Abstract: An optical device is disclosed which comprises a base including a lower cylindrical base member having a common central line and a first diameter and having top and bottom surfaces, a first electrode layer formed on the top surface of the lower base member, a dielectric layer formed on the first electrode, a second electrode layer formed on the dielectric layer, and an upper base member formed on the second electrode layer, the upper base member including a first cylindrical member having the common central line and the first diameter and having top and bottom surfaces, the bottom surface of the first cylindrical member faced on the second electrode layer and a second cylindrical member having the common central line and a second diameter smaller than the first diameter and having a top surface and a bottom surface faced on the top surface of the first cylindrical member; elongated leads supported by the base, the leads being elongated so as to protrude from the bottom surface of the lower base member; a ring