Receiver optical sub-assembly with reduced back reflection

The invention relates to a receiver optical sub-assembly (ROSA) for use in an optical transceiver to convert optical signals transmitted along an optical fiber into electrical signals for use by a host device. Conventionally, light exiting the optical fiber inside an optical coupler of the ROSA encounters a refractive index mismatched interface, e.g. fiber/air, causing a portion of the light to be reflected directly back into the fiber. To minimize back reflections at the interface with the optical fiber, an optical insert is provided having an index of refraction matching that of the optical fiber, thereby moving the mismatched interface remote from the end of the fiber to an interface of the optical insert and a lens, to which the optical insert is attached.