Patent Publication Number: US-2011052121-A1

Title: Fiber ball lens apparatus and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/143,453 filed on Jan. 9, 2009 and U.S. Provisional Patent Application No. 61/251,441 filed on Oct. 14, 2009 in the U.S. Patent and Trademark Office, the disclosures of which are incorporated herein in their entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Methods consistent with the present invention relate to a process for making ball lenses on optical fibers. Ball lenses may be used with optical fibers to aid in focusing light emanating from an optical fiber, coupling light between adjacent optical fibers, and to reduce the precision required when coupling a free space laser and an optical fiber. This results in ball lenses of a non-homogenous structure exhibiting poor focus control. Accordingly, the methods of manufacturing ball lenses in the related art are not capable of controlling the manufacture of ball lenses with precision and produce ball lenses exhibiting inferior performance. 
     Thus, there is a need for an improved ball lens method for manufacturing a ball lens and an improved ball lens device having a homogenous construction. 
     SUMMARY OF THE INVENTION 
     An aspect of the invention is to provide an apparatus for coupling a free laser and an optical fiber that requires less precision in alignment and exhibits improved thermal characteristics. 
     In accordance with an aspect of the present invention, a method for forming a ball lens including determining a feed length of optical fiber based on a target ball lens diameter; providing heat energy to a heating zone; moving, at a predetermined speed, one of the optical fiber and the heating zone so that the end of the optical enters the heating zone to heat the end of the optical fiber; and stopping the heating of the end of the optical fiber when the amount of moving the one of the optical fiber and the heating zone equals the determined feed length. 
     The predetermined speed may be determined based on the amount of heat energy provided and the diameter of the optical fiber from which the ball lens is formed. The heating of the optical fiber may be stopped by shutting off the heat energy or by removing the optical fiber from the heating zone. 
     The method may also include rotating the optical fiber during the heating of the end of the optical fiber. 
     In accordance with another aspect of the present invention, an apparatus is provided that include an optical fiber heating apparatus that provides heat energy and conveys an optical fiber into a heating zone heated by the heat energy; a parameter determination unit that determines a feed length of optical fiber based on a target ball lens diameter; an optical fiber heating apparatus controller that controls the optical fiber heating apparatus to heat the optical fiber and convey the optical fiber the determined feed length. 
     The optical fiber may be conveyed into the heating zone by moving the optical fiber into a stationary heating zone or by moving heating zone onto a stationary optical fiber. Alternatively, the optical fiber may be conveyed into the heating zone by a combination of movement of both the optical fiber and the heating zone. 
     The heating apparatus may also be configured to rotate the optical fiber about an optical axis of the optical fiber during the heating of the optical fiber. 
     The heating apparatus may also be configured to stop the heat energy when the optical fiber is conveyed the determined feed length. 
     In accordance with an aspect of the present invention, a method for forming a ball lens including providing a coreless optical fiber and a second optical fiber different from the coreless optical fiber; splicing the coreless optical fiber to the second optical fiber to form a spliced optical fiber; severing the spliced optical fiber in a portion of the coreless optical fiber at a predetermine distance from a splice point of the spliced optical fiber; determining a feed length of the spliced optical fiber based on a target ball lens diameter; providing heat energy to a heating zone; moving, at a predetermined speed, one of the spliced optical fiber and the heating zone so that the coreless end of the spliced optical fiber enters the heating zone to heat the end of the spliced optical fiber; stopping the heating of the end of the spliced optical fiber when the amount of moving the one of the spliced optical fiber and the heating zone equals the determined feed length. 
     The method may also determine the predetermined speed based on an amount of heat energy provided and a diameter of the spliced optical fiber. 
     It is an aspect of the present invention that the heat energy applied to the spliced optical fiber melts the spliced optical fiber to form a molten ball. 
     The method may stop the heating by either shutting off the heat energy or by removing the optical fiber from the heating zone. 
     The method may also include rotating the optical fiber during the heating of the end of the spliced optical fiber. 
