Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~ Desclription
FACE-LOCK INTERCONNECTION MEANS FOR OPTICAL FIBERS
AND OTHER OPTICAL COMPONENTS. AND MANUFACTURING
METHODS OF THE SAME
Technical Field
This invention pertains generally to the field of optical
components, and particularly to means for interconnecting optical
0 fibers and other optical components.
Background Art
Optical fibers have been used widely for many applications,
most notably for optical fiber communication. In 1 980's the
5 optical fiber communication was mostly for linking the telephone
central offices. In such an application, one optical fiber carries
typically thousands of telephone (voice) channels, and the cost of
the fiber optic components such as fiber-to-fiber connector and
mechanical splice is not a critical issue. However, as the optical
20 fiber communication is inching toward individual offices and
residential area, especially as a part of information superhighway
infrastructure construction, the cost of such components become
the major issue. Actually this issue is at the present time the most
serious stumbling block in constructing the information
2 5 superhighway infrastructure using optical fibers. The cost should
come down by a factor of about ten before optical fibers can be
deployed widely.
The cost of optical fiber connectors and mechanical splices are
30 high due to the small size of the optical fiber cross-section. The
same is true for mating optical fibers to integrated optic planar
channel waveguides. Single-mode fiber, the most-commonly used
fiber, has about 9-micron core surrounded concentrically by about
1 25-micron cladding. When two single-mode fibers, or a single-
3 5 mode fiber and a waveguide channel, are mated, the cores, or thechannels should be aligned within one or two micron in terms of
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the transverse offset. In order to accomplish such a mating
between optical fibers, each of the fiber is inserted in a tubing or
plug with about two or three millimeter (1 millimeter = 1,000
microns), and about 125 micron inside diameter (ID). The
alignment is typically achieved by aligning the plugs inside
another tubing called sleeve. This requires that the size of the hole
or bore of the sleeve be larger than the diameter of the plug by
one or two microns, that the hole or bore of the plug be at the
center with better than one or two microns, that the size of the
0 bore be larger than the fiber diameter by only one or two
microns, that the fiber diameter be 125 microns plus or minus one
or two microns, and that the core be located at the center of the
fiber within one micron or better tolerance. All these tight
dimensional requirements drive up the cost of the optical fiber
connection, and to some degree the cost of the optical fibers as
well. Connection of an optical fiber to a channel waveguide ( such
as found in an integrated optic modulator or a planar waveguide
coupler) has a very similar technical difficulty, which results in a
very high cost. These costs would never be low enough for wide
applications so long as all these requirements should be satisfied
for optical fiber connections.
Similar technical difficulties exist in connecting other optical
components such as laser diode, light emitting diodes, and lenses.
2 5 These interconnections are often found in various fiber optic-
related packages. For example, a light from a laser diode is
coupled to an optical fiber end via a focusing lens. The alignment
of these components require better than one-micron accuracy
along the optical axis.
Disclosure of Invention
Accordingly, it is the primary objective of the present
invention to devise an alternative approach for mating optical
3 5 fibers, waveguide channels, light sources, lenses, etc.
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It is the ultimate objective of the present invention to lower
the interconnection cost for optical interconnection involving
optical fibers, integrated optic waveguides, light sources,
detectors, lenses, and other related optical components so as to
maximize the contribution of the fiber optics to the construction of
information superhighway infrastructure.
The basic approach of the present invention for connecting an
optical fiber to another optical fiber or any other optical devices is
1 o to provide a surface contour on the end facet, or on the extension
of the end facet, of the optical fiber, and to provide a matched
surface contour on the end face, or on the transverse extension of
the end face, of the other optical fiber or the optical devices. The
surface contours of the end faces are designed to be locked in a
stable mating position when the two surfaces are brought
together. This novel mating mechanism is named "Face-Lock" in
this invention disclosure. The surface contours preferably consist
of fine features, with the dimensions of the width and the depth
of the fine features comparable to that of the optical fibers, so as
to have alignment resolution in the order of microns or better.
Photolithographic techniques may be employed to generate
surface contours with sub-micron accuracy. Similar manufacturing
methods may be applied to integrated optic waveguide end-facets,
2 5 and other optical devices that require optical interconnections.
A modular approach is possible in the present invention in
which a selected combination of face-lock embodiments are
stacked together, one on top of the other, to align a number of
optical elements.
Brief Description of Drawings
FIG. 1 shows schematically two optical fibers in the end-butt
3 5 alignment positions.
