Design, analysis and fabrication technology for 1.55 micron strained and strain-compensated multiple quantum well single frequency lasers.

摘要

High performance 1.55 {dollar}mu{dollar}m strained quantum well single frequency lasers are desirable light sources for long-distance communication systems including wavelength division multiplexing (WDM) systems. Two types of most intensively studied single frequency lasers are vertical-cavity surface-emitting lasers (VCSELs) and distributed feedback (DFB) lasers. In this work, we investigate methods to improve the performance of 1.55 {dollar}mu{dollar}m VCSELs, and techniques for low cost fabrication of DFB lasers.; Since strained quantum wells have been extensively used to enhance the performance of 1.55 {dollar}mu{dollar}m lasers, there is a need for a model that depicts device parameters including quantum well width, optical gain and differential gain. Such a model was developed by establishing a set of empirical formulas that agree well with the first principle calculations based on the multi-band effective mass theory. The injection efficiency, and high speed properties in multiple quantum well (MQW) lasers have also been studied using a carrier diffusion model. These empirical formulas are useful for device design and optimization, and the carrier transport study suggests a graded p-doping profile with a characteristic length equal to one half of the ambipolar diffusion length for the best pumping efficiency and signal modulation bandwidth.; To improve the performance of long wavelength VCSELs, strain-compensated MQWs (SC-MQWs) as gain medium are proposed and analyzed in detail. The photopumped long wavelength SC-MQW VCSELs were fabricated and tested. A very low equivalent threshold current density of 2 kA/cm{dollar}sp2{dollar} and a high characteristic temperature of 90 K have been obtained with 98% reflectivity dielectric mirrors. The experimental data shows that threshold and characteristic temperature are greatly improved for a VCSEL with SC-MQWs as gain medium. This result agrees with what the theoretical study predicted.; A new method of fabricating submicron gratings for low-cost DFB lasers and laser arrays from a glass mask is developed and demonstrated. Second-order gratings (0.5 {dollar}mu{dollar}m period) for 1.55 {dollar}mu{dollar}m DFB lasers were fabricated as a proof of principle. This method is more cost effective than E-beam lithography and more insensitive to environmental changes than conventional free space holography. Compared with the existing phase mask techniques, this method is more flexible in the requirement of mask. By offsetting the grating periods on the glass mask, one can achieve multiple-period gratings with a sub-A period spacing for DFB laser arrays using purely optical sources. Four sections of gratings for a four-channel 1.55 {dollar}mu{dollar}m DFB laser array with a channel spacing of 6 A have been fabricated. The periods and spacing of the fabricated gratings agree with the designed values very well. This unique application makes this method particularly attractive for advanced WDM devices.