Yohei Hamachi

Slow light with low dispersion and nonlinear enhancement in a lattice-shifted photonic crystal waveguide

We discovered that a silicon-on-insulator photonic crystal waveguide whose lattice is shifted along the waveguide generates wideband, low-dispersion, slow light with excellent reproducibility. We observed delayed transmission of picosecond optical pulses, as well as two-photon absorption and self-phase modulation enhanced by a high internal light intensity in the slow-light regime.

Fabrication and characterization of chalcogenide glass photonic crystal waveguides

We report on the fabrication of chalcogenide glass (Ag-As(2)Se(3)) photonic crystal waveguides and the first detailed characterization of the linear and nonlinear optical properties. The waveguides, fabricated by e-beam lithography and ICP etching exhibit typical transmission spectra of photonic crystal waveguides, and exhibit high optical nonlinearity. Nonlinear phase shift of 1.5pi through self-phase modulation is observed at 0.78 W input peak power in a 400 microm long device. The effective nonlinear parameter gamma(eff) estimated from this result reaches 2.6 x 10(4) W(-1)m(-1). Four-wave mixing is also observed in the waveguide, while two-photon absorption at optical communication wavelengths is sufficiently small and the corresponding figure of merit is larger than 11.

Dispersion-controlled slow light in photonic crystal waveguides.

Slow light with a markedly low group velocity is a promising solution for optical buffering and advanced time-domain optical signal processing. It is also anticipated to enhance linear and nonlinear effects and so miniaturize functional photonic devices because slow light compresses optical energy in space. Photonic crystal waveguide devices generate on-chip slow light at room temperature with a wide bandwidth and low dispersion suitable for short pulse transmission. This paper first explains the delay-bandwidth product, fractional delay, and tunability as crucial criteria for buffering capacity of slow light devices. Then the paper describes experimental observations of slow light pulse, exhibiting their record high values. It also demonstrates the nonlinear enhancement based on slow light pulse transmission.

Low dispersion slow light and nonlinearity enhancement in lattice-shifted photonic crystal waveguide

We fabricated lattice-shifted photonic crystal waveguides stably showing low dispersion slow light in a wide wavelength bandwidth. The two photon absorption and self-phase modulation were clearly enhanced for sub-ps optical pulses.

Nonlinear photonic crystal waveguide with chalcogenide glass

We demonstrate chalcogenide glass photonic crystal waveguides and their high optical nonlinearity, for the first time. Self-phase modulation and four-wave mixing are observed in a 400-mum-long device without two photon absorption.

Dispersion-Controlled Slow Light in Photonic Crystal Waveguides

Slow light with a markedly low group velocity is a promising solution for optical buffering and advanced time-domain optical signal processing. It is also anticipated to enhance linear and nonlinear effects and so miniaturize functional photonic devices because slow light compresses optical energy in space. Photonic crystal waveguide devices generate on-chip slow light at room temperature with a wide bandwidth and low dispersion suitable for short pulse transmission. This paper first explains the delay-bandwidth product, fractional delay, and tunability as crucial criteria for buffering capacity of slow light devices. Then the paper describes experimental observations of slow light pulse, exhibiting their record high values. It also demonstrates the nonlinear enhancement based on slow light pulse transmission.

Nonlinearity induced ultrafast slow-light tuning in photonic crystal waveguide

We demonstrated ultrafast delay tuning of slow-light pulse with a response time < 10 ps. This is achieved using two types of slow light: dispersion-compensated slow light for the signal pulse; and low-dispersion slow light to enhance the nonlinear effect of the control pulse. These two slow light are generated simultaneously in lattice-shifted photonic crystal waveguides, arising from flat and straight sections of the photonic band, respectively. The control pulse blue-shifts the signal pulse spectrum, through dynamic tuning and cross-phase modulation caused by the plasma effect of two-photonabsorption carriers. This changes the delay by up to 10 ps only when the two pulses overlap within the waveguide, and enables an ultrafast tuning that is not limited by the carrier lifetime. Using this, we succeeded in the delay tuning of one target pulse within a pulse train with 12 ps intervals.

Nonlinearity Enhancement with Low-Dispersion Slow-Light in Chalcogenide Glass Photonic Crystal Waveguide

We demonstrate several-pi phase shift through self-phase modulation in a 400-μm-long chalcogenide-glass photonic-crystal waveguide. The nonlinearity is enhanced by low-dispersion slow-light mode to 160 times higher than in Si wire waveguide.

Control of light speed in photonic crystal waveguide devices

Optical buffering and nonlinear enhancement is demonstrated using slow light in photonic crystal waveguide devices. Nearly 350 ps delay and tunability are obtained in a narrowband device, while 22 bit tunability in a wideband device.

Lattice-shifted photonic crystal waveguide for slow light pulse and nonlinearity enhancement

We fabricated lattice-shifted photonic crystal waveguides stably showing low dispersion slow light in a wide wavelength bandwidth. The two photon absorption and self-phase modulation were clearly enhanced for ps optical pulses.