Sergio Calixto

• Centro de Investigaciones en Optica

For most patients admitted to a hospital, it is a requirement to continuously monitor their vital signs. Among these are the waveforms from ECG and the pulmonary arterial pulse. At present, there are several electronic devices that can measure the arterial pulse waveform. However, they can be affected by electromagnetic wave radiation, and the fabr...

Here is presented the application of the Fabry-Perot interferometer to measure low pressures in the order of tens of Pascals. The fabrication of the interferometer and the method to make the measurements is described.

This paper describes the use of an optical instrument, the Fabry-Perot interferometer, adapted to measure very low pressures. The interferometer consists of two high-reflectance flat mirrors placed one in front of another. In addition, a metallic chamber contains air or a gas. In one of the faces of the chamber, a flexible thin silicone membrane is...

The quantities that are usually measured are time, pressure, temperature, and relative humidity to mention but a few. The word humidity is used when we are dealing with water vapor which is a gas. The instrument used to measure the humidity is the hygrometer that can be based on electronics, optics, mechanics, chemicals, and others. The measurement...

The use of surface relief structures is increasing in the field of optics. A study of photoinduced relief using dichromated gelatin films with different thickness is described in this paper. Two light sources were used: a laser (λ = 468 nm) and an ultraviolet mercury-metal halide lamp. Gratings with low spatial frequencies were contact-copied on th...

A series of phosphor-in-doped glass (PiDG) were fabricated through a CO2 laser heating, blending commercial green phosphor SrAl2O4:Eu²⁺ and Eu³⁺-doped boro-tellurite glass powders. Translucent PiDGs with low loss of the emissive properties of the SrAl2O4:Eu²⁺ phosphor can be only achieved through CO2 laser heating; whereas, sintering of PiDGs by me...

A set of parallel microfluidic channels behaving as a diffraction grating operating in the Raman-Nath regime has been fabricated and studied. The diffraction efficiency of such structure can be tuned by selecting a liquid with a particular refractive index and/or optical anisotropy. Alternatively the optical properties of the liquid can be characte...

We developed two versions of refractometers to measure the refractive index of liquids. One refractometer comprises a glass cell with a surface relief grating on the inner face of one of its walls, while the other one is a microfluidic channel in the form of serpentine that behaves as a grating. Measurements of the liquid refractive index were perf...

Fast sintering of Phosphor-in-Glass (PiG) by means of CO2 laser heating has been successfully achieved. PiGs samples fabricated at different exposure times were characterized and compared with a PiG sample synthetized through an electric furnace. An exposure time as short as 30 s and 12 W of optical power is necessary to sintering PiGs. Results sho...

The use of electronic devices to measure Relative Humidity (RH) is widespread. However, under certain circumstances, for example when explosive gases are present, a spark-free method should be used. Here we suggest the use of stimuli-responsive materials, like gelatin and interpenetrated polymers, to detect RH with an optical method. These material...

The role of graphene nanoplatelets (GnPs) in CH3NH3PbI3 based perovskite device was investigated for the first time. The activated GnPs were introduced in the mesoporous TiO2 by a simple solution process. The morphology and optoelectronic properties of anatase TiO2 layer was modified with the presence of GnPs. The introduction of GnPs modified the...

Because this issue journal is dedicated to Gelatin, here we present a few applications of gelatin in the field of optics. Optics is the science that studies the production, propagation, interaction and detection of light. Various materials sensitive to light (photosensitive) are used for detection of light, such as photomultipliers, CCDs, crystals,...

Because this issue journal is dedicated to Gelatin here we present a few applications of gelatin in the field of optics. It is understood that optics is the science that studies the production, propagation, interaction and detection of light. Regarding the detection there are some materials sensitive to light (photosensitive) that are used like pho...

Polarimeters are useful instruments that measure concentrations of optically active substances in a given solution. The conventional polarimetric principle consists of measuring the rotation angle of linearly polarized light. Here, we present a novel polarimeter based on the study of interference patterns. A Mach–Zehnder interferometer with linearl...

The design, fabrication and testing of hollow Grism and Constant Deviation prisms is shown. Application in the measurement of temperature is done.

This paper describes the design, fabrication, and testing of two hollow prisms. One is a prism with a grating glued to its hypotenuse. This ensemble, prism + grating, is called a grism. It can be applied as an on-axis tunable spectrometer. The other hollow prism is a constant deviation one called a Pellin-Broca. It can be used as a tunable dispersi...

