An optical module to receive Rx-light from a single optical fiber and to transmit Tx-light to the single optical fiber is disclosed. In the optical module, the Rx-light enters a photodiode (PD) via a shortest path within a coupling block that provides surfaces constituting the path. The Tx-light emitted from a laser diode (LD) travels around a WDM filter within the coupling block. Both the Rx-light and the Tx-light enter the WDM filter at an acute angle. The lens to concentrate the Rx-light on the PD and to collimate the Tx-light is precisely aligned with respective devices mounted on a printed circuit board (PCB).