Single-longitudinal mode laser structure based on a very narrow filtering technique

A narrow filtering technique based on the spectral overlapping of two uniform FBGs and applied to obtain a Single Longitudinal Mode (SLM) laser is proposed and demonstrated in this work. The two FBGs are spectrally detuned to reduce their coincident reflection response narrowing the equivalent filter bandwidth. A proof-of-concept linear laser has been built and tested exhibiting SLM operation even with temperature and strain variations.The authors are grateful to the Spanish government project TEC2010-20224-C02, to the Spanish Ministry of Education and Culture, and to the grant AP2009-1403

2020 taxonomic update for phylum Negarnaviricota (Riboviria: Orthornavirae), including the large orders Bunyavirales and Mononegavirales.

In March 2020, following the annual International Committee on Taxonomy of Viruses (ICTV) ratification vote on newly proposed taxa, the phylum Negarnaviricota was amended and emended. At the genus rank, 20 new genera were added, two were deleted, one was moved, and three were renamed. At the species rank, 160 species were added, four were deleted, ten were moved and renamed, and 30 species were renamed. This article presents the updated taxonomy of Negarnaviricota as now accepted by the ICTV

Compound lasing fiber optic ring resonators for sensing

In this work, we present a new method for increasing simultaneously the sensitivity and interrogation stability of fiberoptic intensity sensors. The configuration is based on a double-coupler ring resonator. On one side, the attenuation sensitivity of the sensor is enhanced by placing it inside a ring resonator. On the other side, the stability of the interrogation method is rendered close to perfect by creating an external lasing ring resonator with matched spectral response. The resulting lasers allow the stable interrogation of the sensors with an impressive sensitivity enhancement. In our experiments, the dynamic range of the intensity sensor (and consequently its sensitivity) is increased 15 dB by using this laser-based interrogation system. Simultaneously, the instability of the system is reduced to ±0.05 dB. In comparison with systems based on external interrogation, our method is <100 times more stable and also simpler, as no wavelength tunable elements are required.Ministerio de Educación y CienciaEuropean Commissio

Compound Lasing Fiber Optic Ring Resonators for Sensor Sensitivity Enhancement

In this study, a new method for increasing simultaneously the sensitivity and interrogation stability of fiber-optic intensity sensors is presented. The configuration is based on a double-coupler ring resonator. On one side, the attenuation sensitivity of the sensor is enhanced by placing it inside a ring resonator. On the other side, the stability of the interrogation method is widely improved by creating an external lasing ring resonator with matched spectral response. The combination of the wavelength selective response of the ring resonator and optical amplification from Er-doped fiber amplifier is used to create different fiber lasers. The resulting lasers present an impressive sensitivity enhancement and a dynamic range increment up to 15 dB. Simultaneously, the instability of the system is reduced to ±0.05 dB. In comparison with systems based on tunable laser interrogation, our method is >100 times more stable and also simpler, as no wavelength tunable elements are required.Ministerio de Economía y CompetitividadEuropean Commissio

Fiber laser sensor system based on a random mirror and a compound ring resonator for displacement measurements

24th International Conference on Optical Fibre Sensors (OFS 24), Curitiba, Brazil, Sept. 28-Oct. 2, 2015.In this work, we present a random laser sensor system for increasing simultaneously the sensitivity and interrogation stability of a fiber-optic displacement sensor. The system is based on a random distributed fiber laser modulated by a double-coupler ring resonator within which is placed the sensor. This allows to increase the sensitivity of the sensor and also its interrogation stability. The experimental results show a dynamic range increment (and consequently its sensitivity) of 10dB. Moreover, by using this laser-based interrogation system, the instability is reduced to 0.04 dB. In addition, wavelength filtering elements are not required, simplifying the system.Ministerio de Economía y CompetitividadEuropean Commissio

An Efficient Radiographic Image Retrieval System Using Convolutional Neural Network

Content-Based Medical Image Retrieval (CBMIR) is an important research field in the context of medical data management. In this paper we propose a novel CBMIR system for the automatic retrieval of radiographic images. Our approach employs a Convolutional Neural Network (CNN) to obtain high- level image representations that enable a coarse retrieval of images that are in correspondence to a query image. The retrieved set of images is refined via a non-parametric estimation of putative classes for the query image, which are used to filter out potential outliers in favour of more relevant images belonging to those classes. The refined set of images is finally re-ranked using Edge Histogram Descriptor, i.e. a low-level edge-based image descriptor that allows to capture finer similarities between the retrieved set of images and the query image. To improve the computational efficiency of the system, we employ dimensionality reduction via Principal Component Analysis (PCA). Experiments were carried out to evaluate the effectiveness of the proposed system on medical data from the “Image Retrieval in Medical Applications” (IRMA) benchmark database. The obtained results show the effectiveness of the proposed CBMIR system in the field of medical image retrieval.QC 20161208</p

