WO1998014813A1

WO1998014813A1 - Fiber optic array transmitter/receiver based on flexible circuit technology

Info

Publication number: WO1998014813A1
Application number: PCT/US1997/017502
Authority: WO
Inventors: Ervin H. Mueller; John R. Rowlette, Sr.
Original assignee: The Whitaker Corporation
Priority date: 1996-09-30
Filing date: 1997-09-26
Publication date: 1998-04-09
Also published as: AU4602597A

Abstract

A fiber optic array transmitter/receiver device is disclosed which includes a fiber optic array connector (12) interfacing with a polymer waveguide circuit (20), which interfaces with a multi chip module (19) connected to a flexible circuit (18). The flexible circuit (18) interfaces with a vertical portion (16a) of an L-shaped bracket (16), which is in turn held in place via mounting on a substrate (14) by a horizontal portion (16b) of the L-shaped bracket (16) and a molded housing. The flexible circuit (18) is attached (or an integral part thereof) to the multi chip module (19), and passes through a slot (36) in the L-shaped bracket (16) for attachment to the substrate (14). The connector (12), waveguide circuit (20), and multi chip module (19) are all on the same side of the L-shaped bracket (16) (the connector side).

Description

FIBER OPTIC ARRAY TR7ANSMITTER/RECEIVER BASED ON FLEXIBLE CIRCUIT TECHNOLOGY

The present invention is directed to a fiber optic array transmitter/receiver device which utilizes flexible circuit technology for directly aligning light transmitting and/or receiving components, formed within a multi chip module on a flexible circuit, with the optical path of a fiber optic array connector. The current state of the art uses 45 degree mirrors in a waveguiding media such as optical fiber or polymer waveguides, molded optics such as Lytel transceivers and IBM Jitney data links, or custom ceramic structures to turn the light emitting devices or light beam from a direction perpendicular to the electronic package to one that is parallel. Once the light is parallel with the electronic package, a connector or fiber pigtail approach can more easily be accommodated within the package to provide a disconnectable or permanent optical input/output interface to the data link.

The present invention utilizes flexible circuit technology, such as Multi Chip Module (MCM-E/F) technology, to provide the required 90 degree turn to the light path. This approach allows the light emitting (or receiving) components, formed in the multi chip module and connected to a flexible circuit, to be directly in line with the optical path. The 90 degree turn required to interface with the electronic package is accomplished with the flexible circuit. This provides a relatively, linear optical path that can be easily interfaced with an optical connector. In this case, a Polyguide (TM) polymer optical waveguide circuit accomplishes the connection between a source or receiver within the multi chip module and an optical connector end face. The component parts, including multi chip module, optical waveguide circuit, and the optical connector are passively aligned using alignment pins of the optical connector. The alignment pins are the only components aligning the optical source (or receiver) to cores of the optical fibers in the array connector.

Accordingly, it is an object of this invention to provide a fiber optic array transmitter/receiver based on flexible circuit technology.

It is a further object of this invention to provide a fiber optic array transmitter/receiver based on flexible circuit technology such that the need for a 45 degree mirror in waveguiding media of optical fiber or polymer waveguides is eliminated.

It is a still further object of this invention to provide a fiber optic array transmitter/receiver based on flexible circuit technology in which a passive alignment is accomplished between a multi chip module of a flexible circuit, a metal clip, a polymer waveguide circuit and an optical connector via accurately fabricated and aligned apertures formed in or through each component .

It is still another object of this invention to provide a fiber optic array transmitter/receiver based on flexible circuit technology which is low in cost, is a robust assembly, simple to use and more effective than previous devices .

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: FIG. 1 is an exploded left side perspective view of the invention according to a preferred embodiment thereof ;

FIG. 2 is an exploded right side perspective view of the device of Figure 1 ;

FIG. 3 is a right side view of the assembled device;

FIG. 4 is a cross-sectional view taken along line 4-4 of Figure 3 ; FIG. 5 is a perspective view of a two part flexible circuit used in the present invention;

FIG. 6 is a side view of the two part flexible circuit shown in Figure 5 ;

FIG. 7 is a perspective view of an L-shaped bracket used in the present invention;

