Applied Physics Letters

Optical and electrical control of slow light in p-doped and intrinsic quantum-dot electroabsorbers

Piotr Konrad Kondratko, Shu‐Wei Chang, Hui Su, S. L. Chuang

Published Jun 18, 2007• 10 citations

Abstract

Room temperature p-doped and intrinsic quantum-dot semiconductor electroabsorption modulator is utilized as an optical group delay. Electrical (reverse voltage and forward current, below transparency) and optical controllable delay is realized by means of counterpropagating coherent population oscillation. Because of carrier dynamics, the experimental observations show bandwidth increase with reverse voltage and dependence of group delay on background absorption. Moreover, experimental observations show maximum group delay at a particular pump intensity, which is attributed to inhomogeneous contributions and saturation effects in quantum dots.

DOI: 10.1063/1.2749861

Related papers

Variable Slow Light Using Coherent Population Oscillation in Quantum Dot Electro-absorption Modulator

Piotr Konrad Kondratko, Shu‐Wei Chang, Hui Su +1 more

Room temperature quantum-dot semiconductor electro-absorption modulator is utilized as an optical group delay. Electrical (reverse and forward bias below transparency current level) and optical tunable buffer is realized by means of counter-propagating coherent population oscillation.

Slow and Fast Light (SL)Jan 1, 20062 citations

Room temperature slow and fast light in quantum-dot semiconductor optical amplifiers

Hui Su, Shun Lien Chuang

We demonstrate room temperature optically and electrically controllable group delay using population oscillation in a quantum-dot (QD) semiconductor optical amplifier (SOA). A reduction of the group index up to 10% with a bandwidth of 13 GHz is achieved under different configurations of injection current and optical pump intensity. Our theoretical results based on population pulsation agree well with experimental data. We extract the linewidth enhancement factor and effective carrier diffusion coefficient of the QD SOA. We also observe slow light when the injection current is increased.

Applied Physics LettersFeb 3, 200677 citations

Room-temperature slow light with semiconductor quantum-dot devices

Hui Su, Shun Lien Chuang

We demonstrate room-temperature slow light that is electrically and optically controllable by using a quantum-dot (QD) semiconductor optical amplifier (SOA) at zero and low bias below the transparency current. The absorption spectrum of the QD SOA exhibits a spectral dip with a corresponding group-index dispersion and group delay owing to coherent population oscillation caused by the interaction of pump and probe laser light near resonance of the first heavy-hole-conduction-state transition. At an optical pump power of approximately 0.3 mW inside the single-mode waveguide without current injection, a group-index change of 3.0 with a bandwidth of 2 GHz was measured. This group-index change can be controlled by injection of electrical current and by changing the optical pump power.

Optics LettersJan 15, 200686 citations

Slow Light Based on Coherent Population Oscillation in Quantum Dots at Room Temperature

Shu‐Wei Chang, Piotr Konrad Kondratko, Hui Su +1 more

We develop a model for slow light based on the coherent population oscillation of quantum dots at room temperature. With the absorption dip and corresponding variation of the refractive index due to the coherent population beating induced by the pump and probe signal, quantum dots can be used as a slow-light medium. Our theoretical model matches the experimental results very well. We also experimentally and theoretically demonstrate that both the forward-bias injection current and reverse-bias voltage can change the group index in a semiconductor quantum-dot waveguide. Our results indicate that quantum-dot devices can be potentially used as electrically and optically controllable slow light devices

IEEE Journal of Quantum ElectronicsJan 23, 200731 citations

Slow and Fast Light Using Quantum-Dot and Quantum-Well Semiconductor Optical Amplifiers

Piotr Konrad Kondratko

Controlling the group velocity of light has great potential applications in future optical communication, photonic computing, and microwave signal processing. These applications have recently triggered immense experimental and theoretical interest in the research community. Numerous studies report large optical delays while sacrificing many important aspects of engineering feasibility: bandwidth, device compactness, room temperature operation, ease of integration, and minimized signal insertion loss. Slow and fast light in the quantum-dot and quantum-well semiconductor optical amplifiers (SOAs) address many of these characteristics. First, this dissertation presents variable slow light in quantum-dot SOAs using population oscillation in an absorptive medium. Bandwidth tuning of slow light is observed with forward and reverse bias of quantum-dots. Second, the study explores four-wave mixing and population oscillation in a quantum-well gain medium. Control of optical advance and bandwidth is achieved by the medium's electrical bias or the optical pump power. Moreover, the fast light in the cascade of N number of quantum-well SOAs is experimentally and theoretically investigated. The cascaded scheme uses SOA-to-SOA attenuators to achieve active delay-bandwidth control. Finally, a large delay-bandwidth scheme is presented in which slow-to-fast light is observed by means of absorption to gain switching. More than a half cycle of tunable delay at 1 GHz bandwidth is achieved at optical frequencies.

Jan 1, 20072 citations

Slow Light Based on Quantum Effects in Quantum Wells and Quantum Dots

Shu‐Wei Chang

This is a detailed study of slow light based on quantum effects in semiconductor nanostructures. We propose to implement an optical buffer using semiconductor quantum dots and quantum wells based on coherent population oscillation and spin related electromagnetically induced transparency. We identify different pump-and-probe schemes and develop comprehensive theoretical models which include important physical mechanisms in semiconductors. Semiconductors have unique properties which are inaccessible to other slow light media, and these enable the possibilities of controlling the semiconductor-based optical buffer in addition to the optical method. We investigate how to electrically control group index (slowdown factor) in quantum dots by using reverse bias voltage and forward injection current. We also develop a model to use the anisotropy of the light-hole exciton to vary the slowdown factor via two different mechanisms (coherent population oscillation and spin related electromagnetically induced transparency). Finally, we propose an idea to use the strain to control the spin relaxation time in semiconductors, which can help spin-dependent slow light in semiconductors. This research shows that the semiconductor is a promising candidate to demonstrate an optical buffer and can provide more flexible control than other slow light materials.

Jan 1, 20061 citation