Eisuke Osakabe

Control of crystallinity in sol-gel derived epitaxial LiNbO3 thin films on sapphire

Control of crystallinity in solid phase epitaxial growth of LiNbO 3 thin films derived from methoxyethoxide solution on sapphire substrates has been attempted by investigating growth variables. Crystallization at 700°C for longer than 30min was necessary for full crystallization of LiNbO 3 thin films, although the orientations of the LiNbO 3 crystal planes parallel to the substrates were almost independent of crystallization temperature and crystallization time. Layer-by-layer crystallization and preparation of an ultrathin initial layer have been found to be important in the growth of high-quality epitaxial LiNbO 3 thin films. X-ray diffraction analysis revealed that perfectly single-plane-oriented epitaxial LiNbO 3 thin films, with rocking curve full width at half-maximum of less than 0.07°, were produced on sapphire (001) substrates. Refractive index of 2.24 and optical propagation loss of 3.0 dB/cm were achieved.

Fabrication of electro-optic Pb(Zr, Ti)O3 heterostructure waveguides on Nb-doped SrTiO3 by solid-phase epitaxy

Pb(Zr, Ti)O3 (PZT) heterostructure optical waveguides were grown on low resistivity Nb-doped SrTiO3(100) substrates by solid-phase epitaxy. The propagation loss was reduced to 1.7 dB/cm at the wavelength of 1.3 μm by introducing an epitaxial buffer layer between the PZT waveguide and the Nb-doped SrTiO3 substrate. An electro-optic beam deflector with an indium–tin–oxide prism electrode on the surface of the PZT waveguide showed efficient laser beam deflection as great as 3.3° (58 mrad) by applying 20 V between the prism electrode and the substrate. An index change higher than 0.001 at 5 V and an average apparent electro-optic coefficient larger than 46 pm/V were estimated from the deflection characteristic.

Electrooptical Properties of Heterostructure (Pb, La)(Zr, Ti)O3 Waveguides on Nb–SrTiO3

The electrooptic behavior of (Pb, La)(Zr, Ti)O3 (PLZT) heterostructure waveguides, including PLZT/Pb(Zr0.95Ti0.05)O3 [PZT (95/5)] and Pb(Zr0.52Ti0.48)O3 [PZT (52/48)]/Pb(Zr0.85Ti0.15)O3 [PZT (85/15)] on Nb–ST substrates was examined. Electrooptic behavior was characterized by fabricating beam deflectors using these heterostructures. The heterostructure waveguides exhibited hysteresis-free electrooptic behavior after the application of initial voltage. The electrooptic behavior of PLZT/PZT (95/5) and PZT (52/48)/PZT (85/15) heterostructure waveguides presented a nonlinear dependence and a linear dependence, respectively. The apparent electrooptic coefficient of the PLZT/PZT (95/5) heterostructure obtained from the linear part of the V–θ characteristic above +7.5 V was 53 pm/V, and that of the PZT (52/48)/PZT (85/15) heterostructure was 37 pm/V. The electrooptic coefficient of the PZT (52/48) waveguide layer using an effective voltage was estimated to be 53 pm/V.

Electro-optic beam deflector using epitaxial Pb(Zr,Ti)O3 waveguides on Nb-doped SrTiO3

Pb(Zr,Ti)O3 (PZT) thin-film optical waveguides were grown on Nb-doped SrTiO3 substrates by solid-phase epitaxy to fabricate an electrode/waveguide/conductor structure. The propagation loss was relatively large for a PZT waveguide on a lightly Nb-doped SrTiO3 as compared with the propagation loss of 4 dB/cm for the structure using undoped SrTiO3. An electro-optic beam deflection device was fabricated by preparing a prism electrode on the surface of the PZT waveguide on a lightly Nb-doped SrTiO3 substrate. Efficient deflection of the coupled laser beam in the PZT waveguide as large as 11 mrad was observed by applying 35 V between the prism electrode and the substrate.

Patterning of (Pb, La)(Zr, Ti)O3 waveguides for fabricating micro-optics using wet etching and solid-phase epitaxy

The patterning process of (Pb, La)(Zr, Ti)O3 heterostructure waveguides was examined for fabricating micro-optics, including channels and lenses. After the patterning of the amorphous thin films derived from spin-cast methoxyethoxide precursors by a wet etching, the patterned amorphous film was crystallized by solid-phase epitaxy. A 5-μm-wide ridge-type channel waveguide was fabricated in a Pb0.91La0.09(Zr0.65Ti0.35)O3/Pb(Zr0.52Ti0.48)O3 heterostructure on a SrTiO3 (100) substrate by the process. The optical confinement was successfully observed. A mode index lens was also fabricated in the Pb0.91La0.09(Zr0.65Ti0.35)O3/Pb(Zr0.30Ti0.70)O3 heterostructure on the SrTiO3 (100) substrate. A deflection of the collimated light by the lens was observed.

PLZT electro-optic waveguides and switches

Switches using (Pb,La)(Zr,Ti)O/sub 3/ waveguides on Nb-doped SrTiO/sub 3/ semiconductor substrates were fabricated. A fabricated 1 2 switch showed crosstalk of n22 dB and response of 20 ns at a voltage as low as 10 V.

Low-voltage drive electro-optic Pb(Zr,Ti)O3 waveguide devices fabricated by solid-phase epitaxy

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.