Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
il2~
This invention relates to an optical rotary joint
or slip ring and in particular to an op-tical rotary joint
capable of transmittin~ a plurality of optical channels.
BACKGROUND OF THE INVENTION
Canadian Patent No. 1,15~,466 issued December 13, 1983
to Litton Systems, Inc. discloses an optical slip ring which
uses a pair of axially spaced apart graded index rod lens to
effect efficient optical coupliny between a pair of relat]vely
rotating optic fibers. In the structure of the patent one
lens is mounted in a stator and is connec-ted to one optic
fiber while the other lens is mounted in a rotor and is
connected to the other optic fiber. A small gap separates
the rotor and stator lenses. The lenses used are SELFOC
(trademark~ lenses, avallable from NSG America, Inc. of
Clark, New Jersey, U.S.A.
Optical fibers are relatively fragile and care
must be taXen with a single channel rotary joint to avoid
breaka~e of the fibers used. It is desirable to be able to
reduce the concerns respecting breakage especially where
either the environment is inhospitable to the equipment or
the joint is relatively inaccessible when in use, as for
example when it mignt be used in undersea applications.
SUMMARY OF THE I~VENTION
The present invention overcomes -the problems o the
prior art by providing optical rotary joints which are
capable of transmitting two or more channels of optical
signals. Such a joint provides two distinct advantages over
a single channel joint: -there is redundancy in the circuilry
and there is an expanded transmission capacity.
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In order to achleve efficient optical couplingJ each
fiber optic link should have the relative rotation therein take
place on the axis of the joint. If the first coupling takes
place on axis then any other channel carried by the joint will
have to enter and leave the joint off axis. The problem,
solved by the present invention, is to redirect the light
beams within the joint to bring them to the axis of rotation,
make the couplings with relative rotation, on axis, and then
redirect the light beams off axis again.
The present inven-tion solves the problems mentioned
a~ve by using a pll~ality of aL~rGpriated anqledi~irrors or prisms
within the joint to redtrecta light bea~l from an off-axis path
to an on-axis path. A ~art of the joint is held stationary
relative to a rotatable par-t, both parts housina mirrors or prisMs which
redirect the beam through 90 on to and then off from the joint
axis. Relative rotation takes place while the beam is on-axis
and thus efficient coupling can take place.
In order to keep the off-~xis beam leaving or entering
the rotatable part in alignment with a corresponding fiber
on the joint rotor, to ensure proper transmission, the
rotatable par-t and the rotor are provided with magnets which
interact to ensure -that -the rotatable part rotates in
synchronism with the rotor itself. The magnetic field, which
provides driving and aligning forces will allow the passage
of light, without interruption, through full rotation.
Desirably, the presen-t invention uses graded index
rod lenses, such as SELFOC lenses -to provide an enlarged,
roughly parallel beam of light within the joint. That beam
is more easily manipulated by the Mirrors used to reflect
sd/ -2-
~23~
the signal on to and off the axis o~ the jointO
An important feature is that the rotary joint of the
present invention is bi-directionalO Light may travel in
either direction thxough each fiber and its rotational
interface. In fact the joint itself may be operated in a
bi-directional mode, with light travelling in one direction
through one set of fibers at the same time as light travels in
the opposite direction through another set of fibers.
In summary of the above, therefore, the present
invention may be broadly consldered to provide a multiple pass
optical rotary joint comprising a rotor and a stator each
including a head end and a tail end with the rotor head and
tail ends being bearingly supported by the stator head and
tail ends respectively; an annular body connecting the rotor
head and tail ends together and means including transparent
annular tube means connecting the stator head and tail ends
together, the annular body circumferentially surrounding the
connecting means; first means connecting a plurality of first
optical fiber means to the stator; second means connecting a
plurality of corresponding second optical fiber
means to the rotor; means establishing an optical signal path
between each of -the first fiber means and the corresponding
one of the second fiber means t a portion of each optical signal
path extending along the axis of the joint; rotatable optical
signal reflecting means bearingly supported within the
stator for reflecting at least one optical signal between axial
and non-axial portions of i-ts path Eor even-tual reception by
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~3~8;~%
an appropriate one of the fiber means; and first and second
magnet means secured to the reflecting means and to the
,rotor, respectively, the magnet means being of opposite
polarities, whereby as the rotor rotates magnetic interaction
between the first and second magnet means effects synchronous
rotation of the reflecting means with the rotor and
maintains intact the relative angular orientation between
the reflecting means and the appropriate one of the second
fiber means.
