Abstract:
A hermetically sealed ferrule includes one or more walls cooperating to enclose a volume. At least one of the walls defines an orifice permitting passage to the enclosed volume. A fiber optic ribbon passes through the orifice to the enclosed volume. The fiber optic ribbon includes a plurality of optical fibers with a protective coating surrounding each of the optical fibers. Each optical fiber is exposed where it passes through the orifice. A low-temperature melting point glass seals a space between the exposed optical fibers and the region of the wall defining the orifice. A first epoxy layer extends between the fiber optic ribbon, an outer surface of the region of the wall defining the orifice, and the low-temperature melting point glass. A second epoxy layer extends between the fiber optic ribbon, an inner surface of the region of the wall defining the orifice, and the low-temperature melting point glass.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates generally to optical networking equipment and components, and more particularly to a hermetically sealed ferrule for permitting access to optical components within a housing.  
         BACKGROUND OF THE INVENTION  
         [0002]    Optical networking equipment utilizes passive components, such as prisms, diffraction gratings, and lenses. The passive components are used for precise separation, combination, bending, and focusing of light waves that carry data through the network. It is important for the passive components to have known shapes and chemical compositions, in order for them to operate as desired. For example, a prism operates based upon the principle of dispersion (the principle of dispersion explains the reason why light of different frequencies “bends” different amounts when traveling through a prism). The “bend” exhibited by light of a given frequency is a function of, among other variables, the angle at which the light strikes the surface of the prism and the refractive index of the prism. If, for example, a prism that is epoxy mounted to a metal holder were to be subjected to a humid atmosphere, the epoxy could absorb water and expand, causing the prism to move and thus alter the angle at which the light strikes the prism. Further, the water may weaken the adhesive strength of the epoxy, making the device performance less reliable when exposed to mechanical vibrations or shock. The prism would cease to predictably bend the various frequencies of light, and the optical circuit in which the prism was embedded would either cease to function or would function inefficiently.  
           [0003]    Heretofore, the components of optical networking devices have been contained within a housing that serves to minimize the deleterious effects of environmental factors upon the components it houses. However, optical fibers, which carry the light that propagates through an optical network, must enter and exit the housing. Over time, environmental factors, such as humidity or particulate contaminants, migrate to the interior of the housing through the passageway intended to permit entry and exit of the optical fibers. As described above, this phenomenon has an effect that is inimical to proper functioning of the components housed therein. Consequently, over time, network devices have a tendency to deteriorate.  
           [0004]    As is evident from the preceding discussion, there exists a need for a way to permit optical fibers to enter and exit a housing without allowing environmental factors to enter the interior of the housing. A desirable scheme will be easily integrated into manufacturing processes, and will be relatively inexpensive.  
         SUMMARY OF THE INVENTION  
         [0005]    Against this backdrop the present invention has been developed. A hermetically sealed ferrule may include a set of one or more walls cooperating to enclose a volume. At least one of the walls has a region defining an orifice permitting passage to the enclosed volume. A fiber optic ribbon passes through the orifice to the enclosed volume. The fiber optic ribbon includes a plurality of optical fibers with a protective coating surrounding each of the optical fibers. Each optical fiber is exposed where it passes through the orifice. A low-temperature melting point glass seals a space between the exposed optical fibers and the region of the wall defining the orifice. A first epoxy layer extends between the fiber optic ribbon, an outer surface of the region of the wall defining the orifice, and the low-temperature melting point glass. Additionally, a second epoxy layer extends between the fiber optic ribbon, an inner surface of the region of the wall defining the orifice, and the low-temperature melting point glass.  
