Abstract:
A light module, a fiber optic connector, and a system that each include a screw in communication with an optical fiber that is movable such that the optical fiber may be deformed to a desired level in order to control encircled flux by extinguishing undesired modes of light launched through the optical fiber.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims the benefit of priority of U.S. Provisional Patent Application Ser. No. 61/279,597, filed on Oct. 23, 2010. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the transmission of optical signals through optical fibers, and in particular to methods, devices and systems for controlling the encircled flux of optical signals transmitted through optical fibers to achieve repeatable, consistent optical fiber testing. 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention pertains to transmission of optical signals through optical fibers. Optical signals are transmitted by applying a light source to an optical fiber. The light source and the optical fiber must be appropriately aligned with one another in order to couple as much light as possible into the optical fiber. Light sources may be aligned to two different types of optical fibers, single-mode optical fibers and multi-mode optical fibers. Single-mode optical fibers can accommodate only one mode of light. Multi-mode optical fibers can simultaneously accommodate numerous modes of light. Some of these modes are located near the center of the fiber core and some closer to the cladding interface. The low-order modes are located near the center of the fiber core and are relatively stable as compared to the high-order modes closer to the cladding interface. The modal power distribution, i.e. which modes are excited upon introduction of the light source to the optical fiber, defines the “launch condition.” 
         [0004]    Controlling launch conditions helps to control the optical power loss across a fiber link, commonly referred to as “link loss.” It has been found that link loss is directly related to launch conditions and that carefully controlling launch conditions within well defined parameters is one way to stabilize link losses. If the launch condition is such that too many modes are excited, then the optical fiber will be overfilled and produce link loss measurements that are too high. Thus the loss reading may be overestimated, leading to loss value that will not correspond to reality. If the launch condition is such that too few modes are excited, then the optical fiber will be underfilled and produce link loss measurements that are too low. This may produce misleading and overly optimistic results. Therefore, to achieve repeatable, consistent fiber optic testing, it is desirable to control launch conditions such that only the desired modes are excited. 
         [0005]    Encircled Flux (EF) is a parameter that characterizes the launch conditions of a multi-mode light source. EF is a radial integration of the power distribution in the optical fiber, going from zero at the center to unity at the core boundary, with a definitive set of radial power templates at 850 nm and 1300 nm. EF describes the intensity of the light encircled within a fiber core radius when light is launched into a multi-mode optical fiber. Thus, EF will vary with changes in light source, optical fiber, or how the light source is coupled with the optical fiber, i.e. the launch conditions. 
         [0006]    Controlling launch conditions, and thus EF, can be very challenging. This is especially true considering certain exacting specifications required by the Telecommunications Industry Association (TIA), Electronic Industries Alliance (EIA), and the International Standards Organization (ISO, originator of ISO 14763-3, which details systems and methods to inspect and test optical fiber cabling). Several methods currently exist. 
         [0007]    One method for controlling launch conditions is mandrel wrapping. This method is used when a light source, such as LED, emits light over an area larger than the typical multi-mode fiber core. This overfills the core, exciting both low-order and high-order modes. In this situation, the high-order modes may be removed by tightly wrapping the launch cable around an industry standard round mandrel. The tight bends extinguish the undesirable modes leaving the desired launch condition. 
         [0008]    Although mandrel wrapping is able to achieve the desired results, this method has its disadvantages. Determining the correct size of the mandrel and how many turns of the mandrel are appropriate can be challenging. Several factors, such as optical fiber characteristics and desired modal distribution must be considered in reaching this decision. Mandrel wrapping is also highly dependent on operator skills for accuracy, as there must be no overlapping turns and no tension beyond that which is required to maintain contact between the optical fiber and the mandrel. Finally, and most importantly, fiber optic equipment manufacturers who design fiber optic light sources for use in their products have recently begun to specify ISO 14763-3 compliance for EF directly from the light source, without the use of external launch manipulation such as mandrel wrapping. Therefore, other methods are needed to comply with these requirements. 
