Note: Descriptions are shown in the official language in which they were submitted.
2 ~ 79920
-1-
OPTIC~ I, FIl~FR ~OIL ~NI) ~li~THQ~ QF WlNnlN~ _
BA~ RQU~ QF TRF, IN~,lYTION
Field of the TnvPution
This invention relates to optical fiber coils and to methods of
5 mAmlf~rtnre thereof, and more particularly, to an improved coil pattern.
Des~ " )rofl~Pla~ed,~r~
Fiber optic sensor coils are used, inter alia, in fiber optic
~ylvs~vpcstoprovideanopticaloutputsignalusedindrtl ,lli"i~,grotationofa
vehicle (e.g. an airplane) about an axis of rotation. A typical fiber optic
10 gyroscope uses three sensor coils to sense rotation about each of three orthogonal
axes. The fiber optic gyroscope is typically configured as a Sagnac
interferometer including a light source providing an optical signal, a multi-turn
coil of optical fiber, referred to as a fiber optic ring, and electronic read-out and
control circuits. The optical signal is first applied to an optical beam
15 splitter/combiner which provides two identical optical output signals, each of
which is applied to one end of the fiber optic coil. The two optical signals travel
through the coil in opposite directions and are lccvllllJillcd at the beam
~lilleltcollll,illcl. A rotation of the fiber optic coil about its wound, or
Ir,nghn~iins31 axis will result in a phase shift between the counter-propagatory20 optical signals traveling through the coil. This phase shift is known as the
Sagnac effect phase shift. The Sagnac effect can be explained by relativistic
theory which shows that a wave traveling through a rotating coil in the direction
of rotation requires more time to traverse the path than a wave traveling opposite
to the direction of rotation. This time difference is manifested by phase shift
25 interference pattern of the recombined optical signal. In an optical gyro, the
m:lgnitllf~e of the phase shift is determined by analysis of the l~cvlll'vhled signal
as applied to an output optical detector. The detector output is translated intoelectrical output signals l.,~ llhlg rotation.
~ 2 1 79920 --2--
The phase shift detected at the output detector may be ~ ullsid~l~,.i
as consisting of two parts. The first part is the Sagnac effect phase shift. Theother part of the detected phase shift is due to perturbations in the optical fiber
caused by cllvhvlllll~ l factors. The Sagnac phase shift which defines the
5 mllgnit~l-le and direction of rotation is relatively small, such that any cignifi~nt
phase shift due to ~IIVilUlllllclll~l factors may obscure an accurate reading of the
Sagnac effect phase shift. It is therefore desirable to minimize the effect of
environmental perturbations on the detected phase shift of the l~culul,ll.cd
optical signal.
The two optical signals emanating from the splitter/ combiner in
response to the single optical input signal are in phase and are applied at opposite
ends of the coiled fiber and traverse the fiber in opposite directions. The
undesirable phase shift effects occur when cnvhu~l~u~ l~t~l perturbations affectone of the light signals differently than the other. It is generally It;co~..i,~d that
15 c l~vilulllllell~l perturbations cannot be l~limin~t~orl but that their effect can be
inillli ,~ d if these perturbations are applied equally to the counter propagatory
light signals. A known approach to reducing the effect of c;llvh u~ul~
perturbations is to build a symmetry in the sensing coils. Known sensing coils
include dipole, ~luadl ulJolc, and octupole windings. In these coils the midpoint
20 of a length of optical fiber is placed near one side flange of a spool and the two
optical fiber segments emanating from the midpoint, referred to as the forward
segment and the reverse segment, are then wound around the coil in opposite
directions. In the case of a dipole, the forward and reverse segments are wound
on the spool in ~It~rn~ting layers. In the quadruple, a layer of the forward
25 segment is followed by two layers of the reverse segment, followed by two
Iayers of the for vard segment, and so on. In an octupole c~-nfi~lrsltion, two
layers of the reverse segment are sandwiched between two layers of the forward
segment followed by another set of four layers in which two layers of the
forward segment are sandwiched between layers of the reverse segment. All of
30 these various c~-nfi~ fions are ~tt~ illg to introduce a symmetry such that an
21 7992G
~ -3 -
cllvho~ lc~ l perturbation of the coil will affect the counter-propagating lightsignals in the same manner. However, when the coil is built up of slltt~rn~ting
layers or ~lt~rrl~ting pairs of layers of the forward and reverse segments, the
forward and reverse segments are not necessarily affected in the same way by the5 cllvhulLlll~ l perturbations. This may be better ~In~l~rstood by c~-nc~ ring the
nature of the cllvhvlllllclll~l perturbations.
