Low Threshold Cryogenic Vertical-cavity Lasers

13 Low Threshold Cryogenic Vertical-cavity Lasers--Conductus, Inc., 969 West Maude Avenue, Sunnyvale, CA 94086-2802; (408) 523-9428 Dr. Yongming Zhang, Principal Investigator Mr. William J. Tamblyn, Business Official DOE Grant No. DE-FG03-97ER82355 Amount: $74,970 Ultra-wide bandwidth and low power dissipation make superconducting digital electronic circuits very attractive for routing and processing vast amounts of data via ultrahigh speed optical fiber communication links, required in Department of Energy-sponsored nuclear physics experiments. A weak link for this technology is the laser diode needed to interface the fiber to the superconducting electronics. It is very difficult to drive a laser diode directly by such a circuit because of the low circuit output and large laser threshold current, typically more than 10 mA. This limits the applications of high-speed superconducting circuits for optical data communication, especially for the uplink which requires such circuits to drive laser diodes directly. A record low threshold current (0.8 mA at room temperature) of 1.55 um vertical-cavity lasers (VCLs), recently developed by the water fusion method, makes these VCLs very promising for use in cryogenic data transmission. Wider modulation bandwidth, lower threshold current, and lower power dissipation are expected for a laser at cryogenic temperatures compared with that at room temperature. In Phase I, the cryogenic performance for these low-threshold 1.55 um VCLs will be investigated, and an ultra-low-threshold VCL for cryogenic operation will be designed and tested. In Phase II, the cryogenic performance of the VCL¿s will be optimized, and a cryogenic fiber optic link based on superconducting circuits, cryogenic VCLs and photodetectors will be developed for wide bandwidth (up to 100 Gbits/s) nuclear data transmission. The cryogenic 1.55 um VCLs will surpass their performance at room temperature and provide a technology base for fiber optic data acquisition and transmission at cryogenic temperatures. Commercial Applications and Other Benefits as described by the awardee: The success of this project can lead to immediate application for the products in both nuclear and particle physics instrumentation. The technology development would overcome a bottleneck in the implementation of high-speed superconducting switches and circuits for fiber optic applications in telecommunication networks, ATM networks, wideband local area networks and long-haul data transmissions.