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BRIEF DESCRIPTION_OF T~IE DRAWINGS
FIG~RE 1 illus-trates a first embodimen-t of a mul-tiple
pass optical rotary joint according to -the present invention
in partial axial sectionO
FIG~RE 2 illustrates an end view of the joint of
FIGURE 1.
YIGURES 3 and 4 show sections along the line 3~3 of
FIGURE 1 depicting alternative magnet arrangements.
FIG~RE S illustra-tes a second embodirnent in partial
a~ial section ^- a mul-tiple pass optical ro-tary joint in
accordance with the present invention.
FIG~RE 6 illustrates an end view or the joint of
FIGURE 5.
FIGURE 7 illustrates a third embodiment ln partial
axial section of a multiple pass optical rotary joint in
accordance with the present inventionO
FIGURE 8 is an end view of the joint o~ FIGURE 7.
FIGURE 9 is an enlarged par-tial section of a detail
of a fourth embodiment of a mul-tiple pass optical rotary
joint in accordance with -the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figures l and 2 illustrate a basic -two-channel or
two-pass optical slip joint lO wherein the optical signal
paths through the joint are essen-tially equal in leng-th to
ensure that the losses associated with each path are generally
equal, thereby ensuring equal signal strength for each path.
The joint includes a stator 12 having a head end l~, a -tail
end 16 and an optically -transparent annular tube 18 connec-ting
the head end to the tail end and defining a stator cavi-ty ~0
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~23~ Z
within the stator 12. The head end 14 is cylindrical and
includes a support means including a central bore 22 which
terminates at its inner end at a radially inwardly directed
flange 24. Within the bore 22 is mounted a first bearing
assembly 26, an annular spacer member 28, a second bearing
assembly 30 and an annular retainer such as a circlip 32 which
projects into space 34. A spacer member 36 butts against the
bearing assembly 30 and an external circlip 38 positioned on a
. rotatable reflecting unit 114, to be described hereinafter.
A retaining cap member 40 is fastened to the head end
14 as by threaded bolts 42. The cap member 40 also is provided
with conventional means 44 for securing thereto a first
axially oriented optical fiber 46. The means for securing the
fiber to the cap member need not be described in detail as it
does not form a part of the present invention.
The cap member includes a through bore 48 spaced
radially outwardly from the joint axis "A" through which passes
another conventional means 44 used to secure another first
optical fiber 50 to the head end of the stator. As seen
from Figure l there is an axlal displacement between the two
fibers 46 and 50, the purpose of which will become apparent
hereinafter.
In the preferred form of this embodiment each fiber
terminates in a graded index rod lens 52 such as a SELFOC
(trademark) lens to provide an enlarged, roughly parallel
beam of light which improves the ease of coupling optical
inputs and outputs.
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~2~ 2
As illustrated, the transparent tube, whether of
glass or plastic,is provided with a radially enlarged flange 54
at one end and a threaded retainer 56, when engaged with a
threaded portion of an annular recess 58 of the head end will
abut the flange 54 to securely connect the tube 18 to the head
end 14.
