Akira Matsudaira

Electrically tunable slow and fast lights in a quantum-dot semiconductor optical amplifier near 1.55 μm

We have demonstrated both slow light in the absorption regime and fast light in the gain regime of a 1.55 microm quantum-dot semiconductor optical amplifier at room temperature. The theory with coherent population oscillations and four-wave mixing effects agrees well with the experimental results. We have observed a larger phase delay at the excited state than that at the ground state transition, likely due to the higher gain and smaller saturation power of the excited state.

Cavity-Volume Scaling Law of Quantum-Dot Metal-Cavity Surface-Emitting Microlasers

Quantum-dot (QD) metal-cavity surface-emitting microlasers are designed, fabricated, and characterized for various sizes of cavity volume for both lateral and vertical confinements. Microlasers using submonolayer QDs in the active region are fabricated according to our design model optimized for a resonant metal cavity. The cavity-volume scaling law is studied by our theoretical modeling and experimental demonstration. The smallest laser has a diameter of 1

Metal-cavity nanolasers: How small can they go?

\mu\hbox{m}

Demonstration of metallic nano-cavity light emitters with electrical injection

with silver metal cladding operating at room temperature with electrical injection in pulsed mode. Our experimental results show significant self-heating effect in the smaller devices with a diameter of a few micrometers due to high series resistance and high threshold gain. With the use of hybrid metal-DBR mirrors, the number of DBR pairs in the top hybrid mirror can be reduced from 19.5 to 5.5 without sacrificing threshold current density.

Metal-cavity quantum-dot lasers with enhanced thermal performance

We present a theory of metal-cavity nanolasers and our progress in experiments of metal-cavity surface-emitting microlasers and nanoLEDs with electrical injection at room temperature. After substrate removal, the devices are flip-chip bonded to silicon. The fabrication concepts represent significant progress toward integration of active nanophotonic devices with silicon electronics.

Metal-cavity nanolasers

Metallic nano-cavity light emitters with a cavity volume of 0.19 λ₀³ and the active region is completely encapsulated by metal is demonstrated with current injection at room temperature.

Fast-Light to Slow-Light Switching in a Laser Cavity

We designed, fabricated, and characterized thermal performances of Fabry-Pérot quantum-dot lasers with both metal-coated and conventional dielectric waveguides. With proper design, metals, such as Ag, Au, Cu, and Al can function as a low loss waveguide wall as well as an efficient heat remover. Metal-cavity waveguide lasers showed excellent threshold and characteristic temperature working above 120 °C, while dielectric waveguide lasers ceased operation near 80 °C under the same conditions. The thermal analysis of these lasers showed that metal-cavity lasers have approximately 1.5 times higher thermal conductivity compared with those of the dielectric lasers. We believe that the metal-coating of waveguides and the proper selection of metal efficiently remove the heat from the active region and enable stable lasing operation at high temperature.

Slow and fast light in quantum-well and quantum-dot semiconductor optical amplifiers

Recent progress on nanoscale lasers, especially metal-cavity nanolasers, is highlighted. In spite of the metal loss, metal cavities of subwavelength scales have been used successfully for semiconductor lasers by optical or electrical pumping from low to room temperature. We focus on the demonstration of a substrate-free metal-cavity surface emitting microlaser operating continuous wave at room temperature with electrical injection.

Slow and Fast Lights in a Quantum Dot Semiconductor Optical Amplifier near 1.55 μm

We report on experimental work investigating slow- and fast-light in a ring-laser cavity that utilizes a semiconductor optical amplifier (SOA) as its primary gain medium. By allowing a pulse to propagate around the loop multiple times, we are able to achieve a tunable delay-bandwidth product near 10 for a 10-ps pulse. Our results show a shift between fast-light, as expected in a typical SOA, to slow-light as the pulse propagates around the loop. This slow-light phenomenon in a gain medium is not expected from an SOA, but arises due to the interaction between the lasing mode and the signal mode.

Metal-cavity quantum-dot surface-emitting microlaser: Theory and experiment

Slow and fast light in quantum-well (QW) and quantum-dot (QD) semiconductor optical amplifiers (SOAs) using nonlinear quantum optical effects are presented. We demonstrate electrical and optical controls of fast light using the coherent population oscillation (CPO) and four wave mixing (FWM) in the gain regime of QW SOAs. We then consider the dependence on the wavelength and modal gain of the pump in QW SOAs. To enhance the tunable photonic delay of a single QW SOA, we explore a serial cascade of multiple amplifiers. A model for the number of QW SOAs in series with variable optical attenuation is developed and matched to the experimental data. We demonstrate the scaling law and the bandwidth control by using the serial cascade of multiple QW SOAs. Experimentally, we achieve a phase change of 160° and a scaling factor of four at 1 GHz using the cascade of four QW SOAs. Finally, we investigate CPO and FWM slow and fast light of QD SOAs. The experiment shows that the bandwidth of the time delay as a function of the modulation frequency changes in the absorption and gain regimes due to the carrier-lifetime variation. The tunable phase shift in QD SOA is compared between the ground- and first excited-state transitions with different modal gains.