E0 S~
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FIG. 2 shows schematically the optical fibers of FIG. 1 housed in
connector plugs in an conventional alignment embodiment.
FIG. 3 shows a sectional view of the embodiment of FIG. 3.
5across the U-U' plane.
FIG. 4 shows the basic embodiment of the present invention for
achieving the alignment of the two optical fibers shown in FIG. 1.
FIG. 59 shows a thin-slab with a face-lock features and a
through-hole for terminating an optical fiber.
FIG. 60 shows the sectional view of FIG. 59 across Z-Z'.
FIG. 61 shows the same as in FIG. 59, except that there are
many through-holes for an array of optical fibers.
FIG. 62 shows the sectional view of FIG. 59 across Z-Z' in which
20 the face-lock feature and the through-hole are fabricated by
preferential etching on a ( 100) silicon wafer.
FIG. 63 shows the same as in FIG. 62, except that the face-lock
feature and the through-hole are fabricated on the opposite sides
25 of the (100) silicon wafer.
FIG. 64 shows the masking step in the fabrication process of
making the alignment v-groove shown in FIG. 62 or 63.
30FIG. 65 shows the face view of the embodiment shown in FIG.
64.
FIG. 66 shows the etching step in the fabrication process of
making the alignment v-groove shown in FIG. 62 or 63.
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FIG. 67 shows the same as shown in FIG. 66, except that the
masking layer is stripped off.
FIG. 68 indicates that the same process shown in FIGS. 64
through 67 can be used to make a through-hole as well as the
alignment groove.
FIG. 69 shows the face view of the embodiment shown in
FIG. 68.
FIG. 70 is the same as shown in FIG. 68, except that the etching
masks are laid down on the both sides of the silicon wafer so as to
realize the embodiment shown in FIG. 63.
FIG. 71 shows the same as shown in FIG. 63, except that more
than one through-holes are fabricated.
FIG. 72 repeated the face view of the through-hole of FIG. 69.
FIG. 73 shows one set of three through-holes with slightly
.
varylng dlmenslons.
FIG. 74 shows a two-dimensional array of the set of through-
holes and corresponding alignment grooves located on the both
sldes .
FIG. 75 shows a matched pair of an alignment groove and an
alignment ridge.
FIG. 76 shows two recessed alignment grooves and a cylindrical
face-lock insert in-between.
FIG. 77 shows the sectional view of three alignment grooves of
FIG. 74.
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FIG. 78 shows that the same as shown in FIG. 77, except that
the alignment was shifted by one notch.
FIG. 79 shows that four pieces of face-lock embodiments are
stacked together, one top of the another, for optical alignment
between a light source, a lens, and an optical fiber.
FIG. 80 shows the same as shown in FIG. 79, except that the
path of light from the light source is shown in a schematic
0 manner.
FIG. 81 shows schematically the essence of the face-lock
mechanism of the present invention.
FIG. 82 shows sectional views of one connector part in a
switching embodiment of the present invention.
FIG. 83 shows a second connector part corresponding to the
connector part illustrated in FIG. 82.
FIG. 84 illustrates one possible mating position of the connector
parts shown in FIGS. 82 and 83.
FIG. 85 shows a second possible mating position of the
connector parts shown in FIGS. 82 and 83.
FIG. 86 shows a third possible mating position of the connector
parts shown in FIGS. 82 and 83.
FIG. 87 shows sectional views of one connector part in another
switching embodiment of the present invention, in which a set of
v-squares are used for channel selection.
FIG. 88 shows a second connector part corresponding to the
connector part illustrated in FIG. 87.
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FIG. 89 illustrates one possible mating position of the connector
parts shown in FIGS. 87 and 88.
FIG. 90 shows a second possible mating position of the
connector parts shown in FIGS. 87 and 88.
Best Mode For carrying Out the Invention
FIG. 1 shows in a highly schematic manner two optical fibers
0 ( 1 ) and (2) in an end-butt connecting position. The light (depicted
as arrows) being guided by the optical fibers is largely contained
inside the cores (3) and (4). The region outside the core is called
cladding, and it has a lower index of refraction so as to provide an
optical barrier or wall around the light-guiding core. The
connection or mating is to accomplish the transfer of the light
from one optical fiber to the other. When the mating is releasable,
it is called demountable connection, or simply connection.
Hardware that aids such connection is called an optical fiber
connector or simply a connector. When the mating is meant to be
permanent, it is usually called a permanent splice or simply a
spllce.
