Search results for " óptica"
showing 10 items of 85 documents
High Sensitivity Refractive Index Sensor Based on Highly Overcoupled Tapered Fiber Optic Couplers
2017
In this paper, a simple and compact fiber-optic sensor based on an overcoupled tapered fiber coupler is studied. The coupler is fabricated to be operated well beyond the initial coupling cycles, where the rapid exchange of energy between outputs ports enable the fabrication of a highly sensitive device. The suitability and sensitivity of the proposed scheme is demonstrated by measuring refractive index (RI) variations of sugar concentrations in water. The device presents a linear response in terms of power transmission or wavelength shift versus RI changes. The best achieved sensitivity is 0.442 units of normalized transmission per unit of sugar concentration, with a noise detection limit o…
Applet de Física. Interferencias de dos haces luminosos. Biprisma de Fresnel.
2013
El biprisma de Fresnel es un dispositivo interferencial constituido por dos prismas delgados unidos por sus bases. Cuando el biprisma se ilumina con una fuente puntual monocromática se obtiene un patrón de interferencias, por división del frente de ondas, similar al observado en el experimento clásico de la doble rendija de Young. En esta simulación se puede analizar la dependencia de la interfranja del patrón interferencial con difrentes parámetros tales como: características del biprisma (índice de refracción y ángulo de refringencia), posición axial del biprisma y distancia a la que se encuentra la pantalla de observación. The Fresnel biprism is an interferential device comprising two th…
1.5 μm Ultrafast Fiber Lasers Of Repetition Rates From Single-Shot To GHz Range
2021
Esta tesis se centra en el estudio teórico y experimental del método de bloqueo de modos pasivo basado en espejos absorbentes saturables de semiconductor (SESAM). Este método se utiliza para desarrollar láseres de emisión pulsada ultracorta (duración de pulso desde femtosegundos hasta unos pocos picosegundos) en la banda de 1,5 $ \mu m $ que cubren una amplia gama de aplicaciones científicas e industriales. Los requisitos de frecuencia de repetición de pulsos son diversos para este tipo de láseres, en función de su aplicación. Bajas frecuencias de repetición, desde un solo disparo hasta varios kilohercios, se utilizan en aplicaciones de análisis de muestras donde los tiempos de respuesta so…
Long cavity ring fiber mode-locked laser with decreased net value of nonlinear polarization rotation
2019
We investigate a new configuration of a mode-locked fiber laser by using a nonlinear polarization rotation-based design to generate soliton pulses with low repetition rate. Unlike with previously reported configurations, we introduce a Faraday mirror after the first half of the cavity length to counteract the nonlinear polarization rotation effects. The total cavity length is 437 m including a 400-m long twisted SMF-28 fiber. The fiber was twisted to cancel the linear birefringence and to ensure that the polarization ellipticity is not altered as the pulse travels along the fiber. The strict control of polarization yields a stable relation between the polarization state of the pulses propag…
Intravitreal therapies for non-neovascular age-related macular degeneration with intraretinal or subretinal fluid
2017
OBJECTIVE: To evaluate the efficacy of intravitreal therapies in cases of atrophic age-related macular degeneration (AMD) with subretinal or intraretinal fluid. METHODS: A retrospective review was made of the clinical charts of patients diagnosed with atrophic AMD with subretinal or intraretinal fluid. Fundus photographs and spectral-domain optical coherence tomography images were examined, and an analysis was made on the presence of fluid and its density. Neovascularisation was ruled out by fluorescein and/or indocyanine green angiography. RESULTS: The study included 14 eyes from 13 patients with a mean age of 72.64 years and a mean follow-up of 80.5 weeks. Intraretinal fluid was observed …
Refractive changes in nuclear, cortical and posterior subcapsular cataracts. Effect of the type and grade
2015
Purpose: To determine the effect of main morphological types and grades of age-related cataracts on refractive error. Methods: We measured 276 subjects with optical compensation prior to the development of cataract. We evaluated 224 eyes with nuclear cataract, 125 with cortical cataract, and 103 with posterior subcapsular (PSC) cataract classified with LOCSIII. We measured visual acuity (VA) with their spectacles and best-corrected visual acuity (BCVA) with chart in decimal scale to obtain the optimal compensation with cataract. We evaluated the differences between compensations. Results: A significant myopic shift was observed in nuclear cataract from low to mild grade (p = 0.031), the sam…
Measurement of UV-induced absorption and scattering losses in photosensitive fibers
2018
UV-assisted fabrication of gratings using photosensitive fibers is a well-established technique, based on the UV-induced permanent modification of the refractive index of the fiber material. As a result, the absorption coefficient is also changed. Here, we exploit the thermal sensitivity of whispering gallery mode resonances of the fiber itself to measure the profile of the heating along an irradiated fiber versus the input power and for different UV radiation intensities. Our technique allows discriminating between the absorption and scattering contributions to the overall losses, by comparing the results obtained with our technique with direct transmission measurements. Different photosen…
Development and analysis of a model based on chirped fiber Bragg gratings employed for cracks characterization in materials
2018
In this work a model was developed that allows to understand the behavior of a chirped fiber Bragg grating for the detection and characterization of cracks in materials. In addition to the amplitude response, we show that the group delay of the grating provides useful information for the characterization of the crack. The position of the crack can be determined thanks to the linear chirp of the grating that fixes a correlation between the spatial position and both, the wavelength and the group delay. However, our analysis shows that this simple approach has a source of error, which can be overcome if a controllable external strain can be applied to the embedded grating, additional to the st…
Tunable dual-wavelength operation of an all- fiber thulium-doped fiber laser based on tunable fiber Bragg gratings
2018
Tunable dual-wavelength emission of a Tm-doped fiber laser based on two fiber Bragg gratings (FBGs) is experimentally demonstrated. By using two FBGs with central wavelengths at 2069.30 and 2069.44 nm, stable dual-wavelength laser generation in the 2 ?m wavelength region is achieved by adjusting the differential loss of the two wavelengths in the laser cavity. Strain applied on the FBG allows independent tuning of the simultaneously generated wavelengths with separation between the laser lines in a range from 0.54 to 9 nm. The laser has output power fluctuations less than 0.093% for an output power of 77.3 mW.
Fabrication of long period fiber gratings of subnanometric bandwidth.
2017
This paper reports on the fabrication of long period fiber gratings having subnanometric bandwidth in the 1500 nm spectral region. Large gratings have been photo-inscribed in a high NA fiber, the grating pitch and the order of the HE cladding mode are optimized to produce gratings with a large number of periods and preventing the coupling to TE, TM or EH modes. Resonances with a FWHM of 0.83 nm and 0.68 nm have been achieved for gratings 15 and 20 cm long respectively, the free spectral range between transmission notches is 125 nm. The polarization effects and the sensitivity of the gratings to temperature and to strain variations are presented as well. © 2015 Optical Society of America Thi…