Abstract:
A disclosed feedthrough of a submarine repeater for introducing a tail cable connected to a submarine cable having a transmission line and a feed line into said submarine repeater includes: a tail cable introduction unit having an insulator for internally installing said transmission line and said feed line, said tail cable introduction unit introducing said tail cable connected to said submarine cable into said submarine repeater; a cap member for fixing said tail cable introduction unit on said submarine repeater; and a rubber film formed so as to cover a surface of said insulator.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a U.S. continuation application, filed under 35 USC 111(a) and claiming the benefit under 35 USC 120 and 365(c), of PCT application JP2005/004285 filed Mar. 11, 2005. The foregoing application is hereby incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a feedthrough of a submarine repeater and a submarine repeater and more particularly to a feedthrough of a submarine repeater and a submarine repeater having a waterproof structure for preventing infiltration of seawater.  
         [0004]     2. Description of the Related Art  
         [0005]     Conventionally, submarine repeaters of submarine cables using optical fibers are laid with submarine cables in the deep sea thousands of meters below the surface, so that the submarine repeaters receive a high seawater pressure. Accordingly, such submarine repeaters are required to have high pressure resistance and high water tightness.  
         [0006]     Further, as disclosed in Patent Document 1, for example, a position where the submarine cable is introduced into the submarine repeater is provided with a feedthrough (structure for connecting an optical fiber to a repeater unit in the submarine repeater). Specifically, a pressure-resistant housing lid is disposed on both sides of a pressure-resistant housing for storing the repeater unit and the feedthrough is inserted into a through-hole formed on the pressure-resistant housing lid. In this case, the feedthrough is installed on the pressure-resistant housing lid with high pressure resistance and high water tightness so as not to allow infiltration of seawater into the pressure-resistant housing.  
         [0007]      FIG. 1  shows a feedthrough  100  as a conventional example.  FIG. 1  shows the feedthrough  100  installed on a pressure-resistant housing lid  110  in an enlarged manner. In the figure, to the right of the pressure-resistant housing lid  110  is seawater and to the left is an inside of the housing. A tail cable  103  is constructed by successively coating a copper pipe  125  and an insulator  126  onto a circumference of an optical fiber  123  in a laminated manner. The tail cable  103  is integrally connected to a tail cable introduction unit  122  constituting the feedthrough  100 .  
         [0008]     The cable introduction unit  122  has a cap member  131  installed on a circumferential portion thereof. The cap member  131  includes first and second members  132  and  133  made of metal.  
         [0009]     The first member  132  is fixed on the insulator  126  positioned at an outermost circumference of the cable introduction unit  122  in an inner side of the housing relative to the cable introduction unit  122  (left side of the figure). Further, the second member  133  is fixed on the cable introduction unit  122  by being screwed up on the first member  132 . Moreover, the cable introduction unit  122  on which the cap member  131  is installed is fixed on the pressure-resistant housing lid  110  using a nut  134 .  
         [0010]     A boundary surface  143  where the first and second members  132  and  133  are brought into contact through screwing is a surface also in contact with the insulator  126  made of resin. In this manner, the boundary surface  143  is an extremely important portion in which the first and second members  132  and  133  made of metal and the insulator  126  are brought into contact and seawater pressure is applied, so that voltage resistance, water pressure resistance, and airtightness are required in particular at the same time. Thus, high reliability is required.  
         [0011]     In view of this, conventionally, a rubber cap  141  is disposed between the cap member  131  and the tail cable  103  and polybutene  140  (insulating oil) is filled in a clearance formed by the rubber cap  141 , cap member  131 , and the tail cable introduction unit  122 . Accordingly, a polybutene injection portion  142  for filling the polybutene  140  is disposed on the second member  133  and the polybutene injection portion  142  is closed using a screw after the polybutene  140  is filled.  
         [0012]     In this structure, compression of the polybutene  140  from seawater pressure and volume change from heat are absorbed through elastic deformation of the rubber cap  141 . Further, the rubber cap  141  and the tail cable  103  are strapped with a tape  165  such that seawater is not filtrated between the rubber cap  141  and the tail cable  103 .  
         [0013]     Patent Document 1: Japanese Laid-Open Patent Application No. 2002-118948  
         [0014]     However, in the conventional feedthrough  100 , the rubber cap  141  must be disposed between the second member  133  and the tail cable  103  in a liquid-tight manner so as to absorb the compression of the polybutene  140  from seawater pressure and the volume change from heat. Further, the cap member  131  requires the polybutene injection portion  142  for filling the polybutene  140  and the screw for closing the polybutene injection portion  142  with a high airtightness. Thus, the structure of the feedthrough  100  is complicated, so that a number of components is increased and assembly is troublesome.  
