Title: Optical fiber cable with controlled helix values
Abstract: A fiber optic cable having optical fibers disposed in buffer tubes, the buffer tubes defining at least two layers generally stranded about a center area of the cable. The buffer tube layers define a relatively inner layer of buffer tubes being closer to the center area, and an outer layer of buffer tubes being relatively further from the center area. The inner and outer buffer tube layers each having a respective helix value, the respective helix values being substantially the same. Alternatively, the respective helix values can be substantially non-equal. In addition, fiber optic cable systems including balanced helix factors have optical connections between layers of buffer tubes of the respective cables.
Patent Number: 6,859,592 Issued on 02/22/2005 to Seddon, et al.
| Inventors:
|
Seddon; David A. (Hickory, NC);
Fedoroff; Michael S. (Saskatoon, SK);
Jackman; William S. (Hickory, NC)
|
| Assignee:
|
Corning Cable Systems LLC (Hickory, NC)
|
| Appl. No.:
|
035769 |
| Filed:
|
December 26, 2001 |
| Current U.S. Class: |
385/111; 385/109 |
| Intern'l Class: |
G02B 006//44 |
| Field of Search: |
385/112,111,113,109,54,71
|
References Cited [Referenced By]
U.S. Patent Documents
| 3912362 | Oct., 1975 | Hudson | 385/54.
|
| 3912364 | Oct., 1975 | Hudson | 385/46.
|
| 3917383 | Nov., 1975 | Cook et al. | 385/54.
|
| 4205900 | Jun., 1980 | Eve | 350/96.
|
| 4230395 | Oct., 1980 | Dean et al. | 385/109.
|
| 4478488 | Oct., 1984 | Bagley | 350/96.
|
| 5343549 | Aug., 1994 | Nave et al. | 385/103.
|
| 5440659 | Aug., 1995 | Bergano et al. | 385/100.
|
| 5611016 | Mar., 1997 | Fangmann et al. | 385/100.
|
| 5675680 | Oct., 1997 | Ames et al. | 385/54.
|
| 5930431 | Jul., 1999 | Lail et al. | 385/100.
|
| 5970196 | Oct., 1999 | Greveling et al. | 385/114.
|
| 6005458 | Dec., 1999 | Buer et al. | 333/248.
|
| 6014487 | Jan., 2000 | Field et al. | 385/110.
|
| 6550985 | Apr., 2003 | Nakamura et al. | 385/96.
|
| 6728452 | Apr., 2004 | Nishimura | 385/100.
|
Other References
US2001/0028773A1, "Fiber Optic Cable And Optical Transmission System", Oct.
11, 2001.
US2001/0004415A1, "Optical Fiber Transmission Line And Optical Cable
Including The Same", Jun. 21, 2001.
US2001/0002943A1, "Multiple Fiber Optical Cable And Method Of Manufacturing
The Same", Jun. 7, 2001.
|
Primary Examiner: Hyeon; Hae Moon
Attorney, Agent or Firm: Aberle; Timothy J.
Claims
Accordingly, what is claimed is:
1. A fiber optic cable, comprising:
optical fibers disposed in buffer tubes, said buffer tubes defining at
least two layers generally stranded about a center area of the cable; said
buffer tube layers defining a relatively inner layer of buffer tubes being
closer to said center area, and an outer layer of buffer tubes being
relatively further from said center layer, said inner and outer buffer
tube layers each comprising a respective helix factor value, said
respective helix factor values being substantially the same.
2. The fiber optic cable of claim 1, differing buffer tube diameters with
the same wall thickness and lay length being used in each layer to provide
the minimum helix factor value for each layer, the helix factor value
being within about 0% to about 5% of each other.
3. The fiber optic cable of claim 1, said buffer tubes having inner or
outer diameters that vary from tube layer to tube layer.
4. The fiber optic cable of claim 1, one of said buffer tube layers having
a relatively smaller buffer tube wall thicknesses or the inner tube layer
having buffer tubes with a relatively smaller outer diameter.
