BUSCADOR RECOLECTA

A humidity and temperature optical fiber sensor based on a long-period grating (LPG), which can provide simultaneous response to both magnitudes, is proposed and demonstrated via experiments. Previously, the LPG was fully coated with humidity sensitive nanostructured polymeric thin films by the Layer-by-Layer (LbL) nano assembly technique. Hence the surrounding refractive index was changed, so provoking wavelength shifts of the attenuation bands of the transmission spectrum. This fully coated LPG was exposed to relative humidity (RH) and temperature tests, varying from 20% to 80% RH and from 25 to 85 °C, respectively. Then, half of the LPG coating was chemically removed and this results in the splitting of the main attenuation band into two different contributions. When this semi-coated LPG was also exposed to RH and temperature tests, the new two attenuation bands presented different behaviors for humidity and temperature. This novel dual-wavelength based sensing method enables the simultaneous measurement of RH and temperature using only one LPG., This work was supported in part by the Spanish Ministry of Economy and Competitiveness – through the projects CICYT-FEDER TEC2013-43679-R and TEC2014-60378-C2-1-R. It was also supported by a UPNA pre-doctoral research grant, by the Program of International Excellence Campus VLC/Campus, by the grant of program SANTIAGO GRISOLÍA, and by the Research Excellency Award Program GVA PROMETEO 2013/012.

A fiber optic liquid-level sensor based on a long period grating (LPG) is proposed and experimentally validated. The principle of operation is based on a technique used to analyze microwave photonics filters. A 4-cm-long LPG cascaded with a high-reflectivity fiber Bragg grating is employed to achieve a continuous liquid-level sensor. The measurements have been performed using a modulator and a photo-detector with a modest bandwidth of less than 500 MHz, showing a sensitivity of -12.71 dB/cm and a standard deviation of 0.52 dB. One of the significant advantages of such sensing structure is that it is based on low-bandwidth radio frequency and off-the-shelf photonic components. In addition, the simple proposed scheme presents good repeatable performance and proves to be intrinsically robust against environmental changes, stable, and easy to reconfigure., This work was supported in part by the Acción Financiada por el Ministerio de Educación, Cultura y Deporte through the framework of the Programa de Campus de Excelencia Internacional VLC/Campus, in part by the Spanish MINECO under Project TEC2014-60378-C2-1-R, in part by the Grant of the SANTIAGO GRISOLÍA Program, in part by the Research Excellency Award Program GVA PROMETEO 2013/012, in part by the Project TEC2013-43679-R, and in part by an UPNA Predoctoral Grant.

[EN] We review the introduction of the space dimension into fiber-based technologies to
implement compact and versatile signal processing solutions for microwave and millimeter wave
signals. Built upon multicore fiber links and devices, this approach allows the realization of
fiber-distributed signal processing in the context of fiber-wireless communications, providing both
radiofrequency access distribution and signal processing in the same fiber medium. We present
different space-division multiplexing architectures to implement tunable true time delay lines that
can be applied to a variety of microwave photonics functionalities, such as signal filtering, radio
beamsteering in phased array antennas or optoelectronic oscillation. In particular, this paper gathers
our latest work on the following multicore fiber technologies: dispersion-engineered heterogeneous
multicore fiber links for distributed tunable true time delay line operation; multicavity devices built
upon the selective inscription of gratings in homogenous multicore fibers for compact true time delay
line operation; and multicavity optoelectronic oscillation over both homogeneous and heterogeneous
multicore fibers., This research was supported by the ERC Consolidator Grant 724663; the Spanish Projects TEC2015-62520-ERC, TEC2014-60378-C2-1-R and TEC2016-80150-R; the Valencian Research Excellency Award Program GVA PROMETEO 2013/012; the Spanish MECD FPU Scholarship (FPU13/04675) for J. Hervás; the Spanish scholarships MINECO BES-2015-073359 for S. García; and the Spanish MINECO Ramon y Cajal program RYC-2014-16247 for I. Gasulla.

[EN] Incoherent Optical Fourier-Domain Reflectometry incorporating a dispersive delay line is used for the interrogation of an array of three identical fiber Bragg gratings with a Bragg wavelength of 1552.81 nm, reflectivity of 19.3 dB and 10-cm
separation. The dispersive delay line induces different delays in the wavelengths reflected by each grating, thus being sensitive to Bragg wavelength shifts. Compared with conventional incoherent Optical Fourier-Domain Reflectometry, dispersive effects decrease the spatial resolution, which in our experiments reached a value of 1.2 cm in fiber at a measurement bandwidth of 10 GHz. As a quasi-distributed temperature sensor, the array shows an accuracy of ±0.5ºC for temperatures up to 100ºC, and an estimated total measurement range of 540ºC. Tradeoffs between bandwidth, scan time, dispersion-dependent spatial resolution,
and accuracy, are also analyzed., This work was supported in part by the Generalitat Valenciana, Valencia, within the Research Excellency Award through the GVA PROMETEO Program under Grant 2013/012 and in part by the Ministerio de Economia y Competitividad under Project TEC201-60378-C2-1-R. The work of J. Hervas was supported by the Ministerio de Educacion, Cultura y Deporte through the Formacion Profesorado Scholarship (FPU13/04675).

