S. Gozu

Simultaneous generation of intersubband absorption and quantum well intermixing through silicon ion implantation in undoped InGaAs/AlAsSb coupled double quantum wells

We demonstrated the intersubband absorption in undoped InGaAs/AlAsSb coupled double quantum wells through silicon ion implantation and rapid thermal annealing. For an implantation dose of 1×1014 cm−2, the actual carrier density of a sample annealed at 600 °C for 1 min was ∼7.5×1013 cm−2 (∼75% activation efficiency); the activation energy was ∼1.41 eV. The simultaneously generated quantum well intermixing (QWI) was nonuniform due to the silicon ion distribution. The effects of QWI nonuniformity on both intersubband and interband transitions were explained by eight-band k⋅p calculation. This study will open a route for monolithic integration of intersubband-transition-based high-speed all-optical switches.

All-Optical Cross-Phase Modulation Generation by Ion Implantation in III–V Quantum Wells

Ultrafast all-optical cross-phase modulation (XPM) associated with intersubband transition was generated by silicon ion implantation in undoped InGaAs-AlAsSb coupled double quantum wells. This transverse-magnetic-pump-induced XPM for transverse-electric probe has spectral and temporal features superior to other polarization combinations. The XPM power efficiency in the 500- μm-long implanted waveguide was evaluated to be ~ 0.054 rad/pJ . This technique based on ion implantation can be used to monolithically integrate the novel XPM with other quantum-well-based functional modules.

Interband transitions in strained InGaAs/AlAsSb multiple‐quantum‐well structures

Room temperature photoreflectance (PR) was performed on strained InxGa1−xAs/AlAsSb quantum wells (QWs) grown on InP substrates. We observed clear and well‐resolved structures, which could be attributed to the interband optical transitions originating in the QWs. By comparing the transition energies measured from the PR spectra with those theoretically calculated from the confined energy levels in the QWs, we confirmed that the value of the conduction band offset of In0.8Ga0.2As/AlAsSb was close to 1.7 eV and the nonparabolicity of the conduction band of In0.8Ga0.2As was between 2.25 and 2.5, which is higher than that obtained using a three‐band model.

Four-wave mixing in InGaAs/AlAsSb intersubband transition optical waveguides

Four-wave mixing (FWM) in an InxGa1-xAs/AlAsySb1-y intersubband transition (ISBT) optical waveguide operating in the 1.55-μm wavelength region is discussed. The third-order optical nonlinear susceptibilities of InxGa1-xAs/AlAsySb1-y multiple quantum wells (MQWs) are estimated theoretically. ISBT excitation causes large third-order optical nonlinearity. χ(3) values of more than 1 × 1016 m2/V2 are obtained. The propagation of interacting waves for FWM in InxGa1-xAs/AlAsySb1-y ISBT optical waveguides is discussed. The interaction length is limited not only by phase matching but also by ISBT absorption. Sufficiently high FWM conversion efficiencies were obtained theoretically and experimentally for realizing coherent wavelength convertors. FWM in an InxGa1-xAs/AlAsySb1-y ISBT waveguide is a promising method for realizing compact and high-efficiency coherent wavelength conversion.

Observation of four-wave mixing signals from an AlAsSb/InGaAs ISBT (Inter Sub-Band Transition) optical waveguide

Four-wave mixing (FWM) in an AlAsSb/InGaAs ISBT optical waveguide in 1.55μm wavelength region were examined for the first time. The potential of FWM in ISBT waveguides for transparent wavelength conversion is confirmed.

Theoretical analysis of FWM by ISBT in InGaAs/AlAsSb QWs for wavelength conversion

The mechanism of FWM (four-wave mixing) by ISBT (inter-sub-band transition) in InGaAs/AlAsSb QWs (quantum wells) is analyzed theoretically. The estimated values of the third order nonlinear optical susceptibility are sufficient for coherent wavelength conversion.

Propagation of FWM interacting waves in InGaAs/AlAsSb ISBT optical waveguide for wavelength convertor

The propagation of interacting waves of FWM in InGaAs/AlAsSb ISBT optical waveguides is discussed. The sufficient FWM conversion efficiencies for realizing coherent wavelength converters were obtained theoretically and experimentally.

Intersubband absorption generation through silicon ion implantation in undoped InGaAs/AlAsSb coupled double quantum wells towards monolithic integration of intersubband-transition-based all-optical switches

We demonstrated the intersubband absorption through silicon ion implantation and subsequent rapid thermal annealing in undoped InGaAs/AlAsSb coupled double quantum wells. The effective temperature region of carrier activation for the implanted silicon ions is about 470~600 °C. For the sample with a silicon implantation dose of 1e14 cm−2, we obtained an actual carrier density of ~ 7.5e13 cm−2 (~75% activation efficiency) when it was annealed at 600 °C for 1 min. Simultaneously, a ~160-nm blueshift in interband absorption edge was observed, indicating quantum well intermixing (QWI). QWI and its non-uniformity were confirmed using SIMS and TEM measurements. This technique to generate intersubband absorption opens a route to fabricate monolithically integrated all-optical switches based on intersubband-transition induced cross-phase modulation.

Ultrafast all-optical switching using intersubband transitions in InGaAs/AlAs/AlAsSb quantum wells

Ultrafast all-optical switch based on intersubband transitions in InGaAs/AlAs/AlAsSb quantum well is described. Because of very fast intra-band relaxation in conduction band, we can obtain very fast response of around 1ps. The operation principles and characteristics as an absorption saturation type device are described. Also described is the operation as an all-optical phase modulator. With Mach-Zehnder interferometer configuration, error free all-optical demultiplexing operation from 160-Gb/s to 40-Gb/s was achieved.