Luis Miguel Sanchez-Brea

Complutense University of Madrid | UCM · Department of Optics

The real-time characterization of the polarization state of a light beam is of importance for a variety of applications in Optics and Photonics. We have designed a device that includes a Vector Diffractive Optical Element (VDOE) to determine the polarization state of an incident light beam. The device is able to simultaneously evaluate the four Sto...

The generation of surface plasmon resonances (SPR) in laser-induced periodic surface structures (LIPSS) allows their application in the field of optical sensing, such as the detection of refractive index variations in gases and liquids. We have fabricated gold-coated LIPSS nanostructures on stainless steel substrates by using femtosecond laser nano...

A Sector-based Fresnel zone plate consists of a binary diffractive lens composed of a mosaic of sectors of Fresnel zone plates with different focal distances. When these focal distances are linearly distributed within the sectors, dual focus is obtained. Besides, we explore the possibility to generate an extended depth-of-focus lens by using a cubi...

Objective In this work, a reflective beam-splitter based on a metallic Ronchi diffraction grating normally illuminated is designed and analysed. This kind of beam-splitter could have potential applications in photonics and optical technologies in which robustness is necessary since it may be manufactured over malleable metallic substrates. Methods...

Stainless steel is a basic raw material used in many industries. It can be customized by generating laser-induced periodic surface structure (LIPSS) as subwavelength gratings. Here, we present the capabilities of an LIPSS on stainless steel to modify the polarization state of the reflected radiation at the IR band. These structures have been modele...

We present a simple method to determine the polarimetric properties of spatial light modulators (SLMs) for each grey level by means of irradiance measurements. The Jones matrix of the SLM is obtained without any assumption about its properties, so it can be applied for more devices than previous works. This method is simple enough to be quickly per...

Steel tape gratings are diffraction gratings engraved on a steel substrate, whose slits are commonly manufactured by laser ablation. They behave as amplitude diffraction gratings, since the engraved slits act as strong scatters. Here, we extend previous works to the case of finite-size illumination sources, as they are used in applications such as...

We present a novel method for calibrating a four-axis Mueller matrix polarimeter. This method is valid even for non-ideal optical elements, as it models all polarization elements having both diattenuation and retardance. The method is divided in seven experimental steps, where all the optical elements are calibrated each at a time, plus a numerical...

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...

Surface nanostructuring has received increasing attention in recent years due to the wide range of applications in which it offers advantages. Particularly, Laser-Induced Periodic Surface Structures (LIPSS) have proven useful for surface functionalization. LIPSS are periodic formations generated in most materials when irradiated with linearly polar...

We present in this work a numerical model for characterizing the scattering properties of the human lens. After analyzing the scattering properties of two main scattering particles actually described in the literature through FEM (finite element method) simulations, we have modified a Monte Carlo’s bulk scattering algorithm for computing ray scatte...

We present a new method for calibrating a 4 stepper-motors polarimeter. This method does not require perfect polarizing elements or well-known samples. Experimental results have been obtained with errors lower than 0.1%.

We analyze the far-field diffraction pattern produced by linear spatial chirped gratings. An intuitive analytical interpretation of the generated diffraction orders is proposed for gratings with linear variation of the period and linear variation of the spatial frequency. Also, experiments using Gaussian beams and plane wave illumination are perfor...

In this work, we propose and analyze a novel kind of binary Fresnel zone plate with single focus. It consists of a Fresnel zone plate whose zones have rough edges. We give analytical results for the intensity along the optical axis and demonstrate that lateral roughness of the zones produces the disappearance of secondary foci as a blurring of the...

In this work, we analyze the diffraction produced by Ronchi gratings where the fill factor is not constant, but presents random fluctuations around its nominal value. This effect can be produced while developing the grating with etchers since the process can be slightly unpredictable. We obtain the theoretical formalism to describe the intensity pr...