Ellvhulllll~ l perturbations may be due to mechanical strain,
vibration, shock and t~,llly~lalule changes. It is known, that pred~)min~ntly two
types of I r~ ,r". 1 " . c perturbations have to be dealt with, namely, those due to
10 radial tclllyclaiulc gradients and those due to axial tcllly~,lalulc gradients. A
third gradient type, transverse to the wound (ll~ngit~ in:ll) axis of the spool, is a
less significant problem. As the name implies~ with a radial u "y ~ c
gradient, the trl "l~r~ c varies radially such that an optical fiber segment
cr~mpricing a portion of innermost layer of the coil is at a different l~ "I' . ~ C
15 than fiber segments in layers which are a distance removed from the core of the
coil. An axial gradient extends along the wound axis of the spool. It is therefore
desirable to avoid ~isgnifi~S~nt axial and radial distances between segments of the
optical fiber which are the same distance from the center point of the length ofthe fiber such that cullc~yon.lillg segments of the forward and reverse segment of
20 the coil C~yCIiGllcC the same cllvilvlllllcllldl pcllLIlbaLio~
SUMMARY QF Tl~TF. ~I~VENTIQN
These and other problems of the prior art are overcome in
a~culdallcG with the present invention in a fiber optic sensing coil by
cun~ ,lhlg each of the layers of the coil of ~Itrrn~fing turns of the forward and
25 reverse segments. In acculd~lcc with one aspect of the invention, the coil
comprises an inner layer wound from opposite ends of the length of fiber. The
optical fiber has a midpoint and the midpoint is located at the dyylv~d
midpoint of the innermost layer. Advantageously, the positioning of the
midpoint of the fiber at the midpoint of the innermost layer allows the coil to be
2 1 79920
wound in opposite directions from the midpoint and tends to reduce variations
due to ~;IIVilUlllll~ perturbations. A snhst:~nti~l reduction in the effects of
cl~vilvlllllcll~l perturbations over prior art coils has been observed.
In accv d~ncc with another aspect of the invention, adjacent layers
5 of optical fibers are arranged such that the turns of optical fiber in one layer rest
in grooves formed by adjacent turns in the preceding layer. In one l~mho~liml ntof the invention, adjacent layers of optical fibers have unequal numbers of turns
to allow fibers ûf a next layer to be disposed in grooves formed by the turns ofthe preceding layer. In another ~ bvdh~l~,lll, adjacent layers have equal numbers
10 of turns with each laterally offset from the previous layer by a distance
cllhst~nti~lly equal to one-half fiber diameter, allowing fibers of a next layer to
rest in grooves formed by adjacent turns in the preceding layer. Adv~ g.~ùl ~ly~such an arrangement adds stability to the coil and reduces its overall outside
diameter.
In one particular embodiment of the invention, the pattern of
alternate adjacent segrnents of the fiber is such that the second through the fifth
layers of the coil each have a unique pattern with respect to any preceding layer
and the patterns of the sixth through ninth layers cu..c~l,vnd individually to the
patterns of the second through the fifth layers, .ci~,e~,livcly, with the four-layer
20 pattern conf ~Ir~tiOll repeated in the remaining layers of the coil. In another
ci...bodi...ci..l of the invention, even numbered layers have cvll."~ùnv;llg patterns
and :llt(~rn:lting odd numbered layers have ~;ollc~,uvll.lhlg patterns. In yet another
c...bollill-c~lt of the invention, all layers after the first layer are wound identically.