Experimental observation of anomalous RIN transfer in random distributed feedback Raman fiber lasers

onference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, Munich, Germany, 23–27 June 2019We report the experimental observation of anomalous RIN transfer function in ultralong random distributedfeedback fiber lasers, confirming theoretical predictions and opening up the possibility of low-frequency RIN reduction via laser design

Anomalous relative intensity noise transfer in ultralong random fiber lasers

9 pags., 7 figs., 1 tab.We present, for the first time, an experimental demonstration of RIN noise transfer dampening at low frequencies in random distributed feedback ultralong Raman fibre lasers based on conventional telecommunication fibres. Furthermore, we present a thorough theoretical description of the phenomenon and demonstrate how our model can be used to predict the observed behaviour, identifying the general requirements for system improvement through RIN transfer reduction.Comunidad de Madrid (AEI/FEDER funds TALENTO-CM 2017-T2/TIC-5227, SINFOTON2- CM (S2018-NMT/4326)); Horizon 2020 Framework Programme (Marie Sklodowska-Curie—748839); LAPHIA (Lasers and Photonics in Aquitaine); Conseil Régional d’Aquitaine (2017-1R50302- 00013493); Universidad de Alcalá (CCG19/IA-051); Spanish Government (PID2019-107270RBC22, RTI2018-RTI2018-097957-B-C33)

Watt-level green random laser at 532 nm by SHG of a Yb-doped fiber laser

We have developed a Watt-level random laser at 532 nm. The laser is based on a 1064 nm random distributed ytterbium-gain assisted fiber laser seed with a 0.35 nm line-width 900mW polarized output power. A study for the optimal length of the random distributed mirror was carried out. An ytterbium-doped fiber master oscillator power amplifier architecture is used to amplify the random seeder laser without additional spectral broadening up to 20 W. By using a periodically poled lithium niobate (PPLN) crystal in a single pass configuration we generate in excess of 1 W random laser at 532 nm by second harmonic generation with an efficiency of 9 %. The green random laser exhibits an instability 70 dB, 0.1 nm linewidth and excellent beam quality. Random distributed fiber lasers (RDFLs) based on distributed Rayleigh scattering, have been thoroughly investigated due to their high performances and unique features [1]. Where traditional laser schemes are based in resonant cavities for feedback generation, RDFLs use the Rayleigh scattering of a long fiber as distributed mirror, generating a modeless-behavior laser [2,3]. The research in this field has led to the generation of ultra-high power RDFLs from hundreds of Watts [4] to kWs [5,6], narrower linewidth RDFLs up to sub-gigahertz [7], polarized output RDFLs [8-10], tunable RDFLs [11-13] and pulsed generation [14,15]. Gain in RDFLs can be generated from Raman scattering [2,16], by rare earth-doped fibers [12,13] or a hybrid of both [17]. However, to date random lasers in the visible based on second harmonic generation (SHG) of RDFLs have been only reported in [18] with the generation of 110 mw at 654nm in a magnesium periodically poled lithium niobate (MgPPLN) crystal. In this letter, we report for the first time, to the best of our knowledge, a Watt-level visible random laser at 532 nm based on SHG of a RDFL, with a polarized output power in excess of 1W, instability 70 dB and excellent beam quality. The RDFL is based on a half open-cavity setup assisted by a 3m-long Yb-doped double-clad fiber as gain medium (see Fig. 1). The core and clad radii of the fiber are respectively 10 and 130 m, and its clad absorption is 4.6 dB/m at 976 nm. The Yb-fiber is forward-pumped through a multi-mode (MM) combiner with a 9W multimode laser diode (LD) at 976nm. Forward pumping has been previously reported as more efficient in Yb-gain assisted RDFL [19]. The wavelength selection is carried out by a high-reflective (99.85%) fiber Bragg grating (FBG) centered at 1064.39 nm and with a 0.57 nm bandwidth. The distributed mirror is based on single-mode fiber (SMF28). Although this fiber operates in multimode regime at 1064 nm, the splice with the 1060 fiber at the output-isolator filters the high order modes. Moreover, the SMF core radius (∼9 m) is comparable to the Yb-fiber one, reducing the losses in the splice. A pump power stripper was used before the SMF fiber in order to remove the residual pump. Fig. 1. Schematic of the 532nm random laser. (RDFL: Random Distributed Fiber Laser, MO: Master Oscillator, PA: Power Amplifier, SHG: Second Harmonic Generation, PM ISO: Polarization Maintaining Isolator) To optimize the length of the distributed mirror, we carried out measurements for different SMF lengths from 1.5Km to 3Km. Figure 2 shows the spectra and the output power before the isolator for the different SMF lengths. As expected, Raman scattering becomes significant for longer fibers, starting to be critical for lengths over 3Km. Moreover, the high attenuation of SMF28 at 1064 nm (∼1.5 dB/Km) reduce the efficiency, making shorter fibers more attractive. However, the key-point for the distributed mirror length selection was determined by the random laser behavior. RDFL dynamics are less investigated in rare-earth doped-fiber gain assisted systems than in the based on Raman gain. In order to contribute to the understanding of this class of laser, we carried out a consistent study of the RDF