STRAINED-LAYER QUANTUM-WELL LASER STEUCTURES FOR MICROWAVE APPLICATIONS

High-speed analog optical links for microwave and millimeter wave transmission require new designs for semiconductor lasers, to extend their performance. Laser bandwidths are presently limited by the small differential gain coefficient of the bulk material. This proposal describes a technical approach which will overcome these limitations and allow fabrication of lasers with modulation bandwidths well beyond 30 GHz. The approach takes advantage of the smaller dimensions of vertical cavity surface emitting lasers (VCSELs) which result in increased relaxation oscillation frequency and significantly improved damping of the response. These limitations in VCSELs are significantly improved over those in in-plane lasers. Very high relaxation oscillation frequencies have been demonstrated. A resonance frequency per square root power coefficient of 7.6 GHz per square root milliwatt has been determined using relative intensity noise measurements, and a maximum relaxation oscillation frequency of 71 GHz was observed by streak camera measurements, on an 8 micrometer square VCSEL. Since this performance was obtained at 980 nm wavelengths, the goal of this effort is to develop 1310 and 1550 nm VCSELs with similar or improved high frequency performance. By using VCSELs, we believe that arrays of high-speed microwave optical sources can be produced at low cost.