Microelectronic Engineering 67–68 (2003) 742–748 www.elsevier.com / locate / mee Fabrication of band-gap structures in planar nonlinear waveguides for second harmonic generation a a, b b c c * V. Foglietti , E. Cianci , D. Pezzetta , C. Sibilia , M. Marangoni , R. Osellame , c R. Ramponi a Istituto di Fotonica e Nanotecnologie del CNR, Via Cineto Romano 42, 00156 Roma, Italy b ` INFM at Dipartimento di Energetica, Universita di Roma ‘ La Sapienza’, Via Scarpa 16, 00161 Roma, Italy c INFM at Dipartimento di Fisica-Politecnico di Milano and Istituto di Fotonica e Nanotecnologie del CNR, Piazza Leonardo da Vinci 32, 20133 Milano, Italy Abstract The work presented here deals with the design and fabrication of the linear grating on a LiNbO planar 3 waveguide to obtain an efficient second harmonic generation operating in Cerenkov configuration. The lithium niobate is a nonlinear material particularly suitable for photonic applications where the waveguide can be efficiently fabricated by means of proton exchange. The grating pattern, with a period of 350 nm, covers a square of 1.5-mm sides. The pattern has been fabricated by means of electron beam lithography and reactive ion etching.  2003 Elsevier Science B.V. All rights reserved. Keywords: Nonlinear optics; e-beam lithography 1. Introduction In order to fabricate a second harmonic generator a low-loss waveguide can be used with a high non linear coefficient. The device must work in a configuration which satisfies the phase-matching between the fundamental frequency and the second harmonic mode. In recent years there has been a growing interest in proton-exchanged (PE) waveguides for fabrication of non linear devices on LiNbO and LiTaO crystals [1], where the second harmonic generation can be obtained in 3 3 quasi-phase-matching configuration (QPM) relying on substrates with periodically inverted ferroelec- tric domains. However, it is possible to obtain an efficient second harmonic generation (SHG) using PE waveguides in LiNbO without inversion of ferroelectric domains but operating in Cerenkov 3 *Corresponding author. E-mail address: cianci@iess.rm.cnr.it (E. Cianci). 0167-9317 / 03 / $ – see front matter  2003 Elsevier Science B.V. All rights reserved. doi:10.1016 / S0167-9317(03)00176-X