FIG. 8 is a perspective view of a housing for use in the present invention; and

FIG. 9 is a cross-sectional view of the housing shown in Figure 8. Turning first to Figures 1 and 2, there are shown a left side and a right side exploded view, respectively, of a fiber optic array transmitter/receiver 10. Component parts of the transmitter/receiver include a fiber optic array connector 12 such as an MPX connector having an end face 34 at an exposed end thereof. A substrate 14 such as a plastic ball grid array (PBGA) substrate, ceramic ball grid array (CBGA) , pin grid array (PGA) package ceramic lead frame or the like forms a base for additional components including an L-shaped bracket 16 having a vertical portion 16a and a horizontal portion 16b. The horizontal portion 16b of the L-shaped bracket 16 is mounted to a major surface of the substrate 14. The L-shaped bracket includes an aperture or opening 36 of a somewhat rectangular shape formed through the vertical portion 16a thereof and a pair of slots 16c formed in the horizontal portion 16b thereof as shown in further detail in Figure 7. Although the L-shaped bracket 16 used in the illustrated device is metal, any suitable material of sufficient strength, thermal transfer capability, and durability may be used in place of metal. Further, although the

MPX connector 12 is used by way of example, this data link packaging concept could be modified to use the USCONEC MPO connector, the Berg MAC connector, the

Methode MP connector, or any other array connector that uses alignment pins.

A flexible circuit 18 is mounted on the L-shaped bracket such that a first horizontal portion 18a of the flexible circuit is mounted on the substrate 14, and another extended portion 18b of the flexible circuit 18 extends through the opening 36 of the L-shaped bracket 16. The flexible circuit 18 is preferably the type which includes a flexible circuit based multi chip module (MCM) 19 fabricated using an FE MCM E/F process as described below, and includes the transmitter/receiver elements formed therein. This multi chip module 19 is attached to the flexible circuit 18 on a side of the vertical portion 16a of the L-shaped bracket which opposes the horizontal portion 18a of the flexible circuit. Specifically as shown in the figures, the multi chip module 19 is connected to portion 18b of the flexible circuit 18 such that the flexible circuit forms an effective bridge from the multi chip module 19 mounted on the L-shaped bracket 16 to the electronic substrate 14 thereby achieving an electrical connection therebetween and a 90° signal transition.

Another key aspect to the multi chip module 19 is that it uses flip-chip technology to provide a planar top surface. Also, the size of the aperture or opening 36 in the L-shaped bracket 16 is of a reduced size to provide better thermal and mechanical attachment for the multi chip module 19 to the customers printed circuit board. The MCM attaches to the L-shaped bracket which attaches to the package substrate. The substrate then becomes a part of the transmitter/receives package that the user mounts to a PCB . The multi chip module 19 is formed from a process which includes the steps of laser drilling apertures in polyimide film, conducting a Cu metallization, forming a

Cu pattern, depositing an upper layer dielectric, bonding a chip with adhesive (from a commercial supplier) , laser drilling apertures to the chip, sputtering Ti/Cu and a plating a thick Cu pattern, and adding a plastic substrate. Finally, the multi chip module is encapsulated. In the preferred embodiment, the flex circuit 18 is integrally formed with the multiachip module. The device, either a light source or detector is disposed on the MCM with any other desired electronics. A tail portion of flex circuit connects the devices/electronics of the MCM to the substrate, preferably a ceramic lead frame. Alternatively, the flex circuit could be bonded discretely to the MCM by soldering, for example.

A waveguide circuit 20 such as a Polyguide (TM) polymer waveguide circuit is mounted to a face of the vertical portion 16a of the L-shaped bracket which corresponds to a face to which the multi chip module 19 of the extended portion 18b of the flexible circuit 18 is mounted. This waveguide circuit 20 performs three functions. First, it is an optical quality Aspacer block® that is mounted directly on the surface of the multi chip module 19 and buffers the multi chip module from the optical connector mating forces. Second, it provides an array of waveguides that couple the light from a source/detector array to the array of fibers in the array connector 12, thereby minimizing crosstalk between channels. Third, it provides an air-gap-free optical path from the source/detector array to the array of fibers in the optical array connector 12. It is of interest to note that the air-gap free path would not be used if an alternative coupler such as an HOE or lenses were used.

Each of the vertical portion 16a of the L-shaped bracket 16, the multi chip module 19 of the flexible circuit 18, and the waveguide circuit 20 have at least a pair of apertures formed therethrough at 28, 38, and 26, respectively. A pair of connector or alignment pins 22 are insertable through the apertures 28, 38 and 26.

