Félix Rodríguez-Barrios

Distributed Brillouin Fiber Sensor Assisted by First-Order Raman Amplification

Distributed optical fiber Brillouin sensors provide innovative solutions for the monitoring of temperature and strain in large structures. The effective range of these sensors is typically of the order of 20-30 km, which limits their use in certain applications in which the distance to monitor is larger. In this work, we have developed a new technique to significantly extend the measurement distance of a distributed Brillouin Optical Time-Domain Analysis (BOTDA) sensor. Distributed Raman Amplification in the sensing fiber provides the means to enhance the operating range of the setup. Three Raman pumping configurations are theoretically and experimentally investigated: co-propagating, counter-propagating and bidirectional propagation with respect to the Brillouin pump pulse. We show that some of the amplification schemes tested can extend the measurement range and improve the measurement quality over long distances.

Detrimental effect of self-phase modulation on the performance of Brillouin distributed fiber sensors

We show that the spectral broadening of the pump pulse through self-phase modulation in a time-domain distributed Brillouin sensor has a considerably detrimental effect in the measurement, especially in the case of long distances and high-resolution pulses. Using 30 ns pump pulses with peak power of 276 mW, self-phase modulation leads to a doubling of the effective gain linewidth after some 20 km, which is equivalent to a contrast loss of 2dB in the measurement. The impact is higher for shorter pulses (higher resolution). The theoretical modeling is fully confirmed by experimental results.

An integrating sphere radiometer as a solution for high power calibrations in fibre optics

This paper describes the design, characterization and calibration of a high power transfer standard for optical power measurements in optical fibres based on an integrating sphere radiometer. This radiometer, based on two detectors (Si and InGaAs), can measure powers between 100 nW and 10 W within the wavelength range of (400–1700) nm. The radiometer has been calibrated over the total spectral range of use against an electrically calibrated pyroelectric radiometer and different fibre laser diodes and ion lasers. The total uncertainty obtained is lower than ±1.5% for these wavelengths and power ranges (excluding the water absorption region).

Experimental Study on the Role of Chromatic Dispersion in Continuous-Wave Supercontinuum Generation

The influence of chromatic dispersion on continuous-wave (CW)-pumped supercontinuum (SC) generation in kilometer-long standard fibers is experimentally investigated. We perform our study by means of a tunable, high-power fiber ring laser pumping a dispersion-shifted fiber in the wavelength range of small and medium anomalous dispersion. Our results show that, at low input powers, chromatic dispersion plays a dominant role on nonlinear pump spectral broadening, giving rise to a broader spectrum when pumping just above the zero-dispersion wavelength of the fiber. At higher input powers, however, the width of the generated SC spectrum is mostly due to the Raman effect, hence more independent of the value of the chromatic dispersion coefficient. We show that, in this case, the optimum pumping wavelengths for SC generation are not so close to the zero-dispersion wavelength of the fiber as in the previous case. In these conditions, as the chromatic dispersion grows, we can obtain square-shaped and high-power density spectra, which seem extremely promising for applications in optical coherence tomography.

Raman-assisted BOTDA sensors

We review some recent results on the application of distributed Raman amplification schemes, including ultralong lasers, to the extension of the operating range and contrast in Brillouin optical time domain analysis (BOTDA) distributed sensing systems.

Measurement with 2m resolution using a Raman-assisted BOTDA sensor featuring 75km dynamic range

We have used distributed Raman amplification to extend the measurement distance of a Brillouin Optical Time-Domain Analysis (BOTDA) sensor. We successfully demonstrate a dynamic range of 75 km with 2 meter spatial resolution.

Optimization of pump wavelength for enhancing SC spectral broadening in silica fibers under CW-excitation

Supercontinuum sources generated by continuous-wave excitation are very promising for many applications as they present in general higher spectral power density then their pulsed counterparts. On the other hand, the properties of supercontinuum are very difficult to be controlled as the initial broadening is driven by modulation instability. This latter one breaks-up the CW radiation into a train of ultra-short pulses whose peak power, spectral length and shape strongly depend on the power, coherence and noise of the pump and on the fiber properties. In this paper, we present a preliminary work on the role of chromatic dispersion on supercontinuum spectral broadening in order to study how to optimize SC spectral width under CW regimes. By means of a home-made tunable high-power laser we induce supercontinuum generation by pumping at different dispersion values of the fiber. We show that at low injected powers the wider spectrum is obtained when pumping just above the zero-dispersion wavelength of the fiber. By contrast, for higher injected powers, wide and squared-shaped spectra can be obtained when pumping over a larger range of anomalous dispersion values. These results seem to be very promising for a number of applications requiring smooth, squared and high-power SC spectral profiles such as optical coherence tomography.