Abstract:
An optical waveguide assembly is disclosed. The optical waveguide assembly includes having a substrate face, a cladding disposed on the substrate, and a waveguide core disposed within the cladding. The waveguide core has a waveguide core face such that the waveguide core face is aligned with the substrate face. The assembly further comprises a fiber support assembly having a support face in contact with the substrate face and a fiber having a fiber core face optically aligned with the waveguide core face. Non-adhesive means fixedly connects the substrate face to the support face. A method of non-adhesively bonding an optical waveguide to a fiber support is also disclosed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority from U.S. Provisional Patent Application Serial No. 60/322,163, filed Sep. 14, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Optical telecommunications networks use light transmitted along an optical path between a transmitter and a receiver to transmit light signals at high rates of speed over generally long distances. Typically, the optical path is comprised of optical fiber with a multitude of different types of optical devices disposed along the optical path to perform different functions in the network. The optical fiber generally consists of a core, which guides the light signal, and a surrounding cladding, which retains the light signal in the core through total internal reflection. The optical devices must be connected to and optically aligned with ends of the optical fiber in order to properly transmit the light signals. Increasingly, the optical devices are in the form of planar optical waveguides.  
           [0003]    Planar optical waveguides can be formed by using various materials, such as polymers, glasses, semiconductors, and composite materials as the core and surrounding cladding material, with the core material having a refractive index slightly higher than that of the cladding material in the near infrared region of the optical telecommunication wavelength window. Various optical devices, such as integrated splitters, couplers, arrayed waveguide gratings, and optical waveguide amplifiers can be formed with planar optical waveguides. In order to insert optical waveguide devices into optical fiber communication networks, it is essential to have the capability to connect optical fibers to waveguides.  
           [0004]    Currently available technology for connecting optical fibers to planar optical waveguides uses adhesive bonding, such as epoxy, combined with precision alignment before and during the bonding process. With long exposure to signal light and environmental effects, the adhesive in the optical path between the fiber and the waveguide can suffer, resulting in increased optical absorption and scattering induced performance degradation.  
           [0005]    In a typical prior art method of fiber attachment to a planar optical waveguide, a pre-made fiber attachment subassembly constructed of fiber optic capillary tubes or silicon V-groove arrays is polished at an endface that will be attached to an optical waveguide. The optical waveguide is diced and polished at its endface prior to attachment with the fiber attachment subassembly. The fiber attachment subassembly and the optical waveguide chip are positioned on a six-degrees-of-freedom precision alignment station. After fine mechanical adjustment of the fiber attachment subassembly with the waveguide that produces maximum translational and rotational alignment between the core of the optical fiber and the core of the optical waveguide, an adhesive, such as epoxy, is dispensed between the optical fiber attachment subassembly and the waveguide. The adhesive subsequently undergoes curing, such as by ultra-violet light exposure or thermal treatment, which fixes the relative positioning between the fiber on the fiber attachment subassembly and the waveguide. Due to the fact that single mode optical fiber cores and single mode optical waveguide cores have dimensions in the order of micrometers, the alignment tolerance to achieve acceptable level of optical loss between thr fiber and the waveguide is on the sub-micron level. Further, as the adhesive between the fiber and the waveguide is being cured, in-situ readjustment of the alignment between the optical fiber and the optical waveguide is often required because of adhesive volume shrinkage-induced alignment change.  
           [0006]    It would be beneficial to provide a process for attaching an optical fiber attachment subassembly with a planar optical waveguide without the need for an adhesive and without the need for in-situ adjustment of alignment during the attachment process.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    Briefly, the present invention provides an optical waveguide assembly comprising an optical waveguide having a substrate having a substrate face, a cladding disposed on the substrate, and a waveguide core disposed within the cladding. The waveguide core has a waveguide core face such that the waveguide core face is aligned with the substrate face. The assembly further comprises a fiber support assembly having a support face in contact with the substrate face and a fiber having a fiber core optically aligned with the waveguide core face. Non-adhesive means fixedly connects the substrate face to the support face.  
