[Show abstract][Hide abstract] ABSTRACT: A new technique to investigate the spatial distribution of the reflection spectrum along fabricated long weak fiber Bragg gratings (FBG) is experimentally demonstrated, together with its potential applications for distributed fiber sensing and broadband signal processing. A short pulsed coherent light signal is launched into a FBG and the signal frequency is scanned through the FBG reflection spectrum. When the pulse duration is set much shorter than the transit time through the grating a time-resolved reflected signal can be obtained for each signal frequency. It informs about the distribution of the refractive index periodic perturbation along the entire FBG length, hence the uniformity or frequency chirp information of the fabricated FBG. This technique has been implemented to demonstrate a distributed temperature sensing system with high spatial resolution and to also realize a robust all-fiber tunable delay line for broadband signals.
[Show abstract][Hide abstract] ABSTRACT: This paper reviews the recent advances in the field of radio frequency signal processing using photonic devices and subsystems or microwave photonic (MWP) signal processing. We focus our attention on the results reported during the last six years, as previous work has been adequately addressed in previous review papers. After a brief introduction to the basic concepts involved in MWP signal processing, we focus our attention on the most significant advances reported by different research groups in overcoming their main limitation factors. Recent advances in the emergent topic of integrated MWP signal processors are also covered and the novel approaches toward the evaluation of the main figures of merit are discussed. New proposed applications and future directions of work are also considered.
[Show abstract][Hide abstract] ABSTRACT: The availability of a tunable delay line with a chip-size footprint is a crucial step towards the full implementation of integrated microwave photonic signal processors. Achieving a large and tunable group delay on a millimetre-sized chip is not trivial. Slow light concepts are an appropriate solution, if propagation losses are kept acceptable. Here we use a low-loss 1.5 mm-long photonic crystal waveguide to demonstrate both notch and band-pass microwave filters that can be tuned over the 0-50-GHz spectral band. The waveguide is capable of generating a controllable delay with limited signal attenuation (total insertion loss below 10 dB when the delay is below 70 ps) and degradation. Owing to the very small footprint of the delay line, a fully integrated device is feasible, also featuring more complex and elaborate filter functions.
[Show abstract][Hide abstract] ABSTRACT: Optical sensing offers an attractive solution to the societal concern for prevention of natural and human-generated threats and for efficient use of natural resources. The unprecedented properties of optical fibers make them ideal for implementing a ‘nervous system’ in structural health monitoring: they are small, low-cost and electrically and chemically inert. In particular, the nonlinear interaction of stimulated Brillouin scattering allows for the distributed measurement of strain and temperature with tens of km range. In this work, a novel, radar-inspired technique for random-access Brillouin scattering-based sensors is shown, making a significant step towards a real optical sensing nerve. The method selectively addresses each fiber segment as a distinct sensing element in a synaptic neuronal system. The measurement principle relies on phase-coding of both the Brillouin pump and signal waves by a high-rate, pseudo-random bit sequence. Temperature measurements with 1 cm resolution are reported. The measurement range is scalable to several km.
[Show abstract][Hide abstract] ABSTRACT: We present recent implementations of microwave photonic filters using the following two technologies: InP-based MDR (microdisk resonator) on and coupled to a nanophotonic SOI waveguide and dynamic Brillouin gratings (DBGs) in polarization maintaining fibers (PMF). Quasi-linear and continuously tunable ~360° phase shifts have been experimentally obtained when considering radiofrequencies greater than 18 GHz using MDR. Besides, we have designed and experimentally demonstrated multi-tap MWP filters, based on dynamic Brillouin grating reflectors in polarization maintaining fibers, showing a FSR variation larger than 60% in a two-tap filter.
2012 14th International Conference on Transparent Optical Networks (ICTON), Coventry, UK; 07/2012
[Show abstract][Hide abstract] ABSTRACT: We theoretically and experimentally compare the performance of two fully tunable phase shifter structures based on semiconductor optical amplifiers (SOA) by means of several figures of merit common to microwave photonic systems. A single SOA stage followed by a tailored notch filter is compared with a cascaded implementation comprising three SOA-based phase shifter stages. Attention is focused on the assessment of the RF net gain, noise figure and nonlinear distortion. Recommendations on the performance optimization of this sort of approaches are detailed.
