A. Castelo

Refractive index modification in glass by laser backwriting ablation of metals.

We report the use of laser ablation of metal targets onto a glass substrate as a way of producing waveguiding devices. In the geometry employed, the nanosecond pulses used for the ablation pass through the glass substrate, and are focused on the metal surface, which is located in close proximity with the substrate. We present measurements of the refractive index profile obtained with this technique, and present a discussion of the physical mechanisms that produce the profiles measured.

Gradient-index human lens as a quadratic phase transformer

The correspondence between the linear integral transform and the ray-transfer matrix of a first-order optical system is used to evaluate the transmittance function of gradient-index (GRIN) human lens regarded as a quadratic phase transformer. The size of the GRIN crystalline lens has been considered for redefining the effective transmittance function by the pupil function. The role that the GRIN nature of the human lens plays in the retinal image quality using the point spread function (PSF) is commented on. The simulation results show that the effective radius of the output face of the lens decreases with increasing thickness and that it is higher for flat end surfaces than for curved end faces. On the other hand, the simulation results also show, for small pupil sizes, that the GRIN nature of the human lens is a retinal image degradation source producing the spread of the PSF and that the curved end surfaces of the lens constitute a retinal image quality improve factor contributing to the narrowing of the PSF.

Design of reconfigurable GRIN planar optical interconnects

Design of all-optics reconfigurable GRIN (Gradient-Index) planar structure for crossover and parallel interconnects will be presented. Design represents a unique combination of GRIN materials, simple geometry optics and waveguide technology for both parallel and distributed processing and communication networks. The optical analysis is based on-axis and off-axis multiple imaging property of GRIN components. The analysis includes the study of the Point Spread Function (PSF) for describing the performance of the GRIN planar structure and the evaluation of the Space Bandwidth Product (SBP) for estimating the number of channels which can be handled. The dependence of the number of channels on the wavelength of the light and the aperture of the planar interconnect is shown. The results are given for five working wavelengths of Laser Diode (LD) and for four transverse aperture of reconfigurable optical interconnect.

Talbot effect in selfoc microlens: application in manufacturing

We present a hybrid optical device for the measurement of axial refractive index and gradient parameter variations in a selfoc microlens by the Talbot effect. The intrinsic nature of the device, that combines a linear grating and an inhomogeneous medium, permits us to measure changes of the parameters as functions of the position shift of the first self-image. The potential accuracy of the measurement of these parameters is estimated.

Waveguide formation by laser backwriting ablation of metals unto glass substrates

In this work we present experimental results for the generation of channel waveguides by a laser backwriting technique using a nanosecond pulsed Nd:YAG laser working at 1064 nm. We present a characterization of the resulting refractive index profile, using the refracted near‐field technique, together with a spatially resolved chemical analysis based on energy dispersive x‐ray analysis(EDX). The EDX results confirm that metal ions are embedded in a region close to the substrate interface, up to about a 5 μm depth. We also present a discussion of the physical mechanisms that produce the profiles measured.

Temperature dependence of laser backwriting process on glass

We present the laser backwriting process on glass by laser ablation of metal targets, in order to fabricate waveguides on pyrex glasses. An horizontal position of the sample and the plate was found suitable to improve the effect of the plume in the sample with respect to the alternative vertical arrangement. We have analysed the longitudinal and transversal profiles, using a profilometer and have compared the results for the different laser sources used, speeds and metal targets. We have analyzed the refractive index profile of the samples obtained, in order to evaluate the change in the substrate due to the metal ablation. A cleaning of the surface and a heat treatment of the glass has been made in order to improve the results.

Optical sensor by Talbot effect in selfoc lens

We present a hybrid optical device for measurement of refractive index variation in a selfoc lens by the Talbot effect. The intrinsic nature of the device that combines a linear grating and an inhomogeneous medium permits to measure changes in the refractive index along the axis as a function of the position shift of the first self-image. Possible changes in the temperature during lens fabrication can be extracted from refractive index variation. The hybrid device has a refractive index sensitivity of ±7 x 10-5 per nanometer of position shift of the first self-image.