Optical cable

Abstract

Provided is an optical cable comprising optical units which are laid in a duct by the pneumatic pressure, wherein the optical units each comprise: a bedding layer which at least partially surrounds the circumferences of a plurality of optical fibers and includes a polymer resin; and a coating layer surrounding the bedding layer and forming the sheath of the optical unit, wherein a maximum separation distance between a pair of adjacent optical fibers, from among the plurality of optical fibers arranged in the bedding layer, is less than the outer diameter of the optical fiber and less than a minimum separation distance between the inner circumference of the coating layer and the optical fiber. During the process of branching the optical units, a frictional force between the inner circumference of a jacket and the optical units is minimized, the inside of the optical unit can be stably protected, and at the same time, the optical fibers can be easily separated.

Description

optical cable

[0001] The present invention relates to an optical cable. More specifically, the present invention relates to an optical cable comprising a plurality of optical units for pneumatic installation, each having a bedding layer that stably wraps and protects a plurality of optical fibers, wherein the optical cable minimizes friction between the inner surface of the jacket and the optical units during the process of branching the optical units, stably protects the optical fibers inside the optical units, and facilitates separation of the optical fibers.

[0002] Optical fibers are widely used as a long-distance, high-speed transmission medium due to their low transmission loss and high bandwidth. Recently, optical communication lines are often constructed by pre-installing ducts (or microducts) in conduits (W) and pneumatically laying optical cables or optical units containing multiple optical fibers within the ducts.

[0003] The above duct (or micro duct) is a tube made of polymer material, and by pre-installing the duct in the installation area and blowing air into it using a dedicated pneumatic installation device, an optical cable or optical unit equipped with a propulsion device at the tip can be installed over a range of several kilometers.

[0004] The pneumatic installation light unit is small and flexible, making it easy to install initially through pneumatic installation, and also easy to reinstall for removal and replacement of the already installed light unit.

[0005] In general, optical units for pneumatic installation can be simplified overall in configuration to minimize weight and outer diameter for long-distance transmission during pneumatic installation. However, there is an increasing demand for optical units that can protect optical fibers from friction with ducts and impact, bending, and twisting in bending sections during pneumatic installation.

[0006] The above-mentioned pneumatic installation optical units can be accommodated in multiple units within a jacket to form a single optical cable. Such an optical cable can be installed in a conduit or the like, and then only the necessary number of individual optical units can be extracted from the optical cable at the location where the optical units branch off, and the optical units can be pneumatically installed within the duct as is without a separate optical connection, thereby constructing an optical communication network such as FTTH (Fiber To The Home).

[0007] An optical cable that accommodates multiple optical units, in the process of branching the optical units at an intermediate point, pulls out the optical units already accommodated in the jacket in the reverse direction from the branching point to the destination by a length, winds them, and then pneumatically installs the wound optical units. In the process of pulling out the optical units in this way, the optical units to be branched are subject to tensile force due to friction with the inner surface of the jacket and other optical units accommodated in the jacket, and if the friction force is large, the branching operability of the optical unit to be branched may be reduced or the optical unit may be damaged or broken.

[0008] Accordingly, in an optical cable including a plurality of pneumatic installation optical units, there is an increasing demand for an optical cable that can minimize friction between the inner surface of the jacket and the optical unit during the process of branching the optical unit and stably protect the optical fiber inside the optical unit.

[0009] The present invention provides an optical unit that is installed inside a duct by pneumatic pressure, and can protect an optical fiber from external force during pneumatic installation, and in particular, it is an object of the present invention to provide an optical cable including a plurality of pneumatic installation optical units, in which the frictional force between the inner surface of the jacket and the optical unit is minimized during the process of branching the optical unit, and the optical cable stably protects the optical fiber inside the optical unit.

[0010] In order to solve the above problem, the present invention provides an optical unit that is installed into a duct by pneumatic pressure, the optical unit comprising: a core; a cladding layer surrounding the core; and a coating layer surrounding the cladding layer; a bedding layer that surrounds at least a portion of the circumference of the plurality of optical fibers and is composed of a polymer resin; and a covering layer that surrounds the bedding layer and forms a covering of the optical unit; wherein the maximum separation distance between adjacent pairs of optical fibers among the plurality of optical fibers arranged inside the bedding layer is smaller than the outer diameter of the optical fibers and smaller than the minimum separation distance between the inner circumference of the covering layer and the optical fibers.

[0011] Additionally, the minimum distance between the inner surface of the covering layer and the optical fiber may be smaller than the outer diameter of the optical fiber.

[0012] And, the overall outer diameter of the optical unit may be 0.8 millimeters (mm) to 1.6 millimeters (mm).

[0013] Here, the polymer resin constituting the bedding layer is an acrylate resin, and the bedding layer can be formed by an ultraviolet (UV) curing method.

[0014] In this case, the optical fiber may have an outer diameter of 180 to 265 micrometers (㎛).

[0015] And, the optical unit has four optical fibers, and the four optical fibers can be arranged in a square shape.

[0016] In addition, the optical unit has a circular filler member corresponding to the outer diameter of the optical fiber, and two optical fibers and two filler members can be arranged in a square shape.

[0017] In addition, the covering layer may be composed of a high-density polyethylene (HDPE) material containing silicone.

[0018] Here, the tensile strength of the resin constituting the bedding layer may be 10 MPa to 40 MPa, and the elongation may be 20% to 90%.

[0019] In this case, the bedding layer may additionally include voids.

[0020] And, the cross-sectional area of ​​the gap may be smaller than the cross-sectional area of ​​the bedding layer.

[0021] And, the ratio of the cross-sectional area of ​​the gap to the cross-sectional area of ​​the bedding layer may be 0.1 to 0.5.

[0022] In addition, in order to solve the above problem, the present invention can provide an optical cable characterized by including: a plurality of optical units described above that are pneumatically installed or towed installed within a microduct; a jacket that surrounds and accommodates the plurality of optical units; and a friction reduction layer provided on the inner surface of the jacket and for reducing friction between the optical units and the jacket.