     In accordance with another aspect of the present invention, an optical fiber having a ball lens is provided including a spliced optical fiber including a coreless optical fiber spliced to a second optical fiber; a ball lens attached to the coreless optical fiber, wherein the ball lens is formed of the same material as the coreless optical fiber. The second optical fiber may have a core. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects of the invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  shows an example of a method for forming a ball lens on an optical fiber; 
         FIG. 2  shows an example of another method for forming a ball lens on an optical fiber; 
         FIG. 3  shows an apparatus for forming a ball lens on an optical fiber; 
         FIG. 4  shows an apparatus for forming a ball lens an optical fiber formed by splicing two different optical fiber structures; 
         FIG. 5  shows an apparatus for forming a ball lens and the effects of gravity on the ball lens being formed; 
         FIG. 6  shows an apparatus for forming a ball lens and the effects of gravity on a spliced optical fiber; 
         FIG. 7  shows an apparatus for forming a ball lens while rotating the optical fiber; 
         FIG. 8  shows an apparatus for forming a ball lens while rotating the optical fiber; 
         FIG. 9  shows an apparatus for forming a ball lens on a vertically positioned optical fiber; 
         FIG. 10  shows an apparatus for forming a ball lens on a vertically positioned optical fiber using a laser heat source; 
         FIG. 11  shows an apparatus for forming a ball lens using a filament as a heat source; 
         FIG. 12  shows an apparatus for forming a ball lens on a vertically positioned optical fiber using a laser heat source by moving the laser heat source; 
         FIG. 13  shows a general configuration apparatus for forming a ball lens on an optical fiber; 
         FIG. 14  shows a method for forming a ball lens on an optical fiber; 
         FIG. 15  shows another method for forming a ball lens on an optical fiber; 
         FIG. 16  shows a cross section of an optical fiber; 
         FIG. 17  shows another method of forming a ball lens on an optical fiber. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Hereinafter the exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     The first exemplary embodiment of the present invention provides a method of forming a ball lens  105  on an optical fiber  100 . Generally, according to this exemplary embodiment, a ball lens  105  is formed on an optical fiber  100  by moving an end of the optical fiber  100  in relation to a heat source. As shown in  FIG. 1 , the heat source may comprise an arc discharge generated by a pair of electrodes  300 . In order to form a ball lens  105  on the optical fiber  100 , the heat source melts a portion of the end of the optical fiber  100 . When the portion of the optical fiber  100  is melted into a liquid form, the surface tension of the liquid forms a ball of melted optical fiber material at the end of the optical fiber  100 . Consequently, the heat source should be capable of generating temperatures within the optical fiber that exceed the melting temperature of the material or materials forming the optical fiber  100 . If the optical fiber  100  is horizontal, the optical fiber  100  may be rotated to minimize gravitation effects on ball lens formation. 
     A method for making a ball lens according to an exemplary embodiment of the present invention is shown in  FIG. 14 . The amount of fiber required to make a desired ball lens size is determined as an optical fiber feed length in operation  15 . The length of fiber to be melted may be determined based on the desired ball lens size and the diameter of the optical fiber  100 . The volume of the ball lens and volume of a certain length of fiber may be determined using equations (1) and (2) below: 
       Fiber volume=πr 2 L  (1)
 
       Ball Lens volume=(4/3)π R   3   (2)
 
     where: 
     r—optical fiber radius 
     R—ball lens radius 
     L—length of optical fiber 
     Accordingly, the length of fiber L required to make a ball lens having a diameter D may be determined using equation (3): 
       L=2D 3 /3 d   2   (3)
 
     After determining the feed length of the optical fiber required to make a ball lens of a certain size, heat energy is provided to a heating zone in operation  25 . After the heating zone is generated, the optical fiber is conveyed to the heating zone in operation  35 . The heat energy heats the end of the optical fiber as it enters the heating zone to melt the optical fiber. The rate of conveying the optical fiber is determined based on the amount of heat energy, the thermal properties of the optical fiber and the size of the optical fiber. Generally, higher heat energy will enable faster conveyance rates and larger optical fibers will require lower conveyance rates. The conveying of the optical fiber may be performed by moving the optical fiber toward a stationary heating zone, or alternatively, moving the heating zone toward a stationary optical fiber. After the amount of conveyance meets the determined feed length, the heating is stopped in operation  45 . 
