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Design and testing of an optical instrument for skin flap monitoring
(Scientific Report, 2023-10-05) Moreno Oyervides, Aldo Luis; Diaz Ojeda, Luis; Bonilla Manrique, Óscar Elías; Bonastre-Julia, Jorge; Largo Aramburu, Carlota; Acedo Gallardo, Pablo; Martín Mateos, Pedro; Ministerio de Economía y Competitividad (España)
Flap procedures are complex surgical tools widely used in reconstructive surgery. Flap ischemia is one of the most dangerous complications, both during the surgical procedure and during the patient's recovery, which can quickly lead to tissue necrosis (flap loss) with serious medical and psychological consequences. Today, bedside clinical assessment remains the gold standard for flap monitoring, but timely detection of flap ischemia is a difficult and challenging task, so auxiliary techniques are needed to support flap monitoring. Here we present a prototype of a new optical diagnostic tool, based on visible light absorption in diffuse reflectance spectroscopy, for non-invasive, continuous, real-time monitoring of flaps. The proposed approach is assessed by monitoring flap ischemic scenarios induced on pig animal models. The results obtained support that the proposed approach has great potential, not only for prompt detection of ischemia (in seconds), but also for clear differentiation between an arterial occlusion and venous occlusion.
Characterization of Light-To-Frequency Converter for Visible Light Communication Systems
(MDPI, 2018-08-28) Martínez Ciro, Roger Alexander; López Giraldo, Francisco Eugenio; Betancur Pérez, Andrés Felipe; Luna Rivera, Martín
PIN (positive intrinsic negative) photodiodes and analog-to-digital converters (ADC) are commonly used on visible light communication (VLC) receivers in order to retrieve the data on detected signals. In this paper, a visible light communication receiver based on a light to frequency converter (LTF) is proposed. We characterized the LTF and derived an equation for signal-to-noise ratio (SNR) estimation in terms of its input optical power, and the frequency of the output periodic signal. The experiments show that the periodic signal of the LTF converter has a maximum output frequency of 600 kHz at a distance of 6.2 cm. In this setup, measured SNR reached 18.75 dB, while the lowest obtained SNR with 1.1 m length was roughly −35.1 dB. The results obtained suggest that a bit rate of 150 kbps can be achieved with an on-off keying (OOK) modulation format. We analyzed the results and discuss the advantages and limitations of the LTF converter for optical wireless communication purposes.
Anisotropic excitation of surface plasmon polaritons on a metal film by a scattering-type scanning near-field microscope with a nonrotationally-symmetric probe tip
(De Gruyter, 2017-10-01) Deutsch, Frederik William; Wiecha, Matthias M.; Mecklenbeck, Nicolas; Beldi, Sabri; Keilmann, Fritz; Thomson, Mark D.; Roskos, Hartmut G.
We investigated the excitation of surface plasmon polaritons on gold films with the metallized probe tip of a scattering-type scanning near-field optical microscope (s-SNOM). The emission of the polaritons from the tip, illuminated by near-infrared laser radiation, was found to be anisotropic and not circularly symmetric as expected on the basis of literature data. We furthermore identified an additional excitation channel via light that was reflected off the tip and excited the plasmon polaritons at the edge of the metal film. Our results, while obtained for a non-rotationally-symmetric type of probe tip and thus specific for this situation, indicate that when an s-SNOM is employed for the investigation of plasmonic structures, the unintentional excitation of surface waves and anisotropic surface wave propagation must be considered in order to correctly interpret the signatures of plasmon polariton generation and propagation.
