Download Optical coupling devices

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United States Patent [19]
[11]
Patent Number:
4,569,569
Stewart
[45]
Date of Patent:
Feb. 11, 1986
[54]
OPTICAL COUPLING DEVICES
FOREIGN PATENT DOCUMENTS
[75] Invent”
gilglig‘d‘l' Stewart’ Fmweu’
0012274 6/1980 European Pat. Off. .
[73] Assignee:
Plessey Overseas Limited, Ilford,
2441860 6/1980 France -‘
0016593 10/1980 European Pat. Off. .
England
[21]
Appl. No.: 363,661
[22]
Filed
Mar 31 1982
.
.
................... ..
.
,
References Cited
U.S. PATENT DOCUMENTS
4,111,524
4,185,885
4,208,094
4,239,330
4,245,889
9/1978
1/1980
6/1980
12/1980
1/1981
Primary Examiner-William L; Sikes
Assistant Examiner__Robm E. wise
.
Field of Search ................ .. 350/96.18, 96.19, 102,
350/292, 293, 294, 299
[56]
8/1979 United Kingdom .
2097550 11/1982 United Kingdom .
cg ............................... .sgiiyggnlng'Gglszligi/ig
.
2/1978 United Kingdom .
2091899 8/1982 United Kingdom .
,
[58]
1500257
2014751
Tomlinson, III .
Chown et a1. ................. .. 350/9618
Tomlinson, III et a1. .
Ashkin et al. .
Hoffman ........................... .. 350/ 102
.
__
Ammey' Age“ “Fm”
[57]
.
.
Fle‘t' Ja°°bs°“’ c°hn 8‘ Pm"
ABSTRACT
A coupler for an optical ?bre system includes a retrore
flector which because of its properties allows consider
able relaxation in the positioning of the ?bre in relation
to the retroreflector. The principle may be used to pro
vide switches or couplers.
9 Claims, 9 Drawing Figures
OUT
US. Patent Feb. 11, 1986
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US. Patent Feb. 11,1986
Sheet20f2
4,569,569
1
4,569,569
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being offset from 90° such that light of the wavelength
OPTICAL COUPLING DEVICES
reflectable by the dichroic mirror is re?ected back to a
different position from other wavelengths of light. Thus
The present invention relates to optical devices and
a wavelength seperator and or optical switching cou
more particularly to optical couplers, switches wave 5 pler maybe produced.
length combiners etc. wherein light is modi?ed in direc
The optical ?bres maybe held accurately in position
tion or form. In particular the invention is concerned
by mounting them in V shaped grooves etched in silicon
with light transmitted along optical ?bres. ‘
blocks or by other known accurate mounting means.
Many known optical ?bre couplers, switches, wave
length combiners, etc. use expanded beam techniques.
Optical lens means is preferably used between the
optical ?bre or optical ?bre combination and the retro
re?ector to focus the light beam out of and into the
These techniques use a small lens or mirror to manipu
late a beam of light much larger than the ?bre to
optical ?bres.
achieve this function, the light being ultimately rei
The present invention also provides an optical ?bre
connection device comprising means for holding the
optical ?bre or ?bres in a ?xed relationship with respect
to the retrore?ector, said means being detachable for
disconnection.
maged down onto the original, or another ?bre (or of
course a source or detector.) The basic device of this
type, from which others are derived, may be regarded
as being a device that re?ects the light emerging from a
?bre back into itself. Types of device using this princi
ple are shown in the FIGS. 1 and 2.
Although these expanded beam devices may allow
the relaxing of tolerances in some respects compared to
the equivalent “?bre-only" device the tolerancing on
the crucial ?bre transverse positioning is not improved.
However, according to the present invention, by
replacing the mirror with a retrore?ector such as a
comer cube a device can be made in which the image
Embodiments of the present invention will now be
described, by way of example with reference to the
20
accompanying drawings in which:
FIGS. 1 and 2 show known optical ?bre connection
devices.
FIG. 3 shows a ?rst optical connection device in
accordance
with the present invention employing a
25
corner cube prism as retrore?ector,
FIG. 4 shows a second optical connection device in
accordance with the present invention employing a
concave and convex mirror retrore?ector arrangement,
FIG. 5 shows a Frisnel bi-prism arrangement which
will “track” the object as it is moved in any sideways
direction. Axial tolerances are not improved but these
are less critical in any case.
