Satomi Ishida

Room temperature continuous-wave lasing in photonic crystal nanocavity

We demonstrate room temperature continuous-wave laser operation at 1.3 mum in a photonic crystal nanocavity with InAs/GaAs self-assembled quantum dots by optical pumping. By analyzing a coupled rate equation and the experimental light-light characteristic plot, we evaluate the spontaneous emission coupling factor of the laser to be ~ 0.22. Three-dimensional carrier confinement and a low transparent carrier density due to volume effect in a quantum dot system play important roles in the cw laser operation at room temperature as well as a high quality factor photonic crystal nanocavity.

Lasing oscillation in a three-dimensional photonic crystal nanocavity with a complete bandgap

Researchers demonstrate the first laser confined in all three spatial dimensions by a three-dimensional photonic crystal. The device, in this case driven by quantum dots, represents the long-standing goal of achieving lasing in a cavity formed entirely by a complete-photonic-bandgap medium.

Selective growth of InGaN quantum dot structures and their microphotoluminescence at room temperature

We have fabricated InGaN quantum dot (QD) structures on hexagonal pyramids of GaN, using metalorganic chemical vapor deposition with selective growth. Intense photoluminescence was observed from the sample at room temperature. To directly observe the emitting areas, microphotoluminescence intensity images with a spatial resolution of a few hundred nanometers were used. The images show the emission was only from the tops of the hexagonal pyramids. The width of the emitting areas is about 300 nm, which is comparable to the spatial resolution of the images. Such a narrow width of emission areas indicates that InGaN QDs are formed on the tops of pyramids.

Compact 1 × N thermo-optic switches based on silicon photonic wire waveguides

Using silicon photonic wire waveguides, we constructed compact 1 x 1, 1 x 2, and 1 x 4 Mach-Zehnder interferometer type optical switches on a silicon-on-insulator substrate and demonstrated their switching operations through the thermo-optic effect. These switches were smaller than 140 x 65, 85 x 30, and 190 x 75 mum, respectively. At a 1550-nm wavelength, we obtained an extinction ratio larger than 30 dB, a switching power as low as 90 mW, and a switching response time of less than 100 mus. Furthermore, switching operations were successfully demonstrated for the 1 x 4 switch.

Nonlinear-Optic Silicon-Nanowire Waveguides

Using a 4-mm-long compact silicon-nanowire waveguide, we demonstrated nonlinear-optic effects such as the spectral broadening of optical short pulses due to self-phase modulation and nonlinear transmittance due to two-photon absorption. At a 12 W input power level, we observed a 1.5-π nonlinear phase shift and a strong saturation of optical output power in a sample. We also estimated the third-order nonlinear coefficient n2 and the two-photon absorption coefficient β, and compared them with those previously reported.

Strong coupling between a photonic crystal nanobeam cavity and a single quantum dot

We demonstrated the strong coupling between a one-dimensional photonic crystal nanobeam cavity and a single quantum dot (QD). Thanks to a high quality factor (∼25 000) with small mode volume [0.38×(n/λ)3] of the nanobeam cavity, an anticrossing behavior with a vacuum Rabi splitting of 226 μeV was observed. The ratio of the QD-cavity coupling strength to the cavity decay rate, which is a figure of merit of quantum optical applications, is estimated to 2.1. This is the highest value among any QD-based cavity quantum electrodynamics systems reported so far.

Thermooptic switch based on photonic-crystal line-defect waveguides

A thermooptic switch with a symmetric Mach-Zehnder interferometer structure was demonstrated with silicon photonic-crystal-slab line-defect waveguides. The device size was as small as 160/spl times/65 /spl mu/m. The optic switch operated at a wavelength of 1550 nm, and an extinction ratio greater than 30 dB was obtained by 120-mW heating (switching) power over the wavelength range of 15 nm. The switching on-off response times were about 120 /spl mu/s.

Vacuum Rabi splitting with a single quantum dot embedded in a H1 photonic crystal nanocavity

We report here the first observation of vacuum Rabi splitting in a single quantum dot (QD) embedded in a H1 photonic crystal nanocavity by photoluminescence measurement. The QD emission was tuned into a cavity mode by controlling the temperature. At the resonance condition, clear anticrossing with a Rabi splitting of ∼124 μeV was observed, where the cavity mode possesses the smallest mode volume V∼0.43(λ/n)3 among strongly coupled QD-cavity systems reported to date.

Optical add-drop multiplexers based on Si-wire waveguides

Ultrasmall optical add-drop multiplexers (OADMs) with Si-wire waveguides were demonstrated. Bragg grating reflectors based on Si-wire waveguides were developed and used as the wavelength-selective mechanism in the OADMs. The dropping wavelength bandwidth of the OADMs was less than 0.7 nm, and the dropping wavelengths could be controlled precisely by adjusting the grating period.

Si Photonic Wire Waveguide Devices

Si photonic wire waveguides are attractive for constructing various optical devices that are extremely small because the waveguides can be bent with extremely small curvatures of less than a few micrometers of bending radius. We have fabricated optical directional couplers with the waveguides and demonstrated their fundamental characteristics. Their coupling length was extremely short, several micrometers, because of strong optical coupling between the waveguide cores. We have also demonstrated wavelength-demultiplexing functions for these devices with a long coupled waveguide. Optical outputs from a device with a 100-mum-long coupled waveguide changed reciprocally with a 20-nm wavelength spacing between the parallel and cross ports. We also demonstrated the operation of ultrasmall optical add-drop multiplexers (OADMs) with Bragg grating reflectors made up of the waveguides. The dropping wavelength bandwidth of the OADMs was less than 0.7 nm, and these dropping wavelengths could be precisely designed by adjusting the grating period. Using the Si photonic wire waveguide, we have also demonstrated thermo-optic switches. Metal thin-film heaters were evaporated onto the branch of a Mach-Zehnder interferometer that incorporated the waveguide to achieve switching operations by thermo-optic effects. In these switching operations, we observed more than 30 dB of extinction ratio, less than 90 mW of switching power, and less than 100 mus of switching speed