A 43 Gbit/s receiver optical subassembly (ROSA) module using a compact transistor outline-can (TO-can) package has been developed and successfully demonstrated at transmission over a 2 km single-mode fibre. The electrical interface of the ROSA is made of an impedance-matched flexible printed circuit board (FPCB) which is orthogonally connected to the TO-can package. The measured 3 dB optical-to-electrical bandwidth is ∼31.5 GHz and the receiver sensitivity is <−8.4 dBm at an extinction ratio of 8.2 dB and a bit error rate of 10−12.