A Proof-of-Concept for a multi-channel WDM board-level optical communications link is under development. This
paper is focusing on theoretical and experimental evaluation of thin-glass based nearly single mode graded index optical
waveguides with regard to low loss in the 1310nm regime. Results from waveguide characterization will be reported.
Waveguide modes are determined theoretically from the measured refractive index profiles. Towards improvement of
the robustness of the coupling efficiency against misalignments, investigations on the use of tapered waveguide
structures will be presented too.
Optical interconnects replace electrical links increasingly at shorter distances. At printed circuit board (PCB) level highly
multimodal polymer channel waveguides are the chosen approach to meet bandwidth-length and bandwidth-density
requirements. One important challenge of board integrated waveguides is the coupling problem. The manufacturing
process of PCBs leads to relatively high placement tolerances which cause poor optical coupling efficiency due to
mechanical misalignment between separate components, e.g.: 1) Coupling between a VCSEL and the board integrated waveguides;
2) Coupling between waveguides in two separate boards. This paper deals with the deployment of tapered dielectric multimode waveguides for increasing the optical coupling
robustness towards mechanical misalignments in these two coupling applications.
A coupled mode approach for calculation of the mode coupling and power loss in a taper with decreasing width has been
presented before . In , the two above mentioned coupling applications for tapered dielectric waveguides have been
dealt with, but only the coupling efficiency in case of longitudinal misalignment has been calculated.
In this paper, results of advanced analysis of the two applications are presented. The coupling efficiency in case of
transverse misalignment is simulated by a ray-optical approach. Furthermore the results of measurements of the coupling
behaviour of board integrated tapered waveguides are presented.
The results show that tapered multimodal dielectric waveguides have the capability to increase the coupling efficiency
significantly if some conditions are fulfilled.
From long haul, metro access and intersystem links the trend goes to applying optical interconnection technology at increasingly shorter distances. Intrasystem interconnects such as data busses between microprocessors and memory blocks are still based on copper interconnects today. This causes a bottleneck in computer systems since the achievable bandwidth of electrical interconnects is limited through the underlying physical properties. Approaches to solve this problem by embedding optical multimode polymer waveguides into the board (electro-optical circuit board technology, EOCB) have been reported earlier. The principle feasibility of optical interconnection technology in chip-to-chip applications has been validated in a number of projects. For reasons of cost considerations waveguides with large cross sections are used in order to relax alignment requirements and to allow automatic placement and assembly without any active alignment of components necessary. On the other hand the bandwidth of these highly multimodal waveguides is restricted due to mode dispersion. The advance of WDM technology towards intrasystem applications will provide sufficiently high bandwidth which is required for future high-performance computer systems: Assuming that, for example, 8 wavelength-channels with 12Gbps (SDR<sup>1</sup>) each are given, then optical on-board interconnects with data rates a magnitude higher than the data rates of electrical interconnects for distances typically found at today's computer boards and backplanes can be realized. The data rate will be twice as much, if DDR<sup>2</sup> technology is considered towards the optical signals as well. In this paper we discuss an approach for a hybrid integrated optoelectronic WDM package which might enable the application of WDM technology to EOCB.