[EN] We propose and analyse two novel mesh design geometries for the implementation of tunable optical cores in programmable photonic processors. These geometries are the hexagonal and the triangular lattice. They are compared here to a previously proposed square mesh topology in terms of a series of figures of merit that account for metrics that are relevant to on-chip integration of the mesh. We find that that the hexagonal mesh is the most suitable option of the three considered for the implementation of the reconfigurable optical core in the programmable processor., The authors wish to acknowledge the financial support given by the Research Excellency Award Program GVA PROMETEO II/2013/012, Spanish MINECO projects TEC2013-42332-P PIF4ESP, TEC2015-69787-REDT PIC4TB and TEC2014-60378-C2-1-R MEMES, as well as the projects FEDER UPVOV 10-3E-492 and FEDER UPVOV 08-3E-008. The work of D. Perez was supported by the FPI-UPV Grant Program from the Universitat Politecnica de Valencia and the work of I. Gasulla was supported by the Spanish MINECO through the Ramon y Cajal Program. R. Soref is supported by the Air Force Office of Scientific Research.

[FR] In this letter, we present a novel structure for performing subcarrier multiplexing (SCM) to improve the scanning rate in low coherence interferometry (LCI) systems combined with the microwave photonics (MWP) technology. In this MWP-LCI proposal, the optical path differences (OPDs) produced by different samples between the arms of an interferometer are closely related to the central frequency of different RF resonances generated in the RF domain. By the proposed adaptation of the SCM technique, M subcarriers are multiplexed in the modulation stage and each subcarrier is set to sweep simultaneously a concrete part of the spectrum. The complete electrical transfer function of the structure is obtained combining each individual sweep. Therefore, a considerable reduction of the sweep time is provided to collect the complete electrical transfer function. Therefore, the scanning rate is reduced according to the number of subcarriers (M) employed in the multiplexing stage. An OPD range of 8 mm is achieved with a constant resolution of 120 μm in the whole range. Finally, a maximum sensitivity of 60 dB is also reached for that operation range., The research leading to these results was supported by the National Project TEC2014-60378-C2-1-R funded by the Ministerio de Ciencia y Tecnologia and the regional project PROMETEO FASE II/2013/012 funded by the Generalitat Valenciana. (Corresponding author: J. Mora.)

We propose the use of spatial division multiplexing supported by multicore fibers to implement a new generation of flexible and capacity reconfigurable cloud radio access network front-haul architectures capable of addressing their main present and future challenges. We show that for the majority of radio access scenarios where front-haul optical links are less than 10-km long, the impact of inter-core crosstalk on the electrical carrier-to-noise ratio can be neglected, and thus, link design can be carried independently core by core. In addition, this MCF-based approach, which is compatible with software defined networking and network function virtualization, can also support the integration of a passive optical network overlay., This work was supported in part by the Ministry of Economy and Competitiveness under Project TEC2013-50552-EXP MULTIFUN and Project TEC2014-60378-C2-1-R MEMES and in part by Generalitat Valenciana under Grant PROMETEO 2013/012. The work of I. Gasulla was supported by the Spanish Ministry of Economy and Commerce through the Ramon y Cajal Program.

[EN] A simple scheme for interrogating a 5 m-long photonics device and its potential applications to quasi-distributed fiber sensing is proposed. The sensor consists of an array of 500 identical very weak fiber Bragg gratings (FBGs). The gratings are 9 mm-long and have been serially written in cascade along a single optical fiber. The measurement system is based on a combination of optical time domain reflectrometry (OTDR) and frequency scanning of the interrogating pulse. The time-frequency analysis is performed by launching an optical pulse into the sensor and by retrieving and analyzing the back-reflected signal. The measurement of the temperature, length and position of spot events along the sensors is demonstrated, with good accuracy. As both spatial and temperature resolution of the method depend on the input pulse duration, the system performance can be controlled and optimized by properly choosing the temporal duration of the interrogating pulse. A spatial resolution of 9 mm (ultimately dictated by one grating length) has been obtained with an 80 ps optical pulse; while a temperature resolution of less than 0.42 K has been demonstrated using a 500 ps incident pulse. The sensor proposed proves to be simple, robust, polarization insensitive and alleviates the instrumentation complexity for distributed sensing applications., Ministerio de Educacion, Cultura y Deporte; Ministerio de Economia y Competitividad (TEC2014-60378-C2-1-R); Generalitat Valenciana (GRISOLIA/2013/034); Research Excellency Award Program (GVA PROMETEO 2013/012).

[EN] We propose and experimentally demonstrate an approach to perform high-resolution and temperature-insensitive interrogation of a fiber Bragg grating (FBG)-based multicore fiber (MCF) curvature sensor using a microwave photonics filtering technique. By combining two reflected sample signals from the two FBGs inscribed in MCF and a dispersion device, a two-tap notch microwave photonic filter (MPF) is formed. The notch frequency of MPF is dependent on the time delay difference between the two FBG reflected signals, which is related to wavelength spacing of the two FBGs. Due to the wavelength spacing of the two FBGs is proportional to the curvature, the curvature can be readily interrogated by monitoring the notch frequency of MPF. The proposed interrogation scheme with the sensitivity of 92 MHz/m(-1) is achieved, whilst the sensitivity can be easily adjusted. Moreover, the proposed interrogation scheme is temperature insensitive., This work was supported in part by the National Natural Science Foundation of China under Grant 61405166 and Grant 61775185, in part by the China Scholarship Council, in part by the Generalitat Valenciana under Grant APOSTD/2016/015 and Grant GVA PROMETEO 2013/012, and in part by the Ministerio de Economia y Competitividad under Grant TEC2014-60378-C2-1-R. (Corresponding author: Di Zheng.)

