Abstract:
An automated system and method for location and insertion of a fiber optic end in the ferrule of a hybrid package provides for efficient and accurate alignment. In one embodiment, the fiber is mounted on a fiber chuck that is presented to the package by a micropositioner having four degrees of freedom. These include the three orthogonal cardinal axes (x, y, and z-axes), and a fourth degree of freedom comprising angular rotation θ about the z-axis. Feedback mechanisms may be provided regarding orthogonal and angular positioning in order to optimize coupling efficiency between the fiber optic and the electronic circuit contained in the package. In another embodiment, the fiber chuck includes a longitudinal groove for seating the fiber optic during an alignment procedure. The groove interfaces with a vacuum manifold that serves to secure the optical fiber to the chuck during alignment.

Description:
BACKGROUND OF THE INVENTION 
     In contemporary optical-electronic hybrid systems, an optical fiber typically interfaces with an opto-electronic device. The opto-electronic device usually includes a hermetic package, having conductive leads for electronic communication with devices external to the package. 
     During manufacture, single or multiple fiber optic pigtails are inserted through ferrules provided in sidewalls of the package. Typically, pigtail-level assembly is usually performed manually by assembly personnel who visually align, and then insert, each fiber into its ferrule. The endface of each pigtail is typically positioned and secured to a bench or submount, which is installed within the package. The pigtail is also bonded to its corresponding ferrule to enable hermetic sealing of the package. 
     Additionally, it is also sometimes important to optimize the angular orientation of the fiber endface relative to the optical circuit in order to increase coupling efficiency and/or polarization extinction. Conventionally, angular control is achieved via manual rotation of the fiber prior to bonding by assembly personnel. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a system and method for automated fiber insertion into an opto-electronic hybrid package that overcome the limitations of conventional insertion techniques. In particular, the present invention provides for automated location and insertion of a pigtail into the ferrule, a possibly active or passive alignment to opto-electronic components within the package. 
     In general, according to one aspect, the invention provides for the mounting of a fiber on a fiber chuck, after which it is presented to the package by a system providing for four degrees of freedom. The degrees of freedom include the three orthogonal cardinal axes (x, y, and z-axes), and a fourth degree of freedom corresponding to angular rotation θ about the z-axis. In this manner, the fiber is positioned in the ferrule of the package. 
     In some embodiments, feedback mechanisms are provided for the orthogonal (x, y, and z-axis) and angular positioning in order to optimize coupling efficiency and/or polarization extinction, for example, between the fiber and the electronic circuit mounted in the package. 
     In one implementation, the fiber chuck includes a longitudinal groove for seating the fiber during an alignment procedure. The groove interfaces preferably with a vacuum manifold that serves to seat the fiber in the chuck during alignment. 
     In the present implementation, the system includes a package mount for securing a package having an optical alignment feature. 
     The positioner may receive position data related to the position of the optical alignment feature, and may further utilize the position data during an alignment procedure. 
     In one embodiment, the positioner comprise a longitudinal bench, a lateral bench and a vertical bench, each bench being independently positionable along the directions of the respective longitudinal, lateral, and vertical axes. Position encoders are included for providing position data of the respective benches along the respective axes. 
     A fiber rotation drive is included for rotationally orienting the fiber about the longitudinal axis. In this case, an angular encoder provide angular data of the fiber about the longitudinal axis. A sensor may also be included in the package mount for receiving optical signals transmitted along the fiber optic during an alignment operation, and for providing intensity data to the positioner. 
    
    
     The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings: 
     FIG. 1 is a perspective view of a fiber optic insertion and alignment apparatus, in accordance with the present invention. 
     FIG. 2 is a close-up perspective view of a package mount, illustrating alignment of a fiber optic with a ferrule in a package, in accordance with the present invention. 
     FIGS. 3A and 3B are close-up top and end views respectively of a fiber chuck in accordance with the present invention. 
     FIGS. 4A and 4B are perspective views of a second embodiment of the fiber pigtail insertion and alignment system, according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 1 the fiber alignment and insertion apparatus  18  of a first embodiment of the present invention includes a first carriage  20  and a second carriage  22 , one, or both, being mounted to slide on rail  24  in a direction along a z-axis. 
     The first carriage  20  includes a z-axis platform  32 , a y-axis platform  38 , an x-axis platform  34 , and a fiber chuck  42 . Each platform translates along the z-axis (longitudinal), y-axis (vertical) and x-axis (lateral) respectively so as to allow for three orthogonal degrees of freedom for positioning the fiber chuck  42  relative to a package mounted to the second carriage  22 . A fourth degree of freedom controlled by a chuck rotation drive  44  provides for angular rotation θ of the chuck  42  about the z-axis. Control over the degrees of freedom is preferably provided in a closed-loop feedback system managed by a controller  70 . 