At its opposite end the tube 18 mounts the tail
end 16 of the stator. The tail end is generally cylindrical
and may be sealingly bonded to the tube 18 so that it is
non-rotatably secured thereto. The tail end 16 includes
a central boss 60 defining an axial bore 62 therethrough,
a radial bore 64 which intersects the axial bore 62 and
an axially directed bore 66 which passes through the tail end
and intersects the radial bore 64. At the backside of the
bores 64 and 66 a seat 68 is machined to which is adhered a
reflecting mirror 70 which is positioned at an angle of 45
to the axis of the stator so as to reflect a beam of light
from a path along the bore 66 throuah 90 to a path along
bore 64 (or vice versa). At the intersection of bores 62
and 64 another seat 72 is machined to which is adhered a
reflecting mirror 74. The seats 68 and 72 are carefully
machined so that the mirrors 70 and 74 are exactly parallel
to each otherO Mirror 74 serves to reflect a beam of light
from a path along bore 64 through 90 to a path along bore 62
(or vice versa). As shown in Figure 1 the bore 66 of the
stator tail end 16 is aligned with the axis of fiber 50 so that
a collimated beam of light emitted from the lens 52 will be
reflected by the mirrors 70 and 74 on to the axis of the stator
~/ -7-
~3~2
at the tail end of the stator.
Finally, it is noted that the stator 12 is provided
with an arm or dog member 76 which can be secured to any
appropriate locking means in the apparatus in which the rotary
joint is to be used so as to hold the stator 12 against
rotation.
The joint 10 also includes a rotor 78 which comprises
a head end 80, a tail end 82 and an annular body 84 connecting
the head end to the tail end. The head end 80 is annular and
of larger diameter than the stator head end 14. Rotary
bearings 86 received in corresponding recesses in the rotor
and stator head ends bearingly support the rotor head end on the
stator head end and a circumferential flange 88 welded to the
rotor head end will accept threaded fasteners 90 which secure
a cap member 92 to the flange 88. The cap member and the end
face adjacent the bearing 86 define annular pockets for the
reception of o-rings 94 r 96 respectively which serve to seal
the interior of the joint from the ambient environment.
At the tail end 82 of the rotor it is seen that
the interior wall is stepped so that it conforms generally
to the contours of the stator. The rotor -tail end 82 and the
boss 60 on the stator tail end 16 include corresponding
recesses in which rotary bearings 98 are mounted so as to
bearingly support the rotor tail end on the stator tail end.
The end wall of the rotor tail end 82 is provided with
a central axial bore which, in a conventional manner receives
means 100 which mounts to the rotor tail end a second axially
oriented optical fiber 102. The fiber 102 terminates in a
graded index rod lens 104 which is identical (has the same
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focal length) as the lens 52. As seen in Figure 1 the lens
104 projects into the bore 62 in the boss 60 of the stator tail
end and is positioned on the axis of the joint.
Spaced radially from the axis A is another bore in
the tail end which receives a conventional mounting means 100
by which another second optical fiber 106 is secured to the
tail end of the rotor. Fiber 106 also terminates in a graded
index rod lens 104 the end of which is axially displaced from
the other lens 104 by the same distance separating the ends of
the rod lenses 52.
The tip of the lens 104 on fiber 106 projects slightly
into a cavity 108 in which there is a seat 110 machined at
45 to the optical axis of lens 104, on which seat there is
adhered a reflecting mirror 112. The mirror 112 will reflect
a collimated beam of light from a path along the optical axis
of the adjacent lens 104 through 90 to a path which is in a
plane transverse to the axis A of the joint (and vice versa).
Within the interior of the stator a bearing or
reflecting unit 114 is provided. The unit 114 includes a pair
of mutually perpendicular sections, one of which (116) is
cylindrical and is rotatably supported by bearing assemblies
26 and 30 within the central bore 22 of the stator head end.
The other section 118 is also cylindrical, of larger diameter
but of shorter length and is provided with a radially extending
bore 120 the axis of which lies in the same transverse plane as
the path of a beam reflected by the mirror 112. The section 116
is provided with an axially extending bore 122 which has its
axis aligned with the axis A of the joint 10. The bores 120,
122 meet at the apex of the reflecting unit 114 whereat a
seat 124 is machined to
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which is adhered a reflecting mirror 126 at an angle of 45
to the central axis of each bore 120, 122.
