Influence of Temperature Cycling on Asymmetric Optical Bus Couplers

A novel coupling approach with specific coupling ratios depending on the coupling direction (optical bus to electro-optical device and vice versa) is presented. According to that, an asymmetric optical bus coupler (AOBC) is obtained, where a high amount of light is coupled from a device/module into the optical bus, whereas the ratio in the opposite direction is significantly smaller to keep enough energy in the bus for later coupling. This is realized without any filters by a specific bending of the waveguides. Hence, an up to four times higher coupling ratio in the module-to-bus direction is achieved compared to the opposite direction at the same junction. In contrast, current coupling schemes have a 1:1 coupling, waveguides are interrupted or filters are used. In this paper, we investigate the influence of temperature on the AOBC. For that, we constructed a special measurement setup, which allows for a controlled temperature change only at the coupling point. With this setup, we investigated the influence of temperature (up to 80°C) on the bus coupling over 48 hours. The measurements revealed, that the coupling power rises with increasing temperature and vice versa. With an additional vision system, we observed the enlargement of the contact area of the waveguides (coupling area), because of thermal expansion, which leads to the change of the coupling power. Besides this variation, the coupling point is damaged at 20°C/80°C cycles because of the high mechanical load. However, at 20°C/60°C cycles, the AOBC is stable over the measuring period.