Abstract:
An electro-optic module with an optical coupling efficiency, the module comprising a receptacle assembly, wherein an end of the receptacle assembly is capable of receiving a light guiding element and wherein an opposite end of the receptacle assembly is capable of receiving an optical lens assembly positioned therein the receptacle assembly. An optoelectric package which includes an optoelectronic device is capable of being affixed to the opposite end of the receptacle assembly wherein an optical axis extends from the end to the opposite end of the receptacle assembly such that the light guiding element and the optoelectric device are in communication through a lens included in the optical lens assembly. The optical lens assembly is held fixedly in place against an inward periphery of the receptacle assembly such that a distance between the lens and the optoelectronic device can be adjusted to adjust the optical coupling efficiency.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Application Ser. No. 60/335,307, filed 02 Nov. 2001. 

   FIELD OF THE INVENTION 
   This invention relates to optical-to-electrical and electrical-to-optical modules and more particularly to optical alignment features in such modules. 
   BACKGROUND OF THE INVENTION 
   At the present time, transmitting data by optical fibers is very popular. Optical fibers have a large number of advantages over the standard wire transmission devices, including much higher transmission frequencies, less losses, and much higher data rates. Generally, in the present communication systems, each optical fiber has a module that includes a transmission channel and a reception channel at each end. One of the pair of channels receives electrical signals, converts the electrical signals to an optical (light) beam by way of a laser or the like and introduces the beam into one end of the optical fiber, which then transmits the modulated optical beam to a similar module at the other end of the optical fiber. The second channel of the module receives modulated optical beams from the optical fiber, conveys the modulated optical beam to a photo diode or the like, which converts the optical beam back to an electrical signal. A problem with this system, however, is the optical coupling efficiency which is highly sensitive to the alignment of the optical fiber and the laser or photo diode. 
   It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art. 
   Accordingly, it is an object of the present invention to provide a new and improved electro-optic module. 
   It is an object of the present invention to provide a new and improved electro-optic module which has an improved optical coupling efficiency. 
   It is another object of the present invention to provide a new and improved electro-optic module which can be actively aligned. 
   It is still another object of the present invention to provide a new and improved electro-optic module which is easier to optically align to a higher precision. 
   SUMMARY OF THE INVENTION 
   To achieve the objects and advantages specified above and others, an electro-optic module with an optical coupling efficiency is disclosed. In a preferred embodiment, the electro-optic module includes a receptacle assembly wherein an end of the receptacle assembly is capable of receiving a light guiding element and wherein an opposite end of the receptacle assembly is capable of receiving an optical lens assembly. 
   In the preferred embodiment, an optoelectric package which includes an optoelectronic device is affixed to the opposite end of the receptacle assembly wherein an optical axis extends from the end to the opposite end of the receptacle assembly such that the light guiding element and the optoelectric device are in communication through a lens included in the optical lens assembly. The optical lens assembly is held fixedly in place against an inward periphery of the receptacle assembly such that a distance between the lens and the optoelectronic device can be adjusted to adjust the optical coupling efficiency. 
   In the preferred embodiment, the receptacle assembly includes an elongated ferrule wherein the ferrule includes a radially outwardly directed step formed in the outer periphery to operate as a stop for a resilient sleeve and further includes at least one radially inwardly directed step. In the preferred embodiment, the resilient sleeve includes an inwardly directed flange formed adjacent to one end so as to engage the radially outwardly directed step of the ferrule and prevent relative longitudinal movement between the ferrule and the resilient sleeve in a direction substantially oriented parallel to the optical axis. 
   Further, in the preferred embodiment, the resilient sleeve includes radially outwardly directed ribs or protrusions in an outer periphery which are designed to frictionally engage an inner periphery of an opening in a mounting housing. The ferrule and the resilient sleeve are capable of being press-fit into the opening in the mounting housing which frictionally holds the electro-optic module in place. 