The reflecting unit 114 has secured thereto a first
permanent magnet 128 of a specific polarity. The maonet is desirably
positioned directly opposite the outlet from the radial bore
120. A second magnet 130 is secured to the rotor 78 adjacent
the tube 18 of the stator and desirably dian!etrically opposite the
mirror 112. The magnet 130 is of a polarlity opposite to that
of the magnet 128.
The operation of the rotary joint of this invention
will now be described with reference to Figure 1, it being
assumed that the stator 12 is held stationary and that separate
collimated optical signals are being transmitted along the
first fibers 46 and 50 and that they are to be passed to the
second fibers 102, 106 during rotation of the rotor 78.
As the rotor 78 rotates about the stator on the
bearings 86 and 98 there will be a strong magnetic interaction
between the magnets 128 and 130 and consequently the reflecting
unit 114 will rotate on its bearing assemblies 26,30 in
synchronism with the rotor 78. Through the magnetic interaction
and the conse~uent synchronous rotation the optical axis of the
reflecting unit bore 120 will be maintained in strict aliynment
with the optical axis defined by the reflecting mirror 112 and
any optical signal reflected by the mirror 126 will in turn be
reflected by the mirror 112 for capture by the lens 104
adjacent thereto. Thus, the optical signal from the fiber 46
is enlarged by the lens 52, travels along the axis of -the
joint (along bore 122), is reflected by -the mirror 126,
is reflected by the mirror 112, is captured by the lens 104 and
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is reduced thereby for transmission along the fiber 106.
Since the head and tail ends of the stator are fixed
relative to each other a signal from the fiber 50 is enlarged
by its lens 52, is reflected by mirror 70, and is reflected by
the mirror 74 to the axis of the joint, is captured by the
on-axis lens 104 and is reduced thereby for transmission along
the fiber 102.
The construction according to this embodiment provides
for the transmission of two separate optical signals through a
rotary joint. As seen,a portion of each optical signal path
is coincident with the joint axis and, due to the relatively
staggered positioning of the lenses 52, 52 and 104,104 the
lengths of the two optical paths are essentially identical.
Accordingly transmission losses will be about the same for
each path. In other words the signal strength will not vary
appreciably from one path to the other. By using the lenses
52,104 the optical signal transmitted through the stator is
enlarged to improve coupling between the input and output fibers.
Even though the beam transmitted through the stator is enlarged
there is essentially no detrimental effect when the beams
momentarily cross during rotation.
The use of the seals 94 and 96 ensures that the interior
of the joint is free of contamination and also permits the use
of optical fluids or gases within the joint interior. Only
slight enlargement of -the rotor body would be required to
effect pressure compensation of the joint, as might be required
for oceanographic use.
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~3~ 2
In the just-described embodiment the magnets 128, 130
are shown as being diametrically opposite each other and as
radially aligned with the optical path between mirrors 112 and
126. In fact, the positioning of the magnets is somewhat
arbitrary as long as the mirrors 112 and 126 are maintained in
two perfectly parallel planes at 45 to the axis A at all times.
Figures 3 and 4 show two alternative magnet arrangements
used to achieve synchronous rotation of the reflecting unit 114
with the rotor. In Figure 3 a pair of first magnets 128' of
opposite polarity is secured to the reflecting unit 114 on
opposite sides of the bore 120, symmetrically positioned
relative to the joint axis. In this instance the reflecting
unit 114 would have to be magnetically conductive to complete
the magnetic circuit. A pair of second magnets 130' is
secured to the rotor body 84 via a magnetically conductive
ring 92', generally opposite the magnets 128', with each magnet
pair 128', 130' having opposite polarity. Operation of this
embodiment is identical to that of the first embodiment.