           [0006]    According to another embodiment of the invention, a hermetically sealed ferrule may include a set of one or more walls cooperating to enclose a volume. At least one of the walls has a region defining a first and second orifice permitting passage to the enclosed volume. A first fiber optic ribbon passes through the first orifice to the enclosed volume. The first fiber optic ribbon includes a plurality of optical fibers with a protective coating surrounding each of the optical fibers. Each optical fiber is exposed where it passes through the orifice. A second fiber optic ribbon passes through the second orifice to the enclosed volume. The second fiber optic ribbon also includes a plurality of optical fibers with a protective coating surrounding each of the optical fibers. Each optical fiber is exposed where it passes through the orifice. A low-temperature melting point glass seals a space between the exposed optical fibers of the first optical fiber ribbon and the region of the wall defining the first orifice. A low-temperature melting point glass also seals a space between the exposed optical fibers of the second optical fiber ribbon and the region of the wall defining the second orifice. A first epoxy layer extends between the first fiber optic ribbon, an outer surface of the region of the wall defining the first orifice, and the low-temperature melting point glass. A second epoxy layer extends between the second fiber optic ribbon, an outer surface of the region of the wall defining the second orifice, and the low-temperature melting point glass. A third epoxy layer extends between the first fiber optic ribbon, an inner surface of the region of the wall defining the first orifice, and the low-temperature melting point glass. A fourth epoxy layer extends between the second fiber optic ribbon, an inner surface of the region of the wall defining the second orifice, and the low-temperature melting point glass.  
           [0007]    These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0008]    [0008]FIG. 1 depicts an optical networking device, in accordance with one embodiment of the present invention.  
         [0009]    [0009]FIG. 2 depicts an optical fiber ribbon.  
         [0010]    [0010]FIG. 3 depicts an embodiment of an orifice formed in a housing, wherein an optical ribbon is passed through the orifice, and the orifice is hermetically sealed.  
         [0011]    [0011]FIG. 4 depicts the structure of FIG. 3 with an elongated ring added thereto, in accordance with one embodiment of the present invention.  
         [0012]    [0012]FIG. 5 depicts the structure of FIG. 4 with a sheath fitted over the elongated ring, in accordance with one embodiment of the present invention.  
         [0013]    [0013]FIG. 6 depicts a housing with multiple hermetically sealed orifices, in accordance with one embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    The components within a housing may be shielded from the influences of environmental factors by implementation of the following scheme. First, a fiber optic ribbon is extended through a passageway of a housing. Then, the passageway is hermetically sealed, so that it is not possible for environmental factors to enter by way of the passageway.  
         [0015]    Before the fiber optic ribbon is passed through the passageway, its protective coating is removed from a portion of the ribbon, thereby exposing each of the glass optical fibers contained in the ribbon. The exposed portion of the ribbon is then passed through the passageway, and a low-melting point glass is melted between the exposed optical fiber and the walls of the housing. The low-melting point glass creates a barrier that environmental factors cannot pass.  
         [0016]    Around the low-melting point glass, a mass of epoxy may be disposed. The epoxy lends rigidity to the joint created by the low-melting point glass and the glass in the exposed optical fiber. Optionally, an elongated ring may be attached to the outside of the housing, surrounding the passageway. The fiber optic ribbon passes through the elongated ring and extends through the passageway, thereby reaching the interior of the housing. The interior space of the elongated ring not occupied by the optical ribbon or the first epoxy layer may be filled with a second layer of epoxy.  
         [0017]    Finally, a rubber sheath may be slipped over the elongated ring and may extend along a length of the fiber optic ribbon. The rubber sheath prevents the optical ribbon from making small-diameter bends, and therefore prevents the optical fibers contained therein from breaking. The interior space of the rubber sheath not occupied by the optical ribbon may be filled by a room temperature vulcanized silicon, to enhance rigidity and to adhere the rubber sheath to the optical ribbon.  
         [0018]    The above-summarized description is expounded upon in the following disclosure by reference to FIGS.  1 - 6 . Certain variants are described herein, including variants that permit more than one optical ribbon to enter and/or exit the housing.  
         [0019]    [0019]FIG. 1 depicts an optical networking device  100 . As can be seen from FIG. 1, the optical networking device  100  includes optical components  102  housed within a housing  104 . Examples of optical components  102  are prisms, lenses, diffraction gratings, fan-out circuits, polarization management components, etc. The optical components  102  cooperate to perform a task useful in the context of optical networking. For example, the optical components  102  may multiplex or demultiplex incoming or outgoing optical signals. Additionally, the optical components  102  may take part in adding or dropping an optical signal from a local network (not depicted).  
         [0020]    Optical signals are carried to the optical components  102  via an optical ribbon  108 . As depicted in FIG. 2, the optical ribbon  108  includes several individual optical fibers  200 , each of which is housed within a protective coating  202 . In principle, an optical ribbon  108  may contain any number of optical fibers  200 . In practice, optical ribbons  108  typically contain eight or twelve optical fibers  200 .  
