Kiminori Mizuuchi

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.

Generation of ultraviolet light by frequency doubling of a red laser diode in a first-order periodically poled bulk LiTaO3

Frequency doubling of a 684 nm laser diode in a first-order periodically poled LiTaO3 is presented. Controlling the side growth of the domain inverted region during high-voltage pulse application, a uniform nonlinear grating with a period of 1.7 μm and 50% duty cycle was fabricated over 10 mm interaction length in a 150 μm thick LiTaO3 substrate. A 342 nm wavelength of harmonic ultraviolet light was generated in a single pass through the domain-inverted structure.

HARMONIC BLUE LIGHT GENERATION IN BULK PERIODICALLY POLED LITAO3

Second‐harmonic generation in a LiTaO3 periodically poled by electric field is presented. The side growth of the domain‐inverted region during the poling was found to be suppressed using selective proton exchange. Utilizing this technique, a first‐order periodic domain inversion having uniform periodicity was realized over interaction length of 10 mm in a 300‐μm thick LiTaO3 substrate. A 3.8 mW of harmonic blue light was generated for a conversion efficiency of 1.27% in a single pass through the periodically domain‐inverted structure.

Highly efficient quasi‐phase‐matched second‐harmonic generation using a first‐order periodically domain‐inverted LiTaO3 waveguide

We report blue‐light generation using a first‐order quasi‐phase matched second‐harmonic generation (QPMSHG) in LiTaO3 waveguide. A first‐order periodically domain‐inverted structure can be fabricated using a quick heat‐treatment technique. We have examined the dependence of the depth of the fabricated domain‐inverted region on its width, which critically affects the conversion efficiency of SHG, and designed an optimum domain‐inverted structure for the QPMSHG device. As a result, 15 mW of blue light was generated for a conversion efficiency of 10.3%.

High power blue light generation by frequency doubling of a laser diode in a periodically domain‐inverted LiTaO3 waveguide

We report high power and stable blue‐light generation by frequency doubling a laser diode, stabilized by a grating feedback technique, in a periodically domain‐inverted LiTaO3 waveguide. Due to the deep domain‐inverted regions and strong waveguide confinement formed by proton‐exchange and a quick heat treatment, high efficiency second harmonic generation (SHG) has been obtained. Locking the oscillation wavelength of a laser diode through the waveguide by a grating feedback technique, 8 mW of stable blue SHG has been demonstrated.

Broadening of the phase-matching bandwidth in quasi-phase-matched second-harmonic generation

We report on theoretical analysis and experiments for bandwidth broadening in quasi-phase-matched (QPM) second-harmonic generation (SHG) in LiTaO/sub 3/. QPM waveguides consisting of segments, where each segment has a phase-matching condition different from the others, are proposed to obtain a broad bandwidth and simultaneously, a high SHG efficiency. The waveguides were fabricated by adjusting the phase-matching condition either by changing the grating period of the SHG coefficient or by controlling the width of the waveguide. Consequently, the bandwidth of QPM-SHG was broadened to 0.35 nm with an SHG efficiency of 57 percent/W by modulation of the waveguide width and to 1.12 nm with an SHG efficiency of 29 percent/W by modulation of the grating period. The SHG efficiency and phase-matching characteristics in both types of waveguides showed good agreement with theoretical results. >

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...

Waveguide second-harmonic generation device with broadened flat quasi-phase-matching response by use of a grating structure with located phase shifts.

We report on a theoretical analysis and experiments for bandwidth broadening in quasi-phase-matched (QPM) second-harmonic generation (SHG).We used phase-shifted segments of a periodic grating to obtain a spectrally broadened, nearly flat response simultaneously with high conversion efficiency. We used an x-cut MgO:LiNbO(3) QPM waveguide in our analysis and experiments. The spectral range of the 850-nm fundamental for which SHG conversion exceeded 0.95 of the maximum value broadened from 0.02 to 0.12 nm when a 1-cm-long grating was divided into three segments with optimum phase shift. SHG conversion efficiency was 300%/W for this waveguide. The SHG efficiency and phase-matching characteristics showed good agreement with theoretical results.

Electric-field poling in Mg-doped LiNbO3

We report on electric-field poling of MgO:LiNbO3 (MgLN) using patterned electrodes. Investigation of electric properties of MgLN reveals that polarization switching causes reversible resistance change and that this phenomenon can explain the physical mechanism of random domain growth. Based on these results, we propose a domain-control method in MgLN single crystals by suppressing resistance reduction during the poling process. Using this method, short periodic structures consisting of submicron domain geometries have been achieved in X-, Y-, and Z-cut MgLN crystals. High performances of these periodic domain-inverted structures are also demonstrated by evaluating their potentials as second-harmonic generation devices.

31%-EFFICIENT BLUE SECOND-HARMONIC GENERATION IN A PERIODICALLY POLED MGO :LINBO3 WAVEGUIDE BY FREQUENCY DOUBLING OF AN ALGAAS LASER DIODE

We present a method of controlling the shape of the domain-inverted structure in an off-cut MgO:LiNbO(3) crystal by utilizing a two-dimensional high-voltage application. With this technique a periodically domain-inverted structure with a period of 3.2 microm and a thickness of 2.0 microm was fabricated over a 10-mm interaction length. This structure has made possible sufficient overlaps between propagation modes and domain inversion in the waveguide. Using this structure, we demonstrated cw blue second-harmonic generation of 17.3 mW of power at a wavelength of 426 nm with single-pass 55-mW cw AlGaAs laser diode input, which corresponded to 31% power-conversion efficiency.