In Figure 4 a pair of first magnets 128" is secured to
the reflecting unit 114 in -two adjacent quadrants thereof,
- the magnets being of opposite polarity and touching each other
to complete the magnetic circuitO One of the magnets may be
opposite the outlet to the bore 120. A pair of second magnets
130", touching each other to complete the magnetic circuit is
secured to the interior of -the rotor body 84 ~ia ring 92" in
such a manner that the continuous inner circular surface 132
thereof may cover about 50% of the circumference of the tube 18.
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~23~32~
The two magnets 130" a~e of opposite polarity as are the
magnets 128"t 130" of each magnet pair. ~gain operation of
this embodiment is identical to that of the first embodiment.
Turning now to Figures 5 and 6 another embodiment of
the invention will be described. This particular embodiment
is shown with five optical inputs and outputs although it
should be understood that the structure could be altered to
accommodate any number of input and output channels, the only
constraint being the degree of transmission loss that can be
tolerated. The principle of operation is essentially the
same as that described for the first embodiment although the
execution of those principles differs somewhat from that first
embodiment.
sd/oC ~13-
:~23~ Z2
The joint 200 o this embodiment includes a stator
202 having a head end 204, a tail end 206 and an annular
optically transparent tube 208 connecting the head end to the
tail end. The head end is cylindrical and includes a central
bore 210 as well as circumferentially spaced bores 212 each of
which is adapted to receive conventional means 214 by which
an optical signal carrying fiber is connected to the head end.
The connection need not be described as it is conventional in
nature and does not form a part of the invention. In the
disclosed embodiment the joint accommodates five fibers
designated 216, 218, 220, 222, and 224. Each fiber terminates
at a graded index rod lens 226 such as a SELFOC (trademark~
lens which serves to enlarge the diameter of an optical signal
leaving the lens or to reduce the diameter of an optical
signal entering the lens. As with the first embodiment an arm
or dog member 228 is provided and it can be secured to any
appropriate means in the apparatus in which the rotary joint
is to be used so as to hold the stator against rotation.
On its rear side the head end 204 defines a supporting n~ns
which includes a boss 230 having a large diameter bore 232 which in turn
communicates with the central bore 210 in the head end. In fact the lens 226
attached to the central flber 216 protrudes slightly into the
bore 232. A pair of a~ially spaced apart bearing assemblies 234
is secured within the bore 232 for a purpose to be described
hereinafter.
Spaced apart along and non-rotatably secured to the
transparent tube 208 is a plurality (four being shawn) of separate
supporting means or units 236. Since they are identical to
each other only one will be described.
sd/ -14-
~3~ ,2
Each unit 236 is cylindrical and includes a large
diameter portion 238 through which three circumferentially spaced
bores 240 pass, the bores 240 being alignable with the bores 212
through the head end of the stator. Each unit includes a
fourth through bore 242 which intersects a radially directed
bore 244, the latter in turn intersecting a short bore 246 which
enters the portion 238 from the rear surface thereof on the
a~is of the joint. At the intersection of the bores 242 and
244 a seat 248 is machined so as to receive a reflecting mirror
250 which is positioned at 45 to an axially directed optical
path and to a radially directed optical path. At the inter-
section of the bores 244 and 246 another seat 252 is machined
so as to receive a reflecting mirror 254 which is parallel to
the mirror 250.
As seen in Figure 5 the supporting unit 236. closest
to the head end is oriented and secured within the tube 208 so
that its bore 242 and mirror 250 are on a line to intercept
an optical signal directed from the fiber 220. Since the
other three bores 240 passing through the unit 236 are
unimpeded, optical signals directed to or from the fibers 218,
222 and 224 will pass through appropriate ones of the bores 240.