Because of the precise positioning of the apertures formed through the described components, the polymer waveguide circuit assembly 20 is precisely slid onto the alignment pins 22. Additionally, the end face 34 of the fiber optic array connector 12 has a pair of apertures

32 formed therein which complete the connection of the fiber optic array connector 12, waveguide circuit 20, multi chip module 19 of the flexible circuit 18, and the vertical portion 16a of the L-shaped bracket.

The flexible circuit 18 may alternately be a Kapton

(TM) based flexible film with a custom metallization pattern defining the custom transmitter or receiver circuit. This flexible circuit has the light emitting chip, such as a surface emitting Light Emitting Diode

(SLED) or Vertical Cavity Surface Emitting Laser

(VCSEL) ) , bonded to the circuit. The electronic chip that modulates the source is preferably bonded to the flexible circuit 18. For the receiver product the chips may be a P-I-N diode or a metal-semiconductor-metal MSM detector array and preamplifier/postamplifier chip. Also, an integrated detector/preamp or detector/preamp/postamp could be used. In any event, the surface of the active area of the emitter/detector has a normal vector which is parallel to the optic axis of the device.

In Figures 3 and 4, the assembled device is shown, and in Figures 5, 6, 7, 8, and 9 there are shown details of certain component parts. In particular, upon assembly, a molded housing 24 having an opening 30 formed therein, has features including a clip 25 molded into the design that allow the normal mating/demating action of the connector 12 to be accomplished with the housing 24. The housing 24 is also keyed at 30a to prevent the connector 12 from being inserted into the housing in the wrong orientation (i.e. upside down) . Referring in particular to Figure 4, the substrate

14 fits within a base portion of the housing 24 and the connections between the substrate 14, fiber optic array connector 12, L-shaped bracket 16, flexible circuit 18, waveguide circuit 20, and alignment pins 22 are concealed within the housing 24.

The flexible circuit 18 allows the fiber optic sources and detectors to be positioned in the package on the same axis as the optical fibers held in the fiber optic array connector 12. The optical coupling between the source/detector and the optical fibers in the connector 12 is accomplished via the Polyguide polymer waveguide circuit 20 attached to the surface of the flexible circuit 18. The electrical input/output from the source/driver chip is carried on the flexible circuit down to the substrate 14 and out to the customer printed circuit board (not shown) . The fiber optic array connector 12 is connectable to the substrate 14 only because of the molded housing 24. The substrate 14 and molded housing 24 are bonded together to create the necessary interface to mate with the connector 12.

As a result, the device disclosed allows the light emitting (or receiving) components, mounted on a flexible circuit 18, to be directly in line with the optics path. The 90 degree turn required to interface with the electronic package is accomplished with the two part flexible circuit 18. This provides a straight through, low loss optical path that can be easily interfaced with an optical connector. In this case the Polyguide (TM) polymer optical waveguide circuit 20 accomplishes the coupling between the multi chip module 19 of the flexible circuit 18 and the connector end face 34.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims

Claims

1. A device for connecting electrical circuitry disposed in a plane to an optoelectronic device, said optoelectronic device being optically coupled to a fiber optic waveguide, said plane having a normal vector which is orthonormal to an optic axis of said fiber wave guide, characterized in that: a flexible circuit connects said circuitry to said optoelectronic device, said optoelectronic device having an active area which is parallel to said optic axis of said fiber.

2. A device as recited in claim 1, further characterized in that said device is optically coupled to said fiber by a polymer waveguide.

3. A device as recited in claim 1, further characterized in that said flexible circuit is bent at a 90° angle.

4. A device as recited in claim 3, further characterized in that L-shaped bracket has said flexible circuit disposed thereon.

5. Claim 5 a device as recited in claim 1 further characterized in that said optoelectronic device is an optical emitter.

6. A device as recited in claim 1, further characterized in that said optoelectronic device is an optical detector.

7. A device as recited in claims 1, further characterized in that a lens element optically couples said fiber to said device.

8. A device is recited in claim 7, further characterized in that said lens element is a holographic optical element.

9. A device as recited in claim 1, further characterized in that said flexible circuit is integrally with a multichip module, and said module has said optoelectronic device disposed thereon.

10. A device as recited in claim 1, further characterized in that said substrate is a ceramic lead frame .

11. A device as recited in claim 9, further characterized in that said module has a preamplifier disposed thereon.

12. A device as recited in claim 1, further characterized in that said flexible circuit is integrally formed with said module.