In a method of winding an optical fiber coil in accu.Jdllcc with the
25 invention, the first layer is formed such that portions of the forward and reverse
segments are disposed adjacent opposite side flanges of a spool. The second
layer is formed by winding an alternate turns pattern of the forward segment of
the fiber on the f rst layer such that adjacent turns of the forward segment arespaced apart by a ~ t~ d distance and then winding a portion of the
30 reverse segment in an alternate turns pattern on the first layer between the
2 ~ 79920
-5-
alternate turns pattern of the forward segrnent, thereby forming a layer of
:~lt~ ting turns of the forward and reverse segments. In ac~uld~ulce with a
particular aspect of the invention, the second and additional layers are formed by
winding the next layer such that the turns of the next layer are disposed in
5 grooves formed between turns of the preceding layer.
In a particular ~;.llbod;lll~,lll of the invention, the coil is wound on a
spool and is treated with an adhesive to retain the shape of the core. The coil is
,"l,~ ly removed from the spool to advsnt~lgrol~cly realize weight and
volume savings and potentially improve coil performance.
In another ~lllI,odi~ ,lll of the invention, the core is provided with a
longihl~lin:~l groove to provide an improved first layer of the coil. In yet another
embodiment, the core is provided with ~h-;ulllr~l~lll,dlly-extending parallel
grooves.
BRIEF Vl; ~Cl~ IPTION Ol~Tl~F l~AWING
The invention is described in detail in the following p~a~ hs
with reference to the drawing in which:
FIG. 1 is a schematic l~ cl,ldtion of a cross-section of a portion
of sensing coil constructed in acculJa,.~,e with the principles of this invention;
FIGS. 2 through 4 are alternate embodiments of the invention
2û showing alternate coil winding patterns;
FIG. ~ is a schematic representation of apparatus for winding a
fiber optic coil in acc~lJallcc with the invention;
FIG. 6 is a side view representation of a spool adapted for winding
a fiber optic coil;
FIG. 7 is a side view of a coil would on the core of FIG. 6.
FIG. 8A is an end view of an alternate embodiment of a core;
FIG. 8 is a side view of the core of FIG. 8A; and
FIG. 9 is a side view of another alternate embodiment of a core.
-6- 2 ~ 7992C
DETA~F~n DESCR~PTION
FIG. r is a schematic ~ llalion of a cross section of a sensing
coil 100 wound on a spool 102 having a core 103 and opposing flanges 104, 106.
The coil is constructed as an optical fiber sensing coil for use, for example, in a
5 fiber optic gyro. The coil consists of a cf ntimlollc flber of a selected length
having its midpoint adjacent the core of the spool and its ends exposed. The twooptical fiber segments extending from the midpoint, referred to as the forward
segment and the reverse segment, are wound on the spool in opposite directions.
In use, as explained in the background of the invention, two identical optical
10 signals are individually applied to opposite ends of the coil and propagate
through the forward and reverse segments in opposite directions.
FIG. I depicts a coil 100 having 28 layers, each layer consisting of
a number of turns of oppositely wound fiber segments. For the sake of this
description, turns of the forward fiber segment are depicted as extending away
15 from the viewer and identified by X's and turns of the reverse segment are
depicted as extending toward the viewer and are referred to as O's. The coil 100shown in FIG. I has a first layer (I) having an odd number of turns, e.g., 99
turns. The turns extend in opposite direction from the midpoint of the fiber,
lled by M, toward the opposing flanges 104, 106. The next layer (2) has
20 an even number of alternate, oppositely directed turns of the optical fiber. The
outermost turns of that layer are preferably displaced from each of the flanges
104, 106 by a distance of d~)~lU~illla~ one-half of the diameter of the fiber
such that the second layer has one fewer turn than the first layer. This
arrangement of layers is repeated such that all even numbered layers have one
25 fewer turn than the odd numbered layers. This allows the fiber turns of the next
layer to be positioned in the naturally formed grooves between adjacent turns ofthe previous layer. This ~ ng~... ,.. ,l of layers lends stability to the coil. It also
tends to reduce the overall coil diameter, which is important in space craft andother applications with s~lt st:lnfi:'l space limit~tinn~ Adjacent turns may be
2 1 7q92~
spaced apart by a selected distance to form more pronounced and deeper grooves
for the turns of the next layer.