5. A fiber optic cable system, comprising:
first and second fiber optic cables, each of said first and second fiber
optic cables having respective optical fibers disposed in buffer tubes,
said butter tubes defining at least two layers respectively in said cables
generally stranded about a center area of the respective fiber optic
cables; said buffer tube layers defining a relatively inner layer of
buffer tubes being closer to said center area, and an outer layer of
buffer tubes being relatively further from said center area, said inner
and outer buffer tube layers each comprising a respective helix factor
value, said respective helix factor values within each said cable being
substantially the same; and the optical fibers of the layer of buffer
tubes of said first optical fiber cable being optically connected to the
optical fibers of a corresponding layer of buffer tubes of said second
fiber optic cable.
6. The fiber optic cable system of claim 5, at least some of said optically
interconnected optical fibers having essentially the same overall fiber
length through said cables.
7. A fiber optic cable, comprising:
optical fibers disposed in buffer tubes, said buffer tubes defining at
least two layers generally stranded about a center area of the cable; said
buffer tube layers defining a relatively inner layer of buffer tubes being
closer to said center area, and an outer layer of buffer tubes being
relatively further from said center area, said inner and outer buffer tube
layers each comprising a respective helix factor value, said respective
helix factor values being substantially non-equal.
8. The fiber optic cable of claim 7, said buffer tube having inner or outer
diameters that vary from tube layer to tube layer.
9. The fiber optic cable of claim 7, one of said buffer tubs layers having
a relatively smaller buffer tube wall thicknesses or the inner tube layer
having buffer tubes with a relatively smaller outer diameter.
10. A fiber optic cable system, comprising:
first and second fiber optic cables, each of said first and second fiber
optic cables having respective optical fibers disposed in buffer tubes,
said buffer tubes defining at least two layers respectively in said cables
generally stranded about center areas of the respective fiber optic
cables; said buffer tube layers defining a relatively inner layer of
buffer tubes being closer to said center area, and an outer layer of
buffer tubes being relatively further from said center area, said inner
and outer buffer tube layers each comprising a respective helix factor
value, said respective helix factor values within said first fiber optic
cable being substantially non-equal; and the respective helix factor
values in said second fiber optic cable having the respective helix factor
values such that at least some of the optical fibers in the overall fiber
optic cable system have concatenated fiber lengths being essentially
equal, when the optical fibers of the layers of buffer tubes of said first
optical fiber cable are optically interconnected to the optical fibers of
a corresponding layer of buffer tubes of said second fiber optic cable.
11. A fiber optic cable system with some or all fibers having essentially
the same length, comprising:
first and second fiber optic cables, each of said first and second fiber
optic cables having respective optical fibers disposed in buffer tubes,
said buffer tubes defining at least two layers respectively in said cables
generally stranded about a center area of the respective fiber optic
cables; said buffer tube layers defining a relatively inner layer of
buffer tubes being closer to said center area, and an outer layer of
buffer tubes being relatively further from said center area, said inner
and outer buffer tube layers each comprising a respective helix factor
value, said respective helix factor values within each said cable being
substantially non-equal; and the optical fibers of the layer of buffer
tubes of said first optical fiber cable being optically connected to the
optical fibers of a non-corresponding layer of buffer tubes of said second
fiber optic cable.
12. A fiber optic cable system, comprising:
first and second fiber optic cables, each of said first and second fiber
optic cables having respective optical fibers disposed in buffer tubes,
said buffer tubes defining at least two layers respectively in said cables
generally stranded about a center area of the respective fiber optic
cables, said buffer tube layers defining a relatively inner layer of
buffer tubes being closer to said center area, and an outer layer of
buffer tubes being relatively further from said center area, said inner
and outer buffer tube layers each comprising a respective helix factor
value, said respective helix factor values within each said cable being
substantially the same; and the optical fibers of the inner layer of
buffer tubes of said first optical fiber cable being optically connected
to the optical fibers of a outer layer of buffer tubes of said second
fiber optic cable.
13. The fiber optic cable system of claim 12, at least some of said
optically interconnected optical fibers having essentially the same
overall fiber length through said cables.
Description
The present invention relates to the field of fiber optic cables, and, more
particularly, to fiber optic cables having optical fibers with optical
performance characteristics being managed for signal transmission
performance of high data rate systems.
BACKGROUND OF THE INVENTION
Fiber optic cables are used to transmit telephone, television, and computer
data information in indoor and outdoor environments in non-multiplexed and
multiplexed optical transmission systems. In wave division multiplexed
systems, optical performance characteristics play a significant role in
maintaining high data rate transmission.
