Mikel Sagues

Multi-tap complex-coefficient incoherent microwave photonic filters based on optical single-sideband modulation and narrow band optical filtering

We propose a novel scheme to implement tunable multi-tap complex coefficient filters based on optical single sideband modulation and narrow band optical filtering. A four tap filter is experimentally demonstrated to highlight the enhanced tuning performance provided by complex coefficients. Optical processing is performed by the use of a cascade of four phase-shifted fiber Bragg gratings specifically fabricated for this purpose.

Demonstration of incoherent microwave photonic filters with all-optical complex coefficients

We propose and demonstrate for the first time to our knowledge an incoherent microwave photonic filter with complex coefficients implemented in the optical domain. The system is based on a tunable optically induced RF phase-shift that is obtained by means of a novel optical signal processing technique that makes combined use of optical single-sideband modulation and stimulated Brillouin scattering. A two-tap filter is built demonstrating full tunability of its frequency response by dynamically changing the phase shift of a complex coefficient

Dynamic BOTDA measurements based on Brillouin phase-shift and RF demodulation

We demonstrate a novel dynamic BOTDA sensor based, for the first time to our knowledge, on the use of the Brillouin phase-shift in addition to the conventional Brillouin gain. This provides the advantage of measurements that are largely immune to variations in fiber attenuation or changes in pump pulse power. Furthermore, the optical detection deployed leads to an enhanced precision or measurement time and to the broadening of the measurement range. Proof-of-concept experiments demonstrate 1.66-kHz measurement rate with 1-m resolution over a 160 m sensing fiber length. Moreover, a measurement range of 2560 µε with a precision of 20 µε is successfully proved.

Self-Heterodyne Detection for SNR Improvement and Distributed Phase-Shift Measurements in BOTDA

In this paper we present a Brillouin optical time domain analysis (BOTDA) sensor that takes advantage of the enhanced characteristics obtained employing self-heterodyne optical detection combined with synchronous demodulation. By employing this technique we increase the sensitivity of the sensor and demonstrate experimentally a 10.75-dB enhancement in the SNR compared to conventional direct-detection systems. This detection scheme also enables distributed measurements of the Brillouin phase-shift in an optical fiber, which can lead to enhanced BOTDA schemes.

Dynamic Microwave Photonic Filter Using Separate Carrier Tuning Based on Stimulated Brillouin Scattering in Fibers

Dynamic reconfiguration of a microwave photonic filter by tuning its basic delay based on stimulated Brillouin scattering-induced slow light and optical phase shift of the optical carrier is experimentally implemented. The measurements confirm that the free spectral range of the filter changes when a Brillouin pump is applied. These results demonstrate the potential of the separate carrier technique in microwave photonics applications.

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.

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 proof-of-concept experiment, the orthogonal modulator is deployed for the implementation of an RF phase-shifter.

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.

Overcoming Nonlocal Effects and Brillouin Threshold Limitations in Brillouin Optical Time-Domain Sensors

We demonstrate, for the first time to our knowledge, a Brillouin optical time-domain analysis (BOTDA) sensor that is able to operate with a probe power larger than the Brillouin threshold of the deployed sensing fiber and that is free from detrimental nonlocal effects. The technique is based on a dual-probe-sideband setup in which an optical frequency modulation of the probe waves along the fiber is introduced. This makes the optical frequency of the Brillouin interactions induced by each probe wave on the pump vary along the fiber so that two broadband Brillouin gain and loss spectra that perfectly compensate are created. As a consequence, the pulse spectral components remain undistorted, avoiding nonlocal effects. Therefore, very large probe power can be injected, which improves the signal-to-noise ratio (SNR) in detection for long-range BOTDA. Moreover, the probe power can even exceed the Brillouin threshold limit due to its frequency modulation, which reduces the effective amplification of spontaneous Brillouin scattering in the fiber. Experiments demonstrate the technique in a 50-km sensing link in which 8 dBm of probe power is injected.

Brillouin distributed sensor using RF shaping of pump pulses

We introduce a novel configuration for long-range Brillouin optical time domain analysis (BOTDA) sensors that is based on shaping the pump pulses in the radio frequency instead of the optical domain. This results in a simplified setup that uses just one standard intensity modulator to generate pulses with an extremely high extinction ratio (60 dB in our experiments). We develop a theoretical model for Brillouin interaction in long-distance BOTDA and use simulations to demonstrate that the availability of such pure pulses completely suppresses measurement errors caused by pulse leakage. Finally, experimental results are shown to confirm theoretical predictions. A 25 km fibre is measured with our system and the results compared to those obtained using pump pulses with lower extinction ratios.