Abstract:
A ferrule is constructed with a modified surface to interact with a coordinating housing. The housing is constructed to be integral with the modifications of the ferrule and to fill the recesses in the ferrule body. The coordination between housing and ferrule decreases electromagnetic interference from the ferrule.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to devices for interconnecting multiple optical fibers, and more particularly to a fiber optic ferrule with a high level of insulation from electromagnetic interference. 
     2. Background of the Invention 
     The use of optical fibers for high-speed communication and data transmission via optical signals has become well established. Modem telecommunications and data transmission systems employ numerous optical fiber signal transmission lines and it is necessary to provide connections between the optical fibers at various locations within these systems. 
     Various optical connectors have been used for connection of optical fibers. For instance, in FIG. 1, there is shown an optical connector  10  which comprises a rectangular-parallelpiped ferrule  12  having a contact face  14  at a front portion of ferrule  12  and positioning guide pins  16  formed at opposite sides in a transverse direction of ferrule  12 , and a fiber ribbon  18  having a plurality of optical fibers  20  running in a lateral direction and mounted to a rear portion of ferrule  12 . Guide pins  16  and respective optical fibers  20  are arranged in parallel with each other so that they are perpendicular to contact face  14 . 
     At present, the above-mentioned potential applications of optical fibers are complicated by the fact that the distribution of signals such as radio frequency (RF) signals are disrupted by electromagnetic interference (EMI) which escapes from contact face  14 . 
     As a result of the foregoing, there is a need in the art for a fiber optic ferrule with a high level of insulation from electromagnetic interference. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a fiber optic ferrule which will provide a high level of insulation from electromagnetic interference. 
     It is a further object to provide a fiber optic ferrule with a decreased virtual aperture. 
     It is yet another object to provide a housing that is integral with a ferrule constructed in accordance with the invention. 
     It is yet another object to provide a method for making a modified ferrule. 
     It is yet another object to provide a method for making a housing that is integral with a modified ferrule. 
     In all of the above embodiments, it is an object to provide a reduction in EMI passing through the ferrule. 
     Other objects and features of the present invention will be apparent from the following detailed description of the preferred embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a prior art optical fiber cable ferrule; 
     FIG. 2 is a perspective view of a ferrule constructed in accordance with a preferred embodiment of the invention; 
     FIG. 3 is a side sectional view of a ferrule according to the present invention integral with a housing; 
     FIG. 4 is a front view of a prior art ferrule surrounded by a conventional housing; 
     FIGS. 5A through 5C are explanatory front views of ferrules according to the present invention; 
     FIGS. 6A and 6B are sectional views of ferrules constructed in accordance with the teachings of the present invention; 
     FIG. 7 is a front sectional view of ferrules constructed in accordance with the teachings of the present invention; and 
     FIGS. 8A and 8B are side views of ferrules constructed in accordance with the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Definitions 
     Before the present invention may be described in detail, it is necessary to define several key terms. Where the definition of terms departs from the commonly used meaning of the term, applicant intends to utilize the definitions. provided below, unless specifically indicated. 
     For the purposes of the present invention, the term “optical axis” refers to the “z” direction in which the optical fibers run through a ferrule. 
     For the Purposes of the present invention, the term “y-axis” refers to the direction vertical and perpendicular to the optical axis. 
     For the purposes of the present invention, the term “x-axis” refers to the direction horizontal and perpendicular to the optical axis. 
     For the purposes of the present invention, the term “physical aperture” refers to the surface area of a ferrule contact face. An example of the physical aperture may be seen in FIGS. 1 and 4 as element  14 . 
     For the purposes of the present invention, the term “virtual aperture” refers to a relative open space through which RF radiation exits the ferrule after the various modifications have been made as defined by this invention. Examples of virtual apertures are illustrated in FIGS. 5A,  5 B, and  5 C by elements  100 ,  100 ′ and  100 ″. 
     For the purposes of the present invention, the term “box cut(s)” refers to a cut resulting in the removal of a portion of a ferrule body where cuts are made at approximately right angles relative to an adjacent cut in the ferrule body, but that they do not intersect fiber optic cable(s) or guide pins within the ferrule body. Examples of box cuts may be seen in FIGS. 2 and 6A as elements  32  and  120 . 
     For the purposes of the present invention, the term “angled cut(s)” refers to a cut resulting in the removal of a portion of a ferrule body where the cuts are made at obtuse angles relative to an adjacent cut in the ferrule body, but that do not intersect fiber optic cable(s) or guide pins within the ferrule body. An example of an angled cut may be seen in FIGS. 6B and 8B as element  130 . 