Optical attenuation, the loss in transmitted power, and chromatic
dispersion, the differential transit time at adjacent wavelengths, are
examples of optical performance characteristics in such transmission
systems. Optical attenuation is typically due to absorption, scattering,
and leakage of light from the waveguide and is customarily measured in a
fiber, or cable, as a loss value in dB/km. Chromatic dispersion in fiber
optic waveguides can be viewed as the sum of material and waveguide
dispersions. Changes in refractive index with wavelength give rise to
material dispersion. In bulk glass (silica) fibers, material dispersion
increases with wavelength over a wavelength range of about 0.9 .mu.m to
1.6 .mu.m. Material dispersion can have a negative or a positive sign
depending on the wavelength. Waveguide dispersion results from light
traveling in both the core and cladding of an optical fiber. Waveguide
dispersion is also a function of wavelength and the refractive index
profile. Wavelength and material dispersion affects combine to yield an
overall positive or negative chromatic dispersion characteristic at any
given point in a given optical fiber. Optical performance concerns
regarding pulse spreading caused by chromatic dispersion have created a
need for dispersion compensating systems. Dispersion compensating systems
employing, for example, positive and negative dispersion compensating
fibers, are nevertheless subject to the optical performance constraints
associated with optical attenuation.
A fiber optic cable design that acknowledges chromatic dispersion affects
is described in U.S. Pat. No. 5,611,016. The patent pertains to a
dispersion-balanced optical cable for reducing four-photon mixing in wave
division multiplexing systems, the cable being designed to reduce
cumulative dispersion to near zero. The dispersion-balanced optical cable
requires positive and negative dispersion fibers in the same cable.
Further, the positive dispersion aspect includes a dispersion
characteristic defined as the average of the absolute magnitudes of the
dispersions of the positive dispersion fibers exceeding 0.8 ps/nm.km at a
source wavelength. In addition, the negative dispersion fiber
characteristic requires the average of the absolute magnitudes of the
dispersions of the negative dispersion fibers to exceed 0.8 ps/nm.km at
the source wavelength. The aforementioned optical fibers are ribbonized,
single-mode fibers designed for the transmission of optical signals in the
1550 nm wavelength region. The fibers are non-stranded or non-helically
enclosed within a mono-tube cable, and are described as having an
attenuation at 1550 nm of 0.22-0.25 dB/km, and attenuation at 1310 nm of
<0.50 dB/km. At defined parameters, the positive-dispersion
characteristic is described as being +2.3 ps/nm.km and the
negative-dispersion characteristic is described as being -1.6 ps/nm.km.
Other patents describe optical performance characteristics relating to a
time division, rather than wave division, system. For example, U.S. Pat.
No. 4,478,488 describes selective time compression and time delay of
optical signals, without discussing the problems associated with
attenuation or chromatic dispersion. A system is described using discrete
channels having a dispersive section coupled to a standard multi-waveguide
transmission section, and then another dispersive section. Signals are
intended to propagate spatially out of phase, which can minimize channel
coupling phenomena. An embodiment requires respective plastic coatings
formed on twisted optical fibers, the coatings having varying diameters
for varying the helix of the fibers in the cable. Individual fibers are
spaced from the axis of the twist by different distances. This causes some
fibers to twist more than others and extends the length of fiber located
at the outside of the bundle compared to one nearer the inside of the
bundle. Using a multicore cable made up of cores embedded in a single
cladding, each fiber is fixed at a helix that is different than the helix
of any other fiber.
ASPECTS OF THE INVENTIONS
A fiber optic cable having optical fibers disposed in buffer tubes, the
buffer tubes defining at least two layers generally stranded about the
center of the cable. The buffer tube layers define an inner layer of
buffer tubes being relatively closer to the center area, and an outer
layer of buffer tubes being relatively further from the center area. The
inner and outer buffer tube layers each having a respective helix value,
the respective helix values being substantially the same. Alternatively,
the respective helix values can be substantially non-equal. In addition,
fiber optic cable systems including balanced helix factors have optical
connections between layers of buffer tubes of the respective cables.
BRIEF DESCRIPTION OF THE DRAWING FIGURE
FIG. 1 is a cross sectional view of an exemplary fiber optic cable
according to the present invention.
FIGS. 2 and 2a are schematic representations of a portion of respective
fiber optic cable systems having an optical connection between optical
fibers of a first cable and a second cable.
