Optical cable

Abstract

The present invention relates to an optical cable. More specifically, the present invention relates to an optical cable installed inside a duct by pneumatic pressure and including a bedding layer capable of stably protecting an internal optical fiber and easily separating the optical fiber.

Description

optical cable

[0001] The present invention relates to an optical cable. More specifically, the present invention relates to an optical cable that is installed inside a duct by pneumatic pressure, and that has a bedding layer that stably protects the optical fibers inside while facilitating separation of the optical fibers.

[0002] The pneumatic installation method for laying optical cables is a method of pneumatically blowing a propellant mounted on the tip of an optical cable to propel the optical cable into a duct or microduct for a range of several kilometers.

[0003] In general, an optical cable for pneumatic installation is configured to include an optical fiber inside and a bedding layer to wrap and protect the optical fiber as a whole, so that the overall configuration of the optical cable can be simplified, thereby minimizing the weight and outer diameter of the optical cable.

[0004] An optical cable for pneumatic laying can be configured so that the mechanical properties of the bedding layer are sufficiently secured so that the internal optical fiber is not damaged by external friction or stress during laying of the optical cable.

[0005] At the same time, since a process of separating each optical fiber from the bedding layer is required when terminating an optical cable or joining or splicing an optical cable, the bedding layer must be configured to facilitate separation of individual optical fibers from the bedding layer to prevent breakage or disconnection of the optical fibers.

[0006] Conventionally, technologies related to pneumatic installation optical cables including a bedding layer exist, including Korean registered patent (KR 10-0511938 B1), Japanese published patent (JP 1997-197219 A), and European registered patent (EP 0296836 B1). However, these prior documents do not disclose the mechanical properties of the bedding layer constituting the optical cable, or do not comprehensively consider the range of mechanical properties of each bedding layer so as to easily separate the optical fiber from the bedding layer while stably protecting the optical fiber.

[0007] Accordingly, there is a great demand for an optical cable that is laid inside a duct by pneumatic pressure and has sufficient strength to stably protect the optical fiber inside while also having a bedding layer that allows easy separation of the optical fiber.

[0008] The present invention aims to provide an optical cable that is laid inside a duct by pneumatic pressure, and has a bedding layer that stably protects the optical fiber inside while allowing easy separation of the optical fiber.

[0009] In order to solve the above problem, the present invention provides an optical cable that is installed into a duct by pneumatic pressure, the optical cable comprising: a plurality of optical fibers; a bedding layer that wraps the plurality of optical fibers and is composed of a polymer resin; and a covering layer that wraps the bedding layer and forms a covering of the optical cable; wherein the resin constituting the bedding layer has a tensile strength of 10 MPa to 40 MPa, an elongation of 20% to 90%, and a toughness of 3 MPa to 8 MPa.

[0010] In this case, the toughness of the bedding layer may be (tensile strength x elongation) / 2 of the resin constituting the bedding layer.

[0011] 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.

[0012] Here, the covering layer may be composed of a high-density polyethylene (HDPE) material.

[0013] Additionally, at least one filler member may be further provided together with the optical fiber inside the bedding layer.

[0014] Additionally, each of the optical fibers may have a diameter of 180 to 220 micrometers (㎛).

[0015] And, the thickness of the above-mentioned covering layer may be about 10 to 20 percent (%) of the total outer diameter of the optical cable.

[0016] Here, the outer diameter of the optical cable may be 1.0 millimeter to 5.0 millimeters (mm), and may be 50 percent (%) or less of the inner diameter of the microduct.

[0017] Additionally, the adjacent plurality of optical fibers can be spaced apart from each other by a smaller diameter than the optical fibers.

[0018] In this case, the maximum separation distance between adjacent pairs of optical fibers among the plurality of optical fibers arranged inside the bedding layer may be smaller than the minimum separation distance between the inner surface of the covering layer and the optical fibers.

[0019] In addition, the minimum distance between the inner surface of the covering layer and the optical fiber may be smaller than the diameter of the optical fiber.

[0020] Additionally, the bedding layer may additionally include voids.

[0021] In this case, the cross-sectional area of ​​the gap may be smaller than the cross-sectional area of ​​the bedding layer.

