Search results for "òptica"
showing 10 items of 205 documents
MWP phase shifters integrated in PbS-SU8 waveguides
2015
[EN] We present new kind of microwave phase shifters (MPS) based on dispersion of PbS colloidal quantum dots (QDs) in commercially available photoresist SU8 after a ligand exchange process. Ridge PbS-SU8 waveguides are implemented by integration of the nanocomposite in a silicon platform. When these waveguides are pumped at wavelengths below the band-gap of the PbS QDs, a phase shift in an optically conveyed (at 1550 nm) microwave signal is produced. The strong light confinement produced in the ridge waveguides allows an improvement of the phase shift as compared to the case of planar structures. Moreover, a novel ridge bilayer waveguide composed by a PbS-SU8 nanocomposite and a SU8 passive…
Broadband dispersion compensation using inner cladding modes in photonic crystal fibers.
2012
A photonic crystal fiber is optimized for chromatic dispersion compensation by using inner cladding modes. To this end, a photonic-oriented version of the downhill-simplex algorithm is employed. The numerical results show a dispersion profile that accurately compensates the targeted dispersion curve, as well as its dispersion slope. The presented fiber has a simple structure, while radiation losses can be reduced simply by adding a few more air-hole rings. Fabrication tolerances are also considered showing how fabrication inaccuracies effects can be overridden by just adjusting the compensation length.
Acousto-optic interaction in biconical tapered fibers: shaping of the stopbands
2016
The effect of a gradual reduction of the fiber diameter on the acousto-optic (AO) interaction is reported. The experimental and theoretical study of the intermodal coupling induced by a flexural acoustic wave in a biconical tapered fiber shows that it is possible to shape the transmission spectrum, for example, substantially broadening the bandwidth of the resonant couplings. The geometry of the taper transitions can be regarded as an extra degree of freedom to design the AO devices. Optical bandwidths above 45 nm are reported in a tapered fiber with a gradual reduction of the fiber down to 70 μm diameter. The effect of including long taper transition is also reported in a double-tapered st…
Measurement of phase and group refractive indices and dispersion of thermo-optic and strain-optic coefficients of optical fibers using weak fiber Bra…
2021
In this work we report on the measurement, with record accuracy, of the absolute modal effective refraction index (phase index) of single-mode optical fibers by using Bragg gratings. We also demonstrate a new method to measure the group index of the fibers from the grating’s Bragg wavelength. We present as well the characterization of the thermo-optic and strain-optic coefficients as a function of the wavelength; the values we have obtained are the closest to those of pristine fiber measured with gratings technology so far. The phase index is measured with a set of gratings in the wavelength ranges from 1509 to 1563 nm, and the group index is obtained from the wavelength dependence of the p…
Advanced Optical Processing of Microwave Signals
2005
The authors present a review on the recent approaches proposed to implement transversal RF filters. Different tunable transversal filters consisting of wavelength tunable optical taps and those employing the tunability of dispersive devices are presented showing their high-performance characteristics. A comprehensive review of the fundamentals and a discussion on the main limitation of these structures are also included.
Phase imaging microscopy under the Gabor regime in a minimally modified regular bright-field microscope
2021
Quantitative phase imaging (QPI) is nowadays a powerful tool for visualization and analysis of biological processes. QPI is usually attained from specifically designed optical microscopes retrieving phase information in a quantitative way. In this paper we report on an extremely simple, low cost and compact way to update a standard bright-field microscope with coherent sensing capabilities. It is based on the in-line Gabor holography concept and only needs to replace the illumination broadband source of the regular microscope with a coherent one. The proposed methodology is completed by the recording of a digital in-line Gabor hologram instead of regular imaging conditions and by the numeri…
Terapia visual: ¿por qué existe? ¿Cuándo es aconsejable?
1998
La evolución de la optometría ha sido importante en los últimos años. Cada día se habla más de posibles especialidades. Una de ellas es la Terapia visual sin embargo aún existen Ópticos optometristas que se sorprenden cuando oyen hablar de tratamiento visual mediante ejercicios y los resultados satisfactorios que se han llegado a obtener en muchos casos. El objetivo del presente trabajo es hablar sobre el por qué de la terapia visual así como de la necesidad progresiva que la sociedad actual tiene de estos servicios profesionales, debido a las fuertes demandas visuales con las que se encuentra una persona a lo largo de su vida.
El concepto de las gafas como elemento de protección visual: una revisión de los tres últimos siglos
2020
El ser conscientes de que los lentes oftálmicos son elementos protectores que ayudan a preservar la calidad de la visión de los usuarios no es una cosa de los tiempos recientes. A partir de la segunda mitad del siglo XVIII, se empieza a producir un incremento de los artesanos dedicados a la óptica en España, realizando un producto correcto y de calidad. Unido a ello se difunde a partir de dicha fecha, y poco a poco, el concepto de que las lentes de calidad conservan la vista.
Measurements of total ozone amount over Badajoz (Southwestern Spain) by means of a GUV multiband radiometer
2012
This paper presents the first measurements of total ozone amount performed at the radiometric station of Badajoz (Spain) by means of a multichannel radiometer GUV-2511. The retrieval of total ozone amount from GUV measurements of solar ultraviolet irradiance is performed with the support of look-up tables calculated using the SBDART radiation transfer code. This methodology is based on the different absorption by ozone suffered by the radiation at two certain near wavelengths. In this case the pair 305, 340 nm was chosen because of its better performance than the pair 305, 320 nm. The look-up table contains the ratio between irradiances at the mentioned wavelengths calculated under differen…
Tunable chirped fibre Bragg grating device controlled by variable magnetic fields
2002
A novel dynamic chirping fibre Bragg grating device based on a magnetic field applied to a magnetostrictive transducer capable of tuning its dispersion is presented. Chirping ranges up to 300 ps/nm have been demonstrated, which are suitable for several applications such as tunable transversal filtering and dynamic dispersion compensation.