As depicted in FIG. 1, the first layer, layer 1, consists of half of
each of the forward and reverse segments. After the first layer, a particular
5 pattern of forward and reverse segment turns is developed. The paKern of turnsin the layers shown in FIG. l is such that it is repeated every fourth layer. The
pattern of turns in each of the layers 2 through 5 is unique with respect to any of
the preceding layers. After layer 5, however, the pattern of turns in layers 2
through 5 is repeated in y~ e~ groups of four layers. Thus, layer 6 has the
10 same paKern of turns as layer 2. The other layers shown in FIG. 1, layer 28, has
the same pattern as layer 4.
Other patterns of ~lltPrn~fing turns of the forward and reverse
segment may be created. In the paKern shown in FIG. 2, the even rows, e.g. 2, 4,6, all have the same turns paKern, whereas the odd numbered layers, i.e., 3, 5, 7,
15 and 9 have ~ltPrn~ting turns patterns. Thus the pattern of layer 3 is repeated in
layers 7, I l, etc., and the pattern of layer 5 is repeated in layers 9, 13, etc. Other
patterns, besides those shown in FIG. I and FIG. 2 can be readily envisioned.
The pattern shown in FIG. I and FIG. 2 are for an arrangement in which the firstlayer adjacent to the core 103 has an odd number of turns. FIG. 3 shows an
20 arrangement wherein the first layer, layer 1, has an even number of turns. In that
c-~nfigl-r:~tinn, the odd numbered layers, i.e., 3, 5, etc., have the same turnspattern and the even numbered layers, i.e., 2, 4, 6, etc., have an alternate pattern.
These turns patterns are repeated in every fourth layer. Thus, layer 6 has the
same paKern as layer 2, layer 8 has the same pattern as layer 4, and so on. The
25 formation of the turns patterns in the layers is a function of the method of
winding the coil 100.
It is also possible that the fiber has different diameters in different
areas. For example, a depolarizer may be inserted at various positions in the
fiber. This may result in differing numbers of turns of the fiber in certain layers.
2 ~ 7992û
-8-
FIG.4 is a cross-sectional schematic ~ . a~ llL;lLion of a part of a
sensing coil 100 wound in a fashion such that all layers have the same number ofturns while the fiber turns of adjacent layers are laterally displaced from eachother by a distance a~lu~h.lately equal to one-half of the fiber diameter. In this
5 particular configuration, the even numbered layers have ~ Oll. a~Jolldillg
configurations of forward and reverse segment turns and the odd numbered
layers, beginning with the third layer, have ~ollca~)ulldillg confi~-r~tions of
forward and reverse segment turns. The total number of turns in each layer may
be even or odd. In the sl r:lngement of FIG.4, the first layer is displaced from the
10 right flange 104 by a distance snbstontiolly equal to one-half fiber diameter. A
spacer 105, having a lateral dimension of approximately one-half the fiber
diameter, may be provided adjacent to core 103 and the right flange 104 to
provide the desired spacing of the right most turn of the first layer from the right
flange 104. Layer 2 is displaced from the left flange 106 by a distance
15 sl-hst~nti~lly equal to one-half the fiber diameter with turns of the second layer
disposed in the grooves formed by the turns of the first layer. ~l ~hac~ layers
are alternately spaced away from the right flange 104 and the left ilange 106 tomaintain the one-half fiber diameter offset between adjacent layers.
