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Deposited films of transition metals (Ti, V, and Ni) have been diffused into LiNbO3 crystals to form low-loss TE and TM mode optical waveguides. Using Ti, single-mode low-loss waveguides which confine the guided light to within ∼1 μm of the surface have been constructed. The choice of diffusion parameters allows independent control of important waveguide parameters.

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Planar optical waveguides consisting of thin dielectric films with metal cladding have been investigated theoretically and experimentally. A computer program was devised to provide the phase and attenuation constants and wavefunctions for TE and TM modes in symmetric and asymmetric guides. Approximate expressions suitable for slide-rule calculation were also derived. Numerical results and illustrations are given for films of photoresist with Al, Ag, and Au cladding. Direct measurements of the attenuation and phase constants at 0.633 microm of numerous experimental waveguides are in reasonable agreement with theory. Attenuations <1 dB/cm, which is sufficiently small for application in devices, were measured. Calculated wavefunctions illustrate the mismatch of modes at transitions between unclad and metal-clad waveguides. Experimentally, we find substantial losses at such abrupt junctions. They can be overcome by simple tapered transitions.

The Raman spectra of Liwb03 and LiTa03 have been investigated between 90 and 1100'K. The dependence of optic-mode frequencies and Raman-scattering efBciencies on temperature indicates that the ferroeiectric transition (T, =900'K for LiTaO&, =1480'K for LiNb03) is second order and is associated with an optic phonon mode whose frequency becomes small as the Curie temperature is approached from below. Critical Rayleigh scattering is observed for LiTa03 and the shape of the anomaly is attributed to the combined eRects of lattice polarization Quctuation and the discontinuity in electro-optic eRect at the transition. The absolute scattering efBciency and linewidth data indicate that the stimulated Raman gain for several lattice modes is comparable with or greater than that for the 655-cm ' CS2 line, and calculations show that cw Raman oscillation in these modes is feasible.tional modes for the lowand high-temperature phases are listed in Table I. The nonzero components of infrared absorption and Raman scattering tensors are also noted. In the ferroelectric phase, 22 optic modes are both Ramanand infrared-active (4Ai+9E), and in the paraelectric phase nine of these become Ramanand 13 infrared-active. The macroscopic Geld produced by the infrared-active phonons raises the degeneracy between longitudinal (L) and transverse (T) modes, thereby doubling the number of observed frequencies for these modes. Above T, the Raman-active phonons are nonpolar, so that the TL degeneracy is restored and there are only five (1Ato+4Eo) characteristic Raman shifts expected.The above discussion is based on the point-group symmetry (3ttt below T, and 3m above T,) and is only approximately applicable for the Gnite-wavelength phonons actually observed. In particular, attention must be restricted to phonons propagating along or perpendicular to the unique crystal (c) axis, since for other directions phonons to not in general possess a well-deGned L or T polarization. Even with this restriction, there are additional considerations. For example, a transverse E phonon of 6nite wavelength can propagate either parallel or perpendicular to the optic axis and may have a different frequency in each case. Similarly, transverse A & modes may have different frequencies for propagation along (010) and (110).These latter effects, however, were not observed in the present experiment.The strength of a given Raman-active vibration is given by the scattering efliciency 5/ldQ, where 8 is the fraction of incident power that is scattered into a solid angle dQ near a normal to the optical path length E. A semiclassical expression for (Stokes-shifted) scattering eKciency is4