         [0015]     Further, upon filling the polybutene  140 , it is necessary to perform the filling without allowing air bubbles to get into the polybutene  140 . Thus, in a conventional process, the portion to fulfill the polybutene  140  is subjected to vacuuming via the polybutene injection portion  142 , and then the polybutene  140  is injected. Accordingly, the process for filling the polybutene  140  is very troublesome.  
         [0016]     Moreover, when the submarine repeater on which the feedthrough  100  is installed is subjected to an airtightness test of the pressure-resistant housing, helium gas is supplied to the inside of the pressure-resistant housing. In the airtightness test, the feedthrough  100  is in contact with the helium gas, so that helium gas with small molecules may get into the insulator  126  (polyethylene and the like) made of resin. This is problematic in that the helium may be permeated from the insulator  126  after the test and the polybutene  140  may leak out resulting from this.  
       SUMMARY OF THE INVENTION  
       [0017]     It is a general object of the present invention to provide an improved and useful feedthrough of a submarine repeater and a submarine repeater in which the above-mentioned problems are eliminated.  
         [0018]     A more specific object of the present invention is to provide a feedthrough of a submarine repeater and a submarine repeater that can introduce a tail cable connected to a submarine cable into the inside of the pressure-resistant housing with a simple structure and a high reliability.  
         [0019]     According to one aspect of the present invention, there is provided a feedthrough of a submarine repeater for introducing a tail cable connected to a submarine cable having a transmission line and a feed line into said submarine repeater, said feedthrough comprising: a tail cable introduction unit having an insulator for internally installing said transmission line and said feed line, said tail cable introduction unit introducing said tail cable connected to said submarine cable into said submarine repeater; a cap member for fixing said tail cable introduction unit on said submarine repeater; and a rubber film formed so as to cover a surface of said insulator.  
         [0020]     In accordance with the above-mentioned invention, the boundary surface between the tail cable introduction unit and the cap member is sealed using the rubber film without using conventional insulating oil. Thus, it is possible to perform highly reliable sealing without causing reduced sealing properties resulting from air bubbles generated upon using the insulating oil or reduced sealing properties resulting from a leak of the insulating oil. Further, the necessity of a complicated structure for filing the insulating oil and a troublesome step for filling is eliminated. Thus, it is possible to reduce the number of components and simplify a manufacturing step.  
         [0021]     According to another aspect of the present invention, in the feedthrough of a submarine repeater, preferably, a seal portion is formed on said rubber film so as to define an interface between said insulator and said cap member in a liquid-tight manner.  
         [0022]     According to another aspect of the present invention, in the feedthrough of a submarine repeater, preferably, a seal portion is formed on said rubber film while a film thickness thereof is larger in comparison with a film thickness of other portions so as to define an interface between said insulator and said cap member in a liquid-tight manner.  
         [0023]     In accordance with each of the above-mentioned structures, it is possible to securely seal the interface between said insulator and said cap member where high reliability is required in particular.  
         [0024]     According to another aspect of the present invention, in the feedthrough of a submarine repeater, preferably, the film thickness of said rubber film is set to be equal to or greater than 0.5 mm and equal to or less than 1.0 mm.  
         [0025]     According to another aspect of the present invention, in the feedthrough of a submarine repeater, preferably, said rubber film is formed from said tail cable introduction unit to a portion of said tail cable from said cap member, said tail cable being connected to said submarine cable extending to seawater.  
         [0026]     In accordance with this structure, it is possible to prevent infiltration of seawater into the rubber film.  
         [0027]     According to another aspect of the present invention, in the feedthrough of a submarine repeater, preferably, said cap member is made of metal.  
         [0028]     In accordance with this structure, it is possible to securely protect the tail cable introduction unit from water pressure of seawater.  
         [0029]     According to another aspect of the present invention, in the feedthrough of a submarine repeater, said insulator of said tail cable introduction unit may include polyethylene.  
         [0030]     According to another aspect of the present invention, there is provided a submarine repeater comprising: a pressure-resistant housing including a repeater unit installed therein; a pressure-resistant housing lid disposed on both sides of said repeater unit of said pressure-resistant housing, said pressure-resistant housing lid defining said repeater unit in a liquid-tight manner relative to seawater; and the above-mentioned feedthrough installed on said pressure-resistant housing lid.  
         [0031]     According to the present invention, it is possible to perform highly reliable sealing, reduce the number of components, and simplify a manufacturing step.  
         [0032]     Other objects, features and advantage of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]      FIG. 1  is a cross-sectional view showing a feedthrough as a conventional example;  
         [0034]      FIG. 2  is a cross-sectional view showing a submarine repeater as an embodiment of the present invention; and  
         [0035]      FIG. 3  is a cross-sectional view showing a feedthrough as an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]     The present invention is described in detail based on the embodiments illustrated in the drawings.  
