A minitype optical fiber acceleration sensor based on the cantilever is investigated. The sensor mainly makes up of the cantilever and the distributed feedback (DFB) fiber laser. The beam is deformed when the vibration due to the acoustic field applied on the beam. The DFB fiber laser is stuck on the surface of the cantilever beam. It leads to the frequency shift of the output of the fiber laser. By measuring the frequency shift, the acceleration of the vibration can be realized. The center element of the sensor is the cantilever beam and fiber laser, so the mass and volume of the sensor are greatly reduced. The largest dimension of the cantilever beam in this work is just 30mm. And then the cantilevers are taken into simulations and experiments. The experimental results are coincident with the simulations. The experiments of the sensors shows that the acceleration sensitivity is flat and can reach 108Hz/g below 80Hz. And the highest sensitivity is 2.02×109Hz/g. Compared with existing acceleration sensors, this cantilever acceleration sensor can obtain high sensitivity in small scale and light weight.
A minitype optical fiber acceleration sensor based on the cantilever is investigated. The sensor mainly makes up of the cantilever and the distributed feedback (DFB) fiber laser. The beam is deformed when the vibration due to the acoustic field applied on the beam. The DFB fiber laser is stuck on the surface of the cantilever beam. It leads to the frequency shift of the output of the fiber laser. By measuring the frequency shift, the acceleration of the vibration can be realized. The center element of the sensor is the cantilever beam and fiber laser, so the mass and volume of the sensor are greatly reduced. The largest dimension of the cantilever beam in this work is just 30mm. And then the cantilevers are taken into simulations and experiments. The experimental results are coincident with the simulations. The experiments of the sensors shows that the acceleration sensitivity is flat and can reach 108Hz/g below 80Hz. And the highest sensitivity is 2.02×109Hz/g. Compared with existing acceleration sensors, this cantilever acceleration sensor can obtain high sensitivity in small scale and light weight.
A kind of fiber optic particle velocity sensor based on planar cantilever beam is studied. The fiber laser is attached to the surface of a cantilever. The cantilever beam is deformed by the acoustic field in the vertical direction of the surface, and the frequency of the output of the fiber laser is modulated, so as to realize the acoustic vector sensor. In particular, in viscous fluids, the cantilever is driven by an additional force proportional to the velocity of fluid particle. By selecting the appropriate liquid, the fluid viscous force will become the main driving force of the cantilever beam, making the sensor respond directly to the velocity of water particle, thus having a flat sound pressure sensitivity response curve. According to the cantilever beam equation in fluid, the theoretical simulation of the frequency response of the sensor shows that the acoustic pressure sensitivity is 104Hz/Pa and the acceleration sensitivity is 108Hz/g from 10Hz to 60Hz. The acoustic pressure sensitivity and acceleration sensitivity of the sensor in air and water are studied by experiment, and the results are consistent with the theoretical simulation. Compared with the traditional fiber optic accelerometer, the sensor of this structure has the advantages of small size, simple structure and high sensitivity, which is of great significance for application of vector hydrophone in low frequencies and is beneficial to constitute large scale hydrophone array.
This paper reports a resonant type optical fiber vector hydrophone (OFVH) for deep-sea applications, which is composed of a three-component optical fiber accelerometer and an optical fiber pressure hydrophone. To meet the acoustic requirements in the deep-sea, the orthogonal and unitized structure of the three-component accelerometer is adopted to increase the sensitivity and the operating frequency band of the accelerometer. The results show that the acceleration sensitivity is about 40dB re rad/g and the pressure sensitivity is nearly -147 dB re rad/μPa. The fluctuations of the acceleration and pressure sensitivity are less than 1.5dB over the 10-2000Hz frequency range. The deep-sea trial verified its excellent acoustic detection performance. Both the direction-of-arrival (DOA) and range for distant ship is estimated. The DOA estimation error is no higher than 10° and the range estimation error is less than 10%. This OFVH has a wide application prospect in the deep-sea.
In a phase extraction based phase-sensitive optical time domain reflectometry (Φ-OTDR), external perturbation induced phase variation of Rayleigh backscattered light-wave (RBL) is obtained from time varying interference signal that is comprised of two RBLs with a spatial shift along the sensing fiber. In this paper, the phase of the interference signal in the phase extraction based Φ-OTDR is studied. Derivation is performed on the interference signal considering the interference of multiple RBL within probe pulse covered fiber section. Theoretical analysis and experimental results reveal that the phase of interference signal are wavelength independent while the intensity of interference signal are wavelength dependent.
In this papers, the influence of the line-width of probe light on the phase noise of phase extracted based phase-sensitive optical time domain reflectometry (Φ-OTDR) is theoretical analyzed and experimentally investigated. Analysis indicates that broad line-width probe light suffers time varying wavelength drift and high level of laser phase noise, and thus guarantees high level phase noise of the Φ-OTDR. In distributed acoustic sensing along 500 m sensing fiber, the phase noise is evaluated for probe lights of different line-widths, and experimental results display that the phase noise increases as the line-width of probe light broadens.
