Sánchez Brea, Luis Miguel

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First Name
Luis Miguel
Last Name
Sánchez Brea
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
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Search Results

Now showing 1 - 10 of 45
  • Publication
    Stokes polarimeter using vector diffractive optical elements
    (2023-05-31) Soria García, Ángela; Del Hoyo Muñoz, Jesús; Sánchez Brea, Luis Miguel; Pastor Villarrubia, Verónica; González Fernández, Verónica; Elshorbagy, Mahmoud H.; Alda Serrano, Javier
    We designed, fabricated and tested a Vector Diffractive Optical Element (VDOE) to simultaneously determine the Stokes vector of light. It comprises several sectors. Each one is a vector Fresnel zone plate which focuses the light on separate foci and has different polarization properties. The polarization state is calculated from their intensities. From simulations, we could identify the error sources that were analytically removed. The residual uncertainty after applying our corrections was as low as 6x10^(-5). The uncertainty obtained for our fabricated VDOE, 3.33 %, is competitive with the results from state-of-the-art techniques.
  • Publication
    Near-field diffraction-based focal length determination technique
    (Elsevier, 2017-05) Torcal Milla, Francisco José; Sánchez Brea, Luis Miguel
    An accurate and simple technique for determining the focal length of a lens is presented. It consists of measuring the period of the fringes produced by a diffraction grating at the near field when it is illuminated with a beam focused by the unknown lens. In paraxial approximation, the period of the fringes varies linearly with the distance. After some calculations, a simple extrapolation of data is performed to obtain the locations of the principal plane and the focal plane of the lens. Thus, the focal length is obtained as the distance between the two mentioned planes. The accuracy of the method is limited by the collimation degree of the incident beam and by the algorithm used to obtain the period of the fringes. We have checked the technique with two commercial lenses, one convergent and one divergent, with nominal focal lengths (+100±1) mm and (−100±1) mm respectively. We have experimentally obtained the focal lengths resulting into the interval given by the manufacturer but with an uncertainty of 0.1%, one order of magnitude lesser than the uncertainty given by the manufacturer.
  • Publication
    Optimal achromatic wave retarders using two birefringent wave plates
    (The Optical Society Of America, 2013-03-20) Vilas Prieto, José Luis; Sánchez Brea, Luis Miguel; Bernabeu Martínez, Eusebio
    Two plates of different birefringence material can be combined to obtain an achromatic wave retarder. In this work, we achieve a correction for the overall retardation of the system that extends the relation to any azimuth. Current techniques for the design of achromatic wave retarders do not present a parameter that characterizes its achromatism on a range of wavelengths. Thus, an achromatic degree has been introduced, in order to determine the optimal achromatic design composed with retarder plates for a spectrum of incident light. In particular, we have optimized a quarter retarder using two wave plates for the visible spectrum. Our technique has been compared to previous results, showing significant improvement.
  • Publication
    Self-imaging technique for beam collimation
    (Optical Society of America, 2014) Sánchez Brea, Luis Miguel; Torcal Milla, Francisco José; Herrera Fernández, José María; Morlanes, Tomás; Bernabeu Martínez, Eusebio
    A simple collimation technique based on measuring the period of one self-image produced by a diffraction grating is proposed. Transversal displacement of the grating is not required, and then automatic single-frame processing can be performed. The self-image is acquired with a CMOS camera, and the period is computed using the variogram function. Analytical and experimental results are obtained, which show the simplicity and accuracy of the proposed technique.
  • Publication
    Fast optical source for quantum key distribution based on semiconductor optical amplifiers
    (The Optical Society Of America, 2011-02-28) Jofre, Marc; Gardelein, Arnaud; Anzolin, Gabriele; Amaya, Waldimar; Capmany Francoy, José; Ursin, Rupert; Peñate Quesada, Laura; López Molina, Demetrio; San Juan, J. L.; Carrasco, José Antonio; García de Quirós, Francisco; Torcal Milla, Francisco José; Sánchez Brea, Luis Miguel; Bernabeu Martínez, Eusebio; Perdigues Armengol, Josep Maria; Jennewein, Thomas; Pérez Torres, Juan; Mitchell, Morgan W.; Pruneri, Valerio
    A novel integrated optical source capable of emitting faint pulses with different polarization states and with different intensity levels at 100 MHz has been developed. The source relies on a single laser diode followed by four semiconductor optical amplifiers and thin film polarizers, connected through a fiber network. The use of a single laser ensures high level of indistinguishability in time and spectrum of the pulses for the four different polarizations and three different levels of intensity. The applicability of the source is demonstrated in the lab through a free space quantum key distribution experiment which makes use of the decoy state BB84 protocol. We achieved a lower bound secure key rate of the order of 3.64 Mbps and a quantum bit error ratio as low as 1.14 × 10−2 while the lower bound secure key rate became 187 bps for an equivalent attenuation of 35 dB. To our knowledge, this is the fastest polarization encoded QKD system which has been reported so far. The performance, reduced size, low power consumption and the fact that the components used can be space qualified make the source particularly suitable for secure satellite communication.