         [0037]      FIG. 2  shows a submarine repeater  1  as an embodiment of the present invention. As shown in the figure, the submarine repeater  1  includes a repeater unit  5  stored in a pressure-resistant housing  6 . Further, a coupling unit  2  for connecting to a submarine cable  3  is disposed on both sides of the pressure-resistant housing  6 .  
         [0038]     The repeater unit  5  is fixed inside the pressure-resistant housing  6  via a radiation buffer, the pressure-resistant housing  6  being made of beryllium-copper alloy and the like and having a cylindrical shape. The radiation buffer includes a circumferential radiation buffer  8 - 1  inserted into the pressure-resistant housing  6  and end-face radiation buffers  8 - 2  installed inside the pressure-resistant housing  6  so as to hold both end faces of the circumferential radiation buffer  8 - 1  therebetween.  
         [0039]     The circumferential radiation buffer  8 - 1  is prepared by forming a thin metallic wire into a cylindrical shape with elasticity and coating an outside thereof with a thin metal sheet. The end-face radiation buffer  8 - 2  is prepared by forming a thin metallic wire into a hollow discoid shape with elasticity and coating an outside thereof with a thin metal sheet. An inside diameter thereof is sufficiently smaller than an inside diameter of the circumferential radiation buffer  8 - 1 . The circumferential radiation buffer  8 - 1  is inserted into the pressure-resistant housing  6  and the repeater unit  5  is stored further inside.  
         [0040]     The coupling unit  2  disposed between the submarine cable  3  and the repeater unit  5  includes a function of anchoring the submarine cable  3  and a function of connecting the submarine cable  3  to a tail cable  4  from the submarine repeater  1 . The coupling unit  2  is protected by a coupling housing  7  made of beryllium-copper alloy and the like.  
         [0041]     On the other hand, a pressure-resistant housing lid  10  for closing an opening in an airtight manner is disposed at openings on both ends of the pressure-resistant housing  6 . A feedthrough  20 , which is a main element of the present invention, is disposed on the pressure-resistant housing lid  10 . The tail cable  4  connected to the submarine cable  3  is introduced into the inside of the pressure-resistant housing  6  via the feedthrough  20  in an airtight manner, separated into an optical fiber  23  and a feeder line  24 , and then connected to the repeater unit  5 .  
         [0042]     In the following, a structure of the feedthrough  20  is described with reference to  FIG. 3 . In addition, as shown in  FIG. 3 , the feedthrough  20  is disposed on each of the pressure-resistant housing lids  10  disposed on both ends of the pressure-resistant housing  6 . However, each feedthrough  20  has the same structure, so that the feedthrough  20  in the right side of the  FIG. 2  is shown in  FIG. 3  and only the right-side feedthrough  20  is described.  
         [0043]      FIG. 3  shows the feedthrough  20  installed on the pressure-resistant housing lid  10  in an enlarged manner. In the figure, to the right of the pressure-resistant housing lid  10  is seawater and to the left is the inside of the pressure-resistant housing  6 . Although the seawater side has a high pressure, the inside of the pressure-resistant housing  6  is maintained at the atmospheric pressure.  
         [0044]     The tail cable  4  is constructed by successively coating a copper pipe  25  to be used as a feed line and an insulator  26  for insulating the copper pipe  25  onto a circumference of the optical fiber  23  in a laminated manner. The tail cable  4  is integrally connected to a tail cable introduction unit  22  constituting the feedthrough  20 .  
         [0045]     The tail cable introduction unit  22  includes the optical fiber  23 , the copper pipe  25 , the insulator  26 , a feed line  27 , and the like. The insulator  26  is prepared by forming resin (polyethylene, for example) and the optical fiber  23  is disposed on an axial position thereof. The optical fiber  23  is disposed so as to extend to the inside of the pressure-resistant housing  6  from the seawater side, so that the submarine cable  3  and the repeater unit  5  inside the pressure-resistant housing  6  are optically connected.  
         [0046]     The copper pipe  25  and the feed line  27  are formed so as to cover the optical fiber  23 . The copper pipe  25  and the feed line  27  are soldered, so that the copper pipe  25  and the feed line  27  are electrically connected. In accordance with this, the submarine cable  3  is electrically connected to the repeater unit  5  inside the pressure-resistant housing  6 . Further, a flange unit  28  is screwed between the copper pipe  25  and the feed line  27 , the flange unit  28  having a diameter larger than diameters of the copper pipe  25  and feed line  27 .  
         [0047]     A cap member  31  is installed on a circumferential portion of the tail cable introduction unit  22 . The cap member  31  is made of metal such as beryllium-copper alloy and the like and includes first and second members  32  and  33 . In this manner, by having the metallic cap member  31 , it is possible to securely protect the tail cable introduction unit  22  (optical fiber  23 , copper pipe  25 , insulator  26 , and feed line  27 ) from water pressure of seawater.  