FIG. S is a schematic lc~ lLaLion of an apparatus for winding
20 the coil 100. As shown in FIG.5, the spool 102 is mounted on a drive shaft 204
driven by a drive motor 203. When a fiber is to be wound around the spool I OZ,
the fiber is first wound, starting with opposite ends of the fiber, on two separate
supply spools 209 and 223. The supply spools 209 and 223 are mounted on left
and right support brackets 207 and 221, l~al,e- LiYC;Iy. In apreferred method of25 winding the coil 100, the length of fiber on one of the supply spools, e.g. the
right supply spool 209, is equal to one-half of the total length of the fiber plus the
length co l~ lldi.lg to one half of the first layer, layer I . The midpoint
between the two supply spools may be placed adjacent one of the flanges, for
example, the left flange 106 and wound across to the right flange 104. The
30 midpoint of the length of fiber will then be positioned substantially in alignment
2~ 79920
~ g
with the midpoint of the spool 102, as depicted in FIG. 1. Thereafter, the
remainder of the coil 100 is wound from the two supply spools 209 and 223 .
The left and right support brackets 221 and 207 are attached to the
c~ apulldillg lefl and right shaft sections 204 and 205, respectively. Clutches
215 and 216 are provided to selectively engage shaft sections 204 and 205,
~,a~c~liv~;ly, with drive shaft 203 for rotation with the spool 102. The opticalfiber from supply spool 209 on bracket 207 is fed via a roller 213 to the spool
102. The roller 213 is supported by means of a bracket 211 attached to the
bracket 207. In a similar fashion, bracket 225 connected to bracket 221 supportsa roller 226 to guide the optical fiber from spool 223 on bracket 221 to the spool
102. When the coil 100 is to be wound from supply spool 209 mounted on the
right bracket 207, the left clutch 215 is engaged to lock the left shaft section 204
andbracket221 todriveshaft203 forrotationwiththespool 102. Theright
clutch is ~1ic~-ng~lged from drive shaft 204 and is held in a fixed position.
Similarly, when the soil 100 is to be wound from supply spool 223 on bracket
221, clutch 216 is engaged to lock the right shaft section 205 and bracket 207 to
drive shafi 203 for rotation with the spool 102. Clutch 215 is ~ ngagrd and
bracket221 isheldstationary. Motor201 isreversibletoallowcoil lOOtobe
turned in either the clockwise or counterclockwise direction.
The procedure for winding the coil 100 to obtain the pattern shown
in FIG. 1, using the apparatus l1~L~s~ d in FIG. 5, is described further below.
In the following description, the spool 223 will be referred to as the X spool,
,a~lllhlg the forward segment, and the spool 209 will be referred to as the O
spool, ~ Ca~llLil.g the reverse segment of the optical fiber sensing coil 100. As
25 shown in FIGS. I through 4, the turns in adjacent layers are offset from eachother. This facilitates the winding process, as outlined below, by causing turnsof a next layer to follow grooves provided in the preceding layer. This is
especially helpful in forming a spaced-apart turns pattern wherein adjacent turns
2 1 79920
~ -10-
are spaced apart by a distance equal to or slightly greater than the diameter of the
fiber, as described further below.
The procedure for winding a coil on a spool in the configuration as
shown in FIG. I comprises the following steps:
1. Winding the reverse segment O, supply spool with a length
of fiber cul~.,a~Olldillg to one-half of the total length of the fiber plus the length
required to form one-half of the first layer of the coil on the spool 102, and mark
the endpoint of that segment.
2. Winding the remainder of the optical fiber on the forward
10 segment X, supply spool.
3. Placing the X spool on the left feed bracket 221 and placing
the O spool on the right feed bracket 207.
4. Starting with the marked position of the optical fiber
adjacent the left flange 106 of spool 100, winding the first layer from the O
supply spool in the counterclockwise direction, moving from left to right, to
complete the first layer.
5. Winding one revolution in the counterclockwise direction
from the O supply spool, adjacent the right flange 104, as part of the second
layer.
