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 $2.2°\text{C}/44\mu \epsilon$, respectively.

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 $1550\mathrm{nm}$, allowing for what we believe is the first long-range distributed temperature measurement over single-mode fibers (SMFs). We have achieved $1\mathrm{m}$ spatial resolution over $26\mathrm{km}$ of SMF, attaining $3°\mathrm{C}$ temperature resolution within $30\mathrm{s}$ measurement time.

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 anal ysis (BOTDA) sensors. Combining a return-to-zero modulation format with 25% duty cycle and linear gain preamplification allows for temperature and strain measurements over $120\mathrm{km}$ of standard single-mode fiber with $3\mathrm{m}$ spatial resolution and an rms strain–temperature accuracy of $3.1°\mathrm{C}/60\mathrm{\mu \epsilon }$ respectively.

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.