FIG. 2 shows the fiber (1) housed in a conventional connector
plug (5), and fiber (2) in another identical plug (6). The plug is
typically a cylinder with a hole or bore. FIG. 3 shows the sectional
view of FIG. 2 across the U-U' plane. Let's denote the diameter of
the fiber (1) as "F", and that of the core (3) as "C". The diameter of
the plug is denoted as "P" and the bore size by "H".
3 o In assembling the optical fiber ( 1 ) and the conventional
connector plug (5) as shown in FIG. 2, the hole of the plug (5) is
filled with liquid-form cement material, and the fiber 1 is inserted
through the plug hole until its end sticks out of the hole by a few
millimeters. After the cement material is solidified, the end of the
3 5 plug (5) is polished until the fiber ( 1 ) and the cement material are
flush at the end facet. The second plug 6 is prepared in the same
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way. The two plugs (5) and (6) are inserted in a tubing called
sleeve, and are mated in a face-to-face fashion.
The difficulty of mating of two optical fibers as described
above, and the resulting high cost of fiber connection, may be
understood if the typical dimensions for C, F, H, and P are listed
for the most commonly used optical fibers: C=9 microns, F=125
microns, H=(125 + 1 or 2) microns, and P = 3,000 microns = 3 mm.
In FIG. 1 or FIG. 3, the 9-micron (C) cores (3) and (4) should be
0 aligned within one micron in order not to suffer from a substantial
light loss in the mating. In order to satisfy such a tight alignment
requirement, all the dimensions listed above should be accurate
within one micron or so, and the core (3) and the hole of the plug
(5) should be concentrically located within one micron or so. Even
with such tight tolerances satisfied, the worst-case misalignment
can be as large as a few microns as the deviations can add up in
an unfavorable manner.
The implication of the conventional mating method and the
2 o resulting tight tolerances as described above is quite detrimental.
The optical fibers should be drawn within one or two microns
from the nominal diameter of 125 microns, meaning that any
fibers outside this specification will be rejected. This drives up the
fiber cost. The connector plugs and the sleeve should be fabricated
2 5 with the same resolution. The plug outside diameter P, and the
sleeve's hole size, are typically 2,000 to 3,000 microns plus or
minus one or two microns. Thus one or two micron tolerance is
translated into less than 0.1% of the diameter. This results in high
fabrication cost and low yield. In addition polishing of the plug
-fiber assembly adds to the overall cost. Today, the material cost
for a set of connector for single-mode fibers is over 50 dollars.
Connectorization labor cost itself costs almost as much. In
comparison, a typical connector for electronic coaxial cable is
available at two or three dollars at retail stores, and the
3 5 connectorization procedure is very simple. The high cost of optical
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fiber interconnection spells a disaster in an effort to use optical
fibers in the often-touted national information superhighway.
We notice that the conventional connector and splice are based
on alignment of the side walls, namely inside and/or outside of
the cylindrical surfaces of the optical fiber, the plug and its bore,
and the bore of the sleeve. This element make it necessary to
maintain those inner and outer diameters within one or two
micron accuracy.
Avoiding these detrimental aspect of the conventional fiber
interconnection methods, the connector and splice embodiments of
the present invention are designed around the optical fiber end
facet, instead of the side walls. The essence of the present
invention is depicted in the general term in FIG. 4. In FIG. 4 are
shown four elements: an optical fiber ( 1 ) with its end terminated,
a first surface (7) residing on the plane coinciding with the end-
facet of the optical fiber (1), another optical fiber (2) to be
connected to the optical fiber ( 1), and a second surface 8 residing
2 o on the plane coinciding with the end-facet of the optical fiber (2).
The first surface (7) has an unique contour on it, while the second
surface (8) has another unique contour that may be locked to that
of the first surface (7) in a stable position when brought together.
The optical fibers (1 ) and (2) are located in pre-determined
2 5 locations on the first and the second surfaces, (7) and (8),
respectively in such a way that, when the two surfaces (7) and (8)
are surface-locked into the matching position, the optical fibers
( 1 ) and (2) are aligned properly. The present invention as
depicted in FIG. 4 will be described below in detail using various
examples of possible embodiment.
An important embodiment of the present invention is shown in
FIG. 59, in which a thin-slab has face-lock feature (115) (see FIG.