[0022] In addition, in order to solve the above problem, the present invention can provide a microduct optical cable system in which a plurality of ducts are installed together in a duct placed inside a pipeline, characterized in that it includes a microduct in the shape of a circular pipe; and the optical cable described above that is installed pneumatically or by traction inside the microduct.

[0023] The optical cable according to the present invention has a bedding layer having controlled mechanical properties such as toughness, tensile strength, and elongation, so that when terminating or joining an optical cable, it is easy to separate individual optical fibers from the bedding layer, and at the same time, the mechanical strength of the bedding layer is sufficiently secured, so that the optical fibers inside can be stably protected from friction or stress during pneumatic or traction laying of the optical cable.

[0024] Figure 1 illustrates a state in which an optical cable according to the present invention is pneumatically laid in a duct.

[0025] Figures 2 to 7 illustrate cross-sectional views of various embodiments of an optical cable according to the present invention.

[0026] Figure 8 shows a stress-strain curve of one embodiment of an optical cable according to the present invention.

[0027] Figure 9 shows stress-strain curves of multiple optical cable samples of the present invention.

[0028] Figure 10 is a schematic diagram of a track used for an air-laying test of an optical cable according to the present invention and a photograph of a test site.

[0029] 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.

[0030] Figure 1 illustrates a state in which an optical cable (100) according to the present invention is pneumatically laid in a duct.

[0031] The present invention relates to an optical cable (100) that is pneumatically laid inside a conduit of a general duct or microduct.

[0032] As illustrated in FIG. 1, a receiving space is formed lengthwise inside a conduit (210), a duct (220) is installed in the receiving space, and a plurality of microducts (230) made of a polymer material such as polyethylene (PE) may be provided in a bundle form inside the duct (220), and an optical cable (100) according to the present invention may be laid inside each microduct (230).

[0033] The above duct and the above microduct may be configured in the shape of a circular pipe.

[0034] The above microduct (230) can be pre-installed within the above conduit (210), and the diameter of the microduct (230) can be configured to have a predetermined inner diameter according to standards, etc., and the diameter of the optical cable (100) pneumatically laid within the microduct (230) can be limited according to the inner diameter of the microduct (230).

[0035] In order for the optical cable (100) to be smoothly installed pneumatically inside a narrow microduct (230), the overall configuration of the optical cable (100) can be simplified so that the weight and outer diameter of the optical cable (100) can be minimized.

[0036] In addition, the optical cable (100) can be mostly installed within the microduct (230) using a pneumatic installation method, but depending on the installation environment, pneumatic installation and traction installation may be applied together to some sections of the microduct (230).

[0037] Therefore, the optical cable (100) must be configured so that the internal optical fiber is not damaged by external friction or stress even when pneumatic or traction installation is performed within the microduct (230).

[0038] Furthermore, when terminating, joining or splicing the optical cable (100), a task of separating each optical fiber may be required, and accordingly, the optical cable (100) must be configured to prevent damage or disconnection of the optical fiber during the separation task.

[0039] Hereinafter, the structure of the optical cable (100) according to the present invention will be examined with reference to FIG. 2 and below.

[0040] Figures 2 to 7 illustrate cross-sectional views of various embodiments of an optical cable (100) according to the present invention.

[0041] As illustrated in FIGS. 2 to 7, an optical cable (100) according to the present invention may be configured to include a plurality of optical fibers (10), a bedding layer (20) made of polymer resin and wrapping the plurality of optical fibers (10), and a covering layer (30) wrapping the bedding layer (20) and forming a covering of the optical cable (100).

[0042] Here, the optical cable (100) according to the present invention is configured so that a plurality of optical fibers (10) can be easily separated individually from the bedding layer (20) by controlling the mechanical properties of the bedding layer (20), and at the same time, sufficient strength is secured by the bedding layer (20) so that a plurality of optical fibers (10) can be stably fixed and supported.

[0043] The plurality of optical fibers (10) constituting the optical cable (100) according to the present invention 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).

[0044] Here, the core (11) uses a glass optical fiber made of silica material with a high refractive index. The core (11) of the optical fiber (10) is called a single-mode optical fiber when it has a diameter of several micrometers, a multi-mode optical fiber when it has a diameter of several tens of micrometers, and is classified into a step-shaped optical fiber, a hill-shaped optical fiber, etc., depending on the refractive index distribution of the core (11).

