Zhaogang Wang

Diaphragm-Based Fiber Optic Fabry-Perot Accelerometer With High Consistency

Consistency is one of the most important parameters influenced on the practicability of sensors. A fiber optic Fabry-Perot accelerometer (FPA) with a diaphragm-mass-collimator (DMC) integrated structure to achieve high consistency is presented. This design makes the structure more compacts and the manufacturing process more controllable. Theoretical analysis is used to evaluate the performance of sensitivity, resonant frequency, resolution, and dynamic range. Four DMC fiber optic FPAs were manufactured, and experiments on several technical indicators were carried out. The experimental results are close to the calculated values and show that the maximum sensitivity difference of the DMC-FPAs is less than 0.38 dB (re: 0 dB = 1 V/g) in a frequency band of 10-125 Hz, and the maximum sensitivity fluctuation is less ±0.36 dB. The results verify the improvements on consistency, and the reasons for the good performances are discussed.

Optoelectronic hybrid fiber laser sensor for simultaneous acoustic and magnetic measurement.

An optoelectronic hybrid fiber optic acoustic and magnetic sensor (FOAMS) based on fiber laser sensing is proposed, which can measure acoustic and magnetic field simultaneously. A static magnetic field signal can be carried by an AC Lorentz force, and demodulated in frequency domain together with acoustic signals. Some experiments of acoustic pressure sensitivity, magnetic field sensitivity, and simultaneous acoustic and magnetic measurement on a fabricated FOAMS were carried out. The acoustic pressure sensitivity was about -164.7 dB (0 dB re 1 pm/μPa) and the magnetic field sensitivity was 0.6 dB (0 dB re 1 pm/ (T•A)). The experiment of simultaneous acoustic and magnetic measurement shows that the detections of acoustic and magnetic field have little effect on each other in dynamic range and simultaneously measuring acoustic and magnetic field is feasible.

Liquid-Damped Fiber Laser Accelerometer: Theory and Experiment

Liquid-damped fiber laser accelerometers (LD-FLAs) are promising to be used in some oil-filled and high pressure resistance instruments, such as ocean bottom seismographs and deep-well petroleum seismic geophones. A kind of LD-FLA structure, of which damping liquid could be easily changed, was designed to study its damping characteristic. The principles of an LD-FLA were analyzed comparing with a common FLA, which found that liquid damper could produce additional liquid pressures in vibration so that not only damping response of resonance peak but sensitivity could be changed at the same time. Four double diaphragm-based LD-FLAs were manufactured and experiments under three kinds of damping liquids were carried out. The experimental results are close to the calculated values and show that the average sensitivity of designed LD-FLAs is ~1.3 dB lower than that of air-filled FLAs and the working frequency band turns a little broad. The results verify the theoretical analysis on LD-FLA, and the model provides guidance for others on the practical design of LD-FLA.

Field test of the flow noise of fiber laser hydrophone array

Fiber laser hydrophone has attracted more and more attention because of its potential application in novel sonar system. For a towed fiber optic hydrophone array, the flow noise is an important source of the system noise. This paper presents the field test result of the flow noise of an eight-element fiber laser hydrophone array. The structure of the fiber laser hydrophone and the array is also introduced. The field test shows that obvious flow noise can be measured when the array is towed at the speed of 3 kn.

Fiber optical accelerometer based on 45 degrees Fabry-Perot cavity

The paper proposes an accelerometer construction based on 45-degrees Fabry-Perot (F-P) interferometer cavity. The uniform intensity cantilever consists of a mass block in the middle and a 45-degrees F-P cavity fixed inside the mass. The mass block can oscillate freely when the vibrating sensor is subject to the vibration and the F-P cavity length is changing. The G-lens end face and total reflective film make up the two reflective films of the F-P cavity, and the reflectivity are 4% and 90% respectively. In the F-P cavity, a 45-degrees mirror fixed in the middle of the G-lens and total reflective film. The mirror can change the transmission of the light and increase the optical path difference. The total reflective film fixed in the steel tube and the G-lens fixed in the fine tuning bolt. The bolt can fine adjust the F-P cavity in sensor encapsulating. The sensor structure lead to the optical loss in the airborne and tilted mirror, besides the distance of F-P gap in steel tube and the optical coupling efficiency can’t work out accurately, so we did a series deterministic test before encapsulating, for example the selection of the structures, the diameter of the optical fibers and the diameter of the reflective films. At last, 9/125 μm optical fiber, 1.4 mm total reflective film and the structure of total reflective film out of steel tube were used for the accelerometer. The sensitivity can reach 0.042 rad/g and the resonant frequency of the accelerometer is 400 Hz.

Fiber laser accelerometer-magnetometer

A fiber optic accelerometer-magnetometer (FLAM), which can measure acceleration and magnetic field simultaneously, based on fiber laser sensing is proposed. The principle of the FLAM and the theory of the decoupling the signals of acceleration and magnetic field are presented. The FLAM was interrogated using phase-generated-carrier (PGC) method. A test of simultaneously measuring acceleration and magnetic field was performed. The results show that the responding mixed signal achieves a good SNR and prove that the function of the sensor has been realized and the theory of decoupling signal is reliable.

Fiber laser sensor for simultaneous acceleration and magnetic measurement

An optoelectronic hybrid fiber laser acceleration and magnetic sensor (FLAMS) is proposed. Using a spring-mass system, the acceleration will induce dynamic strain in the fiber laser. The static magnetic field signal can be carried by an AC Ampere force, and result in the dynamic strain at the carrier frequency. Both the acceleration and magnetic field signals are demodulated in frequency domain using phase generated carrier (PGC) method. The acceleration sensitivity was about 20 dB (0 dB re 1 pm/g) and the magnetic field sensitivity was 0.6 dB (0 dB re 1 pm/ (T•A)). The experiment of simultaneous acceleration and magnetic measurement shows that the two measurands have little effect on each other in dynamic range.

Field test of fiber optic ocean bottom seismograph

In this paper we report the field test of fiber optic ocean bottom seismograph (OOBS) which can be used in the active source seismic research. There are three fiber laser accelerometers (FLAs) and one fiber laser hydrophone (FLH), which is wavelength division multiplexed, in the OOBS. The interrogation system is put on shore and is connected with the OOBS with optical fiber cable. The field test of using an air gun is carried out under water with a depth of 30 m. The results show that the OOBS has similar performance as conventional electric OBS.

Fiber optic ocean bottom seismograph

In this paper we report the fiber optic ocean bottom seismograph (FOBS) system which is promising to be installed in the Ocean Bottom Observation Network (OBON). The FOBS system consists of an ocean bottom seismometer and a demodulator. The fiber laser sensors are used in the seismometer to detect the seismic signal. There are four sensors, three fiber laser accelerometers (FLA) and one fiber laser hydrophone (FLH) in the seismometer. The demodulator, with an underwater connector, is designed to be linked to the node of OBON. Tests of durability in marine environment, such as high-temperature test, vibration test, high pressure test, were carried out. In 2014 and 2015, field tests were performed in the Dayindian Lake in Yunnan Province. The results show that the FOBS has similar performance to GOBS, which implies a promising application in OBON.

Simultaneous Acoustic and Magnetic Measurement Using a Fiber Laser Sensor

The acoustic wave induced stress will change the output wavelength of the fiber laser as well as the magnetic field induced Lorentz force. The acoustic and magnetic signals are decoupled in frequency domain.