Patent Publication Number: US-8974148-B2

Title: Deployable optical fiber cartridge

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/793,589, “Deployable Optical Fiber Cartridge” filed Jun. 3, 2010, which is now U.S. Pat. No. 8,556,538, the contents of which are hereby incorporated by reference. 
    
    
     FIELD OF INVENTION 
     The application is directed towards a spool that can be used for storing a fiber in underwater applications. 
     BACKGROUND 
     Fibers such as optical fibers have been used in underwater applications to transmit and receive information. For example, an underwater device can have a propulsion system and a direction control mechanism. The underwater device can be deployed by a support ship and an optical fiber can be coupled between the underwater device and the support ship. The support ship can transmit control information to the underwater device that is used to operate the direction control mechanism. 
     SUMMARY OF THE INVENTION 
     An optical fiber is stored on a spool having a cylindrical portion and a compressible member over the cylindrical portion. The compressible member is not affected by ambient water pressure. Thus, when the spool is submerged, the water will saturate the compressible member and the water pressure will not cause the compressible member to collapse. When the optical fiber is wound on the spool, the tension will cause the compressible member to be slightly compressed. This cushioning prevents excess tension from being applied to the optical fiber. In an embodiment, the compressible member is an open cell foam. When the spool is submerged the water fills the cells and the open cell foam will not collapse under pressure. In other embodiments, the compressible member can include a mechanical spring. When submerged, the water will fill the spaces between the spring and the spool. The springs will not be compressed by the water pressure. In order to improve the movement of water into the compressible member, the spool may have holes or openings. 
     If the compressible member of the spool was made of a closed cell foam, the pressure would eventually cause the compressible member to collapse. This would cause the optical fiber to become loose on the spool and potentially tangled. In order to properly utilize the optical fiber, it must not be tangled as it is removed from the spool. 
     The spool of optical fiber may be placed on a remotely operated vehicle (ROV). As the ROV moves through the water, a feed system will pull the optical fiber from the spool at a rate that is approximately equal to or faster than the movement of the ROV. By emitting the optical fiber from the ROV, the optical fiber is essentially stationary in the water and there is no tension applied to the fiber. If the optical fiber becomes tangled, it will not go through the feed system and the movement of the ROV can create tension and possibly breakage of the optical fiber. In another embodiment, a second spool of optical fiber can be mounted in a surface structure on or adjacent to a surface support ship. A second feed system can be coupled to the second optical fiber spool. If the ship moves, the optical fiber can be released from the second spool to prevent tension in the fiber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an ROV having a spool storing an optical fiber; 
         FIG. 2  illustrates a cross section side view of a spool storing an optical fiber; 
         FIG. 3  illustrates a front view of a spool storing an optical fiber; 
         FIG. 4  illustrates a view of an end of an optical fiber; 
         FIG. 5A  illustrates a cross section side view of a spool with a tangled optical fiber; 
         FIG. 5B  illustrates a front view of a spool for storing an optical fiber; 
         FIG. 6A  illustrates a compressible cylindrical member made of closed cell foam; 
         FIG. 6B  illustrates a detailed view of closed cell foam; 
         FIG. 7A  illustrates a compressible cylindrical member made of open cell foam; 
         FIG. 7B  illustrates an enlarged view of the open cell foam; 
         FIG. 8  illustrates a compressible cylindrical member made of mechanical springs; 
         FIG. 9  illustrates a spool having water flow holes; and 
         FIG. 10  illustrates an ROV and a support boat. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is directed towards a spool for storing a fiber for underwater applications. With reference to  FIG. 1 , in an embodiment, the fiber can be an optical fiber  109  that is stored on a spool  107  that is used for communications between a support ship  103  and a Remotely Operated Vehicle (ROV)  101 . An end of the optical fiber  109  can be coupled to communications equipment on the support ship  103  and the other end of the optical fiber  109  can be coupled to communications and control equipment on the ROV  101 . 
     The spool  107  of the optical fiber  109  is stored on the ROV  101 . As the ROV  101  travels, the spool  107  can rotate which causes the optical fiber  109  to stream out of the ROV  101 . The end of the optical fiber  109  can be coupled to a rotating coupling  111  so the spool  107  can rotate freely. In an embodiment, a sensor can detect the relative velocity of the ROV  101  through the water and then control the rotational rate of the spool  107  to emit the optical fiber  109  at a rate that is substantially equal to or greater than the relative velocity of the ROV  101  through the water. 
