In order to integrate various photonic functions and/or many channels into one chip, (Pb,La)(Zr,Ti)O3 (PLZT) waveguide technologies have been developed. PLZT is one of the best candidates in terms of dense integration and device miniaturization due to its efficient voltage-induced index change and high refractive index. We have established a solid-phase epitaxy to grow low-loss PLZT thin film waveguides, since the formation of low optical propagation loss PLZT waveguides had been difficult with typical vapor phase growth techniques. PLZT waveguides with PLZT buffer layers are grown on Nb-doped semiconductive SrTiO3 substrates for the effective overlap integral of the optical field and the electric field. Efficient control of light coupled in the waveguides is achieved by applying voltage between the top electrodes and the substrates to induce the excellent electro-optic properties of PLZT waveguides. In addition, optical switching devices, which are the key elements of various integrated devices, are fabricated in the PLZT waveguides, showing low-voltage drive and ultra-fast response characteristics. Further key developments such as matrix switches, switch-VOA arrays, and modulator arrays directed toward integrated photonics are also discussed.
Pb(Zr,Ti)O3 (PZT) thin film optical waveguides were grown on Nb-doped SrTiO3(100) substrates by solid-phase epitaxy to fabricate an electrode/waveguide/semiconductor structure. The substrates were spin-coated with methoxyethoxide precursor solutions and preannealed to form amorphous thin films followed by the solid-phase epitaxial crystallization of the thin films above 650 degrees Celsius. The grown epitaxial PZT waveguides had a single perovskite phase and a single (001) orientation. The propagation loss was reduced to 1.7 dB/cm by introducing an epitaxial buffer layer between the PZT waveguide and the Nb-doped SrTiO3 substrate. An electro- optic beam deflector was fabricated by sputtering an ITO prism electrode on the surface of the waveguide. Efficient laser beam deflection larger than 10 mrad was observed by applying 5 V between the prism electrode and the substrate. An index change higher than 0.001 at 5 V and an effective electro-optic coefficient larger than 40 pm/V were estimated from the deflection characteristic. For integrating the electro-optic PZT waveguide devices with passive waveguide components, channel waveguides and waveguide lenses were also fabricated in the PZT waveguides using a simple wet-etching process. These achievements suggest the realization of variety of low- voltage drive integrated waveguide devices including matrix switches as well as the deflectors.
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