The Mueller matrices associated to six homemade special index-guiding microstructured fibers are determined at a transmission wavelength of 1550 nm. Diattenuation, polarizance, and polarization-dependent loss, among other polarimetric parameters, are determined from the Mueller matrix associated to a 2 m length of each fiber studied here. Results s...

A lens containing a liquid medium and having at least one elastic membrane as one of its components is known as an elastic membrane lens (EML). The elastic membrane may have a constant or variable thickness. The optical properties of the EML change by modifying the profile of its elastic membrane(s). The EML formed of elastic constant thickness mem...

We describe a simple and versatile optical sensing device for measuring refractive index of liquids. The sensor consists of a sinusoidal relief grating in a glass cell. Device calibration is done by pouring in the cell different liquids of known refractive indices. Each time a liquid is poured first order intensity is measured. The fabrication proc...

Here we describe the fabrication and testing of a hollow prism and its application in a spectrograph. A hollow prism with a grating (GRISM) is used as a tunable spectrograph.

We report on a novel device to measure relative humidity. The sensor is based on surface diffraction gratings made of gelatin. This material swells and shrinks according to the content of water vapor in air. By sending a light beam to the grating, diffracted orders appear. Due to the gelatin swelling or shrinking, first order intensity changes acco...

Gelatin thin films inserted in a Mach – Zehnder interferometer were used to monitor Relative Humidity (RH). When RH varied, gelatin film thickness and refractive index also changed. As a result interference pattern moved horizontally. A fixed detector, with a pinhole in front of it, was placed at the interference pattern. It sampled the pattern whe...

This paper describes a simple method of measuring refractive indices of liquids with a small hollow prism. When a He-Ne laser beam is sent to the liquid filled prism it is angularly deviated or deflected. If different liquids are injected in the prism, one at a time, the angular position of the emerging beam changes. These angular positions are det...

A relative humidity (RH) detector consisting of a thin gelatin film inserted in a Mach - Zehnder interferometer is proposed. Due to swelling of the gelatin, by the water vapor absorption, interference pattern is modified and RH is measured.

This paper describes design, fabrication and testing of all-silica large-mode-area (LMA) photonic crystal fibers (PCFs) with three full hexagonal air capillaries rings in a cladding. The design is based on V (normalized frequency) andW (normalized transverse attenuation constant) parameters. Capillaries and rods for a PCF preform were fabricated us...

Digital Holographic Microscopy (DHM) typically uses either Michelson or Mach–Zehnder interferometers as interferometric tools to attain digital holograms. These interferometers need not only good optical alignment in order to compensate the spherical aberration, but also a special optical path difference compensation system when a low coherence ill...

Here we present two optofluidic configurations: a spectrometer and a beam aligner. The spectrometer has a compound element that consists of an optofluidic lens and a relief blazed diffraction grating. When light traverses the two optical elements it is focused and diffracted. At the focal length a spectrum is present. This spectrum can be collected...

We present a spectrometer and scanner based on optofluidic configurations. The main optical component of the spectrometer is a compound optical element consisting of an optofluidic lens and standard blazed diffraction grating. The spectrum size can be changed by filling the lens cavity with different liquids. The scanner comprises two hollow 45° an...

In this work, we present a new method to reduce the shot noise in phase imaging of digital holograms. A spatial averaging process of phase images reconstructed at different reconstruction distances is performed, with the reconstruction distance range being specified by the numerical focus depth of the optical system. An improved phase image is atta...

In this work, we present a new method to reduce the shot noise in phase imaging of digital holograms. A spatial averaging process of phase images reconstructed at different reconstruction distances is performed, with the reconstruction distance range being specified by the numerical focus depth of the optical system. An improved phase image is atta...

Usually optofluidic lenses are spherical (ball lenses), plano - concave or plano - convex. Here we present a method to fabricate non - ball small microfluidic lenses in the bulk of a polymer. The cavity of these lenses can be filled with a liquid by means of a syringe. Liquids present different refractive index thus the lens focal distance can be c...

We present a novel optical method, to our knowledge, to measure the refractive index of liquids by means of the images produced by an optofluidic lens. In addition we propose a new method to make optofluidic lenses.

Here we show a method to make compound optofluidic lenses with sizes of some millimeters. These lenses could have several chambers which combined could help to decrease aberrations. Liquids used in the lenses are ionic liquids. We present an optical characterization study of some of these liquids. A two cell compound lens is show.

In this paper we present a method to get the complex amplitude of a digital hologram obtained through phase shifting transmission digital holographic microscopy. This is based on the angular spectrum method as a reconstruction algorithm employing an in–line experimental setup. The reconstruction technique automatically eliminates the zero order and...