The next adjacent unit 236 is oriented at 90 to the just-
described unit so that an optical signal directed from the
fiber 222 will be intercepted by its mirror 250, the signals
from the remaining two fibers 218 and 224 continuing through
the unimpeded bores 240. The next adjacent unit 236 is oriented
at 90 to the previous unit (180 to the unit closest to the
head end) so that an optical signal directed from the fiber 224,
having passed through both preceding support units is inter-
sd/ -15-
cepted by its mirror 250. The optical signal directed from
the remaining fiber 218 will be intercepted by the mirror 250
of the rearmost support unit 236, that unit being oriented
a-t 90 to the preceding unitO
In each case the signal from one of the-fibers 218,
220, 222 or 224 is reflected by a mirror 250 in a corresponding
support unit from a path which is parallel to the joint axis
to a path which is normal or transverse thereto. In each
instance such reflected signal is again reflected through 90
so as to be on-axis by the mirror 254 in the corresponding
- support unit.
Each support unit includes a central boss 230, a
central bore 232 therein communicating with the bore 246, and
bearing assemblies 23~ secured within the bore 232. Each
support unit in turn carries a reflecting unit 256 which is
substantially identical in construction to the reflecting unit
114 described with respect to the first embodiment. Thus each
reflecting unit includes a cylindr cal section 258, a section 26C
at right angles thereto, radial and axial bores 262 and 26~ a reflecting
mirror 266 and a permanent magnet 268. Each reflecting unit
256 is rotatably supported by the bearing assemblies included
in the corresponding support unit, there being one reflecting
unit for each support unit, including the support unit formed
at the back side of the stator head end.
The tail end 206 of the stator is cylindrical in
nature and is secured to the transparent tube 208 in any
conventional manner. A bearing assembly 270 is mounted on the
stator tail end 206 and, similarly, a bearing assernbly 272 is
mounted on the stator head end 20~.
s~/ -16-
~3~
The rotary joint of this embodiment includes a rotor
274 which has a head end 276, a tail end 278 and an annular
body 280 connecting the head end 276 to the tail end 278.
As with the first embodiment the rotor head end is bearingly
supported on the stator head ~nd by the bearing assembly 272
and the rotor tail end is bearingly supported on the stator
tail end by the bearing assembly 270, the annular body 280
surrounding the transparent tube 208. In order to seal the
interior of the joint 200 an o-ring seal 282 of conventional
construction is provided in the rotor cap member 284 for
sealing engagement with the stator head end. The cap member
284 is connected to the rotor head end 276 by machine screws
286 and is sealed thereto by conventional o-ring 288.
The rotor annular body has a plurality (five in
this case) of aligned optical signal carrying fiber members
connected thereto in conventional fashion by connecting means
- 290. From head end to tail end the rotor fibers axe identified
by reference numbers 292, 294, 296, 298 and 300. Each fiber
terminates in a graded i.ndex rod lens 302 having the same focal
length as the rod lenses 226. Each lens 302 projects
through the annular body so as to be closely adjacent the
transparent tube 208. The optical axis of each Eiber and its
- lens coincides with a transverse plane containing the optical
path defined in the bore 262 of a corresponding reflecting
unit 256.
Diametrically opposite each fiber and its lens the
rotor annular body 280 carries a permanent magent 304 of a
polarity opposite that of a corresponding magnet 268 carried
by reflecting unit 256.
sd/ -17-
~3~22
The princlple o~ operation of the optical rotary
joint 200 is essentially the same as for the joint 10
previously described. Optical signals entering the stator
fibers are transmitted to the rotor fibers via optical paths
that include rotatable reflecting members, which members
serve to transmit an optical signal rom the axis of the joint
to the rotating rotor fibers, the reflecting members being
driven, and maintained in alignment with the rotor fibers, by
the magnetic interaction between the magnet pairs 304,268.
