Ultra-High-Capacity Optical Communications and Networking: Ultra High Modulation Rate GaN Quantum Cascade Lasers for C, L and S Bands

Cornell University, Ithaca NY

Investigators

Abstract

This proposal was submitted in response to the solicitation NSF 01-65 on "Ultra-High Capacity Optical Communications and Networking." The objective of the proposed research is conversion of ultra-high bitrates of electrical data to optical signals. The goal of the proposed research is demonstration of GaN unipolar lasers operating at C-, L- and S-band wavelengths, exhibiting a direct modulation bandwidth between 100-250 GHz. This goal will be pursued by elimination of the principle source of speed limitation in conventional bipolar structures exhibiting ten's of GHz bandwidth. Until recently, all semiconductor lasers utilized both holes and electrons for stimulated emission. The low field transport of holes in the active region of such lasers limits the direct modulation bandwidth. A unipolar laser which can be modulated at speeds limited only by very fast high field electron transport and parasitic RC time constants is proposed. Quantum cascade lasers and LEDs made from GaN-based semiconductor materials will be designed, fabricated and characterized. This form of laser utilizes only n-type, and undoped, material to inject electrons into an upper confined quantum well state followed by an optical transition to a lower energy state. The proposed technology could also see application to 100-250 GHz bandwidth modulators and detectors. These lasers will also be valuable as high power IR lasers for such applications as 1480nm pump lasers. High temperature operation of GaN has been demonstrated in FETs where channel temperatures of 300 C are possible due to the wide bandgap and good thermal conductivity of GaN. Superior chemical stability will permit much higher optical output powers without laser mirror degradation compared to the arsenide-phosphide laser materials. These broad bandwidth lasers would dramatically reduce number of active and passive elements required for achieving a desired system capacity. In optical architectures where 2N or N2 elements are required, moving from 20 Gbit/second today to 120 Gbit/sec with GaN quantum cascade lasers could reduce optical systems parts count by figures between 12 and 36.