Here we propose two methods using conventional evaporation process to produce tailored Pd/Au composite thin films for hydrogen sensing. In the first method Pd and Au are evaporated simultaneously using different evaporation rate. In the other, alternated nano-layer of Pd and Au are evaporated. Some characteristics of the thin films and their respon...

Transient diffraction gratings were holographically made in dyed plastic by absorbing laser light. Mean energy values of 40 mJ/cm2 absorbed in a 3-mm thick layer were needed to make gratings that lasted about 10 s. The writing beams and a reading one of different wavelength were simultaneously made to fall on the plastic: the reading beam was diffr...

Here we present a new method to make liquid lenses. It is based on the microfluidics method and involves the preparation of emulsions one drop at a time. Tests of lenses by image formation are presented. Experimental results are compared with results of an optical design program. We also present a new type of lens that we call a Compound Lens which...

We present a method to make liquid lenses. It is based on the microfluidic method to make emulsions. An emulsion is a mixture of two immiscible liquids, where one liquid (the dispersed phase) is dispersed in the form of small droplets in another liquid that forms a continuous phase. The presence of a surfactant is necessary for the long term stabil...

An indirect procedure to measure human skin emissivity is proposed. This procedure uses a 10.6 ¹m CO2 laser, to project a controlled energy on the skin, and a power meter to measure the projected, reflected, emitted and background energies. To eliminate the effects of background radiation, two power measurements are taken: one of the skin and backg...

Here we propose a new optical method, to our knowledge, to measure the pressure in liquids or gases by means of a flexible lens. Images of an object given by the dynamical lens are analyzed, and through the visibility of those images pressure is inferred.

Here we propose optofluidic spherical microlenses that can change their focal distance by varying the refractive index of the liquid that composes them. These lenses are fabricated in the bulk of a polymeric mixture. Results of a characterization study of the profile of the lenses, the image forming capability, and the behavior of the focal distanc...

We have investigated the effect of solvent in the sol–gel process of tetraethylorthosilicate (TEOS) when di-n-butyltin dilaurate (DBTL) is used as polycondensation catalyst. Two sets of materials similar to those employed in the field of stone consolidation were prepared in the laboratory by using either protic or aprotic solvents: (1) xerogels fro...

To study the radiation emitted by the human skin, the emissivity of its surface must be known. We present a new approach to measure the emissivity of the human skin in vivo. Our method is based on the calculation of the difference of two infrared images: one acquired before projecting a CO(2) laser beam on the surface of the skin and the other afte...

We present a new kind of compact, simple, and low cost optical pressure sensor. The physical principle on which the sensor is based, components, layout of the system, and characterization are described. The range of pressures in which the sensor works is from about 0.5 to 3 psi ( 1 psi = 6.895 kPa ).

By using two optical fibers and a capillary it is possible to measure the refractive index of liquids. Light leaving a fiber is sent transversally to a capillary that behaves as a cylindrical lens when liquids are inserted in it. Focused light is collected by a second fiber and sent to a detector.

We propose the use of two optofluidic configurations to measure refractive index and pressure of liquids. The first uses two fibers and a capillary and the second a pressure chamber with a membrane lens and two fibers.

We propose a microfluidic method to measure the refractive index of liquids. This method is based on the dynamic focusing by a capillary when liquids with different refractive indexes are inserted into it. Fabrication of such a refractometer has been done by encapsulating two fibers and a capillary. A calibration method is proposed.

A simple method to fabricate infrared (λ = 10.6 μm) diffractive optical elements that work in a transmission mode is presented. A laser-writing instrument completely under computer control has been built to demonstrate the feasibility of this method. Several diffractive elements, fabricated using the laser-writing instrument, are described. RESUMEN...

In this paper, we develop a sensitive optical method to monitor the surface roughness in the investigation of surfaces. By applying this method to measure the RMS surface roughness of various surfaces, we found RMS values which are comparable to those obtained by atomic force microscopy measurements. In addition, we present a simple empirical model...

Divergent microlenses and low-spatial-frequency interference gratings have been fabricated in low-cost silicone layers. The size of the microlenses ranges from ∼ 1 m m to 100 μ m while spatial frequencies of interference gratings range from 4 to 18 l / mm . The fabrication method involves the recording of spatial distributions of mid-IR light. At r...

Substrate dipping in a composite sol–gel solution was used to prepare both smooth and rough thin films of titanium dioxide (TiO2) on commercial fiberglass. The deposition of a composite film was done in a beaker using a solution of titanium (IV) isopropoxide as the sol–gel precursor and cetyltrimethyl ammonium bromide as the surfactant. In order to...