6. Winding a spaced-apart alternate turns pattern in the
clockwise direction from the X supply spool, moving from left to right.
7. Interchanging the X and O supply spools by moving the O
supply spool from the right bracket 207 to the left bracket 221 and moving the Xspool from the left bracket 221 to the right bracket 207.
8. Winding an alternate turns pattern in the counterclockwise
direction from the O supply spool between the turns of the ~Itl~nulting pattern of
X fiber, moving from right to left, to complete the second layer.
9. Winding a spaced-apart alternate turns pattern in the
clockwise direction from the X supply spool, moving from right to left.
21 7992~
-11-
10. I.lt~l.,hangillg the X and O supply spools by moving the X
supply spool to the left bracket 221 and the O supply spool to the right bracket207.
11. Winding an alternate turns pattern between the alternate
5 turns of X fiber in the counterclochwise direction from the O supply spool,
moving from left to right, to complete the third layer.
12. Winding a spaced-apart alternate turns pattern in the
clochwise direction from the X supply spool, moving from left to right.
13. Interchanging the X and O supply spools by moving the X
10 supply spool to the right bracket 207 and the O supply spool to the left bracket
221.
14. Winding an alternate turns pattern between the alternate
turns of X fiber in the counterclochwise direction from the O supply spool,
moving from right to left, to complete the fourth layer.
15. Winding a spaced-apart alternate turns pattern in the
countcl.,lo.,hwi~e direction from the O supply spool, moving left to right.
16. I..t~l~,Ld~-~ il-g the X and O supply spools by moving the X
supply spool to the left bracket 221 and the O supply spool to the right bracket207.
17. Winding an alternate turns pattern between the alternate
turns of the O fiber in the clockwise direction from the X spool, moving from
right to left, to complete the fifth layer.
18. Repeating steps 5 through 17 for each of the groups of 4
layers (6) through (9), (10) through (13), etc., until the coil is completed.
As outlined above, the optical fiber sensing coil 100 is formed by
winding an optical fiber on a spool 102 in the manner described herein. The
completed coil 100 may be retained on the spool 102 and installed or used as an
integrated assembly. Alt~ , the coil 100 may be removed from the spool
102 and installed or used as a ~ I;.,g coil. In a certain applications it is
desirable to remove the spool 102 to reali~e weight and volume savings and
2~ 79920
~ --12-
potentially improve p~. r(" ".~ of the coil. The rLeP~ - ,.1",g coil may be
formed by applying a bonding agent to the fiber segments to bond adjacent turns
and adjacent layers together in order to form a cohesive coil 100, wherein the
windings of the fiber segments will be retained in proper relationship to each
S other. The process of bonding may be accomplished in a variety of methods
which are well known in the art. A preferred method is to use optical fiber
which has been pretreated with a bonding agent which possesses no adhesive
properties until subjected to a curing process. Ideally, the bonding agent will not
adhere to the spool on which the coil is wound during construction of the coil.
10 The spool may also be treated with a release coating or agent to reduce or
prevent adherence. Once a coil has been formed on a spool in the winding
process outlined earlier herein, the combination of the coil 100 and the spool 102
is subjected to a curing process to activate a bonding agent thereby bonding
adjacent layers of turns of the fiber to each other. After curing, either one or15 both of the spool flanges 104, 106 can be removed from the spool 102 and the
coil 100 can then be removed from the core 103 to yield a fl~ "li"g coil. As
an alternative, a potting compound may be used. Instead of fiber segments
provided with a bonding agent, a potting compound may be applied to the
completed coil 100 and induced in spaces between the turns of optical fiber in a20 known manner. Once the potting compound cures, the coil 100 may be removed
from the spool 102 in the manner described above. Another alternative is to
apply an adhesive bonding agent during the winding process that can be cured as
part of winding each layer or in the completed coil.
A procedure for winding a coil in the configuration shown in FIG.