On the performance of parallelisation schemes for particle filtering
(Springer, 2018-05-25) Míguez Arenas, Joaquín; Ríos Muñoz, Gonzalo Ricardo; Crisan, Dan; Ministerio de Economía y Competitividad (España)
Considerable effort has been recently devoted to the design of schemes for the parallel implementation of sequential Monte Carlo (SMC) methods for dynamical systems, also widely known as particle filters (PFs). In this paper, we present a brief survey of recent techniques, with an emphasis on the availability of analytical results regarding their performance. Most parallelisation methods can be interpreted as running an ensemble of lower-cost PFs, and the differences between schemes depend on the degree of interaction among the members of the ensemble. We also provide some insights on the use of the simplest scheme for the parallelisation of SMC methods, which consists in splitting the computational budget into M non-interacting PFs with N particles each and then obtaining the desired estimators by averaging over the M independent outcomes of the filters. This approach minimises the parallelisation overhead yet still displays desirable theoretical properties. We analyse the mean square error (MSE) of estimators of moments of the optimal filtering distribution and show the effect of the parallelisation scheme on the approximation error rates. Following these results, we propose a time-error index to compare schemes with different degrees of parallelisation. Finally, we provide two numerical examples involving stochastic versions of the Lorenz 63 and Lorenz 96 systems. In both cases, we show that the ensemble of non-interacting PFs can attain the approximation accuracy of a centralised PF (with the same total number of particles) in just a fraction of its running time using a standard multicore computer.
Fast Interrogation of Fiber Bragg Gratings with Electro-Optical Dual Optical Frequency Combs
(MDPI, 2016-11-26) Posada Román, Julio Enrique; García Souto, José Antonio; Poiana, Dragos Andrei; Acedo Gallardo, Pablo; Ministerio de Economía y Competitividad (España)
Optical frequency combs (OFC) generated by electro-optic modulation of continuous-wave lasers provide broadband coherent sources with high power per line and independent control of line spacing and the number of lines. In addition to their application in spectroscopy, they offer flexible and optimized sources for the interrogation of other sensors based on wavelength change or wavelength filtering, such as fiber Bragg grating (FBG) sensors. In this paper, a dual-OFC FBG interrogation system based on a single laser and two optical-phase modulators is presented. This architecture allows for the configuration of multimode optical source parameters such as the number of modes and their position within the reflected spectrum of the FBG. A direct read-out is obtained by mapping the optical spectrum onto the radio-frequency spectrum output of the dual-comb. This interrogation scheme is proposed for measuring fast phenomena such as vibrations and ultrasounds.
Sub-GHz optical resolution mid-infrared hyperspectral imaging with dual-comb
(Elsevier, 2023-11-01) Khan, Farid Ullah; Moreno Oyervides, Aldo Luis; Bonilla Manrique, Óscar Elías; Martín Mateos, Pedro; Agencia Estatal de Investigación (España)
High-performance hyperspectral imaging is becoming one of the most sought-after tools in the world today by providing a wide range of capabilities and applications. However, traditional systems have significant performance limitations, mainly related to the ability to resolve narrow spectral features and to detection sensitivity. With the aim of addressing these weaknesses, we present here the first hyperspectral dual-comb imaging system capable of providing sub-GHz (<0.033 cm−1) optical resolutions and fast acquisition rates in the mid-infrared region. The system has been experimentally demonstrated by analyzing methane at 2968 cm−1 with optical resolutions of down to 300 MHz (0.01 cm−1) and time resolutions well into the sub-second range.
Design and evaluation of a portable frequency comb-referenced laser heterodyne radiometer
(Elsevier, 2023-12-01) Moreno Oyervides, Aldo Luis; Bonilla Manrique, Óscar Elías; García, Omaira; Martín Mateos, Pedro; European Commission; Agencia Estatal de Investigación (España)
In this paper, we present the design of a laser heterodyne radiometry instrument that combines, for the first time, frequency comb calibration and a remarkably high level of portability. A design that can, therefore, be more than capable of addressing the current need for accurate ground-based greenhouse gases monitoring in urban areas and other emission hot spots. Indeed, the compact, battery-powered system allows the acquisition of atmospheric spectral characterizations, at any location, without restrictions. As its most prominent feature, the system is equipped with an electro-optic frequency comb reference that provides a set of calibration ticks from which an accurate characterization of the absorption line shape can be obtained. Besides this, the spectrometer has been designed to promptly switch between traditional operation and wavelength modulation, so the performance of future inversion models may benefit greatly by this complementary data. The system has been tested in different locations in the Madrid region (Spain), where measurements have been carried out under a wide variety of conditions. Here, a set of highly representative results is presented clearly illustrating the capabilities of the developed system.