We investigate the quadrature crosstalk characteristics of three-dimensional optical fiber vector sensor in a time-divisionmultiplexing (TDM) array based on phase generated carrier (PGC) technology in theory and experiment. A theoretical model based on PGC demodulation technology is established. The numerical simulation based on the theoretical model is carried on and indicates that the quadrature crosstalk of the optical fiber vector sensor is governed by the path difference of the interferometer, the length of the delay fiber, the number of array channels and the extinction ratio of the acousto-optic modulator (AOM). A four channels TDM array based on four cascaded interferometers was set up to verify the theoretical analysis. The experimental results agree well with the theoretical analysis. This research provides insight into the quadrature crosstalk in a TDM optical fiber vector sensor array, and can be used to optimize the array design in specific applications.
A numerical simulation model for investigating modulation instability in a Raman-assisted fiber-optics system is presented and used. The modulation instability (MI) spectrum and its threshold are numerically analyzed based on this theoretical model. The different MI behaviors between forward and backward Raman pumping are studied in detail, respectively. The MI threshold in the case of forward Raman pumping is lower than that in the case of backward Raman pumping. Experiments are conducted based on the theoretical analysis, and the results agree well with the numerical calculations.
Ultra-narrow-linewidth lasers are of great interest in many applications, such as precise spectroscopy, optical communications, and sensors. Stimulated Brillouin scattering (SBS), as one of the main nonlinear effects in fibers, is capable of generating narrow-linewidth light emission. We establish a compact Brillouin/erbium fiber laser (BEFL) utilizing 4-m erbium-doped fiber as both the Brillouin gain and linear media. A 360-kHz-linewidth laser diode is injected into the cavity as the Brillouin pump (BP) light and generates Brillouin Stokes lasing light. Both of the phase noise of the BP and BEFL output are measured by a high-accuracy unbalanced Michelson interferometer. It is demonstrated that 53- dB phase noise reduction is achieved after the BP is transferred into Brillouin Stokes emission. The linewidth of the BEFL is indicated at Hz-range by both calculation and experiment.
We analyze the method to uniform the output signal power spectrum for a long-haul wavelength-division-multiplexing (WDM) system using backward multipump Raman amplifiers with arbitrary initial input signal power spectrum. A genetic algorithm is used to optimize the output signal power. The theoretical results show that using variable pump wavelengths is better than using fixed pump wavelengths to decrease the spectral maximum power difference. An experiment is conducted based on the theoretical analysis. The results agree well with the numerical calculations.
High-coherence light is stringently demanded in high-accuracy interferometric optical fiber sensors, where the phase noise of the light source greatly affects the sensitivity of the whole system. Distributed-feedback laser diodes with a phase noise of -80 ~ -90 dB/Hz1/2 at 1 kHz (with 1 m optical path difference) is now easily obtained, but the interferometric fiber sensors requires the laser source with the phase noise lower than -100 dB/Hz1/2. Lasers with ultra-low-noise usually require complicated and sophisticated techniques. We propose a novel structure to realize high-coherence light extraction through a compact Brillouin/erbium fiber laser (BEFL) which uses a length of 4 m erbium-doped fiber as both the Brillouin and linear gain media. The phase noise of the Brillouin pump light is greatly smoothed and suppressed after being transferred to the Brillouin Stokes light. High-coherence light with the phase noise of about -104 dB/Hz1/2 at 1 kHz is extracted through the compact BEFL from a commercialized laser diode with the phase noise of about -89 dB/Hz1/2. The capability of phase noise suppression in the compact BEFL presents much importance especially in large-array interferometric fiber sensor systems.
A Brillouin/erbium fiber laser (BEFL) of 25km single-mode fiber is constructed, and its characteristics of optical carrier
suppression are measured and analyzed. Light wave modulated by an electro-optic intensity modulator (EOIM) with
11GHz microwave frequency is adopted as the testing light. As much as 32 dB optical carrier-suppression ratio is
achieved at 112mW of 980nm pump power inside the BEFL. Meanwhile, the sideband powers remain nearly unchanged
in the process. Moreover, the carrier-suppression ratio is precisely controllable by tuning the 980nm pump power in the
BEFL. These optical carrier-suppression characteristics promise significant applications of such a technique not only to
distributed Brillouin optical fiber sensing based on EOIM but also to microwave photonic signal processing.
Two DFB semiconductor lasers are adopted as master and slave lasers to investigate the properties of the weak injection
locked DFB laser, such as the stable locking range, the phase noise and the power stability. A Brillouin/erbium fiber laser
pumped by the master DFB laser is injected into the slave DFB laser to validate the improvements of power stability and
spectral purity through the laser injection locking technology, which also demonstrates the feasibility of single frequency
extraction. The locked laser acts like a tunable narrow-band optical filter with central frequency and bandwidth decided
by the input signal. The experimental results give rise to some potential configurations useful for Brillouin distributed
fiber sensing and signal processing in microwave photonics.
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