   In one embodiment, the optical lens assembly is formed with radially outwardly projecting ribs or protrusions in an outer periphery so that the optical lens assembly can be press-fit a desired distance along the optical axis within the receptacle assembly. In another embodiment, the optical lens assembly is threadedly engaged within the receptacle assembly to allow for longitudinal adjustments along the optical axis. By allowing precise adjustments of the lens along the optical axis, the optical coupling efficiency can be precisely adjusted. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and further and more specific objects and advantages of the instant invention will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment thereof taken in conjunction with the drawings, in which the single FIGURE is a sectional view of an electro-optic module in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the FIGURE, a sectional view is illustrated of an electrical-to-optical (hereinafter referred to as electro-optic) module  10  in accordance with the present invention. It will be understood by those skilled in the art that modules of the type discussed herein generally include a pair of channels, one of which receives electrical signals, converts the electrical signals to optical (light) beams by way of a laser or the like and introduces them into one end of an optical fiber, which then transmits the modulated optical beams to external apparatus. The second channel of the module receives modulated optical beams from an optical fiber connected to the external apparatus, conveys the modulated optical beams to a photo diode or the like, which converts them to electrical signals. In the following description, the apparatus and methods are primarily designed for use in the electro-optic channel, which will be discussed with the understanding that the description could be applied to either of the channels in some applications. 
   In a preferred embodiment, module  10  of the FIGURE includes a receptacle assembly  11  and an optoelectric package  12  aligned and affixed together, as will be disclosed in more detail below. Receptacle assembly  11  is designed to receive an optical fiber  14  in communication therewith, in a manner that will become clear presently. Optical fiber  14  can be a single or multiple mode fiber and includes a glass core  15  and a cladding layer  16 , or another suitable light guiding element. 
   In the preferred embodiment, optoelectric package  12  includes a base or support plate  40  and a mounting plate  42  positioned thereon. One or more spacer rings  43  may be positioned on or incorporated into plate  42  to provide sufficient distance for components mounted to plate  42 . In this example, a laser  45  is mounted on the upper surface of mounting plate  42  and positioned to transmit light generated therein to a lens block  46 . Alternatively, laser  45  could be a photodiode or the like. Lens block  46  is mounted on mounting plate  42  by some convenient means, such as outwardly extending ears (not shown). In the preferred embodiment, a ring  47  is positioned on spacer ring  43  and a cap or cover  48  is affixed to ring  47 . 
   Generally, the entire assembly, including plate  40 , mounting plate  42 , spacer rings  43 , ring  47  and cover  48  are fixedly attached together by some convenient means, such as welding, gluing, etc. so that laser  45  is enclosed in a hermetically sealed chamber. However, a hermetic seal is not necessary in many embodiments in which the laser or photodiode used is either separately sealed or is not sensitive to atmospheric conditions. Further, it will be understood that while we show one example of the components included in optoelectronic package  12 , it is anticipated that optoelectronic package  12  can include other components fixedly attached together which provide essentially the same function. 
   In the preferred embodiment, a window  50  is sealed in cover  48  so as to be aligned with lens block  46 . Lens block  46  redirects light from laser  45  at an angle (i.e. 90°) out through window  50  and may include one or more lenses or optical surfaces. Further, lens block  46  may be molded from plastic for convenience in manufacturing. In some specific applications, the laser may emit directly through window  50  and in these applications the first lens may be positioned between window  50  and the laser or may be incorporated into window  50 . 
   In the preferred embodiment, receptacle assembly  11  includes an elongated cylindrical ferrule  20  having an end  21  defining a fiber receiving opening and a mounting flange  22  at the opposite end. Ferrule  20  has a radially outwardly directed step  24  formed in the outer periphery to operate as a stop for a resilient sleeve  25 . Sleeve  25  has an inwardly directed flange formed adjacent one end so as to engage step  24  and prevent relative longitudinal movement between ferrule  20  and sleeve  25 . Sleeve  25  also includes radially outwardly directed ribs or protrusions  26  in the outer periphery which are designed to frictionally engage the inner periphery of a cylindrical opening in a mounting housing (not shown). Thus, to easily and conveniently mount module  10  in the housing, ferrule  20  with sleeve  25  engaged thereover is press-fit into the cylindrical opening in the housing and frictionally holds module  10  in place. Preferably, sleeve  25  is formed, completely or partially, of some convenient resilient material and may be electrically conductive or non-conductive as required in the specific application. 
   Progressing from end  21  toward flange  22 , ferrule  20  has two radially inwardly directed steps  32  and  33 . In the preferred embodiment, step  32  provides a surface or stop for the mounting of an optical spacer  35  and step  33  provides a limit or an extreme stop in the positioning of an optical lens assembly  36 . A retaining ring  34  is frictionally engaged in ferrule  20 , generally between steps  32  and  33 , to hold optical spacer  35  fixedly in position against step  32 . In this preferred embodiment, optical fiber  14  is inserted into ferrule  20  so that glass core  15  buts against spacer  35 , which substantially reduces or suppresses return reflections. 
