This Small Business Innovation Research (SBIR) Phase I project will address the problem of high bandwidth (100+ Gb/s), low power, low cost wavelength division multiplexed (WDM) optical communications links of distances up to 2 km inside of data centers. These links are necessary for next generation internet/cloud/supercomputing applications. Specifically, this project will examine the lasers, which make up much of the cost and power requirements. The project will address the problem by improving an existing low cost, low power laser structure, vertical cavity surface emitting lasers (VCSELs), to be suitable for uncooled WDM operation. Specifically, this project will study tunable VCSELs and their combination with a high contrast grating (HCG) optical coupler, which can couple surface-normal VCSELs to an in-plane waveguide with very high efficiency. The chip will include a directly modulated wavelength-tunable VCSEL and a surface-normal to in-plane waveguide coupler, which can be extended into an array for WDM multiplexing an array of VCSELs into one single-mode fiber. The Phase I goals include a theoretical model and design tools for tunable VCSELs with efficient coupler design suitable for WDM applications, and experimental demonstration and characterization of a 1550-nm VCSEL with 10 Gbps direct modulation. The broader impact/commercial potential of this project is a drastic reduction in the cost and energy requirements of optical links inside of data centers and supercomputers. Companies such as Google and other large data-centric companies have been asking for this type of product in the last year to maintain the rate of growth in their data center facilities. Present WDM laser array solutions using DFB lasers require 10X the power and 10X the cost of a VCSEL-based approach. Present 850-nm VCSEL-based links, on the other hand, cannot be made into a WDM source without power-hungry TEC coolers due to their lack of precise, gridded, wavelength control. Additionally they cannot easily be combined into a single mode fiber using present device structures, so they cannot be multiplexed. Using a tunable VCSEL solves both the problem of gridded wavelength control, and an efficient coupler can combine the laser outputs without significant loss. The realization of tunable VCSELs in WDM systems will result in a 10X reduction in both cost and energy requirements in high-speed optical links for data centers, enabling the further scaling of computational power for next generation data center and supercomputer applications.