[0023] And, 12 or 24 light units may be provided inside the jacket.

[0024] Here, the overall outer diameter of the optical cable may be 12 millimeters (mm) to 18 millimeters (mm).

[0025] In this case, the thickness of the jacket may be 2.0 millimeters (mm) to 2.8 millimeters (mm).

[0026] In addition, the optical unit spot ratio defined as the total cross-sectional area of ​​the plurality of optical units compared to the cross-sectional area of ​​the internal space of the jacket may be 15% to 40%.

[0027] Here, the jacket may be made of high-density polyethylene (HDPE) material.

[0028] In this case, the friction reduction layer may be composed of polyethylene terephthalate (PET) material.

[0029] And, the thickness of the friction reduction layer may be 15 micrometers (μm) to 35 micrometers (μm).

[0030] Additionally, at least one tensile line may be provided on the inside of the jacket.

[0031] In addition, in order to solve the above problem, the present invention provides an optical cable system in which an optical unit constituting the above-described optical cable laid in a conduit is branched and laid to an optical consumer node, the optical cable system including at least one first branch box provided on the conduit, the jacket of the optical cable being peeled off inside to expose the optical unit, and including a winding unit capable of winding the optical unit; and the optical unit wound by the winding unit of the first branch box is pneumatically laid into a duct connecting the conduit and the optical consumer node.

[0032] And, the optical cable system can be provided, characterized in that it further includes a second branch box installed spaced apart from the first branch box and in which a branch target optical unit is cut, and the branch target optical unit cut in the second branch box is wound onto the first branch box through a winding unit of the first branch box, and the optical unit wound by the winding unit is pneumatically laid into the duct from the first branch box.

[0033] According to the optical unit according to the present invention, by controlling the properties of the polymer resin constituting the bedding layer, the mechanical strength of the bedding layer is sufficiently secured, and at the same time, a sufficient separation distance is secured between a plurality of optical fibers arranged inside the bedding layer and the covering layer, thereby stably protecting the optical fibers inside from friction or stress during pneumatic laying or traction laying work.

[0034] In addition, according to the optical cable according to the present invention, a friction reduction layer is provided on the inner surface of the jacket, so that when the optical unit is branched for pneumatic installation of the optical unit in the optical cable system, the friction force between the inner surface of the jacket and the covering layer of the optical unit to be branched is sufficiently reduced, and when the jacket is removed, the friction reduction layer performs the function of protecting the optical unit, thereby preventing damage to the optical unit.

[0035] Figure 1 illustrates an optical cable system using an optical cable according to the present invention.

[0036] Figure 2 illustrates a state in which one optical unit constituting an optical cable according to the present invention is pneumatically laid in a duct.

[0037] Figure 3 shows a cross-sectional view of an optical cable according to the present invention.

[0038] Figures 4 to 7 illustrate various embodiments of optical units constituting an optical cable according to the present invention. One embodiment is illustrated.

[0039] Figure 8 illustrates a pneumatic installation test device used to evaluate the installation performance of a light unit in the present invention.

[0040] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosure is thorough and complete, and to sufficiently convey the spirit of the invention to those skilled in the art. Like reference numbers designate like elements throughout the specification.

[0041] Figure 1 illustrates an optical cable system according to the present invention.

[0042] As illustrated in FIG. 1, an optical cable (1000) constituting an optical cable system according to the present invention may be a large-capacity optical cable having a plurality of optical units (100), and the optical cable may be connected to a terminal (T) of an optical communication network while being laid in an (underground) pipeline or the like.

[0043] The above terminal (T) may be in the form of a base station, local telephone office, or branch office on an optical cable line for branching an optical cable, and the optical cable passing through the terminal (T) may be exposed on a conduit (w) and branched.

[0044] In the case of the optical cable system according to the present invention, an optical unit (100) of an optical cable (1000) laid in a conduit is branched, and the branched optical unit (100) is pneumatically laid inside a duct (d) connected to the conduit (w), and then laid to an optical consumer node (H), which is the final consumer of the optical communication network, to form an optical cable system such as FTTH (Fiber To The Home).

[0045] Here, the optical cable (1000) is configured to include a plurality of optical units (100) capable of pneumatic installation inside a duct (d) and a jacket (300) on the outside thereof.

[0046] The optical cable system according to the present invention may be equipped with a plurality of branch boxes (2000a, 2000b) for branching optical cables, and the plurality of branch boxes (2000a, 2000b) may be installed such that an optical cable (1000) passes through them. In addition, the branch box (2000) may be equipped with a cover member (not shown) that covers the optical cable (1000), thereby protecting the optical cable (1000) from external environments such as moisture or contamination.

[0047] Within the plurality of branch boxes (2000), the optical cable (1000) may have at least a portion of the jacket (300) stripped and removed to expose the plurality of optical units (100).

[0048] In addition, the branch box (2000) can be divided into a first branch box (2000a) equipped with a winding unit (2100) and a second branch box (2000b) installed spaced apart from the first branch box (2000a) and in which the branch target optical unit is cut with a cutter or the like in a cutting area (1000c).

[0049] The first branch box (2000a) is provided on the conduit (w), and the jacket (300) of the optical cable is removed from the inside to expose a plurality of optical units (100), and the first branch box (2000a) may include a winding unit (2100) capable of winding the optical units (100).

[0050] In addition, the optical cable system according to the present invention further includes a second branch box (2000b) which is installed spaced apart from the first branch box (2000a) and in which the branch target optical unit is cut, and the first branch box (2000a) uses a winding unit (2100) to wind the branch target optical unit (100) cut in the second branch box (2000b) and pull it to the first branch box (2000a) to wind it, and the optical unit (100) wound by the winding unit (2100) of the first branch box (2000a) can be installed pneumatically into a duct (d) connected to the conduit (w) and installed to an optical demand node (H).

