45 Degree polymer micro-mirror integration for board-level three-dimensional optical interconnects

Abstract

We introduced here a novel method to fabricate polymer optical waveguides with integrated 45º total internal reflection (TIR) micro-mirrors by contact photolithography on printed circuit boards (PCBs) to achieve fully embedded optical interconnects. The 45º TIR mirrors were shaped at the ends of the waveguides in one step to provide surface normal light coupling between waveguides and optoelectronic devices. A tank of de-ionized (D.I.) water is used to couple the ultraviolet (UV) exposure beam through the core polymer layer at 45º angle during the contact photolithography process, and then the 45 mirror facet will be formed after the post-process. Compared to the conventional glass prismpolymer coupling interface, this novel water-polymer interface provides a simple, convenient, and cost efficient solution. This technique is not only compatible with PCB manufacturing facility and technology, but also suitable to large panel board-level manufacturing for optical interconnects. The 45º angle can be controlled with an accuracy of ±1º and has a high reproducibility. The average insertion loss of the 45º TIR uncoated mirrors is around 1.6dB. IntroductionThe ever-increasing need for higher bandwidth and density is one of the motivations for extensive research on planar optoelectronic structures on PCB substrate [1]. Among many applications, optical interconnects [2] have gotten considerable attention in the last decade. In all planar optoelectronic systems, optical waveguides are crucial elements that facilitate signal rooting. As an example, integration of optical waveguides and polymer passive devices on high density PCB substrate is a major area of research in optoelectronics. Low propagation loss, high optical quality, and manufacturability are among the requirements of polymer optical waveguides and polymer passive devices on PCB substrates for practical applications. In three-dimensional fully embedded board-level optical interconnects, another key challenge is to realize efficient optical coupling between in-plane waveguides and laser/detector devices. The 45º TIR micro-mirrors and grating devices [3] integrated on the waveguide have been studied as the surface normal couplers. 45º total internal reflection (TIR) mirror couplers are more widely employed as waveguide couplers compared with the grating couplers, because they are coupling-efficient, easy to fabricate, and relatively insensitive to wavelength variations.Various techniques can be used to construct such 45º TIR micro-mirrors, such as laser ablation [4][5][6], grayscale lithography [7], hard molding [8], soft molding [9], reactive ion etching (RIE) [10], micro-dicing [11], and the X-ray

The Domestic and International Research Situation of Photoelectric Interconnection Technology

“…[2]. Fengtao, etc of Georgia institute of technology made systematic research on micro lens integration of optical waveguide, pillar structure of waveguide mirror, hybrid integration of point to point optical interconnection on circuit board, and Optoelectronics Engineering and Information Technologies in Industry three-dimension photoelectric interconnection respectively [3]. Sun Microsystems, IBM, Ansoft, Omega Optics and other American companies made deeply study on three-dimension photoelectric interconnection in chip, optical interconnection between chips, extension controller of optical interconnection in server and fully embedded board level optical interconnection technology [4].…”