25 1 is described above. The following procedure may be used to obtain a
frePct~n-iing fiber optic coil. In addition to steps I through 18 outlined above,
the following steps may be executed:
Prior to the first step, step 1, of the procedure for winding a coil on
a spool outlined above, the total length of the fiber is coated with an adhesive
2 1 79920
-13-
coating and after the last step, step 18 of the above procedure, the following
additional steps may be executed:
l. Curing the completed fiber coil to activate the adhesive
coating and bond individual turns of the fiber together.
2. Removingthe flanges 104, 106.
3. Removing the completed coil from the spool core 103.
Alt~ la~ ly, a bonding agent may be applied to the fiber during
the winding process and cured on a layer-by-layer basis or after several layers or
the the entire coil have been wound.
FIG. 6 is a ~ lcs~ tion of a spool 202 comprising a spool core
203 and opposing side flanges 204 and 205. The core 203 is particularly adapted
for the winding of a fiber optic sensing coil of the type described earlier herein.
As stated earlier herein, in accordance with the present invention the midpoint of
the optical fiber is located at the a~ v~hlla~ midpoint of the innermost layer. In
lS the embodiment shown in and described with respect to FIGS. I through 4, the
coil is wound by starting the first layer along one side and placing successive
turnsi",.,...ii,,t.1yadjacenteachother. Furthermore,thefirstlayerofacore,
such as depicted in FIGS. l through 4, has a plurality of adjacent turns of fiber of
one direction on one side of the center and a plurality of adjacent turns of the20 other direction on the other side of the center line.
FIG. 6 shows a spool 302 having a core 303 provided with a
groove 3 lO extending between the opposing flanges 302,304 and parallel to the
center line of the core. In winding the core, the midpoint of the optical fiber is
placed in the groove at the midpoint of the groove, i.e., equal distant from the25 flanges 302 and 304. The first layer of the coil to be formed on the core is
formed by winding the portion adjacent one of the two flanges 302, 304 in the
clockwise direction and winding the portion of the fiber adjacent the other of the
two flanges in the opposite direction. The two portions are wound toward
opposite sides with successive turns being spaced apart such that windings of the
30 forward and reverse fiber sections are j u~taposed in the first layer in the same
~ -14- 2 1 79920
manner as other layers of the coil. The second and additional layers are wound
in the same manner as described earlier with respect to FIGS. I through 4.
Accordingly, Altrrnq.~ing direction turns are disposed in juxtaposition in all
layers, thereby further enhancing p~,. rO~ allce of the coil.
A common difficulty in winding the first layer of fibers on a spool
such as a spool 102 is to maintain the fibers in proper spaced relationship to each
other. FIG. 6 shows a plurality of circumferentially extending grooves in the
surface of the core 303. Such core grooves may be formed by mqehining, or
grinding, or etching. The grooves are preferably parallel rather than helical and
10 may be formed, for example, by electronic discharge mqrhining by introducing
a coll.lu.,live wire in tangential contact with the core and rotating the core. With
the first layer of the core formed in the parallel grooves, adjacent turns of the
optical fiber forming the innermost layer are parallel for essentially one complete
revolution and then are displaced to one side by a distance equivalent to one
15 diameter of the fiber. This concept is illustrated in FIG. 7 which is a side view of
an optical fiber 305 wound on the core of FIG. 6, showing the area of
di~l~ldc~.llle.lL of the adjacent turns. The ~ plq~Pment to one side may be
facilitated by the formation of a flat area 312 on the surface of the core wherein
the grooves have been removed from the core by machine processing as depicted
20 in FIGS. 8A and 8B. Alternatively, the di~lacc;lllc;lll may be formed in the
surface of the core by electronic discharge mq~hining, or the like, in a manner
such as depicted in FIG. 9.
It will be lln-lPr~tood that the above-described ArrqngPnnPn~ is
merely illustrative of the application of the principles of the invention and that
25 numerous other arrqngemen~ may be devised by those skilled in the art without departing from the spirit and scope of the invention.
