Takasumi Tanabe

We demonstrate all-optical switching in the telecommunication band, in silicon photonic crystals at high speed (∼50ps), with extremely low switching energy (a few 100fJ), and high switching contrast (∼10dB). The devices consist of ultrasmall high-quality factor nanocavities connected to input and output waveguides. Switching is induced by a nonlinear refractive-index change caused by the plasma effect of carriers generated by two-photon absorption in silicon. The high-quality factor and small mo

We demonstrate extremely low-power all-optical bistability by utilizing silicon photonic crystal nanocavities, based on the plasma effect of carriers generated by two-photon absorption. Owing to the high quality factor and the small volume of the nanocavities, the photon density inside the cavity becomes extremely high, which leads to a large reduction in operation power. Optical bistable operation in a single nanocavity permits optical read-write memory operation, which opens the possibility of

On-chip all-optical switching based on the carrier plasma dispersion in an argon ion (Ar+) implanted photonic crystal (PhC) nanocavity that is connected to input/output waveguides is described. A high dose of Ar+ is introduced, and annealing is used to recrystallize the silicon and thus create dislocation loops at the center of the PhC slab. Dislocation loops enable the fast recombination of the carriers, which allows a fast switching recovery time for PhC switches. The switching window (∼70ps)

Adiabatic frequency shifting is demonstrated by tuning an ultrahigh-Q photonic crystal nanocavity dynamically. By resolving the output temporally and spectrally, we showed that the frequency of the light in the cavity follows the cavity resonance shift and remains in a single mode throughout the process. This confirmed unambiguously that the frequency shift results from the adiabatic tuning. We have employed this process to achieve the dynamic release of a trapped light from an ultrahigh-Q cavit

We have fabricated high-Q photonic crystal nanocavities with a lateral p-i-n structure to demonstrate low-power and high-speed electro-optic modulation in a silicon chip. GHz operation is demonstrated at a very low (microW level) operating power, which is about 4.6 times lower than that reported for other cavities in silicon. This low-power operation is due to the small size and high-Q of the photonic crystal nanocavity.

We demonstrate channel selective 0.1-Gb/s photoreceiver operation at telecom wavelength using a silicon high-Q photonic crystal nanocavity with a laterally integrated p-i-n diode. Due to the good crystal property of silicon the measured dark current is only 15 pA. The linear and nonlinear characteristics are investigated in detail, in which we found that the photocurrent is enhanced of more than 105 due to the ultrahigh-Q (Q≃105). With the help of two-photon absorption, which is visible at a sur

Carrier dynamics in silicon photonic crystal (PhC) nanocavities are studied numerically. The results agree well with previous experimental demonstrations. It is shown that the presence of carrier diffusion makes fast switching possible, which is an advantage of nanocavity switches over other types of larger carrier based nonlinear optical switches. In particular, diffusion is effective in PhC nanocavity switches, which makes the switching recovery time even faster than that of silicon waveguide-

We demonstrate experimentally an all-optical switching operation using the Kerr effect in a silica toroid microcavity. Thanks to the small mode volume and high quality factor of the silica toroid microcavity, we achieved on-chip optical Kerr switching with an input power of 2 mW. This value is the smallest among all previously reported on-chip optical Kerr switches. We also show that this value can be reduced to a few tens of μW by employing a mode with a Q factor of > 2 × 10⁷.

We measured the space–time profile of ultrashort optical pulses shaped with a Fourier pulse shaper. Spatial chirp, which originated in the space–time coupling at the pulse shaper, was observed directly with two-dimensional spatial spectral interferometry. By analyzing the two-dimensional fringe pattern, we successfully obtained a spatial and a temporal distribution in both amplitude and phase for shaped pulses. Numerically predicted spatiotemporal patterns were compared with experimental results

We systematically studied the spectral and temporal characteristics of wavelength-sized ultrahigh-Q photonic crystal nanocavities based on width-modulated line defects. By employing accurate measurements, we confirmed that the cavity exhibits an ultra-sharp resonance width (1.23 pm), an ultrahigh-Q (1.28x 10(6)), and an ultra-long photon lifetime (1.12 ns).We discussed the correlation between the spectral and temporal measurements for various cavities, and obtained extremely good agreement. In a

Photonic crystal (PhC) nanocavities with an extremely high quality factor (Q) based on a point defect are fabricated and their properties are studied. Their confinement of light is based on rotational symmetry, which forms a hexapole mode with a Q of 3.2×105. It demonstrates that this nanocavity is an alternative candidate for achieving an ultrahigh Q. In addition, we observed bistable behavior based on the thermo-optic effect at a threshold power of a few 100μW. We also investigated the dynamic

We demonstrate adiabatic wavelength shifting by electro-optic modulation, using a p-i-n integrated high-Q photonic crystal nanocavity. The wavelength of the trapped light is adiabatically shifted by modulating the resonance of the cavity faster than the photon lifetime. The cavity resonance is changed by injecting electrons through a p-i-n junction to reduce the refractive index. In addition, we employ adiabatic wavelength shifting in a demonstration of dynamic Q tuning by electro-optic modulati

Abstract We review recent trends in the generation of a frequency comb in a microresonator, which is also known as a microcomb. The review includes both its history and applications. We explain on the basics in relation to how phase-locked and soliton states are achieved. Then, issues such as the coupling with optomechanics are discussed, which reveal the rich physics involved in this system. Finally, we describe how to extend the comb generation bandwidth by using stimulated Raman scattering an