Experimental demonstration of a multi - channel micro - optical bridge for multi - Gb / s , free - space intra - MCM interconnects

We demonstrate a 2.5Gb/s optical intra-MCM data link with a four-channel micro-optical bridge. This bridge was fabricated by deep proton lithography and monolithically integrates cylindrical lenses and micro-mirrors. 1. Introduction Future advances in the application of photonic interconnects will involve the insertion of parallel-channel links into Multi-Chip Modules (MCMs) [1]. These will make use of new device-level components such as arrays of Vertical Cavity Surface Emitting Lasers (VCSEL's) [2] or arrays of Micro Cavity Light-Emitting Diodes (MCLED's) [3] and low power photoreceiver circuits [4]. One of the challenges associated with the development of free-space intra-and inter-MCM optoelectronic interconnects is the fabrication of manufacturable, chip-compatible, and high precision monolithic micro-optical pathway blocks. These three-dimensional modules should integrate micro-optical components to optically interconnect surface-normal transmitters and receivers. We use deep proton irradiation of Poly MethylMethAcrylate (PMMA) as a deep etch lithographic technique to fabricate monolithic structures integrating refractive micro-lenses, micro-mirrors, fiber positioning holes, stand-off and alignment features [5] [6]. The technique works as follows: a proton beam in the energy range between 5 and 10 MeV, passing through a metal mask, impinges on a high molecular weight PMMA substrate. The protons break the polymer chains and decrease the material's molecular weight. Using a specific developer the irradiated zone can then be selectively removed, making it possible to structure the sample to depths of several hundreds of microns with an optical surface quality of better than 20 nm. In this paper we will report on the data transcription at 2.5Gb/s with a multi-channel optical bridge made with this deep proton lithographic technique. We have also fabricated a single-channel optical bridge and used this component to demonstrate the proof-of-principle of optical intra-chip interconnects by establishing a digital data link between optoelectronic transceivers positioned on the same chip. Finally we project future performances of this approach for improved lens and emitter characteristics.