           [0008]    Further, the present invention provides a method of connecting an optical waveguide to an optical fiber support. The method comprises providing an optical waveguide having a substrate, wherein the substrate has a substrate face; providing an optical fiber support having a support face; applying non-adhesive means to at least one of the support face and the substrate face; and contacting the support face and the substrate face.  
           [0009]    The present invention further provides a method of connecting an optical waveguide to an optical fiber support. The method comprises providing an optical waveguide having a substrate, wherein the substrate has a substrate face; providing an optical fiber support having a support face; providing a bonding plate having a first portion and a second portion; applying non-adhesive means to at least one of the first portion and the substrate; applying the non-adhesive means to at least one of the second portion and the support; and contacting the first portion to the substrate and contacting the second portion to the support such that the substrate face and the support face are contacting each other. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate presently preferred embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain the features of the invention. In the drawings:  
         [0011]    [0011]FIG. 1 is a perspective view of a planar optical waveguide being attached to an optical fiber attachment subassembly according to a first embodiment of the present invention.  
         [0012]    [0012]FIG. 2 is a side view of the planar optical waveguide and optical fiber attachment subassembly of FIG. 1 after attachment.  
         [0013]    [0013]FIG. 3 is a perspective view of a planar optical waveguide being attached to an optical fiber attachment subassembly according to a second embodiment of the present invention.  
         [0014]    [0014]FIG. 4 is a side view of the planar optical waveguide and the optical fiber attachment subassembly of FIG. 3 after attachment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    In the drawings, like numerals indicate like elements throughout. Certain terminology is used herein for convenience only and is not to be taken as a limitation on the present invention. As used herein, when two elements are “optically aligned” or “in optical alignment”, a light signal can be passed between the two elements. The following describes preferred embodiments of the present invention.  
         [0016]    Referring to FIGS. 1 and 2, a method for connecting an optical waveguide assembly  100  and a fiber support assembly  150  according to a first embodiment of the present invention is shown. The optical waveguide assembly  100  is comprised of a substrate  110  with an optical waveguide  120  disposed on the substrate  110 .  
         [0017]    The substrate  110  can be constructed from any of a polymer, glass, semiconductor, composite material, or metal. The waveguide  120  is comprised of a cladding  122  and a waveguide core  124  disposed within the cladding  122 . Preferably, the cladding  122  and the waveguide core  124  are each constructed from a polymer, and more preferably, halogenated polymers, and most preferably, fluorinated polymers. Although polymers are preferred, those skilled in the art will recognize that other materials, including inorganic glass, semiconductor, metal, or composite material can also be used.  
         [0018]    Preferably, for a polymer substrate, the substrate  110  is from the group consisting of polycarbonate, acrylic, polymethyl methacrylate, cellulosic, thermoplastic elastomer, ethylene butyl acrylate, ethylene vinyl alcohol, ethylene tetrafluoroethylene, fluorinated ethylene propylene, polyetherimide, polyethersulfone, polyetheretherketone, polyperfluoroalkoxyethylene, nylon, polybenzimidazole, polyester, polyethylene, polynorbornene, polyimide, polystyrene, polysulfone, polyvinyl chloride, polyvinylidene fluoride, ABS polymers, polyacrylonitrile butadiene styrene, acetal copolymer, poly[2,2-bistrifluoromethyl1-4,5-difluoro-1,3-dioxole-co-tetrafluoroethylene] (sold under the trademark TEFLON® AF), poly[2,3-(perfluoroalkenyl) perfluorotetrahydrofuran] (sold under the trademark CYTOP®), poly[2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole-co-tetrafluoroethylene] (sold under the trademark HYFLON®), and any other thermoplastic polymers; and thermoset polymers, such as diallyl phthalate, epoxy, furan, phenolic, thermoset polyester, polyurethane, and vinyl ester. However, those skilled in the art will recognize that a blend of at least two of the polymers listed above, or other polymers, can be used. It is also preferred that the substrate  110  has a CTE of approximately between 50 and 300 parts per million per degree Celsius.  