Frequency selective optoelectronic downconversion of a Terahertz Pulse Using ErAs:In(Al)GaAs Photoconductors
(IEEE, 2021-07-02) Fernandez Olvera, Anuar De Jesus; Krause, Benedikt Leander; Betancur Pérez, Andrés Felipe; Nandi, Uttam; Dios Fernández, Cristina de; Acedo Gallardo, Pablo; Preu, Sascha; European Commission
We introduce a new scheme for the detection of terahertz pulses based on the frequency selective optoelectronic downconversion of its individual modes with a continous-wave (CW) ErAs:InGaAs photoconductive antenna (PCA) driven by a comb-based CW photonic signal. The detection scheme can be used as metrology tool for the analysis of the fundamental resolution and stability limits of terahertz pulses and the mode-locked-lasers (MLLs) that drives them, as well as an ultra-high-resolution measurement technique for terahertz components or gas spectroscopy. We demonstrate both applications by measuring the linewidth of two frequency components of the particular terahertz pulse analyzed here (one at 75 GHz and one at 340 GHz) and by measuring a very narrowband filter between 70 and 80 GHz. The main advantage of this technique with respect to other terahertz pulse detection schemes is its capability of performing ultra-high-resolution measurements without the need of unpractically long scanning ranges or synchronization of two MLLs.
Photonic integrated frequency shifter based on double side band modulation: Performance analysis
(MDPI, 2022-11) Betancur Pérez, Andrés Felipe; Dios Fernández, Cristina de; Acedo Gallardo, Pablo; European Commission; Ministerio de Economía y Competitividad (España)
In this research, we present an analysis of a photonic integrated frequency shifter as a stage for a THz dual comb generator. We studied the performance of the PIC by simulating it with standard building blocks, and aimed toward an improvement of the output signal quality. We revised two approaches of the PIC by simulating two modes of generating a double side band modulation suppressed carrier (DSB-SC) with a Mach Zehnder modulator structure (MZM). One approach was using a single Electro-Optic Phase Modulator (EOPM) on an MZM structure (SE-MZM), and the other one was using Double EOPM (DE-MZM). We found a cleaner spectrum with the DE-MZM, since this structure is usually applied to reduce the chirp effect in optical communication systems. We obtained 23 dB of side mode suppression ratio SMSR with one filter, and 44 dB of SMSR with a two-stage filter. In the case of DE-MZM, we obtained a clean tone on intermediate frequency (IF) free of spurious sidebands and comb in IF frequency with 10 dB more power compared to SE-MZM.
Pavement condition sensor based on a dual optical frequency comb generator
(Elsevier, 2022-11) Ruiz Llata, Marta; Lombana Rodriguez, Marco Alfonso; Bonilla Manrique, Óscar Elías; Acedo Gallardo, Pablo; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
A pavement condition sensor aims to estimate the pavement surface grip, and therefore the sensor must detect the presence of water, snow, slush or the like on the surface of the pavement. The leading technology for such a sensor is near infrared diffuse reflectance spectroscopy using a wavelength range around a water absorption peak. In this paper we present a pavement condition sensor based on said technique that uses an electro-optic dual optical frequency comb generator as optical source. The proposed sensor provides unique properties in terms of measuring integration time that are necessary to advance the pavement condition several meters ahead of a moving vehicle.
