Abstract:
Fiber optic connections are accomplished with passive alignment using a modular approach. An improved waveguide substrate has precisely aligned waveguides secured in place, including at an inlet channel, an outlet channel, or both. The waveguides need not extend beyond the face of the inlet or outlet location, and there is no need to have any unsupported fiber optic fibers connect to the waveguide substrate. When provided, a connector module or modules have fiber optic fibers having supported ends which precisely align with the waveguides of the waveguide substrate. Connecting pins typically are provided to insure alignment between waveguides and fibers is easily attained.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention generally relates to fiber optic systems, especially connection techniques and devices. More particularly, the invention relates to technology which is suitable for use in optical multiplexing and demultiplexing. Included are so-called dense wavelength division multiplexing (DWDM) products.  
       BACKGROUND OF THE INVENTION  
       [0002]     In fiber optic transmission systems, signals are transmitted along optical fibers by optical frequency waves (light) generated by sources such as light emitting diode (LED) units, lasers, and the like. Optical fibers typically are fabricated of glass materials and, as optical fiber circuitry has developed, it has become necessary to provide connecting devices which can couple one optical fiber to another. It is important that the connection be in an end-to-end aligned relationship.  
         [0003]     A traditional procedure for making a connection between ends of optical fibers is to initially remove a protective jacket from a given length of fiber at the end of the fiber to be joined. After the jacket is removed, a 250 micron (outside diameter) buffer is exposed which then can be stripped to expose a 125 micron (outer diameter) fiber. In the prior art, the fiber body then is threaded through a passage in a ferrule where it is affixed in place by adhesive and/or crimping. The fiber is inserted so as to extend well beyond a front surface of the ferrule. The exposed fiber material then is cleaved and polished. Any remaining adhesive is removed. The ferrules then are assembled into a connector assembly which is intended to position the optical fibers with their optical axes in alignment for connection to the fibers of a mating connector or other appropriate connecting device.  
         [0004]     Fiber optic ribbon cable has become increasingly popular to provide multiple channels in a single cable structure. An optical ribbon cable is similar to any other well-known ribbon electrical cable to the extent that a plurality of optical fibers or channels are disposed in a line or a generally coplanar relationship. With these approaches, prior art practice for terminating the optical fibers of a fiber optic ribbon cable is generally similar to the procedure summarized above. In general, the unitary protective jacket surrounding the line of fibers is removed so that the buffered fibers are exposed which then are stripped such that the unprotected fibers project from the flat cable in a line. Typically, in the prior art these individual fibers must be inserted into respective individual holes or passages in a prefabricated connector ferrule. The passages align the fibers at a predetermined spacing for coupling to the ends of the fibers in a complementary connector ferrule or other connecting device.  
         [0005]     This terminating process of the individual fibers of a multi-fiber cable is accompanied by a number of problems. Because of the very thin size and extremely fragile nature of the fibers, it can be tedious to insert a fiber into a single aligning hole or passage. Where a plurality of such fibers from a single cable need to be inserted into a plurality of passages, the difficulty is multiplied considerably. For example, if a single fiber of a multiple-fiber cable is broken, the stripped cable end and ferrule either must be discarded, reworked, or both. Since these processes typically have been carried out by hand, they can be extremely inefficient and result in unnecessary expense.  
         [0006]     In the prior art, placing individual fibers of a multi-fiber cable into individual holes or passages in a connector ferrule results in a high percentage of rejects. The ferrules must be inspected hole by hole. In addition to fibers being broken, the holes themselves may be too large or too small, or not circular, or have some other defect. Connector ferrules comprise bodies which are crystalline in nature, typically of ceramic material. Instead, they can be molded of a plastic or polymeric material. For multiple channel ferrules, the fiber-receiving holes or passages must be formed precisely to maintain a proper form or alignment and spacing between the fibers in order to prevent tolerance problems causing transmission losses during mating.  
