Youichi Sakakibara

Ultrashort pulse-generation by saturable absorber mirrors based on polymer-embedded carbon nanotubes.

We demonstrate passive mode locking of solid-state lasers by saturable absorbers based on carbon nanotubes (CNT). These novel absorbers are fabricated by spin-coating a polymer doped with CNTs onto commercial dielectric laser-mirrors. We obtain broadband artificial saturable absorber mirrors with ultrafast recovery times without the use of epitaxial growth techniques and the well-established spin-coating process allows the fabrication of devices based on a large variety of substrate materials. First results on passive mode locking of Nd:glass and Er/Yb:glass lasers are discussed. In the case of Er/Yb:glass we report the to our knowledge shortest pulse generated in a self-starting configuration based on Er/Yb:bulk-glass: 68 fs (45 fs Fourier-limit) at 1570 nm wavelength at a pulse-repetition rate of 85 MHz.

Sub-200-fs pulsed erbium-doped fiber laser using a carbon nanotube-polyvinylalcohol mode locker

We study the difference in mode-locked operations of different saturable absorber films made of single wall carbon nanotube-polyvinylalcohol nanocomposite. The films have different nanotube concentrations and thicknesses. For the study, a mode-locked erbium-doped fiber laser in a ring cavity configuration was constructed by setting the films in a microgap between a pair of fiber end facets. With the optimum film among those we have tested, the shortest pulses with a width of 178fs were achieved at 1.56μm with a repetition rate of 22.8MHz and an average power of 1.55mW.

Ultrafast nonlinear effects in hydrogenated amorphous silicon wire waveguide

We, for the first time, present the ultrafast optical nonlinear response of a hydrogenated amorphous silicon (a-Si:H) wire waveguide using femtosecond pulses. We show cross-phase and cross-absorption modulations measured using the heterodyne pump-probe method and estimate the optical Kerr coefficient and two-photon absorption coefficient for the amorphous silicon waveguide. The pumping energy of 0.8 eV is slightly lower than that required to achieve two-photon excitation at the band gap of a-Si:H (approximately 1.7 eV). An ultrafast response of less than 100 fs is observed, which indicates that the free-carrier effect is suppressed by the localized states in the band gap.

All-polarization-maintaining Er-doped ultrashort-pulse fiber laser using carbon nanotube saturable absorber

We present an all-polarization-maintaining Er-doped ultrashort-pulse fiber laser using a single-wall carbon nanotube polyimide nanocomposite saturable absorber. The maximum average power for single-pulse operation is 4.8 mW, and the repetition frequency is 41.3 MHz. Self-start and stable mode-locking operation is achieved. The RF amplitude noise is also examined and it is confirmed that the noise figure is as low as that of a solid-state laser. Using a polarization-maintaining anomalous dispersive fiber, a 314 fs output pulse is compressed to 107 fs via higher-order soliton compression. The peak power of the compressed pulse is up to 1.1 kW.

Carbon Nanotube-Poly(vinylalcohol) Nanocomposite Film Devices: Applications for Femtosecond Fiber Laser Mode Lockers and Optical Amplifier Noise Suppressors

We fabricated single-wall carbon nanotube (SWNT)/poly(vinylalcohol) (PVA) nanocomposite freestanding films and examined their application in devices in which the saturable absorption of SWNTs at near-infrared optical telecommunication wavelengths can be utilized. In a passively mode-locked fiber laser, we integrated a 30-µm-thick SWNT/PVA film into a fiber connection adaptor with the film sandwiched by a pair of fiber ferrules. A ring fiber laser with a SWNT/PVA saturable absorber was operated very easily in the mode-locked short-pulse mode with a pulse width of about 500 fs. Reproducible stable device performance was confirmed. In examining noise suppression for optical amplifiers, mixed light of semiconductor amplified spontaneous emission (ASE) source and 370 fs laser pulses was passed through a 100-µm-thick SWNT/PVA film. The transmission loss of the femtosecond pulse light was smaller than that of the ASE light. This proved that the SWNT/PVA film has the ability to suppress ASE noise.

Near-Infrared Saturable Absorption of Single-Wall Carbon Nanotubes Prepared by Laser Ablation Method

We investigated the resonance dependence of saturable absorption (SA) properties in near-infrared in single-wall carbon nanotube (SWNT) materials prepared by the laser ablation method. For SWNT thin films coated on glass plates with a distinct single absorption band centered at 1.78 µm, we measured SA properties using the z-scan method with just- or weak-resonance excitation using a femtosecond laser at 1.78 µm or at 1.55 µm, respectively. In the just-resonance experiments the laser intensities of ~50 MW/cm2 induced decreases in the absorption coefficient by ~40%, but in the weak-resonance experiments one-order-higher laser intensities were necessary to obtain absorption changes of similar extents.

Red organic electroluminescence devices with a reduced porphyrin compound, tetraphenylchlorin

We constructed red organic electroluminescence (EL) devices with a reduced porphyrin compound, tetraphenylchlorin, that was doped at various concentrations (0.5, 1.7, and 3.7 wt %) within a tris(8-hydroxyquinoline) aluminum (Alq3) host layer. We measured their EL properties and found that all three devices emitted a red EL band at 660 nm with a width of 20 nm. Emission color of the 1.7 and 3.7 wt % devices was red (chromaticity coordinates x=0.67, y=0.29 and x=0.78, y=0.21) and the luminance maximum was 100 and 24 cdm−2, respectively. The 0.5 wt % device emitted a green Alq3 EL band as well, and showed an increase in relative intensity of the Alq3 emission with increasing applied voltage.

Pattern-effect-free all-optical wavelength conversion using a hydrogenated amorphous silicon waveguide with ultra-fast carrier decay

Ultra-fast carrier decay, recently discovered in a hydrogenated amorphous silicon waveguide, can be exploited for pattern-effect-free all-optical signal processing based on optical Kerr nonlinearity. In this study, we utilized a 10 Gbit/s RZ-OOK data stream as a pump for degenerate four-wave mixing in a low-loss hydrogenated amorphous silicon waveguide. The propagation loss of the waveguide used was 1.0±0.2 dB/cm at 1550 nm. Unlike crystalline silicon waveguides, no noticeable difference was observed in the BER characteristics between the cases of PRBS 2(7)-1 and 2(31)-1.

Polarization-maintaining, high-energy, wavelength-tunable, Er-doped ultrashort pulse fiber laser using carbon-nanotube polyimide film

A high-energy, wavelength-tunable, all-polarization-maintaining Er-doped ultrashort fiber laser was demonstrated using a polyimide film dispersed with single-wall carbon nanotubes. A variable output coupler and wavelength filter were used in the cavity configuration, and high-power operation was demonstrated. The maximum average power was 12.6 mW and pulse energy was 585 pJ for stable single-pulse operation with an output coupling ratio as high as 98.3%. Wide wavelength-tunable operation at 1532-1562 nm was also demonstrated by controlling the wavelength filter. The RF amplitude noise characteristics were examined in terms of their dependence on output coupling ratio and oscillation wavelength.

Dispersion-managed, high-power, Er-doped ultrashort-pulse fiber laser using carbon-nanotube polyimide film

We investigated a dispersion-managed, passively mode-locked, ultrashort-pulse, Er-doped fiber laser using a polyimide film containing dispersed single-wall carbon nanotubes (SWNTs) and examined the dependence on net cavity dispersion and output coupling ratio using normal-dispersion fibers and a variable output coupler. For the dissipative soliton mode-locking condition, we achieved a pulse energy of 3.5 nJ and an average power of 114 mW, the highest values yet reported for an SWNT fiber laser under single-pulse operation.