Optoelectronic packaging

Details Optoelectronic packaging Optoelectronic packaging

2000-02-01

2002-09-24

Spyrou, Cassandra (Department: 2872)

Optical waveguides

With optical coupler

Particular coupling structure

C385S049000, C385S050000, C385S065000

Reexamination Certificate

active

06456766

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates, in general, to micron-scale optoelectronic devices, structures and techniques, and more particularly to devices and structures for facilitating the interaction of optical components such as optical fibers with other fibers and/or with circuit components such as wave guides or active elements such as light sources or light detectors on or connected to micromechanical structures.
Recent developments in micromechanics have successfully led to the fabrication of devices in single crystal substrates utilizing a dry etch process such as reactive ion etching (RIE) for producing micron-scale moveable mechanical structures. Such a process is described in U.S. Pat. No. 5,198,390 as utilizing multiple masks to define small, complex structural elements and related elements such as metal contacts in single-crystal silicon. U.S. Pat. No. 5,393,375 describes a similar process for releasing micromechanical structures in single-crystal materials other than silicon. An improved dry-etch process for the fabrication of microelectromechanical structures is described in U.S. Pat. No. 5,846,849, which discloses a single-mask, low temperature, self-aligned process wherein discrete devices can be made, and wherein such devices can be fabricated in wafers containing integrated circuits. The processes described in these patents may be used to produce a variety of sensor devices such as accelerometers, as well as a variety of actuator devices, resonators, moveable optical reflectors, and the like, either as separate, discrete devices or as components on previously-fabricated integrated circuits. The processes described in these patents may be referred to in general as the SCREAM (Single Crystal Reactive Etch and Metal) process, with the single mask process being referred to as the SCREAM-1 process.
As the field of micromechanical and microelectromechanical devices developed, a problem arose concerning the connection of ultra small components and structures formed on a wafer or substrate with other circuits and components on other wafers or substrates, whether of micron-scale or larger. One solution has been to fabricate solder pads on these devices for use in securing connecting lines or wires to the electrical components on the substrate. However, such a procedure requires precision wire bonding techniques which do not always produce satisfactory results. Furthermore, the use of wires for communication with microcircuits and related devices limits the flow of data between the circuits and devices.
On the other hand, optical fibers provide many advantages in data communication, but problems are encountered in connecting small diameter optical fibers to micromechanical devices such as waveguides and light detectors for transferring data to circuits carried by the substrate, as well as for transferring data from such circuits, as by way of laser light sources on the substrate. A major problem is that of alignment of fibers with each other, with microstructures such as waveguides and reflectors, with light sources such as vertical cavity surface emitting laser (VCSEL) arrays, and with electrical circuit components such as light detectors or the like.
The alignment of VCSEL arrays and detector arrays for direct coupling to optical fiber arrays is challenging, because the fibers must be mounted with their axes perpendicular to the light emitter or detector. The fiber support structure thus must be perpendicular to the detector or emitter, and the fabrication of micromechanical supports for this purpose is difficult.
Misalignment between fibers or between a fiber and a device or structure can occur in three translational directions and can occur around three rotational axes. Optical interconnections are most sensitive to lateral misalignment; that is, misalignment in directions perpendicular to the direction of propagation of light in the fiber, but the connections are also sensitive, to a lesser degree, to angular misalignment and to the axial distance between components in the direction of propagation. For single-mode optical systems such as those employed in telecommunications applications, lateral misalignment between optical components should be less than one micrometer, while for multimode systems, lateral misalignment tolerances are more relaxed; for example, up to about 5 micrometers. In both cases, axial separation tolerances are often greater by a factor 2-5, depending on the components involved. Single-mode interconnections typically can tolerate small angular misalignments; for example, less than 0.5 degree, depending on coupling efficiency requirements. In the case where columnated beams of light are coupled, where the beam waist is often 10-100 times the diameter of typical single-mode fiber beam profiles, angular misalignment of matching beams must be much smaller; for example, less than 0.01 degree. In all cases an accurate alignment is essential to effective, reliable communication.
Accordingly, there is a need for structures and devices for accurately, reliably and easily interconnecting optical fibers with each other, with micromechanical devices and structures and with light detectors and emitters.
SUMMARY OF THE INVENTION
Briefly, the present invention is directed to improved methods and apparatus for easily and accurately interconnecting small-diameter optical fibers in end-to-end axial alignment. The invention is further directed to micron-scale fabrication techniques and to passive optical components fabricated by such techniques for connecting such optical fibers to micromechanical and to microelectromechanical devices such as waveguides and for optically coupling such fibers to electrical circuits by way of active optical elements such as light detectors and laser sources.
The packaging of optical fibers with micromechanical and microelectromechanical devices is carried out, in a first embodiment, by mechanical couplers for connecting optical fibers in end-to-end alignment so as to obtain a maximum transfer of laser light energy or the data carried by such light energy from one optical fiber to another. Such couplers may be used to interconnect a single pair of fibers, or may be used to connect an array of optical fiber pairs, with the couplers providing easy and accurate assembly.
In another embodiment of the invention, an optical coupler interconnects one or more optical fibers with mechanical or electrical components carried by a substrate. The electrical components may be active elements such as light sources or light sensors, for example, which to are electrically connected to corresponding circuit components such as integrated circuits carried by the substrate. Such a coupler may incorporate trenches for receiving and holding optical fibers in alignment with suitable waveguides or reflectors for directing light carried by the optical fibers to corresponding detectors or sensors. In another alternative, the circuits or components on the substrate may consist of light sources such as a solid state lasers which generate light in response to signals from electrical circuits on the substrate, with the light produced by the lasers being directed into the optical fibers by way of the waveguides or reflectors.
In a preferred form of the invention, alignment of optical fibers with active optical components such as optoelectric detectors or laser light sources is attained by securing the optical fiber or fibers in a first substrate, which will be referred to herein as a coupler block. A second substrate, which will be referred to herein as a substrate or a wafer, and which contains the light detectors or light sources, is secured to the coupler block. The substrate may be mounted on or above, and parallel to, the surface of the coupler block, with its active optical components (light detectors or light sources) positioned in alignment with corresponding fibers. Alternatively, the wafer may be edge-mounted on or in the coupler block, as in a trench formed in the coupler block, or may be mounted on an edge of the coupler block. In

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