Conversion efficiency improvement of terahertz wave generation laterally emitted by a ridge-type periodically poled lithium niobate.

We demonstrate terahertz (THz) wave generation by wavelength conversion in a ridge-type/bulk periodically poled lithium niobate (RT-/bulk-PPLN) under almost the same experimental conditions. When using the RT-PPLN, the ridge structure works as a slab waveguide for the incident pump beam (wavelength: ∼1 µm), and the generated THz wave (∼200 µm) was emitted uniformly from the entire side surface of the crystal. The RT-PPLN has a much higher conversion efficiency from the pumping beam to the THz wave than the bulk-PPLN, and the ratio improved several ten times compared with those of previous studies.

Highly efficient phase-sensitive parametric gain in periodically poled LiNbO3 ridge waveguide.

We have developed a periodically poled LiNbO3 (PPLN) ridge waveguide device and experimentally demonstrated a phase-sensitive optical parametric amplification. The highly efficient net phase-sensitive parametric gain of +18.6 dB is obtained in a cascaded second harmonic generation and difference frequency generation configuration. The phase-sensitive gain is greater by +5.8 dB in comparison with the phase-insensitive gain. We successfully confirmed the phase-sensitive amplification with a high gain in the PPLN ridge waveguide.

Linewidth and relative intensity noise measurements of longitudinal modes in ultrahigh-speed mode-locked laser diodes.

The longitudinal linewidth and corresponding relative intensity noise (RIN) of 10- and 40-GHz mode-locked laser diodes are measured for the first time to our knowledge. It is shown that the cavity Q value is a dominant parameter of the linewidth. It is also shown that the linewidth of the individual modes is almost constant. This means that the phase noise of each mode is almost the same in the mode-locked condition. The RIN value is larger for modes that are distant from the center longitudinal mode. This mode dependence is a consequence of the mode partition noise.

40-gHz, 100-fs stimulated-Brillouin-scattering-free pulse generation by combining a mode-locked laser diode and a dispersion-decreasing fiber.

A 40-GHz, 100-fs pulse train was successfully generated by soliton compression of a mode-locked laser diode (MLLD) pulse with a dispersion-decreasing fiber. The MLLD had a longitudinal mode linewidth as broad as 60 MHz, which made it possible to suppress stimulated Brillouin scattering and achieve stable, ultrahigh-speed pulse compression without applying external frequency modulation.