Abstract: A zoom optical system includes a first lens group, a position of which with respect to an imaging plane is adjustable, and including first and second lenses. The zoom optical system also includes a second lens group of which a position with respect to the imaging plane is adjustable and includes third to fifth lenses. The zoom optical system further includes a third lens group including a sixth lens. An object-side surface of the first lens is convex.

Abstract: Disclosed herein is a dual-type system for producing optical fibers. According to this system, a draw tower is partitioned into a first spinning chamber and a second spinning chamber by a central partition frame. A preform feed unit, a furnace, a spinning nozzle and a diameter gauge are installed on each of the first and second spinning chambers in order to spin an optical fiber. Two coating units are installed at the lowest unit of the draw tower at positions corresponding to the first and second spinning chambers and used for coating the surfaces of the optical fibers spun and drawn through the first and second spinning chambers. Two ducts each having a filter are installed on a side of each unit of the draw tower at positions corresponding to the first and second spinning chambers for supplying fresh air to the optical fibers so as to prevent the optical fibers from absorbing foreign substances in addition to cooling the optical fibers.

Abstract: Disclosed herein is a draw tower for optical fiber producing systems. The draw tower supports a preform feed unit, a furnace, a spinning nozzle, a diameter gauge, and a coating unit thereon. The draw tower includes a plurality of vertically assembled frames. Each of the frames consists of a hollow column vertically erected at each corner to form a square structure, a plurality of horizontal beams horizontally extending between the upper ends and the lower ends of the columns, and a cantilever beam diagonally connected between the columns. The cantilever beam of at least one upper frame has a cross-sectional area smaller than that of a conventional cantilever beam, thus reducing weight of the upper part of the draw tower. The hollow columns of at least one lower frame each have the same cross-sectional area as that of a conventional hollow column while having thicker walls than a conventional column, thus reinforcing the lower part of the draw tower in addition to preventing vibration of the draw tower.