Abstract:
A testing device for fiber optic system devices includes a fiber optic loop support that holds a single-mode optical fiber such that an empirically determined loss characteristic associated therewith is unvarying from use to use. In particular, an optical fiber forms a loop, and the loop is supported within a rigid slotted housing. The housing effectively precludes bending losses. Additionally, the housing is small and portable so that field testing may also be performed.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 09/570,801, filed May 15, 2000, now allowed, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a device that supports a loop of optical fiber such that the loop may be used to test fiber optic-related equipment. 
     BACKGROUND OF THE INVENTION 
     Optical fibers were introduced in the early 1970s. Since that time, their use has expanded into numerous settings. Additionally, a number of different forms of optical fibers have appeared. The principle division is between single-mode fibers and multi-mode fibers, with multi-mode fibers being further divided into graded index multi-mode and step-index multimode fibers. As understood in the fiber optic industry, a “mode” is a transverse pattern of energy propagating at a specific velocity through the fiber. 
     Multi-mode fibers, as the name suggests, support a number of modes. Multi-mode fibers offer the advantages of being able to be coupled to incoherent light sources and having a wider tolerance for alignment with these light sources. Multi-mode fibers may be connected and spliced one to another with a fair amount of latitude. Additionally, multi-mode fibers are generally forgiving when it comes to losses induced by bends in the fiber. That is, the fiber may bend fairly substantially without worry about losses induced by the bend. Two disadvantages of multi-mode fibers are intermodal dispersion wherein different modes may travel at different velocities and relatively high attenuation. 
     Single mode fibers, in contrast, only support a single mode, namely the HE 11  mode. Single-mode fibers do not suffer from intermodal dispersion, are generally considered to have higher bandwidth capabilities than multi-mode fibers, and are relatively insensitive to losses induced by local lateral microdisplacements of the fiber from a mean axis (microbending-bends on the order of the size of the core of the fiber). However, single-mode fibers are more susceptible to losses generated by macroscopic bending. As the radius of curvature decreases, losses within the fiber increase. Further, greater care when splicing single-mode fibers is required. 
     Those who use fibers are greatly concerned with losses because loss dictates how far a signal will propagate within the fiber and still be usable. While amplifiers may counteract losses, each amplifier in a system increases costs and requires additional connective infrastructure. Knowledge of a loss profile of a fiber is extremely helpful when designing fiber based systems so that appropriate hardware or signal processing is used to compensate for the known losses. 
     In 1998, SIECOR introduced a duplex connector to replace the traditional SC type connector. This new connector, known as the MT-RJ, is approximately the size of a phone plug, allowing connector density within fiber systems to double effectively over the old SC type connectors and achieve densities equal to, or in some cases better than, copper-based systems. The MT-RJ has rapidly become the industry standard for fiber optic systems. An additional feature of the MT-RJ connector is its ability to be used with both single-mode and multi-mode fibers. 
     As a result of the rapid acceptance of the MT-RJ, new devices within fiber optic systems are now being equipped with MT-RJ female receptacles to mate with the male end of the MT-RJ. Manufacturers of such devices include CISCO,  3 COM, and others within the telecommunications industry. Examples of such devices include Optical Time Domain Reflectometers (OTDRs), routers, optical transceivers, optical amplifiers, and the like. Specific examples include the CATALYST 8500 family of non-blocking multiservice switch routers from CISCO, the CFX-1433M 100 Mbps Fast Ethernet Hub from Canary Communications, and 12R-J3200A HP ADVANCESTACK 10base-T Hubs. However, these devices must frequently be tested to see if they are functioning properly. This is especially important before shipping to a consumer, as the companies producing these devices do not want to ship defective products. Additionally, it may be desirable to test these devices after installation to verify that they are not the source of system failure. 