     In one example, an optical fiber having a diameter of 125 μm was used to make a ball lens having a diameter of 370 μm. The total feeding length of the optical fiber was 2100 μm. The fiber was conveyed at a speed of about 70 μm per second with a rotation of about 6 degrees per second. 
     A method of forming a ball lens according to another exemplary embodiment is shown in  FIG. 15 . In the case where the optical fiber is disposed in a horizontal position, gravity may case the molten ball to sag or bend downward. If the ball lens is to be used in an application where such an effect is undesirable, the ball lens may be made using the method shown in  FIG. 15  to reduce or eliminate the effects due to gravity. This method is substantially similar to the method as described above with reference to  FIG. 14 . However, to reduce the effects of gravity during the heating process, the optical fiber is rotated in operation  55 . The rotation continues during the conveying of the optical fiber into the heating zone and may continue until after the heating has ceased. 
       FIG. 13  is an example of an apparatus for forming a ball lens on an optical fiber  100 . Generally, the apparatus includes an optical fiber heating apparatus  30  that provides heat energy and conveys an optical fiber  100  into a heating zone heated by the heat energy. The apparatus also includes a parameter determination unit  10  that determines a feed length of optical fiber based on a target ball lens diameter. The feed length may be set manually or determined in accord with any of the methods described herein. The apparatus also includes an optical fiber heating apparatus controller  20  that controls the optical fiber heating apparatus  30  to heat the optical fiber  100  and convey the optical fiber the determined feed length. 
       FIG. 3  an example of an apparatus capable of performing the method outlined above. As shown in  FIG. 3 , the method of forming a ball lens  105  on an optical fiber  100  may include heating the optical fiber  100  by moving the optical fiber  100  along its optical axis to heat an end of the optical fiber  100 , such as by an arc discharge  200  from a pair of fixed electrodes  300  disposed on opposite sides of the optical fiber  100 . For example, when the end of the optical fiber  100  enters the heat source, i.e., arc discharge  200 , a portion of the end of the optical fiber  100  is melted into a liquid. As a result of the surface tension of the liquid, a ball is formed on the end of the optical fiber  100 . When the ball cools and solidifies, a ball lens  105  is formed on the end of the optical fiber  100 . 
     In the apparatus shown in  FIG. 3 , a clamp  410  is used to clamp the optical fiber  100  on one side of the electrodes  300 . The clamp  410  is affixed to a movable translation stage  400 . The movable translation stage  400  is mounted onto a bearing  420  which allows motion relative to a base  450 . If the electrodes  300  are fixed to the base  450 , the translation stage thereby moves the end of the optical fiber  100  adjacent to the electrodes  300  and through the heating field of the arc discharge  200  generated by the electrodes  300 . 
     If the optical fiber  100  is held in a horizontal orientation during the heating as shown in  FIG. 3 , ball formed at the end of the optical fiber  100  may sag due to gravity. This is illustrated in the ball lens  105  at the end of the optical fiber  100  in  FIG. 5 . 
     In some cases, the sag of the ball lens  105  may be beneficial. For example, the sag results in some ball bending which may reduce the back-reflection from the ball end. On the other hand, if an application requires a straight optical axis and symmetric positioning of the ball lens  105 , the ball sag may be undesirable. 
