We designed and constructed a 400km interrogated fiber-optics hydrophone (FOH) array for the bottom mounted applications. The experimental results show that the phase noise level of the remote array is -97dB re 1rad/sqrt(Hz) @1kHz, the maximum time division multiplexing (TDM) crosstalk level is -54dB, the wavelength division multiplexing (WDM) crosstalk level is better than -73dB and the signal correlation between two sensors is better than 0.98. The results demonstrate that the performance of this remote array has reached to an acceptable high level, so this architecture would be of great importance in the practical applications.
Fiber Bragg grating written in polarization-maintaining fiber is strongly polarization-dependent, and its spectral character depends on the polarization state of light that interrogates the grating. We propose a novel and practical method to test the spectra character of the polarization-maintaining fiber Bragg grating (PM-FBG) interrogated by a linearly polarized light with a different azimuth for the first time. We specially designed a splice with a different angle in the system to alter the azimuth of the input linearly polarized light. Using this method, we got the transmission and reflection spectra of the PM-FBG measured at different splice angles and then the experimental results were analyzed originally. The analysis result shows that the relationship between the transmission dip and the splice angle obeys the Gaussian distribution. The reflectivity of the two wavelengths of the PM-FBG depends on the azimuth of the input linearly polarized light.
A distributed optical fiber vibration sensing system based on compensating interferometer is established and a distributed
optical fiber vibration waveform detecting technology based on a MZ compensating interferometer and compensating
interference of Rayleigh backscattering lights in adjacent areas is put forward. In laboratory experiment, the sensing fiber
is a 2500m SM fiber. By exerting 500Hz PZT vibration signals on the fiber at 40m, 430m, and 2500m, the locations of
the signals are obtained by phase demodulation. But there is a crosstalk at 40m because of multiple scatterings. The
spatial resolution is 40m and the SNR is 18dB.
Polarization fluctuation in polarization maintaining fiber (PMF) resonator is one of the major noise sources in resonant fiber optic gyroscope (R-FOG). 90-deg polarization-axis rotated splicing in R-FOG is an effective way to suppress the polarization-fluctuation induced noise. 90-deg polarization-axis rotated splicing error influences the noise suppression effect. Here, a polarization-coupling testing system based on white-light interferometry is designed to control 90-deg splicing error in double-coupler PMF resonator first time and a result of 0.37-deg splicing error is obtained for the first time. Then the resonant characteristics of the double-coupler PMF resonator are tested using the saw-tooth waveform scanning method. The finesse of this double-coupler PMF resonator is 24.0 and the phase interval of the two eigenstates of polarization (ESOPs) is π.
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.
A signal demodulation scheme based on heterodyne technique is demonstrated, which can help fiber-optic hydrophone
system meet the demand of large dynamic range and large scale multiplexing. Optical system based on the heterodyne
demodulation is given. Reference signal in the demodulation procedure is obtained from the optical heterodyne output,
which is quite different from other reported heterodyne techniques. This method not only simplifies RF electronics, but
also eliminates the effects of frequency shift vibration generated by the acoustic-optic modulators. Demodulation
algorithm is presented and the maximum signal processing capability is analyze. Experiments are carried out and the
results show that a signal with a frequency of 1kHz and amplitude of 40rad could be demodulated without distortion
when the heterodyne frequency is 64kHz. The same signal is demodulated using PGC scheme with a modulating
frequency equal to the heterodyne frequency, and the result shows distortion. Comparing the two demodulation methods
verifies that the system we have designed works well and is more suitable for the detection of large signal. Besides, this
architecture of system offering advantage of easy to be time-division multiplexed. Together with wavelength-division
multiplexing, it demonstrates the potential for the fiber-optic hydrophone to achieve large-scale arrays with high dynamic
A kind of fiber optical temperature variety sensor based on fiber optical ring resonator is presented. The temperature variety causes the variety of the round-trip phase of the ring and the movement of the resonance dips. The magnitude and rate of the movement are proportional to the magnitude and rate of temperature variety, respectively. Through the measurement of the dips movement, the temperature variety can be sensed. In this paper, we make a theoretic analysis about the sensor, propose the system configuration, present a simple and effective signal detection method, and analyze the performance of the sensor. This kind of temperature sensor has such characteristics as high sensitivity, simple detection method, flexibly changeable sensitivity for different applications and temperature variety detection. Combined with the multiplex technology such as time division multiplexing (TDM), the sensor can form temperature variety sensor array for distributed fiber optic temperature detection.