Optical waveguides – With disengagable mechanical connector – Optical fiber/optical fiber cable termination structure
Reexamination Certificate
2001-05-24
2002-06-25
Patel, Tulsidas (Department: 2839)
Optical waveguides
With disengagable mechanical connector
Optical fiber/optical fiber cable termination structure
Reexamination Certificate
active
06409395
ABSTRACT:
BACKGROUND OF THE INVENTION
In contemporary optical-electronic hybrid systems, an optical fiber interfaces with an opto-electronic device. The opto-electronic device typically includes a hermetic package, having a plurality of 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 side walls of the package. The end face of each pigtail is typically positioned and bonded to a bench or submount installed within the package. The body of each pigtail is bonded to a corresponding ferrule to facilitate the hermetic seal of the package.
As opto-electronic technology continues to evolve, there is a continuous drive toward higher integration. This generally requires an increased number of fiber pigtails to extend across the package perimeter, as well as an increased need for heightened precision in aligning the fiber endfaces with internal opto-electronic components.
A standard fiber optic cross section is illustrated in
FIG. 1. A
fiber core
12
is encased in cladding
14
. The fiber core may for example be comprised of silica, while the cladding may be comprised of silica having a lower index of refraction than that of the core
12
. The cladding
14
is encased in a coating
16
which is, in turn, surrounded by a protective jacket
18
. The coating and protective jacket may, for example, be formed of any of a number of polymers. In a popular configuration, the diameters of the core
12
, cladding
14
, coating
16
, and protective jacket
18
layers are 9 &mgr;m, 125 &mgr;m, 250 &mgr;m, and 900-3000 &mgr;m, respectively.
Despite precision processing during manufacture of optical fibers, a number of variations in the finished fiber can occur. These include variation in the cladding
14
diameter, and variation in the center position of the core
12
relative to the center of the cladding
14
, i.e., core-cladding eccentricity.
With reference to the end view of
FIG. 2
, in order to manage fiber congestion in a device, the fibers are commonly arranged into an array on a silicon bench. The bench
22
includes an upper bench portion
22
A and a lower bench portion
22
B. A number of opposed V-grooves
28
A,
28
B are formed in the upper and lower bench portions
22
A,
22
B. The V-grooves are formed in parallel with respect to each other, and at precise intervals which, for example, may be periodic.
The outer protective jacket
18
and coating
16
are stripped from the fiber ends, and the ends are positioned and bonded between the V-grooves
28
A,
28
B. When the fibers are bonded, the aforementioned variations can result in misalignment of the fiber cores with the intended interface, for example the optical components that are installed in the submount. With reference to the example provided in
FIG. 2
, the respective cladding diameters of fibers
20
A,
20
B, and
20
C are consistent, and therefore their respective fiber center positions
24
A,
24
B,
24
C are properly centered with respect to the upper and lower V-grooves
28
A,
28
B. However, the cladding diameters of fibers
20
D and
20
E are smaller than those of fibers
20
A,
20
B, and
20
C, and therefore their respective fiber center positions
24
D,
24
E are not centered between the upper and lower V-grooves
28
A,
28
B. This variation in cladding outer diameter causes a height offset between the respective fibers in the array.
Ideally, the fiber core
26
D is located directly at the fiber center position
24
D, as shown in fiber
20
D. However, due to manufacturing imprecision, the fiber core
26
A,
26
B,
26
C,
26
E can vary in radial distance from the fiber center position
24
A,
24
B,
24
C,
24
E as shown in fibers
20
A,
20
B,
20
C, and
20
E, i.e., core eccentricity. As a result, the position and angular orientation of the fiber core
26
can vary with respect to the center position of the upper and lower V-grooves
28
A,
28
B, as shown. Such a variance can also cause a height offset, as well as angular offset, between beams emitted from the respective fibers, or the input apertures that define where a beam must be focused to be coupled into, and be propagated by, the fiber.
SUMMARY OF THE INVENTION
The present invention is directed to an apparatus and method that addresses the limitations of conventional approaches described above. Particularly, the present invention provides an apparatus and method by which height offset and/or angular core offset of optical fibers that are mounted in an array are mitigated. In this manner, a level of precision is achieved that is advantageous for application in opto-electronic systems.
The fibers are preferably mounted in the array such that the respective core-to-clad offset axes of the fibers, defined between the fiber core center and the cladding center of each fiber, are at substantially the same angle with respect to the lateral axis of the bench The fiber pigtails are preferably cut from the same fiber spool, ensuring consistency in cladding outer diameter. In this manner, precision in core-to-core pitch and consistency in core-to-core height are achieved in the fiber array.
In one aspect, the present invention is directed to a fiber array. The array includes a bench and fiber pigtails. The bench includes seats for receiving the fiber pigtails. The fibers are mounted in the seats; the fibers include a fiber core and cladding surrounding the fiber core. Each fiber has a core-to-clad offset axis defined between the fiber core center and the cladding center of each fiber. This is a measure of the core eccentricity. The fibers are mounted in the array such that the respective core-to-clad offset axes of the fibers are at substantially the same angle with respect to each other.
In another aspect, the present invention is directed to a fiber array including a bench and fiber pigtails. The bench includes a plurality of parallel seats for receiving the fibers. Fibers are mounted in the seats. The fibers comprise a fiber core and cladding surrounding the fiber core, and are cut from a common fiber spool. The angle between the core-to-clad offset axes and a plane of the submount may be 90 degrees, 0 degrees, or an acute angle.
In preferred embodiments, the seats comprise V-grooves, and the bench comprises silicon. The bench includes an upper portion and a lower portion; the upper and lower portions each include opposed seats for housing inserted fibers. Alternatively, the bench includes an upper portion and a lower portion, wherein the lower portion includes the seats and wherein the upper portion comprises a plate.
In another aspect, the present invention is directed to a method of forming a fiber array. A bench is provided, the bench including a plurality of parallel seats for receiving a plurality of fibers. Fibers are mounted in the seats, the fibers comprising a fiber core and cladding surrounding the fiber core, each fiber having a core-to-clad offset axis defined between the fiber core center and the cladding center of each fiber. The fibers are mounted in the array such that the respective core-to-clad offset axes of the fibers are substantially parallel to each other.
In yet another aspect, the present invention is directed to a method of forming a fiber array. A bench is provided, the bench including a plurality of parallel seats for receiving a plurality of fibers. A plurality of fibers are mounted in the seats, the fibers comprising a fiber core and cladding surrounding the fiber core, the fibers being cut from a common fiber spool.
In another aspect, the present invention is directed to a method for aligning fibers in a fiber array with an optical component on a substrate. Fibers are mounted and rotationally oriented in a fiber bench in response to a direction of core-to-cladding offset axes of the fibers. The fiber bench is in turn mounted to a substrate in alignment with a component mounted to the substrate, such that the fibers are aligned with the component.
REFERENCES:
patent: 4904052 (1990-02-01), Rand et al.
patent: 5073
Flanders Dale C.
Wang Xiaomei
Axsun Technologies, Inc.
Mills & Onello LLP
Patel Tulsidas
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