         [0009]    One alternative method for controlling launch conditions is described in U.S. Pat. No. 7,139,454. This patent describes an optical element from which light rays may impinge on a core or face of an optical fiber which may be a multimode optical fiber. Rays may propagate through the optical fiber and exit the optical fiber at its core or face as light rays or signals. The light rays or signals may be conditioned into light rays or signals to make high speed transmission through optical fibers or other medium possible. Two characteristics of the optical element, taken singly or in combination, may produce the light launch profile on the fiber face core and maintain robust compliance with the EF conditions of the TIA specification. First, one surface of the optical element may have a slope discontinuity at an optical axis. This characteristic provides an axicon function to the optical element. Second, the optical element is defocused relative to the face of the core at the fiber end. 
         [0010]    This method also has drawbacks. Specifically, the optical element in either of the embodiments mentioned above is very delicate. It must be manufactured at significant expense to exacting standards. Any manufacturing imperfection, including scratches, smudges, and thickness variability will render the optical element unusable for its purpose. Moreover, given the precision with which the optical element must be applied to the optical system, even a perfectly manufactured optical element may easily be misaligned or otherwise positioned incorrectly to achieve the desired results. 
         [0011]    Other products that control launch conditions include those that use specialty jumpers. One such product is the Arden Photonics “ModCon” modal controller for multimode optical fiber. However, this product is a jumper that is added to a light source and is not adapted to allow a light source to meet the ISO 14763-3 standard for EF directly from the light source without the use of external launch manipulation. 
         [0012]    Therefore, there is a need for a method for controlling EF that does not present the aforementioned drawbacks. Unlike mandrel wrapping, it should not be difficult to select the correct equipment and it should not rely heavily on operator skill. Moreover, there is a need for devices that do not use external launch manipulation like mandrel wrapping. Unlike optical elements, the equipment necessary should be inexpensive, not easily damaged, and easy to apply to an optical system. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention includes a light module, a fiber optic connector, and a system, each of which includes a movable member, preferably a screw, to controllably deform an optical fiber in order to condition modes. The invention also includes a method for controlling EF through the controlled deformation of an optical fiber. 
         [0014]    In its most basic form, the light module is a conventional fiber optic light module that has an output port that includes a substantially hollow casing. An optical fiber passes through the casing of the output port of the light module, which supports the optical fiber at both ends. The casing is dimensioned to align the optical fiber at both ends thereof and to allow the optical fiber to be deformed within the space between the ends of the casing. A screw is threaded through the casing such that it is in contact with the optical fiber. The screw is dimensioned to contact the optical fiber and exert downward pressure upon it when the screw is advanced in order to deform the optical fiber and, consequently, change the EF of the light passing through the optical fiber. 
         [0015]    In the preferred embodiment, the light source is a light module commonly used within a fiber optic test instrument. This light module combines one or more beams of light and launches the resultant beam into the optical fiber. This optical fiber extends through the output port of the light module, which includes the casing through which the screw is disposed. A tapered strain relief may be attached to the output port to further guide the optical fiber out of the light module and to aid in alleviating strain on the optical fiber. The optical fiber may then be connected through the fiber optic test instrument to another optical fiber to be tested. After the screw face is polished, the screw is brought into contact with the optical fiber through the output port of the light module and is moved downward to controllably apply pressure on the optical fiber. Other than creating the entry point for the screw through the output port of the light module and polishing the screw face, no further modification to the output port, screw, or optical fiber is necessary. As the casing holds the optical fiber in a substantially fixed position at its entry and exit, this pressure causes the optical fiber to deform and alters the EF of the light passing through the optical fiber. 
         [0016]    During manufacture of the light module, the screw may easily be adjusted until the desired EF is achieved, and then permanently affixed in place with epoxy or other known methods of permanently affixing screws in a stationary position. The screw adjustment typically requires three to five turns of the screw once the screw is positioned in contact with the optical fiber. The modified light module, having the affixed screw and the desired EF, is then used within a fiber optic test instrument. Thus, the instrument provides a desired EF without external launch manipulation, like mandrel wrapping, and will produce repeatable, consistent launches with the desired EF in the field. 
