Electric heating – Metal heating – By arc
Reexamination Certificate
2002-12-02
2004-07-20
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121640, C219S121830
Reexamination Certificate
active
06765172
ABSTRACT:
FIELD OF INVENTION
The field of invention relates to optical component technology generally; and, more specifically, to a laser fusion based WDM coupler.
BACKGROUND
WDM Couplers
A Wavelength Division Multiplexed (WDM) coupler module is a device that, through an arrangement of discrete WDM couplers, merges N optical channels onto a single optical fiber.
FIG. 1
shows an embodiment of an 8×1 WDM coupler module that is constructed with an arrangement of seven 2×1 WDM couplers
101
1
through
101
7
. The 8×1 WDM coupler module of
FIG. 1
is responsible for integrating 8 optical channels onto a single optical fiber. An optical channel corresponds to the optical permissiveness of a fiber optic path, as a function of wavelength, within an optical wavelength range that is referenced around a“peak” wavelength.
Optical permissiveness is figure of merit as to the tendency of a fiber optic path to allow light to propagate forward. Thus, if the optical permissiveness of a fiber optic path is “high”, the fiber optic path tends to allow light to propagate forward; and, if the optical permissiveness of a fiber optic path is “low”, the fiber optic path tends to “block” light from propagating forward. Those of ordinary skill typically measure optical permissiveness for an optical device (such as a WDM coupler module) by measuring the intensity of light received at an output as a function of wavelength. The curve that is “traced out” is often referred to as the “spectrum” of the optical path being measured (and which is being referred to herein as optical permissiveness).
Typically, the optical permissiveness of an optical channel within a WDM coupler module “rolls off” as the wavelength deviates from its associated peak wavelength. As such, it may be said that the shape of an optical channel rolls off as optical wavelength deviates from its peak wavelength.
FIG. 1
demonstrates an example by way of a depiction
103
of the optical permissiveness of the 8×1 WDM coupler module (as observed from its output
102
). Note that eight unique optical channels are observed
104
1
through
104
8
. Each of the optical channels
104
1
through
104
8
has its own corresponding peak wavelength &lgr;
1
through &lgr;
8
, respectively. Note that, from their shape, each of the optical channels
104
1
through
104
8
tend to pass light having its corresponding peak wavelength and tend to increasingly reject or block light that deviates from its peak wavelength.
As can be seen from
FIG. 1
, the 8×1 WDM coupler module is formed with seven 2×1 WDM couplers
101
1
through
101
7
. Here, each 2×1 coupler integrates onto its output fiber the light intensity that is received from its pair of input fibers. For example, 2×1 coupler
101
1
is generally designed to receive light intensity (at a first fiber optic input) that peaks at wavelength &lgr;
1
and receive light intensity (at a second input) that peaks at wavelength &lgr;
5
. The 2×1 WDM coupler
101
1
integrates the received light intensity onto its output optical fiber (which also acts as a first input to 2×1 coupler
101
5
). As such, the notation “&lgr;
1
,&lgr;
5
” is used proximate to the output of 2×1 coupler
101
1
.
By nature of the specific combinations of input wavelength observed in the 8×1 WDM coupler module of
FIG. 1
, note that each successive 2×1 coupler (passing forward through the coupler module) may be designed with decreased spacing between neighboring optical channels. For example, the 8×1 WDM coupler module of
FIG. 1
may be designed such that: 1) 2×1 WDM couplers
101
1
through
101
4
each have a neighboring channel peak wavelength spacing of 4(&lgr;
8
−&lgr;
1
)/7; 2) 2×1 WDM couplers
101
5
and
101
6
each have a neighboring channel peak wavelength spacing of 2(&lgr;
8
−&lgr;
1
)/7; and 3) 2×1 WDM coupler
101
7
has a neighboring channel center wavelength spacing of (&lgr;
8
−&lgr;
1
)/7.
Fabrication of WDM Couplers
FIGS. 2
a
through
2
c
relate to the construction of a 2×1 coupler.
FIG. 2
a
shows a cross section of a typical optical fiber. The optical fiber cross section of
FIG. 2
a
shows a central core
201
surrounded by a cladding layer
202
. A protective jacket
203
surrounds the cladding layer
202
. A common embodiment further includes a core
201
diameter of 5-9 &mgr;m and a cladding layer
202
diameter of 125 &mgr;m.
FIG. 2
b
shows an initial manufacturing “setup” just prior to manufacture of a 2×1 WDM coupler. According to the depiction of
FIG. 2
b
a pair of optical fibers which have been stripped of their corresponding jackets are fixedly positioned next to one another. Here,
FIG. 2
b
shows the cladding layer
212
and central core
211
of a first optical fiber; and, the cladding layer
222
and central core
221
of a second optical fiber.
Within a fusion region
230
, the pair of stripped optical fibers neighbor one another. Heat is then applied within the fusion region
230
through the use of an open flame. As a consequence of the extreme heat that is applied to the fusion region
230
, the pair of optical fibers begin to fuse together.
FIG. 2
b
shows a depiction of the pair of optical fibers after they have been fused together (e.g., after the open flame has been removed). Because of the merging of the fibers, a 2×1 coupler can be readily formed. For example, optical fiber end
231
can be viewed as the output of the 2×1 coupler, optical fiber end
211
can be viewed as a first input to the 2×1 coupler, and optical fiber end
221
can be viewed as a second input to the 2×1 coupler. Section
232
can be terminated as “no function” port.
Note that the cores from the pair of optical fibers are merged in the depiction of
FIG. 2
c
. Typically, couplers requiring a narrow neighboring channel spacing (e.g., such as coupler
101
7
of
FIG. 7
) may need to have merger of the cores within the fusion region in order to obtain the narrow channel spacing. Couplers having a more relaxed neighboring channel design (e.g., such as couplers
101
1
through
101
4
of
FIG. 7
) may be able to allow some degree of separation of the fiber optic cores.
Problems with WDM Coupler Fabrication
FIGS. 3
a
and
3
b
relate to a traditional problem involved in the manufacture of WDM couplers.
FIG. 3
a
shows optical permissiveness as a function of wavelength for a typical taper of optical fiber made by a flame fusion process. For any type of optical fiber made by flame fusion, a defect (that is related to the water absorption introduced by a traditional flame fusion process) causes a noticeable and undesirable “bump”
301
in the optical permissiveness of the optical fiber taper (approximately over a wavelength range of 1370 nm to 1420 nm.
The bump
301
has two drawbacks. Firstly, the drop corresponds to increased “insertion loss” of optical devices (such as WDM couplers and coupler modules) that process light having wavelengths in the realm of the bump
301
; and, secondly, such insertion loss varies in the realm of the bump
301
. As increased insertion loss corresponds to more optical rejection—increased insertion loss by itself may threaten the practical use of an optical device (because most optical networks attempt to minimize the insertion loss caused by its various components). Moreover, many optical devices are designed to have substantially even (or “flat”) optical permissiveness over the range of used optical wavelengths (each peak wavelength for the optical channels of a WDM coupler module). The bump
301
corresponds to a deviation from this desired property.
FIG. 3
b
illustrates the combined effect of both drawbacks for a WDM coupler module.
FIG. 3
b
(which may be compared with the optical permissiveness
103
of
FIG. 1
) corresponds to the optical permissiveness of an 8×1 coupler that is made from 2×1 couplers having fiber optic properties that suffer from water absorption. Assuming that the 8×1 coupler is designed to opera
Brewer Tracy
Liang Frank
Liu Xu
Heinrich Samuel M.
Wavesplitter Technologies, Inc.
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