         [0007]     Alignment problems and tolerance problems such as those noted above are further complicated in connector assemblies wherein a pair of mating connector ferrules themselves are placed into mating condition by two alignment pins. These alignment pins typically have one end of each pin extending into a passage of the connector ferrule, and the opposite end of the pin is inserted into a passage in the mating connector ferrule, with a chamfered lead-in on the pin for alignment. The problems of maintaining precise tolerances with the alignment pins and their passages must be added to the tolerance problems in maintaining precise spacing and alignment of the individual holes for the optical fibers of the fiber optic cable. It can be understood why there are such a high number of rejects during the application of prior art connector units.  
         [0008]     With further reference to DWDM products, multiplexing can be used to combine channels of different wavelengths, whereas at the receiving end demultiplexing separates the channels from one another with a minimum inter-channel cross talk. In DWDM products, the separation between adjacent devices is designed to be fairly narrow in order to increase device capacity. A typical separation is 200 GHz to 50 GHz, corresponding to 1.6 nm and 0.4 nm in wavelength, respectively. Currently available DWDM products are of the arrayed waveguide (AWG) type, such as of the 1×8 (1 input, 8 outputs) 1×16, 1×32 and 1×64 configurations. It will be appreciated that a small difference among the lengths of the output waveguides is responsible for separating the stream of wavelengths from one another.  
         [0009]     One of the most important functions in connection with DWDM products is attaching fibers for coupling right in and out of the device with minimum loss. In the past, this has required input and output fibers being first attached to separate platforms at appropriate distances using adhesive glue or curable epoxy. In this prior art approach, these platforms then are bought in close proximity with a device such as a multiplexing and/or demultiplexing device and actively aligned to the appropriate waveguides. An example of a prior art approach is found Yamane et al. U.S. Pat. No. 5,557,695, in which so-called integral waveguides are provided and the optical fibers are laid in guide grooves as part of the cone procedure.  
         [0010]     In the prior art active alignment practice, light is launched into the input fibers, and light emanating from the output fibers is monitored. Determining the optimum coupling position requires using x-y-z movement and rotational movement of the device and the platforms with respect to each other in the vertical and horizontal axes. The pieces then are locked in place with adhesive, glue or curable epoxy. From this it will be appreciated that active alignment is tedious, involved, expensive and slow. Using a fiber optic connector ferrule is useful in precisely aligning a line of fibers for alignment with a complementary ferrule. An example of such an approach and of a type of fixture for assembling same is shown in Bunin et al. U.S. Pat. No. 5,907,657, incorporated hereinto by reference. While ferrules of this type are an important advance in the art, further improvements are realized according to the present invention which achieves an advantageously passive alignment requiring no light up or monitoring of light in the fibers. The passive alignment process of the invention is fast, reproducible, easy and cost effective. So advanced is this approach that accurate alignment according to the invention is achievable in the field by straightforward component removal and replacement. This is a marked improvement over prior art approaches which require alignment in a laboratory environment, typically requiring very expensive alignment equipment.  
       SUMMARY OF THE INVENTION  
       [0011]     In accordance with the present invention, passive alignment fiber optic connection is accomplished using a modular approach. Included is a fiber optic connection system which combines a connector receptacle such as a ferrule together with a receptor substrate which has a plurality of waveguides. The respective ends of these waveguides are positioned such that they are in precise alignment with spacing and positioning of respective ends of the connector receptacle fibers. The substrate can be a chip such as an AWG type of DWDM. It is important to note that the invention avoids the traditional approach of laying fiber optic fibers onto the substrate chip or within grooves of the substrate chip or other component. In order to be assured that the alignment of the respective ends is properly positioned during the passive alignment according to the invention, projecting pins and complementary pin passages orient proper alignment and help to secure that alignment. The invention provides center-to-center alignment between respective ends of fiber optic fibers in one component and respective ends of waveguides of another component when these components are connected to each other.  
         [0012]     It is accordingly a general object of the present invention to provide an improved fiber optic passive alignment connection.  
         [0013]     Another object of this invention is to provide an approved fiber optic connection component which is readily installed in the field and does not require laboratory conditions or expensive equipment.  
         [0014]     Another object of the present invention is to provide an improved system and method which permits replacement of only damaged or faulty components, or those suspected of being faulty, rather than requiring replacement of an-entire assembly.  
