Synthesis of Brillouin frequency shift profiles to compensate non-local effects and Brillouin induced noise in BOTDA sensors

We present a novel technique for Brillouin optical time domain analysis (BOTDA) sensors that simultaneously compensates non local effects and reduces Brillouin noise. The technique relies on the wavelength modulation of the optical source to modify the Brillouin interaction between probe and pump waves during their propagation. The resulting Brillouin distribution mimics the wavelength modulation, creating a virtual Brillouin frequency shift profile along the sensing fiber. The fundamentals of the technique are first described theoretically and using numerical simulations. Then, proof of concept experiments demonstrate the capabilities of the system to reduce large variations of the pump power resulting from the interaction with high probe powers and to decrease the Brillouin induced noise enhancing the signal to noise ratio (SNR) of the system. Furthermore, we show, for the first time to our knowledge, measurements of the Brillouin distribution using an injected optical power higher than the Brillouin threshold of the fiber.The authors wish to acknowledge the financial support from the Spanish Ministerio de Ciencia e Innovación through the project TEC2010-20224-C02-01 and from the Universidad Pública de Navarra

Synthesis of virtual Brillouin frequency shift profiles in BOTDA sensors using optical source dithering

We demonstrate a novel concept for Brillouin optical time domain analysis sensors that is based on synthesizing a virtual Brillouin frequency shift profile along the sensing fiber. The technique is based on modulating the wavelength of the optical source with a periodic waveform that is synchronized to the pump pulse. Application of this new tool to the compensation of non local effects and Brillouin induced noise in distributed sensors is experimentally demonstrated.The authors wish to acknowledge the financial support from the Spanish Ministerio de Ciencia e Innovación through the project TEC2010-20224-C02-01 and from the Universidad Pública de Navarra

Brillouin optical time-domain analysis sensor assisted by Brillouin distributed amplification of pump pulses

We demonstrate the extension of the measurement range of Brillouin optical time-domain analysis (BOTDA) sensors using a distributed Brillouin amplifier (DBA). The technique is based on injecting a DBA pump wave in the fiber to generate an additional Brillouin interaction that amplifies the BOTDA pump pulses and compensates optical fiber attenuation. This amplification does not introduce any significant noise to the BOTDA’s probe wave due to the inherent directionality of the Brillouin gain. Additionally, we deploy a differential pulse-width pair measurement method to avoid measurement errors due to the interplay between the self-phase modulation effect and the changes in the temporal shape of the pulses induced by the transient behavior of Brillouin gain. Experimental proof-of-concept results in a 50-km fiber link demonstrate full compensa- tion of the fiber’s attenuation with no penalty on the signal-to-noise ratio of the detected signal.The authors wish to acknowledge the financial support from the Spanish Ministerio de Economía y Competitividad through project TEC2013-47264-C2-2-R, FEDER funds and the Universidad Pública de Navarra

Brillouin distributed sensing assisted by Brillouin amplification of pump pulses

Trabajo presentado a IEEE Sensors 2014, celebrado en Valencia (España) del 2 al 5 de noviembre de 2014.We demonstrate, for the first time to our knowledge, the extension of the measurement range of Brillouin distributed sensors (BDS) by using a distributed Brillouin amplifier (DBA) to compensate the attenuation of the sensor's pump pulses. The technique is based on injecting an extra DBA pump wave in the fiber to generate an additional Brillouin interaction to that used for sensing. Moreover, the bandwidth of the DBA is tailored to fit that of the pump pulses by deploying a wavelength modulation of the DBA pump that is synchronized to the pump. Experimental proof of concept results demonstrate a fivefold enhancement of the measurement range of a BDS, from 10.36 km to more than 50 km in this particular case. Moreover, it is found that the use of the DBA does not introduce any significant penalty in the detection signal to noise ratio, highlighting the potential of the technique to provide much larger sensing lengths.The authors wish to acknowledge the financial support from the Universidad Pública de Navarra and Spanish Ministerio de Ciencia e Innovación through the projects TEC2010-20224- C02-01 and TEC2013-47264-C2-2-R

Swept optical single sideband modulation for spectral measurement applications using stimulated Brillouin scattering

We propose a technique for the generation of broadband optical single sideband modulated signals. The technique is based on optically processing an optical double sideband signal using stimulated Brillouin scattering effect. An unwanted sideband suppression over 40 dB in a broadband range from 50 MHz to 20 GHz is experimentally demonstrated. In addition, we apply the generated optical single sideband signal for the spectral characterization of polarization dependent parameters of optical components. The experimental characterization of the polarization dependent loss and the differential group delay of a phase-shifted fiber Bragg grating is performed in order to demonstrate the feasibility of the technique.The authors wish to acknowledge the financial support from the Spanish Ministerio de Educación y Ciencia through the projects TEC2007-67987-C02-02 and TEC2010-20224-C02-01

