Nobuhide Fujioka

Group-velocity-matched noncollinear second-harmonic generation in quasi-phase matching

We demonstrate group-velocity-matched second-harmonic generation of 80-fs pulses under noncollinear quasi-phase-matching (QPM) geometry. Second-harmonic pulses of 100-fs duration, 11-nm bandwidth, and0.78-µm center wavelength were generated with 50% efficiency with 3-mm-long periodically poled lithium niobate. We have also numerically studied the dependence of conversion efficiency and pulse durations on pump intensity, propagation length, and noncollinear angle. It is confirmed that our group-velocity-matching scheme requires a much lower pump intensity than the conventional collinear QPM scheme.

Adiabatic compression of quadratic temporal solitons in aperiodic quasi-phase-matching gratings

We numerically show that it is possible to achieve adiabatic compression of femtosecond quadratic solitons in aperiodically poled lithium niobate device. Two-colored solitons of the fundamental wavelength of 1560 nm can be adiabatically shaped by using group-velocity matching schemes available in quasi-phase-matching (QPM) devices. We investigate the performance of the adiabatic compression based on two different group-velocity matching schemes: type-I (e: o + o) collinear QPM geometry and type-0 (e: e + e) non-collinear QPM geometry. Two-colored temporal solitons with pulse duration of 35 fs are generated without visible pedestals from 100-fs fundamental pulse. We also show that walking solitons with shorter pulse durations are adiabatically excited under small group-velocity mismatch condition. The walking solitons experience deceleration or acceleration during compression, depending on the sign of the groupvelocity- mismatch. The demonstrated adiabatic pulse shaping is useful for generation of shorter pulses with clean temporal profiles, efficient femtosecond second harmonic generation and group-velocity control.

Cascaded third-harmonic generation of ultrashort optical pulses in two-dimensional quasi-phase-matching gratings

Cascaded third-harmonic generation (THG) of femtosecond pulses in a two-dimensional periodically poled lithium niobate is demonstrated experimentally. The poling pattern satisfies quasi-phase-matching conditions for both second-harmonic generation (SHG) and the following sum-frequency generation. The pulse-front tilt in noncollinear interactions compensates for group-velocity mismatch among fundamental, second-harmonic (SH), and third-harmonic (TH) pulses, thereby achieving broad acceptance bandwidths in SHG and THG. A 2 mm thick device generates SH and TH pulses of 106 and 110 fs, respectively, from fundamental pulses with temporal duration of 118fs and a 1568 nm center wavelength. The frequency conversion properties are studied theoretically, and the optimal focusing condition for maximum conversion efficiency is derived.

Group-velocity-mismatch compensation in cascaded third-harmonic generation with two- dimensional quasi-phase-matching gratings

A novel scheme to achieve broadband cascaded third-harmonic generation by use of two-dimensional quasi-phase-matching gratings is proposed. Intrinsic group-velocity mismatch is compensated by the pulse front tilt in noncollinear interaction geometry. The presented scheme enables broadband third-harmonic generation in a single device of long interaction length, which reduces the operation intensity dramatically.

Group-velocity-matched cascaded X (2) -processes in two-dimensional QPM gratings

The simultaneously group velocity (GV) matched second harmonic generation (SHG) and third harmonic generation (THG) of femtosecond pulse in a single 2D quasi-phase-matching (QPM) device have been demonstrated. The conversion efficiencies of 27% for SHG and 7% for THG with the pulse duration of -100 fs was achieved. The demonstration has proved that 2D QPM devices are of significant importance for compact and powerful ultrafast coherent sources. It was believed that the same concept is promising for other multistep chi(2) cascading applications of ultrashort pulses.

Ultrashort pulse cascaded third-harmonic generation in two-dimensional quasi-phase-matching structure

We propose and demonstrate group-velocity mismatch compensation in cascaded third-harmonic generation. Second- and third-harmonic generation efficiency of 25% and 7%, respectively, were experimentally obtained for femtosecond pulses by use of two-dimensionally periodically-poled lithium niobate.

2-D Periodically-Poled LiNbO 3 and Its Application to Broadband 2 nd - and 3 rd -Harmonic Generation

We fabricated a two-dimensional quasi-phase-matching device. Efficient cascaded 2nd- and 3rd-harmonic generation of a 100-fs pulse at 1570 nm is demonstrated. Group velocity mismatch is compensated by pulse-front tilt technique with non-collinear geometry.

Adiabatic soliton compression of femtosecond pulses in chirped quasi-phase-matching gratings

We study adiabatic soliton compression of femtosecond pulses in second harmonic generation by using chirped quasi-phase-matching gratings in the absence of group velocity mismatching. Two GV-matching schemes on collinear and non-collinear QPM are numerically investigated.

Group-velocity matched second- and third-harmonic generations using a two-dimensional quasi-phase-matching device

We demonstrate group-velocity matched secondand third-harmonic generations using a two-dimensional quasi-phase-matching device. Broad spectral responses were experimentally confirmed, and several performances of the scheme are studied with numerical simulations.

Simultaneous second- and third-harmonic generations of femtosecond pulses using a two-dimensional nonlinear /spl chi/ photonic crystal

In this paper, we present the GV-matched second- and third-harmonic (TH) generations (THG) of femtosecond pulses in a 2D NPC. In our device, two gratings with different periods (11.6/spl mu/m and 9.36/spl mu/m) are superimposed with an angle of 12/spl deg/, to satisfy the noncollinear QPM conditions for SHG and THG, respectively. In this experiment, TH efficiency was 2% under the condition where the maximum SH efficiency of 25% was obtained.