In describing the structure of the stator 202 it was
pointed out that an optical signal emanating from each of the
stator fibers 216-224 will pass into the stator and will
include a portion which passes from a corresponding support
unit along the axis of the join-t. That portion is reflected
by the mirror 266 of the reflecting unit rotating in the corres-
ponding suppor-t unit and passes through the transparent tube
for reception by the graded index lens 302 of the corresponding
rotor fiber, which fiber is maintained in alignment with -the
optical path exitting the reflecting unit by the previously-
described magnetic interaction. In the embodiment as shown a
signal from the central stator fiber 216 will be received by
the rotor fiber 292; the signal from stator fiber 220 will be
received by rotor fiber 294; and the signals from stator
fibers 222, 224 and 218 will be received by rotor fibers 296,
298 and 300 respectively. Of course, signals could just as
easily tbe transmi-tted in a reverse direction from the rotor
fibers through the reflected paths to the stator fibers.
Additionally, a combination of signal directions could be
used with, say, signals passing in the rotor to stator direction
sd/ -18-
~Z3~
alony two paths and signals passing in the stator to rotor
direction along the other pa-ths. Crossing of the various
signal paths during rotation of the rotor does not seriously
affect the signal since the duration of such interference is
infinitessimal.
While not separately illustrated it should be under-
stood that alternative magnet configurations such as those
previously describe~ for the two-channel rotary joint
could also be used in the multi-channel rotary joint of
Figures 5 and 6.
It is a characteristic of SELFOC lenses when used as
an optical coupling that transmission losses are proportional
to the distance between them. In the embodiment just described
losses will be at a minimum for the coupling between fibers
216 and 292 but they will be progressively larger Eor each
channel as the separation between lens increases. Therefore,
althougn the number of channels which could be carried by such
a rotary joint is virtually unlimited the maximum number of
channels to be carried will be determined by the maximum degree
of transmission losses that can be tolerated. The embodiments
shown in Figures 7, 8 and 9 are intended to overcome the loss
problem for loss-critical situations. These embodiments reduce
losses by reducing the distance between the S~LFOC lenses of
each optical couple.
The arrangement shown in Figures 7 and 8 is
particularly applicable for all off-axis channels such as would
be carried by fibers 218-224. No change is required for
the on-axis or center channel 216.
- sd/ -19-
~3~2~
In this embodiment the rotary joint 400 includes a
rotor 274 identical to that shown in Figure 5 and accordingly
the same reference numbers apply. Similarly the reflecting
units 256 used within the stator 402 are identical to those
of the previous embodiment and accordingly the same reference
numbers apply.
The stator 402 is similar to stator 202 in that it
has a head end 404 and a tail end 406, both of which resemble
their counterparts in the s-tator 202. However in stator head
end 404 three of the bores 408 receiving the off-center fibers
pass through the head end and the fourth bore 410 extends
deeply into the head end but terminates short of the rear face
thereof. Each off-center fiber 218-224 -terminates in a
commercially available bulkhead termination 412 at the outer
face of the head end 404. Instead of a light beam running
parallel to the axis of the joint through whatever medium is
within the stator it is transmitted along a bare optic fiber,
one end of which texminates at the bulkhead termination 412,
the other end of which terminates at a SELFOC lens contained
within the stator.
Considering fiber 220 a short bare fiber 414
connects the lens 416 to the termination 412 and hence to
the fiber 220. The lens 416 is held in bore 410 by a spring
clip 418 which is secured at one end to the stator and has at
its other end passinq through an opening 420 to bear against
a Elange 422 orl-the lens, thereby biasing the lens against
the bottom of bore 410. The end of lens 416 projects -through
a smaller diameter hole in the head end whereby the optical
path from the lens 416 -to the lens 302 of rotor :Eibex 294 is
sd/ 20-
~3~32~
not significantly different to the path length from the on-
axis lens 226 to the lens 302 of its rotor fiber 292.