         [0021]    Returning to FIG. 1, it can be seen that the optical ribbon  108  enters/exits the housing  104  through a passageway (also referred to herein as an “orifice”)  106 . The passageway  106  may take on several different shapes (e.g., a slot), depending upon the shape of the optical ribbon  108  to be passed through the orifice  106 .  
         [0022]    [0022]FIG. 3 depicts an enlarged cross-sectional view of the housing  104  and orifice  106  referred to in FIG. 1. As can be seen from FIG. 3, an optical ribbon  108  passes through the orifice  106 . Where the optical ribbon  108  passes through the orifice  106 , its protective coating  202  has been stripped away, revealing each of the optical fibers  200  contained therein. Many methods are available for removing the protective coating  202  of the optical ribbon  108 . For example, the portion of the protective coating  202  to be removed may be heated using a heat stripper, thereby melting the protective coating  202 . Thereafter, the melted portion may be immersed in a methylene chloride bath, so as to eat away the melted portion. An advantage of this technique is that the portion of the protective coating  202  that is removed can be carefully controlled. Other methods of removing the protective coating  202  are known in the art and are within the scope of this application.  
         [0023]    A low-melting point glass  300  is used to hermetically seal the area between the exposed optical fibers  200  and the portion of the wall  104  forming the orifice  106 . The low melting-point glass  300  may have a melting point below 400° C. It is applied by placing beads of the low-melting point glass in the area of the orifice  106  and then heating the beads to their melting point. The beads respond by melting and forming a seal between the wall  104  and the optical fibers  200 . An example of a low-melting point glass is DM2700, available from Diemat, Inc.  
         [0024]    As is evident from FIG. 3, the protective coating  202  does not pass from one side of the wall  104  to the other. One reason for this design choice is that the protective coating  202  is water permeable to some extent. Thus, if the protective coating  202  were to be left in place, water could be carried into the interior of the housing  104  by way of migration through the protective coating  108 . However, glass (such as the glass comprising the optical fiber  200  or the low-temperature melting point glass  300 ) is not permeable by either water or other contaminants. In fact, the barrier created by the optical fiber  200  and the low-temperature melting point glass  300  is hermetic, allowing less than 1*10 −8  cubic centimeters per second of helium to pass through.  
         [0025]    A first layer of epoxy  302  may surround the low-melting point glass  300 . The epoxy  302  may join the low-melting point glass  300 , the optical ribbon  108 , and either the interior or exterior surface of the wall  104 . One advantage of the epoxy layer  302  is that it lends rigidity to the joint formed by the optical fiber  200  and the low-temperature melting point glass  300 . Thus, during subsequent manufacturing stages, the joint is less likely to become damaged. Additionally, the exposed optical fibers  200  are less likely to become damaged. The epoxy layer  302  may be composed of an ultraviolet curable epoxy. Such an epoxy may be cured by exposure to ultraviolet radiation for as little as approximately one minute.  
         [0026]    [0026]FIG. 4 depicts an enlarged cross-sectional view of the joint described with reference to FIG. 3. As can be seen from FIG. 4, an elongated ring  400  surrounds the orifice  106 , attached to the outer surface of the wall  104 . The elongated ring  400  may have an enlarged surface  402 , permitting reliable attachment of the ring  400  to the outer surface of the wall  104 . The ring  400  extends along a length of the optical ribbon  108 , with the ribbon  108  passing through the interior region of the ring  400 , through the orifice  106 , and into the interior of the housing  104 .  
         [0027]    The interior region of the ring  400  is filled with a layer of epoxy  404 . The epoxy  404  serves to add additional rigidity to the structure and to adhere the optical ribbon  108  to the ring  400 . The epoxy layer  404  may or may not be of the same form as that used to encapsulate the low-melting point glass  300 . One advantage of the elongated ring  400  is that it prevents bending of the optical ribbon  108  at the point at which its optical fibers  200  are exposed.  
