Fiber optic microstructure turbulence sensors (FOMTS) with fiber Bragg gratings can measure the rate of tangential velocity change caused by ocean turbulence. The theoretical principles of the FOMTS and demodulation were verified by a prototype. The demodulation system resolution reached 0.001 pm / Hz, the sensitivity was 4.37 × 10 − 16 m2 s2 / kg, and its natural frequency in air was 595 Hz, similar to the theoretical values. Its resonance frequency in water (534 Hz), exceeded the highest frequency of ocean turbulence (200 Hz). Furthermore, comparative experiments between the FOMTS and a commercially available sensor were performed. Good signal correspondence was observed, proving the effectiveness of the FOMTS and verifying the design principle.
The improvement of the detection limit of gas sensors has always been the focus of sensor research. Compared with the improvement of hardware, the improvement of the algorithm is still relatively less. In this study, a dual-channel methane gas sensor system based on mid-infrared LED light source was designed. We apply the wavelet denoising algorithm to the high-frequency noise suppression of the sensor system, which achieves a 36dB signal-to-noise ratio improvement over the traditional low-pass filter, making the detection limit of the sensing system reach the level below 3ppm. We give an estimation method for the detection limit of the sensing system. The detection limits estimated by this theory are basically the same as those obtained by the Allen deviation analysis in the conventional method. Implementing better algorithms to improve sensor SNR in software can reduce the demands of improving sensor SNR solely from hardware improvements.
We designed and manufactured all optical fiber CTD to monitor ocean based on the sensitive characteristics about
optical fiber grating. A series of works have done, including the calibration work for sensor in laboratory, simulated
experiment outside and the local test of ocean parameter. The results we got show that the precision of temperature is
0.01℃ and of pressure is better than 0.1%, both of them overtake the secondary standard of GB/T23246-2009, moreover,
close to the primary standard, and of salinity in laboratory has reached 708 pm/1% closely to the secondary standard. It is
satisfied with the ocean monitoring requirements.
A new fiber Bragg grating (FBG) based accelerometer is developed for monitoring seismic activities induced by moving
vehicles. A theoretical model of the sensor is established, and analytical formulas of describing the sensitivity and
resonant frequency are provided. Sensors of this type are fabricated and tested. The experimental results show that they
have a sensitivity of 162.8 pm/G and a resonant frequency of 242.9Hz. The minimum detectable signal of the whole
sensing system is about 12.1 &mgr;g. A field test is carried out to find out that for tracked vehicles' monitoring, a single sensor
has a detection range of about 300 meters, indicating a promising future in practical use.
This paper describes a high-performance multiplexed vibration sensor system using fiber lasers. A serial vibration sensor
array consists of four short cavity fiber lasers. The system employs a single, polarization-insensitive, unbalanced
Michelson interferometer to translate individual laser wavelength shifts induced by vibration signals into interferometer
phase shifts. A dense wavelength division demultiplexor (DWDM) with high channel isolation is inserted to demultiplex
each laser signal as a wavelength filter. Finally, a digital phase demodulator based on the phase generated carrier
technique is used to achieve high-resolution interrogation. Experimental results show that no observable crosstalk is
measured on the output channels, and the minimal detectable acceleration of this system is ~200ng/&sqrt;Hz at 250Hz, which
is fundamentally limited by the frequency noise of the lasers.