   In the preferred embodiment, lens assembly  36  includes a cylindrically shaped body with an outer diameter slightly smaller than the inner diameter of ferrule  20 . The cylindrically shaped body defines a central opening for the transmission of light therethrough from an end  37  to an opposite end  38  along an optical axis Z. A lens  39  (which may include one or more lens elements) is integrally formed in the central opening of the cylindrically shaped body. In one embodiment, lens assembly  36  is formed with radially outwardly projecting ribs or protrusions in the outer periphery so that it can be press-fit a desired distance into ferrule  20 . In another embodiment, lens assembly  36  is threadedly engaged in ferrule  20  to allow for very small longitudinal adjustments, as will be described in more detail presently. 
   In the preferred embodiment, lens assembly  36  is formed of plastic and may be, for example, molded to simplify manufacturing of module  10 . It should be understood that the term “plastic” is used herein as a generic term to describe any non-glass optical material that operates to transmit optical beams of interest therethrough and which can be conveniently formed into lenses and the like. For example, in most optical modules used at the present time the optical beams are generated by a laser that operates in the infra-red band and any materials that transmit this light, including some oxides and nitrides, come within this definition. 
   In the preferred embodiment, optoelectric package  12  is affixed to receptacle assembly  11  with flange  22  of ferrule  20  butting against the exposed surface of cover  48 . Further, optoelectric package  12  is optically aligned with receptacle assembly  11  so that light from laser  45  is directed into core  15  of optical fiber  14 . This alignment can be accomplished in different ways but one reliable method is known as active alignment. In the active alignment process, laser  45  is activated and receptacle assembly  11  is positioned approximately over optoelectric package  12 . The light in optical fiber  14  is measured and the alignment is adjusted for maximum light. When maximum light is measured, alignment has been achieved and receptacle assembly  11  is fixed to optoelectric package  12  by some convenient means, such as welding or adhesive. 
   Referring generally to the components of module  10  for purposes of orientation, laser  45  supplies light through optical block  46 , window  50 , lens  39 , and spacer  35  to core  15  of optical fiber  14 . The main purpose of the optics in module  10  is to make sure that light from laser  45  is generally collimated (parallel beams) along optical axis Z and to focus the collimated beam finally on the end of core  15  of optical fiber  14 . In this example, the lens system includes at least two lenses or lens elements,  46  and  39 , that provide the collimating and focusing. Generally, the distance between laser  45  and optical block  46  is critical, since most of the optical power is in the first curved lens and the second lens simply provides minor adjustment. If the placement of laser  45  and optical block  46  is done to a high accuracy (e.g. ±1 micron) with expensive placement equipment, then lens  39  may be placed in a fixed position. If optical block  46  is very accurately positioned, the distances between lens  39  and spacer  35  and between lens  39  and optical block  46  are not critical because the light is collimated and slight variances in position simply produce a small amount of light loss. 
   However, the present invention incorporates a more cost effective apparatus and method in which optical block  46  and lens assembly  36  are placed with standard placement equipment to a greatly relieved tolerance (e.g. approximately ±10 microns). Lens assembly  36  is then moved to compensate for any less than ideal spacing that may occur between laser  45 , optical block  46 , lens  39 , and spacer  35 . The correct positioning of lens assembly  36  is accomplished by a simple mechanical fixture which is adjustable over a required range. As mentioned above, lens assembly  36  may be frictionally engaged in ferrule  20 , in which case it is simply moved axially along the optical axis Z, or it may be threadedly engaged in ferrule  20 , in which case it is rotated to move it farther in or out of ferrule  20 . In either case, the power of the two lens system is set so that lens  39  may be moved over a relatively large distance (e.g. approximately several hundred microns) to compensate for any mis-positioning, generally of a few microns, between laser  45  and optical block  46 . 
   It will be understood that other methods and apparatus for achieving relative movement of lens assembly  36  within ferrule  20  may be devised and the described apparatus and methods are intended to illustrate the concept. Thus, apparatus and methods for achieving cost effective fabrication and assembly of an electro-optic module are disclosed wherein the initial positioning of optical block  36  and lens  39 , for example, is less critical so that assembly tolerances are relaxed and manufacturing is easier and less costly. 
   Various changes and modifications to the embodiments herein chosen for purposes of illustration will readily occur to those skilled in the art. To the extent that such modifications and variations do not depart from the spirit of the invention, they are intended to be included within the scope thereof which is assessed only by a fair interpretation of the following claims.