Analysis of Micro-Channel Free-Space Optical-Interconnects

Student: James Lindley

Supervisor: Aleksandar Rakic

Category: Engineering Thesis Project - Communications

Computer clock speeds and computing power look to increase for the foreseeable future. However current inter-chip and board-to-board interconnects, based on conventional electronics, are reaching their ultimate communication capacity. A possible answer to this bottleneck is to use optical technology instead.

Free Space Optical Interconnects (FSOI) are increasingly seen as the preferred solution. FSOI architecture consists of an emitter array, generally made up of Vertical Cavity Surface Emitting Lasers (VCSEL), an optical system, and a detector array, generally Metal-Semiconductor-Metal (MSM) detectors. A micro-channel design, in which the optical system consists of two parallel arrays of microlenses was studied in this project. Due to the small size of optical components used in FSOI designs, diffraction and misalignment are major problems. Code V, a general optical modeling program, capable of handling diffraction related problems was used to simulate the FSOI designs.

The tolerances of two basic micro-channel FSOI designs operating over a distance of 1cm were compared. One system had the microlens arrays set apart from the VCSEL and MSM arrays, the other had microlenses monolithically integrated with the VCSEL and MSM arrays. Interconnection length, lateral misalignment, lens radius, lens-VCSEL length and lens tilt were all examined. The monolithically integrated design proved much more tolerant. In a realistic system multiple misalignments can be expected. Tolerance of the monolithic design to lateral misalignment and tilt was examined. The effect of tilt was greatly amplified by relatively small lateral misalignments. Small changes in lens radius and substrate thickness significantly amplified the effect again.

Thesis Document (PDF)