Datacenters experience massive traffic growth due to expansive growth of cloud services and online gaming [1]. This trend leads to technical and economic challenges to keep up scalability for bandwidth in short reach optical interconnects. It is of critical importance to enable a cost-efficient solution for 400 Gbps links [2]. Solution for 400 GbE based on four optical lanes [3] or even two optical lanes [4] may be more attractive to reduce power consumption and complexity of parallelism. This requires InP and silicon opto-electronic components with more than 70 GHz bandwidth [2]. In this talk, we report on several experimental demonstrations for short reach optical interconnects in C-band. We review demonstrations of up to 200 Gbit/s 4-pulse amplitude modulation (PAM) [4] and up to 200 Gbit/s discrete multitone (DMT) [5] transmission with a cost-efficient monolithically integrated externally modulated laser (EML) with large bandwidth. Related digital signal processing techniques are also discussed in terms of practical implementation and complexity, paving the way for cost-effective interconnects using high speed advanced modulation formats.