Tetsuo Taniuchi

Second‐harmonic generation of blue light in a LiTaO3 waveguide

We report blue light generation in a LiTaO3 waveguide by quasi‐phase‐matched (QPM) second‐harmonic generation (SHG). A periodically domain‐inverted structure for QPM is fabricated in LiTaO3 by proton exchange of a selective Ta‐masked area using pyrophosphoric acid followed by heat treatment. By utilizing this structure and low‐loss proton‐exhanged waveguides, we have realized a third‐order QPM‐SHG device. As a result, 0.13 mW of harmonic blue light was generated for a conversion efficiency of 18%/W.

Characteristics of periodically domain‐inverted LiNbO3 and LiTaO3 waveguides for second harmonic generation

Characteristics of waveguides with periodically domain‐inverted regions in LiNbO3 and LiTaO3 for quasi‐phase‐matched (QPM) second harmonic generation are investigated. The domain‐inverted regions in LiNbO3 are formed by heat treatment using selective SiO2 mask and those in LiTaO3 are formed by heat treatment using selective proton exchange. The domain‐inverted region in LiTaO3 is fabricated up to 2.7 μm depth, which is twice as deep as that in LiNbO3. The channel waveguides incorporating the regions are fabricated using proton exchange by pyrophosphoric acid. The propagation loss (0.9 dB/cm) of LiTaO3 waveguide is much lower than that of LiNbO3 waveguide (2.9 dB/cm). The second harmonic power generated in LiTaO3 waveguide by third‐order QPM consequently has three time higher conversion efficiency, compared to that in LiNbO3 waveguide. In domain‐inverted LiNbO3 waveguide, we have observed optical damage. On the other hand, in domain‐inverted LiTaO3 waveguide, stable blue light (421 nm) has been obtained wi...

Milliwatt-order blue-light generation in a periodically domain-inverted LiTaO(3) waveguide.

We report the characterization of a quasi-phase-matched second-harmonic generation device in LiTaO(3) that has a periodically domain-inverted region and a proton-exchanged channel waveguide. A blue-light power of 2.4 mW was obtained at a 424-nm wavelength. The observed temperature bandwidth for FWHM power is approximately 3 degrees C-cm, which is three times wider than that in a similar device in LiNbO(3). It is also shown that diffraction-limited focusing of the generated blue light may be obtained.

SIMULTANEOUS SUM-FREQUENCY AND SECOND-HARMONIC GENERATION FROM A PROTON-EXCHANGED MGO-DOPED LINBO3 WAVEGUIDE

Frequency conversion of two laser diodes in a proton‐exchanged MgO‐doped LiNbO3 waveguide is reported. Simultaneous generation of blue (0.43 μm), green (0.52 μm), and red (0.65 μm) coherent radiation by sum‐frequency and second‐harmonic generation of laser diodes at wavelengths of 0.86 and 1.3 μm has been observed for the first time. This is made possible by the wide phase‐matching bandwidth of the Cherenkov radiation scheme.

Characteristics of pyrophosphoric acid proton‐exchanged waveguides in LiNbO3

The characteristics of proton‐exchanged LiNbO3 waveguides fabricated using pyrophosphoric acid process are reported. Using this process, high index change waveguides with step profile have been realized. Low‐loss (0.7 dB/cm) channel waveguides have been also obtained by pyrophosphoric acid process. The loss is much lower than that given by conventional benzoic acid process. We show that the reason for low‐loss waveguide fabrication is due to the uniform proton‐exchange formed by this process, compared with the benzoic acid process.

Picosecond blue light pulse generation by frequency doubling of a gain‐switched GaAlAs laser diode with saturable absorbers

Picosecond blue light pulse generation by frequency doubling of a gain‐switched GaAlAs laser diode in a proton‐exchanged MgO:LiNbO3 waveguide is reported. High‐peak fundamental pulse power of 1.23 W is obtained by employing a laser diode with saturable absorbers. Blue light pulse of 7.88 mW maximum peak power and 28.7 ps pulse width is generated in the form of Cherenkov radiation.

Quasi-phase-matched second harmonic generation in a LiTaO/sub 3/ waveguide

The authors report third-order quasi-matched (QPM) second harmonic generation (SHG) in a LiTaO/sub 3/ channel waveguide. A deep domain-inverted region is first fabricated by a proton-exchange and heat treatment technique. Then a uniform and low-pass channel waveguide is fabricated by pyrophosphoric acid proton exchange. Consequently, 12 mW of blue light is obtained at 424 nm wavelength with a conversion efficiency of 6%. The observed FWHM (full-width half maximum) temperature acceptance width for SHG power is 3.2 degrees C and FWHM wavelength acceptance bandwidth for that is 0.2 nm. It is also shown that diffraction limited focusing of the generated blue light may be obtained. >