[0045] 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 transmits a signal by causing total reflection of light passing through the center.

[0046] 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.

[0047] 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).

[0048] The above plurality of optical fibers (10) may each be optical fibers having a diameter of 180 to 265 micrometers (㎛), and preferably, optical fibers having a diameter of 220 micrometers (㎛) or less may be applied to reduce the outer diameter of the optical cable (100).

[0049] An optical cable (100) according to the present invention is configured to include a bedding layer (20) that entirely wraps a plurality of optical fibers (10).

[0050] 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 cable (100). The bedding layer (20) itself has an outer surface formed with a circular cross-section, thereby maintaining the circularity of the optical cable (100).

[0051] In addition, the resin constituting the bedding layer (20) is a photocurable polymer resin that is cured by ultraviolet (UV) irradiation, and may preferably be composed of an acrylate-based polymer resin.

[0052] Here, in order to allow the resin constituting the bedding layer (20) to quickly harden when exposed to ultraviolet rays, a photocurable initiator such as 4,4-bis(dimethylamino)benzophenone (4,4′benzophenone) may be additionally added to the acrylate polymer resin as a component of the bedding layer (20).

[0053] The resin constituting the above bedding layer (20) can be formed to wrap around the entire circumference of a plurality of optical fibers (10), and can be formed as a solid type that is hardened in a state in which it permeates the inside without leaving any empty space between the optical fibers (10), or can be formed as an incomplete type in which some empty space exists between the optical fibers (10) or between the optical fibers (10) and a filler member (40) described later.

[0054] As described above, when the optical cable (100) according to the present invention is terminated after being laid into a duct or when performing work such as joining or splicing, it is necessary to separate the optical fiber (10) from the bedding layer (20). In general, the separation work of the optical fiber (10) can be performed by a worker using a separation work tool such as a stripper or cutter to strip the covering layer (30) from the bedding layer (20) and removing the bedding layer (20) with the separation work tool or bare hands, thereby separating the optical fiber (10) from the bedding layer (20).

[0055] Accordingly, the optical cable (100) according to the present invention should be such that the mechanical properties of each of the bedding layers (20) are comprehensively controlled so that the separation of the optical fibers (10) joined by the bedding layer (20) is easy, while a plurality of the optical fibers (10) should be stably fixed within the bedding layer (20).

[0056] Specifically, the toughness of the resin constituting the bedding layer (20) may be in the range of 3 MPa to 8 MPa. Here, the toughness of the resin refers to the energy per unit volume applied to the resin until the resin is fractured.

[0057] Here, if the toughness of the resin constituting the bedding layer (20) is less than 3 MPa, when the covering layer (40) is peeled off from the bedding layer (20) during the separation of the optical fiber (10), the bedding layer (20) may be broken or cracked, or if the bedding layer (20) is broken during the separation of the optical fiber (10) from the bedding layer (20), the optical fiber (10) may be contaminated with the residue of the broken bedding layer (20), requiring additional residue removal work. On the other hand, if the toughness of the resin constituting the bedding layer (20) is more than 8 MPa, it is difficult to remove the bedding layer (20), so there is a problem that the workability of the work of separating each optical fiber (10) from the bedding layer (20) is reduced.

[0058] The optical cable (100) according to the present invention may further include at least one filler member (40) inside the bedding layer (20) together with the optical fiber (10).

[0059] The embodiment illustrated in FIG. 2 has four optical fibers (10) provided inside the bedding layer (20), and may have a cross-sectional structure similar to the optical cable (100) illustrated in FIG. 3, which has two optical fibers (10) and two filler members (40).

[0060] If only two optical fibers (10) are accommodated inside the bedding layer (20), it is not easy to configure the cross-sectional shape of the optical cable (100) into a circle, and it is difficult to secure sufficient tensile strength, so two filler members (40) in the form of an interposition can be added to configure an optical cable having a structure similar to the optical cable (100) illustrated in FIG. 2, in which four optical fibers (10) are provided inside the bedding layer (20).

[0061] For the same reason, the embodiment illustrated in FIG. 4 can be provided with six optical fibers (10) and two filler members (40) inside the bedding layer (20) of the optical cable (100), and although not illustrated, it is of course possible to configure the optical cable (100) by providing only eight optical fibers (10) without the filler members (40) inside the bedding layer (20).