[Show abstract][Hide abstract] ABSTRACT: In this work, we apply a recent technique for the generation of
stimulated Brillouin scattering (SBS) dynamic gratings that are both
localized and stationary to realize high-resolution distributed
temperature sensing. The gratings generation method relies on the phase
modulation of two pump waves by a common pseudo-random bit sequence
(PRBS), with a symbol duration that is much shorter than the acoustic
lifetime. This way the acoustic wave can efficiently build up in the
medium at discrete locations only, where the phase difference between
the two waves does not temporarily vary. The separation between
neighboring correlation peaks can be made arbitrarily long. Using the
proposed method, we experimentally demonstrate distributed temperature
sensing with 5 cm resolution, based on modifications to both the local
birefringence and the local Brillouin frequency shift in polarization
maintaining fibers. The localization method does not require wideband
detection and can generate the grating at any random position along the
fiber, with complete flexibility. The phase-coding method is equally
applicable to high-resolution SBS distributed sensing over standard
Proceedings of SPIE - The International Society for Optical Engineering 05/2012; DOI:10.1117/12.922976 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A novel technique for the localization of stimulated Brillouin scattering (SBS) interaction is proposed, analyzed and demonstrated experimentally. The method relies on the phase modulation of two counter-propagating optical waves by a common pseudo-random bit sequence (PRBS), these waves being spectrally detuned by the Brillouin frequency shift. The PRBS symbol duration is much shorter than the acoustic lifetime. The interference between the two modulated waves gives rise to an acoustic grating that is confined to narrow correlation peaks, as short as 1.7 cm. The separation between neighboring peaks, which is governed by the PRBS length, can be made arbitrarily long. The method is demonstrated in the generation and applications of dynamic gratings in polarization maintaining (PM) fibers. Localized and stationary acoustic gratings are induced by two phase modulated pumps that are polarized along one principal axis of the PM fiber, and interrogated by a third, readout wave which is polarized along the orthogonal axis. Using the proposed technique, we demonstrate the variable delay of 1 ns-long readout pulses by as much as 770 ns. Noise due to reflections from residual off-peak gratings and its implications on the potential variable delay of optical communication data are discussed. The method is equally applicable to the modulation of pump and probe waves in SBS over standard fibers.
[Show abstract][Hide abstract] ABSTRACT: We propose and experimentally demonstrate new architectures to realize multi-tap microwave photonic filters, based on the generation of a single or multiple dynamic Brillouin gratings in polarization maintaining fibers. The spectral range and selectivity of the proposed periodic filters is extensively tunable, simply by reconfiguring the positions and the number of dynamic gratings along the fiber respectively. In this paper, we present a complete analysis of three different configurations comprising a microwave photonic filter implementation: a simple notch-type Mach-Zehnder approach with a single movable dynamic grating, a multi-tap performance based on multiple dynamic gratings and finally a stationary grating configuration based on the phase modulation of two counter-propagating optical waves by a common pseudo-random bit sequence (PRBS).
[Show abstract][Hide abstract] ABSTRACT: Reflections from movable, dynamic acoustic gratings in polarization maintaining (PM) fibers are employed in the long variable delay of periodic, isolated pulses. The gratings are introduced by stimulated Brillouin scattering (SBS) interaction between two counter-propagating pump waves, which are spectrally detuned by the Brillouin frequency shift of the PM fiber and are both polarized along one of its principal axes. The gratings are interrogated by the reflections of read-out signals that are polarized along the orthogonal principal axis. High-rate phase modulation of both pump waves by a pseudo-random binary sequence introduces dynamic gratings that are both localized and stationary, at specific locations in which the modulated pumps are correlated. The separation between adjacent correlation peaks can be made arbitrarily long. Long variable delays are readily obtained by scanning the grating along the fiber, via changing either the length or the rate of the modulation sequence. At the same time, the short length of the gratings, on the order of a cm, accommodates the delay of broadband pulses. The technique is therefore free of the delay-times-bandwidth product limitation that undermines the performance of SBS-based 'slow light' delay: we report the delay 1-ns long pulses by as much as 770 ns. In addition, the combined reflections from two dynamic gratings with a variable separation are used to implement radio-frequency photonic filters of tunable free spectral range. At the current stage, the technique is restricted by noise from residual scattering that takes place outside of the correlation peaks. Hence, it is thus far limited to the processing of repetitive signals, for which the noise may be effectively averaged out.