DETAILED DESCRIPTION OF THE INVENTIONS
Referring to FIG. 1, an exemplary fiber optic cable 10 is shown and
described for use in an optical transmission system, for example, a
dispersion managed cable system (DMCS). Fiber optic cables according to
the present invention are of a loose tube construction and can include a
single, silica-based optical fiber type or they can define a hybrid design
containing at least two different optical fiber types. For example, the
cables can include both positive and negative dispersion compensating
fibers (DMCS fibers) or a single type of dispersion managed fiber in
combination with non-DMCS fibers, for example, LEAF.RTM., SMF-28, or
METROCOR.TM. fibers made available by Corning Inc. DMCS optical fibers
used in cables according to the present invention have predetermined
attenuation and chromatic dispersion characteristics such that, in the
1500-1600 nm wavelength regime, the range of absolute values of the
chromatic dispersion is between about ten to about forty ps/nm.km. For
example, the positive dispersion optical fibers have a dispersion of about
ten to thirty ps/nm.km, and the negative dispersion optical fibers have a
dispersion of about negative twenty to about negative forty ps/nm.km.
A DMCS fiber is nevertheless subject to optical performance constraints
associated with, for example, optical attenuation. The inventors of the
present inventions have recognized that optical attenuation and the
magnitude of the local chromatic dispersion are both directly proportional
to a helix factor. The inventors of the present invention have furthermore
discovered a way of managing factors that reduce variations in optical
performance, e.g., optical attenuation, in a way that enhances chromatic
dispersion management systems. While the magnitude of optical parameters
are of major interest in maximizing the reach of a system, the reduction
in variation in parameters also allows a greater reach. One factor
currently being used to define a digital system quality is the Q factor
which is effectively the ratio of the difference between the received "1"
and "0" power levels divided by the sum of the standard deviations of the
"1" and "0" power levels. An increased Q (good) is associated with more
power going through (Low attenuation) and consistencies of the power (low
variation) in attenuation and chromatic dispersion. If dispersion is not
fully compensated the variation in the "1"s and "0"s increase.
In accordance with the concepts of the present inventions, fiber optic
cables having multiple layers of optical fibers, in a loose tube
construction, have controlled helix factors and strain windows for
controlling optical attenuation and dispersion, enhancing dispersion
management and resulting in acceptable Q factors.
Features of the present invention are the minimization of the absolute
fiber length in the cable, with control of the relative fiber length
between layers in multi-layer optical fiber stranded cables while
maintaining desired cable dimensional, thermal, and tensile performance
criteria. The present invention achieves a balance of controlling the
helix factor, extensile and compressive strain windows, the strength
elements in the cable, and the composite thermal expansion characteristics
of the cable.
To manufacture multi-layer controlled and minimized helix factor cables
cable design parameters are controlled. According to the present inventive
concepts, several equations are disclosed. First, the helix factor for
each fiber can be determined by the lay length and the pitch diameter of
that fiber. Equation 1 shows the relationship between the helix factor,
the lay length and the pitch diameter:
##EQU1##
Where H.sub.i =the helix factor for fiber i,
P.sub.i =the pitch diameter for fiber i, and
L.sub.i =the lay length for fiber i.
The helix factor is commonly expressed as a percent.
The extensile strain window for stranded loose tube cables can be defined
as the percent axial elongation the cable can experience before the fibers
experience fiber strain. Equation 2 shows a method for estimating the
strain window for fibers in a given buffer tube for use in the present
inventions.
##EQU2##
Where M.sub.ej =Extensile strain window,
L.sub.j =lay length of buffer tube j,
D.sub.j =the diameter of the core or core components, around which the
buffer tube j is stranded,
d.sub.j =the outer diameter of buffer tube j,
.DELTA..sub.j =the increase in pitch diameter caused by fiber excess length
in buffer tube j,
t.sub.j =the thickness of the tube wall for buffer tube j, and
b.sub.j =the effective diameter of the fiber or fiber bundle in buffer tube
j.
The cable extensile strain window M.sub.c is the minimum Buffer tube
extensile strain window and is normally expressed as a percent.
The compressive strain window for stranded loose tube cables is commonly
defined as the percent axial compression the cable can withstand before
fiber compression occurs. Equation 3 shows a method for estimating the
compressive strain window for buffer tube j.