[0051] The optical cable system illustrated in Fig. 1 is configured such that the optical unit (100) to be branched is branched in the optical cable branch area (1000s) and then pneumatically laid inside the duct (d) to be connected to each optical demand node (H), thereby minimizing the number of communication equipment such as the necessary optical cable (1000), duct (d), and optical splitter (not shown), thereby enabling the construction of an efficient optical communication network.

[0052] The above conduit (w) is a concept that includes a main conduit connected to a terminal (T) and a branch conduit branched from the main conduit to an optical consumer node. The main conduit of the above conduit (w) is formed in the length direction of the optical cable (1000) and can be branched from the main conduit to each branch conduit side and connected to an optical consumer node (H).

[0053] In this way, when branching an optical unit (100) from an optical cable (1000) using the branch box (2000), a traction force or a tensile force according to the traction force is applied to the optical unit (100) to be branched during the winding or pulling process. If the frictional force generated between the optical unit (100) to be branched and the inner surface of the jacket (300) or between the optical unit (100) to be branched and other optical units (100) housed together in the jacket (300) is large due to the traction force or tensile force, the optical unit (100) to be branched being pulled out may not be smoothly wound, or the stress added to the optical unit (100) may cause damage to the optical fiber.

[0054] Accordingly, the present invention provides an optical unit (100) configured to sufficiently protect an internally accommodated optical fiber (10) and an optical cable (100) capable of minimizing frictional force between the optical unit (100) and the inner surface of a jacket (300). The structures of the optical cable (1000) and the optical unit (100) according to the present invention will be examined in detail below.

[0055] Figure 2 illustrates a state in which one optical unit constituting an optical cable according to the present invention is laid in a duct.

[0056] As illustrated in Fig. 2, the duct (d) may be configured in the form of a circular pipe and may be made of a polymer resin material such as polyethylene (PE). In addition, microducts (not shown) smaller than the outer diameter of the duct (d) are provided in a bundle shape inside the duct (d), so that the optical unit (100) can be pneumatically installed inside each microduct (not shown).

[0057] The diameter of the above duct (d) can be configured to have different inner diameters according to conventional standards, etc., and the diameter of the light unit (100) pneumatically installed inside the duct (d) can be limited according to the inner diameter of the duct (d).

[0058] In addition, the above-mentioned light unit (100) is mostly installed in the duct (d) using a pneumatic installation method, but depending on the installation environment, pneumatic installation and traction installation of the light unit (100) may be applied together in some sections of the duct (d).

[0059] Therefore, the optical unit (100) must be configured so that the internal optical fiber (10) is not damaged by external friction or stress even when pneumatic or traction installation is performed within the duct (d).

[0060] Hereinafter, the structure of an optical cable according to the present invention will be described with reference to FIG. 3. FIG. 3 illustrates a cross-sectional view of an optical cable according to the present invention.

[0061] As illustrated in FIG. 3, an optical cable (1000) according to the present invention may be configured to include a plurality of optical units (100) for installation into a duct (d) by means of air blowing using pneumatic pressure; and a jacket (300) having a friction reducing layer (200) for reducing friction provided on the inner surface thereof and wrapping and accommodating a plurality of the optical units (100).

[0062] The optical cable (1000) according to the present invention can accommodate a plurality of pneumatic installation optical units (100) inside the jacket (300). Preferably, 12 or 24 optical units (100) can be accommodated inside the jacket (300), and after removing the jacket (300), the worker can branch the necessary number of optical units (100) from among the plurality of optical units (100) and pneumatically install them inside the duct (d).

[0063] The outer diameter (D) of the optical cable (1000) according to the present invention is configured to be in the range of 12 millimeters (mm) to 18 millimeters (mm), so that it can be smoothly installed inside a specific branch box (2000) constituting the optical cable system illustrated in FIG. 1.

[0064] In addition, the thickness (t) of the jacket (300) constituting the optical cable (1000) according to the present invention may be in the range of 2.0 millimeters (mm) to 2.8 millimeters (mm). If the thickness (t) of the jacket (300) is less than 2.0 millimeters (mm), the optical unit (100) cannot be sufficiently protected from external friction and stress, whereas if the thickness (t) of the jacket (300) exceeds 2.8 millimeters (mm), there is a problem that the outer diameter (D) and the overall weight of the optical cable (1000) increase and flexibility decreases.

[0065] In addition, the outer diameter (d) of each of the light units (100) inside the jacket (300) is configured to be in the range of 0.8 millimeters (mm) to 1.6 millimeters (mm), so that the light units (100) can be easily pneumatically installed from about 500 meters (m) to 2000 meters (m) by air pressure inside the duct.

[0066] When the outer diameter (d) of the above optical unit (100) is less than 0.8 millimeters (mm), the mechanical strength of the optical unit is insufficient to effectively protect the internal structure, whereas when the outer diameter (d) of the optical unit (100) exceeds 1.6 millimeters (mm), the size and weight of the optical unit (100) increase, making it difficult to easily pneumatically install the optical unit inside a duct or microduct.

[0067] An optical cable (1000) according to the present invention is provided with a jacket (300) that entirely surrounds a plurality of optical units (100). A plurality of optical units (100) are accommodated in the internal space of the jacket (300) to have a predetermined spot ratio.

[0068] Specifically, the optical unit (100) spot ratio, which is defined as the total cross-sectional area of ​​multiple optical units (100) compared to the cross-sectional area of ​​the internal space of the jacket (300), can be calculated using the following [Equation 1].

[0069] [Formula 1]

[0070]

[0071] Here, 'D' represents the outer diameter of the optical cable (1000), 'd' represents the outer diameter of the optical unit (100), 'n' represents the number of optical units (100), 't' represents the thickness of the jacket (300), and 'd' represents the outer diameter of the optical unit (100).

