Phase-sensitive correlation optical time-domain reflectometer using quantum phase noise of laser light

Ultra-long chaotic FBG sensing with high-order random fiber lasing amplification

We propose and demonstrate an ultra-long chaotic fiber Bragg grating (FBG) sensing system based on wavelength-scanning correlation optical time-domain reflectometry (COTDR) assisted by sixth-order random fiber lasing amplification (RFLA). Cascaded random Raman fiber lasing generated in the long fiber span can provide up to sixth-order distributed Raman amplification for the chaotic probe light and its echo signal without ruining the chaotic behavior, which can significantly extend the sensing distance of COTDR. As a result, a 152-km-long wavelength-scanning COTDR is experimentally demonstrated to simultaneously realize FBG sensing and location with a spatial resolution as high as 6 cm, which is the longest COTDR to the best of our knowledge. Temperature sensing of the specific FBG is performed, and the temperature sensitivity of the proposed system is 0.25 dB/°C with a good linearity. The proposed chaotic FBG sensing system with high-order RFLA can act as a new platform for ultra-long, large-capacity FBG sensing, which has potential applications in overhead transmission powerline monitoring and structural health monitoring.

Passive quadrature demodulation of multiplexed interferometric sensors using a CW correlation reflectometer with a single DFB diode laser

In this Letter, we report a novel, to the best of our knowledge, and simple approach for passive quadrature-phase demodulation of relatively long multiplexed interferometers based on two-channel coherence correlation reflectometry. Two-wavelength channels are generated using a single unmodulated CW-DFB diode laser and an acousto-optic frequency shifter. The introduced frequency shift determines the optical lengths of the interferometers. In our experiments, all interferometers have the same optical length of 32 cm corresponding to the π/2 phase difference between channel signals. An additional fiber delay line was introduced between channels to destroy coherence between initial and frequency-shifted channels. Demultiplexing of channels and sensors was performed using correlation-based signal processing. Amplitudes of cross correlation peaks obtained for both channels were used to extract the interferometric phase for each interferometer. Phase demodulation of relatively long multiplexed interferometers is experimentally demonstrated. Experimental results prove that the proposed technique is suitable for interrogating a serial array of relatively long interferometers dynamically modulated with phase excursions exceeding 2π. Simultaneous interrogation and phase demodulation were experimentally demonstrated using an in-line array of low-finesse Fabry-Perot interferometric sensors.

Correlation-based multiplexing of spectral channels and fiber-optic sensors using unmodulated continuous-wave distributed feedback diode lasers

In this Letter, we demonstrate a method for the multiplexing of spectral channels and fiber-optic sensors. The method makes use of the correlation-based demultiplexing technique. In our approach, each light source has an inherent phase noise which we propose to use as a "fingerprint" for correlation-based recognition and demultiplexing of spectral channels as well as signals from different sensors in each spectral channel. The proposed method requires for its implementation an extremely simple and robust scheme and can be attractive for budget-sensitive applications. As active elements, it uses only two standard free-running CW distributed feedback (DFB) diode lasers. No modulators or optical filters are required for operation. Results of proof-of-concept experiments are presented for the interrogation of several ultra-weak fiber Bragg gratings (FBGs) with reflectivity of 0.05% in a 4-km-long fiber for temperature measurements with the resolution of 0.1°C.

Generation of random on-off modulation pulses by optically injecting a gain-switched Fabry-Pérot semiconductor laser with a dual-mode injection for random-modulation pulsed lidar applications

We study the generation of random on-off modulation pulses by optically injecting a gain-switched Fabry-Pérot semiconductor laser with a dual-mode injection for random-modulation pulsed lidar applications. In the dual-mode injection scheme proposed, the first master laser (ML1) injecting on a resonant sidemode of the gain-switched slave laser (SL) randomly locks such injected sidemode and suppresses the output pulses in the center mode through gain-competition. The second master laser (ML2) injecting on the center mode then stabilizes and enhances the output pulses to have equal amplitudes suitable for digital threshold detection and time-correlated single photon counting. Under different injection conditions, we identify dynamical states including unlocked, stable locking, bistable, and instability. By operating the laser in the bistable states randomly switching between the unlocked and stable locking states, we successfully generate random on-off modulation pulses without employing any digital circuits or external modulators. We analyze the signal-to-noise ratio (SNR) and detection probability of the proposed scheme to show its feasibility in random-modulation pulsed lidar applications. Moreover, we study its anti-interference capability by adding interference from additional channels with similar modulated pulses. We show that, with injection strengths of 0.418 and 0.038 from the ML1 and ML2 and a correlation length T_c = 90 µs, a detection probability of 1 can be readily achieved even under the interference from more than 49 additional channels.