25-GHz Vertical-Cavity Surface-Emitting Laser Arrays for Microwave Applications

The next generation of high-speed (> 25 GHz) optical links require new designs for semiconductor laser. Photonics Research Incorporated (PRI) proposes to design, fabricate and test a new breed of laser diode which inherently operates at higher speeds, lower thresholds, and wider temperature range. This new type of laser, called the vertical-cavity surface-emitting laser (VCSEL), can be fabricated in arbitrary, one- and two-dimensional arrays (tradenamed LASE-ARRAY by PRI), thus, providing laser source arrays which integrate simply and efficiently to optical fiber ribbons or micro-optic arrays. Fundamentally, there are three things which will increase the bandwidth of a semiconductor laser: (1) increase the photon density; (2) increase the optical gain amplitude; or (3) decrease the photon lifetime. VCSEL cavities have very high finesse (R1, R2 > 0.995) but are very short (L=1). Consequently, the photon density can be > 100 times higher than in edge-emitters while the photon lifetime remains constant. To further increase the bandwidth of VCSELs, PRI will employ strained quantum-well (QW) active regions such as InGaAs on GaAs to increase the optical gain amplitude, increase the thermal stability, and decrease the laser threshold. PRI will explore the effects of p-type modulation-doping (in the QW barriers) on increasing gain and photon density. Finally, PRI will implement its low-resistance VCSEL design to minimize parasitics.