Vapor diffused optical waveguides in strontium barium niobate (SBN: 60)

Single mode planar and channel waveguides have been produced in Sr0.6Ba0.4Nb2O6 (tungsten bronze structure) by sulfur diffusion in a sealed ampule, followed by oxidation in an open tube. Losses in channel waveguides were ∼15–20 dB/cm for TM polarization and ∼27–32 dB/cm for the TE polarization in z-cut substrates. Electro-optic modulation was observed after poling of the substrate. The experimentally determined value of the effective electro-optic coefficient was slightly greater than reported earlier for bulk samples of SBN:60, and about 15 times greater than for LiNbO3. Based on measurements with the S35 radioisotope, the average atomic sulfur concentration was estimated to be about 4×1017/cm3 in the region extending from the surface to a depth of 2.5 μm, and a significant background concentration (∼5×1016/cm3) was present to depths in excess of 20 μm.