Preparation and characterization of plasma-derived fibrin hydrogels modified by alginate di-aldehyde
(MDPI, 2022-04-02) Sanz Horta, Raúl; Matesanz Fernandez-Arias, Ana; Jorcano Noval, José Luis; Velasco Bayón, Diego; Acedo Gallardo, Pablo; Gallardo, Alberto; Reinecke, Helmut; Comunidad de Madrid; Ministerio de Ciencia e Innovación (España)
Fibrin hydrogels are one of the most popular scaffolds used in tissue engineering due to their excellent biological properties. Special attention should be paid to the use of human plasma-derived fibrin hydrogels as a 3D scaffold in the production of autologous skin grafts, skeletal muscle regeneration and bone tissue repair. However, mechanical weakness and rapid degradation, which causes plasma-derived fibrin matrices to shrink significantly, prompted us to improve their stability. In our study, plasma-derived fibrin was chemically bonded to oxidized alginate (alginate di-aldehyde, ADA) at 10%, 20%, 50% and 80% oxidation, by Schiff base formation, to produce natural hydrogels for tissue engineering applications. First, gelling time studies showed that the degree of ADA oxidation inhibits fibrin polymerization, which we associate with fiber increment and decreased fiber density; moreover, the storage modulus increased when increasing the final volume of CaCl2 (1% w/v) from 80 µL to 200 µL per milliliter of hydrogel. The contraction was similar in matrices with and without human primary fibroblasts (hFBs). In addition, proliferation studies with encapsulated hFBs showed an increment in cell viability in hydrogels with ADA at 10% oxidation at days 1 and 3 with 80 µL of CaCl2; by increasing this compound (CaCl2), the proliferation does not significantly increase until day 7. In the presence of 10% alginate oxidation, the proliferation results are similar to the control, in contrast to the sample with 20% oxidation whose proliferation decreases. Finally, the viability studies showed that the hFB morphology was maintained regardless of the degree of oxidation used; however, the quantity of CaCl2 influences the spread of the hFBs
High frequency modulation and (quasi) single-sideband emission of mid-infrared ring and ridge quantum cascade lasers
(Optica, 2019-05-13) Hinkov, Borislav; Hayden, Jackob; Szedlak, Rolf; Martín Mateos, Pedro; Jerez González, Borja; Acedo Gallardo, Pablo; Strasser, Gottfried; Lendl, Bernhard; Austrian Science Fund (FWF) (F49-P09, M2485-N34); Austria Research Promotion Agency (FFG) (4241316)
We investigate the high frequency modulation characteristics of mid-infrared surface-emitting ring and edge-emitting ridge quantum cascade lasers (QCLs). In particular, a detailed comparison between circular ring devices and ridge-QCLs from the same laser material, which have a linear waveguide in a "Fabry-Perot (FP) type" cavity, reveals distinct similarities and differences. Both device types are single-mode emitting, based on either 2nd-(ring-QCL) or 1st-order (ridge-QCL) distributed feedback (DFB) gratings with an emission wavelength around 7.56 mum. Their modulation characteristics are investigated in the frequency-domain using an optical frequency-to-amplitude conversion technique based on the ro-vibrational absorptions of CH 4. We observe that the amplitude of frequency tuning Delta f over intensity modulation index in as function of the modulation frequency behaves similarly for both types of devices, while the ring-QCLs typically show higher values. The frequency-to-intensity modulation (FM-IM) phase shift shows a decrease starting from similar to 72 degrees at a modulation frequency of 800 kHz to about 0 degrees at 160 MHz. In addition, we also observe a quasi single-sideband (qSSB) regime for modulation frequencies above 100 MHz, which is identified by a vanishing-1 st-order sideband for both devices. This special FM-state can be observed in DFB QCLs and is in strong contrast to the behavior of regular DFB diode lasers, which do not achieve any significant sideband suppression. By analyzing these important high frequency characteristics of ring-QCLs and comparing them to ridge DFB-QCLs, it shows the potential of intersubband devices for applications in e.g. novel spectroscopic techniques and highly-integrated and high-bitrate free-space data communication. In addition, the obtained results close an existing gap in literature for high frequency modulation characteristics of QCLs.
Implementation and characterization of a thermal infrared laser heterodyne radiometer based on a wavelength modulated local oscillator laser
(Optica, 2019-05-27) Martín Mateos, Pedro; Genner, Andreas; Moser, Harald; Lendl, Bernhard; Ministerio de Economía y Competitividad (España)
This article presents the first implementation and the experimental characterization of a thermal infrared wavelength modulation laser heterodyne radiometer (WM-LHR) based on an external cavity quantum cascade laser. This novel WM-LHR system has demonstrated calibration-free operation, a superior signal to noise ratio and, more importantly, has opened the door for cost-efficient wide spectral range laser heterodyne radiometry in the near future.
