Overdrive short pulse high peak power diode lasers without catastrophic optical damage

Light Imaging Detection and Ranging (LIDAR) and Optoacoustic biomedical imaging techniques are applications that have a specific laser source requirements: short pulses, high peak power per pulse and high repetition rates. A custom current driver has been designed to fulfill these requirements and characterized in order to generate high current short pulses to drive High Power Diode Lasers (HPDL) beyond their maximum rating value, with a maximum current capacity of 120 A in a range of less than 10 nanoseconds pulse width, rise times up to 2 ns and a repetition rate of 1 kHz. Four commercial HPDLs have been driven generating optical pulses of less than 10 ns and more than four times the maximum rated optical peak power. A single laser device reached a maximum peak power of 880.6 W at 6 ns pulse width, demonstrating stable operation without catastrophic optical damage and improving the typical operation characteristics of the HPDLs for high speed short pulse applications.This work was supported by Comunidad de Madrid under Grant S2018/NMT-4333 MARTINLARA-CM project within the Programa de Actividades de I+D entre grupos de investigación de la Comunidad de Madrid en Tecnologías 2018

Invited Article: Experimental evaluation of gold nanoparticles as infrared scatterers for advanced cardiovascular optical imaging

Documento escrito por un elevado número de autores/as, solo se referencia el/la que aparece en primer lugar y los/las autores/as pertenecientes a la UC3MThe tremendous impact that cardiovascular diseases have in modern society is motivating the research of novel imaging techniques that would make possible early diagnosis and, therefore, efficient treatments. Cardiovascular optical coherence tomography (CV-OCT) emerged as a result of such a demand, and it has already been used at the clinical level. Full utilization of CV-OCT requires the development of novel contrast molecular agents characterized by a large scattering efficiency in the infrared (800-1400 nm). Gold nanoparticles (GNPs) seem to be the best candidates, but their scattering properties in the infrared are hardly known. In most of the cases, scattering properties are extracted from numerical simulations. This knowledge gap here is covered by providing an experimental evaluation of the infrared scattering properties of different GNPs (nanoshells, nanostars, and nanorods). These GNPs display remarkable extinction coefficients in the first and second biological windows, including the particular CV-OCT wavelength. We use a unique combination of techniques (thermal loading experiments, infrared optical coherence tomography, infrared dark field microscopy, and optoacoustic spectroscopy) to experimentally determine the scattering efficiency at three different near-infrared wavelengths (808 nm, 980 nm, and 1280 nm), lying in the first and second biological windows. Consequently, this work determines experimentally the influence of particle morphology on the infrared scattering efficiency of GNPs and evidences the existence of remarkable discrepancies between experimental data and numerical simulations. (C) 2018 Author(s).This work was supported by the Spanish Ministerio de Economía y Competitividad under Project No. MAT2016-75362-C3-1-R. J.A.S.-G. and D.R.A. acknowledge the partial financial support from the Spanish Ministerio de Economía y Competitividad  through the grant LENSBEAM (No. FIS2015-69295-C3-2-P), Ministerio de Educación, Cultura y Deporte through a Ph.D. Fellowship (No. FPU15/03566), and also Consejo Superior de Investigaciones Científicas (i-COOP LIGHT 2015CD0011). J.H. acknowledges the scholarship from the China Scholarship Council (CSC, No. 201506650003). D.T. and P.R.G. acknowledge the Mineco and MdM Excellence Intiative (Nos. FJCI-2014-22398, RYC-2012-10059, CTQ2013-45433-P[FEDER], and MDM-2014-0370-04)

Wavelength tuning of polymer optical fibre Bragg grating at longer wavelengths permanently

Permanent Bragg wavelength tuning of polymer optical fibre Bragg grating (POFBG) at longer wavelengths has been demonstrated for the first time utilising the thermal annealing process. In general, exposing the polymer material above its β-Transition temperature, the fibre shrinks in length, the Bragg grating period becomes shorter and the Bragg wavelength shifts permanently to shorter wavelengths. In this work, a positive tuning of Bragg wavelength has been shown to be feasible when the polymer fibre is stretched during its thermal exposure. The results show that the degree of Bragg wavelength tuning strongly depends on the applying fibre strain or equivalently stress. The work presented in this paper can be used to multiplex POFBGs at any desirable wavelength

Calibration of a high spatial resolution laser two-color heterodyne interferometer for density profile measurements in the TJ-II stellarator

Proceedings of: 17th Topical Conference on High-Temperature Plasma Diagnostics, Albuquerque, New Mexico, 11-15 May 2008A high spatial resolution two-color (CO2, lambda=10.6 mum, He-Ne, lambda=633 nm) interferometer for density profile measurements in the TJ-II stellarator is under development and installation, based in the currently operational single channel two-color heterodyne interferometer. To achieve the objectives of 32 channels, with 4-5 mm lateral separation between plasma chords, careful design and calibration of the interferometric waveforms for both the measurement and vibration compensation wavelengths are undertaken. The first step has been to set up in our laboratories an expanded-beam heterodyne/homodyne interferometer to evaluate the quality of both interferometric wavefronts, a reported source of poor vibration compensation and thus low resolution in the density profile measurements. This novel interferometric setup has allowed us to calibrate the spatial resolution in the profile measurements resulting in ~2 mm lateral resolution in the reconstruction of the interferometric wavefront

Utilising thermal annealing for multiplexing and sensitivity enhancement of polymer optical fibre sensors

