An optical module for inputting and outputting light in a direction of a predetermined axis, and a method of manufacturing the optical module are provided. The optical module includes a stem having a mount and a principal surface crossing the predetermined axis. The mount has a first mounting surface, a second mounting surface, and an optical path. An optical filter is attached to the mount. A semiconductor light emitting device emitting light of a first wavelength is disposed on the first mounting surface and is optically coupled to the optical filter. A semiconductor light receiving device being responsive to light of a second wavelength is positioned on the second mounting surface in alignment with the optical path and is optically coupled to the optical filter through the optical path, thereby receiving the light of the second wavelength from the optical filter.