     In an embodiment, a feeder mechanism  301  is used to remove the optical fiber  109  from the spool  107 . The spool  107  can be mounted on an axle which allows the spool  107  to rotate. The feed mechanism  301  can be coupled to a velocity sensor  303  that detects the speed of the ROV  101  through the water. The feed mechanism  301  can remove the optical fiber  109  from the spool  107  at a rate that is equal to or greater than the velocity of the ROV  101 . In order for the optical fiber  109  to be removed smoothly, the compressible cylindrical structure must maintain a constant tension on the optical fiber  109  regardless of the ambient pressure. 
     In order for the optical fiber  109  to be properly drawn from the spool  107 , the optical fiber  109  must be wrapped around the spool  107  with a small amount of tension, for example, less than  1  pound of tension. If the optical fiber  109  is loose on the spool  107 , it may become tangled as it is removed from the spool  107 . This can result in damage or breakage of the optical fiber  109 . The optical fiber  109  can have a tensile strength of about 10 pounds, however, it is very brittle and can be easily broken if bent. Thus, if the tangles to the optical fiber results in excessive tension or bending, the optical fiber  109  can very easily break resulting in a complete loss of control and communication between the ROV  101  and the support ship  103 . 
     In order to maintain a proper tension of the optical fiber  109  on the spool  107 , the optical fiber  109  can be wrapped around a compressible cylindrical structure  121 . In an embodiment,  FIG. 2  is a cross sectional view of the spool  107  at the plane A-A shown in  FIG. 3  which is a front view of the spool  107 . The spool  107  can include a rigid center cylindrical portion  115 , flanges  117  and an elastic compressible cylindrical structure  121  that surrounds the rigid center cylindrical portion  115 . In an embodiment, the outer diameter of the compressible cylindrical structure  121  may be about 5-9 inches in diameter. However, in other embodiments, the diameter can be larger or smaller. The optical fiber  109  is wrapped around the outer diameter of the compressible cylindrical structure  121 . The optical fiber  109  is wrapped at a predetermined tension around the compressible cylindrical structure  121 . In an embodiment, the tension can be between about 0.001 to 1 pounds of force. 
     With reference to  FIG. 4 , in an embodiment the optical fiber can include a core  501  that is an optical transmitter and a plastic coating  505 . In an embodiment, the core  501  may be about 10 .mu.m in diameter and can be surrounded by a coating  505  that has an outer diameter of about 125 .mu.m. In other embodiments, the core can be about 5-400 .mu.m in diameter and the coating can have a diameter of about 50-500 .mu.m. The core can be made of glass. However, in other embodiments, the core can be made of other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses as well as crystalline materials like sapphire. Silica and fluoride glasses usually have refractive indices of about 1.5, but some materials such as the chalcogenides can have indices as high as 3. Typically the index difference between core  501  and coating  505  is less than one percent. In other embodiments, the core  501  can be made of plastic optical fibers (POF) that may have a core diameter of 0.5 millimeters or larger. 
     The optical fiber  501  can have one or more coatings. An inner primary coating  505  can act as a shock absorber to minimize attenuation caused by microbending. Fiber optic coatings can be applied in various different methods. In a “wet-on-dry” process, the optical fiber passes through a primary coating application, which is then UV cured. The fiber optic coating is applied in a concentric manner to prevent damage to the fiber during the drawing application and to maximize fiber strength and microbend resistance. 
     Because the spool is being used in a pressurized underwater environment, the compressible cylindrical structure cannot be deformed by increased water pressure. The ambient pressure is directly proportional to the depth of the ROV in the water. For example, in fresh water the pressure increase is about 0.43 pounds per square inch gage (PSIG) per foot of depth and in salt water, the pressure increase is about 0.44 PSI per foot of depth. Thus, a 100 foot dive will result in an ambient pressure of 43-44 PSIG and a 5,000 foot dive will result in an ambient pressure of 2,150-2,200 PSIG. The compressible cylindrical structure  121  must be able to retain its shape and remain compressible in very high ambient pressures. With reference to  FIG. 5A , if the compressible cylindrical structure  121  is made of a material that deforms under pressure and the spool is submerged, the optical fiber  109  will become loose at a fairly shallow depth. This will cause the optical fibers  109  to be disorganized on the spool  107  and possibly tangled. As the optical fiber  109  is drawn from the spool  107 , the tension will not be uniform and the optical fiber  109  will become tangled.  FIG. 5B  is a front view of the spool  107  with flanges  117  for storing the optical fiber  109 . 