         [0017]    The fiber optic connector of the present invention adjusts the EF in substantially the same manner as the light module discussed above, but is adapted for external attachment to the fiber port of a conventional fiber optic test instrument. In its most basic form, the connector includes a hollow casing, a fiber port extending from one end of the casing and a fiber port connector extending from the opposite end of the casing and dimensioned to mate with a fiber port of a conventional fiber optic test instrument. The fiber port and fiber port connector each include fiber openings that are aligned with one another. An optical fiber passes through the fiber opening in the fiber port connector and the casing and terminates within the opening in the fiber port. The casing supports the optical fiber at both ends and is dimensioned to align the optical fiber at both ends thereof and to allow the optical fiber to be deformed within the space between the ends of the casing. A screw is threaded through the casing such that it is in contact with the optical fiber. The screw is dimensioned to contact the optical fiber and exert downward pressure upon it when the screw is advanced in order to deform the optical fiber and, consequently, changes the EF of the light passing through the optical fiber until it reaches a desired result. 
         [0018]    The fiber port connector of the fiber optic connector is attached to the fiber port of a conventional fiber optic test instrument such that the optical fiber within the fiber optic connector abuts an optical fiber within the fiber port of the test instrument. The instrument is then energized, which causes light to be emitted through the optical fiber within the fiber optic connector. The EF of this light is measured and the screw through the casing is adjusted until the desired EF is achieved. The screw may then be permanently affixed in place with epoxy or other known methods of permanently affixing screws in a stationary position, or it may be left unsecured so that it may subsequently be used with other fiber optic test instruments. 
         [0019]    The system of the present invention includes a fiber optic test instrument, either having a light module of the present invention disposed within the fiber optic test instrument&#39;s casing, or a fiber optic connector of the present invention attached to the fiber optic test instrument&#39;s fiber port, combined with a power meter. In the preferred embodiment of the system, the power meter is a portable power meter, such as is commonly used in the art of fiber optic testing. The fiber optic test instrument and power meter are applied to each end of an optical fiber. The device launches light with a desired EF through the optical fiber and the power meter measures the link loss across that optical fiber. As each launch of the device will have the desired EF, repeatable, consistent testing may be achieved. 
         [0020]    The method for controlling EF includes the steps of applying a light through an optical fiber of a light source, disposing a screw through the output port of the light source such that the screw contacts the optical fiber such that it may apply variable pressure on the optical fiber such that it is deformed, and adjusting the screw until the optical fiber is deformed such that the desired EF is obtained. 
         [0021]    Therefore, it is an aspect of the invention to provide an inexpensive and robust alternative to current methods and devices for controlling EF. 
         [0022]    It is a further aspect of the present invention to provide an alternative to current methods and devices for controlling EF that is easy to use, thus relying little on operator skill. 
         [0023]    It is a further aspect of the present invention to provide a method and/or device for controlling EF that may be easily adapted to existing fiber optic testing equipment. 
         [0024]    It is a further aspect of the present invention to provide a device that provides launches of a specified EF without external launch manipulation. 
         [0025]    These aspects of the present invention are not meant to be exclusive and other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0026]      FIG. 1  is a cut away side view of a prior art light module. 
           [0027]      FIG. 2A  is a cut away side view of a light module in accordance with the present invention with the optical fiber in an undeflected position. 
           [0028]      FIG. 2B  is a cut away side view of a light module in accordance with the present invention with the optical fiber in a deflected position. 
           [0029]      FIG. 3  is a cut away side view of a fiber optic connector in accordance with the present invention. 
           [0030]      FIG. 4A  is a cut away side view of a prior art portable light source having a conventional light module. 
           [0031]      FIG. 4B  is a cut away side view of a portable light source to which the fiber optic connector of the present invention is attached. 
