José Ramón Salgueiro

High efficiency diffractive lenses: Deduction of kinoform profile

The zone plates (diffractive lenses) are not commonly used as image formation systems owing to their low efficiency and multifocal characteristics. In this paper we make a revision of the Fresnel zone plate principles, and present various kinds of zone plates designed to solve the problem of obtaining a limited number of foci with higher efficiency. The purpose of this work was to design, by using Fermat’s principle, a zone-plate profile with high focusing efficiency in only one or two foci, while maintaining a low efficiency in the others. Applying Fermat’s principle to this task results in the kinoform profile of the plate. Calculation of the kinoform profile efficiency reveals that it is the best possible solution to this problem.

Fabrication of a multichannel wavelength-division multiplexing–passive optical net demultiplexer with arrayed-waveguide gratings and diffractive optical elements

A novel, to our knowledge, integrated wavelength-division multiplexing-passive optical net demultiplexer that uses an arrayed-waveguide grating and diffractive optical elements is presented. The demultiplexer is used to distribute 1.3-microm wavelength signals and to multiplex an eight-channel wavelength-division multiplexer spectrum at a 1.55-microm wavelength. The device shows high functionality and good optical performance. The measured cross talk was less than -21 dB, and the 3-dB bandwidth was determined to be 97 GHz, which is close to the theoretical value of 93 GHz. Average losses of 4.5 and 8 dB were measured for the 1.3- and the 1.55-microm signals, respectively.

Model of linewidth for laser writing on a photoresist.

We present a theoretical model to describe the feature size produced by direct laser writing upon a photoresist relative to various experimental parameters. The model allows the number of parameters required for describing the linewidth to be reduced and shows how the description can be made in terms of the ratio of laser power to writing velocity. Both of the limiting cases of the truncation of the laser beam are analyzed; i.e., the case of a nontruncated (Gaussian) beam and the case of a strongly truncated beam (simplified with uniform illumination assumed). Experimental measurements are presented that are fitted to the model to permit its validity to be assessed and for a comparison of these two regimes, which are shown to be different.

Glass processing by ion exchange to fabricate integrated optical planar components: applications

Ion-Exchanged Glass Integrated Optics has received a considerably attention during the laser years because of their well-known advantages. On the other hand, ion- exchanged waveguide components are finding important applications in the implementation of analogue processing devices, optical sensing devices and some kind of circuit for optical communications. Many of these develop devices are based on channel guides, however planar components with optical confinement in only one dimension have been also recognized to be among the basic components of glass integrated optics. In this paper we show the specific advantages of using these kinds of integrated optical elements. Thus, conventional photolithographic techniques can be used with a great accuracy but within the high requirements needed for channeled devices. Likewise, as it will be shown, the components can be realized by simple selective ion-exchange processes in a few steps, and with a high transmission of guided light, in a monomode regime, through the various boundaries shaping the planar components. Finally, their planar configuration facilitates considerably the use of glass integrated devices with other materials and thus a high-performance hybrid optical devices can be achieved. In short, we show various approaches to the design and fabrication of planar components and presents several passive components implementing simple functions such as: beam-splitting, focusing, and so on, which are important for optical sensing and processing applications.

System for laser writing to lithograph masks for integrated optics

A simple and low-cost laser writing system that allows one to obtain micrometer features with high-quality borders is presented. After an overview of the complete fabrication process of masks to carry out the ion-exchange technique in glass in a selective way, a complete description of the experimental setup for direct laser writing is given, including details about such important parts as the control of the motorized stage and the system to perform focusing and alignment. A discussion of the way of focusing the laser beam in order to get the best performance is presented. Results of the characterization of the laser writing system and some examples of integrated optical elements and masks to fabricate them are shown.

Accurate interferometric system to perform the substrate focusing and alignment in laser writing processes

A simple, low cost system useful in laser writing processes to set the focal spot on the substrate surface with micrometre precision is described. Evaluation of its sensitivity is also presented. The lack of essential critical adjustments accounts for the utility of this system and its performance.

Electronic speckle pattern interferometry (ESPI) applied to the study of mechanical behavior of human jaws

The study of the mechanical behavior of the human jaw during chewing is helpful in several specific medical fields that cover the maxillo-facial area. In this work, electronic speckle pattern interferometry has been applied to study dead jaw bones under external stress which simulates the deformations induced during chewing. Fringes obtained after subtraction of two images of the jaw, the image of the relaxed jaw and that of the jaw under stress, give us information about the most stressed zones. The interferometric analysis proposed here is attractive as it can be done in real time with the jaw under progressive stress. Image processing can be applied for improving the quality of fringes. This research can be of help in orthognathic surgery, for example in diagnosis and treatment of fractured jaws, in oral surgery, and in orthodontics because it would help us to know the stress dispersion when we insert an osseointegrated implant or place an orthodontic appliance, respectively. Studying fragments of human jaw some results about its elasticity and flexibility were obtained.

Laser lithography technique to fabricate integrated optical elements by ion exchange in glass

A simple, effective and low cost laser writing lithographic system is presented. This system with a simple optical design and interferometric control of the alignment is able to produce smallest optical features as 1 micrometers wide with high quality edges to produce prototypes of integrated optical elements by ion exchange in research laboratories. Results of several kinds of mask that can be generated for this systems as well as some of the integrated elements produced are shown.

Design of channel directional couplers fabricated on a buffer planar waveguide

In this work we present the study of step-index channel directional couplers which can be fabricated on a buffer planar guide in a such a way that they can be properly designed to support separable modal fields, though the index profile is non separable. The main advantage of this approach is the great simplicity in the analysis, design and fabrication of the directional couplers, or other different integrated strucutures, since it is possible to apply, for instance, the effective index method obtaining a quasi-exact solution for the modal fields. Analytical and numerical results will be presented to confirm that an accurate design of the operation properties of the directional coupler can be achieved.

Laser processing of silver ion-exchanged glass waveguides and applications to integrated optics

We present a technique to directly process silver ion- exchanged planar waveguides fabricated in soda-lime glass. The technique, that is regarded as complementary to the conventional lithography but with the inherent advantages of the direct processing of the material, is based on laser writing with a focused laser bema from an Ar+ laser, which induces a redistribution and aggregation of the small sliver clusters created in the glass during the ion-exchange process. We give a theoretical explanation of the physical processes that take place in the glass and expose experimental reslut of processing of silver ion-exchanged guides under different irradiation conditions. We expose the possible applications of this technique to integrated optics for 2D waveguiding, to optoelectronics for one-step electrode and waveguide fabrication, to planar optics for patterning of reflective components and to diffractive optics to fabricate conventional elements. We finally demonstrate some of this applications presenting devices fabricated by means of this technique.