     In another exemplary embodiment of the present invention, this sagging may be prevented by a method and apparatus in which the optical fiber  100  is rotated during the heating. As shown in  FIG. 7 , the optical fiber  100  is again held horizontally. In the exemplary embodiment shown in  FIG. 7 , the sagging of the ball may be prevented by rotating the optical fiber  100  in a circular direction  480  about its optical axis during the heating. If the optical fiber  100  is rotated while being heated, the gravitational effect will be balanced and counteracted. This may be accomplished by integrating rotation mechanisms into the clamp  410  which clamp the optical fiber  100 . Additionally, the sagging may also be prevented by mounting the apparatus so that the fiber is fed into the heat source, i.e., arc discharge  200 , in a vertical direction.  FIG. 12  shows the apparatus of  FIGS. 3 ,  5  and  7  mounted in this fashion. 
     When the optical fiber  100  is oriented vertically, the gravitational force is directed along the axis of the optical fiber  100  and there is no tendency for the ball at the end of the optical fiber  100  to sag with respect to the optical axis as it is heated. With the optical fiber mounted vertically, such as when the configuration of  FIG. 3  is mounted as shown in  FIG. 12 , the movable translation stage  400  moves vertically and carries the clamp  410  and the optical fiber  100 , thereby translating the end of optical fiber  100  vertically toward the electrodes  300  and into the heating field of the arc discharge  200 . Once again, the movable translation stage  400  is attached to a bearing  420  and translated relative to a base  450  to which the electrodes  300  are affixed. Because gravity affects the ball formed at the end of optical fiber  100  uniformly along its optical axis, the sagging of the optical fiber  100  shown in  FIG. 5  may be prevented. 
     Any other suitable heat source may be used to heat the optical fiber  100  sufficiently to melt the end of the optical fiber  100  to form a ball lens  105 . As shown in  FIGS. 10 and 12 , a laser  500  may be used in the apparatuses and methods described above as the heat source for melting the optical fiber  100  to form a ball lens  105  at the end of the optical fiber  100 . In this case the laser beam  510  is shaped and controlled by optical elements such as a lens  520 , and the laser beam  510  may be directed towards the optical fiber  100  by a mirror  530  so that the concentrated and focused optical fiber creates a heating area  540  which heats the end of the optical fiber  100 . 
     Alternatively, a gas flame may be used as the heat source to melt the optical fiber  100 . Also, as shown in  FIG. 11 , a filament  700  may be used as the heat source to melt optical fiber  100 . Such filaments have been employed for splicing optical fibers, as well as for other fiber-related tasks. For these applications, the filament is typically shaped like the Greek letter Omega and the optical fiber  100  is disposed to pass through the center of the filament  700  as shown in  FIG. 14 . If the end optical fiber  100  is translated along its optical axis in the direction  710  shown in  FIG. 14  such that it passes through the filament  700 , the end of the optical fiber  100  may be heated and a ball lens  105  formed. 
     Another exemplary embodiment of an apparatus for performing a method of the invention is shown in  FIG. 12 . In this case, the optical fiber  100  is held stationary with respect to the base  450  by the use a clamp  410 , and the heat source is moved relative to the optical fiber  100 . In the example shown in  FIG. 12 , the heat source is a laser  500  with a lens  520  and a mirror ( 530 ). The laser  500 , the lens  520 , and the mirror  530  are mounted to the movable translation stage  400  which is attached to a bearing  420 . The bearing  420  allows motion relative to the base  450 . Translation of the movable translation stage  400  therefore moves the laser  500 , the lens  520 , and the mirror  530  so that the laser beam  510  and the concentrated and focused heating area  540  scanned along the optical axis of to the end of the optical fiber  100 . 
     An appropriate combination of heating power and conveying speed is different for different types and sizes of optical fibers. These parameters also vary based on the specifications of the heating apparatus used to perform the ball lens forming method described above. 
     According to another exemplary embodiment, a method is provided for forming a ball lens which utilizes both a coreless optical fiber  101  and an optical fiber  100 . A typical optical fiber for telecommunications use is shown in  FIG. 16  and includes a core  130  surrounded by a cladding  120  that is surrounded by a protective coating  110 . The cladding  120  is typically pure silica glass. The core  130  is typically doped with trace amounts of germania in order to raise the index of refraction of the core  130  relative to the cladding  120 . The coating  110  is typically an acrylate plastic material that serves to protect the glass optical fiber from damage. 
