Abstract: The present invention provides a periodically-poled structure with high conversion efficiency and improved manufacturing yield. The method for manufacturing a periodically-poled structure in a second order nonlinear optical crystal having a single domain structure (31) includes the steps of forming a resist pattern (32) which matches a polarization-inverted period on a ?Z surface of the second order nonlinear optical crystal (31), and applying voltage to the ?Z surface as a negative voltage where the resist pattern (32) is formed, and a +Z surface as a positive voltage so as to apply an electric field in the second order nonlinear optical crystal (31), wherein the second order nonlinear optical crystal (31) contains at least one element as a dopant which compensate for the crystal defects.

Abstract: The center component 18a around the connector 2 is made of an insulating material such as synthetic resin, and there is a middle flange 19 formed around its middle section that protrudes outward in the radial direction around its entire circumference. There are insulating-tube side flanges 21, 21 that are formed around the opening ends of external semiconductive layers 13a, 13a of the insulating tubes 20a, 20a at the ends of the cables 4, 4, respectively. These insulating-tube side flanges 21, 21, are connected and joined to the middle flange 19 with O-rings 25, 25 therebetween.