     For the purposes of the present invention, the term “differentiated serrated cut(s)” refers to cuts made in the direction of an optical axis or “z” axis of a ferrule that resemble a toothed edge of a saw and have relatively higher peaks that correspond to the presence of guide pin(s) or fiber optic cables(s) within the ferrule body. Examples of differentiated serrated cuts may be seen in FIGS. 7,  8 A, and  8 B as elements  140  and  146 . 
     For the purposes of the present invention, the term “cavity cut(s)” refers to cuts made in the direction of the y-axis that proceed entirely through a ferrule, but that do not intersect the fiber optic cable(s) or guide pins within the ferrule body. An example of a cavity cut may be seen in FIG. 2 as element  32 ′. 
     For the purposes of the present invention, the term “extruding cut(s)” refers to any cut that results in the removal of a portion of a ferrule body, including, but not limited to box cuts, angled cuts, cavity cuts, and differentiated serrated cuts. 
     For the purposes of the present invention, the term “waveguide” is used in this application to mean any device used to channel an optical signal, at any frequency. Specific examples of waveguides include, but are not limited to: fiber-optic waveguides, planar glass, as well as crystalline and semiconductor waveguides. 
     The term “fiber optic cable” or “fiber optic waveguide” is used in this application to mean any waveguide utilized to guide light waves from one point to another. This definition specifically includes both single mode and multi-mode fibers as well as any waveguide having any cross-sectional shape. In addition, this term also includes any waveguide whether doped or undoped. 
     Description 
     With reference to FIG. 1, a ferrule  12  is attached to an end of a multi-fiber optical cable or ribbon  18  to provide, at contact face  14  of ferrule  12 , a set of spaced-apart aligned end facets  20  of fibers in multi-fiber cable  18 . A pair of guide pins  16  extend parallel to one another and orthogonally outward from contact face  14  of ferrule  12 . 
     FIG. 4 illustrates a front view of optical fiber cable ferrule  12  surrounded by housing  80 . Contact face  14  is constrained in dimension by the interface with other ferrules and defines a physical aperture. The physical aperture of ferrule  12  in FIG. 4 is merely contact face  14 , the front planar surface, of a rectangular-parallelpiped ferrule. It should be appreciated that in prior art devices, the physical aperture and the virtual aperture are identical. 
     Now that a prior art device has been described, we will turn to describing the preferred embodiment of an optical interconnect  10  and in particular to how the virtual aperture is modified to reduce EMI emissions. As seen clearly in FIG. 2, portions of the body of ferrule  30  are removed through extruding cuts  32 ,  32 ′. While several extruding cuts are illustrated, it should be appreciated that only one need be present. The other extruding cuts are illustrated by dashed lines to show that they are optional. Extruding cuts  32 ,  32 ′ may be made in any direction, but preferably do not bisect any of optical fibers or waveguides  34  or guide pins  36 . In an alternate embodiment, extruding cuts  32 ,  32 ′ may be made to directly expose guide pins  36  or bisect waveguides  34 . It should be appreciated that in this embodiment, guide pins  36  may be grounded or at least electrically accessed. Optical fibers  34  may be collected in a multi-fiber optical cable, a single fiber cable, a ribbon cable or remain bare at the end of ferrule  30  opposite contact face  38 . In an alternate embodiment, at least two extruding cuts are separated by a distance of one-half wavelength of the EMI emission. This has the added advantage of a destructive interference being developed which may significantly reduce the magnitude of the EMI emission. 
     It should be appreciated that the drawings illustrate cuts  32 ,  32 ′ after being made. In the operational device, it is preferable to substantially fill all cuts with a conductive material. The drawings do not illustrate this feature so that cuts  32 ,  32 ′ are not obfuscated by the filled material. 
     The description generally refers to ferrules  30  of the invention being manufactured by a series of cuts being made in a typical ferrule  12 . Making cuts is but one method to make ferrule  30 , but is preferable only when ferrule  30  is made from a hard material, for example, but not limited to silicon. If ferrule  30  is made from a hard material, the cuts may be etched into ferrule  30  by any means known in the chemical and/or mechanical etching arts. After the cuts are made, they are later substantially filled with a conductive material. 