         [0015]     Another object of this invention is an improved system and method which provide a modular approach to fiber optic connection.  
         [0016]     Another object of the present invention is to provide an improved chip substrate structure that is a waveguide substrate which neither utilizes fiber optic fibers at points of connection nor receives fiber optic fibers from other components.  
         [0017]     These and other objects, features and advantages of the present invention will be apparent from and clearly understood through a consideration of the following detailed description.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     In the course of this description, reference will be made to the attached drawings, wherein:  
         [0019]      FIG. 1  is a perspective, partially exploded, view of an illustrated embodiment showing a plurality of connectors or ferrules being passively aligned with a chip substrate having a structure according to the invention;  
         [0020]      FIG. 2  is an enlarged prospective view of one of the connector receptacles illustrated in  FIG. 1 :  
         [0021]      FIG. 3  is a perspective view of a connector receptacle in general alignment for connection with an example of a chip substrate according to the invention;  
         [0022]      FIG. 4  is a perspective view in accordance with  FIG. 3  and showing the chip substrate in exploded perspective;  
         [0023]      FIG. 5  is a different perspective view of the assembly of  FIG. 4 ;  
         [0024]      FIG. 6  is an end or face view along the line  6 - 6  of  FIG. 3 ;  
         [0025]      FIG. 7  is an enlarged, detail cross-sectional view along the line  7 - 7  of  FIG. 3 , after assembly; and  
         [0026]      FIG. 8  is a further enlarged, detail cross-sectional view in a direction opposite from that of  FIG. 7 , through the fiber and after assembly.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     In the embodiment which is illustrated in  FIG. 1 , a connector receptacle or connector ferrule  21  is in general position for aligning assembly with one attachment location of a substrate  22 , shown in exploited form in this view. Another connector receptacle  23  likewise is shown in a general mating alignment with a different attachment location of the substrate  22 . Each attachment location provides a connection location at which passive alignment takes place, as explained more fully elsewhere herein.  
         [0028]     For purposes of illustration, substrate  22  has an input end  24  and an output end  25 . The illustrated input end is arranged for accommodating a relatively low number of optical channels  26 , while the illustrated output end accommodates a greater number of optical channels  27 . Corresponding, connector receptacle  23  has a fiber optic cable  28  having a relatively low number of optical fibers, while the fiber optic cable  29  has a higher number of optical fibers. It will be appreciated that the number of fibers in each fiber optic cable can vary as required for communication with the particular substrate or chip. For example, both fiber optic cables  28  and  29  can contain the same number of optical fibers. A typical fiber optic ribbon can have 12 fibers, for example. The substrate  22  of  FIG. 1  can be seen as an illustration of a 1×12 AWG type DWDM product. Clearly, other combinations of input channels and output channels are contemplated.  
         [0029]     The illustrated connector ferrule  21  is shown in more detail in  FIG. 2 . Fibers  31  of the fiber optic cable  29  are shown. Ends  32  of these fibers are illustrated at the mating face  33 . A ferrule body  34  also is shown. Attachment pins in the connector component or in the substrate component are provided to mate with pin passageways in the other component. In the illustrated embodiment, the pins are on the connector component, and the pin passageways or receptors are in the substrate component. As shown, two attachment pins  35  project from the face  33 . In a typical assembly each pin  35  is secured within a pin passage  36 .  
         [0030]     It will be appreciated that these various components of the connector are immovably assembled with respect to each other. Thus, the fiber ends  32  are secured in place, as are the pins  35 , in accordance with a predetermined alignment pattern. Pins  35  preferably are precision cylindrical pins having a round cross-section, a typical standard pin in this regard having a diameter of 700 microns, plus or minus 1 micron. A suitable connector receptacle can be made in accordance with Bunin et al. U.S. Pat. No. 5,907,651, incorporated by reference hereinto.  FIG. 2  shows a typical suitable example of an empty connector and of its component parts.  