##EQU3##
Where M.sub.cj equals the compressive strain window and the rest of the
parameters are as defined for Equation 2. The cable compressive strain
window M.sub.c is the M.sub.cj with the minimum absolute value and is
normally expressed as a percent.
The composite thermal coefficient of a cable can be estimated by Equation
4:
##EQU4##
Where .alpha..sub.c =the composite thermal expansion coefficient,
.alpha..sub.i =the Thermal Coefficient of expansion for material i,
E.sub.i =the Young's modulus of material i,
A.sub.i =the Cross sectional area of material i, and
N=the number of materials under stress in the cable.
The allowable temperature limits can be found from Equations 5 and 6.
##EQU5##
Where T.sub.max =maximum temperature for design purposes,
M.sub.c =cable extensile strain window,
S.sub.a =allowable fiber strain,
.alpha.=composite thermal coefficient, and
T.sub.Nom =the nominal design temperature for cable characteristic
calculations.
##EQU6##
Where T.sub.min =minimum temperature for design purposes,
M.sub.c =cable compressive strain window,
C.sub.a =allowable fiber compression,
.alpha.=composite thermal coefficient, and
T.sub.Nom =the nominal design temperature for cable characteristic
calculations.
Strain window is a property of the cable geometry that limits the strain
that fibers experience when the cable is stretched, through the
application of an external force, or when it contracts or expands in
response to thermal affects. Exceeding the strain window can
disadvantageously cause optical attenuation and PMD.
In accordance with the present inventive concepts, the respective helix
factor values, for respective layers of buffer tubes in the cable, are
controlled. The layers of tubes are concentric with respect to a center of
the cable, and tubes of a given layer are spaced from the center at about
the same distance. For example, the helix value(s) for at least two layers
of buffer tubes can be made substantially the same, for example, within
about 0 to 2% or 0% to 5% of each other. Other embodiments would include
controlled, non-equal helix values for each layer, for example, respective
helix values being within about 5-10% or 10-20% of each other.
Fiber optic cable 10 preferably includes at least two layers of buffer
tubes 14,18, at least some of the buffer tubes contain bundled optical
fibers 15,19 defining a respective bundle diameter. Tubes 14 comprise an
inner layer of tubes, and tubes 18 comprise an outer layer. The buffer
tubes are formed of materials with known temperature coefficients of
expansion/contraction. As noted above, the optical fibers in the tubes can
be positive and/or negative, dispersion compensating, and can include
non-dispersion shifted fibers, for example, LEAF.RTM., SMF-28 optical
fibers, or METROCOR.TM. fibers made available by Corning Inc. One or more
tube positions can be occupied by a filler rod (not shown). Tubes 14,18
are preferably stranded about the center of the cable, which is preferably
occupied by a central strength member 12. Water swellable tapes 16 can be
disposed adjacent the buffer tubes. A surrounding cable jacket 20 formed
of, for example, polyethylene, is extruded over the components.
In preferred embodiments the buffer tube outer diameters (OD) vary from
tube layer to tube layer, but the outer diameters will preferably be
generally the same within a given layer. Preferably the tube layers having
relatively smaller outer tube diameters occupy the inner tube layer. Also,
the number of fibers and fiber types in the tubes could be different
between layers or tubes within a layer. Preferably, all cable components
are made within suitable manufacturing specifications, and are of known or
measurable material, mechanical, or geometrical characteristics. For
example, the respective moduli of the components are known, each buffer
tube is substantially round and has an inner and outer diameter defining a
generally constant tube wall thickness, and the buffer tubes are stranded
along a defined lay length or pitch. Preferably, helix values are
controlled from tube layer to tube layer. In one embodiment, cables made
according to the present inventions advantageously have the helix values
essentially the same for at least two layers of buffer tubes.
In accordance with the present inventive concepts, the compression margin
is different for each layer and is a function of, for example, buffer tube
dimensions and lay lengths. The thermal limit for fiber optic cables
according to the present inventions is preferably determined by the
highest minimum temperature rating between the at least two layers. In
other words, the desired strain window is preferably based on a minimum
temperature limit.