           [0032]      FIG. 5  is a graph showing the measured EF before and after adjustment and the upper and lower limits of acceptable EF. 
           [0033]      FIG. 6A  is a cut away side view of one embodiment of the system of the present invention in which the light source includes a light module of the present invention. 
           [0034]      FIG. 6B  is a cut away side view of one embodiment of the system of the present invention in which the light source includes the fiber optic connector of the present invention. 
           [0035]      FIG. 7  is a block diagram depicting the steps of the method of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    Referring first to  FIG. 1 , an illustration of a prior art light module  10  is shown. The light module  10  shown in  FIG. 1  is a type commonly used within fiber optic test instruments. Examples of such light modules are the FOD 3105 Dual LED Module, the FOD 3206 Laser Diode Module, and the FOD 3226 Triple LD Module, manufactured by Fiber Optic Devices of Vilnius, Lithuania. These light modules may have single or multiple light sources and may produce light of any wavelength. Such a light module may be used within any portable or stationary fiber optic test instrument, such as the EXFO FLS-300 Light Source, the FOD 2114 Triple Laser Light Source, the AFL Telecommunications Noyes® OLS1-Dual LED Light Source with Wave ID, the EXFO IQS-2100 Light Source, and the EXFO FLS-2200 Broadband Source, that may test single or multi-mode optical fibers. 
         [0037]    The light module  10  of  FIG. 1  is a dual light emitting diode (LED) light module that includes a housing  12 , two LEDs  14  and  16  from which power leads  18  and  20  extend respectively, and an output port  34  dimensioned to accept an optical fiber  30 . Output port  34  may include a strain relief  35  and an output connector  37  that joins the output port  34  to the housing  12 . First LED  14  and second LED  16  extend into the inside  13  of the housing  12  and are disposed such that each is in substantially perpendicular relation to the other. Lenses  15  and  17  are affixed adjacent to LEDs  14  and  16  respectively within the inside  13  of the housing  12 . Transparent tubes, preferably glass tubes  19  and  21 , connect LEDs  14  and  16  respectively with two sides of transparent glass cube  27 . A transparent cube, preferably glass cube  27 , surrounds beam splitter  26 . Beam splitter  26  is disposed at a location where the beams of light  22 ,  32  from the first LED  14  and second LED  16  intersect. The beams of light  22 ,  32  travel through glass tubes  19  and  21  respectively and are directed upon the beam splitter  26 , which combines the beams of light  22 ,  32  and directs a combined beam of light  28  through glass tube  29 . Lens  33  is affixed within glass tube  29  such that it is between and parallel to output connector  37  and a side of glass cube  27 . The end  31  of the optical fiber  30  may be in contact with lens  33  and extend out of housing  12  through glass tube  29  and output port  34 . The combined beam of light  28  then passes through the optical fiber  30  and output port  34 . 
         [0038]      FIGS. 2A and 2B  show a light module  100  of the present invention. The light module  100  is substantially the same as the prior art light module  10  except for the replacement of output port  34  with output port  39 . Output port  39  preferably includes a strain relief  35  similar to the prior art guide, but replaces the output connector  37  with a substantially hollow casing  40 . Casing  40  is attached to housing  12  and includes an exit opening  46  proximate to the strain relief  35  and an entry opening  48  proximate to the housing  12 . Exit opening  46  and entry opening  48  are preferably aligned with one another and are each dimensioned to allow the optical fiber  30  to pass therethrough and to support the optical fiber  30  during deformation. Exit opening  46  and entry opening  48  may be lined with rubber bushings (not shown) to further aid in alleviating strain on optical fiber  30 . The walls  42  of the casing  40  define a hollow interior  44  that is dimensioned to allow the optical fiber  30  to be sufficiently deformed to allow the EF of the light passing through the optical fiber  30  to be properly adjusted. The interior  44  of the casing  40  shown in  FIGS. 2A and 2B  extends both above and below the optical fiber  30 . However, as illustrated in the connector  110  of  FIG. 3 , it is recognized that the hollow interior  44  may only be disposed below the optical fiber  30  and that the casing  40  may be substantially solid in the area above the optical fiber  30 . 
