High Performance Quantum Dot Laser WDM Arrays for Optical Interconnects.

Abstract

Robust photonic integrated circuits (PICs) capable of operating at high temperatures with low power consumption, low delay, and good signal integrity will be essential for future on-chip communication. The most practical communication system would be a WDM or DWDM optical communication system consisting of an array of closely spaced (in wavelength) tunable lasers. Ultimately, for such a communication system, integrated photo-transceivers capable of delivering a high data rate (20-40 GB/s) with low power consumption (1mW/GB/s) are desirable. The lasers and photonic circuits must also function reliably in the microprocessor environment, where the case and junction temperatures can reach ~100°C. In other words the form factor and reliability must be consistent with CPU systems. InAs/GaAs self-organized quantum-dots (QDs) lasers on GaAs substrates for 1300 nm light source, as an alternative to the traditional InP lasers, have drawn much attention recently. The GaAs-based QD lasers have achieved low threshold current density, high output CW-power, and high characteristic temperature (T0). Such devices are well suited to act as the optical source for next generation interconnects. Additionally, such devices should meet several requirements including being single mode (both longitudinal and transverse), be high speed, and should provide some mechanism for easily controlling the output wavelength. To these ends, I designed and fabricated such GaAs-based quantum dot lasers. Single longitudinal mode lasers are created by using a DBR or DFB grating designed to provide strong optical feedback, allowing only a single cavity mode to overcome the loss and lase. Single transverse mode output is created by incorporating single mode silicon nitride waveguides and by using cross mode filters as part of the laser structure. By using the excited state of the quantum dots, the modulation bandwidth can be greatly enhanced allowing for the direct modulation of the lasers. A single laser heterostructure can be used to create multiple single mode light using schemes including tunable DBRs, comb lasers, or by varying the laser cavity length to select the output wavelength.