Abstract:
An opto-electronic package includes an enclosed package, a plurality of the electrical contacts extending into the enclosed package, an optical integrated circuit mounted within the package and coupled to the electrical contacts, and optical fibers extending through opposite ends of the package to the optical integrated circuit along a common plane. The package is comprised of a package body and an opposite package lid joined together at an interface substantially at the common plane, and configured to form end pipes around the optical fibers at the opposite ends of the package. This enables the optical fibers to be laid into feedthroughs formed by opposing portions of the package body and the package lid before they are joined together, eliminating the need to feed the fibers through opposite apertures in the package body and for a separate subassembly to mount the opposite fibers and the integrated circuit. The package body and the package lid are solder sealed to each other, and the optical fibers are solder sealed with the end pipes at the opposite ends of the package, to form a hermetically sealed package.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to opto-electronic packages in which optical fibers are sealed, and more particularly to packages in which an optical integrated circuit controls optical fibers coupled thereto in conjunction with electrical leads coupled to the package.  
           [0003]    2. History of the Prior Art  
           [0004]    Opto-electronic devices are known in which the optical fibers are coupled for control in conjunction with electrical leads coupled to an optical integrated circuit (IOC). Examples of such devices include optical switches, lasers, detectors, amplifiers, and modulators. The optical integrated circuit switches the optical fiber inputs and outputs in response to signals provided on the electrical leads.  
           [0005]    Opto-electronic devices of the type described are typically made by attaching an optical integrated circuit to a package body, wire bonding the optical integrated circuit to the body for coupling to leads attached to the body, optically aligning and attaching optical fibers to the optical integrated circuit, sealing the optical fibers to the package body, sealing a lid over the package body to provide an enclosed package, and anchoring the optical fibers at the opposite ends of the package. Many applications of the opto-electronic devices require hermetic sealing of the package body. Hermeticity requires that the enclosure be sealed, including the fiber interfaces therewith, with no organic material within the boundaries of the enclosure.  
           [0006]    One conventional construction of an opto-electronic package for integrated sealing of optical fibers utilizes a separate submount assembly in conjunction with the package body. The submount, which defines a separate substrate for the package, has an optical integrated circuit mounted thereon together with fiber arrays at opposite sides of the optical integrated circuit. The optical integrated circuit is wire bonded to electrical connections on the submount, and the opposite fiber arrays are aligned and attached to the submount. The submount assembly is then placed within a package body in such a way that the opposite fiber arrays are threaded through end pipes at opposite ends of the package body. When the fiber arrays are positioned within the end pipes, the submount assembly is positioned in a central location within the package body, where it is secured to the body. The submount assembly is then wire bonded to electrical leads which extend into the interior of the package body from opposite sides thereof. The optical fiber arrays are then sealed within the end pipes. A lid for the package is placed over the open package body, and is sealed thereon such as by seam welding. The fiber arrays are then sealed at the fiber pipes, such as with cured epoxy, to complete the opto-electronic package.  
           [0007]    Opto-electronic packages of the type described in the preceding paragraph suffer from a number of disadvantages. For one thing, the package must be large enough to thread the fiber arrays through the opposite end pipes without overstressing the fibers. Moreover, even with relatively large packages, the fibers must be bent when attaching the submount assembly. Even when the amount of fiber bending is minimized, fiber damage can occur with the result that signal insertion loss is increased and long term reliability problems sometimes arise. The opposite fiber arrays are jacketed at the outside of bare portions of the fibers. Because the jacketed portions of the fibers are substantially larger than the bare portions, apertures in the end pipes must be large enough for the jacketed portions to be threaded therethrough, even though the smaller bare portions of the fibers are sealed within the end pipes. The bare portions of the fibers are metallized, and sealing is accomplished by dispensing molten solder through vertical apertures in the end pipes. Because the apertures in the end pipes must be large enough to accommodate the jacketed portions of the fibers, they are relatively large, thereby requiring a large amount of solder to fill the apertures and accomplish sealing of the fibers thereto. Automated assembly of the opto-electronic package further requires the use of the separate submount assembly.  
           [0008]    In an effort to eliminate some of the disadvantages of such conventional opto-electronic packages, alternative arrangements are sometimes used. In one such alternative arrangement, input/output fiber arrays are inserted into the package first, followed by optical alignment and attachment in the package. However, fiber array insertion is difficult to automate in such arrangement. While this approach does not require an increase in package size, the optical alignment process cannot be easily automated because the higher package walls get in the way of machine tooling. In a further alternative approach, the fibers are sealed in the fiber pipe before attaching this assembly to the package. However, the fiber pipe-to-package joint must be performed at a sufficiently low temperature to prevent the re-flow of the completed fiber seal. This leads to potential reliability problems, when the product is close to the end of the assembly cycle.  