[0062] The embodiment illustrated in FIG. 5 may be provided with 10 optical fibers (10) and 2 filler members (40) inside the bedding layer (20) of the optical cable (100). Similarly, although not illustrated, the optical cable (100) may be configured by providing only 12 optical fibers (10) without filler members (40) inside the bedding layer (20).

[0063] Meanwhile, when the optical cable (100) has a filler member (40) as shown in FIGS. 4 and 5, the filler member (40) may be configured with a circular cross-section to correspond to the size and shape of the optical fiber (10).

[0064] The optical cable (100) according to the present invention can be arranged so that the empty space inside the optical cable (100) is minimized as in the embodiments illustrated in FIGS. 2 to 5, thereby minimizing the outer diameter of the optical cable (100). The optical fiber (10) or filler member (40) arranged inside the bedding layer (20) can be arranged so as to be in external contact with each adjacent optical fiber (10) or filler member (40).

[0065] In addition, the optical cable (100) according to the present invention may have multiple optical fibers (10) arranged inside the bedding layer (20) as shown in the embodiments of FIGS. 6 and 7, such that adjacent optical fibers (10) may be arranged with each other spaced apart from the other.

[0066] In this case, among the plurality of optical fibers (10) arranged inside the bedding layer (20), a pair of adjacent optical fibers (10) may be spaced apart by a distance smaller than the diameter (D) of the optical fibers (10).

[0067] The optical cable (100) according to the present invention can sufficiently improve the bending characteristics of the optical cable (100) by spacing adjacent pairs of optical fibers (10) apart from each other by a distance smaller than the diameter (D) of the optical fibers (10), thereby minimizing movement of the optical fibers (10) and stably maintaining the structure of the optical cable (100).

[0068] Furthermore, the optical cable (100) according to the present invention may be configured such that a pair of adjacent optical fibers (10) are spaced apart from each other within the bedding layer (20), and at the same time, the maximum separation distance (A) between an adjacent pair of optical fibers (10) among the plurality of optical fibers (10) arranged within the bedding layer (20) may be smaller than the minimum separation distance (B) between the inner surface of the covering layer (30) and the optical fibers (10).

[0069] Here, the distance between a pair of optical fibers (10) means the shortest distance between the outer surfaces of adjacent pairs of optical fibers (10), and the maximum separation distance (A) between adjacent pairs of optical fibers (10) among a plurality of optical fibers (10) means the maximum distance between each pair of optical fibers (10) arranged adjacently among a plurality of optical fibers (10).

[0070] In addition, the distance between the inner surface of the covering layer (30) and the optical fiber (10) means the shortest distance between the inner surface of the covering layer (30) and the outer surface of the optical fiber (10), and the minimum separation distance (B) between the inner surface of the covering layer (30) and the optical fiber (10) means the minimum distance among the distances between each optical fiber (10) among a plurality of optical fibers (10) and the inner surface of the covering layer (30).

[0071] In this way, the optical cable (100) according to the present invention is configured so that the maximum separation distance (A) between a pair of adjacent optical fibers (10) is smaller than the minimum separation distance (B) between the inner surface of the covering layer (30) and the optical fibers (10), thereby allowing a plurality of optical fibers (10) to be gathered within a relatively close distance within the bedding layer (20), thereby preventing unnecessary increase in the outer diameter of the optical cable (100) due to the distant position of any one optical fiber (10), and securing a bedding layer (20) of sufficient thickness to protect the optical fibers (10).

[0072] And, each optical fiber (10) arranged inside the bedding layer (20) is arranged to be spaced apart from the inner surface of the covering layer (30) by a predetermined distance, but the minimum distance (B) between the inner surface of the covering layer (30) and the optical fiber (10) may be smaller than the diameter (D) of the optical fiber (10).

[0073] In this way, the optical cable (100) according to the present invention can minimize an increase in the outer diameter of the optical cable (100) by configuring the minimum distance (B) between the inner surface of the covering layer (30) and the optical fiber (10) to be smaller than the diameter (D) of the optical fiber (10).

