An optical sub-assembly for an optoelectronic module (M), designed to provide conversion of an electrical signal from an application electronic board into an optical signal or vice-versa, comprising: - a carrier electronic board , designed to serve as an interface with another electronic board; - an optoelectronic component designed to emit or to receive a light signal via its upper surface along an optical axis (X), the optoelectronic component being fixed onto the top of the carrier electronic board and electrically connected to the circuit of the carrier electronic board directly or via an electronic control component ; - an annular alignment ring , arranged around the optoelectronic component while being fixed to the carrier electronic board, the annular alignment ring comprising a central opening coming out opposite the optoelectronic component; - a mechanical sub-assembly comprising: • a fixed fiber optic ferrule running around its central axis (X1); • a holding and alignment connection designed to both hold and center the fixed fiber optic ferrule of the sub-assembly, sub-assembly wherein: the holding and alignment connection is mechanically aligned and centered by the annular alignment ring while being fixed onto the latter, such that the fixed fiber optic ferrule is pushed into the central opening of the annular alignment ring with the central axis (X1) of the fixed fiber optic ferrule coincident with the optical axis (X), characterized in that the distance from the end of the fixed fiber optic ferrule to the surface of the optoelectronic component is fixed by an end stop of the holding and alignment connection against the annular alignment ring , the end stop of the holding and alignment connection also defining the distance from the end of the fixed fiber optic ferrule with respect to the holding and alignment connection, wherein the holding and alignment connection has a peripheral surface in plane-to-plane contact against a peripheral surface of the annular alignment ring, and wherein the fixed fiber optic ferrule is held in the holding and alignment connection in such a manner that the face of its free end is in the plane (P) of the peripheral surface of the holding and alignment connection and hence in the contact plane between annular alignment ring and holding and alignment connection. - a carrier electronic board , designed to serve as an interface with another electronic board; - an optoelectronic component designed to emit or to receive a light signal via its upper surface along an optical axis (X), the optoelectronic component being fixed onto the top of the carrier electronic board and electrically connected to the circuit of the carrier electronic board directly or via an electronic control component ; - an annular alignment ring , arranged around the optoelectronic component while being fixed to the carrier electronic board, the annular alignment ring comprising a central opening coming out opposite the optoelectronic component; - a mechanical sub-assembly comprising: • a fixed fiber optic ferrule running around its central axis (X1); • a holding and alignment connection designed to both hold and center the fixed fiber optic ferrule of the sub-assembly, • a fixed fiber optic ferrule running around its central axis (X1); • a holding and alignment connection designed to both hold and center the fixed fiber optic ferrule of the sub-assembly, wherein the holding and alignment connection has a peripheral surface in plane-to-plane contact against a peripheral surface of the annular alignment ring, and wherein the fixed fiber optic ferrule is held in the holding and alignment connection in such a manner that the face of its free end is in the plane (P) of the peripheral surface of the holding and alignment connection and hence in the contact plane between annular alignment ring and holding and alignment connection. <EOS>