         [0039]    The face  38  of screw  36  is preferably polished prior to being brought in contact with the optical fiber  30 . Screw  36  passes through a threaded opening in the wall  42  of the casing  40  and the face  38  of screw  36  contacts the optical fiber  30 . Screw  36  may be any type of threaded fastener that may be threaded into and out of the wall  42  of the casing  40  and that will not damage the optical fiber  30  during contact therewith, but is preferably an Allen-style M 1.6 screw without head and with a polished face  38 . As shown in  FIG. 2A , when the optical fiber  30  is in an undeformed position, it is substantially straight through the entry opening  48  and exit opening  46  across its entire length. As the screw  36  is threaded into the interior  44  of the casing  40 , the face  38  of the screw  36  exerts downward pressure on optical fiber  30  so as to depress the optical fiber  30  downward into the interior  44  of the casing  40 . Because the optical fiber  30  is supported by the entry opening  48  and exit opening  46 , the portion of the optical fiber  30  between the entry opening  48  and exit opening  46  becomes deformed downward in the manner shown in  FIG. 2B . The adjustment of the position of screw  36 , and resultant deformation of the optical fiber  30 , changes the EF of the beam of light  28  within optical fiber  30 . Thus, screw  36  is incrementally adjusted, while the EF of beam of light  28  through the optical fiber  30  is assessed, until the desired EF is obtained. Once the desired EF is obtained, screw  36  may be affixed in such position by any means commonly used for such affixation, such as soldering, gluing, or by known mechanical means, such as a locking pin or screw. 
         [0040]    A test instrument that includes the light module  100  of the present invention will meet the specifications for EF without the use of additional devices, such a mandrel wrapping, and will emit consistent launch conditions with the desired EF, thus providing repeatable, consistent fiber optic testing. 
         [0041]    The present invention also includes a fiber optic connector  110  that is adapted to attach to a fiber port of an existing test instrument. As shown in  FIG. 3 , the fiber optic connector  110  is similar to the output port  39  of the light module  100  of  FIGS. 2A and 2B  insofar as it includes a substantially hollow casing  40  having a first casing end  41 , a second casing end  43 , a casing interior  44 , an entry opening  48 , an exit opening  46 , and screw  36  that is threaded through the wall  42  of the casing  40 . However, it also includes a fiber port connector  52 , shown as a male fiber port connector in  FIG. 3 , attached to one end of the casing  40 , a fiber port  122  attached to the opposite end of the casing  40  and an optical fiber  230  that terminates within the fiber port  122  and extends through the casing  40  and out of the connector  110  through an opening in the fiber port connector  52 . 
         [0042]    The fiber port  122  is preferably an industry standard port for connecting an optical fiber to a test instrument. Fiber port  122  includes a body  126  and a ceramic tube  131  disposed through an opening in the body  126 . A fiber guide  128  is disposed through the ceramic tube  131  and extends through fiber port connectors  127  and  124 , which extend from each end of the body  126 . Optical fiber  230  is disposed through the fiber guide  128  and terminates at a second end  231  at a fiber junction  132  within the fiber guide  128  and at a first end  229  at a position outside of the fiber port connector  52  that allows the optical fiber  230  to be inserted within the fiber port of the test instrument (shown in  FIG. 4B ). Fiber port connector  52  is dimensioned to mate with and secure the fiber optic connector  110  to a fiber port of an existing fiber optic test instrument (shown in  FIG. 4B ). In  FIG. 3 , fiber port connector  52  is a threaded male fiber port connector. However, it is recognized that other types of fiber port connectors may be substituted to achieve similar results. 
