Optical waveguides – With disengagable mechanical connector – Optical fiber/optical fiber cable termination structure
Reexamination Certificate
2001-08-13
2003-09-23
Chang, Andrey (Department: 2872)
Optical waveguides
With disengagable mechanical connector
Optical fiber/optical fiber cable termination structure
C385S078000, C385S084000
Reexamination Certificate
active
06623176
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally directed to optical fiber assemblies, and more particularly to an optical fiber assembly which allows sufficient curing of an interiorly positioned epoxy to provide optical stability to the optical fiber.
BACKGROUND
Several different techniques are known for attaching optical fibers to optoelectronic packages. Two of the more widely used techniques are solder attachment of a metallized optical fiber in a metal sleeve mounted to a wall of an optoelectronic package, and laser welding of an optical fiber assembly to a wall of an optoelectronic package.
When optical fibers are, for example, laser welded to optoelectronic packages, the alignment and positioning of the fiber relative to the optical axis of the optoelectronic package is performed by way of active alignment. Specifically, the optoelectronic package is held in a fixture that provides mechanical stability, spatial positioning, spatial manipulation and electrical biasing for the optoelectronic elements within the package. The optoelectronic elements generally include at least an optical element, such as, for example, a laser diode, photodiode, or lens, an optical fiber assembly including a metal ferrule at one end to be attached to the package and a bare fiber or optical connector, a light source, and a detector. The light source may be a solid state laser inside of the optoelectronic package or a laser source connected to the connector end of the fiber. The detector may be the photodioode or a detector at the connector end of the fiber.
The optical fiber assembly is held in the fixture, and the connector is connected either to a photodetector, in the case of a laser within the package, or to a laser in the case of a photodiode within the package. An electrical bias is then applied to the optoelectronic elements within the package. While the bias is applied, the package and/or the optical fiber is spatially manipulated to find a position which provides a desired level of optical power to the detector. Once the desired level is obtained, the optical fiber and the ferrule are affixed to the optoelectronic package by laser welding.
Typically, laser welding utilizes a high power laser source, such as a YAG laser, and the laser source is positioned to direct light onto the fiber and the portion of the ferrule in contact with the optoelectronic package. When the YAG laser is modulated, the metallic ferrule absorbs the energy locally, causing the temperature of the ferrule and the package to rapidly rise and eventually causing the ferrule and the package to melt locally such that a weld joint between the optoelectronic package wall and the ferrule is formed.
FIGS. 1-2
illustrate an optical fiber assembly
10
, which includes an optical fiber
12
positioned within a ferrule
20
. The ferrule
20
includes a metallized body
22
with a thin wall section
26
surrounding a defined interior space
24
and a thick wall section
28
surrounding a channel
30
. A mid-section of the ferrule body
22
, shown between a pair of dashed lines in FIG.
2
and designated generally as element
36
, is located between a ferrule body first end
32
and a ferrule body second end
34
. The channel
30
leads from the defined interior space
24
to the body second end
34
.
The fiber
12
extends through the ferrule
20
. The end of the fiber
12
nearest the body first end
32
extends through a channel
16
of a jacket
14
. An epoxy
40
fills out the space remaining in the defined interior space
24
and the channel
30
after positioning of the fiber
12
and the jacket
14
. The spacing between the fiber
12
and the wall of the channel
30
, as well as the spacing between the jacket
14
and the inner wall of the ferrule body
22
is small, typically on the order of a few microns. Such small spacing minimizes the potential for movement of the optical fiber
12
. The spacing between the fiber
12
outside of the jacket
14
but within the defined interior space
24
and the inner wall of the ferrule body
22
is significantly larger than the spacing between either the fiber
12
and the wall of the channel
30
or between the jacket
14
and the inner wall of the ferrule body
22
. Although an epoxy is shown in the defined interior space
24
in
FIG. 2
, other materials, such as, for example, a ceramic or other hard material insert may also be placed within the defined interior space
24
.
The epoxy
40
is utilized to attach the fiber
12
to the wall of the channel
30
and to the inner wall of the ferrule body
22
. The epoxy
40
is inserted within the ferrule
20
in a liquid or semi-liquid form, and during the epoxy cure cycle, the epoxy within the channel
30
and between the jacket
14
and the inner wall of the ferrule body
22
typically cures faster than the epoxy
40
residing in the remainder of the defined interior space
24
. The variable curing time is due to a lesser volume in and a more efficient heat transfer through the small open-spaced regions, namely within the channel
30
and between the jacket
14
and the inner wall of the ferrule body
22
, than in the large open-spaced region, namely the remainder of the defined interior space
24
.
Because the epoxy
40
in the small open-spaced regions cures faster than the epoxy
40
in the large open spaced region and because the small open-spaced regions are on either side of the large open-spaced region, the curing time in the large open-spaced region is further retarded. Curing of the epoxy
40
leads to the production of gaseous reaction products in accordance with Equation 1 below:
The nomenclature [m], [n], [o] and [p] are constants for balancing out Equation 1. Diffusion of the gaseous reaction products is slower through cured epoxy than through non-cured epoxy. The slower diffusion rates of the epoxy
40
in the small open-spaced regions leads to a build up of gaseous reaction products in the large open spaced region.
The build up of the gaseous reaction products further retards the curing time of the epoxy
40
in the large open spaced region. As illustrated in the equation above, epoxy rings react with a curing agent when energy, such as heat or light, is applied to the system to form a polymeric epoxy material plus the gaseous reaction products. In an equilibrium, Equation 1 above is constant. In other words, as noted in Equation 2 below:
Constant
=
[
Polymeric
epoxy
]
o
[
gaseous
reaction
products
]
p
[
Epoxy
ring
]
n
[
Cure
agent
]
m
=
k
1
k
2
Equation
2
Since the total gaseous reaction products are composed of the gaseous reaction products from new reactions and the trapped gaseous reaction products, and given that the epoxy
40
within the ferrule
20
is an equilibrium system, then as the amount of trapped gaseous reaction products increases, the reaction rate defining the formation of polymeric epoxy decreases. Thus, the ferrule assembly
10
has the potential for creating a system in which the epoxy
40
in the large open spaced region, and especially in the mid-section
36
, never fully cures.
The state of cure of epoxy can be defined with reference to its glass transition temperature T
g
, which may be defined as the temperature range at which the mechanical properties of a material, in this case epoxy, change such that above the range the epoxy is elastic and below that range the epoxy is brittle.
FIG. 3
illustrates the general elastic modulus behavior for a defined epoxy system over a temperature range. The same starting epoxy system, cured to a different degree, namely to a different T
g
, is shown in the graph. As shown in
FIG. 3
, the general elastic modulus behavior of an epoxy system increases with an increasing T
g
, while the magnitude of the temperature range over which there is a significant change in the general elastic modulus behavior increases with decreasing T
g
.
The change in general elastic modulus behavior with a change in T
g
translates into a change in the magnitude and time dependence of the reversible
Jack Curtis A.
Osenbach John W.
Allen Denise S.
Chang Andrey
Dickstein , Shapiro, Morin & Oshinsky, LLP
TriQuint Technology Holding Co.
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