Doped anatase thin films on glass were deposited by ultra-spinning from titanium isopropoxide-based sol-gels. To test the self-cleaning properties of anatasecoated glass, crystalline fluoranthene, a polycyclic aromatic compound, was sprayed over the glass and then irradiated using a 365 nm UV source. This anthropogenic contaminant was removed until...

A Raman system, with the 514.5 and 632.8 nm excitations wavelengths, was used to qualitatively detect the surface roughness of a CdS wafer sample. Anti-Stokes Raman spectra were obtained from several sample zones with different mean roughness levels, previously measured with Atomic Force Microscopy. Our results show that there is a spectrum profile...

A Raman spectroscopic study was performed to detect the surface roughness of a cadmium telluride (CdTe) wafer sample, using the 514.5, 632.8 and 830.0 nm excitations wavelengths. To verify the relation between the roughness and the structure of Raman spectra, in certain zones of the sample, we measured their roughness with an atomic force microscop...

We show that it is possible to make biconvex microlenses at the end of capillary tubes. These lenses can be fixed to the flat end of photonic crystal fibers and can collimate their light.

Anatase thin films (<200 nm in thickness) embedding Degussa P25 TiO2 were prepared by sol–gel method. TiO2-anatase thin films were deposited on a fiberglass substrate and then ground to obtain glass microrods containing the composite films. The film structure was characterized using Raman spectroscopy, atomic absorption and UV–vis spectrophotometry...

Substrate dipping in a composite sol-gel solution was used to prepare smooth and rough thin films of TiO2 on fiberglass. The deposition of films was done using a solution of titanium (IV) isopropoxide as sol-gel precursor and cetyltrimethyl-ammonium bromide as surfactant. The samples were characterized using Raman and Uv-vis spectroscopy, scanning...

The use of large-mode-area tapered holey fibers with collapsed air holes for refractive index sensing is demonstrated. The collapsing of the holes is achieved by tapering the fibers with a “slow-and-hot” method. This non adiabatic process makes the core mode to couple to multiple modes of the solid taper waist. Owing to the beating between the mode...

The fabrication and testing of glass microlenses with rod and spherical shapes are described. The sizes of the lenses range from tens of micrometers to several millimeters. The surfaces of the lenses were fabricated by the melting method. These surfaces have been studied by several methods. The theoretical behavior of the lenses was investigated by...

Large-mode-area photonic crystal fibers with a limited number of air channels in the cladding are investigated theoretically and experimentally. An impact of the relative hole diameter on single-mode operation, the fiber transmission, and bending loss is addressed in detail.

We present a mathematical model of the surface relief formation suffered by photographic emulsions when an intensity pattern is recorded. Traditional explanations consider that this relief is due to silver compounds, but mainly to a mass transfer process in presence of tension forces. According to this description, the model considers diffusion and...

A holographic lens is recorded superimposing two beams with orthogonal linear polarizations on an azobenzene polymer film. The polarization pattern on the interference plane induces two modulations in the media: the volume and the surface modulation. The spatial frequency of the surface relief is twice the one for the volumetric modulation resultin...

It is shown that micro lenses with rod and spherical shape can be fabricated with the melting method. Size of the lenses ranges between tens of microns to about several millimeters. These lenses can modulate light coming from VCSELs.

Refracting surfaces of spherical and rod microlenses have been made with the melting method. Size of spherical lenses ranged between tens of microns to hundreds of them. Length of rod lenses ranged between hundreds of microns to about some millimeters. Diameter of these last lenses ranged between hundreds of microns to about 1.2 mm. The testing of...

We have used chemical deposition of copper complex solution to prepare CuO thin films on commercial fiberglass. The deposition of copper oxides was done in a beaker using a solution of thiosulfatocuprate (I) as precursor and NaOH as a film conditioner. In order to establish a correlation between experimental conditions and the produced copper speci...

Polarization holographic gratings in azopolymers are due to three photoinduced effects: linear anisotropy, circular anisotropy, and surface relief. In our polymers the surface relief grating is with doubled frequency with respect to the volume anisotropic grating. A theoretical analysis is presented and compared with experimental data.

Silica holey fibers with a core surrounded by a few rings of air holes of a large diameter and pitched by a large spacing are fabricated and characterized in terms of their linear-optical properties (i.e., light-delivering quality and optical losses). An optimal value of the relative hole diameter, 0.52 ± 0.05, is found, which provides a single-mod...