     With reference to  FIGS. 6A and 6B ,  FIG. 6A  illustrates a foam cylinder  121  and  FIG. 6B  illustrates a detailed view of the closed cell foam  549  in a small portion  551  of the cylinder  121 . Closed cell foams  549  are an example of a material that will deform under pressure. Solid foams have individual pore structures or cells that are not interconnected. Because the cells are filled with a compressible gas, when the closed cell foam  549  is exposed to high pressure, the cells collapse. As the ROV travels deeper into the water, the ambient pressure can cause the cylindrical structure  121  to be compressed. When the compressible cylindrical structure  121  compressed, the outer diameter is compressed and the optical fiber  109  will become loose on the spool  107 . Thus, a closed cell foam  549  or any other pressure compressible material should not be used as the compressible cylindrical structure  121  material. 
     With reference to  FIGS. 7A and 7B ,  FIG. 7A  illustrates another foam cylinder  121  and  FIG. 7B  illustrates a detailed view of the open cell foam structure  555  in a small portion  553  of the cylinder  121 . In contrast to closed cell foam, in an embodiment the compressible cylindrical structure  121  can be made of an open cell foam material  555 . As the ROV is submerged into a body of water, the water can fill the open cells of the compressible cylindrical structure  121 . Thus, the increased ambient pressure will not cause the cylindrical structure  121  to compress. The cylindrical structure  121  maintains the tension on the optical fiber and allows the optical fiber to be removed from the spool without becoming tangled. 
     In other embodiments, other materials or structures can be used that do not compress with ambient pressure. With reference to  FIG. 8 , in another embodiment, the spool  107  may include a plurality of springs  561  that make the cylindrical structure compressible. The springs  561  may be elongated sheets of a flexible material. When tension is applied to the optical fiber  109 , the tension will compress the springs  561  towards the center of the spool  107 . Because the springs  561  have an open design, water can freely flow around the springs  561  so that the ambient pressure does not cause the springs  561  to compress. 
     Because the optical fiber can be very closely spaced when wound on the spool, water may not flow through the optical fiber to compressible cylindrical structure of the spool easily. Similarly, if the spool is not made of a water permeable material, the water may not be able to easily reach the cylindrical structure when the spool is submerged. The water can be blocked from the inner diameter by the inner surface of the spool and the flanges can block water from the sides. 
     With reference to  FIG. 9 , in order to ease the ability of the water to reach the compressible cylindrical structure, holes  581  may be placed in the flanges  117  and/or in the cylindrical portions  115  of the spool  107 . Thus, water can flow through the holes  581  and fill the compressible cylindrical structure. If the compressible cylindrical structure is made of an open cell foam or other open construction, the water can flow through the holes  581  of the spool  107  and into the open cells or other open features of the compressible cylindrical structure. 
     With reference to  FIG. 10 , in an embodiment, the opposite ends of the optical fiber  109  can be wrapped around two separate spools or the system can use two optical fibers wound on two different spools that are connected. Each of the spools can be similar to the spool shown in  FIG. 1 . One spool can be mounted in an ROV  111  that travels away from a support ship and a second spool can be mounted close to the surface and may be connected to a support ship  103 . The ROV  111  can be a “winged submersible” that is described in U.S. Pat. No. 7,131,389 which is hereby incorporated by reference. As the ROV  111  travels away from the support ship  103 , the optical fiber  109  is removed from the spool in the ROV  111 . Similarly, as the support ship  103  moves through the water due to propulsion or current, the optical fiber  109  is removed from the second spool. Thus, the optical fiber  109  is not tensioned significantly even if the ROV  111  and the support ship  103  move. Because even a low amount of pressure may be sufficient to compress a closed cell foam, the spool  107  used with the support ship may also include a compressible cylindrical structure  121  that is not compressed by ambient fluid pressure. 
     It will be understood that the inventive system has been described with reference to particular embodiments, however additions, deletions and changes could be made to these embodiments without departing from the scope of the inventive system. Although the systems that have been described include various components, it is well understood that these components and the described configuration can be modified and rearranged in various other configurations.