[0072] The optical unit (100) filling ratio calculated by the above [Formula 1] may be configured in the range of 15% to 40%. If the optical unit (100) filling ratio is less than 15%, there is a problem that an excessive amount of empty space is formed inside the jacket (300), unnecessarily increasing the outer diameter (D) of the optical cable (1000). On the other hand, if it is more than 40%, the flexibility of the optical cable (1000) is reduced, and when the optical unit (100) is pulled out, there is a problem that the optical fiber (10) of the optical unit (100) is damaged due to friction between the optical units (100) inside the jacket (300).

[0073] In addition, the jacket (300) may be composed of a polyethylene polymer resin having excellent chemical resistance, wear resistance, impact resistance, etc. to effectively protect the internal optical unit (100).

[0074] Specifically, the jacket (300) may use at least one resin selected from the group consisting of high-density polyethylene (HDPE) resin, medium-density polyethylene (MDPE) resin, low-density polyethylene (LDPE) resin, and linear low-density polyethylene (LLDPE) resin, and may preferably be configured to include high-density polyethylene (HDPE) resin.

[0075] In addition, the optical cable (1000) according to the present invention has a friction reduction layer (200) on the inner surface of the jacket (300). The friction reduction layer (200) is formed by wrapping a PET tape made of a polyethylene terephthalate (PET) material having excellent transparency, heat resistance, rigidity, and moisture barrier properties, and the thickness of the friction reduction layer (200) is formed in the range of 15 micrometers (μm) to 35 micrometers (μm).

[0076] The above friction reduction layer (200) can be formed in the length direction of the optical cable (1000) on the inner surface of the jacket (300) by accommodating a plurality of optical units (100) inside while the ends of the PET tape are overlapped and wrapped with a predetermined overlapping width, for example, in the range of 2 millimeters (mm) to 3 millimeters (mm), and then vacuum extruding the PET tape. The jacket (300) can be extruded on the outer side of the friction reduction layer (200).

[0077] Referring to FIG. 1, in the process of branching at least one optical unit (100) in the optical cable (1000) according to the present invention, the optical fiber (10) to be branched is pulled by the winding unit (2100) of the branch box (2000), so friction between the inner surface of the jacket (300) and the optical unit (100) may frequently occur.

[0078] Here, if the frictional force between the inner surface of the jacket (300) and the optical unit (100) is large, a large force is required to pull the optical unit (100) during the branching process of the optical unit (100), which results in poor workability, and problems such as damage to the surface of the optical unit (100), disconnection of the optical unit (100), damage to the optical fiber (10) constituting the optical unit (100), or deterioration of the transmission characteristics of the optical unit (100) occur due to the frictional force.

[0079] Accordingly, the optical cable (1000) according to the present invention has a friction reduction layer (200) on the inner surface of the jacket (300), so that when the optical unit (100) is branched for pneumatic installation, the frictional force between the inner surface of the jacket (300) and the optical unit covering layer (30) is sufficiently reduced, thereby improving the branching workability of the optical unit (100).

[0080] Meanwhile, since the jacket (300) of the optical cable (1000) according to the present invention and the optical unit (100) covering layer (30) must stably protect the internal structure from external friction, tensile force, moisture, etc., it is preferable that the jacket (300) and the optical unit covering layer (30) are composed of a polyethylene resin having excellent mechanical properties, preferably a high-density polyethylene (HDPE) resin.

[0081] In this way, when the jacket (300) and the optical unit covering layer (30) are made of the same material and a separate layer such as a friction reduction layer (200) is not provided on the inner surface of the jacket (300), there was a problem in that the jacket (300) and the optical unit covering layer (30) were stuck to each other due to heat and pressure during the jacket (300) extrusion process to the outside of a plurality of optical units (100) in the manufacturing process of the optical cable (1000) according to the present invention.

[0082] In the past, there were attempts to provide a layer composed of various materials such as a binder fiber layer or a silicone resin layer instead of the friction reduction layer (200) of the present invention between the jacket (300) and a plurality of optical fibers (10), but it was not easy to form the layer because it was partially bonded to the jacket (300) or difficult to pull out.

[0083] The optical cable (1000) according to the present invention uses polyethylene terephthalate (PET) resin as the friction reduction layer (200) material, so that when the jacket (300) is extruded, the phenomenon of the jacket (300) and the optical unit covering layer (30) having the same material sticking to each other is effectively prevented, and the productivity and quality of the optical cable (1000) can be further improved.

[0084] Furthermore, since the optical cable (1000) according to the present invention has a friction reduction layer (200) on the inner surface of the jacket (300), when the jacket (300) is stripped, the cutter does not come into direct contact with the optical unit (100), but rather the friction reduction layer (200) is first exposed, so that the cutter comes into contact with the optical unit (100) first before it comes into contact with the optical unit (100), thereby performing a function of protecting the optical unit (100), thereby preventing damage and breakage of the optical unit (100) due to cutter stabbing during the jacket (300) stripping.

[0085] Additionally, at least one tensile line (400) extending in the longitudinal direction of the optical cable (1000) may be further provided inside the jacket (300). The tensile line (400) serves to improve the tensile strength of the cable.

[0086] The above tensile wire (400) may be made of Kevlar aramid yarn, fiber glass epoxy rod, fiber reinforced polyethylene (FRP), high-strength fiber, steel, steel wire, or a combination thereof, and the above tensile wire (400) may be provided in pairs facing each other, but is not limited thereto.

[0087] Hereinafter, with reference to FIG. 4 and below, the structure of the optical unit (100) constituting the optical cable (1000) according to the present invention will be examined.

[0088] Figures 4 to 7 illustrate various embodiments of an optical unit according to the present invention. One embodiment is illustrated.

[0089] As illustrated in FIGS. 4 to 7, the optical unit (100) according to the present invention is a pneumatic installation optical unit (100), which may be configured to include a plurality of optical fibers (10); a bedding layer (20) made of polymer resin and wrapping the optical fibers (10); and a covering layer (30) wrapping the bedding layer (20).

[0090] Here, the optical unit (100) according to the present invention is configured to control the mechanical properties of the bedding layer (20) and at the same time, to appropriately place a plurality of optical fibers (10) inside the bedding layer (20) so that sufficient strength is secured by the bedding layer (20) so that the plurality of optical fibers (10) can be stably fixed and supported.

