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In this work, continuous-wave broadly tunable simultaneous generation of red ͑650-690 nm͒, green ͑520-575 nm͒, and blue ͑425-495 nm͒ light in aperiodically poled Zn-diffused LiNbO 3 :Er 3ϩ /Yb 3ϩ channel waveguides is reported after Ti:sapphire excitation in the 850-990 nm range. The red and green emissions arise from energy transfer and upconversion mechanisms between Yb 3ϩ and Er 3ϩ ions, while the blue light with a maximum efficiency of 0.04% W Ϫ1 cm Ϫ1 is produced by quasi-phase matching processes. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1617367͔ Lithium niobate (LiNbO 3 ) compares favorably with other ferroelectric crystals for nonlinear optical applications not only because of its large nonlinear coefficients but also because of the possibility of modulating them, offering the option of nonlinear frequency conversion via quasi-phase matching ͑QPM͒ processes. Several nonlinear devices based on periodic ͑PPLN͒ or aperiodically ͑APPLN͒ poled LiNbO 3 have been reported, including the additional advantage of using waveguiding structures, where high power densities are easily available. [1][2][3][4][5][6][7][8] In this work, nonlinear channel waveguides fabricated by Zn diffusion in Er 3ϩ /Yb 3ϩ codoped APPLN are used to generate simultaneous red, green, and blue ͑RGB͒ light. AP-PLN crystals were grown by the off-centered Czochralski method, along the a axis, with automatic diameter control by a crucible-weighting technique. The initial melts containing congruent LiNbO 3 (͓Li͔/͓Nb͔ϭ0.945) were doped with Er 2 O 3 and Yb 2 O 3 with a purity grade of 99.99%.The growth conditions, pulling and rotation rates and the seed crystal shift, were adjusted appropriately to favor the formation of modulated ferroelectric domain distributions 9 in order to achieve red, green, and blue light under excitation in the 880-1040 nm spectral range (Yb 3ϩ absorption band͒. Using this procedure chirped-period-poled domain structures are obtained. The domain pattern from a y-cut wafer was revealed by etching in a diluted solution of HF:HNO 3 ͑1:2 by volume͒ for 1 h and then checked by conventional optical microscopy. As illustrated in Fig. 1, the wafer exhibits several chirped-period-poled domain structures with periods ranging from 5 to 16 m, being the averaged period of ϳ7 m.The wafer was then polished to optical grade in order to fabricate the channel waveguides by Zn diffusion. 7,10,11 In the present work, the metal diffusion was performed following a two-step procedure ͑exchange and diffusion͒ [12][13][14] which preserves the initial wafer ferroelectric pattern. 15 The exchange process at 550°C for 2 h was performed followed by annealing in open atmosphere at 850°C for 4 h. These conditions produce a 4 m depth Gaussian index profile, with a maximum index change of 0.15% and 0.20% in the extraordinary and ordinary refractive indices, respectively. These waveguides support two modes in the visible range and are single mode at the IR pump wavelengths used in the experiments.The experimental configuration used in the mea...

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Abslracr 'The lattice sites of a number of trivalent mdopanfs (In, Nd. Gd, Er, Tm, and Lu) have k e n determined in IiNbOs aystals doped also with Mg, using the Rutherford back-sraltering and proton-induced x-ray emission channelling techniques, In. Er and IN have been found mainly on li sites, but a mall fraction of In and Lu may substitute for Nb ions. Gd and Tm ions also replace mainly Li, but some of these ions seem to be present in other posilions, possibly related lo some kinds of aggregate, eg. selfampensating p a i n A fraction of Nd ions probably m u p i e s interstitial sites in stmcturalg empty oxygen octahedm, while olher Nd ions m y substitute f o r host cations. In addition lo the already known effect of Cr, Fe and Nd ions, In, Lu and also k give rise U) an OH-absorption hand between 3499 and 3523 m-l, which is attributed to Mg2t@ site)-OH-(0 site)-M'+(Nb site) wmpler defects No such band is otselved for Y, Gd, Er and Tm wdoped crystals.