Frequency-comb-based BOTDA sensors for high-spatial-resolution/long-distance sensing.

Frequency-comb-based Brillouin optical time-domain analysis (BOTDA) sensors were developed to achieve acquisition-time reduction and high-spatial-resolution/long-distance sensing simultaneously. We found that, for the standard frequency-comb-based BOTDA, the use of a double-sideband (DSB) pulse generates a series of pulse pairs that simultaneously propagate along the sensing fiber, leading to a nonlinear interaction between the two sidebands of each frequency comb pulse, and a significant splitting of the Brillouin gain spectrum (BGS). This problem prevents its application in high-spatial-resolution sensing due to the higher pulse power requirement. Thus, one of the sidebands of DSB pulse was proposed for greatly suppressing the BGS distortion. In combination with the phonon pre-excitation technique based on phase-shifted pulse, a sensor with a spatial-resolution approximately 60 cm along a fiber approximately 592 m in length was demonstrated. Furthermore, we explored the detailed performance of long-distance sensing by frequency- comb-based BOTDA. The use of a frequency comb for the probe wave can suppress the pulse distortion and non-local effect, which is helpful for extending the sensing distance. A spatial resolution of approximately 6 m along a sensing fiber approximately 74.2 km in length was successfully demonstrated.

BOTDA sensors enhanced using high-efficiency second-order distributed Brillouin amplification.

A novel approach for long-distance sensing through Brillouin optical time-domain analysis (BOTDA) assisted by second-order distributed Brillouin amplification (DBA) was proposed and experimentally demonstrated. To the best of our knowledge, this is the first BOTDA study that used second-order DBA. Compared with BOTDA assisted by first-order DBA, the proposed approach enhanced the signal-to-noise ratio of the Brillouin trace by ~3 dB for a range featuring minimum sensing intensity. Long-distance sensing with ~5 m spatial resolution and ± 1.6°C measurement uncertainty over ~99 km fiber was successfully realized by employing high-efficiency pumping using ~6 dBm second-order and ~1.5 dBm first-order pumps.

Syndrome Differentiation Analysis on Mars500 Data of Traditional Chinese Medicine.

Mars500 study was a psychological and physiological isolation experiment conducted by Russia, the European Space Agency, and China, in preparation for an unspecified future manned spaceflight to the planet Mars. Its intention was to yield valuable psychological and medical data on the effects of the planned long-term deep space mission. In this paper, we present data mining methods to mine medical data collected from the crew consisting of six spaceman volunteers. The synthesis of the four diagnostic methods of TCM, inspection, listening, inquiry, and palpation, is used in our syndrome differentiation. We adopt statistics method to describe the syndrome factor regular pattern of spaceman volunteers. Hybrid optimization based multilabel (HOML) is used as feature selection method and multilabel k-nearest neighbors (ML-KNN) is applied. According to the syndrome factor statistical result, we find that qi deficiency is a base syndrome pattern throughout the entire experiment process and, at the same time, there are different associated syndromes such as liver depression, spleen deficiency, dampness stagnancy, and yin deficiency, due to differences of individual situation. With feature selection, we screen out ten key factors which are essential to syndrome differentiation in TCM. The average precision of multilabel classification model reaches 80%.

Analysis of all-optical temporal integrator employing phased-shifted DFB-SOA.

All-optical temporal integrator using phase-shifted distributed-feedback semiconductor optical amplifier (DFB-SOA) is investigated. The influences of system parameters on its energy transmittance and integration error are explored in detail. The numerical analysis shows that, enhanced energy transmittance and integration time window can be simultaneously achieved by increased injected current in the vicinity of lasing threshold. We find that the range of input pulse-width with lower integration error is highly sensitive to the injected optical power, due to gain saturation and induced detuning deviation mechanism. The initial frequency detuning should also be carefully chosen to suppress the integration deviation with ideal waveform output.

Ultra-long high-sensitivity Φ-OTDR for high spatial resolution intrusion detection of pipelines.

An ultra-long phase-sensitive optical time domain reflectometry (Φ-OTDR) that can achieve high-sensitivity intrusion detection over 131.5km fiber with high spatial resolution of 8m is presented, which is the longest Φ-OTDR reported to date, to the best of our knowledge. It is found that the combination of distributed Raman amplification with heterodyne detection can extend the sensing distance and enhances the sensitivity substantially, leading to the realization of ultra-long Φ-OTDR with high sensitivity and spatial resolution. Furthermore, the feasibility of applying such an ultra-long Φ-OTDR to pipeline security monitoring is demonstrated and the features of intrusion signal can be extracted with improved SNR by using the wavelet detrending/denoising method proposed.

[94 km Brillouin distributed optical fiber sensors based on ultra-long fiber ring laser pumping].