Highly collimated beams are required in numerous applications and techniques. Different methods have been proposed for collimating monochromatic point light sources during the recent years. In this work, we analyze how a finite size and polychromatic light source can be collimated using only one diffraction grating and a CMOS camera placed after th...

In this Letter, we analyze the near-field diffraction pattern produced by chirped gratings. An intuitive analytical interpretation of the generated diffraction orders is proposed. Several interesting properties of the near-field diffraction pattern can be determined, such as the period of the fringes and its visibility. Diffraction orders present d...

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...

In this work, we obtain analytical expressions for the near-and far-field diffraction of random Ronchi diffraction gratings where the slits of the grating are randomly displaced around their periodical positions. We theoretically show that the effect of randomness in the position of the slits of the grating produces a decrease of the contrast and e...

We propose an accurate technique for obtaining highly collimated beams, which also allows testing the collimation degree of a beam. It is based on comparing the period of two different self-images produced by a single diffraction grating. In this way, variations in the period of the diffraction grating do not affect to the measuring procedure. Self...

Self-imaging phenomenon has been widely used in many research areas and applications. We investigate how polychromatism joined to finite size of the source affect the self-imaging process. Under some restrictive circumstances, an achromatic and continuous self-imaging regime is produced. An intuitive analytical interpretation of the achromatic beha...

A superachromatic quarter-wave retarder using an arbitrary number of waveplates in a broadband spectral range has been proposed. Their design is based on the optimization of a merit function, the achromatism degree (AcD), which represents a global behavior metric for the retardation. By means of this technique, the thickness and azimuth of each wav...

In this work we develop a device for determining the linear displacement between a linear grating and a scanning head. Then, the standard technique used for generating the optical signals is double grating imaging: Moiré, Talbot or Generalized grating imaging configurations. The accuracy and resolution of optical encoders improves when the period o...

We analyze the field produced by a cylindrical convex diffraction grating at the Fresnel regime for several kinds of light sources, including a monochromatic quasipunctual source, finite size, and polychromatic sources. These results can help one understand the functioning of rotary optical encoder technology. A decrease in the self-image contrast...

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. An...

The generation of circularly polarized light with a high circularity degree and low azimuthal error sensitivity was analyzed using a system composed by two waveplates. It is shown how the high circularity degree is achieved using a combination of a half- (λ/2) and a quarter- (λ/4) waveplate λ/2+λ/4 configuration. However, the lowest azimuthal sensi...

We obtain a general analytical. formulation for determining the near field produced by N diffraction gratings disposed in stack using a scalar approximation. Parameters of the gratings such as type-amplitude/phase-, fill factors, periods and relative positions between gratings along the x and y axes are considered. The obtained formulation is usefu...

This reply attempts to cast some more light on the achromatic systems composed by wave plates, in particular to the calculus of the overall retardation and the use of the Jones matrix equivalence theorem. An equivalent expression for the overall retardation of the system in terms of the trace is also given.

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 o...

In previous works, the authors have analyzed diffraction gratings with surface roughness on their strips. Appl. Opt. 46 (2007) 3668 determined the near field of a grating whose strips present two kinds of roughness, one of them so rough that the grating acts as an amplitude grating. On the other hand, in J. Opt. Soc. Am. A 25 (2008) 2390, a grating...

We analyze the effect of the fill factor of binary diffraction gratings on the near field propagation. We show that the location of the best-visibility planes changes with the configuration parameters of the grating, that is, the amplitude and phase modulation and the fill factor. Moreover, different intensity patterns and contrast shapes can be ob...

We analyze the effect of the fill factor of binary diffraction gratings on the near field propagation. We show that the location of the best-visibility planes changes with the configuration parameters of the grating, that is, the amplitude and phase modulation and the fill factor. Moreover, different intensity patterns and contrast shapes can be ob...

Iterative algorithms based on Fourier transform are used for the design of diffractive optical elements (DOEs), which produce a given intensity distribution, usually at the far field. For the near field, these algorithms can also be used by changing the Fourier transform for the Fresnel transform. However, when the distance between the DOE and the...