     The second carriage  22  includes a package chuck or pallet  26 , including a package clamp  28  and an electrical lead clamp  30 . The package clamps  28 - 1 ,  28 - 2  secure a package in position during an alignment operation. Lead clamps  30 - 1 ,  30 - 2  make electrical contact to the package electrical leads or pins. In one embodiment, the second carriage  22  is fixed to the rail  24 . In another embodiment, the second carriage  22  slides on the rail under control of the controller  70 , in order to allow for translation along the z-axis. 
     The close-up perspective view of FIG. 2 illustrates alignment of the fiber optic pigtail  56  with the package  60 . A fiber chuck  42  includes a longitudinal groove (illustrated and described in detail below in conjunction with FIGS.  3 A and  3 B), in which the pigtail  56  is mounted. The end of the pigtail  56  projects toward the ferrule from the chuck  42 . The chuck  42  is positioned along the x, y and z-axes, and angularly rotatable θ about the z-axis, with respect to the package  60 , under control of the controller  70 . 
     The package  60  includes single, or multiple, ferrules  62 , through each of which an end of the fiber optic  56  is inserted during an installation/alignment operation. A plurality of wire bonding pads  66  are provided within the package for bonding between an opto-electronic component and the package leads or pins  64 . External lead pads  67  are provided as a bonding surface for the external package leads  64 . 
     In one embodiment, an optical bench or submount  81  is installed within the package  60 , typically on a thermoelectric cooler that provides for temperature control within the package  60 . An opto-electronic component  87  is installed on this bench  81 . In one implementation, this opto-electronic component  87  is an opto-electronic detector, possibly with a tunable Fabry-Perot filter. In another embodiment, it is an opto-electronic signal generator, such as a semiconductor laser or laser system. A wire bond is provided between the opto-electronic component  87  and the bond pads  66 . 
     During fabrication of the package, or upon receipt of the package from a vendor, data related to the positioning of the ferrules  62  with respect to the package body, as well as the length of the ferrules, are recorded. When a package is mounted on the alignment system of the present invention, these data are made available to the controller  70  (see FIG.  1 ), in order to provide detailed information related to the specific physical geometry of the individual package. 
     A package body  60  is mounted to the chuck  26  as shown. An aperture  68  in the chuck  26  houses first and second package clamps  28 - 1 ,  28 - 2 , which physically secure the package in position on the chuck  26 . An optional reference pin or feature  83  serves as a positional reference for the package when mounted to the chuck. The package leads  64  are likewise secured by the lead clamps  30 , including pivoting paddles  58 , preferably imparting null insertion force on the leads, for establishing electrical continuity. 
     Following registration and clamping of a package  60  on the chuck, the optical fiber  56  is inserted into the axial bore of the ferrule  62  by the micropositioner. In one embodiment, an optical signal is injected into a distal end of the fiber pigtail  56  (see FIG. 1) by signal source  84  during an alignment sequence, during which sensors  82  detect light emitted from the end face of the fiber to determine optimal orthogonal and rotational alignment. Alternatively, the optoelectronic component  87  is a laser, which is energized via the leads  64 . Component  80  functions as a detector to determine the coupling efficiency of light from the laser into the fiber via the endface. As an example, optimal alignment is determined as a function of signal coupling efficiency between the endface of the pigtail and the opto-electronic component in the package. Sensor feedback is provided to the controller  70  (see FIG. 1) to provide a closed-loop positioning system. 
     Following insertion and alignment, the fiber is soldered or otherwise bonded to the bench in the package  60 . 
     Returning to FIG. 1, the first carriage  20  includes an z-axis platform  32  that slides on the rail  24 . The interface between the z-axis platform  32  and rail  24  preferably comprises an air bearing that permits nearly frictionless motion of the platform  32  relative to the rail  24 . A z-translation motor  76 , for example a voice-coil, translates the z-axis platform  32  along the z-axis. Positional encoders  77  provide feedback to the z-translation motor  76 , and the controller  70 , to provide for a closed-loop system. 
     Preferably, the position encoder is an optical encoder, such as a traditional chrome-on-glass encoder or preferably an optical encoder including a diffractive phase grating, a laser diode, and a detector array. In one embodiment, the laser detector combination is secured to the z-axis platform  32  and the grating is secured to the slide  24 . 
