Brillouin optical time-domain analyzer with a fiber ring laser working on the SLM regime

In this paper we present the employment of an Erbium Fiber Ring Laser structure working on the Single Longitudinal Mode regime within a Brillouin optical time domain analyzer. An analysis of some key laser parameters will be carried out, proving that a very stable operation is achieved. The associated performance of the BOTDA system, as well as the possible benefits derived from the use of the proposed laser design will also be discussed.This work has been supported by the projects TEC2013-47264-C2-1-R and TEC2016-76021-C2-2-R

Feasibility study of a fiber ring laser working on the SLM regime in a BOTDA sensor

A feasibility study of the employment of a fiber laser working as the laser source of a Brillouin distributed sensor is presented in this paper. The erbium fiber ring laser structure designed works on the single longitudinal mode regime. The main parameters of the ring cavity are analyzed in terms of the laser requirements and the performance of a Brillouin optical time domain analysis sensor using the fiber laser as light source.This work was supported by the Spanish Government and FEDER funds under Project TEC2016-76021-C2-2-

Electro-optic correlator for large-format microwave interferometry: Up-conversionand correlation stages performance analysis

In this paper, a microwave interferometer prototype with a near-infra-red optical correlator is proposed as a solution to get a large-format interferometer with hundreds of receivers for radio astronomy applications. A 10 Gbits/s Lithium Niobate modulator has been tested as part of an electro-optic correlator up-conversion stage that will be integrated in the interferometer prototype. Its internal circuitry consists of a single-drive modulator biased by a SubMiniature version A (SMA) connector allowing to up-convert microwave signals with bandwidths up to 12.5 GHz to the near infrared band. In order to characterize it, a 12 GHz tone and a bias voltage were applied to the SMA input using a polarization tee. Two different experimental techniques to stabilize the modulator operation point in its minimum optical carrier output power are described. The best achieved results showed a rather stable spectrum in amplitude and wavelength at the output of the modulator with an optical carrier level 23 dB lower than the signal of interest. On the other hand, preliminary measurements were made to analyze the correlation stage, using 4f and 6f optical configurations to characterize both the antenna/fiber array configuration and the corresponding point spread function.This work was supported by the Ministerio de Economía y Competitividad, Spain, under the Plan Nacional de I+D+i project with Reference No. ESP2015-70646-C2-1-R cofinanced with EU FEDER funds and the CONSOLIDER INGENIO 2010 programme under the Reference No. CSD2010-00064. The authors would like to thank Félix Gracia from Instituto Astrofísico de Canarias (IAC) for his assistance and help

High-temperature distributed sensor system via BOTDA and multimode gold-coated fiber

A high-temperature distributed sensor solution based on a Brillouin Optical Time Domain Analyzer and a multimode gold-coated fiber is presented and experimentally validated in this paper. Distributed temperature measurements up to 600°C will be demonstrated.This work has been supported by the Universidad de Cantabria and by the Spanish Ministerio de Ciencia e Innovación through project TEC2013-47264-C2-1-R

Feasibility study of strain and temperature discrimination in a BOTDA system via artificial neural networks

Automatic discrimination between strain and temperature in a Brillouin optical time domain analyzer via artificial neural networks is proposed and discussed in this paper. Using a standard monomode optical fiber as the sensing element, the ability of the proposed solution to detect the known changes that the Brillouin gain spectrum exhibits depending on the applied temperature and/or strain will be studied. Experimental results, where different simultaneous strain and temperature situations have been considered, will show the feasibility of this technique.This work has been supported by the projects TEC2013-47264-C2-1-R and TEC2016-76021-C2-2-R

Single longitudinal mode fiber ring laser

In this work, a dual-wavelength fiber ring laser working on the SLM regime is proposed and experimentally verified. A proof-of-concept device has been tested employing high precision small-sized SLM fiber lasers to complement the feedback produced by a passive FBG. The ring laser output inherits the spectral benefits of its SLM seed lasers but maintaining some power-related properties of ring cavities. These spectral benefits can also be achieved for a single wavelength, simplifying the requirements regarding power equalization between different wavelengths to obtain the SLM regime. The experimental results exhibit a remarkably good wavelength stability and SLM operation of a fiber ring laser with several meters of cavity length, both with single and multi-wavelength configurations.This work has been supported by the project TEC2016-76021-C2-2-R of the Spanish Government cofunded by EU/FEDER funds. Special thanks to Fibercore for their support

On-line role-play as a teaching method in engineering studies

In this paper we propose adapting role-play teaching methodology to engineering studies. The role of a maintenance technician, a relevant job profile for engineering graduates is has chosen. The interaction is based on email exchange, with the instructor included in the simulation to help guide the activity and achieve learning objectives. In this paper, we present experience with this methodology, its implementation, results, and student feedback

Hyperspectral imaging for diagnosis and quality control in agri-food and industrial sectors

Optical spectroscopy has been utilized in various fields of science, industry and medicine, since each substance is discernible from all others by its spectral properties. However, optical spectroscopy traditionally generates information on the bulk properties of the whole sample, and mainly in the agri-food industry some product properties result from the heterogeneity in its composition. This monitoring is considerably more challenging and can be successfully achieved by the so-called hyperspectral imaging technology, which allows the simultaneous determination of the optical spectrum and the spatial location of an object in a surface. In addition, it is a nonintrusive and non-contact technique which gives rise to a great potential for industrial applications and it does not require any particular preparation of the samples, which is a primary concern in food monitoring. This work illustrates an overview of approaches based on this technology to address different problems in agri-food and industrial sectors. The hyperspectral system was originally designed and tested for raw material on-line discrimination, which is a key factor in the input stages of many industrial sectors. The combination of the acquisition of the spectral information across transversal lines while materials are being transported on a conveyor belt, and appropriate image analyses have been successfully validated in the tobacco industry. Lastly, the use of imaging spectroscopy applied to online welding quality monitoring is discussed and compared with traditional spectroscopic approaches in this regard

Use of the plasma RMS signal for on-line welding quality monitoring

In this paper a new spectroscopic monitoring parameter is proposed for the on-line monitoring of welding processes, the plasma RMS signal, which is determined by considering the contribution from the spectral samples over a particular spectral window. This parameter is directly related to the heat input that can be estimated by measuring both welding voltage and current, but it exhibits a higher sensitivity to the appearance of weld defects. A comparison between the results obtained from the different spectroscopic parameters will be presented, with data from both experimental and field arc-welding tests

Brillouin frequency shift estimation in BOTDA via subpixel processing

In this paper we propose the employment of sub-pixel algorithms for the estimation of the central frequency of the Brillouin Gain Spectrum in a Brillouin Optical Time Domain Analyzer. The experimental results will show that the proposed solution shows a good performance when the chosen frequency step for the required frequency sweep is high. If the improved computational efficiency in comparison to the traditional Lorentzian fitting is also considered, it can be concluded that this approach may be of great interest for dynamic measurement scenarios.This work has been supported by the Universidad de Cantabria and by the Spanish Ministerio de Ciencia e Innovación through project TEC2013-47264-C2-1-R