Hiroki Itoh

Laser-diode-driven ultrafast all-optical switching by using highly nonlinear chalcogenide glass fiber

Laser-diode-driven all-optical switching is demonstrated with an As2S3-based glass fiber only 2 m long and assistance from an erbium-doped fiber amplifier. The laser-diode operation makes it easy to control ultrafast pulse trains with low timing jitter. Ultrafast switching at as much as 80-GHz repetition rates is successfully demonstrated. The nonlinear refractive index of the fiber is estimated to be 9.3 × 10−15 (cm2/W) at a 1.55-μm wavelength.

Reducing photorefractive effect in periodically poled ZnO- and MgO-doped LiNbO3 wavelength converters

The photorefractive effect in annealed proton-exchanged waveguides in periodically poled nondoped, MgO- and ZnO-doped LiNbO3 was evaluated by monitoring the quasiphase matching (QPM) wavelength shift induced by a 0.784-μm-irradiating light. The QPM wavelength shift was reduced at room temperature by a factor of 3–6 in ZnO- and MgO-doped samples compared with the nondoped samples within a 104–105-W/cm2-irradiation intensity range. The doped samples exhibited no significant wavelength shifts when the temperature was raised to slightly above room temperature (50–60 °C).

All-optical switching based on cascading of second-order nonlinearities in a periodically poled titanium-diffused lithium niobate waveguide

We report efficient all-optical switching by using a periodically poled titanium-diffused lithium niobate (Ti:PPLN) waveguide. The periodically domain inversion of the Ti:PPLN waveguide is achieved by electric field poling. The switching is driven by the second-order nonlinear effect of the cascading of phase-matched sum-frequency-generation and difference-frequency-generation processes. It is found that about 12% of the signal is switched by a 20-W gate power.

All-optical switching by use of cascading of phase-matched sum-frequency-generation and difference-frequency-generation processes in periodically poled LiNbO(3).

We show that all-optical switching is feasible by means of cascading of sum-frequency-generation and difference-frequency-generation processes under phase-matched conditions. Three-terminal switching is demonstrated experimentally with bulk periodically poled LiNbO(3). The cascading under phase-matched conditions facilitates switching with lower power than that required under phase-mismatched conditions.

Generation of 5 THz repetition optical pulses by modulation instability in optical fibers

5 THz repetition rate optical pulses have been achieved with modulation instability in an optical fiber. The detailed investigation on the relationship between fiber anomalous dispersion and modulation frequency enables high repetition rate optical pulses, yielding a control method of pulse repetition rate.

Continuous-wave-pumped modulational instablity in an optical fiber

Continuous-wave-pumped modulational instability in an optical fiber has been demonstrated for the first time to our knowledge by using a 5-km single-mode fiber that has a small core area and anomalous group-velocity dispersion. This cw-pumped modulational instability has permitted the generation of a continuous optical pulse train with a pulse repetition rate of greater than 100 GHz, although stimulated Brillouin scattering occurred along with the modulational instability.

New cavity configurations of Nd:MgO:LiNBO3 self-frequency-doubled lasers

Abstract Two types of self-frequency-doubled Nd:MgO:LiNbO3 laser are demonstrated. Their oscillation polarization directions were controlled for second harmonic generation with new cavity configurations which are smaller than the conventional cavity configuration containing a Brewster window. The first laser uses an etalon effect to select the oscillation polarization direction. It emits 0.27 mW of green light (0.546 μm) from a single side of the cavity in quasi CW mode when the crystal absorbs 33 mW of pump light (0.813 μm) from a laser diode. The second laser has a monolithic cavity and the polarization selection is achieved with angle-walk-off caused by birefringence. It emits about 0.2 mW of green light in quasi CW mode when about 100 mW of pump light is incident. In addition to these experiments, the effectiveness of these polarization selection methods is numerically confirmed.

Ultrafast all-optical switching in a walk-off-suppressed nonlinear fiber loop mirror switch

Abstract The walk-off effect of a nonlinear fiber loop mirror switch was experimentally investigated. Using 3 ps pulse pumping at 1.32 μm, a wavelength tunable signal pulse around 1.55 μm, and a dispersion shifted polarization maintaining (PANDA) fiber as a loop, the group delay mismatch was minimized. A switching time of 4.9 ps was obtained at a switching power of 5.5 W.

Measurement of chromatic dispersions in Ti-diffused LiNbO 3 optical waveguides

Chromatic dispersion properties of the Ti:LiNbO(3) optical waveguide have been investigated. Dispersion values of the waveguide fabricated in Z-cut LiNbO(3) were sigma(TE) = -2.0 fsec cm(-1) nm(-l) at a wavelength of 1.3 microm and sigma(TE) = -1.3 fsec cm(-1) nm(-1) at a wavelength of 1.5 microm. Measurement results were compared with theoretical values that take into account the bulk dispersion data and the waveguide dispersion characteristics.

High Δ, small core, single-mode fibers and theiruses

High Delta, small core single-mode fibers were investigated with emphasis on clarifying both their fundamental optical characteristics and on possible uses. Preparation of such high Delta single-mode fibers through the vapor phase axial deposition process made it possible to achieve the low transmission losses of 0.82 dB/km (at 1.61 microm) for a 2.9%-Delta fiber and 0.68 dB/km (at 1.62 microm) for a 1.9%-Delta fiber. Measurements of fundamental characteristics such as transmission loss spectrum, bending loss, dispersion, stimulated Raman scattering, and frequency chirping were made for high Delta single-mode fibers. Two possible uses were investigated: a direct coupling experiment achieved 43% coupling efficiency between high Delta fiber and a LED, and an optical pulse compression experiment in the 1.5-microm wavelength region provided pedestal-free optical pulses with 1.2-ps (FWHM) width.