The characteristics of bi-periodic sensitivity of semiconductor laser and its application in the incoherent light detection sensor are studied. From the simulation results, it can be found that the unmoving point of an optoelectronic time-delay feedback semiconductor laser shifts when there is external light injection, two unmoving points are conduced to show, and implies high instability dynamics existing in the system. So the external light injection will inevitably result in destructing the referent laser state condition and changing the state, thus the incoherent light intensity change can be monitored via detecting the referent state change. In this paper, a bi-periodic optical pulse is generated by the optoelectronic time-delay feedback semiconductor laser, and the bi-periodic laser system is used as a sensor for incoherent light detection. A bi-periodic state in the laser is a highly unstable nonlinear dynamic state, it is very sensitive to external conditions and influences. When a beam of external incoherent light enters into the bi-periodic laser sensor, it will inevitably lead to the destruction of the bi-periodic state condition and the state variation. A novel bi-periodic laser incoherent light detection sensor is proposed based on the above principle. By using this sensor, the injected incoherent light can be used as the sensor's recognition signal, and by detecting the change of the laser output behavior, the external incoherent light intensity can be measured. The simulation results show that the sensor has high ability to recognize the injected incoherent light and can measure it accurately. The results of the proposed sensor are quite useful for the research of new laser sensor and application of photoelectric detection technology
We study control-chaos of a dual-ring erbium-doped fiber laser using an anti-parameter pair modulation. And we study this control-chaos method via the inverse modulation of the gain parameters of two key physical parameters of the dualring erbium-doped fiber laser. In terms of physical mechanism, the optical effects of alternating excitation or alternating attenuation of two gain parameters of the laser are found. The control of chaos laser and its new nonlinear dynamic changes are derived. In the control mechanism, the double-parameter reverse modulation pair is found where the laser behavior is very sensitive to the anti-parameter pair modulation because this reverse action modulation combines with induction control dynamic changes. The laser can be controlled to a single-periodic state, a double-periodic state, a threeperiodic state, a four-periodic state, a five-periodic state, a six-periodic state, a seven-periodic state and other highperiodic states. Double-dynamics, frequency controlled-locking and semi-frequency controlled-locking regions are found. The laser exhibits a very imaginative dynamic behavior that has never been seen before, which has important reference value for the study of chaos dynamics, laser technology and control technology.
The phase-sensitive optical time-domain reflectometry (Φ-OTDR) has been developed rapidly as a fully fiber-optic distributed vibration sensing technology. However, the demodulation technique based on the phase term would induce a serious false alarm problem due to the signal fading effect. An effective method to suppress fading-induced false alarms in the Φ-OTDR system is proposed, which is based on the suppression mask and numerical relationship between phase and amplitudes of Rayleigh backscattering. The performance of the proposed method has been experimentally demonstrated in both laboratory environment and in-field situation test. Without any hardware addition in a traditional Φ-OTDR equipment, false alarms rate can be reduced from 4.81% to 0.15%, whereas low missing alarms rate can be achieved at the same time. In-field results show that this work provides a low-cost solution to enhance the performance for real-life engineering application of the phase-discrimination Φ-OTDR system.
KEYWORDS: Signal to noise ratio, Filtering (signal processing), Electronic filtering, Digital signal processing, Signal processing, Reflectometry, Optical filters, Interference (communication), Wavelets, Denoising
Phase-sensitive optical time-domain reflectometry (ϕ-OTDR) has been widely used to interrogate multipoint vibration events in the health monitoring of large-scale infrastructures. Since high signal-to-noise ratio (SNR) is the core parameter for evaluating the performance of ϕ-OTDR, many researchers have presented digital signal processing (DSP) methods for SNR enhancement. However, the DSP methods using fixed parameters cannot achieve the optimum SNR for different vibration events. In addition, although transform domain analysis methods such as wavelet transform could provide multiscale observation for target events, a large amount of computation would be required simultaneously. Matched filtering is a commonly used technique to extract noisy signals in traditional wireless radar systems. Mathematical theory has indicated that matched filtering is also suitable for signal extraction in ϕ-OTDR. The optimization of system performance could be realized when the filter scale matches the length of vibration events. For different lengths of disturbance region, a multiscale matching filtering method has been proposed, which makes it possible to choose appropriate filter scale and finally obtain the optimal SNR. Experimental results have shown that the proposed multiscale matching filtering method could improve the SNR by over 6 dB even under strong noise influence and reach the lowest locating uncertainty of 0.49 m with low time consumption, compared to conventional methods.
An improved data processing and analysis method is proposed to realize simultaneous monitor of multiple vibrations using polarization optical time domain reflectometry system. In our method, a differential trace of the frequency component along the fiber is got by doing subtraction of the distance traces with different number of vibrations at a certain frequency, and the vibrations vibrating at different time can be located by analyzing the response power variation of the differential trace. For multiple vibration points vibrating with the same frequency and at the same time, multiple vibration events can also be distinguished by extracting the modulated frequency component, and the frequency component is obtained at the starting or ceasing state of the vibrations because the initial phases of vibration sources are unsteady and different. With our method, a POTDR sensing system which can simultaneously monitor multiple vibration points over 3km with 10m spatial resolution is demonstrated.
Factors that affect the transient effect on small duty-cycle pulse in a cascaded erbium-doped fiber amplifier (EDFA) system are studied in simulation and experiment. The considered factors consist of the numbers of cascaded EDFAs, the peak power and the extinction ratio of optical pulse, with results showing that the optical pulse will be severely distorted by the transient effect of EDFA. The distortion becomes more serious with the increase of the three parameters. To avoid or mitigate the transient effect, a method of adding another optical signal with a different wavelength to the objective pulse is employed in the experiment. The experimental results show that this method could effectively restrain the transient effect in a cascaded EDFA system.
The technology of Polarization Optical Time Domain Reflectometer (POTDR) can be used to obtain the external
events' information by measuring the change of state of polarization (SOP) of the Rayleigh backscattering in fiber. When
the fiber is disturbed at two different positions simultaneously, we analyze the frequency spectrums of the change of
Rayleigh backscattering light which are obtained by POTDR theoretically for ideal fiber, and by numerical simulation
for single mode fibers. We find that the frequency spectrums between the first and second events contain the first
vibration's frequency and its frequency multiplication. The frequency components of the spectrums after the second
event are the linear combination of the first and the second events' frequencies. So we can obtain the location and the
frequency information of the two events by analyzing the frequency spectrums. In addition, the frequency distribution in
the frequency spectrums from different positions are different because of the different initial SOPs at different positions.
So all the actual frequency information can not be obtained from only one frequency spectrum. We add up the frequency
spectrums from the positions within a beat length to obtain the perturbation's frequency and the method can reduce the
misdiagnosis rate because the sum of the frequency spectrums contains all the initial SOP within a beat length.
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