Low-cost electro-optical package for use with PCB-embedded waveguides

Abstract

We present a novel approach for packaging high-speed opto-electronic 12x-array devices in a compact, low-cost package for waveguide-based intra-system links. In order to avoid optical signal loss and crosstalk, the mutual alignment between PCB-embedded multimode waveguides and the opto-electronic components needs to be in the order of 5-10 micrometer, which is an order of magnitude tighter than standard PCB manufacturing tolerances. Our packaging concept uses a combination of passive alignment steps, tolerance stackup reduction and a misalignment-tolerant coupling scheme in order to bridge this gap in a cost competitive way. Using flip-chip technology, the opto-electronic components are placed onto a very thin substrate with holes for the light path. The top side of the 25 µm liquid crystal polymer (LCP) substrate not only provides fast and low-loss electrical connections, but also serves as alignment reference plane for the entire module, avoiding alignment tolerance accumulation over different assembly steps. Openings for the laser beams, passive lens alignment features, centering holes for mechanical alignment pins between module and board and optional MT-guide receptacles are all laser-cut within one single process step, with a precision better than 5 µm. A similar approach is used for the PCB-side optics, and a lens-pair coupling scheme provides for a sufficiently large misalignment tolerance between the package and the PCB. Mechanical rigidity of the package and thermal protection are provided by an epoxy filled aluminum frame. We will present our design considerations, the basic package concept, the actual experimental implementation and characterization results of our first prototype package.