[EN] We report, for the first time to our knowledge. distributed radiofrequency signal processing built upon true time delay operation on a step-index few-mode fiber. Two 3-sample configurations with different time delay properties are implemented over the same 60-meter 4-LP-mode fiber link. The inscription of a long period grating at a specific fiber position converts part of the LP01 mode into the LP02, permitting sample time delay engineering. Delay line performance is experimentally demonstrated when applied to radiofrequency signal filtering. example of fiber-distributed processing functionality exhibiting one order or magnitude gain in terms of compactness. (C) 2018 Optical Society of America America under the terms of the OSA Open Access Publishing Agreement, H2020 European Research Council (ERC) (Consolidator Grant 724663); Spanish MINECO (TEC2014-60378-C2-1-R and TEC2016-80150-R projects, BES-2015-073359 scholarship for S. Garcia, Ramon y Cajal fellowship RYC-2014-16247 for I. Gasulla)., © 2018 Optical Society of America. One print or electronic copy may be made for personal use only.
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[EN] In this work, a multiplexed sensor system is proposed by means of the combination
of low coherence interferometry (LCI) and microwave photonics (MWP). Variations of
physical magnitudes can be measured in an array of head sensors by monitoring the optical
path difference generated by each sensor. In this case, the characterization of the multiplexed
sensor system is done through the electrical transfer function corresponding to the MWP-LCI
system. Moreover, the effect produced by the mutual interaction among head sensors is
analyzed in this work. Experimental and theoretical demonstration of the system is provided
comparing single detection and balanced detection approaches., National Project TEC2014-60378; Research Excellency Award Program GVA PROMETEO 2013/012.

[EN] Multicore optical fibers are especially attractive for the fabrication of curvature and shape sensors due to the spatial distribution of the different cores. Fiber Bragg gratings have been used in the past for the implementation of these sensors, however, despite their inherent properties, they have a very limited sensitivity. In this paper, we study the use of long period gratings (LPGs) for the implementation of a directional curvature sensor. We inscribed a set of three different LPGs in a seven core optical fiber using a selective inscription technique. We inscribed a single LPG in the external cores and an array of three LPGs in the central core. We have characterized the proposed sensor for strain, torsion, and curvature magnitude and direction. The proposed sensor shows a linear response for curvature magnitudes from 0 to 1.77 m(-1) with a maximum curvature sensitivity of -4.85 nm/m(-1) and shows a near sinusoidal behavior in all the cores with curvature directions from 0 degrees to 360 degrees. The sensor shows a good insensitivity to strain. The torsion in the multicore optical fibers can be detected and measured using the maximum attenuation of the LPGs in the external cores., This work was supported in part by the Sistema Nacional de Garantia Juvenil under Grant PEJ-2014-A-75865 (Promocion de Empleo Joven e Implantacion de la Garantia Juvenil 2014, MINECO), in part by the Ministry of Economy and Competitiveness under Project TEC2014-60378-C2-1-R, in part by the FINESSE the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Action Grant 722509, and in part by the Generalitat Valenciana under Grant APOSTD/2016/015.

[EN] In this letter, a novel structure combining low coherence interferometry (LCI) and microwave photonics (MWP) is proposed. In this case, the electro-optic modulator is strategically placed inside the interferometric structure in order to modify the behavior of the whole MWP-LCI system. Specifically, limiting effects which are inherently generated as the DC term, the self-reflection term and the carrier suppression effect are avoided. This fact enables the improvement of the MWP-LCI operating range in comparison to previous proposals. Moreover, a detailed description of the MWP-LCI structure is addressed in this letter to support the corresponding experimental demonstration and theoretical development. In addition, typical LCI capabilities such as penetration depth, resolution, and sensitivity are also measured. For the MWP-LCI structure proposed here, a 1 cm penetration depth with a resolution of 120 mu m and a sensitivity beyond 50 dB are achieved., This work was supported in part by the National Project TEC2014-60378 through the Ministerio de Ciencia y Tecnologia and in part by the Regional Project PROMETEO FASE II/2013/012 through the Generalitat Valenciana. (Corresponding author: J. Mora.)

[EN] In this letter, optical OFDM signal transmission is
demonstrated by using a broadband optical source over a 10 km
fiber link. OFDM signal transmission usually employs lasers to
generate the optical carrier since the chromatic fiber dispersion
prevents the use of broadband optical sources. However, an
interferometric system is introduced to allow signal transmission
at a given RF band when a broadband optical source is
employed. Optical sources with different optical bandwidths have
been employed to explore the limitations of the system. OFDM
transmission at 2 Gb/s using both QPSK and 16QAM modulation
is demonstrated over 10 km., This work was supported in part by the National Project MINECO under Grant TEC2014-60378-C2-1-R MEMES and in part the Regional GVA funded Prometeo 2013/012 Project on Next Generation Microwave Photonic technologies.

In this letter, we propose and experimentally demonstrate an efficient and scalable photonic superstructure employed for ultrawideband (UWB) pulses modulation purposes. This design is based on the combination of a phase modulation to intensity modulation stage with a customized pulse shaper. Pulse shaping is achieved by means of a photonic structure composed by concatenated fiber Bragg gratings. The proposed scheme holds the capacity of generating high-order UWB signals, a feature that enables the implementation of widely employed modulation formats such as: pulse position modulation, pulse shape modulation, and bi-phase modulation. Theoretical and experimental measurements are exposed to sustain the validity of this system., This work was supported in part by the Ministerio de Ciencia y Tecnologia under Grant TEC2014-60378-C2-1-R and Grant TEC2014-58048-C2-2-P and in part the Regional Project PROMETEO FASE II/2013/012 through the Generalitat Valenciana.

