Shigehiro Nagano

Pulsed High Peak Power Millimeter Wave Generation via Difference Frequency Generation Using Periodically Poled Lithium Niobate

We successfully demonstrated pulsed high-peak-power millimeter wave generation using periodically poled lithium niobate (PPLN) under collinear phase matching. We fabricated 0.5-mm-thick PPLN with a 40 mm interaction length for generating 250 and 300 GHz waves. Pump waves with very close dual wavelength output from a KTiOPO4 (KTP) optical parametric oscillator had a pulse energy of 2 mJ, pulse duration of 15 ns, and wavelength around 1300 nm. Millimeter waves were generated successfully, and the highest peak power obtained was estimated to be about 0.1 mW. This value is sufficiently high for envelope detection using a Schottky barrier diode. An active imaging system in the millimeter wave range could be realized using such a pulsed emitter and a Schottky barrier diode array.

Entangled photon generation in two-period quasi-phase-matched parametric down-conversion.

We proposed and demonstrated a simple but deterministic scheme for generating polarization-entangled photon pairs at telecommunication wavelengths with type-II quasi-phase-matched spontaneous parametric down-conversion (QPM-SPDC) having two poling periods. We fabricated a LiNbO3 crystal having two poling periods so as to generate entangled photons at two wavelengths, i.e., 1506 nm and 1594 nm. We characterized the two-photon polarization state with state tomography and confirmed that the state was highly entangled.

800-nm Band Cross-Polarized Photon Pair Source Using Type-II Parametric Down-Conversion in Periodically Poled Lithium Niobate

We report a high-efficiency source of cross-polarized photon pairs via type-II quasi-phase matched spontaneous parametric down-conversion using periodically poled lithium niobate (PPLN). The photon pairs are generated from the PPLN in a fifth-order quasi-phase matching condition around 800 nm, which matches the wavelength band of efficient Si avalanche photodiodes. We obtained the photon-pair production rate of 6.8×105 s-1 mW-1.

Generation of Cross-Polarized Photon Pairs via Type-II Third-Order Quasi-Phase Matched Parametric Down-Conversion

We have developed a high-efficiency source of cross-polarized photon pairs generated via type-II spontaneous parametric down-conversion using periodically poled lithium niobate (PPLN). The photon pairs are generated from bulk PPLN under third-order quasi-phase-matched conditions around 800 nm. We achieved a photon-pair production rate of N=1.95×106 s-1mW-1.

Very-Deep Nanometer-Size Domain Inversion in LiNbO3: Proposal for Circular Form Full Cover Electrodes

Very-deep nanometer-size domain inversions in lithium niobate (LiNbO3) substrate have been realized using circular form full cover electrode (CF-FCE). From the calculated results, circular form electrode is better than that of rectangular type for fine domain inversion patterns. Domain inversion was performed by applying high voltage to CF-FCE. Using the proposed CF-FCE, we successfully fabricated 2 µm periodic domain inversion in a 500-µm-thick congruent LiNbO3 (C-LN) crystal. It is also shown that smaller domain inversion width in the nanometer regime with high aspect ratio is possible using this technique. We obtained an aspect ratio as high as 870 for a domain inversion width of 575 nm. To our knowledge, such a high aspect ratio is reported for the first time.

Efficient Up-Conversion Detection of 1550 nm Photons Using Bulk Periodically-Poled LiNbO3

We demonstrate efficient up-conversion detection of photons at 1550 nm utilizing bulk periodically-poled LiNbO3 (PPLN) and nanosecond-pulsed pumping. An internal conversion efficiency of 96% and an overall photon detection efficiency of 19% including the efficiency of a visible photon detector were achieved with a low dark count rate.

Duty Ratio Dependence of Difference Frequency Generation for Millimeter–Terahertz Wave Spectra Using Periodically Poled Lithium Niobate

We demonstrate difference frequency generation of millimeter wave and terahertz (THz) radiation using periodically poled lithium niobate (PPLN). We fabricated PPLN crystals with a 286-µm period, and with 50.0 and 33.3% duty ratio. Millimeter and THz waves were successfully generated, and higher-order quasi-phase matching (QPM) modes were obtained. We investigated behaviors of the radiation and the influence of the duty cycle on the spectrum using numerical simulation. Higher-order QPM modes could be generated with the proper duty cycle. The conversion efficiency of higher-order modes was controllable by varying the duty cycle of the QPM device.

Temperature dependence of blue light-induced near-infrared absorption of ferroelectric crystals

We studied blue light-induced near-infrared absorption (BLINIRA) and its temperature dependence in ferroelectric crystals, i.e., MgO-doped stoichiometric-LiNbO₃, congruent-LiNbO₃, MgO-doped stoichiometric-LiTaO₃, and stoichiometric-LiTaO₃. We found the BLINIRA decreased with the increase of temperature.

Generation of cross-polarized photon pairs in a 800-nm band via Type II parametric down-conversion using a periodically poled Lithium Niobate

We have developed a high-efficiency source of cross-polarized photon pairs via type-II quasi-phase matched spontaneous parametric down-conversion using periodically poled lithium niobate (PPLN). The photon pairs are generated from the PPLN in fifth-order quasi-phase matched condition around 800 nm, which matches the wavelength band of efficient Si avalanche photodiodes. We obtained 25,000 coincidence counts sec-1mW-1of the photon pairs.

Cross-Polarized Photon Pair Source using Type-II Quasi-Phase Matched Parametric Down-Conversion

We have developed a high-efficiency source of cross-polarized photon pairs in a 800-nm band via type-II quasi-phase matched spontaneous parametric down-conversion using periodically poled lithium niobate. We obtained 25,000 coincidence counts sec-1 mW-1 of the photon pairs.