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Journal of Applied Physics

All-optical modulation using an n-doped quantum-well structure

Susumu Noda, Tetsuya Uemura, Takao Yamashita, Akio Sasaki

Published Dec 15, 1990• 83 citations
Publisher

Abstract

The modulation of interband-resonant light by intersubband-resonant light using an n-doped quantum well is proposed, and results of the theoretical analysis are reported. It is shown that a large change in absorption coefficient from 100 to 3160 cm−1 for interband-resonant light can be obtained by changing the intensity of intersubband-resonant light from 0 to 1 MW/cm2. Very fast modulation speed (∼ps) can be expected.

DOI
10.1063/1.346830

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The modulation of interband-resonant light by intersubband-resonant light using an n-doped quantum well is proposed, and results of the theoretical analysis are reported. It is shown that a large change in absorption coefficient from 100 to 3160 cm−1 for interband-resonant light can be obtained by changing the intensity of intersubband-resonant light from 0 to 1 MW/cm2. Very fast modulation speed (∼ps) can be expected.
The authors describe a theoretical analysis on interband-resonant light modulation by intersubband-resonant light in the n-doped quantum well. The modulation principle is briefly explained. The theoretical formulation for the modulation is derived by using density matrix theory. The modulation characteristics concerning the absorption coefficient and refractive index are calculated for various parameters. It is shown that the absorption coefficient for the interband-resonant light can be greatly changed by the incidence of intersubband-resonant light.>
The optimum condition for achieving highly efficient ultrafast all-optical pulse modulation by modification of the absorption of a pulsed interband light field by ultrasubband control-light pulses in a doped quantum well is investigated. The modulation efficiency in the femtosecond domain can be maximized by an intersubband control light with a pulse width (200 fs) that is comparable with the phase-relaxation time of the system and an intensity that is close to the intersubband saturation intensity.
We explore the transient characteristics of an interband resonant light modulation process by ultrashort intersubband resonant light pulses in semiconductor quantum wells (QW's). The modulation characteristics in a three-level semiconductor QW system, including the effects due to in-plane momentum, have been investigated by a numerical analysis of the coupled Bloch equations using a density-matrix approach. We have studied the effect of the carrier density and the nature of the intersubband coupling light on the transient absorption features of the interband light. The modulation process has been compared in doped and undoped QW's. The switching behavior of the strong interband light field in presence of a train of intersubband light pulses has also been discussed.
Interband-resonant light modulation by intersubband-resonant light in undoped quantum wells is investigated. Theoretical calculation for the modulation is carried out by considering not only the excitonic interband-transition but also the continuous level transition between the conduction and valence bands. The modulation characteristics are compared with those of the modulation using n-doped quantum wells. The possibility of the modulation using undoped quantum well is successfully shown by real-time single-shot experiment using Ti-Al/sub 2/O/sub 3/ and CO/sub 2/ lasers for interband- and intersubband-resonant lights at room temperature.
An efficient modulation scheme at relatively lower control light intensities is proposed using ultrashort interband and intersubband-resonant coupling light pulses in a novel asymmetric In x Ga1-x As/AlAs semiconductor quantum well structure. The shape of the intersubband-control light pulses can manipulate the interband-signal light pulse absorption. The carrier relaxation rate of the quantum well system can be estimated from the interband nonlinear optical parameters induced by the intersubband control light field. The modulation efficiency in the proposed structure is twice than in a conventional symmetric quantum well structure. This reduces the threshold optical energy below 1 pJ in a 100-µm2 waveguide structure on using 500 fs control light pulses owing to the enhanced optical nonlinearities in the proposed structure.
We analyze the optical modulation of an interband resonant light pulse by intersubband resonant light pulses in a three-level quantum well system. The origin of the third order self-saturation optical nonlinearity resulting in the modification of the interband light absorption is assumed to lie in the carrier density modulation induced by the interband and intersubband transitions. The optical nonlinearity can be optimized to achieve the maximum modulation by applying control light pulses shorter than the intersubband energy relaxation time but longer than the intersubband phase relaxation time. We have also experimentally investigated the material system suitable for optical communication regime and have observed that the In0.53Ga0.47As/AlAs0.56Sb0.44 quantum well lattice matched to InP yielding an intersubband transition as short as 1.4 μm is the most suitable system for the proposed modulation scheme.