Hiroto Ota

Fabrication of two-color surface emitting device of a coupled vertical cavity structure with InAs quantum dots formed by wafer bonding

We fabricated the two color surface emitting device of a coupled cavity structure which is applicable to terahertz light source. GaAs/AlGaAs vertical multilayer cavity structures were grown on a (001) and (113)B GaAs substrates and the coupled multilayer cavity structure was fabricated by wafer-bonding of them. The top cavity contains self-assembled InAs quantum dots (QDs) as optical gain materials for two-color emission of cavity-mode lights. The bonding position was optimized for the equivalent intensity of two-color emission. We formed a current injection structure, and two-color emission was observed by current injection, although lasing was not observed.

Two-color surface-emitting lasers using a semiconductor coupled multilayer cavity

Two-color surface-emitting lasers were demonstrated, employing a GaAs/AlGaAs coupled multilayer cavity composed of two cavity layers and three distributed Bragg reflector (DBR) multilayers. InGaAs multiple quantum wells (MQWs) with two different well widths were introduced only in the upper cavity, sandwiched between p-type and n-type DBRs. This current-injection type device exhibited two-color lasing in the near-infrared region under room temperature pulsed conditions. This two-color lasing was obtained when the lower cavity had an optimal thickness relative to the upper cavity thickness and the MQW emission properties.

GaAs/AlAs triple-coupled cavity with InAs quantum dots for ultrafast wavelength conversion devices

We have investigated a GaAs/AlAs triple-coupled multilayer cavity structure with InAs quantum dots for an ultrafast wavelength conversion device. Three cavity modes with the resonance frequencies ω1, ω2, and ω3 were used for efficient wavelength conversion via a four-wave mixing (FWM) process. Identical frequency separation between two adjacent modes (ω1 − ω2 = ω2 − ω3) was successfully realized using a controlled lateral thickness variation across the wafer. Time-resolved FWM signals from the triple-coupled multilayer cavity were measured using 100 fs laser pulses. The incident laser pulses were divided into two pulses and each of them was spectrally shaped individually so that the input and control pulses only covered the ω1 and ω2 modes, respectively. The wavelength-converted FWM signal with a frequency of ω3 (= 2ω2 − ω1) was clearly observed when the sample was simultaneously irradiated with the input and control laser pulses.

Current-injection two-color lasing in a wafer-bonded coupled multilayer cavity with InGaAs multiple quantum wells

Current-injection two-color lasing has been demonstrated using a GaAs/AlGaAs coupled multilayer cavity that is a good candidate for novel terahertz-emitting devices based on difference-frequency generation (DFG) inside the structure. The coupled cavity structure was fabricated by the direct wafer bonding of (001)- and (113)B-oriented epitaxial wafers for the efficient DFG of two modes in the (113)B side cavity, and two types of InGaAs multiple quantum wells (MQWs) were introduced only in the (001) side cavity as optical gain materials. The threshold behavior was clearly observed in the current–light output curve even at room temperature. Two-color lasing was successfully observed when the gain peaks of MQWs were considerably tuned to the cavity modes by the operating temperature.

Two-color lasing from a GaAs/AlGaAs coupled multilayer cavity by current injection

Two-color lasing at the room temperature has been demonstrated by current injection into a GaAs/AlGaAs coupled multilayer cavity. By introducing InGaAs quantum wells in the topside cavity layer, we observed two-color lasing in the near-infrared region (972.3 and 981.9 nm) with the frequency difference of 3.0 THz. A novel type of terahertz emitting device based on difference-frequency generation of the two modes is expected when the other side cavity is allowed to have the second-order nonlinearity.