[0091] A plurality of optical fibers (10) may each be configured to include a core (11) at the center, a cladding layer (12) surrounding the core (11), and a coating layer (13) surrounding the cladding layer (12).

[0092] The core (11) above can use a glass optical fiber (10) made of silica material with a high refractive index, and the core (11) can use a single-mode optical fiber (10) with a diameter of several micrometers or a multi-mode optical fiber (10) with a diameter of several tens of micrometers. Depending on the refractive index distribution of the core (11), it can be classified into a stepped optical fiber (10), a hill-shaped optical fiber (10), etc.

[0093] The above cladding layer (12) is composed of glass or synthetic resin made of silica having a relatively lower refractive index than the core (11), and the cladding layer (12) performs the role of transmitting a signal by causing total reflection of light passing through the core.

[0094] The above coating layer (13) is composed of an acrylate polymer resin or the like, and serves to protect the core (11) and the cladding layer (12) from external force, and may be composed of multiple layers.

[0095] In addition, a coloring layer (not shown) may be provided on the outermost surface of the coating layer (13) to provide different colors to the optical fiber (10) to facilitate identification of the optical fiber (10).

[0096] The above optical fiber (10) may be a general optical fiber (10) having a diameter of 180 micrometers (㎛) to 265 micrometers (㎛).

[0097] The above optical unit (100) is configured to include a bedding layer (20) that entirely wraps a plurality of optical fibers (10).

[0098] The above bedding layer (20) is composed of a polymer resin material and is formed to at least partially surround the circumference of a plurality of optical fibers (10), thereby supporting and accommodating the plurality of optical fibers (10) so as to suppress movement in the longitudinal direction of the optical unit (100), and the above bedding layer (20) is formed so that the surface of the optical unit (100) has a circular cross-section, thereby supporting the optical unit (100) so as to maintain its circularity.

[0099] The polymer resin constituting the above bedding layer (20) is a photocurable polymer resin that is cured by ultraviolet (UV) irradiation, and may preferably be composed of an acrylate resin.

[0100] In order to enable the polymer resin constituting the above bedding layer (20) to quickly harden when exposed to ultraviolet rays, a photocurable initiator such as 4,4-bis(dimethylamino)benzophenone (4,4′(diethylamino)benzophenone) may be additionally added to the acrylate polymer resin as a component of the above bedding layer (20).

[0101] In addition, the optical unit (100) may further include at least one filler member (40) together with an optical fiber (10) inside the bedding layer (20).

[0102] The above filler member (40) is configured with a circular cross-section corresponding to the size and shape of the optical fiber (10) to maintain the circularity of the optical unit (100) and to evenly distribute bending stress, installation tension, or tensile force applied to the optical unit (100) during pneumatic installation of the optical unit (100), thereby minimizing damage to the bedding layer (20) and the optical fiber (10).

[0103] The embodiment illustrated in FIG. 5 is equipped with two optical fibers (10) and two filler members (40), and may have a cross-sectional structure similar to the optical unit (100) illustrated in FIG. 4, which accommodates only four optical fibers (10).

[0104] If only two optical fibers (10) are provided inside the bedding layer (20), it is not easy to form a circular cross-sectional shape of the optical unit (100), and it is difficult to secure sufficient tensile strength of the optical unit (100), so by providing two more filler members (40) in the form of interposition, an optical unit (100) having a structure similar to the optical unit (100) illustrated in FIG. 4, in which four optical fibers (10) are provided inside the bedding layer (20), can be formed.

[0105] Meanwhile, in addition to the embodiments shown in FIGS. 4 and 5, the number and arrangement structure of optical fibers (10) and filler members (40) constituting the optical unit (100) may be varied.

[0106] In the embodiments illustrated in FIGS. 4 and 5, the optical fibers (10) or filler members (40) are mutually externally arranged in a square shape within the bedding layer (20), thereby preventing movement of the optical fibers (10) or filler members (40) during the curing process of the bedding layer (20) and minimizing the outer diameter of the optical unit (100).

[0107] The above bedding layer (20) can be formed to surround all optical fibers (10) or the optical fibers (10) and the filler member (40) within the optical unit (100), and can be formed in a solid form by being hardened while permeating the inside so that there is no empty space between the optical fibers (10) or the optical fibers (10) and the filler member (40), or can be formed so that there is an empty space between the optical fibers (10) or between the optical fibers (10) and the filler member (40).

[0108] The covering layer (30) may be provided on the outer periphery of the above bedding layer (20) to form an outer covering of the light unit (100). The covering layer (30) maintains the circular structure of the light unit (100) and protects the internal configuration.

[0109] The above covering layer (30) must be composed of a material having a sufficiently low coefficient of friction to reduce friction between the inner surface of the duct (d) and the covering layer of the light unit (100) when the light unit (100) is pneumatically installed inside the duct (d), and further to minimize friction between multiple light units (100) accommodated inside the jacket (300).

[0110] Specifically, the covering layer (30) may be made of a mixture of silicone and polyethylene resin to sufficiently reduce the coefficient of friction while ensuring mechanical strength.

[0111] The polyolefin resin constituting the above covering layer (30) may include, similarly to the jacket (300), a high-density polyethylene (HDPE) resin, a medium-density polyethylene (MDPE) resin, a low-density polyethylene (LDPE) resin, and a linear low-density polyethylene (LLDPE) resin, preferably a high-density polyethylene (HDPE) resin.

[0112] In addition, the thickness of the covering layer (30) is preferably configured to be about 10 to 20 percent (%) of the outer diameter of the optical unit (100) in consideration of the tensile strength and flexibility of the optical unit (100).

[0113] In addition, the overall outer diameter of the covering layer (30) is not limited to a specific range, but is preferably about 1.0 millimeter to 5.0 millimeters (mm), or less than half the inner diameter of the duct (d) or microduct in which the light unit (100) is pneumatically installed, so that easy pneumatic installation can be performed inside a narrow space.