[0074] In addition, as illustrated in FIG. 7, in order to improve the workability of the separation operation of separating individual optical fibers (10) from the bedding layer (20), the optical cable (100) according to the present invention may additionally have a gap (21) formed inside the bedding layer (20) in the longitudinal direction of the optical cable (100).

[0075] In this case, the bedding layer (20) is formed to surround the outer area of ​​a plurality of optical fibers (10), and the gap (21) can be formed in an empty space defined by the bedding layer (20) and the plurality of optical fibers (10) arranged inside the bedding layer (20).

[0076] And, based on the cross-section of the optical cable (100), the cross-sectional area of ​​the gap (21) formed inside the bedding layer (20) may be smaller than the cross-sectional area of ​​the bedding layer (20).

[0077] If the cross-sectional area of ​​the gap (21) is larger than the cross-sectional area of ​​the bedding layer (20), there is an advantage in that the separation workability of the optical fiber (10) from the bedding layer (20) is further improved, but since a plurality of optical fibers (10) cannot be stably supported and fixed inside the bedding layer (20) due to a decrease in the overall cross-sectional area of ​​the bedding layer (20), it is desirable that the cross-sectional area of ​​the gap (21) formed inside the bedding layer (20) is smaller than the cross-sectional area of ​​the bedding layer (20).

[0078] The optical cable (100) according to the present invention may have a covering layer (30) forming an outer covering of the optical cable provided on the outer periphery of the bedding layer (20).

[0079] The above covering layer (30) may be composed of a polymer material that maintains the circular shape of the optical cable (100) and reduces friction with the inner surface of the microduct (230) when the optical cable (100) is pneumatically laid within the microduct (230).

[0080] The above-mentioned covering layer (30) may be composed of a polyethylene polymer resin having a low coefficient of friction and excellent tensile strength. For example, the covering layer (30) may be composed of very low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), etc., either singly or in combination, and preferably, the covering layer (30) may be composed of a high-density polyethylene (HDPE) resin material.

[0081] The thickness of the above covering layer (30) is preferably configured to be about 10 to 20 percent (%) of the total outer diameter of the optical cable (100) in consideration of the tensile strength and flexibility of the optical cable.

[0082] In addition, the overall outer diameter of the covering layer (30) is not limited to a specific range, but is preferably configured to be about 1.0 millimeter to 5.0 millimeters (mm) so as to enable easy pneumatic installation into a narrow pipe such as a microduct (230).

[0083] In addition, it is preferable that the outer diameter of the optical cable (100) be 50 percent (%) or less compared to the inner diameter of the microduct (230) in consideration of the pneumatic installation characteristics of the optical cable.

[0084] FIG. 8 illustrates a stress-strain curve obtained by measuring the strain when stress is applied to a specimen made of a resin constituting the bedding layer (20) of one embodiment of the optical cable (100) of the present invention. The stress-strain curve described above is obtained by measuring the stress and strain while pulling a dumbbell-shaped specimen of the IEC60811-1-1 standard, made of the composition of the bedding layer (20) with a width of 4 mm × a thickness of 1 mm, at a speed of 250 mm / min according to the evaluation method according to the EN60811 standard.

[0085] The tensile strength of the resin constituting the above bedding layer (20) may preferably be configured in the range of 10 MPa to 40 MPa as the stress at the time of fracture of the resin specimen in the above stress-strain curve.

[0086] When the tensile strength of the resin constituting the bedding layer (20) is less than 10 MPa, during the production process of the optical cable (100), when the resin constituting the bedding layer (20) is applied to the outside of the optical fiber (10) and hardened to form the bedding layer (20) or when forming the covering layer (30) on the outside of the bedding layer (20), a small load applied to the resin constituting the bedding layer (20) or an impact, bending, or twisting received by the optical cable (100) during pneumatic laying may cause cracks or damage to the bedding layer (20), which may cause separation from the optical fiber (10). On the other hand, when the tensile strength of the resin constituting the bedding layer (20) exceeds 40 MPa, a problem occurs in which excessive force is required to remove and peel the bedding layer (20) in order to separate the optical fiber (10).

[0087] And, the elongation of the resin constituting the bedding layer (20) may preferably be configured in the range of 20% to 90% as the strain at the time of fracture of the resin specimen in the stress-strain curve described above.

