A mode coupler that enables low-loss coupling between optical modes of two waveguides with different index difference. The apparatus has an identification information allocating unit for allocating base station identification information for specifying an arbitrary one of the plurality of terminals on the basis of a predetermined condition to the arbitrary terminal at a timing of forming a link with the arbitrary terminal. The orientation of the handle centers the mass of the saw below the hand and positions the cutting section of the blade in a vertical plane so it will engage a work piece at a preferred angle selected by the user. The present invention, using a zero bleed, electric powered architecture, does not suffer from this drawback of the conventional ECS.