Systems to interrogate photonic sensors based on long fiber Bragg gratings (FBGs) are illustrated and experimentally validated. The FBGs-based devices are used as quasi-distributed sensors and have demonstrated their ability to detect and measure the precise location of several spot events. The principle of operation is based on a technique used to analyze microwave photonics (MWP) filters. The overall idea beyond this work has been borne out and demonstrated step by step starting from preliminary test that have led to the development of a very-long distributed sensor based on an array of 500 equal and weak FBGs. Firstly, we have demonstrated the feasibility of the MWP filtering technique to interrogate a 10 cm-long high reflectivity (&#8776;99%) FBG. Then, a pair of low-reflectivity (<6%) FBGs has been employed as sensing device. The latter has laid the foundation for the development and implementation of a 5 m-long fiber optic sensor based on 500 very weak FBGs. Spot events have been detected with a good spatial accuracy of less than 1 mm using a modulator and a photo-detector (PD) with a modest bandwidth of only 500 MHz. The simple proposed schemes result cost effective, intrinsically robust against environmental changes and easy to reconfigure., This work was support by the Accion Financiada por el Ministerio de Educacion, Cultura y Deporte within the framework of the Programa de Campus de Excelencia Internacional VLC/Campus, by the Spanish MINECO through projects TEC2014-60378-C2-1-R, by the Grant of the program SANTIAGO GRISOLIA (Grant number GRISOLIA/2013/034), and by the Research Excellency Award Program GVA PROMETEO 2013/012.

[EN] The Karhunen-Loeve transform (KLT) is used to
retrieve the wavelength information of several fiber Bragg
gratings (FBGs) that are acting as a multiplexed sensor. The
modulated light of a broadband source is launched to the FBG
cascade in order to capture the electrical frequency response of
the system. Thanks to a dispersive media, the wavelengths of the
FBGs are mapped in radiofrequency (RF) delays. Wavelength
changes are determined by the amplitude change of the samples
in the impulse response, a change which is followed by the
eigenvalue calculated by the KLT routine. The use of the KLT
routine reduces by three orders of magnitude the amount of
points needed to have a sub-degree resolution in temperature
sensing, while keeping the accuracy almost intact., This work was supported in part by the Spanish MINECO through Project TEC2014-60378, and in part by the Government of Valencia through the Research Excellency Award Program GVA PROMETEO 2013/012. The work of J. Hervas was supported by the MECD FPU Scholarship (FPU13/04675).

[EN] In this letter, a sensitivity improvement for systems combining low-coherence interferometry (LCI) and microwave photonics (MWP) is demonstrated. This improvement is due to the introduction of a different modulation format and an exhaustive control of the optical source profile compared with previous MWP-LCI schemes. Our proposal allows to retrieve the visibility of low-coherence interferograms through the analysis of the interference pattern using a dispersive element. We demonstrate that the use of a phase modulator offers better stability and lower insertion loss since a bias point configuration is not needed compared with the intensity modulators typically used in these schemes. The process for controlling the optical source profile permits a comparison between uniform and Gaussian profiles. In this way, the limiting effects of the sidelobes over the achieved sensitivity level are analyzed. The proposed MWP-LCI structure is experimentally demonstrated through the characterization of the electrical transfer function. In this case, a maximum sensitivity of 65 dB is achieved in our MWP-LCI structure showing a 30-dB improvement compared with current proposals., This work was supported in part by the National Project through the Ministerio de Ciencia y Tecnologia under Grant TEC2014-60378-C2-1-R and in part by the Generalitat Valenciana under Grant PROMETEO FASE II/2013/012. (Corresponding author: J. Mora.)

[EN] A photonic structure is proposed by exploiting the advantages of the Microwave Photonics technology over conventional low coherence interferometry. The proposed scheme is based in the analysis of the interference pattern of an incoherent optical signal which is amplitude modulated and transmitted through a dispersive element. The strategic allocation of an interferometric structure combined with balanced photodetection are used to improve the system performance compared to the previous proposals. To the best of our knowledge, an exhaustive theoretical analysis and an experimental demonstration of the structure for multilayered samples are provided in this paper., This work was supported in part by the Ministerio de Ciencia y Tecnologia under Project TEC2014-60378 and in part by the Generalitat Valenciana under the regional Project PROMETEO 2017/103 TECNOLOGIAS Y APLICACIONES FUTURAS DE LA FOTONICA DE MICROONDAS.

Polymer optical fiber (POF) is a growing technology in short distance telecommunication due to its flexibility, easy connectorization, and lower cost than the mostly deployed silica optical fiber technology. Microstructured POFs (mPOFs) have particular promising potential applications in the sensors and telecommunications field, and they could specially help to reduce losses in polymer fibers by using hollow-core fibers or reduce the modal dispersion by providing a large mode area endlessly single-mode. However, mPOFs are intrinsically more difficult to cut due to the cladding hole structure and it becomes necessary to have a high quality POF cleaver. In the well-known hot-blade cutting process, fiber and blade are heated, which requires electrical components and increases cost. A new method has recently been identified, allowing POF to be cut without the need for heating the blade and fiber, thus opening up the possibility of an electrically passive cleaver. In this letter, we describe the implementation and testing of a high quality cleaver based on a mechanical system formed by a constant force spring and a damper, which leads to the first reported electrical passive and portable cleaver., This work was supported in part by the Juan de la Cierva Program of the Spanish Government, in part by the National Project MINECO under Grant TEC2014-60378-C2-1-R MEMES, in part by the Regional GVA funded PROMETEO 2013/012 Project on Next Generation Microwave Photonic Technologies, and in part by the China Scholarship Council.