Micro-optical devices embedded in transparent materials are usually manufactured focusing a pulsed laser in bulk fused silica. Under this condition, pulsewidth becomes the most important parameter that rules the size of the inscriptions. Ultrafast pulses (pico- and femtosecond pulses) avoid thermal effects and the results present a high efficiency....

Diffraction gratings are used in measurement devices for scientific and industrial applications. As it is well known, self-images appear in the near field when diffraction gratings are illuminated with a coherent beam, such as a plane wave. This effect has been analyzed in depth and its behavior is well known under ideal grating and illumination co...

Steel tape is used in optical applications due to its mechanical properties. However, roughness of steel surfaces affects to wave propagation. The effect can be observed using diffraction gratings with low periods. In such a case, self-images of the grating appear at certain periodic distances from the grating (Talbot planes). When standard steel i...

In this work we analyze the near-field intensity distribution produced by a rough grating illuminated with a Gaussian-Schell-model beam. This kind of grating is formed by rough and smooth slits. Statistical techniques are used to describe the grating, and the Fresnel approach is used to perform the propagation of light. Two kinds of coherence affec...

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 en...

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 analyz...

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 o...

A diffractive optical element having equal-width concentric square rings is analyzed in this article. This constant width makes possible its realization using spatial light modulators or square pixels phase screens. It allows a simple analytical treatment. and the element is also simulated using the Rayleigh-Sommerfeld approach. An experimental ver...

We analyze the focusing properties of Fresnel zone plates fabricated over steel tapes using laser ablation. Our intention is to implement the use of micro-optical elements when the use of conventional chrome-glass elements is not indicated. Because of the manufacture process, the surface presents a certain anisotropic roughness, which reduces the f...

Diffraction gratings produce self-images in the near field. Defects on the surface of the grating may occur due to the manufacturing process. These devices are often placed in dirty industrial environments. Dust particles or drops of liquid can be deposited over their surface. In this work, we analyze the effect of surface defects placed over the g...

Polygonal Fresnel zone plates can be configured in a variety of forms depending on the number of sides of the polygon and the number of phase steps used. This contribution deals with some specific polygonal designs that tessellate the plane: triangles, squares, and hexagons. The phase distribution is chosen as a continuous one to form a polygonal k...

We analyze the near-field behavior of binary amplitude/phase diffraction gratings, which modulate at the same time the amplitude and phase of the incident light beam. As it is expected, the distance between two consecutive self-images of the grating depends only on the period of the grating and the wavelength of the illumination. However, the locat...

Two-grating measurement systems are routinely employed for high-resolution measurements of angular and linear displacement. Usually, these systems incorporate zero reference codes (ZRCs) to obtain a zero reference signal (ZRS), which is used as a stage-homing signal. This signal provides absolute information of the position to the otherwise relativ...

We analyze the Talbot effect produced by a mask composed of two diffraction gratings. Combinations with phase and amplitude gratings have been studied in the near-field regime. For a two-phase-gratings configuration, the Talbot effect is canceled, even when using monochromatic light; that is, the intensity distribution is nearly independent of the...

We analyze the optical behavior of square Fresnel zones plates. A theoretical analysis and numerical simulations based on the Rayleigh–Sommerfeld approach have been developed analyzing properties such as the depth of focus and the intensity of the focus in terms of the number of zones. In addition, an experimental verification has been performed us...

We analyze the far-field intensity distribution of binary phase gratings whose strips present certain randomness in their height. A statistical analysis based on the mutual coherence function is done in the plane just after the grating. Then, the mutual coherence function is propagated to the far field and the intensity distribution is obtained. Ge...

Polygonal Fresnel zone plates with a low number of sides have deserved attention in micro and nanoptics, because they can be straightforwardly integrated in photonic devices, and, at the same time, they represent a balance between the high-focusing performance of a circular zone plate and the easiness of fabrication at micro and nano-scales of poly...