         [0031]      FIG. 3 ,  FIG. 4  and  FIG. 5  show a portion of the assembly or system of  FIG. 1 . Only one connector is shown, and the substrate is shown in simplified form in order to of illustrated important aspects of the invention. For purposes of illustration, these views show what can be considered to be a portion of the substrate  22  of  FIG. 1 . For purposes of illustration, this will be identified as a substrate output portion  37 . This substrate  37  is composed of two principal structural components, namely an upper wafer  38  and a lower wafer  39 , as viewed in the drawings.  
         [0032]     When wafers  38  and  39  are assembled together, pin passageways  41  are formed, as illustrated in  FIG. 3 . In addition, there are one or more waveguide locations  42 . These waveguide locations  42  can be formed into the wafer assembly (as shown), or they can be locations which are present between wafers without requiring any channels, grooves or the like formed into a wafer. It is important to note that these waveguide locations are present or are formed without requiring the laying of any optical fibers thereat.  
         [0033]     In the embodiment where channels are formed into the wafer assembly, each waveguide location  42  includes a waveguide channel  43  containing a waveguide  44 . In this embodiment which is shown, each waveguide channel  43  is triangular in cross-section and is formed into the upper wafer, as viewed in the drawings. In this embodiment as shown, each waveguide  44  is positioned on the lower wafer, as viewed in the drawings. As is typical of waveguides, those illustrated are of a square cross section.  
         [0034]     Each of the upper wafer  38  and the lower wafer  39  are made of suitable available materials, and their respective features can be made or located by incorporating generally known techniques and materials. After fabrication, these wafers are secured to each other to form the waveguide substrate  37 .  
         [0035]     When channels  43  are formed in the upper wafer  38  for example, they typically are formed by means of an etching procedure, such as one incorporating the use of potassium hydroxide. Precise positing of the channels  43  and of upper portions  45  of the pin passageways can be accomplished by using photoresist and masking techniques and known photolithographic types of procedures. This type of approach accomplishes the predetermined alignment pattern discussed herein with respect to the channels and passageways of the upper wafer  38 .  
         [0036]     The location of the waveguides  44  and of lower portions  46  of the pin passageways  41  in the lower wafer  39  can be formed by known techniques in order to provide the predetermined alignment pattern characteristic of the waveguide substrate  37 . Examples of specific processing steps which can be incorporated in forming the features of the waveguide substrate can be found in Yamane et al. U.S. Pat. No. 5,557,695, which is incorporated hereinto by reference. As needed, multiple layers having different refraction indices, typically formed by suitable deposition techniques, can be incorporated. Usually the substrate body is a silicon substrate. Mask patterns having the precise predetermined alignment pattern and spacing typically will be deposited by vapor deposition, sputtering, or some other suitable approach. Typically, these are used in association with an etching procedure. Appropriate energy sources are used, and several steps may be incorporated, in order to complete formation of the predetermined alignment pattern of the waveguide substrate. The waveguides typically are formed of sol-gel materials, silicon dioxide materials, or other suitable material.  
         [0037]     In an important aspect of the invention, the predetermined alignment pattern which is characteristic of the waveguide substrate module  37  is duplicated by an alignment pattern of the fiber ends  32  and the attachment pins  35  of each connector module  21 . This is illustrated more particularly by reference to  FIG. 6 , to  FIG. 7  and to  FIG. 8 .  
         [0038]      FIG. 6  illustrates a typical predetermined alignment pattern of the waveguide substrate  37 . Ends of the waveguides  44 , more particularly the respective centers thereof, are precisely spaced and aligned with respect to each other and with respect to pin passageways  41 , more particularly the respective centers thereof. Preferably, these ends of the waveguides also are in alignment with respect to mating face  47  of the waveguide substrate. There is no need for the waveguides to project beyond this mating face  47 . In an important embodiment, these waveguide ends are flush with this mating face.  
         [0039]     This alignment pattern of the waveguide ends and pin passageways  41  of the waveguide substrate  37  is duplicated in the connector  21 . More specifically, fiber ends  32 , more particularly the respective centers thereof, follow the identical predetermined alignment pattern of the ends of the waveguides  44 . Preferably, these ends  32  of the optical fibers also are in alignment with respect to mating face  33  of the connector module. There is no need for the fibers to project beyond this mating face  33 . In an important embodiment, these fiber ends are flush with this mating face.  