Considering fiber 224 a relatively long bare fiber 424
connects the lens 426 to the termination 412 and hence to the
fiber 224. The lens 426 is held in a bore 428 of the middle
support unit 430 in the same manner as lens 416 is held in bore
410, that is by a spring clip 418. Since as with the previous
embodiment the support units 430 have circumferentially
arranged through bores 432 and since they are oriented at 90
to each other it will be possible for the bare fibers, such
as 424, to pass through the appropriate bore (or bores) 432
asthey pass from the head end to the lens-receiving support
unit 430. In the case of fiber 224 the optical path from lens
426 to the lens 302 of rotor fiber 298 is essentially equal
to the length of the optical path from lens 416 to the lens
302 of rotor fiber 294 and thus the optical or transmission
losses for fibers 220 and 224 will essentially be the same.
While not specifically illustrated the fibers 218 and
222 will have axially displaced lenses associated therewith so
that the optical path from each such lens to the lens 302 of
the associated rotor fiber 296 and 298, xespectively, will
be essentially equal to the length of the just-described
optical paths.
Figure 7 shows an alternative construction which
facilitates the assembly of the alternate lens arrangement
illustrated therein. In this case a short length of transparent
tubing 434 connects the head end 404 to the adjacent support
unit 430. A similar length of tubing 434 interconnects adjacent
sd/ -21~
~;~3~2~
pairs of support units 430 and the last support unit 430 to
the tail end 406. The tubing lengths 434 may be positively
adhered to the units 430 as by a suitable bonding agent or
the entire assembly may be held toqether, without adhesive,
through the use of a disc spring 436 positioned between the
tail end 406 and the end face of the rotor, the spring 436
applying a compressive force to the stator assembly.
It should be mentioned that there will be virtually
no interference caused by the bare fiber intersecting
momentarily the expanded optical beam as it is projected
radially from the reflecting unit 430 to the receptor lens
302. The expanded beam will have a diameter o~ about 0.07
inches while the bare fiber has a diameter of about 0.01
inches. Thus the area of interference is relatively small
and is insignificant with respect to the operating efficiency
of the joint.
Figure 9 illustrates another improvement to the
design of the ligh-t path but with increased complexity. In
this embodiment the support unit 530 is similar to unit 430
and retains mirrors 536 and 538 in the same position as
mirrors 250 and 2S4 respectively in the body of Figure 5.
However, the bores 540, 542 and 544 in the unit are much
smaller than the corresponding bores 242, 244 and 246, just
being large enough to accept and retain a SELFOC lens. In
this case bore 540 receives a lens 546, bore 542 receives a
lens 548 and bore 544 receives a lens 550. The lenses are
sized and are located relative to the mirros 536 and 538 so
that the focal point 552 of the lenses 546 and 548 is coin-
cident with that of the mirror 536 and so that the focal point
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554 of the lenses 548 and 550 is coincident with that of
the mirror 53~.
The reflecting unit 556 has its bores 558 and 560
sized to receive SELFOC lenses 562 and 564 respectively.
The focal point 566 of those lenses is coincident with that
of the reflecting mirror 568.
As a result of -this combination of lenses and
mirrors a light beam entering the unit off-axis, as by way of
lens 546 is redirected until it is on-axis and then relative
rotation can take place between the supporting unit 530 and
the reflecting unit 556. The on-axis expanded beam can then
be redirected off-axis again through the tube 560 to a
receptor SELFOC lens and the continuing optical fiber. By
using adjacent closely coupled lenses as described the
proportion of the light beam travelling in free space is
drastically reduced and this has the effect of reducing the
transmission losses.
The foregoing has described several embodiments of
an optical rotary joint, each embodiment utilizing essentially
the same principle of operation. It is expected that skilled
practitioners in the art could effect other structures without
departing from the spirit of the invention. For example,
while the drawings illustrate, and the disclosure describes,
mirrors as the reflecting means for the invention it is
understood that other devices which serve the same purpose
could be used, one such device being an appropriately
dimensioned prism. Accordingly the protection to be afforded
the invention is -to be determined from the claims appended
hereto.
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