     Consequently, when the typical optical fiber is melted to form a ball lens, the core material remains in the ball lens leading to an inhomogeneous ball lens material distribution. This may lead to poor focus control of the ball lens. As aspect of this embodiment is to utilize a coreless optical fiber  101  to form the ball lens  105  of a relatively homogeneous material distribution. As a result, a ball lens  105  can be formed which has improved focus control. 
     The ball lens  105  of this embodiment may be formed using the any of the methods set forth above. However, this embodiment differs in the initial preparation of the optical fiber. As shown in  FIG. 2 , the optical fiber is formed by splicing a coreless optical fiber  101  to another optical fiber  100 . The optical fiber  100  may be of any configuration, i.e., an optical fiber having a core, a single clad optical fiber, a double clad optical fiber, etc. However, splicing would not be required if the optical fiber  100  is of the same configuration as the coreless optical fiber  101 . Thus, according to this method a coreless optical fiber  101  is spliced to another optical fiber  100  using a heating source, such as an arc discharge formed by electrodes  300 . After the splicing operation, a portion of the coreless optical fiber  101  positioned away from the splice point  106  and severed. The coreless optical fiber  101  may be severed using the arc discharge from the electrodes  300 . The distance in which the severing occurs from the splice point  106  may correspond to the amount of fiber required to form the ball lens of a particular diameter. However, this length may be greater wherein a predetermined portion of the coreless optical fiber extends between the ball lens  105  and the splice point  106 . 
     A ball lens  105  is then formed on the spliced optical fiber which includes a coreless optical fiber  101  and another optical fiber  100 . The ball lens  105  may be formed by any of the methods and apparatuses described above by inserting the coreless optical fiber end of the spliced optical fiber into a heating zone generated by the arc discharge of electrodes  300 . 
     A method for making a ball lens according to this exemplary embodiment of the present invention is shown in  FIG. 17 . Both a coreless optical fiber  101  and another optical fiber  100  are provided in operation  65 . Then the coreless optical fiber  101  is spliced to the other optical fiber  100  in operation  75 . After the coreless optical fiber  101  is spliced to the other optical fiber  100 , the spliced optical fiber is severed in the coreless optical fiber portion at a distance from the splice point  106  in operation  85 . Finally, a ball lens is foamed on the coreless optical fiber end of the spliced optical fiber in operation  95 . The ball lens  105  may be formed using any of the methods and apparatuses described above. 
       FIG. 4  an example of an apparatus for performing the method outlined above. As shown in  FIG. 4 , an arc discharge  200  is generated by a pair of fixed electrodes  300 . The coreless optical fiber  101  placed adjacent to the other optical fiber  100  and heated using the arc discharge  200  for form a splice at the splice point  106  (shown to the right of the arc discharge in  FIG. 4 ). In the apparatus shown in  FIG. 4 , two clamps  410  are used to clamp the coreless optical fiber  101  and the other optical fiber  100  on either side of the electrodes  300 . The two clamps  410  are affixed to a movable translation stage  400 . The movable translation stage  400  is mounted onto a bearing  420  which allows motion relative to a base  450 . If the electrodes  300  are fixed to the base  450 , the translation stage thereby moves the optical fiber  100  past the electrodes  300  and through the heating zone of the arc discharge  200 . After the splicing operation is completed, the spliced optical fiber is moved to the right in  FIG. 3  by a predetermined distance and the spliced optical fiber is severed in the coreless portion of the optical fiber using the heat source, i.e., arc discharge. Then, as set forth above with regard to  FIGS. 4 and 7 , a ball lens is formed on the coreless end of the spliced optical fiber. 
     If the optical fiber  100  is held in a horizontal orientation during the heating, the optical fiber  100  may sag due to gravity. This is illustrated by the sagging portion  190  of the optical fiber  100  in  FIG. 6 . If the optical fiber  100  sags and no longer has a straight optical axis, optical power carried by the optical fiber may be lost. 
