Teruo Mozume

Ultralow Intersubband Absorption Saturation Intensity at Communication Wavelength Achieved in Novel Strain Compensated InGaAs/AlAs/AlAsSb Quantum Wells Grown by Molecular Beam Epitaxy

We have markedly improved the optical properties of extremely thin quantum wells (QWs) required for ISBT devices operating at optical communication wavelengths using novel InGaAs/AlAs/AlAsSb QW structures with 4–7 monolayers (MLs) of AlAs. The intersubband saturation intensity (Is) was reduced to 3 fJ/µm2. This represented an IS reduction of nearly 3 orders of magnitude relative to that of the previous samples, whether or not the sample had a 1-ML AlAs interface. In this paper, we report the properties of novel InGaAs/AlAs/AlAsSb quantum wells grown by molecular beam epitaxy, and discuss the linear and nonlinear optical responses of ISBT.

Intersubband absorption saturation in InGaAs-AlAsSb quantum wells

We present intersubband absorption saturation studies in InGaAs-AlAsSb quantum wells. We carried out a density matrix calculation to simulate the pulsed excitation condition after including the dephasing time and the short pulse profile to estimate the saturation intensity (I/sub S/). We compare the calculated results with measurements for both resonant and nonresonant excitation. We also present our results on the effect of pulsewidth on Is estimation.

Ultrafast intersubband transitions in InGaAs/AlAs coupled double quantum well structures for near-infrared all-optical switching

We propose in this paper a coupled double quantum well (C-DQW) structure which enables intersubband transition (ISBT) responses useful for near-infrared ultrafast all-optical switching and ultrashort optical pulse emission. We show the capability of all-optical absorption and gain-switching between two ISBT wavelengths which can be tuned down to 1.5 /spl mu/m in InGaAs-AlAs DQW on GaAs substrates.

Ultrafast intersubband transitions in heavily doped InGaAs/AlAsSb coupled double quantum well structures for all-optical switching

We analyze the carrier density dependence of intersubband transition (ISB-T) responses at 1.55 gm in InGaAs/AlAsSb coupled double quantum well (C-DQW) structures and show the capability of all-optical switching faster than 700 fs due to ultrafast carrier redistribution in heavily doped C-DQW. We also show an experimental demonstration of ultrafast response of ISB absorption in this structure.

Optical and structural properties of In[sub 0.64]Ga[sub 0.36]As∕Al[sub x]Ga[sub 1−x]As(x≤0.2)∕AlAsSb coupled double quantum wells

We have studied optical and structural properties of In0.64Ga0.36As/AlxGa1−xAs(x≤0.2)/AlAsSb coupled double quantum wells (CDQWs) for controlling the interband transition energy of CDQWs as well as changing the residual strain of CDQWs. By changing Al composition of AlxGa1−xAs center barrier, the interband transition energy was successfully controlled due to changing coupling strength between the double quantum wells. Comparing with our previous study, In composition of InGaAs wells was reduced and consequently, residual strain of the CDQWs was also changed.

Realization of ultrafast and low power all-optical switches using intersubband transitions in a novel InGaAs/AlAs/AlAsSb quantum well structure

We have dramatically improved the optical properties of extremely thin QWs required for ISBT devices operating at optical communication wavelengths using novel InGaAs/AlAs/AlAsSb QW structures with 4-7 monolayers (MLs) of AlAs. The intersubband saturation intensity (Is) was reduced to 3fj/μm2. This represented an Is reduction of nearly 3 orders of magnitude relative to the previous samples whether or not such sample featured 1 ML of AlAs interface layer. This paper reviews the recent results of novel InGaAs/AlAs/AlAsSb quantum well properties grown by molecular beam epitaxy, and discusses the linear and nonlinear optical responses of ISBT.

Ultrafast all-optical switching using near-infrared intersubband transitions in quantum wells

In this paper, we report on all-optical switching using ultrafast optical nonlinearities originating from intersubband transitions (ISB-Ts) in InGaAs/AlAsSb quantum wells. The use of coupled double quantum wells (C-DQWs) for ISB-T-based all-optical switching is proposed, and its advantages are discussed. Sub-picosecond responses of C-DQW are simulated by rate equation analysis and measured using pump-probe experiments. We describe demonstrations of all-optical demultiplexing from 1 Tb/s signal pulse trains and reshaping/retiming functions at the optical-communication wavelength of 1.55 /spl mu/m, using an InGaAs/AlAsSb C-DQW waveguide. We also report on our recent attempts to improve ISB-T characteristics using a novel InGaAs/AlAs/AlAsSb quantum well structure, which led to the observation of an ultra-low absorption saturation intensity of 3 fJ//spl mu/m/sup 2/.

Ultrafast all-optical switching using intersubband transitions in InGaAs/AlAsSb quantum well structures

This paper describes all-optical switching using intersubband transitions in InGaAs/AlAsSb quantum wells. Subpicosecond all-optical gating and demultiplexing from 1-Tb/s signal pulses at 1.55 µm are demonstrated by proposing and fabricating coupled double quantum well structures.