Frequency accurate coherent electro-optic dual-comb spectroscopy in real-time
(Optica, 2018-04-16) Martín Mateos, Pedro; Jerez González, Borja; Largo Izquierdo, Pedro; Acedo Gallardo, Pablo; Ministerio de Economía y Competitividad (España); Ministerio de Educación, Cultura y Deporte (España)
Electro-optic dual-comb spectrometers have proved to be a promising technology for sensitive, high-resolution and rapid spectral measurements. Electro-optic combs possess very attractive features like simplicity. reliability, bright optical teeth, and typically moderate but quickly tunable optical spans. Furthermore; in a dual-comb arrangement; narrowband electro-optic combs are generated with a level of mutual coherence that is sufficiently high to enable optical multiheterodyning Without inter-comb stabilization or signal processing systems. However, this valuable tool still presents several limitations, for instance; on most systems; absolute frequency accuracy and long-term stability cannot be guaranteed; likewise; interferometer-induced phase noise restricts coherence time and limits the attainable signal-to-noise ratio. In this paper, We address these drawbacks and demonstrate a cost-efficient absolute electro-optic dual-comb instrument based on a frequency stabilization mechanism and a novel adaptive interferogram acquisition approach devised for electro-optic dual-combs capable of operating in real-time. The spectrometer, completely built from commercial components, provides sub-ppm frequency uncertainties and enables a signal-to-noise ratio of 10000 (intensity noise) in 30 seconds of integration time.
A quantum cascade laser-based multi-gas sensor for ambient air monitoring
(MDPI, 2020-04-01) Genner, Andreas; Martín Mateos, Pedro; Moser, Harald; Lendl, Bernhard
A quantum cascade laser-based sensor for ambient air monitoring is presented and five gases, a ecting the air quality, can be quantified. The light sources are selected to measure CO, NO, NO2, N2O and SO2. The footprint of the measurement setup is designed to fit in two standard 19" rack (48 cm x 65 cm) with 4 height units (18 cm) whereas one is holding the optical components and the other one contains the electronics and data processing unit. The concentrations of the individual analytes are measured using 2f-Wavelength Modulation Spectroscopy (2f-WMS) and a commercially available multipass gas cell defines the optical path. In addition, CO can also be measured with a dispersion-based technique, which allows one to cover a wider concentration range than 2f-WMS. The performance of this prototype has been evaluated in the lab and detection limits in the range of 1ppbv have been achieved. Finally, the applicability of this prototype for ambient air monitoring is shown in a five-week measurement campaign in cooperation with the Municipal Department for Environmental Protection (MA 22) of Vienna, Austria.
Direct hyperspectral dual-comb imaging
(Optica, 2020-03-20) Martín Mateos, Pedro; Khan, Farid Ullah; Bonilla Manrique, Óscar Elías; European Commission
Even though dual-comb-based systems are employed almost routinely nowadays in an ever-increasing number of applica-tions, an efficient combination of this effective technique withan imaging arrangement, which would undoubtedly revolu-tionize hyperspectral imaging, had not yet been demonstrated. Here we present, to our knowledge, the first hyperspectral dual-comb imaging system in which interferograms are directly detected by a video camera. The system, based on a dual-comb scheme capable of consistently generating interfer-ograms at a rate of 1 Hz and below, combines fast hyperspectral imaging with unprecedented optical resolution and fully multiplex operation. Various proof-of-principle experiments demonstrating hyperspectral imaging of molecular resonances have proved that the direct hyperspectral dual-comb imaging method presented here is capable of characterizing a scene with super-fine resolution in a narrow optical span within 1 s.
