Optical Interconnections on Electrical Boards Using Embedded Active Optoelectronic Components

Significant opportunities are emerging for optical interconnections at the board, module, and chip level if compact, low loss, high data rate optical interconnections can be integrated into these electrical interconnection systems. This paper describes an integration process for creating optical interconnections which can be integrated in a postprocessing format onto standard boards, modules, and integrated circuits. These optical interconnections utilize active thin-film optoelectronic components embedded in waveguides, which are integrated onto or into the interconnection substrate, thus providing an electrical output on the substrate from an optical interconnection. These embedded optical interconnections are reported herein using BCB (Benzocyclobutene) polymer optical waveguides in two different formats, as well as a third waveguide structure using a BCB cladding with an Ultem core. All of these waveguides were fabricated with InGaAs-based thin-film inverted metal–semiconductor–metal (I-MSM) photodetectors embedded in the waveguide layer, thus eliminating the need for beam turning elements at the output of the waveguide. These embedded interconnections have been fabricated and tested, and the coupling efficiency of the optical signals from the waveguides to the embedded photodetectors was estimated from these measurements. These measurement-based estimates are then compared to theoretical models of the coupling efficiency. Using the theoretical coupling efficiency model, variable coupling can be engineered into the interconnect design, thus enabling partial coupling for arrays of photodetectors embedded in waveguide interconnections.