     SIECOR has introduced a device coupled to an MT-RJ connector that allows testing of system devices using multi-mode fibers. However, this device has a flexible fiber element and is inappropriate for use with a single-mode fiber. In particular, this device is especially susceptible to drooping as a result of temperature increases. This droop induced bending is acceptable in a multi-mode fiber, but not for a comparable single-mode fiber. As a result, there is still a need for a device that utilizes a single-mode fiber to test the functionality of fiber optic system devices. 
     In response to the popularity of the MT-RJ connector, LUCENT has introduced a connector that is not a duplex connector, but two of these connectors may be paired with a yoke to form a duplex connector. The LUCENT connector is approximately a third to a half the size of the MT-RJ, and may rapidly reach the market saturation of the MT-RJ. Many of the concerns about the ability to test devices that use MT-RJs will be true of devices that use the LUCENT connectors, and thus, there will be a comparable need for an appropriate testing device. The LUCENT device is embodied in U.S. Pat. No. 6,196,713, and is known by the commercial name LC. 
     SUMMARY OF THE INVENTION 
     The shortcomings of the prior art are addressed by providing a rigid support that holds a single-mode fiber in a position with a relatively constant or repeatable loss profile and further is adapted to connect to an MT-RJ connector. An exemplary embodiment of the present invention comprises a generally planar, rigid, plastic housing. The housing may be approximately three and a half (3.625) inches long and have a slotted first end. The slot gives access to a cavity extending substantially the length of the housing, in effect forming a sleeve. The slot includes an arcuate center area sized to accommodate the standard protuberance on the end of a standard MT-RJ connector. In use, a single-mode fiber or filament is secured to the MT-RJ and then slipped into the slot. The protuberance on the MT-RJ may be secured to the housing to form the testing device. In essence, the support acts like a sleeve positioned over the filament that is secured to the MT-RJ. The loss characteristics of the testing device may then be determined empirically, and the testing device labeled with appropriate indicia indicative of the empirically determined loss characteristic. Subsequently, the testing device may be used repeatedly to verify the functionality of other fiber optic system devices. The housing holds the filament loop such that the loss characteristic of the loop does not change between uses and likewise is not susceptible to bending such as may occur in the SIECOR multi-mode testing unit. 
     Another embodiment is adapted to be used with LUCENT&#39;s duplex connector pair. The method and support remain relatively unchanged, however the attachment interface between the support and the connector reflects the different shape and size of the LUCENT device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art MT-RJ connector; 
     FIG. 2 is a top plan view of the fiber optic loop support of the present invention; 
     FIG. 3 is a side elevational view of the support of FIG. 2; 
     FIG. 4 is a front elevational view of the support of FIG. 2; 
     FIG. 5 is a perspective view of the support coupled to the connector to form a testing device; 
     FIG. 6 is a simplified version of the testing device in use to test a fiber optic system device; 
     FIG. 7 is a perspective view of prior art LUCENT connectors forming a duplex connector pair; and 
     FIG. 8 is a perspective view of the support coupled to the duplex connector pair of FIG. 7 to format a testing device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A typical MT-RJ connector  100  is shown in FIG.  1 . MT-RJ connector  100  includes a body  102  having a spring-mounted fiber interface  104  contained therein. A biased clip  106  allows the MT-RJ  100  to be secured in a conventional receptacle or fiber optic system device (neither shown). A protuberance  108  provides a connective surface for a fiber or filament (the terms are used interchangeably herein) to be connected to the MT-RJ  100 . In particular, most fibers are covered by at least two protective coatings. A strain relief (not shown) is secured to the protective coating and to the protuberance. The fiber interface  104  includes duplex fiber orifices  110 A and  110 B. It should be appreciated that the MT-RJ  100  is approximately the size of a conventional phone plug and, thus, is highly desirable in the fiber optic industry to improve density over the old SC connectors. MT-RJ  100  may be used with both single-mode and multimode fibers. In practice, optical fibers are secured at a first end to the fiber interface  104 , with the second end extending through the protuberance  108 . Light is then transmitted and received through orifices  110 A and  110 B. For example, light may be transmitted through orifice  110 A, down a filament to a remote transceiver that replies with a light signal transmitted through a second filament and received through orifice  110 B by the original transceiver. Thus, the two orifices  110 A and  110 B allow for duplex communications. 
