Mohammad Taki

Simplex-Coded BOTDA Sensor Over 120-km SMF With 1-m Spatial Resolution Assisted by Optimized Bidirectional Raman Amplification

Bidirectional low-noise Raman amplification and simplex coding based on the return-to-zero modulation format are optimized through numerical simulations for long-range Brillouin optical time-domain analysis sensing. Experimental results are reported on sensing capabilities along 120-km distance with 1-m spatial resolution, and worst-case temperature and strain resolution values of 1.3 and 26 , respectively.

Optimization of a DPP-BOTDA sensor with 25 cm spatial resolution over 60 km standard single-mode fiber using Simplex codes and optical pre-amplification

Sub-meter distributed optical fiber sensing based on Brillouin optical time-domain analysis with differential pulse-width pairs (DPP-BOTDA) is combined with the use of optical pre-amplification and pulse coding. In order to provide significant measurement SNR enhancement and to avoid distortions in the Brillouin gain spectrum due to acoustic-wave pre-excitation, the pulse width and duty cycle of Simplex coding based on return-to-zero pulses are optimized through simulations. In addition, the use of linear optical pre-amplification increases the receiver sensitivity and the overall dynamic range of DPP-BOTDA measurements. Experimental results demonstrate for first time a spatial resolution of ~25 cm over a 60 km standard single-mode fiber (equivalent to ~240 k discrete sensing points) with temperature resolution of 1.2°C and strain resolution of 24 με.

Cyclic pulse coding for fast BOTDA fiber sensors

A cyclic pulse coding technique is proposed and experimentally demonstrated for fast implementation of long-range Brillouin optical time-domain analysis (BOTDA). The proposed technique allows for accurate temperature and strain measurements with meter-scale spatial resolution over kilometers of standard single-mode fiber, with subsecond measurement times.

Hybrid Raman/fiber Bragg grating sensor for distributed temperature and discrete dynamic strain measurements

We propose and experimentally demonstrate a hybrid fiber optic sensing technique that effectively combines Raman optical time domain reflectometry and in-line time-division-multiplexing for fiber Bragg grating (FBG) dynamic interrogation. The highly integrated proposed scheme employs broadband apodized low reflectivity FBGs with a single narrowband optical source and a shared receiver block, allowing for simultaneous measurements of distributed static temperature and discrete dynamic strain, over the same sensing fiber.

Long-range accelerated BOTDA sensor using adaptive linear prediction and cyclic coding

We propose and experimentally demonstrate a long-range accelerated Brillouin optical time domain analysis (BOTDA) sensor that exploits the complementary noise reduction benefits of adaptive linear prediction and optical pulse coding. The combined technique allows using orders of magnitude less the number of averages of the backscattered BOTDA traces compared to a standard single pulse BOTDA, enabling distributed strain measurement over 10 km of a standard single mode fiber with meter-scale spatial resolution and 1.8 MHz Brillouin frequency shift resolution. By optimizing the system parameters, the measurement is achieved with only 20 averages for each Brillouin gain spectrum scanned frequency, allowing for an eight times faster strain measurement compared to the use of cyclic pulse coding alone.

Hybrid BOTDA/FBG sensor for discrete dynamic and distributed static strain/temperature measurements

We propose and experimentally demonstrate a hybrid fiber optic sensing technique that effectively combines Brillouin optical time-domain analysis and a time-domain multiplexing interrogation technique for Fiber Bragg Gratings (FBGs). The highly-integrated proposed scheme employs broadband apodized low-reflectivity FBGs with a single optical source and a shared receiver block, allowing for simultaneous measurements of distributed static and discrete dynamic temperature and strain, over the same sensing fiber.

High-performance hybrid Raman/fiber Bragg grating fiber-optic sensor based on simplex cyclic pulse coding

We propose and experimentally demonstrate the use of cyclic pulse coding to improve the performance of hybrid Raman/fiber Bragg grating (FBG) fiber-optic sensors, for simultaneous measurement of distributed static temperature and discrete dynamic strain over the same sensing fiber. Effective noise reduction is achieved in both Raman optical time-domain reflectometry and dynamic interrogation of time-division-multiplexed fiber FBG sensors, enhancing the sensing range resolution and providing real-time point dynamic strain measurement capabilities. The highly integrated sensor scheme employs broadband apodized low-reflectivity FBGs, a single narrowband optical source, and a shared receiver block.

Study of Raman amplification in DPP-BOTDA sensing employing Simplex coding for sub-meter scale spatial resolution over long fiber distances

Abstract The impact of Raman amplification and Simplex coding is studied in combination withdifferential pulse-width pair Brillouin optical time-domain analysis (DPP-BOTDA) to achievesub-meter spatial resolution over very long sensing distances. An optimization of the powerlevels for the Raman pumps, Brillouin pump and signal has been carried out through numericalsimulations, maximizing the signal levels and avoiding at the same time nonlinear effects andpump depletion. A reduction of acoustic-wave-induced distortions in the Brillouin gainspectrum down to negligible levels has also been achieved by numerical optimization of thepulse width and duty cycle of return-to-zero Simplex coding, providing significantsignal-to-noise ratio enhancement. Strain–temperature sensing over 93 km standard SMF isachieved with a strain / temperature accuracy of 34 μe/ 1.7 ◦ C, and 50 cm spatial resolutionthroughout the fiber length. Keywords: fiber optics, sensors, Brillouin scattering, coding(Some figures may appear in colour only in the online journal)

High Performance Time Domain FBG Dynamic Interrogation Scheme Based on Pulse Coding

A novel method to improve the measurement range, resolution, and multiplexing capability of time division multiplexed (TDM) fiber Bragg grating (FBM) sensors, based on advanced cyclic pulse coding, is proposed and experimentally demonstrated. The mechanism of noise reduction by quasi-periodic cyclic coding is quantitatively demonstrated, pointing out significant improvement in dynamic strain resolution with respect to single pulse TDM FBG interrogation. The use of cycling pulse coding allows for enhanced dynamic performance of real time strain measurement with respect to other coding techniques. The proposed technique can also enhance the sensing range of hybrid optical fiber sensor systems in which continuous static temperature/strain distributions and discrete dynamic strain in specific critical points are simultaneously measured over the same sensing fiber.

Optimized Hybrid Raman/Fast-BOTDA Sensor for Temperature and Strain Measurements in Large Infrastructures

An optimized hybrid Raman/BOTDA optical fiber sensor based on cyclic Simplex pulse coding is proposed to overcome temperature and strain cross-sensitivity issues, allowing at the same time fast implementation of Brillouin optical time domain analysis with subsecond measurement times. By providing a real-time diagnostic system for safe operation, the proposed sensor can play a key role for in-service monitoring of large critical infrastructures. Experimental results demonstrate the capability of the proposed technique to effectively discriminate the Brillouin frequency shift contributions due to strain and temperature variations simultaneously applied to the same fiber section along 10 km of standard single mode optical fiber, with 1-m spatial resolution and a worst-case strain resolution value of 62 με. The proposed scheme uses a single narrowband laser source and one sensing fiber only.