Optical systems for Z-axis alignment of fiber, lens and...

Details Optical systems for Z-axis alignment of fiber, lens and... Optical systems for Z-axis alignment of fiber, lens and...

2000-12-15

2003-01-21

Kim, Robert H. (Department: 2882)

Optical waveguides

With optical coupler

Input/output coupler

C385S092000, C385S093000, C385S050000, C385S056000, C385S070000

Reexamination Certificate

active

06510262

ABSTRACT:

TECHNICAL FIELD
The invention relates generally to optoelectronic devices and more particularly to maintaining source-to-lens alignment along three perpendicular axes.
BACKGROUND ART
Transmitting data using optical signals is increasingly taking the place of the traditional approach of exchanging data via electrical signals. An optoelectronic module provides the interface between an optical transfer medium and an electrical medium. For example, the optical transfer medium may be a fiber cable that terminates with a connector that exposes ends of an array of optical fibers. Laser diodes, such as Fabry-Perot lasers or Vertical Cavity Surface Emitting Lasers (VCSELs), are commonly used to generate optical signals in response to electrical excitation signals. Laser diodes are preferred in many applications, since they provide high performance signaling in a miniaturized environment.
FIG. 1
illustrates key components of an optoelectronic system. In the illustrated embodiment, the system is a twelve-channel parallel fiber arrangement. Light sources
10
, such as VCSELs, are fabricated on a substrate
12
. The substrate may be a semiconductor die, such as a gallium arsenide chip. A lens array
14
resides between the light sources and an array of parallel optical fibers
16
. The lens array is shown as including a number of optical elements
18
, which are used to manipulate light rays passing from the sources
10
to the fibers
16
. For example, the optical elements may be diffractive elements.
While not shown in
FIG. 1
, an optoelectronic module includes hardware components that secure the light sources
10
, the lens array
14
, and the optical fibers
16
. As is well known in the art, the optical components should be aligned along x and y axes to ensure integrity of signal exchanges. Often, guide pins are used to provide the alignment. For example, guide pins extending along the z axis may have central regions that pass through the lens array
14
, so that end portions can extend into both the substrate
12
and the removable connector that supports the optical fibers
16
. U.S. Pat. No. 5,917,976 to Yamaguchi describes an optical transmission path coupling apparatus that includes guide pins and guide pin holes to provide alignment of fibers to microlenses and light receivers/emitters, with the alignment being along the x and y axes. U.S. Pat. No. 5,867,621 to Luther et al. describes the use of guide pins to properly position two optical fiber connectors, so that the fibers of the connectors are aligned along the x and y axes.
Alignment along the z axis is also important to achieving desired performance in a high speed application. In one example, the desired distance between the light sources
10
and the optical elements
18
may be 2.0 millimeters, with a tolerance of ±35 microns in order to pass a sufficient percentage of emitted light to maintain performance. Z-axis alignment is set in some products by lowering the lens array
14
over the array of light sources
10
while sensing the light that is transmitted through the optical elements
18
. The lens array is fixed in position relative to the light sources when maximum light is transmitted through the optical elements.
Another z-axis alignment that is critical to optimal performance is the alignment of the ends of the fibers
16
from the optical elements
18
. As one example, the target distance may be 0.475 millimeters, with a tolerance of ±25 microns. This may be achieved by using an alignment tool to join a connector receptacle to another component of the optoelectronic module to which the lens array
14
is attached.
While the use of known alignment tools and procedures may provide the target results, the process is often time consuming, so that production throughput is lowered. What is needed is a system and method that provide repeatable precision alignments for an optoelectronic module, with alignments along three axes being achieved without the need of alignment fixtures.
SUMMARY OF THE INVENTION
An optical coupling system utilizes a one-piece, separation-setting member for defining precise spatial relationships from a lens array to both an array of light sources and an array of optical fibers. The optical fibers are arranged along an end face of a fiber connector that abuts an exterior connector-contacting surface of the separation-setting member. The connector-contacting surface is configured to locate and align the optical fibers along a “target” plane.
The separation-setting member includes an interior region in which the lens array resides. The lens array abuts a shoulder having a precisely controlled distance from the target plane having the ends of the optical fibers when the fiber connector is seated against the connector-contacting surface. This precisely controlled distance is based upon maximizing the light transfer through the optical lenses of the lens array to the fibers. The lens array is seated in a manner in which it is parallel to the target plane and is exposed to the target plane through an opening within the separation-setting member.
The separation-setting member also includes a back surface that has a precisely controlled distance from the shoulder against which the lens array is seated. During assembly, the back surface is positioned against a substrate that supports the array of light sources. For example, the substrate may be a flex circuit having conductive traces to a semiconductor chip on which light sources, such as VCSELs, are integrated. Because the back surface is at the precisely controlled distance from the shoulder and because the back surface is parallel to the shoulder and the target plane, the light sources will have a desired orientation and distance relative to the lens array. In the preferred embodiment, the portion of the back surface that abuts the light source-supporting substrate is comprised of a number of feet that are strategically positioned to ensure that the parallelism is maintained while providing some access to the interior for a bonding step.
An advantage of the invention is that fabricating the separation-setting member to tight tolerances enables the spatial relationships to be achieved without the use of special z-axis alignment steps or tools. Axial alignments along x and y axes are achieved using conventional techniques. For example, the lens array is precisely positioned along the shoulder using a visual alignment system prior to gluing the lens array to the shoulder. Subsequently, x-direction alignment and y-direction alignment between the lens array and the array of light sources may be achieved using active alignment in which power through the lenses from the light sources is monitored while the relative positioning of the two arrays is stepped in increments of one micron. The separation-setting member is fixed in the position at which power is at a maximum. Guide pins are used to provide x and y axes alignment of the connector. It should be noted that the use of guide pins requires exacting positional tolerances of the guide pin holes. The guide pins should extend through the separation-setting member into holes of both the fiber connector and the light source-supporting substrate.
The preferred embodiment of the optical coupling system includes a connector receptacle that releasably attaches the fiber connector such that the fiber ends are aligned along the target plane. That is, the receptacle should position the connector to abut the separation-setting member. In this preferred embodiment, the receptacle has both a locked position and a release position relative to the separation-setting member. In the locked position, the receptacle physically engages the separation-setting member, so that the one-piece components are in a desired orientation. However, by rotating the receptacle, the receptacle is moved to its release position in which it can be removed from the separation-setting member.
In accordance with the method, the lens array is seated within the interior region of the separation-setting member, so as to contact the sh

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