[EN] New optical fiber based spectroscopic tools open the possibility to develop more robust and efficient characterization experiments. Spectral filtering and light reflection have been used to produce compact and versatile fiber based optical cavities and sensors. Moreover, these technologies would be also suitable to study N-photon correlations, where high collection efficiency and frequency tunability is desirable. We demonstrated single photon emission of a single quantum dot emitting at 1300 nm, using a Fiber Bragg Grating for wavelength filtering and InGaAs Avalanche Photodiodes operated in Geiger mode for single photon detection. As we do not observe any significant fine structure splitting for the neutral exciton transition within our spectral resolution (46 mu eV), metamorphic QD single photon emission studied with our all-fiber Hanbury Brown & Twiss interferometer could lead to a more efficient analysis of entangled photon sources at telecom wavelength. This all-optical fiber scheme opens the door to new first and second order interferometers to study photon indistinguishability, entangled photon and photon cross correlation in the more interesting telecom wavelengths., G Munoz-Matutano thanks the Spanish Juan de la Cierva program (JCI-2011-10686). We acknowledge the support of the Spanish MINECO through projects TEC2014-53727-C2-1-R & TEC2014-60378-C2-1-R, the Research Excellency Award Program GVA PROMETEO 2013/012 PROMETEOII/2014/059 and the Explora Ciencia Tecnologia TEC2013-50552-EXP MULTIFUN project, and the Nanoscale Quantum Optics MPNS COST Action MP1403.

A fiber optic liquid-level sensor based on a long period grating (LPG) is proposed and experimentally validated. The principle of operation is based on a technique used to analyze microwave photonics filters. A 4-cm-long LPG cascaded with a high-reflectivity fiber Bragg grating is employed to achieve a continuous liquid-level sensor. The measurements have been performed using a modulator and a photo-detector with a modest bandwidth of less than 500 MHz, showing a sensitivity of &#8722;12.71 dB/cm and a standard deviation of 0.52 dB. One of the significant advantages of such sensing structure is that it is based on low-bandwidth radio frequency and off-the-shelf photonic components. In addition, the simple proposed scheme presents good repeatable performance and proves to be intrinsically robust against environmental changes, stable, and easy to reconfigure., This work was supported in part by the Accion Financiada por el Ministerio de Educacion, Cultura y Deporte through the framework of the Programa de Campus de Excelencia Internacional VLC/Campus, in part by the Spanish MINECO under Project TEC2014-60378-C2-1-R, in part by the Grant of the SANTIAGO GRISOLIA Program, in part by the Research Excellency Award Program GVA PROMETEO 2013/012, in part by the Project TEC2013-43679-R, and in part by an UPNA Predoctoral Grant. The associate editor coordinating the review of this paper and approving it for publication was Dr. Anna G. Mignani.

We derive analytical approximations for the variation of the effective indices of the fundamental transverse electric (TE) and transverse magnetic (TM) modes with the chemical potential of graphene in three common types of silicon graphene waveguides. In all cases, a third-order polynomial provides an excellent degree of approximation (<; 10-4) over the 1540-1560 nm wavelength band. The approximations can be useful in the design of complex-integrated photonic circuits where graphene is employed to tune the refractive of the dielectric waveguides., This work was supported in part by the Research Excellency Award Program GVA PROMETEO II/2013/012; in part by Spanish MINECO projects TEC2013-42332-P PIF4ESP, TEC2015-69787-REDT PIC4TB, and TEC2014-60378-C2-1-R MEMES; and in part by projects FEDER UPVOV 10-3E-492 and FEDER UPVOV 08-3E-008. The work of D. Perez was supported by the FPI-UPV Grant Program from the Universitat Politecnica de Valencia.

[EN] The use of Spatial Division Multiplexing for Microwave Photonics signal processing is proposed and experimentally demonstrated, for the first time to our knowledge, based on the selective inscription of Bragg gratings in homogeneous multicore fibers. The fabricated devices behave as sampled true time delay elements for radiofrequency signals offering a wide range of operation possibilities within the same optical fiber. The key to processing flexibility comes from the implementation of novel multicavity configurations by inscribing a variety of different fiber Bragg gratings along the different cores of a 7-core fiber. This entails the development of the first fabrication method to inscribe high-quality gratings characterized by arbitrary frequency spectra and located in arbitrary longitudinal positions along the individual cores of a multicore fiber. Our work opens the way towards the development of unique compact fiber-based solutions that enable the implementation of a wide variety of 2D (spatial and wavelength diversity) signal processing functionalities that will be key in future fiber-wireless communications scenarios. We envisage that Microwave Photonics systems and networks will benefit from this technology in terms of compactness, operation versatility and performance stability., We thank Prof. Jose Capmany for the thoughtful discussions and recommendations that greatly contribute to this work. This research was supported by the Spanish MINECO Projects TEC2014-60378-C2-1-R and TEC2015-62520-ERC, the Valencian Research Excellency Award Program GVA PROMETEO 2013/012, the Spanish MECD FPU Scholarship (FPU13/04675) for J. Hervas, and the Spanish MINECO Ramon y Cajal Program (RYC-2014-16247) for I. Gasulla.

Single Indium Arsenide Quantum Dot emission spectra have been recorded using a four-core, crosstalk-free, multicore fiber placed at the collection arm of a confocal microscope. We developed two different measurement set-ups depending on the relative configuration of the excitation and collection spots. In the single-matched mode, the emission from the excited area is collected by a single core in the multicore fiber, whereas the three remaining cores capture the emission from neighboring, non-excited areas. This procedure allows for the recording of the Quantum Dot emission from carrier diffusion between sample positions separated by more than 6 &#956;m.
In the multiple-matched mode, the excitation spot overlaps the four cores emission area. This configuration permits the acquisition of the micro-photoluminescence spectra at different sample positions without scanning. These results show the possibilities offered by multicore fibers for the spectroscopic analysis of single semiconductor Quantum Dot optical emission., This work was supported in part by the Research Excellency Award Program GVA PROMETEO under Grant 2013/012, in part by the Explora Ciencia Tecnologia through the MULTIFUN Project under Grant TEC2013-50552-EXP, in part by the Research Excellency Award Program GVA PROMETEOII under Grant 2014/059, and in part by the Ministerio de Economia y Competitividad under Grant TEC2014-53727-C2-1-R and Grant TEC2014-60378-C2-1-R. The work of G. Munoz-Matutano was supported by the Spanish Ministerio de Economia y Competitividad through the Juan de la Cierva Program under Grant JCI-2011-10686. The work of I. Gasulla was supported by the Spanish Ministerio de Economia y Competitividad through the Ramon y Cajal Program under Grant RyC-2014-16247.

