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Ultra efficient manufacturing of optical wave guides

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Propagación de luz guiada.

José Olivares (CSIC) and Fernando Agulló (UAM) have used irradiation with very high-energy heavy ions (> 100 MeV) to efficiently manufacture very thick optical wave guides. Such thick guides are required in infrared-guided applications of special interest in the field of astronomy and astrophotonics, for example to detect planets outside the solar system.

Optical wave guides (physical structure that guides light waves) are key elements in the manufacture of photonic devices, such as, for example electro-optical modulators which allow the generation and detection of information. The high efficiency is obtained due to a high degree of light confinement in very small-section regions. This makes it possible to minimise the power requirements, both of the guided light itself and of the electric fields applied to obtain the desired electro-optical functionality.

Basically, to manufacture an optical guide in or on a given material, it is necessary to modify its properties to obtain a region with a greater refraction index than that of the substrate surrounding it. The size or section of the optical guides must be the same as the wavelength (lambda) chosen to be worked with. For light in the visible or near infrared range, lambda is in the order of a micron. It is possible to use different thin film manufacturing technologies by deposit or diffusion to manufacture optical guides as thin as one micron.

However, to handle electromagnetic radiation in the medium infrared, with wavelengths of several microns, it is necessary to be able to manufacture or modify regions of several microns' in thickness and this is not easy to do with classic technologies.

In the work published in OPTICS EXPRESS by José Olivares from the Institute of Optics (CSIC) and Fernando Agulló López from the Materials Microanalysis Centre (UAM), irradiation has been used with high-energy heavy ions to process crystals, in particular of LiNbO3, reaching thicknesses of up to several dozen microns.

The essence of the processing method lies in using the great electronic excitation induced in the materials when irradiated with high-energy heavy ions (>10 MeV). This excitation produces “electronic damage” with an intensity and localisation that can be controlled by suitably choosing the type of ion used for irradiation, its energy and the total quantity of ions irradiated. As a result, crystal regions are achieved which have suffered more “electronic damage” and where the refraction index is decreased to a greater extent. A functional optical guide is thus defined in the regions that have undergone least damage and that have a greater relative refraction index.

This work concludes the line of research on a new manufacturing method using irradiation that was tried out in the accelerator of the Madrid Microanalysis Centre of the UAM and is produced by several Spanish and international research groups: the FOTION group of José Olivares of the Institute of Optics of the CSIC, the collaboration of Fernando Agulló López in the Materials Microanalysis Centre (CMAM) of the UAM (with the participation of Olga Caballero Calero, Miguel Luis Crespillo, Almenara, Mª Dolores Ynsa Alcalá, Ángel García Cabañes) and the GANIL (France) and GSI (Germany) centres.

Download here:  Ultra efficient manufacturing of optical wave guides (Spanish)