G. Bolognini

Simplex-coded BOTDA fiber sensor with 1 m spatial resolution over a 50 km range

In this Letter, we propose the use of optical pulse coding techniques for long-range distributed sensors based on Brillouin optical time-domain analysis (BOTDA). Compared to conventional BOTDA sensors, optical coding provides a significant sensing-range enhancement, allowing for temperature and strain measurements with 1 m spatial resolution over 50 km of standard single-mode fiber, with an accuracy of 2.2 degrees C/44 muepsilon, respectively.

Analysis of distributed temperature sensing based on Raman scattering using OTDR coding and discrete Raman amplification

The behaviour of distributed temperature sensors based on spontaneous Raman scattering and coded OTDR (optical time domain reflectometry) is studied both theoretically and experimentally; in particular a high performance scheme has been implemented using amplitude modulation according to Simplex coding, direct detection and additional use of lumped Raman amplification to further extend the sensing range. An efficient and cost-effective distributed temperature sensing system operating along 30 km of dispersion-shifted fibre with 17 m spatial resolution and 5 K temperature resolution is theoretically demonstrated and experimentally achieved using 255 bit Simplex coding and low-power commercially available laser diodes (80 mW CW power). Use of lumped Raman amplification to produce high-power coded pulses allows further 10 km distance enhancement, resulting in a total measurement range of 40 km.

Analysis of pulse modulation format in coded BOTDA sensors

A theoretical and experimental analysis of the impact of pulse modulation format on Brillouin optical time-domain analysis (BOTDA) sensors using pulse coding techniques has been carried out. Pulse coding with conventional non-return-to-zero (NRZ) modulation format is shown to induce significant distortions in the measured Brillouin gain spectrum (BGS), especially in proximity of abrupt changes in the fiber gain spectra. Such an effect, as confirmed by the theoretical analysis, is due to acoustic wave pre-excitation and non-uniform gain which depends on the bit patterns defined by the different codewords. A successful use of pulse coding techniques then requires to suitably optimize the employed modulation format in order to avoid spurious oscillations causing severe penalties in the attained accuracy. Coding technique with return-to-zero (RZ) modulation format is analyzed under different duty-cycle conditions for a 25 km-long sensing scheme, showing that low duty-cycle values are able to effectively suppress the induced distortions in the BGS and allow for spatially-accurate, high-resolution strain and temperature measurements being able to fully exploit the provided coding gain (approximately 7.2 dB along 25 km distance) with unaltered spatial resolution (1 meter). Although Simplex coding is used in our analysis, the validity of the results is general and can be directly applied to any intensity-modulation coding scheme.

Optimization of long-range BOTDA sensors with high resolution using first-order bi-directional Raman amplification

In this paper we perform an optimization of Brillouin optical time-domain analysis (BOTDA) sensors for achieving high resolution over long sensing ranges using distributed Raman amplification. By employing an optimized first-order bi-directional Raman amplification scheme and combining high-power fiber-Raman lasers and Fabry-Pérot lasers with low relative-intensity-noise (RIN), we demonstrate distributed sensing over 120 km of standard single-mode fiber with 2 meter spatial resolution and with a strain/temperature accuracy of 45με/2.1°C respectively.

Raman-based distributed temperature sensor with simplex coding and link optimization

In this letter, a coded, Raman-based distributed temperature sensor system using 255-bit Simplex coded optical time domain reflectometry (OTDR) and optimized sensing link composed of cascaded fibers with different Raman coefficients, is proposed. This system is compared to a system with an uncoded OTDR on standard single-mode fiber, demonstrating significant enhancement in the interrogation distance (19.5 km from coding gain, and 9.6 km from link optimization). Total sensing range of 37 km at 17-m/3-K spatial/temperature resolution were achieved, while employing conventional low power (80 mW) laser diodes

Long-range simplex-coded BOTDA sensor over 120km distance employing optical preamplification

In this Letter, we combine the use of optical preamplification at the receiver and optical pulse coding techniques with an optimized modulation format to effectively extend the sensing range of Brillouin optical time-domain analysis (BOTDA) sensors. Combining a return-to-zero modulation format with 25% duty cycle and linear gain preamplification allows for temperature and strain measurements over 120 km of standard single-mode fiber with 3 m spatial resolution and an rms strain-temperature accuracy of 3.1 °C/60 με respectively.

Analysis of optical pulse coding in spontaneous Brillouin-based distributed temperature sensors

A theoretical and experimental analysis of optical pulse coding techniques applied to distributed optical fiber temperature sensors based on spontaneous Brillouin scattering using the Landau-Placzek ratio (LPR) scheme is presented, quantifying in particular the impact of Simplex coding on stimulated Brillouin and Raman power thresholds. The signal-to-noise ratio (SNR) enhancement and temperature resolution improvement provided by coding are also characterized. Experimental results confirm that, differently from Raman-based sensors, pulse coding affects the stimulated Brillouin threshold, resulting in lower optimal input power levels; these features allow one to achieve high sensing performance avoiding the use of high peak power pulses.

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.

Raman-based distributed temperature sensor with 1 m spatial resolution over 26 km SMF using low-repetition-rate cyclic pulse coding

We experimentally investigate the benefits of a new optical pulse coding technique for long-range, meter and submeter scale Raman-based distributed temperature sensing on standard single-mode optical fibers. The proposed scheme combines a low-repetition-rate quasi-periodic pulse coding technique with the use of standard high-power fiber lasers operating at 1550 nm, allowing for what we believe is the first long-range distributed temperature measurement over single-mode fibers (SMFs). We have achieved 1 m spatial resolution over 26 km of SMF, attaining 3°C temperature resolution within 30 s measurement time.

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.