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impaginato corretto fullone_Layout 1 13/10/15 12.09 Pagina 53 Department of Engineering, ICT and Technologies for Energy and Transport Patent Title Title Method for measuring the Brillouin shift 10.88 BOFDA Optical demodulation based technique Method the shift for measuring Brillouin distribution along an optical fiber based on the 10.86 distribution along an optical fiber based on the optical demodulation of the signals, and related 10.84 optical demodulation of the signals, and related 10.82 apparatus. Brillouin frequency shift [GHz] 10.80 apparatus. Ref. CNR 1745 10.78 Ref. CNR 1745 10.76 Assignee(s): CNR 10.74 CNR Institute: IREA 10.72 0 50 Position along the fiber [m] 200 250 100 150 Main Inventor: Romeo Bernini Countries: US Priority date: 09/06/2006 Abstract Abstract The present invention refers to a system and a method for measurement of the Brillouin frequency shift The present invention refers to a system and a method for measurement of the Brillouin frequency shift profile along an optical fiber. The proposed approach is based on the stimulated Brillouin shift scattering profile along an optical fiber. The proposed approach is based on the stimulated Brillouin shift scattering – available also in standard telecommunication fibers – and permits to performs distributed available also in standard telecommunication fibers – and permits to performs distributed strain/temperature measurements. The proposed approach performs frequency domain measurements, strain/temperature measurements. The proposed approach performs frequency domain measurements, avoiding the need to detect fast signal as usually happen in time domain approaches. In particular, the avoiding the need to detect fast signal as usually happen in time domain approaches. In particular, the system is based on an optical demodulation of the signals that permits to measure the Brillouin shift system is based on an optical demodulation of the signals that permits to measure the Brillouin shift profile with high resolution and accuracy. profile with high resolution and accuracy. Background Background Nowadays, distributed fiber optic sensors based on stimulated Brillouin scattering are widely used for Nowadays, distributed fiber optic sensors based on stimulated Brillouin scattering are widely used for distributed strain monitoring. However, the sensors developed at the state of the art require measurement distributed strain monitoring. However, the sensors developed at the state of the art require measurement system working in time domain that requires the use of high frequency electronics. system working in time domain that requires the use of high frequency electronics. Technology Technology The method can be implemented using two approaches. In the first one, a pump signal with sinusoidal The method can be implemented using two approaches. In the first one, a pump signal with sinusoidal modulation at frequency f1 and an optical probe signal with sinusoidal modulation at frequency f2 are modulation at frequency f1 and an optical probe signal with sinusoidal modulation at frequency f2 are launched into the fiber. In the second one, a continuous pump signal and an optical probe signal with launched into the fiber. In the second one, a continuous pump signal and an optical probe signal with sinusoidal modulation at frequency f2 are used. The probe signal at the exit of the measurement fiber is sinusoidal modulation at frequency f2 are used. The probe signal at the exit of the measurement fiber is optically demodulated at a frequency f1. optically demodulated at a frequency f1. Advantages and Applicatons Advantages and Applications The patent refers to a system and a method for measurement of the Brillouin frequency shift profile along The patent refers to a system and a method for measurement of the Brillouin frequency shift profile along an optical fiber. In particular, particular optical demodulation techniques are used, in order to increase the an optical fiber. In particular, particular optical demodulation techniques are used, in order to increase the resolution and the accuracy and, furthermore, to permit a simplifications of the measuring systems avoiding resolution and the accuracy and, furthermore, to permit a simplifications of the measuring systems avoiding the use of high frequency electronics. In fact, the signal to be measured is a low frequency signal at a fixed the use of high frequency electronics. In fact, the signal to be measured is a low frequency signal at a fixed frequency fm. frequency fm. Development stage Development stage The proposed approach has been validated by some experimental laboratory tests with a spatial The proposed approach has been validated by some experimental laboratory tests with a spatial 53 resolution of 3m along a 230m long fiber. resolution of 3m along a 230m long fiber.