A precision high-frequency capacitor includes a dielectric layer formed on the front side surface of a semiconductor substrate and a first electrode on top of the dielectric layer. This splicing method splices opposing end faces of two optical fibers by fusion, and heats a formed fusion splice to match mode field diameters of the two optical fibers in the fusion splice, wherein the two optical fibers are fixed with an axial tension applied or not applied to the fusion splice, after the formation of the fusion splice, before the fusion splice is heated. Once the double tread is cured and cooled, it is cut along the centerline with a double tread separation apparatus to expose a soft non-oxidized inner rubber. Therefore, generation of a moat in the trench insulating film is avoided. The shafts of the extruder are designed with a double lead in a degassing zone, and with a triple lead in a pressure build-up zone.