Extraordinary versus ordinary refractive index change in planar LiNbO3:Ti waveguides

Abstract

Various planar waveguides are fabricated by indiffussion of one or two titanium layers into y-cut LiNbO, substrates. The effective indices of guided TE-and TM-modes are measured for red, green, and blue light. The refractive index profiles are reconstructed by a new reliable inverse WKB procedure. Despite of widely differing profiles there is, for each wavelength, a one to one relationship between the changes An, of the ordinary and An, of the extraordinary refractive index. For low and for high refractive index changes An, and An, grow proportionally, but their ratios differ appreciably. The results support recent findings that the LiNb0,:Ti system exists in two distinct phases. Verschiedene planare Wellenleiter werden durch Eindiffusion von einer oder zwei Titanschichten in y-geschnittene LiNb0,-Substrate hergestellt. Die effektiven Indizes der gefuhrten TEund TM-Moden werden fur rotes, griines und blaues Licht gemessen. Mit einem neuen zuverlassigen inversen WKB-Verfahren werden die Brechungsindexprofile rekonstruiert. Trotz stark unterschiedlicher Profile existiert fur jede Wellenlange eine eins-zu-eins-Beziehung zwischen den Anderungen An,, des ordentlichen und An, des aul3erordentlichen Brechungsindexes. Fur niedrige und hohe Brechungsindexanderungen wachsen An, und An, proportional, jedoch unterscheiden sich ihre Verhlltnisse betrachtlich. Die Ergebnisse bestatigen die kurzlich gemachte Entdeckung, daB das LiNbO, :Ti-System in zwei unterschiedlichen Phasen existiert.

Model of Ti: LiNbO3 Two-Mode-Interference Polarization-Independent Switch and Polarization Splitter

“…In our previous work [18] we approximated this dependence by a two-segment piecewise linear function. This approximation has been recently supported by other experiments and physically explained by the different location of titanium atoms in the LiNbO 3 crystal lattice at low and higher titanium concentrations [19]. Threesegment piecewise linear approximation has been used recently in [20].…”

“…In Fig. 2 we present the dependence of Δη 0 on An e (at a wavelength 0.6328 μπι) given by [19,20] and obtained from our very recent measurements on planar waveguides. Since our results agree quite well with [19], we use them in the calculations.…”

Location of Ti Atoms Diffused into Nearly Perfect Crystals of LiNbO 3 : An X-Ray Standing-Wave Study

“…A summary of coherent positions and coherent fractions extracted from these data is given in table I. No significant dependence of the Ti position on the amount of indiffused Ti was detected in this range of Ti concentrations (2).…”

Photorefractive Waveguides

“…In LiNbO 3 the extraordinary refractive index increases linearly with titanium concentration, whereas the ordinary index shows a slightly sublinear behavior [26]. Larger changes are obtained for extraordinarily polarized light.…”