Compact optical cable

A compact optical cable comprises a tube having the shape of a hollow cylinder and including multiple cores of optical fibers mounted therein; a sheath formed by an extrusion process to surround the tube at a certain thickness; a plurality of strength members arranged inside the sheath; and, a plurality of pads arranged inside the sheath to ensure that each pad intervenes between the tube and the strength members.

CLAIM OF PRIORITY

This application claims priority to an application entitled “SMALL, LIGHTWEIGHT OPTICAL CABLE”, filed in the Korean Industrial Property Office on Mar. 4, 2002 and assigned Serial No. 2002-11282, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical cable, and more particularly to a high-density optical cable.

2. Description of the Related Art

Currently, the demands for compact, light weight, and high-density optical cables are growing as there is a shortage of installation spaces for the new cables due to the already occupied optical cables. To address this, an attempt to reduce the outer diameter of the optical cables has been made to make possible installation of such cables in the existing narrow ducts.

FIG. 1is a sectional view illustrating a conventional compact optical cable. The compact optical cable comprises multiple cores of optical fibers110, a tube120surrounding the optical core members, two pairs of core strength members140, and a sheath130. The tube120has the shape of a hollow cylinder and includes the multiple cores of optical fibers110mounted therein. The tube120has a thickness of about 1 mm. The sheath130with a predetermined thickness is formed by an extrusion process and surrounds the tube120. The sheath constitutes the outermost layer of the compact optical cable to protect its interior components against the external environment.

The two pairs of the core strength members140complement the mechanical weakness of the optical cables to a certain extent. However, if the external stress is severe, the strength members tend to deteriorate the mechanical properties of the optical cables.

FIGS. 2 and 3are illustrates the shape of the compact optical cables shown inFIG. 1when an excessive stress is applied. As shown inFIG. 2, the external stress150is applied to the outer sheath layer of the cable, then, as shown inFIG. 3, the optical cable gets severely deformed by the stress applied thereto. The strength members140, which have been originally arranged inside the sheath130, penetrate into inside the sheath and press the tube120when subject to stress. Note that the tube120has a thickness of about 1 mm, but the strength members140have a higher degree of hardness than those of the tube120or sheath130. As result, the optical fibers110mounted inside the tube120are subject to severe stress due to the movement of the strength members140.

As described above, the conventional compact optical cable is provided with a plurality of strength members to increase the mechanical strength of the cable. However, the strength members tend to have opposite effect if excessive external stress is applied to the cable.

SUMMARY OF THE INVENTION

The present invention overcomes the above-described problems, and provides additional advantages, by providing a small, lightweight optical cable, fabricated to prevent the strength members from penetrating into the inside a sheath, thereby making it possible to minimize the deterioration of its mechanical properties upon application of excessive external stress.

According to one aspect of the invention, the inventive lightweight optical cable includes: a tube having a shape of a hollow cylinder including multiple cores of optical fibers mounted therein; a first sheath formed by an extrusion process to surround the tube at a predetermined thickness; a second sheath formed by an extrusion process to surround the first sheath at a predetermined thickness; and, a plurality of strength members arranged inside the second sheath.

According to another aspect of the present invention, the small, lightweight optical cable includes a tube having a shape of a hollow cylinder and including multiple cores of optical fibers mounted therein; a sheath formed by an extrusion process to surround the tube at a predetermined thickness; a plurality of strength members arranged inside the sheath; and, a plurality of pads intervening between the tube and the strength members, each pad being separately formed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, preferred embodiments of the present invention will be described in detail with reference to the annexed drawings. For the purposes of clarity and simplicity, a detailed description of known functions and configurations incorporated herein will be omitted as it may make the subject matter of the present invention rather unclear.

FIG. 4shows the configuration of a small, lightweight optical cable in accordance with a preferred embodiment of the present invention. The inventive optical cable includes a plurality of cores210, a tube220surrounding the cores, a first sheath250, a second sheath230and two pairs of core strength members240at both sides. The tube220has a shape of a hollow cylinder and has a thickness of 1 mm and below. The first sheath250with a predetermined thickness is formed by an extrusion process and surrounds the tube220, leaving a circumferential gap235, between the exterior surface of the tube220and the interior surface of the first sheath250. The first sheath250performs the function of blocking the penetration by the strength members240into the second sheath230when an external stress applied thereto. As a material for the first sheath250, a high-density polyethylene (HDPE) maybe used.

The second sheath230with a predetermined thickness is formed by an extrusion process to surround the first sheath250. The second sheath230constitutes the outermost layer of the inventive optical cable and protects its interior components from external environments. As a material for the second sheath230, a polyvinyl chloride (PVC) or polyethylene (PE) may be used.

The two pairs of the core strength members240are arranged inside the second sheath230, and each pair is arranged symmetrically around the tube220. Each of the strength members240has a long thread shape like the optical fibers210. The strength members240perform the function of enhancing the mechanical properties of the inventive optical cable. As a material for the strength members240, a fiberglass reinforced plastic (FRP) may be used. For forming the first and second sheaths250and230, a dual extrusion process may be used.

FIG. 5shows the configuration of a small, lightweight optical cable in accordance with another preferred embodiment of the present invention. The inventive optical cable includes a tube320surrounding a plurality of optical cores310, two pads350, a sheath330, and two pairs of the core strength members340. The tube320has the shape of a hollow cylinder and has a thickness of 1 mm and below. It can be seen from the Figure that there is a circumferential gap335arranged between the outer surface of the tube320and the inner surface of the sheath330.

The two pads350are arranged symmetrically within a solid area of the sheath330and occupy a portion of the sheath330between the tube320and the pairs of the strength members340. The pads350perform the function of blocking penetration of the strength members340into the sheath330when an external stress is applied. As shown inFIG. 5the pads350intervene between the rube and the strength members without affecting the area of the circumferential gap. As a material for the pads350, a fiberglass reinforced plastic (FRP) may be used.

The sheath330with a certain thickness is formed by an extrusion process and surrounds the two pads350and the tube320. The sheath330constitutes the outermost layer of the inventive optical cable and protects its interior components against external environments. As a material for the sheath330, a polyvinyl chloride (PVC) or polyethylene (PE) may be used.

Two pairs of the strength members340are arranged inside the sheath330, each pair of the strength members being arranged symmetrically around the tube320. Each of the strength members340has a long thread shape similar to the optical fibers310. The strength members340serve to enhance the mechanical properties of the inventive optical cable. As a material for the strength members340, a fiberglass reinforced plastic (FRP) may be used. For forming the sheath330, a dual extrusion process may be used.

While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes and modifications may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the present invention. In addition, many modifications may be made to adapt to a particular situation and the teaching of the present invention without departing from the central scope. Therefore, it is intended that the present invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the present invention, but that the present invention include all embodiments falling within the scope of the appended claims.