         [0019]    The substrate  110  can also be constructed from various glasses, such as silicate, alumino-silicate, or soda lime glasses. The substrate  110  can also be constructed from various semiconductors, such as silicon, germanium gallium-arsenide, indium-phosphide, or other known semiconductor materials. Alternatively, the substrate  110  can be constructed from various metals, such as aluminum, copper, titanium, or alloys of various metals.  
         [0020]    As shown in FIG. 1, the substrate  110  has an endface  112 . The endface  112  is generally planar and is preferably perpendicular to a top surface  114  and a bottom surface  116  of the substrate  110 . However, those skilled in the art will recognize that the endface  112  need not necessarily be perpendicular to either of the top or bottom surfaces  114 ,  116 . Further, the waveguide core  122  has a waveguide core face  124  not covered by the cladding  120 , which is generally coplanar with the endface  112  of the substrate  110 .  
         [0021]    The optical fiber attachment subassembly  150  is used to provide a solid platform for an optical fiber  160  to be optically aligned with the core  122  of the optical waveguide  100 . Preferably, the optical fiber attachment subassembly  150  is constructed from the same or a similar material as the substrate  110 , so that thermal and other environmental effects do not disturb the relation between the substrate  110  and the optical fiber attachment subassembly  150  after attachment.  
         [0022]    The optical fiber attachment subassembly  150  includes a generally planar endface  152 , which is preferably angled at a complementary angle to that of the substrate endface  112 , so that the subassembly endface  152  can be butted against the substrate endface  112  and form a stable engagement between the two endfaces  112 ,  152  when the endfaces  112 ,  152  are contacted together, as will be described in more detail later herein.  
         [0023]    The optical fiber attachment subassembly  150  further includes a bottom surface  154  and a fiber channel  156  disposed generally distal from the bottom surface  154 . The fiber channel  156  is sized to allow the optical fiber  160  to be disposed within the channel  156  with little or no slack between the fiber channel  156  and the optical fiber  160 . As shown in FIGS. 1 and 2, a portion of the fiber  160  can extend beyond the channel  156 .  
         [0024]    The optical fiber  160  includes a cladding  162  and a fiber core  164 , which is generally surrounded by the cladding  162 . The core fiber  164  includes a fiber core face  166 , which is preferably generally coplanar with the endface  152  of the optical fiber attachment subassembly  150 .  
         [0025]    One method of manufacturing the optical fiber attachment subassembly  150  for supporting the optical fiber  160  is disclosed in U.S. Provisional Patent Application Serial No. 60/382,414, filed May 21, 2002 (Attorney Docket No. PHX-0079), which is incorporated herein by reference in its entirety. However, this method is not meant to be limiting, as those skilled in the art will recognize other methods of manufacturing the optical fiber attachment subassembly  150 .  
         [0026]    Prior to bonding the waveguide  100  to the optical fiber subassembly  150 , the waveguide core face  124  is optically aligned with the fiber core face  166 . This alignment can be performed according to any method known to those skilled in the art.  
         [0027]    To bond the substrate  110  to the optical fiber attachment subassembly  150 , a solvent  168  is applied to at least one of the endface  112  of the substrate  110  and the endface  152  of the subassembly  150 . As shown in FIG. 1, the solvent  168  is applied to the endface  112  of the substrate  110 , although those skilled in the art will recognize that the solvent  168  can be alternatively/also applied to the endface  152  of the subassembly  150 . Preferably, the solvent  168  can be at least one of cyclohexanone, methylene chloride, methyl ethyl ketone, trichloroethylene, or any combination of these solvents. Further, those skilled in the art will recognize that other solvents suitable for bonding polymer materials may be used. Referring to FIG. 2, the solvent  168  dissolves and softens an interfacial layer at the endface  112  of the substrate and at the endface  152  of the optical fiber attachment subassembly  150 , merging the endfaces  112 ,  152  with each other, forming a monolithic bond  170 . After the solvent  168  evaporates, the monolithic bond  170  formed between the optical fiber attachment subassembly  150  and the substrate  110  results in an adhesive-flee attachment of a polymer waveguide on a polymer substrate  110  to a polymer optical fiber attachment subassembly  150 .  
