We report high-speed Fiber Bragg Grating (FBG) interrogation based on fiber interferometry. An electro-optical modulator, used as a tunable retarder, is implemented in a fiber Sagnac loop, enabling fast tuning of the interference fringes. Applying an active modulation scheme, the wavelength of the FBG can be retrieved without any requirement of the spectral position of the FBG with respect to the fringes, with no need of tunable sources or spectral analysis. We report experimental results of wavelength measurements with a bandwidth of 100 kHz (only limited by our data acquisition rate) and a dynamic wavelength resolution of σ = 3.7 fm/ $\sqrt Hz$ (corresponding to a strain resolution of 3.1 nσ/ $\sqrt Hz$ ). We also show that the system can track a continuous tunable laser sweep of 40 nm along the C-band. The technique is polarization-independent and allows wavelength division multiplexing schemes using only one interferometer for all the sensing points. The system is fully based on low-cost off-the-shelf fiber-optical components, and the free-spectral-range of the interferometer can be easily modified by just changing the length of the polarization-maintaining fiber segment.

We propose the use of pulse Simplex-coding in distributed temperature sensors based on spontaneous Brillouin scattering. The analysis shows achieved performance improvement and the effect on stimulated Brillouin threshold, resulting in lower required input power.

We experimentally investigate dynamic bit-error rate (BER) performance impairments induced by add-drop operations in semiconductor-optical amplifer (SOA)-based wavelength-division-multiplexing (WDM) metro-ring networks. Link control techniques in short-medium span networks provide effective performance improvement and significant BER transient reduction during add-drop operation, with respect to SOA linear operating condition (low input signal power). This behavior is confirmed by dynamic BER measurements and optical signal-to-noise penalty analysis.

Differential pulse-width-pair BOTDA technique is combined with bi-directional Raman amplification and Simplex coding to achieve sub-meter spatial resolution over very long sensing distances. Numerical simulations are used to optimize the power levels of the Raman pumps, avoiding nonlinear effects and pump depletion. Distortions in the Brillouin gain spectrum due to acoustic-wave pre-excitation are also avoided by numerical optimization of the pulse width and duty cycle of return-to-zero Simplex coding, providing significant SNR enhancement. We demonstrate 50 cm spatial resolution over 93 km of standard SMF with a strain/temperature accuracy of 34με/1.7 °C, respectively.

In this paper we propose the use of multi-longitudinal mode lasers, such as Fabry-Pérot (FP) lasers, for simultaneous distributed strain and temperature sensing based on hybrid Brillouin and Raman scattering. Fabry-Pérot lasers allow for high-power Raman intensity measurement and the simultaneous detection of the Brillouin frequency shift parameter for all FP longitudinal modes, by using a self-heterodyne detection scheme based on a multi-wavelength optical local oscillator. Experiments point out significant improvement in hybrid sensor performance, also suggesting further potential benefits when combining the use of FP lasers with optical coding techniques and/or optical amplification.