An optical sub-assembly (OSA) module for suppressing optical back-reflection and effectively guiding light from a light source to an optical waveguide is disclosed. The module comprises a light source for emitting light to said optical waveguide and at least one light transmitting element installed between said light source and said optical waveguide. The at least one light transmitting element is arranged to have a configuration for avoiding light to reflect back to the light source and to cause a light beam from said light source to point to said core of said optical waveguide. Thereby, the working distance is increased, and the assembling process of the OSA module is simplified. This new optical design scheme will greatly improve the optical characteristics of an OSA module, increase the optical transceiver propagation distance, and reduce the difficulty of OSA assembly process.