According to the present invention there is therefore
when used in conjunction with the arrangement of FIG.
3 or FIG. 4 will provide two tracking images,
provided an optical ?bre connection device comprising
a retrore?ector, means for holding a ?rst optical ?bre in
a ?rst position in front of the retore?ector such that
FIG. 6 shows a third optical connection device simi
lar to FIG. 3 but including a dichroic mirror surface
re?ected by the retrore?ector along a de?ned path so as 35 within the comer cube prism offset from one face of the
prism,
to be received at the plane of the ?rst optical ?bre at a
FIG. 7 shows a switching coupler using a corner cube
de?ned second position with respect to said ?rst posi
light emitted from said ?rst optical ?bre is received and
tion said device being such that within the working
angle of said retrore?ector the ?rst position maybe
varied whilst maintaining the relative distance between
said ?rst and second positions.
In a ?rst preferred embodiment the retrore?ector is
retro prism with one “off-90°” face,
FIG. 9 shows a connector emboding the corner cube
retro prism as shown in FIG. 3.
Referring now to the drawings it maybe seen that in
the arrangement of FIG. 1 or FIG. 2 the vertical or
formed by a comer cube prism and in a second pre
ferred embodiment the retrore?ector is formed by a
concave mirror and convex mirror arrangement.
horizontal displacement of the end of the optical ?bre 1
The present invention also provides an optical
switching coupler comprising a retrore?ector, means
for holding a rotatable optical ?bre combination in
position in front of and within the working angle of said
retrore?ector, said optical ?bre combination compris
ing a ?rst optical ?bre capable of emitting light to be
re?ected by said retrore?ector and one or more further
_
FIG. 8 shows the rotatable optical ?bre combination
40 device used to secure the optical ?bres in position in the
arrangement of FIG. 7, and
from its position will cause problems because the re
?ected beam will not return to that spot. Thus the posi
50
tioning of the ?bre is critical.
As illustrated in FIG. 1, light beam or ray 12 is emit
ted and received by optical ?ber 1. The emitted ray is
transmitted through lens 2 toward a planar re?ective
optical ?bres displaced a ?xed distance apart from said
?rst optical ?bre in a ?xed relationship, in which the
surface 14. The lens illustrated in FIG. 1 is a complex
position and the further optical ?bres are arranged
symetrically and concentrically around ?rst optical
?bre 1 as it is moved from position 19 to any position 20
as in FIG. 3. Hence, the present invention is less suscep
tible to the crucial transverse positioning of prior art
devices. Thus any beam emitted by the ?bre will return
to the same ?bre providing that the corner cube prism
lens including a convex and a concave lens combina
retrore?ector is modi?ed by alteration of one or more 55 tion. In FIG. 2, optical ?bre 1 emits ray 12 towards a
re?ection angles to displace the re?ected beam by an
concave re?ective surface 16 and also the ?bre receives
ray 12.
amount equal to said ?xed distance when said re?ected
beam reaches said optical ?bre combination.
In the arrangement of FIG. 3 or 4 however the
Preferably the ?rst optical ?bre is held in a central
retore?ector used causes the re?ected beam to track the
?bre. The retrore?ector used may in a preferred em
bodiment be a corner ~cube prism with one face offset
from 90° with respect to its adjoining face by a small
angle. The optical ?bre combination is preferably rotat
able around the central optical ?bre.
65 18 or concave and convex mirror arrangements 3,4 are
accurate because the illustrated optical systems utilize a
‘ In a further embodiment a dichroic mirror surface
degenerate self-conjugated retrore?ector, i.e., retore
maybe positioned within the corner cube prism, its face
?ectors which return the light beam back to its source.
3
4,569,569
The comer cube prism 18 is shown for simplicity as
an angle in two dimensions only but will of course com
prise mirrors in three dimensions.
The mirrors 3,4 shown in FIG. 4 are concentric. In
practice however M2, mirror 4, may be planar, with
some loss of performance. Central obstruction will gen
erally be minimal. As illustrated in FIG. 4, emitted ray
21 is re?ected twice by M1, mirror 3, and once by M2,
mirror 4, and is returned to optical ?bre 1.
