| Free-space optical interconnects (FSOIs) promise to deliver tremendous gains in connectivity and architectural freedom in future computing systems, especially at the backplane level. However, a critical hurdle that must be overcome for FSOIs to deliver on their promise is that of optical packaging. The objective of optical packaging in FSOIs is to implement an optical design within the specified alignment budget and support the associated optoelectronics. It is a multidisciplinary field combining aspects of mechanical, optical and electrical engineering. This thesis explores optical packaging issues for FSOIs such as: type of optical interconnect, impact of device technology, environmental effects, and fabrication issues. Approaches taken to address these issues in previous optical systems described in the literature are then studied; key points are the importance of improving diagnostic techniques and the benefits of microoptic/optoelectronic device integration. To further study these aspects, the optical packaging for a four-stage hybrid macrolens/lenslet FSOI backplane is designed, built, and characterized. A non-obtrusive, in-situ alignment diagnostic system which uses dedicated alignment beams running parallel to the main link is also designed, implemented and characterized. An analysis of optical crosstalk and signal-to-crosstalk ratio considerations due to misalignment is then presented and it is shown that crosstalk can be exploited to yield alignment diagnostic information at the expense of few additional components. A novel approach for simplifying prealignment of microoptics and optoelectronics during fabrication is then presented. This consists of using on-die reflective diffractive structures to generate reference marks for use during alignment and fabrication of integrated microoptic/optoelectronic packages. Future avenues of research are then discussed. |
