Research On Soft-lithography-based Short-range Optical Interconnection

The rapid advance in the processor speed and processing power in recent years has dramatically increased the data transfer rates between modules, boards, backplanes and cabinets. In the advanced high performance computing systems, interactive multimedia and high speed switching network communication systems, data transfer rates are exceeding 3 Gbps; nevertheless, the demand for higher data transfer rates and the increasing complexity and costs in finding electrical solutions for intra- and inter-chip interconnect have led to several major laboratory activities worldwide to develop optical interconnect into a viable alternative to the copper solution.The optical interconnect technology offers higher data bandwidth, increased I/O density, reduced crosstalk, ease of impedance control, insensitive to EMI, and reduced weight and size of cabling. The applications of optical interconnect in advanced computers and communication systems, however, have been hindered by relatively high costs of optoelectronic components, modules, connectors, and the transmission media for relatively short range communication of less than one meter. For final aim of full-optical interconnection, a strong focus has now been placed upon optics-embedded printed circuit boards (PCBs), or hybrid electro-optical PCBs in which the optical and electrical layers are integrated into one board, as their fabrication can take advantage of existing PCB manufacturing processes while it can also provide better system performance. To a large extent, a high efficient and low-cost way of integrating the optical layer into or on the conventional printed circuit board (PCB) is a key technical roadblock.In this dissertation, based on investigation of problems facing short-range optical interconnection, especially polymer-waveguide-based optical interconnection for chip-to-chip interconnection, circuit termination coupler for waveguide/transceiver coupling, horizontal circuit layout criteria, vertical coupling structure for multilayered optical interconnect and passive optical components are deeply researched, while the practical technological schemes are proposed, then experimental prototypes of high precision, low-cost interconnection circuits and passive optical components are fabricated by using soft lithography. The main innovative achievements of this dissertation are presented as following:1. The primary application of soft lithography to short-range optical interconnection is not only demonstrated to provide simple, low cost and high quality interconnection circuit fabrication schemes, but also has a high compatibility to the present electrical interconnect systems. The soft-lithography fabrication process of the coupling interconnection design allows for significant advantages over traditional designs and fabrication methods in terms of insertion loss as well as 3D integration capability, when used in high-bandwidth PCBs. A novel soft-lithography-based compact-size polymeric multimode power splitter is successfully fabricated, which suggests a solution to low cost and mass production of passive optical components for optical interconnection. More important, combined with micro-engraving and polishing, soft lithography can overcome the roughness sidewall problem caused by other photosensitive-resist-based molding methods, so propagation loss of the waveguide can be greatly reduced which is valuable for low-BER short-range optical interconnection.2. A low-cost, versatile circuit termination coupler featuring a monolithic integration of a polymeric waveguide, beam ducts, and end-reflectors is designed and prototyped, capable of easing the coupling between transceiver and waveguide significantly. It is also demonstrated to be capable of sustaining high misalignment errors whilst maintaining a reasonable coupling efficiency.3. Characteristics of crossing and branching nodes in monolayer soft-lithography-based polymer optical interconnects are investigated with experimental and theoretical analysis. The theoretical crosstalk, as calculated by a function of crossing angle, is determined for a set of interconnect pairs with varying cross-sections, and is compared with experimental measurements. Furthermore, a suitable no-leakage branching angle was found for branching node and the effects of short-distance mode scrambling in highly multimode polymer waveguides are studied in detail. The results have a high degree of applicability to future optics-integrated PCBs featuring soft-lithography-fabricated interconnect structures.4. A layer-to-layer coupling featuring a simple S-shaped structure with lower insertion loss is proposed for multilayered optical interconnect. The soft-lithography fabrication process of this coupling interconnection design allows for significant advantages over traditional designs and fabrication methods in terms of connecting loss as well as 3D integration capability, when used in high-bandwidth printed circuit boards.