Abstract: An insulating sheet having through holes formed therein at positions where circuit patterns formed on its both surfaces are electrically connected is prepared. A sheet for forming a hole bottom is attached to one surface of the insulating sheet. Subsequently, a first-layer circuit pattern is printed on the other surface of the insulating sheet to which the hole-bottom sheet is not attached, and a conductive paste is filled into the holes. Thereafter, the hole-bottom sheet is removed. Then, a second-layer circuit pattern is printed on the surface of the insulating sheet, from which the hole-bottom sheet is removed. With this process, a two-layer printed circuit sheet is manufactured.

Abstract: An optical switch having a pair of optical fibers which has a stopper projected on the inner surface of a housing, the paired large diameter optical fibers being formed at the ends thereof, inserted into the housing and contacted with the ends thereof opposed on the same axis with both ends of the stopper at a predetermined interval between relative end faces thereof, and a light shielding plate disposed telescopically in or out between the end faces of the optical fibers in the housing for conducting or interrupting an optical path over both the optical fibers, and an optical keyboard utilizing the optical switch.