       FIG. 8  shows a method of preventing the sagging problem described above. As shown in  FIG. 8 , the optical fiber  100  is held horizontally. Here, the sagging may be prevented by rotating the optical fiber  100  and the coreless optical fiber  101  in a circular direction  480  about its optical axis during the heating. If the optical fiber  100  is rotated while being heated, the gravitational effect will be balanced and counteracted. This may be accomplished by integrating rotation mechanisms into the two clamps  410  which clamp the optical fiber  100  and the coreless optical fiber  101 . 
       FIG. 9  shows another method of preventing the sagging problem described above. As shown in  FIG. 9 , the optical fiber  100  and the coreless optical fiber  101  may be oriented vertically. In this case the gravitational force is directed along the axis of the optical fibers and there is no tendency for the optical fibers to bend as they are heated. With the optical fiber mounted vertically as shown in  FIG. 9 , the movable translation stage  400  moves vertically and carries the two clamps  410 , the optical fiber  100  and the coreless optical fiber  101 , thereby translating the optical fibers vertically past the electrodes  300  and through the heating field of the arc discharge  200 . Once again, the movable translation stage  400  is attached to a bearing  420  and translated relative to a base  450  to which the electrodes  300  are affixed. Because gravity affects the optical fibers uniformly along their optical axis, the sagging of the optical fibers may be prevented. 
     Any other suitable heat source may be used to heat the optical fibers sufficiently to form the splice and the ball lens. In another exemplary embodiment of the invention as shown in  FIG. 103 , a laser  500  is used as the heat source for splicing the coreless optical fiber  101  to the other optical fiber  100 , and also forming the ball lens on the coreless end of the spliced optical fiber. In this case the laser beam  510  is shaped and controlled by optical elements such as a lens  520 , and the laser beam  510  may be directed towards the optical fibers by a mirror  530  so that the concentrated and focused optical fiber creates a heating area  540  which heats the optical fibers. 
     Alternatively, a gas flame may be used as the heat source to round the optical fibers. Also, as shown in  FIG. 11 , a filament  700  may be used as the heat source to splice the optical fibers and form the ball lens. Such filaments have been employed for splicing optical fibers, as well as for other fiber-related tasks. For these applications, the filament is typically shaped like the Greek letter Omega and the optical fibers  100  are disposed to pass through the center of the filament  700  as shown in  FIG. 11 . If the optical fiber  100  is translated along its optical axis in the direction  710  shown in  FIG. 11  such that is passes through the filament  700 , a section of the optical fiber may be heated. 
     Another exemplary embodiment of the invention is shown in  FIG. 12 . In this case, the optical fibers are held stationary with respect to the base  450  by the use of two clamps  410 , and the heat source is moved relative to the fiber. In the example shown in  FIG. 12 , the heat source is a laser  500  with a lens  520  and a mirror  530 . The laser  500 , the lens  520 , and the mirror  530  are mounted to the movable translation stage  400  which is attached to a bearing  420 . The bearing  420  allows motion relative to the base  450 . Translation of the movable translation stage  400  therefore moves the laser  500 , the lens  520 , and the mirror  530  so that the laser beam  510  and the concentrated and focused heating area  540  are positioned along the optical axis of the optical fibers at the appropriate portions. 
     The present invention is described hereinafter with reference to flowchart illustrations of user interfaces, methods, and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart block or blocks. These computer program instructions may also be stored in a computer usable or computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer usable or computer-readable memory produce an article of manufacture including instruction means that implement the function specified in the flowchart block or blocks. The computer program instructions may also be loaded into a computer or other programmable data processing apparatus to cause a series of operational steps to be performed in the computer or other programmable apparatus to produce a computer implemented process such that the instructions that execute in the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. 
     And each block of the flowchart illustrations may represent a module, segment, or portion of code, which includes one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of order. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in reverse order, depending upon the functionality involved. 
     Although a few exemplary embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.