High-Resolution Optical Thickness Measurement Based on Electro-Optic Dual-Optical Frequency Comb Sources
(IEEE, 2017-03-01) Bonilla Manrique, Óscar Elías; Martín Mateos, Pedro; Jerez González, Borja; Ruiz Llata, Marta; Acedo Gallardo, Pablo; Ministerio de Economía y Competitividad (España)
We propose an optical thickness measurement device based on electro-optic dual-optical frequency combs (dual-OFCs). Optical frequency combs (OFCs) are light sources that provide an optical signal consisting of many equidistant monochromatic tones. In this paper, we present an agile dual-OFC architecture with adjustable frequency separation of the comb modes and total frequency span, allowing high-resolution measurements of the thickness of transparent thick samples. This architecture is based on a single continuous-wave laser diode and external electro-optic devices to implement the dual-comb sensor, allowing easy control of the optical spectrum of the interrogation source (dual-OFC). As it is characteristic of dual-OFC systems, the optical transmittance function of the sample (etalon) is directly translated to the radiofrequency domain, where detection, demodulation, and processing of signals are performed. The shift in the complexity of implementation from the optical to the electronic domain yields many advantages, as acquisition and signal processing are made independently on the optical characteristics of the sample (thickness).
Sub-ppm-level ammonia detection using photoacoustic spectroscopy with an optical microphone based on a phase interferometer
(MDPI, 2019-07-01) Bonilla Manrique, Óscar Elías; Posada Román, Julio Enrique; García Souto, José Antonio; Ruiz Llata, Marta; Ministerio de Economía y Competitividad (España)
A sensitive optical microphone for photoacoustic spectroscopy based on the common path topology of a fibre laser Doppler vibrometer (FLDV) using phase-generated carrier demodulation and a slim diaphragm as an acoustic wave transducer was demonstrated. A resonant gas cell was adapted to enhance gas-detection performance and simultaneously provide efficient cancellation of the window background acoustic signal. Ammonia (NH3) was selected as the target gas. The absorption line was experimentally identified using a distributed feedback laser diode emitting at 1530 nm. The linearity and sensitivity of the gas sensor were measured using wavelength modulation spectroscopy with second harmonic detection. A Teflon diaphragm was used to implement the optical microphone, along with the FLDV, showing a minimum detectable pressure of 79.5 mu Pa/Hz(1/2). The noise-equivalent absorption sensitivity for NH3 detection at the absorption line at 1531.7 nm was 1.85 x 10(-8) W cm(-1) Hz(-1/2), and the limit of detection was 785 ppbv.
Hydrogen Sulfide Detection in the Midinfrared Using a 3D-Printed Resonant Gas Cell
(Hindawi, 2019-03-14) Bonilla Manrique, Óscar Elías; Moser, Harald; Martín Mateos, Pedro; Lendl, Bernhard; Ruiz Llata, Marta; Ministerio de Economía y Competitividad (España); Universidad Carlos III de Madrid
A fast and reliable photoacoustic (PA) sensor for trace gas detection is reported. The sensor is based on a 3D-printed resonant cell in combination with a continuous wave mode-hop-free external cavity quantum cascade laser to rapidly acquire gas absorption data in the midinfrared range. The cell is designed so as to minimize the window PA background at a selected acoustic resonance. The goal is a resonant PA cell capable of detecting the traces of gases using wavelength modulation of the laser source and second harmonic detection. The versatility and enhancement of the limit of detection at sub-ppm levels are investigated by monitoring specific lines of hydrogen sulfide (H2S). The noise-equivalent absorption normalized to laser-beam power and detection bandwidth is 1.07 x 10-8 W cm-1 Hz-1/2 for H2S targeting the absorption line at 1247.2cm-1. These properties make the sensor suitable for various practical sensors for water quality applications.
Photonic Integrated Fully Tunable Comb Generator Cascading Optical Modulators
(IEEE, 2018-10-21) Nicola, Andriolli; Cassese, Tomasso; Chiesa, Marco; Dios Fernández, Cristina de; Contestabile, Giampiero; European Commission
We report the first monolithic InP photonic integrated comb generator made by cascading optical modulators. The device is extremely compact and tunable both in repetition frequency and wavelength, making real-world applications possible. A distributed Bragg reflector laser, a Mach-Zehnder intensity modulator, and two phase modulators are monolithically integrated on a 4.5 x 2.5 mm(2) chip that also includes a booster semiconductor optical amplifier at the output. Modulators integrated on the circuit have a 3 dB bandwidth of 7 GHz and can generate up to 28 comb lines within a 5 dB power range when properly electrically driven (here demonstrated in the range 4-5 GHz). Operation up to 10 GHz is also reported.

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