Thermal annealing was initially introduced for multiplexing purposes, since it can induce a permanent negative Bragg wavelength shift for polymer fibre grating sensors. At a later stage, it is shown that annealing can also provide additional benefits, such as strain and humidity sensitivity enhancement and augmented temperature operational range. In this paper, we report additional usage of thermal annealing on PMMA fibre Bragg grating sensors. We show the possibility to tune Bragg wavelengths to longer wavelengths permanently by stretching the polymer optical fibre during the thermal annealing process. An array of sensors fabricated with only one phase-mask, demonstrates the concept by having Bragg wavelengths below and above the original inscribed spectral position. In addition, we report that thermal annealing can be also used to enhance the performance of sensors when used for stress and force monitoring

Photonic-based integrated sources and antenna arrays for broadband wireless links in terahertz communications

This paper analyzes integrated components for ultra-broadband millimeter-wave wireless transmitters enabling the 5 G objective to increase the wireless data rates 10x to 100x . We have pursued the photonic-based approach to generate the millimeter-wave carrier (approximate to 97GHz in this paper) through photomixing. We have achieved up to 10 Gb s(-1) data rate using an OOK modulation format (to reduce latency) and either direct detection (DD) or coherent detection. We show that coherent detection enables a sensitivity improvement of 17 dB over DD. We also demonstrate in this work that such improvement can be achieved using as the transmitter a novel integrated antenna array-the self-complementary chessboard array. This avoids the use of complex coherent schemes at the receiver, enabling simple DD for ultra-broadband links.The authors acknowledge Dr David Gonzalez Ovejero for fruitful discussions on antenna simulation. This work has been financially supported by Ministerio de Economia, Industria y Competitividad iTWIT Proyect with references TEC2016-76 997-C3-2-R and TEC2016-76 997-C3-3-R. Authors also acknowledge Ayuda Fundacion BBVA a Investigadores y Creadores Culturales 2016' and 'Estancias de movilidad de profesores PRX16/00 021'

Optimization of a Hardware Implementation for Pulse Coupled Neural Networks for Image Applications

Pulse Coupled Neural Networks are a very useful tool for image processing and visual applications, since it has the advantages of being invariant to image changes as rotation, scale, or certain distortion. Among other characteristics, the PCNN changes a given image input into a temporal representation which can be easily later analyzed for pattern recognition. The structure of a PCNN though, makes it necessary to determine all of its parameters very carefully in order to function optimally, so that the responses to the kind of inputs it will be subjected are clearly discriminated allowing for an easy and fast post-processing yielding useful results. This tweaking of the system is a taxing process. In this paper we analyze and compare two methods for modeling PCNNs. A purely mathematical model is programmed and a similar circuital model is also designed. Both are then used to determine the optimal values of the several parameters of a PCNN: gain, threshold, time constants for feed-in and threshold and linking leading to an optimal design for image recognition. The results are compared for usefulness, accuracy and speed, as well as the performance and time requirements for fast and easy design, thus providing a tool for future ease of management of a PCNN for different tasks

Stabilization in an optical fiber interferometer using semiconductor laser

Micro-optical Technologies for Measurement, Sensors, and Microsystems II and Optical Fiber Sensor Technologies and Applications, Munich (Germany), 18 june 1997.In this paper we present results of our stabilization scheme for an optical fiber Mach-Zehnder interferometer with a diode laser as light source. It is developed for compensating the drift path difference produced by external parameters as the environmental temperature. The optoelectronic setup in which the interference signal is fed back to the injection current of the laser diode is investigated in order to obtain a stabilized system. Details on parameter characterization, system design and the results observed are given.Publicad

Invited Article: Experimental evaluation of gold nanoparticles as infrared scatterers for advanced cardiovascular optical imaging

The tremendous impact that cardiovascular diseases have in modern society is motivating the research of novel imaging techniques that would make possible early diagnosis and, therefore, efficient treatments. Cardiovascular optical coherence tomography (CV-OCT) emerged as a result of such a demand, and it has already been used at the clinical level. Full utilization of CV-OCT requires the development of novel contrast molecular agents characterized by a large scattering efficiency in the infrared (800-1400 nm). Gold nanoparticles (GNPs) seem to be the best candidates, but their scattering properties in the infrared are hardly known. In most of the cases, scattering properties are extracted from numerical simulations. This knowledge gap here is covered by providing an experimental evaluation of the infrared scattering properties of different GNPs (nanoshells, nanostars, and nanorods). These GNPs display remarkable extinction coefficients in the first and second biological windows, including the particular CV-OCT wavelength. We use a unique combination of techniques (thermal loading experiments, infrared optical coherence tomography, infrared dark field microscopy, and optoacoustic spectroscopy) to experimentally determine the scattering efficiency at three different near-infrared wavelengths (808 nm, 980 nm, and 1280 nm), lying in the first and second biological windows. Consequently, this work determines experimentally the influence of particle morphology on the infrared scattering efficiency of GNPs and evidences the existence of remarkable discrepancies between experimental data and numerical simulations.This work was supported by the Spanish Ministerio de Economía y Competitividad under Project No. MAT2016-75362-C3-1-R. J.A.S.-G. and D.R.A. acknowledge the partial financial support from the Spanish Ministerio de Economía y Competitividad through the grant LENSBEAM (No. FIS2015-69295-C3-2-P), Ministerio de Educación, Cultura y Deporte through a Ph.D. Fellowship (No. FPU15/03566), and also Consejo Superior de Investigaciones Científicas (i-COOP LIGHT 2015CD0011). J.H. acknowledges the scholarship from the China Scholarship Council (CSC, No. 201506650003). D.T. and P.R.G. acknowledge the Mineco and MdM Excellence Intiative (Nos. FJCI-2014-22398, RYC-2012-10059, CTQ2013-45433-P[FEDER], and MDM-2014-0370-04)