Zhengliang Hu

Design and Analysis of a High Sensitivity FBG Accelerometer Based on Local Strain Amplification

A fiber Bragg grating (FBG) accelerometer based on a push-pull elastic cylinder structure is demonstrated. First, the model based on the uniform cylinder structure is analyzed and the optimized accelerometer parameters are given. Then, by designing a radius-varying cylinder structure, the FBG strain becomes larger than the cylinder strain, which leads to enhanced sensitivity amplification for a small accelerometer size and relatively high resonant frequency. Meanwhile, the influence of the transverse force on the accelerometer is theoretically analyzed. These results indicate that the transverse-induced FBG deformation is very big so that a strict transverse constrain is needed. The formula of the strain magnification is derived and the design rules of the strain magnification are given. After structure optimization according to the rules, the FBG strain increases to 1.5 times, the sensitivity increases to 1.82 times, whereas the resonant frequency reduces to 0.9 times compared with the parameters of accelerometer based on uniform cylinder structure. Finally, the accelerometer size reduces to Φ20 mm × 34 mm, the sensitivity increases to 623 pm/g, and the resonant frequency reduces to 449 Hz.

A Miniaturized FBG Accelerometer Based on a Thin Polyurethane Shell

A miniaturized fiber bragg grating accelerometer based on a thin polyurethane shell is designed and tested. The FBG accelerometer is based on spring-mass structure. The elastic body is a thin polyurethane cylindrical shell. By inserting the mass into the inner of the shell, the accelerometer axial size is reduced by half compared with traditional ones in which masses are exposed outside. The theoretical performance limit of the miniaturized accelerometer is discussed. Test results show the miniaturized accelerometer has similar sensing performance as the traditional one. Size of the miniaturized accelerometer is Φ23 mm × 17 mm, sensitivity over the flat frequency response zone is 54 pm/g, and resonant frequency is 480 Hz. Furthermore, orthogonal crosstalk of the miniaturized accelerometer is -17.75 dB which is 3 dB lower than the traditional one. Thus, this miniaturized design can reduce both size and orthogonal crosstalk of accelerometers based on elastic shells. This miniaturized structure can also be used in other fiber optic accelerometers based on shells.

Polarization maintaining fiber magnetic sensor based on the digital phase generated carrier technology

A polarization maintaining fiber (PMF) magnetic field sensor based on a digital phase generated carrier (PGC) technology is presented. A magnetic sensor constructed with two magnetostrictive strips attached on the sensing fiber is joined in the sensing arm of a fiber Michelson interferometer. The fiber optic interferometric system is made of all PMF, which inhibits the polarization-induced signal fading. The light source is a fiber laser which can be modulated directly. The PGC metnod is used to demodulate magnetic field signal avoiding phase induced interferometric signal fading, and ensure the sensing partto be all fiber structure. A fiber optic magnetic field sensor with appreciate size for the fiber optic hydrophone towed array is obtained, which can be used to sense the enviromental magnetic field along the sensing direction.This sensor is a good choice for the directional angle measurement through sensing the Earth magnetic field in the array shape measurement of a fiber optic hydrophone towed array.

Interrogation of miniature extrinsic Fabry-Pérot sensor using path matched differential interferometer and phase generated carrier scheme

Study of fiber optic extrinsic Fabry-Pérot sensors utilizing state-of-the-art MEMS technology mostly focus on sensor fabrication for various applications, while the signal interrogation is still insatiable to current application. In this paper, we propose a white light path matched differential interferometer dynamic sensing system utilizing phase generated carrier demodulation scheme. A step motor with a movable mirror and a fiber-wound piezoelectric transducer string are used to act path matching and phase modulation respectively. Experimental results show that the sensing signal could be correctly recovered with low distortion and the phase noise spectrum level is less than -100 dB re. rad/√Hz above 2.5 kHz.

A new method for reflectivity measurement of ultra-weak fiber Bragg gratings

An approach for reflectivity measurement of ultra-weak fiber Bragg gratings is demonstrated. The scheme uses a referenced high-reflectivity FBG to combine with the measured FBG. They have different center wavelengths. By using two referenced FBGs, the reflectivity of one measured FBG is calculated to be 0.298% and 0.287% respectively. For reflectivity measurement of ultra-weak FBG, to eliminate the influence of the reflection spectra side lobe for the referenced FBG, we get the reflection spectrum of the referenced FBG and measured FBG respectively under the same input intensity. The reflectivity of an ultra-weak FBG is measured to be 0.00916% (-40.38dB) and 0.00803%(-40.95dB) based on the two referenced FBGs. The results presents that the method is feasible.

Stability control of the polarization switching

ABSTRACT Pulse polarization switching is an important new method to eliminate the polarization-induced fading (PIF) in the interferometric fiber sensing system. An integrated Ti-indiffused LiNbO 3 Machx96Zehnder modulator is used to achieve high-speed switch of the polarization state by switching the voltage between two appropriate voltages applied to the modulator. The stability of the polarization switching is affected by environmental f actors, especially th e temperature. In this paper, the stability of the polarization switching is studie d. Firstly, the structure of the modulator and the principle o f the polarization switching are introduced. Secondly, a feedback control method to overcome the switch instability is proposed. The output polarization state could be obtained by monitoring the intensity of the output light. Finally, the high-speed and high-accuracy stable switching between two orthogonal polarization states is realized using this method and experimentally demonstrated. Keywords: Polarization-induced fading, Polarization switching, Feedback control, LiNbO

Recent progress toward fiber optic hydrophone research, application and commercialization in China

The fiber optic hydrophone research in China has a history of over 20 years. This talk will summarize some remarkable millstones in this history. Recent progress toward the fiber optic hydrophone research and application will be discussed. Some commercialization explorations will also be introduced.

Induced mode hopping phenomenon via resonant cavity disturbances in ultra-narrow linewidth erbium-doped fiber ring lasers

It is known that the incorporation of a self-induced grating in a saturable absorber can be used to drive fiber ring lasers to single-mode operation with ultra-narrow linewidth output. However, ultra-narrow linewidth erbium-doped fiber ring lasers (EDFRLs) usually suffer inevitably environmental perturbations for the relatively long resonant cavity, which may deteriorate the single-mode stability and practical applications in optical coherence detection. In this paper, the singlemode stability of the EDFRL under low-frequency resonant cavity disturbances has been investigated experimentally, and the induced mode hops have been measured to demonstrate that the occurrence of mode hopping can be triggered regularly by stretching the cavity fiber. The phenomenon of induced mode hopping indicates that the self-induced grating can only dynamically adjust itself to small disturbances in the cavity parameters within a finite range.

Design and Analysis of a Novel Dual FBG Accelerometer Based on Lantern Shape Metallic Shells

A novel dual FBG (DFBG) accelerometer based on lantern shape metallic shells is designed and analyzed. The DFBG accelerometer is based on the push–pull structure, which is used to eliminate common noises and disturbances. The axial size of the DFBG accelerometer is shortened by special combination of the mass and the elastic shells. The size of the optimized DFBG accelerometer is only 24 mm<inline-formula> <tex-math notation=LaTeX>

Study on time-frequency characteristics of transient response of the dynamic gratings in erbium-doped fiber

times 24