In a preferred embodiment, cable 10 has a minimum temperature limit of
-40.degree. C. and a maximum temperature limit of 70.degree. C. with 8-9
buffer tubes on the inner layer, and 12-13 tubes on the outer layer. The
cable meeting these temperature requirements can be made with identical
3.0/2.3 mm (OD/ID) tubes on the inner and outer layer has a minimum helix
value of 1.61%. A reduced helix value of 1.45% can be achieved by using a
3.0/2.3 mm tube in the outer layer and a 2.4/1.7 mm tube in the inner
layer. An even lower Helix of 0.96% can be achieved by using 3.15/2.9 mm
tube in the outer layer and a 2.9/2.2 tube in the inner layer. The
foregoing assumes known or measurable material, mechanical, and
geometrical characteristics for use in the foregoing equations. Other
constraints on the cable design, such as maximum allowed diameters and
weights tonically provide the limiting factor for the cables to be used in
a particular system.
Buffer tube geometries are illustrative. A preferred tube outer diameter
range is about 1.5 mm to about 8.0 mm with a lay length range of about 60
mm to about 600 mm. In general, the tubes of the inner layer have a
different outside diameter and inside diameter than buffer tubes in the at
least one other layer. In one example, the inner layer has 2.5/1.8 mm
tubes and the outer layer has 3.0/2.3 mm tubes, all with 12 fibers. This
enables a lay length such that the cable has a controlled helix value,
e.g., essentially the same helix value (percentage) in both layers, and
meets both the thermal and tensile rating requirements. This also enables
the overall diameter of the cable to be minimized for a given fiber count
having at least two layers and essentially balanced helix values.
Fiber optic cables according the present invention can be optically
interconnected by, for example, fusion splicing, defining a cable system.
In one system embodiment, concatenated cables have minimum variation in
fiber length without the need to do cross splicing between inner and outer
layers of buffer tubes of the respective cables, thereby minimizing
differential fiber length (FIG. 2). Layers of buffer tubes having like
helix values have at least some of their respective optical fibers
optically interconnected. In other words, the fiber optic cable system has
first 10 and second 10' fiber optic cables, each of the first 10 and
second 10' fiber optic cables having respective optical fibers 15, 15',
19, 19' that arm disposed in respective buffer tubes 14, 14', 18, 18'. The
buffer tubes defining at least two layers respectively in the cables, and
are generally stranded about center areas of the respective fiber optic
cables. The buffer tube layers define a relatively inner layer of buffer
tubes closer to the center area, and an outer layer of buffer tubes being
relatively further from the center area. The inner and outer buffer tube
layers each define a respective helix value, the respective helix values
within each cable can be substantially the same; and the layer of buffer
tubea having optical fibers of the first optical fiber cable is optically
connected to a corresponding layer of buffer tubes having optical fibers
of the second fiber optic cable, e.g., by fusion splicing. For example,
optical fibers 15 of inner layer 14 can be optically connected to optical
fibers 15' of inner layer 14' from cable 10 to cable 10'.
Other balanced cable systems are possible as well. For example, where the
respective helix values within each of the cables are substantially
non-equal, and the layer of buffer tubes having optical fibers of the
first optical fiber cable 10 are optically connected to a
non-corresponding layer of buffer tubes having optical fibers of the
second fiber optic cable 10' (FIG. 2a). For example, an outer layer of
buffer tubes 18 of a first cable 10 can be connected to an inner layer of
buffer tubes 14' of a second cable 10', and vice versa. The respective
helix values are established to as needed for the system requirements.
Helix values of the interconnected layers can be substantially the same or
non-equal.
The cables and/or systems of the present invention can be used as space
diversity backup system, for example, where one fiber optic cable is used
as a backup for two other fiber optic cables with differing helix values
in the same system. To minimize the differences in back up fiber length
from the main system fibers, the helix value in each layer of a fiber
optic cable according to the present invention can be made to correspond
to the helix values in the cables being backed up.
The present invention has thus been described with reference to the
foregoing embodiments, and are intended to be illustrative of the
inventive concepts rather than limiting. Persons of skill in the art will
appreciate that variations and modifications of the foregoing embodiments
may be made without departing from the scope of the appended claims. In
the exemplary embodiment described, the fiber optic cable can include
ripcords 28, tapes, water-blocking components, armor, anti-buckling
members, buffer tube filling compounds, core binders, and/or other cable
components disclosed in U.S. Pat. Nos. 5,930,431, 5,970,196, or U.S. Pat.
No. 6,014,487, which are respectively incorporated by reference herein.
*