[0114] As illustrated in FIG. 6, among the plurality of optical fibers (10) constituting the optical unit (100) according to the present invention, at least two of the optical fibers (10) can be spaced apart from each other inside the bedding layer (20).

[0115] In the embodiment illustrated in FIG. 6, all four optical fibers (10) constituting the optical unit (100) are illustrated as being spaced apart from each other, but the present invention is not limited thereto. For example, when the optical unit (100) is composed of four optical fibers (10), the optical unit (100) may be configured in a shape in which one optical fiber set composed of two optical fibers (10) in contact with each other and two optical fibers (10) spaced apart from the optical fiber set are arranged, or one optical fiber set composed of three optical fibers (10) in contact with each other and one optical fiber (10) spaced apart from the optical fiber set are arranged, or two optical fiber sets composed of two optical fibers (10) in contact with each other are arranged spaced apart from each other.

[0116] The maximum separation distance (A) between adjacent pairs of optical fibers (10) among the above-mentioned spaced-apart optical fibers (10) is defined as the longest distance among the separation distances between adjacent pairs of optical fibers (10).

[0117] Here, the pair of adjacently arranged optical fibers (10) refers to an optical fiber pair consisting of one optical fiber and the other optical fiber having the shortest distance from the optical fiber (10) among the optical fibers (10) arranged within the bedding layer (20). Hereinafter, the pair of adjacently arranged optical fibers (10) will be referred to as an 'adjacent optical fiber pair'.

[0118] At this time, the maximum separation distance (A) between the adjacent optical fiber pairs may be configured to be smaller than the optical fiber outer diameter (D), that is, the optical fiber outer diameter (D) range of 180 micrometers (㎛) to 265 micrometers (㎛).

[0119] In this way, when the maximum separation distance (A) between adjacent optical fiber pairs is configured to be smaller than the outer diameter (D) of the optical fiber, the optical unit (100) can be made thinner to facilitate pneumatic installation, the optical fiber (10) arrangement structure within the bedding layer (20) can be stably maintained, and the thickness of the bedding layer (20) surrounding the plurality of optical fibers (10) can be formed sufficiently thick to stably protect the optical fibers (10).

[0120] In addition, the maximum separation distance (A) between the adjacent optical fiber pairs inside the optical unit (100) according to the present invention may be configured to be smaller than the minimum separation distance (B) between the inner surface of the covering layer (30) and the optical fiber (10), and the minimum separation distance (B) between the inner surface of the covering layer (30) and the optical fiber (10) may also be configured to be smaller than the outer diameter (D) of the optical fiber.

[0121] In this way, when the maximum separation distance (A) between the adjacent optical fiber pairs is configured to be smaller than the minimum separation distance (B) between the inner surface of the covering layer (30) and the optical fiber (10), all optical fibers (10) accommodated in the bedding layer (20) can be prevented from being biased to one side from the center of the optical unit (100), and the thickness of the bedding layer (20) provided on the inner periphery of the covering layer (30) can be secured to be sufficiently thick to stably protect the optical fibers (10) inside.

[0122] Here, the relationship that the maximum separation distance (A) between adjacent optical fiber pairs is smaller than the outer diameter (D) of the optical fiber (10) and the maximum separation distance (A) between adjacent optical fiber pairs is smaller than the minimum separation distance (B) between the inner surface of the covering layer (30) and the optical fiber (10) must be continuously maintained for a considerable length in the longitudinal direction of the optical unit (100) so that the optical cable (100) can be thinned and the optical fiber (10) can be expected to have a stable protection effect.

[0123] As illustrated in FIG. 7, the bedding layer (20) of the optical unit (100) constituting the optical cable according to the present invention additionally includes a gap (21) inside, so that the workability of the separation operation of each optical fiber (10) in the bedding layer (20) of the optical unit (100) laid inside the duct can be further improved.

[0124] The above-mentioned gap (21) is formed at least once inside the bedding layer (20), but in order to maintain the structural stability of the optical cable (100), the cross-sectional area of ​​the gap (21) may be formed to be smaller than the cross-sectional area of ​​the bedding layer (20).

[0125] Preferably, based on the cross-sectional area of ​​the optical unit (100), the gap cross-sectional area ratio (R), which is the ratio of the cross-sectional area of ​​the gap (21) to the cross-sectional area of ​​the bedding layer (20), may be configured in the range of 0.1 to 0.5. Here, it means a value obtained by dividing the cross-sectional area of ​​the gap (21) by the cross-sectional area of ​​the bedding layer (20).

[0126] When the above-mentioned pore cross-sectional area ratio (R) is less than 0.1, the effect of improving the separation workability of the optical fiber (10) from the bedding layer (20) is insufficient, whereas when the above-mentioned pore cross-sectional area ratio (R) is more than 0.5, the fixing force of the bedding layer (20) to the optical fiber (10) is reduced, so that the internal structure of the optical cable (100) cannot be stably maintained, and in particular, a problem may occur in which the optical fiber (10) cannot be stably protected in the micro-bending section.

[0127] Below, the results of confirming the pneumatic installation characteristics of multiple optical unit samples are described with reference to Fig. 8 and Table 1.

[0128] Sample 123456789101112 Unit Optical fiber outer diameter (D) 180200250180180200250180200250250250μm Cable outer diameter (O) 1.21.21.21.41.21.21.41.21.21.21.6mm Maximum separation distance between adjacent optical fibers (A) 82505919322521628172140613757μm Minimum separation distance between cladding layer and optical fiber (B) 16712573204896861571073051204μm Air gap Cross-sectional area ratio (R) 0.410.170.220.230.440.350.40.160.260.220.520.25 Pneumatic installation test ○○○○○○○○○○○○X Signal transmission test ○○○XXXXXXXX-

[0129] The pneumatic installation test in Table 1 above is an item for evaluating the installation properties of an optical unit, and each sample is an optical unit (100) having a structure in which four-core optical fibers (10) are differently arranged inside a bedding layer (20), and FIG. 8 illustrates a pneumatic installation test device used to evaluate the installation properties of an optical unit in the present invention.