[0088] If the elongation of the resin constituting the bedding layer (20) is less than 20%, the bedding layer (20) can easily be broken or deformed even by a small strain during the process of forming the bedding layer (20) or covering layer (30) in the production process of the optical cable (100) or during the process of pneumatically laying the optical cable (100), whereas if the elongation of the resin constituting the bedding layer (20) is more than 90%, there is a problem in that the resin of the bedding layer (20) is excessively stretched during the process of separating the optical fiber (10) from the bedding layer (20) and is not cleanly removed and peeled.

[0089] In addition to controlling the tensile strength and elongation of the resin constituting the bedding layer (20), controlling the toughness of the resin is required. Toughness can be defined as the energy per unit volume that a material can absorb until it breaks.

[0090] Accordingly, the toughness of the resin can be obtained as the static integral area for the lower region from the stress-strain curve to the point of fracture of the resin specimen (the fracture point X in Fig. 8), and can preferably be configured in the range of 3 MPa to 8 MPa.

[0091] If the toughness of the resin constituting the bedding layer (20) is less than 3 MPa, the bedding layer (20) is easily broken and cannot sufficiently protect the optical fiber (10) wrapped with the bedding layer (20), whereas if it is more than 8 MPa, the separation workability of the bedding layer (20) from the optical fiber (10) may be reduced.

[0092] Here, the static integral area (S) for the lower region of the stress-strain curve (A) of the resin constituting the bedding layer (20) shown in Fig. 8(a) A ) is the area (S) of the lower region of the straight line (B) that connects the tensile strength and elongation values ​​of the resin constituting the bedding layer (20) from the origin shown in Fig. 8(b). B ), it is easy to obtain an approximate value of toughness, which is half the product of the tensile strength and elongation of the resin constituting the bedding layer (20), without additional toughness evaluation, and by appropriately adjusting the toughness of the resin with this value, the desired physical properties of the bedding layer can be controlled.

[0093] FIG. 9 illustrates a stress-strain curve obtained by measuring the strain and stress of the resin constituting the bedding layer (20) in multiple samples of the optical cable (100) of the present invention.

[0094] Hereinafter, the results of confirming the characteristics during pneumatic laying of multiple optical cable (100) samples having different properties of resins constituting the bedding layer (20) are described with reference to Table 1.

[0095] [Table 1]

[0096]

[0097] The above-mentioned plurality of samples are optical cables (100) composed of four optical fibers (10), a bedding layer (20) that wraps the four optical fibers and is formed of a resin having different tensile strengths and elongations and has an outer diameter of about 0.8 mm, and a covering layer (30) that wraps the bedding layer (20) and has an outer diameter of about 1.2 mm. The optical signal transmission characteristics and stripping characteristics of normally transmitted samples were evaluated through a pneumatic installation test of the above-mentioned plurality of samples.

[0098] The above pneumatic installation test was performed by installing a microduct (230) having an inner diameter of 3 mm and an outer diameter of 6 mm in a track implemented as in Fig. 10(b) with a plurality of macro-bending and micro-bending sections as in Fig. 10(a), and using a pneumatic installation device Minijet P400 from Plumettaz, the inside of the microduct (230) was pneumatically transmitted for more than 1 km. The signal transmission characteristics were evaluated by measuring the optical signal loss at a wavelength of 1550 nm at room temperature (23°C) to determine whether the loss value was 0.35 dB / km or less, and the stripping characteristics were evaluated by evaluating whether the bedding layer (20) could be cleanly removed with a small force of 15 MPa or less without damaging the optical fiber (10) using a tool for separation work or bare hands.

[0099] It was confirmed that samples 1 to 3, in which the properties of the resin constituting the bedding layer (20) were within a desirable range, had good signal transmission characteristics and stripping characteristics of the optical cable (100) after pneumatic transmission.

[0100] However, in sample 4, although the bedding layer (20) was easily peeled off from the optical fiber (10), the elongation of the resin constituting the bedding layer (20) was low, so that the structure of the optical fiber (10) placed in the bedding layer (20) could not be stably maintained due to stresses such as impact, bending, and twisting received in the bending section during the pneumatic installation test, resulting in deterioration of the signal transmission characteristics. In samples 5 and 6, the elongation of the resin constituting the bedding layer (20) was high, so that the bedding layer (20) wrapping the optical fiber (10) was elongated during the peeling and then broke, requiring additional work to remove the extended bedding layer, and thus the peeling characteristics were not good.