         BRIEF SUMMARY OF THE INVENTION  
         [0009]    Briefly stated, the present invention provides an opto-electronic package for integrated sealing of optical fibers having an enclosed package which is split at or close to the plane of the fiber axes. This enables the fibers to be laid in the package body with the opposing lid then being placed over the body to form the enclosed package. Threading of the fibers through the opposite end pipes is eliminated, with the result that the package can be made much smaller. Also, because the optical fibers are laid in rather than threaded, the opposite end pipes formed by mating portions of the package body and a lid need only have apertures therein which are very slightly larger than the fibers themselves, eliminating the large apertures which must be solder sealed in prior arrangements. It is not necessary to thread the jacketed portions of the optical fibers through the end pipes.  
           [0010]    In opto-electronic packages according to the invention, automated techniques for fiber alignment and attachment can be accomplished without the need for an intermediate subassembly. The optical integrated circuit is mounted directly on the package base assembly and is wire bonded thereto to complete the required electrical interconnections. The package base may be built as a multi-layer ceramic substrate to provide the required electrical connectivity. Alternatively, the package may have a metal base. In either case, a metal seal ring is used for fiber sealing. The package lid is designed to have the necessary mating features such as to provide the fiber feedthrough for optical fiber sealing and fiber jacket strain relief. The optical fibers can be fully terminated at both ends prior to the final assembly and package sealing operations. The package lid may be sealed to the package body such as by using solder sealing. The optical fibers can be sealed to the assembled package such as by solder sealing metal coated fibers, solder sealing bare fibers, or low temperature glass sealing. The package lid can be sealed in place prior to the sealing of the optical fibers at the opposite ends of the package. However, because both sealing operations typically involve solder sealing, they can be accomplished simultaneously, thereby improving over prior art arrangements in which separate lid and fiber sealing are required. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The above and other objects, features and advantages of the invention will be apparent from the following description when taken in conjunction with the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 is a perspective view of an opto-electronic package for integrated sealing of optical fibers in accordance with the invention.  
         [0013]    [0013]FIG. 2 is a perspective view of a package body of the package of FIG. 1.  
         [0014]    [0014]FIG. 3 is a perspective view of a package lid of the package of FIG. 1, inverted to show the details of the underside thereof.  
         [0015]    [0015]FIG. 4 is a perspective view of the package body of FIG. 2 with an optical integrated circuit mounted in place thereon.  
         [0016]    [0016]FIG. 5 is a perspective view of the structure of FIG. 4 with optical fibers aligned and attached thereto.  
         [0017]    [0017]FIG. 6 is a detailed perspective view of a portion of the arrangement of FIG. 5 showing the manner in which the optical fibers are easily laid into the package body of FIG. 2.  
         [0018]    [0018]FIG. 7 is a block diagram of the successive steps in a method of making the package of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    [0019]FIG. 1 shows an opto-electronic package  10  for integrated sealing of optical fibers, in accordance with the invention. The opto-electronic package  10  has an enclosed package  12  comprised of a package body  14  and an opposing, mating package lid  16 . Electrical leads  18  extend into the enclosed package  12  from opposite sides of the package body  14 . Also, opposite arrays  20  and  22  of optical fibers extend into the enclosed package  12  from opposite ends  24  and  26  thereof, respectively.  
         [0020]    The opto-electronic package  10  in accordance with the invention is shown and described in FIG. 1 and in the other figures of drawing in terms of the opposite arrays  20  and  22  of optical fibers with each of the arrays  20  and  22  being comprised of a plurality of individual fibers. However, those skilled in the art will appreciate from the description to follow that the principles of the invention apply to arrangements having only a single array of fibers at one end of the package as well as those having a single optical fiber at one or both ends of the package.  
         [0021]    [0021]FIG. 2 shows the details of the package body  14 . As shown therein, the electrical leads  18  extend into the package body  14  from opposite sides  28  and  30  thereof The electrical leads  18  are electrically coupled to wire bond pads  32  within a hollow interior  34  of the package body  14 . Opposite fiber feedthroughs  36  and  38  extend from the opposite ends  24  and  26 , respectively, and are of hollowed-out configuration.  