         [0043]    The walls  42  of the casing  40  define a hollow interior  44  that is dimensioned to allow the optical fiber  230  to be sufficiently deformed to allow the EF to be properly adjusted. In the embodiment of  FIG. 3 , the hollow casing interior  44  of the casing  40  is only disposed below the optical fiber  230  and the casing  40  is substantially solid in the area above the entry opening  48  and exit opening  46 . However, as shown in  FIG. 4B , the casing interior  44  of the casing  40  may extend above the entry opening  48  and exit opening  46 . 
         [0044]    The operation of the fiber optic connector  110  of the present invention is illustrated with reference to  FIGS. 4A and 4B .  FIG. 4A  shows a prior art portable light source  120 , which is a fiber optic test instrument commonly used in fiber link loss measurement on both single and multi-mode optical fibers. Examples of such portable light sources include the EXFO FLS-300 Light Source, the FOD 2107 LD Light Source, the AFL Telecommunications Noyes® OLS1 LED Light Source, the FOD 2114 Triple Laser Light Source, the AFL Telecommunications Noyes® OLS1-Dual LED Light Source with Wave ID, and the FOD 2119C ASE Light Source C-Band. These light sources or fiber optic test instruments are handheld and designed to perform link loss measurements when used in conjunction with an optical power meter. Specifically, they may test Ethernet, Gigabit Ethernet (GBE), Token Ring, and other multi-mode LAN systems, and Passive Optical Networks (PONs). The results of the tests may be used to certify the optical fiber for TIA/EIA or ISO standards. Some of these light sources may be paired with an optical fiber identifier, in which case they may perform the further function of fiber identification prior to splicing. 
         [0045]    The portable light source  120  of  FIG. 4A  includes a substantially hollow housing  121  having an interior  123  within which a light module  10  is disposed. An optical fiber  30  extends through the housing  121 , from the light module  10  to its termination within a fiber port  142 . Fiber port  142  is an industry standard port that may include a body  156 , a fiber connector  157  disposed in the interior  123  of housing  121 , a fiber guide  158 , a ceramic tube  151 , and a fiber port connector  154  extending from the body  156  outside of the housing  121 . Body  156  immediately surrounds ceramic tube  151 , which immediately surrounds fiber guide  158 . Optical fiber  30  is extended from the interior  123  of housing  121  through first fiber port connector  157  and fiber guide  158  to fiber junction  152 . An optical fiber  130  to be tested is coupled with the fiber port connector  154  such that optical fiber  130  extends within the fiber port  142  and, specifically, within the fiber guide  158 , and is joined to optical fiber  30  at fiber junction  152  such that the light passing through optical fiber  30  also passes through optical fiber  130 . 
         [0046]    The housing  121  of light source  120  is preferably box-like, made of plastic, and small enough to be handheld. The exterior of the light source  120  may also include at least one control button and a screen (not shown), which may display information such as pass/fail results, emitted wavelengths, tone frequency, and battery condition. The interior  123  of the housing  121  of the light source  120  may also include a battery (not shown) and other art recognized electronics (not shown) for controlling the operation of the light source  120 . 
         [0047]      FIG. 4B  shows the portable light source  120  with a fiber optic connector  110  of the present invention attached to the fiber port  142 . In this embodiment, the fiber optic connector  110  is attached to the fiber port  142  of the light source  120  such that the optical fiber  230  of the fiber optic connector  110  extends within fiber port  142  and is joined to optical fiber  30  at fiber junction  152  such that the light passing through optical fiber  30  also passes through optical fiber  230 . The light source  120  is then energized, and screw  36  is moved downward to apply pressure upon the optical fiber  230 , causing it to deform in the manner shown in  FIG. 2B . The EF of the light passing through the optical fiber  230  is then measured and the screw  36  is adjusted until the EF is at a desired level. The screw  36  may then be permanently affixed in place or it may be left unsecured so that it may subsequently be used with other fiber optic test instruments. Once the fiber optic connector  110  has been used to properly adjust the EF of the light, the light source  120  with fiber optic connector  110  may be used in a conventional manner except that, rather than joining the optical fiber  130  to be tested with the optical fiber  30  within fiber port  142 , the optical fiber  130  to be tested extends within fiber port  122  and is joined to optical fiber  230  at fiber junction  132  such that the light passing through optical fiber  230  also passes through optical fiber  130 . 