[0130] The above pneumatic installation test was performed by installing a microduct with an inner diameter of 3 mm and an outer diameter of 6 mm in a track designed to include a number of macro-bending and micro-bending sections as shown in Fig. 8(a) and an implemented section as shown in Fig. 8(b), and then pneumatically sending each sample inside the microduct through a Minijet P400, a pneumatic installation device from Plumettaz, to evaluate whether it could be sent for more than 1 km to determine whether it was acceptable.

[0131] In addition, the optical characteristic evaluation of Table 1 above was performed by performing an optical signal loss test at a wavelength of 1550 nm at room temperature (23°C) on a pneumatically installed sample, and evaluating whether the loss value was 0.35 dB / km or less to determine whether it was acceptable or not.

[0132] Here, the structure of each sample in Table 1 was measured 10 times continuously at 1 m intervals from an arbitrary position on the end face of the sample, and the structure of the cross-section of each sample was evaluated based on the worst measurement value.

[0133] That is, the maximum separation distance (A) between adjacent optical fiber pairs in the above Table 1 is the maximum value among the values ​​of the maximum separation distance between adjacent optical fiber pairs measured 10 times in the cross-section of the optical unit (100), the minimum separation distance (B) between the cladding layer and the optical fiber is the minimum value among the values ​​of the minimum separation distance between the inner surface of the cladding layer (30) and the optical fiber (10) measured 10 times in the cross-section of the optical unit (100), and the air gap cross-sectional area ratio (R) is the maximum value among the values ​​of the air gap cross-sectional area ratio (R) measured 10 times in the cross-section of the optical unit (100).

[0134] Samples 1 to 3 each have an outer diameter smaller than half the inner diameter of the microduct. The maximum separation distance (A) between adjacent optical fiber pairs of the optical unit (100) samples is smaller than the outer diameter (D) of the optical fiber and smaller than the minimum separation distance (B) between the covering layer and the optical fiber, so it was confirmed that the installation performance of the optical unit (100) and the signal transmission characteristics of the installed optical unit (100) were good during the pneumatic installation test.

[0135] However, it was confirmed that samples 4 to 7 had a maximum separation distance (A) between adjacent optical fiber pairs of each optical unit (100) sample larger than the outer diameter (D) of the optical fiber, and thus the structure of the optical fiber (10) placed in the bedding layer (20) could not be stably maintained due to the stress received in the bending section during the pneumatic installation test, resulting in deterioration of the signal transmission characteristics.

[0136] In particular, in samples 5 to 7, the maximum separation distance (A) between adjacent optical fiber pairs of each optical unit (100) sample was arranged to be large, and thus the minimum separation distance (B) between the covering layer and the optical fiber was small, and it was confirmed that the optical fiber (10) was not sufficiently protected from the impact received in the bending section during the pneumatic installation test, resulting in deterioration of the signal transmission characteristics.

[0137] In addition, it was confirmed that samples 8 to 10 did not secure sufficient bedding layer (20) thickness because the minimum separation distance (B) between the covering layer and the optical fiber of each optical unit (100) sample was smaller than the maximum separation distance (A) between adjacent optical fiber pairs, and thus the optical fiber (10) was not sufficiently protected from the impact received in the bending section during the pneumatic installation test, resulting in deterioration of the signal transmission characteristics.

[0138] In addition, it was confirmed that sample 11 had a high ratio of voids in the bedding layer (20), and thus the structure of the optical fiber (10) placed in the bedding layer (20) could not be stably maintained due to the stress received in the bending section during the pneumatic installation test, resulting in deterioration of the signal transmission characteristics. It was also confirmed that sample 12 had an outer diameter of the optical unit (100) sample larger than half the inner diameter of the microduct, resulting in deterioration of the installation properties of the optical unit (100).

[0139] Meanwhile, the optical unit (100) configured with the above-described structure can be subjected to termination processing, bonding, or splicing after being pneumatically installed into the duct (d), which requires separation of each optical fiber (10) from the bedding layer (20).

[0140] This optical fiber (10) separation operation can typically be performed by a worker peeling the covering layer (30) from the bedding layer (20) and then removing the bedding layer (20) to separate each optical fiber (10).

[0141] Accordingly, the optical unit (100) should be configured so that the optical fiber (10) can be easily separated from the bedding layer (20) while the mechanical strength of the bedding layer (20) is secured so that the optical fiber (10) accommodated within the bedding layer (20) is stably protected.

[0142] Additionally, the tensile strength and elongation of the polymer resin can be additionally controlled.

[0143] Here, the tensile strength and elongation of the resin refer to the tensile strength and elongation values ​​measured at a speed of 250 mm / min on a dumbbell-shaped specimen of the IEC60811-1-1 standard manufactured with the composition of the bedding layer (20) having a width of 4 mm × a thickness of 1 mm, respectively, according to the evaluation method according to the EN60811 standard.

[0144] Specifically, the tensile strength of the polymer resin constituting the bedding layer (20) may be configured in the range of 10 MPa to 40 MPa. Here, the tensile strength corresponds to the magnitude of the stress applied to the resin instantaneously at the time of destruction of the polymer resin.

[0145] When the tensile strength of the polymer resin constituting the bedding layer (20) is less than 10 MPa, the mechanical strength of the bedding layer (20) is insufficient, and cracks and breakage may occur in the bedding layer (20) during the peeling process of the covering layer (30), whereas when the tensile strength of the polymer resin exceeds 40 MPa, excessive force is required to remove the bedding layer (20), and the problem of reduced workability in separating the optical fiber (10) occurs.

[0146] In addition, the elongation of the polymer resin constituting the bedding layer (20) may be configured in the range of 20% to 90%. Here, the elongation refers to the degree to which the resin is finally stretched and deformed at the time of resin destruction.