Other alternative forms of retore?ector may be used
for example, a length of graded index rod with a plane
4
merely restricts the number of arrangements of 3 signs
achieved by any one cube to 6 of the possible 8.
The angular de?ection of any one beam (of the six
possible as above) is a sum of 3 vectors in angular space
(ie. on a diagram of 0,, vs 6y) orientated at 120° intervals
and each of a magnitude related to the angle of one of
the roofs according to:
de?ection = 2
2/3 80
with the angle 0 de?ned as before. The factor \fgarises
because the roof prism is tilted away from the normal.
Useful devices may be made from these (any of
The six possible spots are obtained by adding the 3
FIGS. 1-4 in some cases) using extra components. For
example the use of a Fresnel bi-prism, 23 FIG. 5, close 5 vectors with any combination of signs, except for two
as indicated above. This gives the six output beam direc
to the mirror (M1) or lens will give two “tracking”
tions needed to make the 6-way splitter. If one of the
images either side of the input ?bre at spacings deter
roofs is exactly 90° (max. interfacial angle) there will of
mined by the prism angle. If other ?bres are placed at
course be only 4 spots, but two will be bright the two
these points a splitter is obtained. The relative positions
dim. If two faces are perfect right angles there will be
of these ?bres may easily be accurately controlled us
mirror at the end.
ing, for example, precision etched silicon V-grooves.
Variations of this using a dispersive prism or a diffrac
tion grating to achieve wavelength separated images are
obvious. A similar effect could be achieved in FIG. 3 by
using slightly tilted dichroic mirrors one behind the
other as one face of the comer cube (FIG. 6). FIG. 6
illustrates a mirror surface 22 and a dichroic mirror 24
and another mirror surface 26. As illustrated in the
just two output spots (equally bright.) All spots appear
in diametrically opposite pairs, and it is, unfortunately,
not possible to obtain 6 in a single row, the nearest being
4 in a row with two out of line.
To produce a connector as shown in FIG. 7 a retro
prism with a slightly tilted face is used. This re?ects the
beam back to two de?ned points close to the original
source and hence if a receiving ?bres are mounted at
?gure, dichroic mirror 24 is offset slightly from a plane
normal to the surface 22, i.e., the angle between mirror
22 and mirror 24 is different than the angle between
mirror 22 and mirror 26. Therefore, the offset angle is
the difference between 90° and the actual angle of any
those points in accurate ?xed relationships to the emit
ting ?bre the light will transfer.
The illustrated retrore?ector is a non-degenerate
conjugate retrore?ector because the device has a conju
mirror. As illustrated, ray 28 is re?ected off of mirror
22. Dichroic mirror 24 re?ects a selected spectral band,
i.e., wavelength, as ray 30. The balance of ray 28 is
mined distance apart. When a pair of ?bres, separated
by this distance, is placed at or near the conjugate plane,
light is directed from one ?bre to the other ?bre irre
spective of the location of the pair- relative to the optical
gate focal plane for which conjugate pairs (e. g., B) of all
randomly selected foci (e.g., A) are a ?xed predeter
transmitted by mirror 24 and re?ected by mirror 26 as,
ray 32. Hence, wavelength sepearation is achieved as
axis of the coupling assembly.
described earlier. A grating might also be used here and 40 A switching coupler as shown in FIG. 8 may be
a split face, with different parts tilted differently, could
produced by using the arrangement of FIG. 7, the
replace the bi-prism.
A particularly simple way to produce a splitter is to
use a corner cube with off-90° interfacial angles. This
switching action being performed by rotation of the
prism about the system axis A-—A1. By this means any
two of several output ?bres may be selected. The spe
ci?c advantage of this form of switch lies again in terms
of insensitivity to both angular and spatial movement of
can be arranged to produce 2, 4 or 6 spots; according to 45
the description below. The division of power is mode
along diameters in the far ?eld, and is thus made unse
the retroprism or similar moving part (see FIGS. 2, 3
lective.
etc.)