[EN] We analyze and explore the potential that waveguide-mesh-based architectures used in programmable photonic integrated circuits can be configured to enable true time optical delay lines, which can find applications in different microwave photonics functionalities, such as beamforming and optical filtering. We also propose and experimentally demonstrate an alternative standalone tunable basic unit (TBU) architecture where its internal coupling device is implemented by means of a dual-drive tunable directional coupler (DD-TDC) that performs independent amplitude beam splitting and phase shifting. Compared to the previous alternatives based on 3-dB balanced Mach-Zehnder interferometers, the DD-TDC reduces by more than two times the insertion losses of TBUs enabling the potential realization of larger meshes with a three-fold enhanced step-time resolution. Bandwidth and robustness analysis are also considered., This work was supported in part by the European Research Council under Grant ERC-ADG-2016-471715 UMWP-CHIP, in part by the COST Action CA16220 EUWMP, in part by the Spanish MINECO Projects TEC2014-60378-C2-1-R, and in part by the Gen. Valenciana PROMETEO Project 2017/103.

[EN] We report, for the first time to our knowledge, the experimental demonstration of multi-cavity optoelectronic oscillators where the cavities are provided by the different cores of a multicore fiber. We implemented two multi-cavity architectures over a 20-m-long 7-core fiber link: unbalanced dual-cavity oscillation (the cavity lengths are a multiple of a reference value) and multi-cavity Vernier oscillation (the cavity lengths are slightly different). Since all the cavities are hosted under a single fiber cladding and are subject to the same environmental and mechanical conditions, optoelectronic oscillators built upon multicore fibers benefit from improved performance stability as compared to independent singlemode fiber cavities., H2020 European Research Council (ERC) (724663); Ministerio de Economia y Competitividad (TEC2014-60378-C2-1-R, TEC2016-80150-R, BES-2015- 073359, RYC2014-16247)

[EN] We report a trench-assisted heterogeneous multicore fiber optimized in terms of higher-order dispersion and crosstalk for radiofrequency true time delay operation. The analysis of the influence of the core refractive index profile on the dispersion slope and effective index reveals a tradeoff between the behavior of the crosstalk against fiber curvatures and the linearity of the propagation group delay. We investigate the optimization of the multicore fiber in the framework of this tradeoff and present a design that features a group delay relative error below 5% for an optical wavelength range up to 100 nm and a crosstalk level below -80 dB for bending radii larger than 103 mm. The performance of the true time delay line is validated in the context of microwave signal filtering and optical beamforming for phased array antennas. This work opens the way towards the development of compact fiber-integrated solutions that enable the implementation of a variety of distributed signal processing functionalities that will be key in future fiber-wireless communications networks and systems. (C) 2016 Optical Society of America, Spanish MINECO (TEC2015-62520-ERC Project); Spanish MINECO (TEC2014-60378-C2-1-R MEMES Project); Spanish MINECO (BES-2015-073359 fellowship); Spanish MINECO Ramon y Cajal Program (RYC-2014-16247).

Chirped pulses generation is evaluated and experimentally demonstrated by means of the processing of incoherent optical signals using a non-linear dispersive element. The capability of generating chirped electrical pulses, in which the instantaneous frequency changes with time, has been demonstrated for a Gaussian waveform envelope similar to photonic coherent techniques. For pulse compression radar
systems, the control of the pulse envelope permits to increase the coverage distance of the transmitted signals and the spatial resolution of the system. In this sense, the envelope control of the
generated waveform has been also experimentally demonstrated for different profiles such as gradual, hyperbolic tangent and uniform by means of the optical signal power spectral density. Indeed, we have experimentally probed how the resolution and the coverage distance of the signals can be increased for a uniform waveform in a pulse compression radar system., This work was supported in part by the Ministerio de Ciencia y Tecnologia through the National Project under Grant TEC2014-60378-C2-1-R and in part by Generalitat Valenciana through the Regional Project under Grant PROMETEO FASE II/2013/012.

[EN] We implement "fiber-distributed signal processing" in the context of fiber-wireless
communications by using different multicore fibers, providing both radio access distribution and microwave photonics signal processing in the same fiber medium., This research was supported by the ERC Consolidator Grant 724663, the Spanish Projects TEC2014-60378-C2-1-R, TEC2015-62520-ERC and TEC2016-80150-R, the Spanish scholarships MECD FPU13/04675 for J. Hervás and MINECO BES-2015-073359 for S. García, and Spanish MINECO Ramón y Cajal RYC-2014-16247 for I. Gasulla

[EN] We have inscribed a tilted fiber Bragg grating (TFBG) in selected cores of a multicore optical fiber. The presence of the TFBG permits to couple light from the incident guided mode to the cladding modes and to the neighbor cores and this interaction can be used for optical sensing. We have considered to measure different magnitudes: strain, curvature magnitude and direction and external refractive index. The curvature results show a linear dependence of the maximum crosstalk with the curvature magnitude with a sensitivity of 2.5dB/m-1 as the curvature magnitude increases and at the same time a wavelength shift of 70pm/m-1. Changes in the external refractive index gradually vanishes the cladding modes resonances and the crosstalk between the different cores obtaining a reduction of the 90% of the optical spectra integral area for refractive indexes between 1.398 to 1.474., Generalitat Valenciana (APOSTD/2016/015, GVA PROMETEO 2013/012); Ministerio de Economia y Competitividad (MINECO) (TEC2014-60378-C2-1-R).