         [0022]    [0022]FIG. 3 shows the package lid  16 , which is inverted to show the details of the underside thereof. The package lid  16  has a hollow interior  40  which combines with the hollow interior  34  of the package body  14  to define a hollow interior within the enclosed package  12 . An edge portion  42  extending around the hollow interior  40  of the package lid  16  forms an interface with a mating edge portion  44  of the package body  14  when the package lid  16  is mounted over the package body  14 , as shown in FIG. 1. With the package lid  16  mounted on the package body  14 , opposite fiber feedthroughs  46  and  48  are disposed over the fiber feedthroughs  36  and  38 , respectively, of the package body  14 .  
         [0023]    [0023]FIG. 4 shows the package body  14  with an optical integrated circuit  50  mounted thereon. The optical integrated circuit  50  has conductive pads thereon (not shown) which are wire bonded to the wire bond pad  32  of the package body  14  to provide desired electrical interconnection of the optical integrated circuit  50  with the electric leads  18 .  
         [0024]    [0024]FIG. 5 shows the structure of FIG. 4 with the opposite optical fiber arrays  20  and  22  aligned and attached thereto. The fiber arrays  20  and  22  are coupled to opposite sides of the optical integrated circuit  50 . Individual optical fibers of the arrays  20  and  22  extend along the opposite fiber feedthroughs  36  and  38  of the package body  14 .  
         [0025]    [0025]FIG. 6 is a detailed showing of a portion of the arrangement of FIG. 5, illustrating the manner in which individual optical fibers  52  of the fiber array  22  are placed within grooves  54  in the fiber feedthrough  38  of the package body  14 .  
         [0026]    The opposite fiber feedthroughs  36  and  38  of the package body  14  lie within and form a continuous feedthrough path that extends through the hollow interior of the enclosed package  12 . The individual optical fibers  52  of the opposite arrays  20  and  22  lie within a common plane extending horizontally along the common feedthrough. In accordance with the invention, the opposite feedthroughs  36  and  38  of the package body  14  and the opposite feedthroughs  46  and  48  of the package lid  16  lie within or substantially within the common plane. The edge portions  42  and  44  of the package body  14  and package lid  16  also lie within the common plane. This allows the optical fiber arrays  20  and  22  to simply be laid in within the feedthroughs  36  and  38  of the package body  14 , as shown and described in connection with FIG. 5. When the package lid  16  is placed over the package body  14 , and is sealed in place, the enclosed package  12  is formed. This is highly advantageous over those prior art techniques in which the optical fibers must be carefully threaded through end pipes or other apertures at the opposite ends of the package body with a separate submount assembly for mounting the optical integrated circuit  50  and the optical fiber arrays  20  and  22  then being moved into place and secured within a central location in the package body.  
         [0027]    The package lid  16  is sealed to the package body  14 , such as by solder sealing around the edge portions  42  and  44  using an electrode, after the package lid  16  is placed over the package body  14 . With the package lid  16  mounted on the package body  14 , the opposite fiber feedthroughs  36 ,  38 ,  46  and  48  form opposite end pipes  56  and  58  within which the optical fiber arrays  20  and  22  reside. The individual optical fibers  52  of the arrays  20  and  22  are sealed within the end pipes  56  and  58  by one of several different techniques. The optical fibers  52  can be metallized by providing a thin metal coating thereon, in which event solder sealing of the fibers  52  within the end pipes  56  and  58  can be accomplished by dropping molten solder through vertical holes in the end pipes  56  and  58 . Alternatively, solder sealing of bare optical fibers can be performed. Still further, low temperature glass sealing can be used. Epoxy sealing can be used for non-hermetic applications.  
         [0028]    The sealing of the optical fiber arrays  20  and  22  within the end pipes  56  and  58  can be done in a separate and subsequent step from the sealing of the package lid  16  on the package body  14 . Where both sealing operations are performed by solder sealing, the two operations can be combined into a single step, inasmuch as the solder used for both sealing operations melts at essentially the same temperature. As previously noted, a hermetic seal is considered to have been accomplished when the enclosure formed by the enclosed package and the optical fiber interfaces are sealed, such as by use of the solder sealing described, and without any organic material within the boundaries.  
         [0029]    In certain prior art opto-electronic packages, it is necessary to thread the optical fibers through the opposite end pipes. Consequently, the openings within the end pipes must be large enough to accommodate jacketed portions of the optical fibers as well as the thinner bare portions thereof. This leaves a relatively large space between the walls of the apertures within the end pipes and the optical fibers, to be filled with solder during sealing of the optical fibers. As a result, substantial amounts of solder are required, and an effective, hermetic seal is more difficult to achieve. In arrangements according to the present invention, the optical fibers are simply laid in place within the feedthroughs. Because the optical fibers  52  are simply laid in place within the feedthrough portions, the grooves  54  can sized so as to be just large enough to accommodate the optical fibers  52 , with the size of the apertures within the end pipes  56  and  58  being just slightly larger than the size of the optical fiber arrays  20  and  22 . Consequently, the spaces to be solder sealed are relatively small, and an effective, hermetic seal of the optical fibers is easy to achieve.  