  • Publication
    Fabrication effects in the optical performance of DOEs engraved with femtosecond lasers
    (SPIE, 2021-09-17) Soria García, Ángela; Fantova, Jorge; San Blas, Alejandro; Hoyo Muñoz, Jesús del; Sánchez Brea, Luis Miguel; Alda Serrano, Javier; Rodríguez González, Ainara; Olaizola Izquierdo, Santiago M.
    The development of DOEs fabrication techniques is continuously growing due to the wide range of industrial applications, such as beam manipulation or optical position encoders. In this work, we use Femtosecond laser direct writing to manufacture DOEs, which uses a simpler and more efficient way to fabricate amplitude binary masks. Also, we have analyzed the performance of the DOEs. The fabrication technique is validated since the experimental results are in accordance to numerical simulations.
  • Publication
    Calibration of the complete Jones matrix of SLMs
    (SPIE-International Society Optical Engineering, 2021-09) Hoyo Muñoz, Jesús del; Sánchez Brea, Luis Miguel; Soria García, Ángela
    Spatial light modulators are very common in many applications. They are used to implement amplitude, phase and polarization masks. In order to optimize its performance, it is important to characterize it, which means determining its Jones matrix. Here we present a method which consists on performing several intensity measurements for each gray level. It is simple enough that can be quickly performed, but offers much better results than previous methods.
  • Publication
    Self-imaging with curved gratings
    (Elsevier Science BV, 2010-10-15) Torcal Milla, Francisco José; Sánchez Brea, Luis Miguel; Salgado Remacha, Francisco Javier; Bernabeu Martínez, Eusebio
    We analyze the near field behavior of binary amplitude gratings which present a curved profile. This configuration has an important application in rotary optical encoders. This kind of encoders is used to measure the angular displacement between two different parts of the devices. To our knowledge, its behavior in the near field has not been analyzed yet. We have found that Talbot effect is produced but the period of the self-images and Talbot distances change as we separate from the grating. We have fabricated a curved grating and have performed the experiment to corroborate the behavior theoretically found. This fact could be useful in systems that use Talbot effect to measure displacements, since the mechanical tolerances grow.
  • Publication
    Femtosecond laser fabrication of LIPSS-based waveplates on metallic surfaces
    (Elsevier Science B. V., 2020-08-01) San Blas, A.; Martínez Calderón, M.; Buencuerpo Fariña, Jerónimo; Sánchez Brea, Luis Miguel; Hoyo, J. del; Gómez Aranzadi, M.; Rodriguez, A.; Olaizola, S.M.
    A fast and reliable method for the fabrication of polarization modifying devices using femtosecond laser is reported. A setup based on line focusing is used for the generation of LIPSS on stainless steel, processing at different speeds between 0.8 and 2.4 mm/s with constant energy per pulse of 1.4 mJ. SEM and AFM characterizations of the LIPSS show a progressive increase in period as the processing speed increases, while height remains approximately constant in the studied range. Optical characterization of the devices shows an induced change in the polarization of the reflected beam that varies with the processing speed, which allows a controlled fabrication of these devices.
  • Publication
    Collimation method using a double grating system
    (The Optical Society Of America, 2010-06-10) Sánchez Brea, Luis Miguel; Torcal Milla, Francisco José; Salgado Remacha, Francisco Javier; Morlanes Calvo, Tomás; Jiménez Castillo, Isidoro; Bernabeu Martínez, Eusebio
    We present a collimation technique based on a double grating system to locate with high accuracy an emitter in the focal plane of a lens. Talbot self-images are projected onto the second grating producing moiré interferences. By means of two photodetectors positioned just behind the second grating, it is possible to determine the optimal position of the light source for collimation by measuring the phase shift between the signals over the two photodetectors. We obtain mathematical expressions of the signal in terms of defocus. This allows us to perform an automated technique for collimation. In addition, a simple and accurate visual criterion for collimating a light source using a lens is proposed. Experimental results that corroborate the proposed technique are also presented.