[0147] If the elongation of the polymer resin constituting the bedding layer (20) is less than 20%, deformation of the bedding layer (20) may occur during the peeling of the covering layer (30), whereas if the elongation of the polymer resin constituting the bedding layer (20) is more than 90%, the polymer resin is not cleanly removed during the process of separating the optical fiber (10) from the bedding layer (20) and is stretched, which causes a problem in that the workability of separating the optical fiber (10) is reduced.

[0148] That is, the optical cable (1000) according to the present invention has mechanical properties such as toughness, tensile strength, and elongation of the coating layer (20) constituting the optical unit (100) in a complex manner, so that when terminating or joining a branched optical unit (100), the optical fiber (10) can be easily separated from the coating layer (20), and at the same time, the mechanical strength of the coating layer (20) is sufficiently secured, so that the optical fiber (10) can be stably protected from external friction and stress.

[0149] In this way, the optical unit (100) according to the present invention has an excellent effect of stably protecting the internal optical fibers (10) from friction or stress during pneumatic laying or traction laying work by ensuring sufficient mechanical strength of the bedding layer (20) by controlling the properties of the polymer resin constituting the bedding layer (20), and at the same time, securing a sufficient separation distance between the plurality of optical fibers (10) arranged inside the bedding layer (20) and the covering layer (20).

[0150] While this specification has described preferred embodiments of the present invention, those skilled in the art will appreciate that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention as defined in the claims below. Therefore, any modified implementation that fundamentally includes the elements of the claims should be considered within the technical scope of the present invention.

Claims

1. An optical unit installed into a duct by pneumatic pressure, A plurality of optical fibers comprising a core, a cladding layer surrounding the core, and a coating layer surrounding the cladding layer; A bedding layer comprising a polymer resin and wrapping at least part of the circumference of the plurality of optical fibers; and A covering layer that surrounds the bedding layer and forms a covering of the optical unit; An optical unit characterized in that the maximum separation distance between adjacent pairs of optical fibers among a plurality of optical fibers arranged inside the bedding layer is smaller than the outer diameter of the optical fibers and smaller than the minimum separation distance between the inner surface of the covering layer and the optical fibers.

2. In paragraph 1, An optical unit characterized in that the minimum distance between the inner surface of the covering layer and the optical fiber is smaller than the outer diameter of the optical fiber.

3. In paragraph 1, An optical unit characterized in that the overall outer diameter of the optical unit is 0.8 millimeters (mm) to 1.6 millimeters (mm).

4. In paragraph 1, An optical unit characterized in that the polymer resin constituting the above bedding layer is an acrylate resin, and the above bedding layer is formed by an ultraviolet (UV) curing method.

5. In paragraph 1, An optical unit characterized in that the optical fiber has an outer diameter of 180 to 265 micrometers (㎛).

6. In paragraph 1, An optical unit characterized in that the above optical unit comprises four optical fibers, and the four optical fibers are arranged in a square shape.

7. In paragraph 1, An optical unit characterized in that the optical unit has a circular filler member corresponding to the outer diameter of the optical fiber, and two optical fibers and two filler members are arranged in a square shape.

8. In paragraph 1, An optical unit characterized in that the above covering layer is composed of a high-density polyethylene (HDPE) material containing silicon.

9. In paragraph 1, An optical unit characterized in that the tensile strength of the resin constituting the above bedding layer is 10 MPa to 40 MPa and the elongation is 20% to 90%.

10. In paragraph 1, An optical unit characterized in that the above bedding layer additionally includes a void.

11. In paragraph 10, An optical unit characterized in that the cross-sectional area of ​​the above gap is smaller than the cross-sectional area of ​​the above bedding layer.

12. In paragraph 11, An optical unit characterized in that the ratio of the cross-sectional area of ​​the gap to the cross-sectional area of ​​the bedding layer is 0.1 to 0.

5.

13. A plurality of optical units of any one of claims 1 to 12, which are pneumatically installed or traction installed within a microduct; A jacket that surrounds and accommodates a plurality of the above optical units; and An optical cable characterized by including a friction reducing layer provided on the inner surface of the jacket to reduce friction between the optical unit and the jacket.

14. In paragraph 13, An optical cable characterized in that 12 or 24 optical units are provided inside the jacket.

15. In paragraph 13, An optical cable characterized in that the overall outer diameter of the optical cable is 12 millimeters (mm) to 18 millimeters (mm).

16. In paragraph 13, An optical cable characterized in that the thickness of the jacket is 2.0 millimeters (mm) to 2.8 millimeters (mm).

17. In paragraph 13, An optical cable characterized in that the optical unit space ratio, which is defined as the total cross-sectional area of ​​a plurality of optical units compared to the internal space cross-sectional area of ​​the jacket, is 15% to 40%.

18. In paragraph 13, An optical cable characterized in that the jacket is made of high-density polyethylene (HDPE) material.

19. In paragraph 13, An optical cable characterized in that the friction reduction layer is composed of polyethylene terephthalate (PET) material.

20. In paragraph 13, An optical cable characterized in that the thickness of the friction reduction layer is 15 micrometers (μm) to 35 micrometers (μm).

21. In paragraph 13, An optical cable characterized in that at least one tensile line is provided on the inside of the jacket.

22. In an optical cable system in which an optical unit constituting an optical cable of any one of clauses 13 to 21 laid in a pipeline is branched and laid to an optical demand node, At least one first branch box is provided on the above-mentioned pipe, the jacket of the optical cable is removed from the inside to expose the optical unit, and includes a winding unit capable of winding the optical unit; An optical cable system characterized in that the optical unit wound by the winding unit of the above first branch box is pneumatically installed into a duct connecting the above conduit and the above optical demand node.

23. In paragraph 22, It further includes a second branch box installed separately from the first branch box and in which the branch target optical unit is cut; An optical cable system characterized in that the optical unit to be branched, cut from the second branch box, is wound onto the first branch box through the winding unit of the first branch box, and the optical unit wound by the winding unit is pneumatically installed into the duct from the first branch box.

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