Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2000-01-12
2004-03-30
Bovernick, Rodney (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S089000, C385S092000
Reexamination Certificate
active
06712527
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to fiber optical connections and, more particularly, to a structure and method for coupling a multiple channel fiber optic cable to a multiple channel Vertical Cavity Surface Emitting Laser (VCSEL) transmitter and a multiple channel Perpendicularly Aligned Integrated Die (PAID) receiver.
BACKGROUND OF THE INVENTION
The invention seeks to construct a package for coupling a multiple channel fiber optic cable to a multiple channel Vertical Cavity Surface Emitting Laser (VCSEL) transmitter and a multiple channel Perpendicularly Aligned Integrated Die (PAID) receiver. The active surface of both the receiving and transmitting dies (hereinafter “optoelectronic dies”) are oriented perpendicular to the plane of the laminate package. The package can be soldered directly to an end user card with its cables plugged directly through the tail stock. In other words, the cable can exit from the card in a direction parallel to the plane of the card.
Other advantages of this design are:
1) it has integrated strain relief, a latching detent, and safety features;
2) it uses available processes and materials;
3) it comprises a plastic ball grid array (PBGA) laminate for high speed operation and low cost;
4) it has a two-part construction design with independent testing of each part to improve overall yield;
5) it allows two strategies for removing heat from the package;
6) it includes various incorporated features to minimize electrical cross-talk, radiated RF and susceptibility to external RF; and
7) it incorporates several features that serve to protect optical surfaces and electronic components from damage.
The development of this type of design has proven to be difficult, since solid state devices (often referred to either as dies or chips), with active components on one side only, are usually mounted parallel to the card, with their optically active features perpendicularly oriented to receive or emit light. It becomes necessary, therefore, to provide means for orienting the optoelectronic chips perpendicular to the card so that the emitted or received light enters the package parallel to the card while maintaining the profile (height above the card) low enough to meet specified limitations imposed by the end user.
Among the features incorporated into the design are:
1) an overmolded ball grid array (BGA) that strengthens and stiffens the relatively weak BGA laminate. (This is needed because the carefully aligned optics, which must be held in place, are integrated into the package);
2) a package having integrated strain relief for the cable/connector with direct mechanical coupling to the card, to prevent disturbing the optical portions;
3) use of relatively low cost materials, assembly procedures and standard processes;
4) separate grounds within the BGA, a two part lid, a shroud and pins on the carriers for minimizing:
a) cross-talk from receiver to transmitter,
b) radiated RF power, and
c) susceptibility to RF pickup;
5) incorporation of many standard features of overmolded packages to minimize cost and susceptibility to damage;
6) an improved assembly/test strategy (to keep yields high and costs low); and
7) a dual path strategy for removing heat from the package to keep the optoelectronic parts cool enough for high speed operation.
DISCUSSION OF RELATED ART
There have been a number of attempts to develop a package and/or product that meets the general requirements of a parallel fiber optic link. A package developed for the JITNEY project, a government funded package developed at IBM by M. S. Cohen et al., “Packaging Aspects of the Jitney Parallel Optical Interconnect,” 1998 ECTC, pp. 1206-1215; and J. Crow et al., “The Jitney Parallel Optical Interconnect,” 1996 ECTC, pp. 292-300, consisted of separate transmitter and receiver modules and two separate cables to complete a bi-directional optical link. The cable contained 20 fibers for the simultaneous transmission of 20 channels of information at the full data rate. This design permitted the transmission of two bytes of information, along with four bits of overhead, in each bit time. The transmitter module contained a driver chip (differential inputs) and a VCSEL transmitter. Both chips were mounted on a heatsink. The heatsink and chips were parallel to the module and the card.
A specially designed array lens served to redirect the light emitted from the VCSEL (perpendicular to the card) into the input face of the fibers which were disposed parallel to the card. Similarly, the receiver module contained a receiver chip (generating differential outputs) also oriented parallel to the module. The same array lens was used to redirect the light emerging from the optical fibers into the direction perpendicular to the card, so that the light to be detected impinged upon the surface of the receiver substantially perpendicular to the photosensitive surface of the receiver. Although several similarities may be found in the JITNEY package, it did not attempt to solve the crosstalk problem (transmitter to receiver). It used two separate modules. JITNEY had a separate strain-relief, used a leadframe (instead of a BGA), and generally did not use packaging techniques expected to support data transmission rates of 1 Gigabit per second per channel or more.
Two versions of link transceiver modules developed for the Motorola Optobus project are described in two papers: “Characteristics of VCSEL Arrays for Parallel Optical Interconnects,” 1996 Electronic Components and Technology Conference (ECTC), pp. 279-291; and “Optobus I: A Production Parallel Fiber Optical Interconnect,” 1997 ECTC, pp. 204-209. Both modules have in common a number of packaging features: 1) a surface emitting VCSEL array is used, the light path is parallel to the host card plane, and the optoelectronic component is mounted perpendicular to the module's BGA laminate, 2) a molded plastic waveguide structure conducts the light to/from the optoelectronic die to endfaces of the fibers in ribbon optical cables, the cables being terminated with MT connectors, 3) a glob encapsulated, multi-chip pin grid array laminate board is provided on which the optoelectronic subassembly is mounted, and 4) the resulting package is nonhermetic.
As fabricated, the loss of the low-loss waveguides is some tenths of a dB/cm. To meet safety goals and to increase the amount of optical power reaching the detector, the waveguides for the transmitter and for the receiver portions of this transceiver are not constructed identically. On the transmitter side, the waveguide is designed to increase the numerical aperture of the entering beam as the light passes from the VCSEL to the optical fiber. On the receiver side, the waveguide is designed to improve coupling efficiency from the optical fiber to the photodetector. A passive alignment procedure (i.e., the optical elements are not electrically activated during the procedure) is used to align the array of optically active elements on the optoelectronic dies to the molded structure which contain an array of waveguides.
In the Optobus transceiver (the 1996 paper), a leadframe for delivering the electrical signals to the optoelectronic die is overmolded and serves as the supporting structure for the waveguide arrays. Electrical connections are made from finished ends of the leadframe conductors, a nonstandard packaging approach, to contact pads on the top surface of the optoelectronic dies. The other end of each of the leadframe's conductors, which are routed to exit points along the side of the molded waveguide structure and then bent down to attachment points, are electrically connected to pads on the top surface of the laminate board.
In the optobus I transceiver (the 1997 paper), a tape automated bonding (TAB) leadframe is used to replace the electrical function of the standard leadframe in the earlier version. The conductors on one end of this TAB leadframe make electrical contact to the optoelectronic dies and, on the other end, to contacts on the top surface to the laminate board. The TAB leadframe is be
Chan Benson
Cohen Mitchell S.
Fortier Paul F.
Freitag Ladd W.
Hall Richard R.
Bovernick Rodney
Fraley Lawrence R.
Kang Juliana K.
Salzman & Levy
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