We review our recent progress toward transmission speeds per channel of 100Gbit/s and beyond, focusing on optical modulators and receivers for coherent transmission using PLC integration technology. We have used PLC-LiNbO₃ hybrid integration technology to develop optical multilevel modulators, including a DP-QPSK modulator and a 64QAM modulator for 100Gbit/s and post 100Gbit/s. This technology provides practical performance and scalability for various advanced modulations. We have also developed flexible-format modulators for future elastic networks, which will enable the efficient use of the spectral resource. This modulator can select an optimum carrier number and modulation level according to the transmission conditions. In terms of receivers, we have developed integrated optical receiver front-ends for 100Gbit/s DP-QPSK based on hermetically sealed O/E converters. PLC hybrid-integration technologies are promising for compact, practical, cost-effective, and highly reliable coherent optical modulators and receivers.