         [0028]    Alternatively, instead of using the solvent  168 , other methods of forming an adhesive-free bond between the endface  112  of the substrate  110  and the endface  152  of the fiber attachment subassembly  150  can include localized ultrasonic or laser heating, where the surface at the endfaces  112 ,  152  melts and merges, forming the monolithic bond  170 . In this process, the endfaces  112 ,  152  are first aligned and butted up against each other so that the waveguide core face  124  is optically aligned with the fiber core face  166 . Ultrasonic or laser energy is then applied at the interface.  
         [0029]    An alternative embodiment of the present invention is shown in FIGS. 3 and 4. The same waveguide  100  and optical fiber subassembly  150  described above and shown in FIGS. 1 and 2 are used, with the addition of a bonding support plate  250 , shown in FIGS. 3 and 4. Preferably, the bonding support plate  250  is constructed from the same material as either or both of the substrate  110  and the optical fiber subassembly  150 . The bonding support plate  250  has a first portion  252  which is bonded to the bottom surface  116  of the substrate  110  and a second portion  254 , which is bonded to the bottom surface  154  of the optical fiber attachment subassembly  150 .  
         [0030]    Referring to FIG. 4, the solvent  168  dissolves and softens thin layers at the first and second portions  252 ,  254  of the bonding support plate  250  and the bottom surface  116  of the substrate  110  and the bottom surface  154  of the optical fiber attachment subassembly  150 , merging the bottom surfaces  116 ,  254  with the first and second portions  252 ,  254 , respectively, forming a monolithic bond  270 . After the solvent  168  evaporates, the monolithic bond  270  formed between the optical fiber attachment subassembly  150  and the substrate  110  results in an adhesive-free attachment of a polymer waveguide on a polymer substrate  110  to a polymer optical fiber subassembly  150 . The method described herein with respect to the second embodiment keeps the solvent  168  away from the cores  122 ,  164 , reducing the risk of damaging the waveguide core face  124  and the fiber core face  166  with the solvent  168 . Further, the bonding support plate  250  provides additional strength to the combined waveguide  100  and optical fiber subassembly  150 .  
         [0031]    Although, as shown in FIG. 4, the solvent  168  is applied to the first and second portions  252 ,  254  of the bonding support plate  250 , those skilled in the art will recognize that the solvent  168  can alternatively/also be applied to the substrate  110  and the fiber attachment subassembly  150 . Further, although FIG. 4 shows the bonding support plate  250  attached to the bottom of the substrate  110  and the optical fiber subassembly  150 , those skilled in the art will recognize that the bonding support plate  250  can be connected to the sides of the substrate  110  and the optical fiber subassembly  150 .  
         [0032]    As with the first embodiment, alternatively, instead of using the solvent  168 , other methods of forming an adhesive free bond between the substrate  110  and the fiber attachment subassembly  150  include using localized ultrasonic or laser heating, where the first and second portions  252 ,  254  of the bonding support plate  250  and the bottom surfaces  116 ,  154  of the substrate  110  and the fiber attachment subassembly  150  melt and merge, forming the monolithic bond  270 .  
         [0033]    Further, although not shown, those skilled in the art will recognize that a combination of the first and second embodiments of the present invention can be used, with the solvent, ultrasonic heating, laser heating, or whatever method used to bond the waveguide  100  and the fiber attachment subassembly  150 , by applying the method to both the endfaces  112 ,  152  and th the bottom surfaces  116 ,  154 , with the bonding support plate  250 .  
         [0034]    It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.