Brilloun optical time domain analysis sensor assisted by a Brillouin distributed amplifier

We demonstrate the extension of the measurement range of Brillouin optical time-domain analysis (BOTDA) sensors using a distributed Brillouin amplifier (DBA). The technique is based on injecting a DBA pump wave in the fiber to generate an additional Brillouin interaction that amplifies the BOTDA pump pulses. Furthermore, the differential pulse-width pair method is used to counteract the detrimental effects of the DBA amplification on the temporal shape of the pulses. Experimental proof-of-concept results in a 50-km fiber link demonstrate full compensation of the fiber’s attenuation with no penalty on the signal-to-noise ratio of the detected probe wave.The authors acknowledge support from the Spanish Ministerio de Economa y Competitividad project TEC2013-47264-C2-2-R, FEDER funds and the Universidad Pública de Navarra

Phase-shift based BOTDA measurements tolerant to non-local effects

We demonstrate a BOTDA sensor based on the use of the Brillouin phase shift that performs measurements tolerant to non local effects. This technique raises opportunities to increase the distance covered by these sensors and the maximum optical power of the probe wave injected to the fiber. As a result, the system has the potential to increase the SNR achieved at the last meters of the fiber. Proof-of-concept experiments demonstrate unaltered measurements of the phase shift spectrum in a 20Km long fiber for large frequency-dependent distortions of the pump pulse.The authors wish to acknowledge financial support from the Spanish Ministerio de Educación y Ciencia through the project TEC2010-20224-C02-01 and from the Universidad Pública de Navarra

BOTDA measurements tolerant to non-local effects by using a phase-modulated probe wave and RF demodulation

We demonstrate a Brillouin optical time domain analysis sensor based on a phase modulated probe wave and RF demodulation that provides measurements tolerant to frequency dependent variations of the pump pulse power induced by non local effects. The tolerance to non local effects is based on the special characteristics of the detection process, which provides an RF phase shift signal that is largely independent of the Brillouin gain magnitude. Proof of concept experiments performed over a 20 km long fiber demonstrate that the measured RF phase shift spectrum remains unaltered for large frequency dependent deformations of the pump pulse power. Therefore, it allows the use of a higher optical power of the probe wave, which leads to an enhancement of the detected signal to noise ratio. This can be used to extend the sensing distance, to improve the accuracy of the Brillouin frequency shift measurements, and to reduce the measurement time.The authors wish to acknowledge the financial support from the Spanish Ministerio de Educación y Ciencia through the project TEC2010-20224-C02-01, from the Spanish Ministerio de Economía y Competitividad through the project IPT-2011-12-920000 and from the Universidad Pública de Navarra

Phasorial differential pulse-width pair technique for long-range Brillouin optical time-domain analysis sensors

We introduce a novel phasorial differential pulse width pair (PDPP) method for Brillouin optical time domain analysis (BOTDA) sensors that combines spatial resolution enhancement with increased tolerance to non local effects. It is based on the subtraction of the complex time domain traces supplied by a sensor configuration that uses a phase modulated probe wave and RF demodulation. The fundamentals of the technique are first described theoretically and using numerical simulation of the propagating waves. Then, proof of concept experiments demonstrate the measurement of the Brillouin frequency shift distribution over 50 km. The system is shown to withstand large variations of the pump power generated by its interaction with a powerful probe wave along the fiber; hence, highlighting the potential of the PDPP technique to increase the detected signal to noise ratio in long range BOTDA. Moreover, the PDPP is also shown to increase the measurement contrast by allowing the use of relatively long duration pulses while retaining 1 m spatial resolution.The authors wish to acknowledge the financial support from the Spanish Ministerio de Ciencia e Innovación through the project TEC2010-20224-C02-01 and from the Universidad Pública de Navarra

Orthogonally polarized optical single sideband modulation for microwave photonics processing using stimulated Brillouin scattering

We present a novel technique to generate orthogonally polarized optical single sideband modulated signals. The modulation scheme is based on all optical stimulated Brillouin scattering processing of the optical carrier of an optical single sideband modulated signal, by means of the polarization state dragging induced by this non-linear effect. This modulation technique can be used in several microwave photonics applications, such as antenna beamforming or microwave photonics filters. In order to perform a proofof-concept experiment, the orthogonal modulator is deployed for the implementation of an RF phase-shifter.The authors wish to acknowledge the financial support from the Spanish Ministerio de Educación y Ciencia through the projects TEC2007-67987-C02-02 and TEC2010-20224-C02- 01