Novel Coating Technology Improves Ball Lenses for Fiber Coupling

Small ball (full sphere) lenses in the 0.5-mm to 3.0-mm diameter range offer a number of practical advantages for fiber-to-fiber coupling and fiber collimation. Ball lenses are more physically compact and less expensive than commonly used gradient index (GRIN) lenses. Furthermore, the complete rotational symmetry of ball lenses makes them easier to mount, position, and align to a fiber than the cylindrically shaped GRIN lenses. Despite these advantages, the wide-scale use of ball lenses in the fiber telecommunications business has been limited, because of difficulties in depositing high-performance antireflection (AR) coatings on these lenses. Specifically, coatings produced using traditional evaporative technology are highly nonuniform; also, the tooling used leaves an uncoated stripe on the part. Together, these factors then require that the micro-ball lenses be precisely oriented during coupler or collimator assembly. In work performed at Deposition Sciences Incorporated (DSI), low-pressure chemical vapor deposition (LPCVD) technology has been adapted to uniformly coat the entire surface of ball lenses. The economics of this process make it viable for the volume production of components for the telecommunications market.