The physical mechanism of gain motivation is the main theoretical bottleneck that restricts the signal-to-noise ratio (SNR) and results in a mono-merit implementation for the existing stimulated Brillouin scattering-based fiber sensors. A phase-chaos laser (PCL) is proposed and introduced in the Brillouin optical correlation domain analysis (BOCDA) scheme to promote the SNR and achieve a high-accuracy measurement. The PCL characteristics are presented, and a theoretical model of chaos gain accumulation and extraction is perfected. Then, the simulation results reveal that the SNR is improved by 5.56 dB, and the signal-to-background noise ratio (SBR) of the Brillouin gain spectrum (BGS) is promoted by 8.28 dB with a 100-km sensing distance. Further, the PCL is experimentally generated. In the proof-of-concept experiment, the accuracy of the Brillouin frequency shift is upgraded to ±0.64 MHz, and the SBR of BGS is improved by 10.77 dB. The PCL provides a new research direction for optical chaos, and the PCL-BOCDA showcases a promising future for optimal-merit-coupling sensing and its application.
We propose and experimentally demonstrate a long-range chaotic Brillouin optical correlation domain analysis by employing an optimized time-gated scheme and differential denoising configuration, where the number of effective resolving points largely increases to more than one million. The deterioration of the chaotic Brillouin gain spectrum (BGS) and limitation of sensing range owing to the intrinsic noise structure, resulting from the time delay signature (TDS) and nonzero background of chaotic laser, is theoretically analyzed. The optimized time-gated scheme with a higher extinction ratio is used to eliminate the TDS-induced impact. The signal-to-background ratio of the measured BGS is enhanced by the differential denoising scheme to furthest remove the accumulated nonzero noise floor along the fiber, and the pure chaotic BGS is ulteriorly obtained by the Lorentz fit. Ultimately, distributed strain sensing along a 27.54-km fiber with a 2.69-cm spatial resolution is experimentally demonstrated, and the number of effective resolving points is more than 1,020,000.
We proposed and experimentally demonstrated a distributed optic-fiber sensor based on the Raman loop configuration and fiber loss characteristic for detecting the temperature and structure's crack. Among them, the Raman loop configuration with reference fiber is proposed to detect the temperature profile along the sensing fiber. It can eliminate the influence of external physical perturbation on the temperature measurement results, and don't require pre-calibration process before measurement. This proposed method improves the engineering applicability of optic-fiber sensors. In addition, the information of crack is detected by using the fiber loss characteristics based on OTDR technology.
Two novel configurations of multi-parameter fiber-optic sensing systems based on the fiber random grating are reported. The fiber random grating is fabricated through femtosecond laser induced refractive index modification over a 10cm standard telecom single mode fiber. In one configuration, the reflective spectrum of the fiber random grating is directly detected and a wavelength-division spectral cross-correlation algorithm is adopted to extract the spectral shifts for simultaneous measurement of temperature, axial strain, and surrounding refractive index. In the other configuration, a random fiber ring laser is constructed by incorporating the random feedback from the random grating. Numerous polarization-dependent spectral filters are formed along the random grating and superimposed to provide multiple lasing lines with high signal-to-noise ratio up to 40dB, which enables a high-fidelity multi-parameter sensing scheme by monitoring the spectral shifts of the lasing lines. Without the need of phase mask for fabrication and with the high physical strength, the random grating based sensors are much simpler and more compact, which could be potentially an excellent alternative for liquid medical sample sensing in biomedical and biochemical applications.
A polarization optical time-domain reflectometer (POTDR) can distributedly measure the vibration of fiber by detecting the vibration induced polarization variation only with a polarization analyzer. It has great potential in the monitoring of the border intrusion, structural healthy, anti-stealing of pipeline and so on, because of its simple configuration, fast response speed and distributed measuring ability. However, it is difficult to distinguish two vibrations with the same frequency for POTDR because the signal induced by the first vibration would bury the other vibration induced signal. This paper proposes a simple method to resolve this problem in POTDR by analyzing the phase of the vibration induced signal. The effectiveness of this method in distinguishing two vibrations with the same frequency for POTDR is proved by simulation.
We experimentally investigated the wavelength matching between the probe light and injection-locked modes of FP-LD
(Fabry-Perot laser diode) for wavelength conversion configuration. Wavelength conversion from 1552.9nm to 1548.5nm
was obtained experimentally based on cross-gain modulation with the 10GHz repetition rate optical pulse train in a
FP-LD. Our results indicate that there always exists a selected longitudinal mode of the probe light in the FP-LD to
maximize the extinction ratio of the conversion signal. Moreover, there also exists an optimum injection signal pulse
power to improve the conversion signal further under the same matching mode of probe light wavelength with the
constant input power, and the constant detuning between the probe light and signal pulse wavelengths and the locked
modes of FP-LD with a certain bias current range.
We propose and experimentally demonstrate a novel technique that uses a single Fabry-Perot laser diode (FP-LD) to
perform simultaneous all-optical clock division and wavelength conversion. Utilizing the period-two oscillations
characteristics in an optically injected semiconductor laser and the cross-gain modulation effect of the injection locked
semiconductor laser, we achieve the simultaneous all optical clock division and wavelength conversion in a single FP-LD.
Clock frequency division of 12.8 GHz to 6.4 GHz with simultaneous wavelength conversion from 1550.24 nm to
1545.91 nm is obtained. The experimental results indicate there is a certain injection signal power to obtain stable clock
frequency division in an optimum wavelength detuning. It was empirically found that the best clock division and
wavelength conversion occurred when the injected signal power was approximately 2~2.5 times as the injected probe
light power, and the range of optimum wavelength detuning was about from -0.01 nm to 0.06 nm. Moreover, the FP-LD's
bias current also influence the clock frequency divisions, we demonstrate that the most effective conversion can be
obtain when bias current is located in the range of 1.6Ith~2.3Ith. The experimental investigations further show that there
is an optimum matching mode between the FP-LD and the probe light for obtaining the largest extinction ratio in
wavelength conversion.
We experimentally study the period doubling phenomenon of gain-switched multiple quantum well Fabry-Perot laser
diodes with/without external optical injection. The relations between resonance frequency and modulation frequency are
analyzed detailedly when period doubling occurs. The obtained research results indicate that external optical injection
may be an effective technique to suppress or enhance period doubling of a gain switched laser diode with injection
optical power. Experiments show that the period doubling would appear in a broader frequency range with external
optical injection, and indicate that period doubling occurs over a wide range of modulation frequency in laser diode as
the injection power increases. Moreover, we have studied in detail that period doubling easily occurs when bias current is
located between 1.1Ith and 1.3Ith, and modulation current is set between 0.5Idc and 2.5Idc.
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