A technique for developing recording gratings in situ in Photoresist Shipley S-1822 is described. The developing process is accomplished by use of a spray without removing the sample from the optical setup. The results for the diffraction efficiency show that there is not a large difference between gratings achieved with the traditional wet develop...

Fiber ends are irradiated by a focused CO2 beam causing material to melt. Surface tension shapes the melted material into a spherical microlens that remains joined to the fiber. Such lenses can be used to form images or to focus light. Back focal distances and other parameters of the lenses have been measured.

We investigated the fabrication of continuous surface relief micro-optical elements, using binary and halftone masks, on photographic emulsions. Smoothly varying relieves were obtained recording gray-scale patterns by means of two photographic techniques. The first one involved the defocused image of a binary mask. In the second technique, a halfto...

The optical response of a photopolymerizable formulation consisting of a bisphenol A epoxy acrylate oligomer, a divinyl ether, and a photoinitiator system containing Rose Bengal was studied by recording holographic gratings. This blend is sensitive to blue-green light. Single- and double-exposure volume phase holograms were recorded. In addition to...

It is shown that a relief is generated when spatial distributions of infrared light (λ = 10.6 μm) are recorded on albumen films. The relief can be applied to the fabrication of microelements, such as diffraction gratings and microlenses. Examples are shown.

Surface-relief transmissive diffractive elements were fabricated by embossing. The master was made by lithography with a self-developing photopolymer. The highly cross-linked structure exhibited by the polymer has made possible the direct replication by thermal embossing of polyethylene substrates. Fabricated elements are meant to work with mid-inf...

© 2002 Optical Society of America

Interference gratings, plano-convex microlenses, and spherical microlenses have been made in silicone. Lenses were fabricated by the melting method. Two substrates have been tried: glass and Teflon. The latter substrate lets us fabricate low-f-number lenses. We made spherical microlenses by placing pieces of silicone near a thermal source and studi...

Microlenses, microlens arrays, and diffraction gratings can be made by irradiating a polyethylene substrate with a CO2 laser. These elements are meant to work with mid- infrared light (10.6-micrometers wavelength). The influence of some fabrication process variables in the final parameters of the elements is analyzed. Their quality was characterize...

Microlenses, microlens arrays and diffraction gratings can be made by using polymer materials. These elements can work with mid-infrared light. The influence of some fabrication process variables in the fmal parameters of the elements is analyzed. The surface shapes of the fabricated elements were investigated by a surface analyzer and an interfere...

We discuss the optical recording and relaxation of low spatial frequency gratings and negative microlenses by a dyed polyacrylamide gel. An analysis of the grating diffraction efficiency and the focal distance of microlenses is shown. A study of the evolution of the surface modulation of both types of elements with an interference microscope is als...

The use of a self-processing dry photopolymer layer capable of memorizing optical information as a local change in thickness, is proposed for the fabrication of microlenses, binary holograms and gratings. Relief micro-optical elements are generated by direct imagewise exposure through a mask. A gradient of chemical composition and a gradient of su...

It is shown that by using the melting method it is possible to fabricate microlenses that work with mid-IR radiation. The fabrication method is described, and the characteristics of the polymeric material and the fabricated lenses are shown.

Mid-infrared optical microelements, like lenses or array of them, can be used to couple light or to form images. We present simple methods to fabricate mid-infrared microlenses and other optical elements by means of irradiation of a polymer substrate with CO2 laser or by the melting method. Application of these methods can lead to a mass production...

Mid-infrared optical microelements, like lenses or array of them, can be used to couple light or to form images. We present simple methods to fabricate mid-infrared microlenses and other optical elements by means of irradiation of a polymer substrate with CO2 laser or by the melting method. Application of these methods can lead to a mass production...

It is shown that micromirrors can be made by ablating a dyed plastic using visible light. To test the optical quality of the micromirrors, methods such as the Ronchi and Foucault tests are applied. A commercial interferometer is also used to find their aberrations.

A photographic method using silver halide emulsions as photoresist medium has been used for the fabrication of relief blazed diffractive elements. The fabrication method comprises the design of half tone masks in the computer and the recording of a reduced image of the mask on the emulsion. After development a thin film of aluminum is laid over the...

The use of photographic emulsions as a photoresist medium for fabricating relief blazed zone plates is described. Lithographic methods with masks with 256 gray levels were used in the fabrication process. An example of a zone plate working in the reflection mode at 45° and having 82% diffraction efficiency is shown.

Relief microlenses and micromirrors are fabricated in dichromated gelatin layers. Microelements typically have diameters of approximately a few hundred micrometers and have focal distances ranging from 4 to 15 mm.