     Another method of manufacturing ferrules  30  is through an injection molding process. According to this process, ferrule  30  would be made of a moldable plastic. Preferably, the plastic would be filled with an additive, for example, but not limited to glass for rigidity, graphite for conductivity, or steel for rigidity and conductivity. 
     Another method for manufacturing ferrule  30  is to utilize a ceramic material. This ceramic material may be conventional in nature or may be an advanced composite. An example of such an advanced composite is taught in U.S. Pat. No. 4,000,110; by Kazumi et al. This reference is hereby incorporated in its entirety. This reference teaches that detailed ceramic products may be manufactured by the process of injection molding. First, suitable organic substances such as thermoplastic resin, thermosetting resin, lubricant and plasticizer is added to raw material of ceramics to render it a thermoplastic. Next, the shape of the article is produced by injecting the raw compound into a mold. Then, the added organic substances are subjected to thermal decomposition and evaporation. Finally, the raw mass is baked to harden into articles of complicated shape and high dimensional precision. 
     Another method of manufacturing ferrules  30  is through a die casting process. Die casting is a well known way of shaping articles in which a liquid material, such as molten metal, is placed in a cavity which is formed in the shape of the desired article between separable die members. The liquid material fills the die cavity and solidifies therein in the shape of the desired article. The die members are then separated and the article is removed from the die cavity. In pressure die casting, the liquid material is forced or injected into the die cavity under pressure. 
     The ferrules of this invention may also be constructed by taking one of ferrules  30  as mentioned above and filling the voids, i.e., the extruding cuts  32 , 32 ′, with another material. The spaces may be filled with a conformable material, for example rubber or putty, that would assist the engagement of housing  60 . The spaces may also be filled with a non-conformable plastic or polymer with a nylon base, preferably with glass added for increased rigidity. The spaces may also be filled with a conductive material, for example zinc and aluminum. It should be appreciated that the spaces may be filled by any of the methods describe above, in combination or singularly or by any other means. Filling the space with a non-conformable material would allow the ferrule to be used in conventional housings and is therefore the preferred method. 
     FIG. 2 illustrates a cavity cut  32 ′. As may be seen, cavity cut  32 ′ refers to cuts made in the direction of the y-axis that proceed entirely through ferrule  30 , but that do not intersect fiber optic cable(s)  34  within the ferrule body. It should be appreciated that cavity cuts do not need to go through the ferrule body and then would be better described as box cuts. 
     FIG. 3 illustrates housing  60  integral with ferrule  30  having guide pins  36 . Housing  60  is manufactured with ferrule contact members  64  that terminate in space filling extensions  66  that cooperate with extruding cuts  32  made in ferrule  30 . Housing  60  is preferably constructed of a molded plastic or polymer with a nylon base constructed via an injection molding process. The nylon could have glass or other material added for increased rigidity or conductivity. Housing  60  may also be a die cast zinc and aluminum composite or other metal. Housing  60  may be a conductor itself. Housing  60  may be constructed in either one part or multiple parts. Preferably, housing  60  is constructed as two parts that fit together in a clam shell arrangement. If constructed as one part, it may be necessary to alter cuts  32  to insure that ferrule  30  may be easily connected to housing  60 . One way to insure connectivity when housing  60  is constructed of only one part is to use angled cuts  130 , as illustrated in FIG. 8B, so that insertion of ferrule  30  does not strain housing  60 . A pair of clips  70  grounds housing  60  to contact face  72  and aids in electrical conductivity. Clips  70  are preferably spring clips made of a high conductive metal, for example, but not limited to copper, aluminum, steel or an alloy. Housing  60  is open at the bottom so that a PC board  74  or other circuit board may be inserted. In an alternate embodiment, the bottom of housing  60  would be closed if a clam shell structure is utilized. 
     FIGS. 5A through 5C illustrate examples of virtual apertures  100 ,  100 ′ and  100 ″ of ferrules  38  resulting from modifications according to the present invention. Contact face  36  as shown in FIG. 3 remains intact but virtual apertures  100 ,  100 ′ and  100 ″ as shown in FIGS. 5A through 5C are decreased by the interaction between extruding cuts  32 , 32 ′ and outer housing  60  which fills space left by extruding cuts  32 . Virtual aperture  100 ,  100 ′ and  100 ″ defines the space through which an EMI wave may flow. Guide pins  36 , if grounded, prevent the flow of EMI radiation through the space immediately surrounding guide pins  82 . The largest physical dimension of vertical virtual aperture  100 ,  100 ′ and  100 ″ defines the largest wavelength of RF radiation that may escape through ferrule  12 , 30 . Therefore, the smaller virtual aperture  100 ,  100 ′ and  100 ″ is made, the shorter the wavelength of the RF radiation there is to cause EMI with frequencies of concern. As may be seen, there is a significant difference in size and shape between physical aperture  14  and virtual aperture  100 ,  100 ′ and  100 ″. This is due to all of cuts  32 , 32 ′ interacting to create the virtual aperture as illustrated in one plane as element  100 ,  100 ′ and  100 ″. While this concept may seem simple, it is not obvious. The prior art devices utilize structures that do not address the EMI problem and have avoided this issue. Applicant has found that by utilizing a more complex structure as described above, one is able to finally address this RMI problem. 
