Phase-sensitive optical time domain reflectometry (Φ-OTDR) realizes quantitative measurement of the dynamic strain employing phase demodulation. Unfortunately, it is difficult to measure large with conventional Φ-OTDR due restriction unwrapping algorithm. In this work, an approach based on two-wavelength probe proposed and demonstrated improve measurable range in Φ-OTDR. By utilizing difference between two phases acquiring different lasers, can be recovered. experiments, strains peak values...

An approach of phase-shift transform is proposed and demonstrated to suppress the interference fading in phase sensitive optical time domain reflectometry (Φ-OTDR). The executed digital complicated frequency modulation not required. operation principle carefully analyzed a signal with complementary amplitude can be obtained this method. Through synthesizing signals, false phases corrected. Benefiting from flexibility approach, multiple transforms are implemented make sure that all retrieved...

A phase demodulation algorithm in phase-sensitive optical time domain reflectometry (φ-OTDR) with self-interference balance detection is proposed. With a simple differentiate-and-cross-multiply (DCM) operation to acquire the perturbation waveform, and further second-order compensate amplitude fluctuation of phase, can be extracted accurately. The structure equivalently achieve function dual-pulse detection, but avoid negative impact common-mode noise difference between dual pulses on...

In phase-sensitive optical time domain reflectometry ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">Φ</mml:mi><mml:mtext>-</mml:mtext><mml:mrow class="MJX-TeXAtom-ORD"><mml:mi mathvariant="normal">O</mml:mi><mml:mi mathvariant="normal">T</mml:mi><mml:mi mathvariant="normal">D</mml:mi><mml:mi mathvariant="normal">R</mml:mi></mml:mrow></mml:math> ), false phase peaks caused by interference fading have been observed experimentally;...

A novel multi-frequency decomposition (MFD) scheme is proposed to achieve a fading-free phase-sensitive optical time-domain reflectometry ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi $ </tex-math></inline-formula> -OTDR). By performing short-time Fourier transform (STFT) on the detected signal, spectrum contents of normal probe pulse can be fully utilized and decomposed in time-frequency domain...

Stimulated Brillouin scattering (SBS)-based distributed fiber optic sensing technique has found pervasive applications in measurement of real-world environmental variables. Its capability, however, is affected by the tradeoff between distance and spatial resolution. Herein, we propose experimentally verify a wideband amplification (WBA)-boosted BOCDA to achieve high resolution longer distance. The WBA generated exploiting phase-uncorrelated SBS process pump probe waves. Through WBA, pulses...

A novel demodulation method for Sagnac loop interferometer based sensor has been proposed and demonstrated, by unwrapping the phase changes with birefringence interrogation. temperature on used to verify feasibility of method. Several tests 40 °C range have accomplished a great linearity 0.9996 in full range. The scheme is universal all sensors it unlimited linear measurable which overwhelming conventional peak/dip tracing. Furthermore, influence wavelength sampling interval span error...

The measurement accuracy of a Brillouin optical time domain analysis (BOTDA) fiber sensor is determined by the signal-to-noise ratio (SNR) received sensing signal. Here, new hybrid aperiodic coding method proposed to improve SNR. In method, two pre-discovered short seed codes (SA-codes) are used construct code (HA-code) in nested way. HA-code inherits good denoising capabilities SA-codes and features high gain. proof-of-concept experiment, SNR improvement up 8 dB obtained, which improves...

In this Letter, a chirped-pulse conversion algorithm (CPCA) is proposed to convert normal probe pulse into an equivalent chirped by convolving chirp factor on the received signal in coherent phase-sensitive optical time-domain reflectometry ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi mathvariant="normal">Φ</mml:mi> </mml:math> -OTDR). With algorithm, Rayleigh interference pattern (RIP) demodulation once applied -OTDR can be adopted quantify dynamic...

We present a viscosity sensing method based on fiber Bragg grating (FBG), which is longitudinally excited by an acoustic transducer. The reflection spectrum of the FBG broadened spatial modulation caused applied wave. bandwidth acoustically modulated decreases with increasing liquid surrounding FBG. mechanism relies reduction in spatially periodic strain fluid. Experimental results show that changes from 0.41 to 0.27 nm as increases 1.0 5.5 mPa·s.

A Brillouin phase spectra (BPS) demodulation approach in optical time-domain analysis (BOTDA) based on to intensity conversion is proposed and demonstrated. By utilizing the cascaded modulation of probe light coherent detection a symmetric double-sidebands BOTDA, shift transferred into signal so that it can be recovered with simple envelope detection. Moreover, measurement accuracy significantly improved by reduction noise caused fiber transmission. 2-m spatial resolution over 39.1-km 0.7 °C...

An approach of backscattering Rayleigh light detection has been prosed to compensate the nonlocal effect in BOTDA. A hotspot measured accurately at end 39-km sensing fiber. Brillouin frequency shift error 13MHz induced by 2dBm probe power corrected.

A new method for viscosity measurement has been proposed based on the acousto-optic modulation FBG. Theoretical analysis shows bandwidth of modulated FBG is related to liquid around The experimental results show sensitivity as increases from 1 mPa·s 5.5 mPa·s.

We describe a computer simulation technique for generating the monochromatic light diffraction from arbitrary apertures. For Fresnel of rectangular and circular apertures, simple form equation intensity distribution is derived. A method displaying color on monitor presented. On this basis, we implement white formed via mixing three lights λ=700,546.1,435.8 nm with same ratio in RGB space CIE1931 system.

A co-propagating dual-wave interferometer- assisted Brillouin optical time domain analysis (DWI-BOTDA) integrated sensing system is proposed and experimentally demonstrated for high sampling rate dynamic sensing. Fast strain measurement achieved by the DWI based on analyzing relative phase variation between two light waves with significantly improved range (DSMR). Meanwhile, BOTDA spatial resolution employed to locate events accurately. In experiment, enhancements DSMR stability in are...

A phase demodulation method immune to laser noise based on time-delay beat-frequency coherent Φ-OTDR is proposed. In this method, the two Rayleigh backscattered light beams with time delay are beat local respectively, and difference of signals used instead traditional distance-difference obtain disturbance information. way, impact introduce by avoid, constraint linewidth performance weakened. experiment, a accuracy -63.5dB rad <sup xmlns:mml="http://www.w3.org/1998/Math/MathML"...

A novel birefringence measurement method was developed to interrogate the Sagnac loop interferometer based sensor. The response is linearized in full sensing range and not restricted by free spectrum range.

We propose a frequency splicing code-based Brillouin optical time domain collider (FSC-BOTDC) for fast dynamic sensing. By delicately designing the code (FSC), multiple collision modes with controllable characteristics are realized probing target areas high sampling rate. Moreover, sensing system is simpler and more robust than previous BOTDC. In experiment, FSC-BOTDC 10-time enhanced rate implemented single measurements. Results demonstrate that tailorable measurements can be achieved by...