AlGaAs/GaAs active optical switch matrices

Optical switch matrices are one of the fundamental devices in all optical communications systems. The branch switches perform the splitting of optical signals, while the crossbar switches route the optical signals and can be reconfigured. High-speed optical switches may be used for time-division multiplexing to utilize the high bandwidth of common single mode fibers, and as external modulators for signal encoding. Semi-insulating substrates are favorable for monolithic integration. Most current optical switches are passive, suffering from long coupling length(typical1y 0.5-1 .O cm), and losses. Active optical switches, however, can overcome these problems. They can be zero loss or even provide gain at lengths of only a few hundred micrometers. From a practical standpoint the high frequency response and simple structure of an active optical switch are its most attractive features. In this paper, we will present the 1x1, 1x2, and 2x2 active optical switch matrices as modulators, branch switches, and photonic crossbars respectively. All of these switches are lossless, 500 micrometer in length and fabricated on a semiinsulating substrate. The switches basically are ridge waveguide semiconductor optical amplifiers. The semiconductor amplifiers are composed of separate confinement multiple-quantum wells sandwiched within a heterostructure for high differential gain, narrow linewidth, low chirp, and high modulation frequency 1. The quantum wells are heavily doped p-type to improve the frequency response*-4. The ridge waveguide structure in our devices has been designed to support only the fundamental TE and TM modes which are degenerate. The 1x1 switch/modulator has been tested for a switch with about 30 dB extinguish ratio and for a modulator with a 19 GHz 3dB bandwidth small signal response. Equal power splitting/routing or signal gain will be shown in the 1x2 switch. Simultaneous routing of two optical signals will be shown in the 2x2 crossbar with signal gain. With properly biasing condition, the signal gain or attenuation can be enhanced. Efficient heat sink will improve the performance of the switches. All of these switch matrices are integrable with other electronic or optoelectronic devices.