A novel optical amplification configuration based on ultra-long fiber laser with a ring cavity was proposed and applied to Brillouin optical time-domain analysis (BOTDA) sensing system, in order to extend the measurement distance significantly. The parameters used in the experiment were optimized, considering the main limitations of the setup, such as depletion, self-phase modulation (SPM) and pump-signal relative intensity noise (RIN) transfer. Through analyzing Brillouin gain spectrum, we demonstrated distributed sensing over 94 km of standard single-mode fiber with 3 meter spatial resolution and strain/temperature accuracy of 28 /1. 4 degree C.

Random-lasing-based distributed fiber-optic amplification.

The gain and noise characteristics of distributed Raman amplification (DRA) based on random fiber laser (RFL) (including forward and backward random laser pumping) have been experimentally investigated through comparison with conventional bi-directional 1st-order and 2nd-order pumping. The results show that, the forward random laser pumping exhibits larger averaged gain and gain fluctuation while the backward random laser pumping has lower averaged gain and nonlinear impairment under the same signal input power and on-off gain. The effective noise figure (ENF) of the forward random laser pumping is lower than that of the bi-directional 1st-order pumping by ~2.3 dB, and lower than that of bi-directional 2nd-order pumping by ~1.3 dB at transparency transmission, respectively. The results also show that the spectra and power of RFL are uniquely insensitive to environmental temperature variation, unlike all the other lasers. Therefore, random-lasing-based distributed fiber-optic amplification could offer low-noise and stable DRA for long-distance transmission.

Distributed Raman amplification using ultra-long fiber laser with a ring cavity: characteristics and sensing application.

Distributed Raman amplification (DRA) based on ultra-long fiber laser (UL-FL) pumping with a ring cavity is promising for repeaterless transmission and sensing. In this work, the characteristics (including gain, nonlinear impairment and noise figure) for forward and backward pumping of the ring-cavity based DRA scheme are fully investigated. Furthermore, as a typical application of the proposed configuration, ultra-long-distance distributed sensing with Brillouin optical time-domain analysis (BOTDA) over 142.2 km fiber with 5m spatial resolution and ± 1.5 °C temperature uncertainty is achieved, without any repeater. The key point for the significant performance improvement is the system could offer both of uniform gain distribution and considerably suppressed pump-probe relative intensity noise (RIN) transfer, by optimized design of system structure and parameters.

Hybrid distributed Raman amplification combining random fiber laser based 2nd-order and low-noise LD based 1st-order pumping.

A configuration of hybrid distributed Raman amplification (H-DRA), that is formed by incorporating a random fiber laser (RFL) based 2nd-order pump and a low-noise laser-diode (LD) based 1st-order pump, is proposed in this paper. In comparison to conventional bi-directional 1st-order DRA, the effective noise figure (ENF) is found to be lower by amount of 0 to 4 dB due to the RFL-based 2nd-order pump, depending on the on-off gain, while the low-noise 1st-order Raman pump is used for compensating the worsened signal-to-noise ratio (SNR) in the vicinity towards the far end of the fiber and avoiding the potential nonlinear impact induced by excess injection of pump power and suppressing the pump-signal relative intensity noise (RIN) transfer. As a result, the gain distribution can be optimized along ultra-long fiber link, due to combination of the 2nd-order RFL and low-noise 1st-order pumping, making the transmission distance be extended significantly. We utilized such a configuration to achieve ultra-long-distance distributed sensing based on Brillouin optical time-domain analysis (BOTDA). A repeater-less sensing distance record of up to 154.4 km with 5 m spatial resolution and ~ ± 1.4 °C temperature uncertainty is successfully demonstrated.

Low threshold 2nd-order random lasing of a fiber laser with a half-opened cavity.

In this paper, we reported the realization of 2nd-order random lasing in a half-opened fiber cavity, which is formed by a FBG with central wavelength at the 1st-order Raman Stokes wavelength and a single-mode fiber (SMF) performing as a random distributed feedback mirror. Using this proposed method, the threshold of 1st-order (2nd-order) random lasing is reduced to 0.7 (2.0) W, which is nearly 2 times lower than that observed in a completely-opened cavity.

Analysis of bistable steady characteristics and dynamic stability of linearly tapered nonlinear Bragg gratings.

Based on the nonlinearly coupled mode equations (NLCME), the bistable steady characteristics and dynamic stability of linearly tapered nonlinear Bragg grating (LT-NLBG) have been investigated in detail. The results show that, when the device is tuned near an edge of "photonic band gap" (PBG), in contrast with the free-tapered grating, the negative-tapered grating enhances the switching-on threshold, but increases the on-off switching ratio, enlarges the stable regime, and strengthens the stability significantly. On the other hand, the positive-tapered grating decreases the switching-on threshold, but lower the on-off switching ratio, and worsen the stability remarkably.