We demonstrate a low-cost hybrid integrated and compact 100 GBaud four-lane coarse wavelength division multiplexing (CWDM) receiver optical sub-assembly (ROSA) based on an arrayed waveguide grating de-multiplexer in the O band. To achieve the horizontal light coupling between the planar light-wave circuit (PLC) based arrayed waveguide grating de-multiplexer and photodetector array, a 42° polished facet is applied for total reflection. A flexible printed circuit with high-frequency coplanar waveguides is used for a power supply of trans-impedance amplifier and signal transmission. The fabricated CWDM ROSA module, whose size is 18mm×22mm×6mm, shows a 3 dB bandwidth of 21.2, 18.4, 19.6, and 19.3 GHz, respectively, in each lane. The overall symbol error rates are at a magnitude of 10 7 for 25 GBaud four-level pulse amplitude modulation (PAM-4) transmission with an average input optical power of 5 dBm.