         [0040]     In addition, the precise predetermined alignment pattern which is characteristic of the pin passageways  41  of the waveguide substrate module is precisely repeated for the attachment pins  35  of the connector module, more particularly the respective centers of the passageways  41  and pins  35 .  
         [0041]     In summary, after pins  35  are inserted into pin passageways  41 , there is passively achieved precise center-to-center alignment of each optical waveguide end with each respective optical fiber end. Whole registry of these respective ends is facilitated by center-to-center alignment of the respective attachment pins  35  and pin passageways  41 , in conjunction with a precise sizing of pins  35  and pin passageways  41  which allows for sliding insertion while avoiding play or movement of the pins within the pin passageways.  
         [0042]      FIG. 7  shows waveguide channels  43  accommodating waveguides  44 . When desired a suitable filler  48 , such as a set epoxy, other adhesive, or other suitable filler material, can be included as shown. Ends of the optic fibers  31  are shown in broken lines in  FIG. 7  in order to illustrate the passive center-to-center alignment which is achieved according to the invention. Each end includes a fiber core  51 , which is surrounded by body  52  of the fiber itself. This same relationship is shown from an opposite point of view in  FIG. 8 . It will be appreciated that the relative sizing between the fibers and the waveguide is not to scale in  FIG. 7  and  FIG. 8 . In a typical structure, each waveguide has a side width of about 7 microns, while each fiber core  51  has a diameter of about 9 microns. A typical fiber body  52  has an outer diameter of about 125 microns. A typical cladding which has been removed therefrom at this location of the connector  21  has an outer diameter of about 250 microns.  
         [0043]     Preferably, the ends  32  of the fibers, and thus the fiber cores  51  and fiber bodies  52 , do not project beyond the mating face  33  of each connector  21 . This helps to protect the fibers and to assure that they remain in the predetermined alignment pattern because they are fully supported by the mating face  33 . Typically, ends  32  are flush with the mating face  33 , with the fibers being embedded within the connector  21 .  
         [0044]     In a typical manufacturing approach, an epoxy or other suitable filler which sets is used. An assembly procedure such as this is instrumental in maintaining the needed alignment. Often, an assembly approach such as this includes polishing the ends and at least a portion of the mating face; which helps to insure a smooth, planer surface for alignment mating with face  47  which opposes face  33  after assembly of a connector with the waveguide substrate.  
         [0045]     With the present invention, there is no requirement for any optical fiber to enter into a receptor of any kind such as a channel associated with the waveguide substrate. Likewise, there is no requirement for any optical waveguide to enter into the connector. There is no need to provide any grooved receptors or the like for aligning or connecting any optical fiber.  
         [0046]     When desired, the passively aligned connection which is characteristic of the invention can be rendered more stable and secure by attaching together the mating faces  33  and  47 . Any suitable attachment means is possible, including a setting adhesive or other glue-type component, specifically including an epoxy adhesive system. Such attachment preferably is at or near the periphery of the engaging faces, so as to not interfere with the optical communication between the fiber ends and the waveguide ends.  
         [0047]     The present invention avoids the labor intensive, tedious and potentially imprecise laying down of optical fibers in order to make an optical fiber connection, which typically is accomplished successfully only in a laboratory environment. Instead, with the present invention, a component such as a connector module or a chip module which is damaged or suspected as being defective is removed, such as by pulling the components apart while sliding the attachment pins  35  out of the pin passageways  41 , followed by reinsertion after appropriate replacement. This can be accomplished in the field, rather than requiring return to a manufacturing facility or laboratory environment in order to achieve the needed connection when replacements or repairs are needed. Moreover, this field work can be in the nature of “trouble shooting” work during which modules can be exchanged until the defective component is identified and replaced.  
         [0048]     It will be understood that the embodiments of the present invention which have been described are illustrative of some of the applications of the principles of the present invention. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention.