Javier Camacho

Polarization optics of GRIN lenses

In this paper we show that the matrix representation for a linear retarder, given by Jones calculus, can be successfully applied to describe the birefringence properties of GRIN lenses for meridional rays. The usefulness of this description is experimentally verified by comparing the output pattern of a GRIN lens obtained in a linear polariscope with the predicted conoscopic pattern.

Water jet: a promising method for cutting optical glass

We present an alternative method for cutting optical glass. It works with a high-pressure fluid, carring abrasive powder. This technique offers some advantages over conventional methods that use diamond abrasive covered wires or disks. We make a critical comparison between those two techniques, characterizing cuts with interferometric, polarimetric, and Ronchi testing. The main feature of the water-jet technique is that it allows surface of any shape, already polished, to be cut safely.

Birefringence characterization of quarter-pitch gradient index lenses

A measurement procedure developed for quarter-pitch gradient index lenses is presented. It is based on the use of a polarization interferometer and a waveguide refractometer. The use of a commercial waveguide refractometer allows the identification of the refractive index profile associated with each polarization mode and the selection of the reference refractive index profile. Using a conoscopic setup and the reference refractive index profile (radial polarization mode), the refractive index profile of the tangential polarization mode is determined. The measurements performed with the polarization interferometer are especially valuable on axis, while the waveguide refractometer provides a higher precision at the edge of the cylindrical sample.

Ordinary and extraordinary rays in gradient-index lenses

We assume that the polarization modes of a gradient-index medium with circular cylindrical symmetry are radial and tangential. Making use of a ray-optics method developed for anisotropic crystals,we relate the polarization modes with the permittivity and the dielectric tensor constant of the medium. The polarized imaging response of gradient-index lenses is used to associate ordinary rays with the tangential mode and extraordinary rays with the radial mode. The polarization-mode description is in agreement with the experimental results here. These experimental results allow extending the mode description developed for meridional rays to include skew rays.

Conoscopic evaluation of the birefringence of gradient-index lenses: infidelity sources

Gradient-index lenses are samples whose special characteristics must be taken into account to design the optical polariscopes that can be applied in the evaluation of their birefringence. We discuss the main infidelity sources that modify the conoscopic patterns when a traditional polariscopic setup is used.

High accuracy refractometry using reflectometry: practical limitations

Abstract The accuracy, sensitivity and main sources of systematic errors of reflectometric techniques applied to optical glass refractometry are analyzed. The results show how real performances of the light source, collimators and polarizers limit the accuracy of reflectometry as refractometric technique. The observation geometrics that have been considered are: normal incidence, Brewster angle and 45° incidence.

Refractive index evaluation using reflectometry: accuracy analysis

Modern optical design requires measurement of the refractive index of optical glass to the sixth or the seventh decimal place. Reflectometry represents an interesting option to go beyond the fifth decimal place, since from the literature we know that this technique can work to the fifth decimal place. In addition to that, this method does not use a large area of the sample, a condition that helps to increase the contribution of systematic errors. The techniques used to determine the refractive index of optical materials include transmission and reflection methods. The highest accuracy transmission techniques used in refractometry are: minimum deviation and critical angle goniometry, moire deflectometry, and interferometry. The main systematic errors that limit the measuring accuracy of each of these techniques are mentioned. The techniques used for the determination of the refractive index of optical materials from measurements of the ratio of the reflectance coefficients of its surface are widely used. Many of these methods rest on simplifications of Fresnel equations at specific angles of incidence. The geometries used include: normal incidence, 45 degree(s), Brewster angle, and other angular positions related with the specific sample to be evaluated. The analyses reported in the literature contain just the parameters present in the simplified formulas obtained for the Fresnel coefficients of each specific configuration. In this work a more complete analysis of these techniques is presented.

Polarization optics for out-of-plane light trajectories: GRIN lenses and optical fibers

The volution of the state of polarization along an out-of- plane trajectory has been widely studied for monomode optical fibers. To demonstrate the validity of our proposal we compare the results predicted by our model with experimental result obtained for helically wound optical fibers and the conoscopic patterns obtained for GRIN lenses when oblique illumination is used.

Optical description of an interface

The refractive index is the parameter used to describe the physical medium through which light propagates. It is considered that for homogeneous and isotropic materials it has a unique value at any point; hence a material border is represented by a step index function. This description assumes that the physical properties of the materia at the surface are the same as those of the bulk. From the physics of surfaces we know that in the case of a solid, the interaction between the atoms of the solid and its surroundings are responsible of processes such as adsorption, desorption, etc. In this work we present two basic models that can be sued to characterize, in terms of gradient index profiles, the physical properties of the interface. These models were developed within the physical chemistry of solids to describe the interfacial state, and we have translated them to refractive index profiles following recent results reported for optical wave-guides. The ray tracing equations obtained for light traveling through such refractive index profiles predict Goos-Hanchen effect and satisfy the reflection laws.

Geometrical ray tracing for the characterization of a heterogeneous interface

The presence of contaminants in optical interfaces modifies their optical properties. In the presence of contaminants, the organization of the molecules within the medium is no longer the same for the interior and the surface. Such an interface becomes a region of some finite thickness in which there is a gradual change of physical properties. In this case, a step refractive index profile cannot be used to describe this region, as is generally used in refractometry. In general, the refractive index at a surface or an interface should be presented as a gradient. The profile of the refractive index distribution at an interface is defined by the physical-chemical properties of the base medium and the contaminant. From the thermodynamic models developed for interfaces, a refractive index distribution can be proposed. The description of the interface in terms of a refractive index profile allows the use of optical testing methods developed for the characterization of optical materials. In particular, geometrical and interferometric testing procedures can be used. Ray tracing is required become the analysis of interferograms and light distribution in the outcome of geometrical test relays on an a-priori knowledge of the optical path followed by light. In this work we propose refractive index distributions based on the thermodynamic potentials of typical interfaces. Making use of the mathematical forumlism based on Fermats principle, the ray tracing equation associated to each case is presented. The information about these light trajectories is necessary to determine the thickness, concentration, as well as the type of contaminant in the contaminated region.