[0101] In addition, although sample 7 was easily stripped, the tensile strength of the resin constituting the bedding layer (20) was low, so the optical fiber (10) was not sufficiently protected from the impact received at the bending section during the pneumatic installation test, resulting in deterioration of the signal transmission characteristics. In addition, samples 8 and 9 had high tensile strengths of the resin constituting the bedding layer (20), so a high stripping force was required during stripping, confirming that the stripping characteristics were not good. In particular, sample 8 had a problem in that a part of the coating layer of the optical fiber was damaged during the additional removal of a part of the bedding layer (20) that remained attached to the optical fiber after stripping, confirming that the stripping characteristics were not very good.

[0102] And, although the elongation and tensile strength of the resin constituting the bedding layer (20) of Samples 10 and 11 were within the desirable range, Sample 11, which had low toughness, had good peeling characteristics, but after the pneumatic installation test, many damaged parts of the bedding layer (20) were found and the signal transmission characteristics were not good, and Sample 12, which had high toughness, required a high peeling force during peeling.

[0103] In addition, sample 12 was found to have very poor stripping characteristics as both the elongation and tensile strength of the resin constituting the bedding layer (20) were outside the normal range, making it impossible to strip with bare hands. In addition, when stripping using a separation tool, high stripping force was required, and at the same time, the bedding layer was elongated, requiring additional removal of the extended bedding layer.

[0104] That is, the optical cable (100) according to the present invention has mechanical properties such as toughness, tensile strength and elongation of the bedding layer (20) each controlled, so that when terminating or joining the optical cable (100), it is easy to separate individual optical fibers (10) from the bedding layer (20), and at the same time, the mechanical strength of the bedding layer (20) is sufficiently secured, so that the optical fibers (100) inside can be stably protected from external friction or stress during pneumatic or traction laying of the optical cable (100).

[0105] 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 cable installed into a duct by pneumatic pressure, The above optical cable comprises a plurality of optical fibers; A bedding layer comprising a polymer resin and wrapping a plurality of the optical fibers; and A covering layer that wraps the bedding layer and forms the covering of the optical cable; An optical cable characterized in that the tensile strength of the resin constituting the above bedding layer is 10 MPa to 40 MPa, the elongation is 20% to 90%, and the toughness is 3 MPa to 8 MPa.

2. In paragraph 1, An optical cable characterized in that the toughness of the bedding layer is (tensile strength x elongation) / 2 of the resin constituting the bedding layer.

3. In paragraph 1, An optical cable 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.

4. In paragraph 1, An optical cable characterized in that the above covering layer is composed of high-density polyethylene (HDPE) material.

5. In paragraph 1, An optical cable characterized in that at least one filler member is further provided together with the optical fiber inside the bedding layer.

6. In paragraph 1, An optical cable, wherein each of the optical fibers has a diameter of 180 to 220 micrometers (㎛).

7. In paragraph 1, An optical cable characterized in that the thickness of the above-mentioned covering layer is about 10 to 20 percent (%) of the total outer diameter of the optical cable.

8. In paragraph 1, An optical cable characterized in that the outer diameter of the optical cable is 1.0 millimeter to 5.0 millimeters (mm) and is 50 percent (%) or less compared to the inner diameter of the microduct.

9. In paragraph 1, An optical cable characterized in that the adjacent plurality of optical fibers are spaced apart from each other by a distance smaller than the diameter of the optical fibers.

10. In paragraph 9, An optical cable characterized in that 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 minimum separation distance between the inner surface of the covering layer and the optical fibers.

11. In paragraph 10, An optical cable characterized in that the minimum distance between the inner surface of the covering layer and the optical fiber is smaller than the diameter of the optical fiber.

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

13. In paragraph 12, An optical cable characterized in that the cross-sectional area of ​​the above gap is smaller than the cross-sectional area of ​​the above bedding layer.

14. In a microduct optical cable system in which multiple ducts are installed together in a duct placed inside a pipeline, Microducts in the form of circular pipes; and, A microduct optical cable system characterized by comprising an optical cable of any one of claims 1 to 9, which is pneumatically installed or towed installed within the microduct.

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