[EN] We propose and experimentally demonstrate a fullyreconfigurable generator of chirped microwave pulses based on the processing of an incoherent optical signal by means of a dispersive element with a non-uniform optical spectral shaping. The system performance has been proven by the generation of different chirped microwave pulses. Different capabilities of the system have been experimentally demonstrated as frequency tunability and time-bandwidth product control by means of the dispersive element and optical source power distribution. Furthermore, the possibility for generating chirped microwave pulses with positive and negative chirp characteristic has been shown achieving similar chirps in terms of magnitude but opposite sign. For it, the chirp characteristic is introduced by proper shaping of the optical source signal power distribution., This work was supported in part by the National Project under Grant TEC2014-60378-C2-1-R funded by the Ministerio de Ciencia y Tecnologia and in part by the Regional Project PROMETEO FASE under Grant II/2013/012 funded by the Generalitat Valenciana.

[EN] This paper presents a review and discussion of the
applications of Microwave Photonic techniques and
functionalities to the field of optical fiber sensors. A specific
end-to end model for its characterization is presented here for the
first time that yields the sensitivity of the different figures of
merit in terms of measurand variations. Experimental techniques
to characterize these systems are presented and applications of
two specific microwave photonic functionalities to high-resolution
discrete and quasi-distributed optical sensing are illustrated.
Future directions of research are also highlighted., This work was supported in part by the Spanish MINECO through projects TEC2014-60378-C2-1-R MEMES and in part by the Government of Valencia through the Research Excellency Award Program GVA PROMETEO II/2013/012. The work of J. Hervas was supported by the MECD FPU scholarship (FPU13/04675). The work of Ming Li was supported in part by the National Natural Science Foundation of China under Grants 61377002, 61522509, and 61535012and in part by the Thousand Young Talent program

[EN] We present a model to compute the figures of merit of self-beating Microwave Photonic systems, a novel class of systems that work on a self-homodyne fashion by sharing the same laser source for information bearing and local oscillator tasks. General and simplified expressions are given and, as an example, we have considered their application to the design of a tunable RF MWP BS/UE front end for band selection, based on a Chebyshev Type-II optical filter. The applicability and usefulness of the model are also discussed., This research work is funded by INTEL Corporation. In addition, the authors wish to acknowledge the financial support given by the Research Excellency Award Program GVA PROMETEO II/2013/012, Spanish MINECO projects TEC2013-42332-P PIF4ESP, TEC2015-69787-REDT PIC4TB and TEC2014-60378-C2-1-R MEMES, as well as the projects FEDER UPVOV 10-3E-492 and FEDER UPVOV 08-3E-008. The work of D. Perez was supported by the FPI-UPV Grant Program from the Universitat Politecnica de Valencia and the work of I. Gasulla was supported by the Spanish MINECO through the Ramon y Cajal Program.

In this letter, we present a high-order impulseradio ultra-wideband (UWB) pulses generator based on the processing of incoherent optical signals by a dispersive element. The full waveform reconfigurability is achieved by the control of the optical signal power spectral density profile. Operation principle is experimentally shown by the generation of classical UWB pulses: monocycle and doublet. High-order UWB pulses generation is experimentally demonstrated by the generation of triplet and quadruplet. Also, the proper adjustment of the optical signal power distribution permits to reduce the baseband content of the synthesized waveform, which is critical in UWB environments to achieve spectrally efficient solutions. Moreover, system flexibility allows the adaptation to a bi-phase modulation scheme. This feature has been proved by the generation of the inverted version of the UWB pulses achieved in this letter., This work was supported in part by the Ministerio de Ciencia y Tecnologia through the National Project under Grant TEC2014-60378-C2-1-R and in part by the Generalitat Valenciana through the Regional Project under Grant PROMETEO FASE II/2013/012.

[EN] Low coherence interferometry (LCI) is an optical measurement technique that has attracted the interest for relevant fields like medicine or sensing. With the objective of improving LCI capabilities, microwave photonics (MWP) arises as an innovative technology to enhance LCI possibilities. In this letter, a novel MWP-LCI approach is proposed and experimentally demonstrated to measure the optical path difference (OPD) of a sample. The operation principle of the technique is based on the analysis of the interference pattern through a dispersive element to retrieve its visibility using a vector network analyzer. Different capabilities of the system in terms of sensitivity, resolution, and SNR have been proved. In this case, the proposal is able to avoid carrier-suppression effect leading to a sensitivity improvement of 20 dB in comparison with previous structures for certain values of the OPD. Moreover, the OPD range has been extended up to 10 mm achieving an invariant resolution over all operation range. Finally, the improvement of the SNR of the system has been experimentally demonstrated by controlling properly the RF resonance profile through the adjustment of the optical source power distribution. We have observed an improvement of the dynamic range close to 40 dB for a Gaussian profile., This work was supported in part by the National Project funded by the Ministerio de Ciencia y Tecnologia under Grant TEC2014-60378-C2-1-R and in part by the Regional Project PROMETEO FASE under funded by the Generalitat Valenciana Grant II/2013/012.