         [0048]    As noted above, EF is a radial integration of the power distribution in an optical fiber, going from zero at the center to unity at the core boundary. EF describes the intensity of the light encircled within a fiber core radius when light is launched into a multi-mode optical fiber. There are a number of devices currently available to measure EF, including the MPX Modal Explorer manufactured by Arden Photonics, Ltd. of Great Britain, the 2440 Launch Analyzer manufactured by Photon Kinetics, Inc. of Beaverton, Oreg., and others, and any of these devices may be used to measure EF in connection with the adjustment of EF performed in connection with the present invention. 
         [0049]    Referring now to  FIG. 5 , EF is typically measured and displayed by current devices with reference to a graph showing the EF on the Y-axis and the radius of the fiber on the X-axis. Current standards place an upper limit and a lower limit on the EF as a function of the radius. 
         [0050]    The upper limit on EF that complies with the current standards is shown as plot  300  in  FIG. 5 , while the lower limit is shown as plot  310 . In practice, the EF will be measured before it is adjusted and plot  320  is exemplary of the results of such a pre-adjustment measurement. During adjustment, EF will be continually measured until it is shown to, in all respects, fall within the upper limit plot  300  and lower limit plot  310  in the graph. Plot  330  is an exemplary plot for EF after it is fully adjusted. 
         [0051]      FIGS. 6A and 6B  illustrate two embodiments of the system  150  of the present invention. This system  150  includes a light source  120 , a power meter  140 , and an optical fiber  130  to be tested. In  FIG. 6A , light source  120  includes the light module  100  of the present invention. In  FIG. 6B , a conventional light source  120  is modified by attaching the fiber optic connector  110  of the present invention thereto. 
         [0052]    Power meter  140  may be any of those commonly used in link loss measurement, such as the FOD 1202 Triple Wavelength Power Meter, the EXFO FiberBasix EPM-100 Power Meter, the FOD 1206 Optical Return Loss Meter, the AFL Telecommunications Noyes® OPM1 Optical Power Meter, the FOD 1203 Optical Tester, the EXFO PM-1100 Power Meter, and the EXFO PM-1600 High-Speed Power Meter, and includes a fiber port  162  that may be substantially identical to the fiber port  142  described with reference to the light source  120 , and an internal device  145  for measuring the optical power of the light through the optical fiber  130 . The optical fiber  130  being tested for link loss may be among a class of optical fibers that include single or multi-mode; of short or long distance; Ethernet, GBE, or other LAN systems. Light source  120  and power meter  140  may be applied to either end of the optical fiber  130  that is to be tested. 
         [0053]    In each embodiment of the system, the EF from the light source  120  has been controlled by adjusting the screw  36  of either the light module  100  or the fiber optic connector  110  of the present invention such that the light launched into the optical fiber  130  has an EF that is within the upper and lower limits of the applicable standards. Accordingly, the power meter  140  will provide repeatable, consistent measurements of link loss across optical fiber  130  without the need for mandrel wrapping or other methods of controlling EF. 
         [0054]    In another embodiment of the present invention, a method for controlling EF is provided.  FIG. 7  is a block diagram depicting the steps of method  400 . The steps method  400  include applying a screw to an optical fiber coupled with a light source  402 , where the application and light source are as described above with reference to either  FIGS. 2A and 2B  or  FIGS. 3 and 4B ; launching a beam of light through the light source  404 ; assessing the EF of the launch  406 ; and adjusting the screw until a desired EF is obtained  408 . The method may further include the step of affixing the screw in place once a desired EF is obtained  410 . 
         [0055]    Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions would be readily apparent to those of ordinary skill in the art. Therefore, the spirit and scope of the description should not be limited to the description of the preferred versions contained herein.