         [0048]     The first member  32  is fixed on the insulator  26  positioned at an outermost circumference of the tail cable introduction unit  22  in an inner side of the housing relative to the tail cable introduction unit  22  (left side of the figure). Specifically, a corrugated concavity and convexity portion  37  is formed at an inner circumferential position of the first member  32  and when the concavity and convexity portion  37  is engaged with the insulator  26 , the first member  32  is securely fixed on the tail cable introduction unit  22 . Further, the second member  33  is fixed on the tail cable introduction unit  22  by being screwed on the first member  32  via a screw portion  41 . In accordance with this, the cap member  31  is installed on the tail cable introduction unit  22  in an integrated manner.  
         [0049]     On the other hand, on the pressure-resistant housing lid  10 , there is formed in advance a concave portion for installation allowing installation of the tail cable introduction unit  22  on which the first member  32  is fixed. After the tail cable introduction unit  22  on which the cap member  31  is fixed is installed on the concave portion for installation, the tail cable introduction unit  22  is fixed on the pressure-resistant housing lid  10  by screwing a nut  34  on a screw portion  36 .  
         [0050]     Specifically, a third stage portion  42  is formed on the second member  33  and when the nut  34  presses the third stage portion  42  to the pressure-resistant housing lid  10 , the tail cable introduction unit  22  on which the cap member  31  is fixed is fixed on the pressure-resistant housing lid  10 . Moreover, a seal member  35  is disposed on the first member  32  constituting the cap member  31 , so that the cap member  31  (tail cable introduction unit  22 ) and the pressure-resistant housing lid  10  are defined in a liquid-tight manner using the seal member  35 .  
         [0051]     When the first member  32  and the second member  33  are screwed, a first stage portion  38  formed on the first member  32  is brought into abutment with a second stage portion  39  formed on the second member  33 . In this abutment position, the metallic cap member  31  also confronts the insulator  26  (tail cable introduction unit  22 ) made of resin and seawater pressure is applied. This position is an extremely important position in which voltage resistance, water pressure resistance, and airtightness are required at the same time. Thus, high reliability is required in particular.  
         [0052]     In the present embodiment, a rubber film  60  is disposed on a position facing the insulator  26  of the tail cable introduction unit  22  and the cap member  31 . The rubber film  60  is formed so as to cover the insulator  26 . Moreover, a film thickness of the rubber film  60  is set within a range from 0.5 mm to 1.0 mm.  
         [0053]     The rubber film  60  is disposed from the position where the insulator  26 , the first member  32 , and the second member  33  are confronted with one another to a halfway position of the extended tail cable  4  (namely, up to a position in seawater) in an elongated manner. In particular, in the position where the insulator  26 , the first member  32 , and the second member  33  are confronted with one another, a seal portion  61  is formed by setting the film thickness of the rubber film  60  to be larger than the film thickness of other portions.  
         [0054]     In accordance with, in the feedthrough  20  according to the present embodiment, a boundary portion between the tail cable introduction unit  22  and the cap member  31  is sealed using the rubber film  60  without using the polybutene  140  (refer to  FIG. 1 ) as in a conventional method. Thus, it is possible to perform highly reliable sealing without causing reduced sealing properties resulting from air bubbles generated upon using the polybutene  140  or reduced sealing properties resulting from a leak of the polybutene  140 .  
         [0055]     Further, the rubber film  60  is readily installed, so that the conventional necessity of a complicated structure for filing the polybutene  140  and a troublesome step for filling is eliminated. Thus, it is possible to reduce the number of components and simplify a manufacturing step.  
         [0056]     Moreover, in the present embodiment, the seal portion  61  is formed on the interface portion where the first member  32  and the second member  33  are brought into abutment with each other and the insulator  26  is confronted. The film thickness of the seal portion  61  is set to be larger than the film thickness of other portions of the rubber film  60 , so that a structure equivalent to a structure of an  0 -ring is provided and high sealing properties are realized. Thus, by forming the seal portion  61  on the rubber film  60 , it is possible to securely seal the interface portion where high reliability is required in particular.  
         [0057]     Also, it the present embodiment, the rubber film  60  is formed to a portion of the tail cable  4  extending from the cap member  31  to the seawater side, so that it is possible to prevent seawater from infiltrating into the rubber film  60 . In this manner, even when the rubber film  60  is configured to be positioned in seawater, seawater has a high pressure, so that the rubber film  60  is brought into close contact with the tail cable  4  from the pressure. Thus, air bubbles and the like are not held inside.  
         [0058]     It is possible to apply the present invention as a sealing structure of a device disposed in an environment such as the sea bottom with a high pressure where high sealing properties are required.  
         [0059]     The present invention is not limited to the specifically disclosed embodiment, and variations and modifications may be made without departing from the scope of the present invention.