Abstract

Recently a novel multiple quantum well heterostructure that uses bandfilling for intensity modulation has been demonstrated in which applied voltage transfers electrons from a reservoir into a quantum well. In this paper we report the first GaAs/AIGaAs waveguide modulator based on this concept. These modulators have high speed potential and are well suited to applications using high power AlGaAs lasers near 860 nm, such as optical data storage and pumping of miniature Nd:YAG lasers. The n-i-n waveguide consists of AlGaAs cladding layers enclosing five periods of the electron transfer structure and is cleaved to 490 pm. At 10V, the quantum well is empty and the waveguide is highly absorbing. As applied voltage decreases, the waveguide becomes more transmitting, as a result of both reduction in the quantum confined Stark effect (QCSE) and bandfilling due to electrons flooding the quantum well. The QCSE becomes prominent again at -10V consequently reducing the transmission. Bandfilling produces the most efficient modulation of 75:1 at 864.5 nm for a voltage swing -5V to 10V. The above phenomena are successfully interpreted in terms of the calculated energy band diagrams and the photocurrent spectra. Our calculations also indicate clear ways to improve the structure and enhance the performance.

© 1990 Optical Society of America