Diffraction gratings are not always ideal but, due to the fabrication process, several errors can be produced. In this work we show that when the strips of a binary phase diffraction grating present certain randomness in their height, the intensity of the diffraction orders varies with respect to that obtained with a perfect grating. To show this,...

Diffraction gratings are one of the most used elements in optics and even in other fields of science. They are used also like part of measurement devices in scientific and industrial applications. As it is well known, self-imaging effect appears when a diffraction grating is illuminated with a coherent beam, such as a plane wave. This effect has be...

Diffraction gratings have been successfully used in Optical Metrology for a long time. They can be found in scientific and industrial applications, such as optical encoders for determining the linear or angular displacement, spectrometers, robots, etc. Defects on the surface of the grating may occur due to the manufacturing process. Also dust parti...

We elaborate on a geometrical picture of diffraction gratings. Exact paraxial propagation including coherence effects is obtained by allowing the geometrical rays to transport Wigner function instead of simply specific intensity. We apply this formalism to perfect and less than perfect gratings, illuminated by plane and Gaussian waves. (C) 2009 Els...

Diffraction gratings have been successfully used in Optical Metrology for a long time. They can be found in scientific and industrial applications, such as optical encoders for determining the linear or angular displacement, spectrometers, robots, etc. Defects on the surface of the grating may occur due to the manufacturing process. Also dust parti...

Kriging is an estimation technique that has been proved useful in image processing since it behaves, under regular sampling, as a convolution. The uncertainty obtained with kriging has also been shown to behave as a convolution for the case of regular sampling. The convolution kernel for the uncertainty exclusively depends on the spatial correlatio...

Steel tape gratings are used in different metrology applications. As the period of these gratings was large (around 100 mu m), its analytical study has been performed, up to date, using a geometrical approach. Nowadays, steel tape gratings can be manufactured with lower periods, around 20-40 mu m, and diffractive effects must be taken into account....

We analyze the far field and near field diffraction pattern produced by an amplitude grating whose strips present rough edges. Due to the stochastic nature of the edges a statistical approach is performed. The grating with rough edges is not purely periodic, although it still divides the incident beam in diffracted orders. The intensity of each dif...

Optical encoders are commonly used for high accuracy position measurement, both linear and angular. In order to determine the position, the optical encoder generates two electrical signals that are combined using the arctangent algorithm. There are a number of situations, optical, mechanical and electronic, that affect these signals and produce an...

We analyze the self-imaging process produced by a transmission grating whose strips present two different roughness levels. This kind of grating periodically modulates the transmitted light owing only to the different microtopographic properties of the strips. In spite of the fact that the grating is not purely periodic, it produces a kind of self-...

We present a model to determine the far-field diffraction pattern of a metallic cylinder of infinite length when it is illuminated in oblique incidence. This model is based on the Helmholtz-Kirchhoff integral using the Beckmann conditions for reflection. It considers the three-dimensional nature of the diffracting object as well as the material of...

The Talbot effect is a well studied phenomenon by which grating pseudoimages appear at certain periodic distances when monochromatic light is used. Recently, numerical simulations have shown a new phenomenon; when a polychromatic light beam is used in a double grating system, the intensity of the pseudoimages presents a transverse-profile that rema...

In this work, we analyze the far-field pattern produced by a grating made of strips with two different random roughness levels. The efficiency and shape of the diffraction orders is obtained, which are shown to depend on the statistical properties of roughness. We assume for the calculations that the grating can be used in a mobile mechanical syste...

A tomographiclike method based on the inverse radon transform is used to retrieve the irradiance map of a focused laser beam. The results obtained from multiple knife-edge measurements have been processed through a kriging technique. This technique allows us to map both the beam irradiance and the uncertainty associated with the measurement method....

Metallic gratings can be found in applications such as optical metrology. Due to their fabrication process, the surface presents a certain roughness. In this work, the effect of roughness on Talbot effect has been analyzed when the grating is illuminated with a Gaussian beam. A model based on Fresnel regime is used in order to determine the intensi...