     An x-axis rail  36  is mounted on the z-axis platform such that the longitudinal axis of the x-axis rail  36  is orthogonal to the z-axis. An x-axis platform  34  slides on the x-axis rail  36 , for example interfacing via a roller bearing or air bearing. An x-translation motor  72 , for example a voice-coil, provides for translation of the x-axis platform  34  along the x-axis. Positional encoders  75  such as optical encoders, provide feedback to the x-translation motor  72 , and the controller  70 , to provide for a closed-loop system. 
     A plurality of y-axis precision dowel pins  40  extend vertically from the x-axis platform  34 , and are oriented orthogonally with respect to the x-axis and z-axis. A y-axis platform  38  includes corresponding TEFLON® fluoropolymer bearings  41  to provide for a low friction interface between the y-axis platform  38  and the dowel pins  40  along the y-axis. A y-translation motor  74 , for example a voice-coil, provides for translation of the y-axis platform  38  along the y-axis. Positional encoders  71  provide feedback to the y-translation motor  74 , and the controller  70 , to provide for a closed-loop system. 
     The chuck  42  is positioned on the y-axis platform  38  as shown, oriented such that its longitudinal axis is directed along the z-axis. Specifically, the fiber chuck  42  is supported on four cylindrical rollers  90 - 1 ,  90 - 2 ,  90 - 3 ,  90 - 4 , which are journaled to the y-axis platform  38 . Optional rare earth magnets  46  having an inner circular contour closely matching an outer circular. contour of the chuck  42 . They are used to flatten the fiber, held in the chuck, into the chuck&#39;s channel. 
     A chuck rotation drive  44  is fixed to the outer surface of the chuck  42  to provide for rotational motion of the chuck  42  about the z-axis on front and back rollers  90 . The drive comprises, for example, a plastic worm gear driven by a screw, in turn driven by chuck rotation motor  78 . In the current embodiment, optional angular encoders  45  provide feedback to the chuck rotation motor  78 , which, in conjunction with optical feedback provided by sensors  82  (see FIG.  2 ), provide for a closed-loop system. At least 260 degrees of chuck rotation is preferably provided in order to fully inspect and evaluate the fiber endface&#39;s far or near field emission pattern in the package, to enable optimization of the coupling efficiency between the endface  56  and component  87 . 
     FIGS. 3A and 3B are close-up top and end views respectively of the fiber chuck  42 . The body of the fiber chuck  42  is circular in cross-section and includes a V-shaped groove  50 . A slit  48  is provided at the base of the V-groove. The slit  48  extends into a longitudinal vacuum manifold  54 . The slit is preferably of a width less than the diameter of the fiber optic for which the chuck is designed for use such that the fiber  56  rests tangentially in the groove  50 , as shown in FIG.  3 B. 
     A vacuum is drawn in the vacuum manifold  54  by vacuum unit  80  (see FIG.  1 ). The vacuum draws air from the slit  48 , thereby sealing and securing the inserted fiber optic  56  against the walls of the V-groove  50  in cooperation with magnets  46 . By virtue of the inwardly directed force imparted by the vacuum, the fiber optic is longitudinally and rotationally secured in the chuck  42  during an alignment procedure. A distal end  52  of the chuck  42  is provided with a flat profile, so as to allow for improved dexterity in aligning the fiber optic with the package ferrule. 
     FIGS. 4A and 4B illustrates a second embodiment of the fiber alignment and insertion apparatus. The second embodiment is generally similar to the first embodiment, having similar reference numerals to indicate similar features. 
     The second embodiment, however, differs insofar as it uses a flexure-based positioning system. Specifically, Y-axis platform  38  is connected to x-axis platform  34  via a flexure  410 . A Y-axis optical encoder system  71  detects the Y-axis height of the Y-axis platform  38 . A Y-axis voice coil and stator system (y-axis translation motor)  74  operate as the Y-axis actuation system. The X-axis platform  34  is connected to the Z-axis platform  32  via two X-axis flexures  414 - 1 ,  414 - 2 . X-axis voice coil or translation motor  72  functions as the X-axis actuation system to pivot the X-axis platform  34  on the flexures  414 - 1 ,  414 - 2  relative to the Z-axis platform  32 . An X-axis position detector  75  detects the X-axis position of the X-axis platform  34  relative to the Z-axis platform  32 . Again, this position detection system is preferably an optical encoder having a grating and detector pair. 
     In this manner, the present invention provides an apparatus and method by which a fiber optic is automatically aligned with a ferrule in an optical-electrical hybrid package in manner that provides for improved precision and reduced assembly costs. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made herein without departing from the spirit and scope of the invention as defined by the appended claims.