Masatoshi Fujimura

Highly efficient second-harmonic generation in buried waveguides formed by annealed and reverse proton exchange in periodically poled lithium niobate

Efficient three-wave mixing devices have numerous applications, including wavelength conversion, dispersion compensation, and all-optical switching. Second-harmonic generation (SHG) is a useful diagnostic for near-degenerate operation of these devices. With buried waveguides formed in periodically poled lithium niobate by annealed and reverse proton exchange, we demonstrate what is believed to be the highest normalized conversion efficiency (150%/W cm(2)) for SHG in the 1550-nm communications band reported to date.

High-efficiency LiNbO/sub 3/ waveguide second-harmonic generation devices with ferroelectric-domain-inverted gratings fabricated by applying voltage

The characteristics of the ferroelectric-domain-inverted gratings fabricated by applying voltage at room temperature in Z-cut LiNbO/sub 3/ crystal were examined for waveguide quasiphase-matched second-harmonic generation (QPM-SHG) devices. Conditions suitable for reproducible fabrication of uniform grating structure were clarified. Devices with uniform and fan-out grating for green and blue light generation were fabricated, and the performances were examined. A normalized SHG efficiency as high as 150%/W was obtained in blue light generation device with uniform grating of 3 mm interaction length.

Low-power all-optical gate based on sum frequency mixing in APE waveguides in PPLN

We present an all-optical gate implemented in periodically poled lithium niobate (PPLN) (LiNbO/sub 3/). Efficient mixing is achieved by using a phase-matched guided-wave interaction. A control wave at 1.537 /spl mu/m is used to gate a signal at 1.552 /spl mu/m, where a control power of 185 mW is sufficient to achieve 96% depletion of a low-power signal. A simple switch configuration is described whereby high-contrast low-power all-optical switching can be performed.

Wavelength-conversion type picosecond optical switching using a waveguide QPM-SHG/DFG device

We report picosecond all-optical switching in optical communication band using a LiNbO3 waveguide quasi-phase matched second-harmonic generation/difference-frequency generation device. Analysis based on the beam propagation method showed that 1 ps switching with 3.1% efficiency is feasible with 10 W peak control pulse power. Switching efficiency of −22 dB was demonstrated using control pulses of 10 ps width and 2 W peak power.

LiNbO/sub 3/ waveguide quasi-phase-matching second harmonic generation devices with ferroelectric-domain-inverted gratings formed by electron-beam scanning

The characteristics of the formation of LiNbO/sub 3/ ferroelectric-domain-inverted gratings using electron-beam scanning are examined and discussed for application to waveguide quasi-phase-matching second-harmonic-generation (SHG) devices. It is found that the domain inversion tends to occur in segmented regions, and the inversion width is thinner near the crystal surface than inside the crystal. The dependence of the SHG efficiency on the grating structure is examined theoretically. Prototype devices for green and blue light generation have been fabricated and the device performance examined. Normalized SHG efficiencies as high as 50%/W and 70%/W, respectively, are obtained in green and blue light generation devices of 3.3-mm length. The experimental results are compared with the theoretical results. >

Quasi-phase-matched self-frequency-doubling waveguide laser in Nd:LiNbO/sub 3/

A Nd:LiNbO/sub 3/ quasi-phase-matched self-frequency-doubling waveguide laser is demonstrated for the first time. Fabrication of domain-inverted gratings in Nd:LiNbO/sub 3/ for quasi-phase-matched second-harmonic generation (QPM-SHG) was a key for implementation of the device. A simple fabrication method was found and employed in a prototype device fabrication. The device was optically-pumped at 814-nm wavelength. A laser oscillation took place at 1084 nm and green light emission was obtained at 542 nm by intracavity QPM-SHG.

Waveguide quasi-phase-matched sum-frequency generation device for high-efficiency optical sampling

A LiNbO/sub 3/ waveguide quasi-phase-matched sum-frequency generation (SFG) device using a fan out domain-inverted grating for picosecond optical sampling was designed and fabricated. Sampling of signal waves at 1.5-/spl mu/m wavelength by 25-ps sampling pulses generated by a gain-switched laser diode is demonstrated in a device of 5 mm length with a normalized SFG efficiency as high as 43%/W.

Generation of Polarization-Entangled Photons by Type-II Quasi-Phase-Matched Waveguide Nonlinear-Optic Device

A cross-polarized twin-photon generation device was implemented with Ti-indiffused LiNbO3 waveguides and gratings for type-II (TE rarr TE + TM) quasi-phase matching. Generation of polarization-entangled twin-photon beams by a simple system using the fabricated device is demonstrated through quantum interference and photon polarization measurement experiment.

Formation of Domain-Inverted Grating in MgO:LiNbO3 by Voltage Application with Insulation Layer Cladding

We demonstrate an effective method for formation of domain-inverted gratings in MgO:LiNbO3 for quasi-phase-matched nonlinear-optic devices. It was found that domain-inverted gratings could be obtained by application of voltage pulses with SiO2 insulation layer cladding. An insulation layer on the -Z face reduces the leakage current, and another insulation layer over a periodic electrode on the +Z face reduces excessive expansion of domain-inverted regions. Good-quality domain-inverted gratings with a period of 18 µm were obtained.

Cross-polarized twin photon generation device using quasi-phase matched LiNbO/sub 3/ waveguide

We demonstrate a cross-polarized twin photon generation device using a LiNbO/sub 3/ waveguide for the first time. The twin photons can easily be split into each photon, and the device has applications to polarization-entangled photon generation. Type II quasi-phase matching (TE/spl rarr/TE+TM) and nonlinear tensor element d/sub 24/ were used for twin photon generation in the 1.55-/spl mu/m band by the parametric fluorescence.