An optical module with a sleeve assembly is disclosed. The sleeve assembly, which receives a ferrule secured in an end of the optical connector and is primarily made of resin material, provides a buried member made of a material, typically meal, having a polygonal cross section, a linear thermal expansion coefficient less than that of the resin material and a Young's Modulus greater than that of the resin material. The bore of the sleeve assembly has a deformed circular shape with a first diameter less than the outer diameter of the ferrule.