     In a standard ferrule known as the “MT ferrule,” contact face  14  as shown in FIGS. 1 and 4 is 4.4 mm in the horizontal direction and 2.5 mm in the vertical direction and the diagonal is 5.1 mm. Guide pins  16  are 0.72 mm in diameter and 3.3 mm from the outer edge of one guide pin  16  to the outer edge of the other guide pin  16 . Guide pins  16  are 3.4 mm measured along the diagonal and 2.6 mm from the center of one guide pin  16  to the center of the other guide pin  16 . 
     The housing  60  of this invention is constructed to fill the spaces or cuts  68  made in ferrules  30  and to virtually wrap around fibers  34 . The virtual wrapping effect is achieved by the coordination between housing  60  and ferrule  30 . Because of the decreased virtual aperture  100 ,  100 ′ and  100 ″, the available space for RF radiation to pass through is also decreased. The only constraint on how much of ferrule  30  may be removed or how little of the ferrule body need be present is that fibers  34  can not be intersected. 
     Extruding cuts  32  may take on several forms. FIG. 6A shows a typical box cut  120 . FIG. 6B shows a typical angled cut  130 . Both box cuts  120  and angled cuts  130  are preferably made in either direction perpendicular to the optical axis, but could be made parallel to the optical axis as well. FIG. 2 also shows a typical cavity cut  32 ′. Cavity cuts are preferably made in the direction of the y-axis, but could also be made in the direction of the x-axis or the optical axis. In a preferred embodiment of the invention, cuts  32  are staggered, as in FIG. 2, so as to maintain the structural integrity of ferrule  30 . As may be seen, both box and angled cuts  120 ,  130  may extend to any desired depth and length as indicated by the break lines so long as fibers  34  are not intersected. Cavity cuts  32 ′ may also not intersect fibers  34 . 
     FIG. 7 shows a front sectional view of a differentiated serrated cut  135 . Minor serrations  140  are cut to correspond with optical fibers  34  and major serrations  146  are cut to correspond with the guide pins  36 . As may be seen, both minor and major serrations  140 ,  146  may extend to any desired height and width as indicated by the break lines so long as fibers  34  are not intersected. 
     FIGS. 8A and 8B illustrate examples of multiple extruding cuts. FIG. 8A shows the result of box cut  120  perpendicular to the optical axis, i.e., normal to the x axis, and along the top or the bottom of ferrule  30  followed by a differentiated serrated cut  135  made parallel to the optical axis and in recess  68  left by the box cut. FIG. 8B shows the result of an angled cut  130  perpendicular to the optical axis, i.e., normal to the x axis, and along the top or the bottom of ferrule  30  followed up by a differentiated serrated cut  135  made parallel to the optical axis and in recess  68  left by the angled cut. Once box cut  120  or an angled cut  130  has been made, a further extruding cut or cuts  32  may be made in recess  68  of the first cut. It should be appreciated that while only three examples of extruding cuts  32  have been provided and that only three combinations of these cuts have been discussed, numerous types of extruding cuts are possible and any combination of these may be used to form ferrule  30 . 
     While we have discussed that cuts  32 ,  32 ′ do not contact waveguides  34 , it should be appreciated that these cuts may contact and extend below waveguides  34 . In this embodiment, waveguides  34  are supported in a cantilever fashion until conductive material is added to substantially fill cuts  32 ,  32 ′. It is preferred that unsupported span of waveguides  34  be minimized since this puts a strain on waveguides  34 . 
     It should be appreciated that the teachings of this invention may be utilized in any MT connector, mini-MT connector, MTP connector, or any other connector having an aperture and sensitivity to EMI. 
     Although the present invention has been fully described in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, it is to be understood that various changes and modifications may be apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom.