibits good results in the experiment.