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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Variable optical buffer using slow light in semiconductor nanostructures

C. C. Kuo, Connie J. Chang-Hasnain, Jungho Kim, S. L. Chuang

Published Jun 17, 2004• 32 citations
Publisher

Abstract

We proposed a compact variable all-optical buffer using slow-light in semiconductor nanostructures. We discuss the general design principle via dispersion engineering. The buffering effect is achieved by slowing down the optical signal using an external control light source to vary the dispersion characteristic of the medium via electromagnetically induced transparency effect. We demonstrate that the semiconductor quantum dot structures can be used as a slow-light medium. In such structure, the total buffering time is variable and controlled by an external pump laser. We present a theoretical investigation of the criteria for achieving slow light in semiconductor quantum dots. New pump scheme is proposed to overcome the sample nonuniformity. Finally, optical signal propagation through the semiconductor optical buffer is presented to demonstrate the feasibility for practical applications.

DOI
10.1117/12.531799

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We proposed a compact variable all-optical buffer using slow-light in semiconductor nanostructures. We discuss the general design principle via dispersion engineering. The buffering effect is achieved by slowing down the optical signal using an external control light source to vary the dispersion characteristic of the medium via electromagnetically induced transparency effect. We demonstrate that the semiconductor quantum dot structures can be used as a slow-light medium. In such structure, the total buffering time is variable and controlled by an external pump laser. We present a theoretical investigation of the criteria for achieving slow light in semiconductor quantum dots. New pump scheme is proposed to overcome the sample nonuniformity. Finally, optical signal propagation through the semiconductor optical buffer is presented to demonstrate the feasibility for practical applications.
A compact variable all-optical buffer using semiconductor quantum dot (QD) structures is proposed and analyzed. The buffering effect is achieved by slowing down the optical signal using an external control light source to vary the dispersion characteristic of the medium via an electromagnetically induced transparency effect. We present a theoretical investigation of the criteria for achieving slow light in semiconductor QDs. A QD structure in the presence of strain is analyzed with the inclusion of polarization-dependent intersubband dipole selection rules. Experimental methods to synthesize and the measurements of coherent properties in state-of-the-art QDs are surveyed. Slow-light effects in uniform and nonuniform QDs are compared. Finally, optical signal propagation through the semiconductor optical buffer is presented to demonstrate the feasibility for practical applications.
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.
A variable semiconductor optical buffer based on the electromagnetically induced transparency in a quantum dot waveguide is theoretically investigated with feasible parameters for applications to a 40 Gbps optical network. We show the refractive index and absorption spectra of the quantum dot waveguide at various pump levels, which exhibit an optimal pump power for maximum slow-down factor, in agreement with the previous experimental observation using a Pr-doped solid. The group velocity slow-down factor is theoretically analysed as a function of the pump intensity at different broadened linewidths. Inhomogeneous broadening in self-assembled quantum dots degrades the slow-down factor. In order to reduce the inhomogeneous broadening effects, we propose to use a resonant microcavity structure with quantum dots embedded in the active layer to enhance the slow-down factor.
We propose a novel design of optical buffer to generate slow light based on delay time. In the framework of the nonlinear waveguide, we investigate propagation of solitons through microring resonators. Dynamical control over slow-light solitons is realized via controlling fields generated by bright soliton and Gaussian pulse. The nonlinear dependence of the velocity of the signal on the controlling field is analytically described. The buffering effect is achieved by slowing the optical signal using an external control light source to vary the dispersion characteristic of the medium via microring resonators. A graphical approach with a signal flow graph method is used to derive the optical transfer functions in z-domain of filters. The characteristics of the optical buffer devices including the transmittance and time delay of the through and drop port are simulated. Simulated results show the criteria of achieving slow light in semiconductor microring resonators. Finally, output signal shows the delay time rate by propagation through the semiconductor microring resonators.
The ability to manipulate the speed of light has recently become one of the most exciting emergent topics in optics. There are several experimental demonstrations showing the capability to slow down light more than six orders of magnitude in a variety of media, ranging from atomic vapor, solid state crystal, to semiconductors. These results have led to intensive research into new materials, devices, and system studies that examine their impact to new applications. It is believed that we are on the verge of a dramatic change in the way we envision and construct communication, processing and control systems. One direct application of slow and fast light devices is in the area of communications. One grand challenge remaining in information technology today is to store and buffer optical signals directly in optical format. As such, optical signals must be converted to electronic signals to route, switch, or be processed. This resulted in significant latencies and traffic congestions in current networks. In addition, keeping the data in optical domain during the routing process can greatly reduce the power, complexity and size of the routers. To this end, a controllable optical delay line can effectively function as an optical buffer, and the storage is proportional to the variability of the group velocity. In addition to optical buffers, slow and fast light devices can be used as tunable true-time delay elements in microwave photonics, which are important for remotely controlling phased array antenna. Other novel applications include nonlinear optics, optical signal processing, and quantum information processing. There are various approaches that can be used to vary the optical group velocity. Ultraslow or fast group velocity may result from a large material dispersion, waveguide dispersion, or both. In this paper, the authors provide a review of recent progress of slow and fast light using semiconductor devices. Specifically, they will discuss results obtained using semiconductor quantum-well/quantum-dot absorber and optical amplifiers. Slow and fast light are controllable electrically by changing the bias current or voltage as well as optically by changing the pump laser intensity and wavelength. Delay-bandwidth tradeoff and other figures of merits are analyzed