Research on Integrated Nonlinear Optic Quasi-Phase-Matched Wavelength Conversion Devices for Wavelength-Division-Multiplexing Optical Communication of Next Generation

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Design, fabrication, and evaluation of quasi-phase matched waveguide nonlinear-optic wavelength conversion devices for future photonic network and their applications to ultrafast optical signal processing were studied. The obtained results are summarized as follows.1 Elementary fabrication techniques were established and improved. Technique to form high-quality ferroelectric domain- inverted gratings for quasi-phase matching up to 30 X 25 mm^2 area was established. Possibility of forming domain inverted gratings of submicrion period was shown. Technique to fabricate low-loss Zn-diffused LiNbO_3 waveguides was developed.2 Technique for designing wavelength conversion devices of difference-frequency generation type was established. In the standard configuration, normalized conversion efficiency of 324 %/W was obtained. In a high-index cladding waveguide type proposed for improvement of efficiency, an efficiency as high as 790 %/W was accomplished.3 A new device construction was proposed for polarization-independent wavelength conversion. As a preliminary experiment, a QPM device was fabricated using a Zn : LiNbO_3O waveguide, and SHG efficiency of 15 %/W was demonstrated.4 As applications to ultrafast optical signal processing for optical communication, an optical switch based on cascaded second-harmonic generation and difference-frequency generation, and an optical gate switch based on an integrated interferometer and sum-frequency generation device, were proposed and fabricated. Picosecond optical switching was demonstrated.5 Integrated high-power semiconductor lasers for application as a pump-wave source for the wavelength convension devices were studied. A high-power external-cavity tunable laser was proposed and fabricated. Output power of 105 mW, wavelength tuning rage of 22 nm and nearly-diffraction-limited collimated beam output were demonstrated.