The following is a description of the mode of opera
The key advantage of these techniques is the relaxing
tion of an ‘imperfect’ corner cube.
of ?bre positioning tolerances and a switch coupler
A corner cube maybe regarded as constructed of
incorporating the corner cube prism arrangement is
three mutually perpendicular roof prisms, each of
which returns a ray de?ected at an angle of i2 80
shown in FIG. 9. By using an imperfect (oneface “off
90°) comer cube prism of course an optical switch cou
where 89 is the angle by which the roof angle differs
pler can be constructed using the principles described
from 90°, and the sign depends upon the direction in 55 above.
which the ray appears (viewed from the front) to cross
the roof apex. In the complete cube all rays of interest
As illustrated in FIG. 9, a ?bre bundle 48 is held by
block 52. Bundle 48 includes a plurality of ?bres, at least
are re?ected from each face once and therefore cross
one of which is an emitting ?bre and at least another is
the line of each roof apex (a re?ection of this in the
a receiving ?bre as discussed in relation to FIG. 3
opposite face is equally counted.) The negligible pro 60 above. Emitted rays 49 and received rays 51 clearly
portion of rays striking the vertex of the cube is ignored.
illustrate bundle 48’s dual components. Block 52 is se
If the directions across each apex are labelled consis
cured within cylinder 50 as is the illustrated complex
tently (ie. in a similar way) it can easily be shown that
lens 53, lens 2 and corner cube prism 18. Additionally,
the signs of the angular tilts always alternate. Rays may
lenses 53, 2 and retrore?ector 18 are retained by sup
therefore cross the 3 roofs with any combination of 65 ports 54, 56 and 58, respectively, as is shown in FIG. 9.
signs except all +ve or all -—ve. Since the individual
What I claim is:
i
roof angles may each be +ve or —ve (ie.> or <90“),
1. An optical coupling device for optically coupling
this does not restrict the combinations achieved, but
an emitting ?rst optical ?bre and a receiving second
5
4,569,569
optical ?bre comprising: an imperfect, non-degenerate
6
5. An optical coupling device as claimed in claim 1
wherein said means for holding said ?rst and second
conjugate retrore?ector; means for holding said retro~
re?ector; means for holding said ?rst optical ?bre at a
optical ?bres is detachable for disconnection.
?rst arbitrary position, in close proximity to an optical
6. An optical switching coupler comprising:
conjugate focal plane of said retrore?ector, and for 5
an optical ?bre combination including a ?rst optical
holding said second optical ?bre at a de?ned second
?bre capable of emitting light and a plurality of
position laterally displaced with respect to said ?rst
second optical ?bres displaced a ?xed distance
position, both said ?rst and second positions being in
apart from said ?rst optical ?bre in a ?xed relation
front of the retrore?ector and within the working angle
ship;
thereof such that light emitted from said ?rst optical
means for rotatably holding said optical ?bre combi
?bre is received and re?ected by the retrore?ector so as
to be received by said second optical ?bre at the plane
of the ?rst optical ?bre.
nation;
an imperfect corner cube prism having at least one
off-90° interfacial angle, said angle displacing the
2. An optical coupling device as claimed in claim 1 in
which the imperfect retrore?ector is formed by a com 15
bination of lens means and an imperfect corner cube
re?ector, said re?ector being imperfect in that at least
re?ected beam by an amount equal to said ?xed
distance when said re?ected beam reaches said
optical ?bre combination; and
means for holding said imperfect cube prism such that
said optical ?bre combination is in front of and
one face thereof is offset off-90° relative to an adjoining
face.
within the working angle of said comer cube
3. An optical coupling device as claimed in claim 2 in 20
prism.
which a dichroic mirror surface is positioned within the
7. An optical switching coupler as claimed in claim 6
corner cube re?ector, the re?ecting surface of said
in which the ?rst optical ?bre is held in a central posi
mirror being offset from 90“ relative to said adjoining
tion and said second optical ?bres are arranged symmet
face such that light of the wavelength re?ectable by the
rically and concentrically around said ?rst optical ?bre.
dichroic mirror is re?ected back to a different position 25
8. An optical switching coupler as claimed in claim 6
from other wavelengths of light, thus forming a wave
in which said interfacial angle is small as compared with
length separator.
90".
4. An optical coupling device as claimed in claim 1 in
9. An optical switching coupler as claimed in claim 6
which said ?rst and second optical ?bres are held accu
in which the optical ?bre combination is rotatable
rately in position by mounting the ?bres in grooves
30
etched in silicon blocks.
around the central optical ?bre.
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