Proceedings of SPIE - The International Society for Optical Engineering 03/2012; DOI:10.1117/12.914725 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We propose and experimentally demonstrate the suitability of exploiting the dispersive feature of a chip-size delay line to perform microwave photonic filtering tasks. A band-pass microwave filter based on wavelength multiplexing which can be tuned over the 0-50 GHz spectral band is presented. The tunable delay line comprises a low-loss 1.5 mm long photonic crystal waveguide capable of generating a controllable delay exceeding 100 ps, still with limited signal attenuation and degradation.
Microwave Photonics (MWP), 2012 International Topical Meeting on; 01/2012
[Show abstract][Hide abstract] ABSTRACT: A fully tunable microwave photonic phase shifter involving a single semiconductor optical amplifier (SOA) is proposed and demonstrated. 360° microwave phase shift has been achieved by tuning the carrier wavelength and the optical input power injected in an SOA while properly profiting from the dispersion feature of a conveniently designed notch filter. It is shown that the optical filter can be advantageously employed to switch between positive and negative microwave phase shifts. Numerical calculations corroborate the experimental results showing an excellent agreement.
[Show abstract][Hide abstract] ABSTRACT: In this work we evaluate dynamic range degradation in a Slow Light cascaded SOA-based stages microwave phase shifter when tuning the induced phase shift. The fundamental signal and third order intermodulation distortion have been evaluated at both the phase shifter input and output attending this purpose. Results show a slight degradation when the phase shift is tuned from the minimum to the maximum value.
Information Photonics (IP), 2011 ICO International Conference on; 06/2011
[Show abstract][Hide abstract] ABSTRACT: A complex-valued multi-tap tunable microwave photonic filter based on single silicon-on-insulator microring resonator is presented. The degree of tunability of the approach involving two, three and four taps is theoretical and experimentally characterized, respectively. The constraints of exploiting the optical phase transfer function of a microring resonator aiming at implementing complex-valued multi-tap filtering schemes are also reported. The trade-off between the degree of tunability without changing the free spectral range and the number of taps is studied in-depth. Different window based scenarios are evaluated for improving the filter performance in terms of the side-lobe level.
[Show abstract][Hide abstract] ABSTRACT: Different optical filtering scenarios involving microwave photonic phase
shifters based on semiconductor optical amplifiers are investigated numerically
as well as experimentally with respect to noise performance. Investigations
on the role of the modulation depth and number of elements in cascaded shifting
stages are also carried out. Suppression of the noise level by more than 5
dB has been achieved in schemes based on band-pass optical filtering when
three phase shifting stages are cascaded.
Journal of Lightwave Technology 06/2011; 29(12):1746-1752. · 2.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The noise figure of Slow and Fast Light Microwave Photonic phase shifters made up by SOA followed by optical filtering stages is experimentally evaluated. Noise figure results show compression when adding the third cascaded stage.
[Show abstract][Hide abstract] ABSTRACT: We review the potential applicability of SFL techniques to the field of Microwave photonics. The main results obtained for several applications such as filtering, phased array antennas, arbitrary waveform generation and OEO will be analyzed.
[Show abstract][Hide abstract] ABSTRACT: Different optical filtering scenarios involving mi- crowave photonic phase shifters based on semiconductor optical amplifiers are investigated numerically as well as experimentally with respect to noise performance. Investigations on the role of the modulation depth and number of elements in cascaded shifting stages are also carried out. Suppression of the noise level by more than 5 dB has been achieved in schemes based on band-pass optical filtering when three phase shifting stages are cascaded. Index Terms—Noise figure, phase shifter, semiconductor optical amplifier (SOA), slow and fast light (SFL).
[Show abstract][Hide abstract] ABSTRACT: We present a brief review of recent accomplishments in the field of Microwave Photonics (MWP). Recent research across a broad range of MWP applications is summarized, including photonic generation of microwave, millimeter, and Terahertz waves; broadband optical beamforming for phased array antennas; tunable, reconfigurable, and adaptive microwave photonic filtering, as well as the application of slow and fast light effects to the implementation of tunable microwave phase shifting and true time delay operations.