         [0028]    [0028]FIG. 5 depicts an enlarged cross-sectional view of the joint and ring described with reference to FIG. 4. As shown in FIG. 5, an optional sheath  500  is fitted over the elongated ring  400 , extending along a length of the optical ribbon  108 . The sheath  500  may be made of rubber or another suitable material. The ribbon  108  passes through the interior of the sheath  500 , through the elongated ring  400 , through the orifice  106 , and into the interior of the housing  104 . The sheath  500  may be shaped so as to fit over the ring  400 , and thereafter taper inwardly toward the ribbon  108 . This shape permits relatively little flexibility at the base of the sheath (where the sheath is relatively thick), and progressively more flexibility as the sheath  500  tapers inwardly toward the ribbon  108 .  
         [0029]    The interior region of the rubber sheath  500  may be filled with a room temperature vulcanized silicone  502 . The room temperature vulcanized silicone  502  lends additional rigidity to the sheath structure  500 , and serves to adhere the sheath  500  to the ribbon  108 . One advantage of the sheath  500  is that it prevents the optical ribbon  108  from making a small-diameter bend at the point where the ribbon  108  exits/enters the ring  400 , meaning that the optical fibers  200  contained therein are further protected from damage due to bending.  
         [0030]    Optionally, the elongated ring  400  may contain an outwardly protruding lip (not depicted). The sheath  500  may fit over the outwardly protruding lip, thereby further securing the sheath  500  to the ring  400 .  
         [0031]    [0031]FIG. 6 depicts a ferrule permitting multiple optical ribbons to enter and exit the housing. As can be seen from FIG. 6, the housing  104  may contain first and second orifices  600  and  602 . Each orifice  600  and  602  permits an optical ribbon  604  and  606  to pass into the interior of the housing  104 . As shown in FIG. 6, the orifices  600  and  602  are juxtaposed.  
         [0032]    As was the case with the embodiments shown in FIGS.  1 - 5 , each optical ribbon  604  and  606  contains optical fibers  608  and  610 , which are exposed where they pass through the orifices  600  and  602 . A low-melting point glass  610  is melted between the exposed fibers  608  and  610  and the housing  104 . A layer of epoxy  612  is disposed over the low-melting point glass  612 , so as to reinforce the joint created by the low-melting point glass  610  and the exposed optical fibers  608  and  610 . An elongated ring  614  is attached to the outer surface of the housing  104 , surrounding both orifices  600  and  602 . The elongated ring  614  extends along a length of the optical ribbons  604  and  606 , with the optical ribbons  604  and  606  passing through the interior region of the ring  614 . The interior region of the ring is filled with an epoxy layer  616 . The epoxy layer  616  lends rigidity to the structure and adheres the ring to the optical ribbons  604  and  606 .  
         [0033]    As illustrated in FIG. 6, silicon wafers  618  may be inserted in the interior of the ring  614 . The silicon wafers  618  may be situated on either side of the optical ribbons  604  and  606 , so as to support the ribbons and prevent them from bending or twisting. Another advantage of the wafers  618  is that they occupy space in the interior of the ring  614  that would otherwise be filled by the epoxy layer  616 . Epoxy  616  tends to shrink as it sets. Consequently, stress is imparted to the ribbons  604  and  606 , damaging the optical fibers  608  and  610  contained therein. By reducing the amount epoxy housed in the interior of the ring  614 , the hostile effects of epoxy shrinkage are attenuated.  
         [0034]    A sheath  620  may be fitted over the elongated ring  614 , extending along a length of the optical ribbons  604  and  606 . The sheath  620  may be made of rubber or another suitable material. The sheath  620  may be shaped so as to fit over the ring  614 , and thereafter tape inwardly toward the ribbons  604  and  606 . This shape permits relatively little flexibility at the base of the sheath (where the sheath is relatively thick), and progressively more flexibility as the sheath  620  tapers inwardly toward the ribbons  604  and  606 .  
         [0035]    The interior region of the sheath  620  may be filled with a room temperature vulcanized silicone  622 . The room temperature vulcanized silicone  622  lends additional rigidity to the sheath structure  620 , and serves to adhere the sheath  620  to the ribbons  604  and  606 .  
         [0036]    It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While a presently preferred embodiment has been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope of the present invention. For example, other forms of materials having properties known to be similar to the materials disclosed herein may be used. Additionally, the orifices may take on shapes other than slots (the orifices may be circular, for example). Still further, if the housing contains numerous orifices, the orifices need not be in proximity to one another, and need not be encircled by a single elongated ring. Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the invention disclosed and as defined in the appended claims.