         [0030]    [0030]FIG. 7 is a block diagram of the successive steps in a method of making the opto-electronic package  10  in accordance with the invention. In a first step  60 , the package body  14  is provided. As shown in FIG. 2, the package body  14 , as provided, has the electrical leads  18  and the opposite fiber feedthroughs  36  and  38 .  
         [0031]    In a second step  62 , the package lid  16  is provided. As shown in FIG. 3, the package lid  16  is provided with the opposite fiber feedthroughs  46  and  48 .  
         [0032]    In a third step  64 , the optical integrated circuit  50  is mounted on the package body  14 . This was shown and previously described in connection with FIG. 4.  
         [0033]    In a fourth step  66 , the optical integrated circuit  50  is electrically coupled to the package body  14  by wire bonding pads thereon to wire bond pads on the optical integrated circuit  50 .  
         [0034]    In a fifth step  68 , the opposite optical fiber arrays  20  and  22  are laid in place by placement on opposite sides of the optical integrated circuit  50  and within the fiber feedthrough path including the feedthroughs  36  and  38 , within the package body  14 . Following lay in, the optical fiber arrays  20  and  22  are aligned with the optical integrated circuit  50 .  
         [0035]    In a sixth step  70 , the package lid  16  is placed over the package body  14 , and is sealed in place around the interface therebetween formed by the edge portions  42  and  44  of the package body  14  and the package lid  16 , such as by solder sealing.  
         [0036]    In a seventh step  72 , the optical fibers  52  are sealed within the end pipes  56  and  58  formed by the fiber feedthroughs  36 ,  38 ,  46  and  48 . As previously described, this may be accomplished by dropping molten solder through vertical holes in the end pipes  56  and  58 . Also, as previously described, the sealing of the optical fibers  52  within the enclosed package  12  need not be performed as a separate step but can be accomplished at the same time that the package lid  16  is sealed to the package body  14  in the sixth step  70 , such as where solder sealing is employed for both sealing operations.  
         [0037]    In a final and eighth step  74 , the optical fibers  52  are anchored at the opposite ends of the enclosed package  12 . Because the optical fibers  52  are relatively brittle and subject to damage, they are anchored at the opposite end pipes  56  and  58 . This may be accomplished by applying organic epoxy between the jacketed portions of the fibers and the pipes  56  and  58 , and then curing the epoxy.  
         [0038]    It will be appreciated by those skilled in the art that opto-electronic packages in accordance with the invention provide various advantages. For one thing, fiber alignment and attachment to the opto-electronic device can be automated without the need for additional substrates, thereby reducing product costs. The package base can be built as a multi-layer ceramic substrate, where desired, to provide the required electrical connectivity. Alternatively, the package may have a metal base. In both cases, a metal seal ring can be used to accomplish optical fiber sealing. The package lid is designed to have the necessary mating features which provide the fiber feedthrough for optical fiber sealing and fiber jacket strain relief. The optical fibers can be fully terminated at both ends prior to the final assembly and the package sealing operations. The design of the opto-electronic package is particularly advantageous for products which require the use of arrays of multiple optical fibers at the opposite sides of the device.  
         [0039]    By splitting the enclosed package of the opto-electronic package in or close to the plane of the optical fiber axes, the fibers or fiber arrays can be laid in without having to thread the optical fibers through openings in the package wall. The sealing of the optical fibers may be accomplished by any suitable means. Hermetic sealing requirements are met by using sealing techniques such as solder sealing of metal-coated fibers, solder sealing of bare fibers, and low temperature glass sealing of fibers. Once the necessary assembly operations have been accomplished, the package lid is attached, and this completes the fiber feedthrough. As previously noted, fiber sealing may be done subsequent to or concurrently with the lid sealing operation.  
         [0040]    For an opto-electronic package with low electrical pin count requirements, the package body may contain a set of glass-sealed pins, such as in a traditional butterfly-style package. If the product requires controlled impedance for higher electrical signal speeds, a ceramic multi-layer feedthrough may be used instead. For higher electrical pin count requirements, the package base may contain a multi-layer ceramic substrate to provide the required electrical connectivity. For products requiring low thermal impedance, the package base may be constructed of a material with high thermal conductivity, such as aluminum nitride or copper-tungsten.  
         [0041]    It will be understood by those skill in the art that the invention is not limited to the embodiments shown and described herein. Such embodiments have been provided only as examples.