     As noted, single-mode fibers are especially susceptible to losses induced by macroscopic bending. Thus, if a testing device is to be created for a single-mode fiber, that device must be able to support the single-mode fiber such that the loss profile of the fiber remains relatively constant between uses. While loss is acceptable, a fiber with a variable loss is not acceptable. To this end, a fiber optic loop support  10  is illustrated in FIGS. 2-4. Specifically, the fiber optic loop support  10  includes a substantially rigid body  12 , preferably made out of a durable plastic. At a first end  20  of the elongated body  12 , a protuberance receptacle  14  is positioned. Protuberance receptacle  14  includes an aperture  22  (FIG. 4) which is sized appropriately to receive the protuberance  108  of an MT-RJ  100 . On either side of the aperture  22 , a slot aperture  24  is located. On the terminal ends of slot aperture  24  are rounded end points  18 . Note that rounded end points  18  are purely optional, and the housing may include squared off endpoints that may be easier to manufacture in a molding process. Slot aperture  24  and aperture  22  open into cavity  16  that extends substantially the length of the body  12 . As a further optional feature, the body  12  may include a through hole (not shown) near second end  30 . 
     In an exemplary embodiment, the body  12  is approximately three and a half inches (3.625) long, as indicated by length  26 , and approximately one-half inch (0.683) wide, as indicated by width  28 . Second end  30  has a vertical radius of approximately {fraction (1/32)} inch (FIG.  3 ). Slot aperture  24  has a vertical height of approximately 0.045 inch and rounded end points  18  have a radius of approximately 0.04 inch. The walls of the housing may be approximately 0.062 inch thick when made from a plastic material such as PVC, ABS, polycarbonate, or the like. These dimensions are for illustrative purposes only and are not intended to be limiting; however, dimensions such as those recited do provide adequate size and space for the present invention to be practiced. At a very minimum, the slot height should be sufficiently large to insert a 250 micron optical fiber therein. 
     It should be appreciated that fiber optic supports other than that described are also contemplated. Size, shape, material, and the like may be varied. Since the purpose of the support is to prevent unanticipated losses, the support should keep the optical fiber positioned such that the loss profile associated with the fiber is relatively uniform from use to use. Note further that the present invention could also be used with a multi-mode fiber if desired. 
     A completed testing device  50  is shown in FIG. 5 comprising a loop support  10  and an MT-RJ  100 , coupled with a single-mode optical fiber  40 . The single-mode fiber  40  is secured to the MT-RJ  100  in a looped fashion with a first end  42  operating through orifice  110 A and a second end  44  operating through orifice  110 B. The looped portion of the fiber  40  extends from the interface  104 , out through the protuberance  108 . After securing the fiber  40  to the MT-RJ  100 , the fiber  40  is placed within the cavity  16 , such as by simple insertion, and allowed to rest therein. The protuberance  108  may be pressure fit within aperture  22  but may, alternatively, be secured through a conventional adhesive or other fastener. While the loop of fiber  40  is shown in one configuration, it should be appreciated that the actual configuration may be almost any shape within the cavity  16 . 
     In use, a loss characteristic of the testing device  50  is empirically determined after assembly. Appropriate indicia may be placed on the testing device  50  on a planar surface or with the accompanying literature. For example, the testing device could be labeled “1 dB loss” if in fact the testing device  50  had a 1 dB loss. In use, the MT-RJ  100  end of the testing device is inserted like a conventional connector into a female receptacle  202  on the device  200  (FIG.  6 ). Thus, when the testing device  50  is used to determine whether the piece of equipment  200  is working properly, a known signal may be transmitted from device  200  through the loop of fiber  40  and back to the device  200 . The output received through orifice  110 B may then be compared to the original transmitted waveform. The output is compensated for the known loss characteristics of the testing device  50  and, if the waveforms match, the device  200  is working properly. 
     Testing device  50  may be used repeatedly, such as on an assembly line to verify that each device  200  produced is functioning properly. The loss characteristic of testing device  50  does not change significantly from test to test, allowing quick and easy verification of the operability of the device  200 . Further, the testing device  50  is small, light weight, and easily portable, allowing for field use as well. During installation of fiber optic system components in the field, the testing device  50  may be used to verify operability of the device  200  after shipping and handling. Additionally, the ease of use of the MT-RJ connector  100  used with the testing device  50  means that even in installed systems, the testing device  50  may be used to help isolate failures. 
     A prior art LUCENT duplex connector pair  150  is illustrated in FIG.  7 . In particular, the duplex connector pair  150  includes a first connector  152 , a second connector  154  and a yoke  160 . The duplex connector pair  150  is linked to optical fibers  156 ,  158  through connectors  152 ,  154  respectively. Yoke  160  holds connectors  152  and  154  together. Each connector  152 ,  154  has an interface  162 ,  164  respectively that operates to allow transmission from a source into optical fibers  156 ,  158  respectively. Yoke  160  in effect acts as a protuberance. Strain reliefs  170  may be positioned over fibers  156  and  158  abutting yoke  160  as needed or desired. Note that yoke  160  is generally rectilinear. 
     FIG. 8 illustrates the LUCENT duplex connector pair  150  secured to a loop support  300  thereby forming a testing device  350 . Support  300  is substantially similar to support  10 , however the protuberance receptacle  14  has been changed to yoke receptacle  314  to accommodate the yoke  160 . Cavity  16  and elongated body  12  remain essentially the same. Likewise, apertures  22  and  24  remain essentially the same although the protuberance aperture has been resized to accommodate the yoke  160 . 
     A single-mode optical fiber  40  forms a loop between first connector  152  and second connector  154 . The looped portion of the fiber  40  extends from the interface  162 , out through the yoke  160 , back to the yoke  160 , and to the interface  164 . After securing the fiber  40  to the duplex connector pair  150 , the fiber  40  is placed within the cavity  16 , such as by simple insertion, and allowed to rest therein. The yoke  160  may be pressure fit within protuberance receptacle  314 , just as was described with respect to protuberance  108 , with accommodations for the different size and shape of the yoke  160 , but may, alternatively, be secured through a conventional adhesive or other fastener. While the loop of fiber  40  is shown in one configuration, it should be appreciated that the actual configuration may be almost any shape within the cavity  16 . 
     In use, a loss characteristic of the testing device  350  is empirically determined after assembly. Appropriate indicia may be placed on the testing device  350  on a planar surface or with the accompanying literature. For example, the testing device could be labeled “1 dB loss” if in fact the testing device  350  had a 1 dB loss. In use, the duplex connector pair  150  end of the testing device is inserted like a conventional connector into a female receptacle  202  on the device  200  (not shown, but comparable to FIG.  6 ). Thus, when the testing device  350  is used to determine whether the piece of equipment  200  is working properly, a known signal may be transmitted from device  200  through the loop of fiber  40  and back to the device  200 . The output received through interface  164  may then be compared to the original transmitted waveform. The output is compensated for the known loss characteristics of the testing device  350  and, if the waveforms match, the device  200  is working properly. 
     Testing device  350  may be used repeatedly, such as on an assembly line to verify that each device  200  produced is functioning properly. The loss characteristic of testing device  350  does not change significantly from test to test, allowing quick and easy verification of the operability of the device  200 . Further, the testing device  350  is small, light weight, and easily portable, allowing for field use as well. During installation of fiber optic system components in the field, the testing device  50  may be used to verify operability of the device  200  after shipping and handling. Additionally, the ease of use of the duplex connector pair  150  used with the testing device  350  means that even in installed systems, the testing device  350  may be used to help isolate failures. 
     The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.