| Summary: | 博士 === 國立交通大學 === 光電工程研究所 === 103 === An obvious trend of cloud applications, e.g. the internet of things and big data, has changed every aspect of our lives. Capable to manage and store such huge volume of data, data centers have been a key basis to realizing these cloud applications. Cost-effective, high-speed, and long-reach optical interconnects based on vertical-cavity surface-emitting lasers (VCSELs) and multimode fibers (MMFs) will be needed in modern/future mega data centers. However, the modal dispersion of MMFs leads to a severe limitation in available system bandwidth with increasing the transmission distance. VCSELs with fewer transverse modes can excite fewer modes and facilitate elongating the transmission distance. Nevertheless, the spatial hole burning effect usually limits the modulation speed of the VCSEL with less transverse modes. Therefore, it is essential to optimize the VCSEL structure to achieve few-mode and high-speed characteristics. In this work, we design Zn-diffusion and oxide-relief structures to control the number of transverse modes of VCSELs and mitigate the spatial hole burning effect simultaneously. According to our results, the modulation bandwidth of the few-mode VCSEL is slightly sacrificed. In order to boost the data throughput, we use high spectral-efficiency discrete multitone (DMT) modulation with bit-loading algorithm, which also facilitate the system bandwidth requirement. By using the 850 nm single-mode VCSEL with optimized structures and DMT modulation with bit-loading algorithm, we have successfully achieve a record-high bit-rate distance product (BRDP). Therefore, the proposed system may be another alternative for low-cost, high-speed, and long-reach optical interconnection in modern/future data centers.
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