[EN] This paper is focused on the characterization of a fiber Bragg grating (FBG) sensor interrogation system based on a fiber ring laser with a semiconductor optical amplifier as the gain medium, and an in-loop electro-optical modulator. This system operates as a switchable active (pulsed) mode-locked laser. The operation principle of the system is explained theoretically and validated experimentally. The ability of the system to interrogate an array of different FBGs in wavelength and spatial domain is demonstrated. Simultaneously, the influence of several important parameters on the performance of the interrogation technique has been investigated. Specifically, the effects of the bandwidth and the reflectivity of the FBGs, the SOA gain, and the depth of the intensity modulation have been addressed. (C) 2017 Optical Society of America, This work has been partially supported by the Spanish MINECO through project TEC2014-60378-C2-1-R MEMES; the Generalitat Valenciana (APOSTD/2016/015), Sistema Nacional de Garantia Juvenil grant PEJ-2014-A-75865 (Promocion de Empleo Joven e Implantacion de la Garantia Juvenil 2014, MINECO); the Galician Regional Government under project GRC2015/018; the support of FINESSE the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska - Curie Action grant agreement no 722509; the National Natural Science Foundation of China (61405166) and the China Scholarship Council.

[EN] We propose and experimentally demonstrate distributed microwave photonics signal processing over a few-mode fiber link by implementing 4-sample true time delay line operation. The inscription of a set of long period gratings at specific locations along the few-mode fiber allows the excitation of the higher-order modes while adjusting the individual sample group delays and amplitudes that are required for sampled true time delay line behavior. Since solely the injection of the fundamental mode at the few-mode fiber input is required, we render this signal processing system independent of any preceding fiber link that may be required in addition to distribute the signal. We experimentally validate the performance of the implemented true time delay line when applied to radiofrequency signal filtering., European Research Council (ERC) (Consolidator Grant 724663); Spanish MINECO (TEC2014-60378-C2-1-R and TEC2016-80150-R projects, BES-2015-073359 scholarship for S. Garcia, IJCI-2017-32476 fellowship for D. Barrera, Ramon y Cajal fellowship RYC-2014-16247 for I. Gasulla); Universitat Politecnica de Valencia (PAID-01-18 scholarship for J. Madrigal).

[EN] A simple, spectral-drift-insensitive interrogation scheme for
a multicore fiber Bragg grating (FBG)-based directional
curvature sensor is proposed. The basic principle is to transform
the wavelength shift of FBGs into the reflected power
variation, which is accomplished by utilizing a broadband
source with a sinusoidal spectrum. The closed-form expression
of the relationship between the reflected power of the
FBG and the corresponding peak wavelength is derived for
the first time, to the best of our knowledge; therefore, the
peak wavelength of the FBG can be precisely interrogated
by using a single photodiode. The experimental results
show that, with respect to conventional wavelength measurement
by an optical spectrum analyzer, the demodulated
wavelength error by our proposed interrogation scheme is
within 20 pm. The proposed scheme is further extended
to interrogate the direction and curvature using a multicore
FBG-based curvature sensor; the interrogated curvature
with an error less than 8% is achieved., National Natural Science Foundation of China (NSFC) (61405166); China Scholarship Council (CSC); Generalitat Valenciana (APOSTD/2016/015, GVA PROMETEO 2013/012); Ministerio de Economia y Competitividad (MINECO) (TEC2014-60378-C2-1-R).

A humidity and temperature optical fiber sensor based on a long-period grating (LPG), which can provide simultaneous response to both magnitudes, is proposed and demonstrated via experiments. Previously, the LPG was fully coated with humidity sensitive nanostructured polymeric thin films by the Layer-by-Layer (LbL) nano assembly technique. Hence the surrounding refractive index was changed, so provoking wavelength shifts of the attenuation bands of the transmission spectrum. This fully coated LPG was exposed to relative humidity (RH) and temperature tests, varying from 20% to 80% RH and from 25 to 85ºC, respectively. Then, half of the LPG coating was chemically removed and this results in the splitting of the main attenuation band into two different contributions. When this semi-coated LPG was also exposed to RH and temperature tests, the new two attenuation bands presented different behaviors for humidity and temperature. This novel dual-wavelength based sensing method enables the simultaneous measurement of RH and temperature using only one LPG., This work was supported in part by the Spanish Ministry of Economy and Competitiveness - through the projects CICYT-FEDER TEC2013-43679-R and TEC2014-60378-C2-1-R. It was also supported by a UPNA pre-doctoral research grant, by the Program of International Excellence Campus VLC/Campus, by the grant of program SANTIAGO GRISOLIA, and by the Research Excellency Award Program GVA PROMETEO 2013/012.

A technique is proposed to interrogate a distributed
photonic sensor composed of seven standard fiber Bragg gratings
in cascade. A microwave-modulated optical signal is launched into
an FBG cascade and subsequently undergoes dispersion in standard
single-mode fiber, so that the different Bragg wavelengths are
mapped into the radio-frequency (RF) delays that determine the
peaks in the electrical impulse response of the optical link. Shifts
in Bragg wavelengths have been determined from the shifts in the
impulse response s peaks by recording the link s RF response in
the range dc-20 GHz using a vector network analyzer (VNA), and
then performing its inverse Fourier transform. A resolution of 14
pm is experimentally demonstrated after zero-padding the VNA
traces., This work was supported in part by the Spanish MINECO under Projects TEC201-60378-C2-1-R and -2-R, by the EU Infraestructura FEDER Operative Program 2007-2013, and by the Government of Valencia under the Research Excellency Award Program GVA PROMETEO 2013/012. The work of J. Hervas was supported by the MECD FPU Scholarship (FPU13/04675).