60 for its sectional view across Z-Z': the detailed shapes of the
3 5 grooves and the through-hole can be different from shown) and a
through-hole (116) through which an optical fiber (117) is
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terminated at the surface of the thin-slab (114). The alignment of
the optical fiber in mating depends on the precise registration of
the through-hole (116) with respect to the surface-lock feature
(115). And the size of the through-hole (116) should be very close
to the diameter of the optical fiber (117). This is a technical
challenge by itself. However, it will be easier and cheaper to
achieve such dimensional control on a planar thin-slab as shown
in FIG. 59, when compared to the conventional approach as
sketched in FIGS. 2 and 3.
Once the embodiment as shown in FIG. 59 can be fabricated, it
is straightforward to extend the embodiment and the fabrication
technique to a multi-fiber array embodiment as shown in FIG. 61,
in which an array of optical fibers (118) are terminated on a thin-
slab (119). This array capability is another powerful advantage of
the present invention compared to the conventional plug-sleeve
approach which cannot be readily extended to an array
embodiment.
One manufacturing method for making the embodiments
shown in FIGS. 59 and 61 will be now described. The fabrication is
based on the well-known preferential etching of a silicon wafer
with either (100) or (110) facet. For example, on a (100) silicon
wafer, v-grooves can be fabricated in which the side walls of the
v-groove have a definite angle with respect to the surface
regardless of the groove size. Utilizing the technique, a v-groove
(120) and through-holes (121) and (122) as shown in FIGS. 62 and
63, respectively, can be fabricated on the surfaces of (100) silicon
wafer (123), realizing the embodiment shown in FIG. 59. The
detailed fabrication steps are as follows: as indicated in FIG. 64, a
mask layer (124) is patterned on one side and another layer (125)
on the other side (this second mask is to prevent etching of the
back side) on the silicon wafer using photolithography technique,
which has sub micron resolution in positioning a desired pattern
on a pre-determined position. The face view of the section shown
in FIG. 64 is sketched in FIG. 65. Then the wafer (123) is
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immersed in an etchant that etches the wafer in <100> direction
much faster than in < 111 > direction (by a factor of about SOO to
1,()00) . The etchant etches the silicon material into the < 100>
direction, that is in the direction perpendicular to the wafer
surface. The side-walls inside the v-groove (120) shown in FIG. 66
are the hard-to-etch facets, namely the (111) facets. Accordingly,
the depth of the V-groove depends solely on the width W of the
opening of the mask (124). The masks (124) and (125) are
stripped off when the etching is completed. The mask layer (124)
0 may be modified as shown in FIG. 68 to fabricate two V-grooves
(120) and (121). The face view of the section shown in FIG. 68 is
shown in FIG. 69, which indicates that the larger v- section (121) is
a tapered square hole with four (111) side walls. This square
groove (121) is actually too large to remain within the wafer body
(123), as indicated in FIG. 68, and thus punch through the wafer,
forming a through-hole (121) as desired (see FIG. 62). Again, the
angle of the side walls are universally the same as it is defined by
the (111) facets of the silicon. Accordingly, if the size of the hole
W2 and the wafer thickness T are known, the value for the mask
opening W3 can be calculated. The separation S between the V-
groove (120) and the thorough-hole (121) may be replicated with
better than O.S micron accuracy.
Since the optical fiber (117) is entering from the left side of the
through-hole as shown in FIG. 59 in our example, it would be
convenient to have the through-hole tapered out to the left side of
the wafer, as shown in FIG. 63. This can be realized by modifying
the mask layer (125) on the left-side as shown in FIG. 70, in
which etching is done on the both sides of the wafer (123). The
separation S can be precisely registered by using a mask-aligner
that uses infrared light with see-through capability, which allows
viewing simultaneously the both sides of the wafer during the
mask pattern registration before exposure. The mask layer (124)
in FIG. 70 may be made of a transparent, thin-film dielectric
material such as glass. It does not have to be removed since it
may work as a window for optical fiber being inserted in the
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through-hole (122). The window may be one or two micron thick.
FIG. 71 shows a straightforward extension of the embodiment and
the technique described in FIG. 64 through 70 to an array form, in
which two through-holes (126) and (127) are prepared in the
same manner for aligning two optical fibers (128) and (129).
When the window (124) described in FIG. 70 remains in
embodiment shown in FIG. 71, the end facet of the optical fibers
(128) or (129) may be glued to the window.
0 When the through-hole (121) or (122) in FIG. 69 or 70 are
fabricated, the hole clearance W2 should be very close to the
diameter of the optical fiber for precision fiber alignment. The
through-hole (121) of FIG. 69 is shown separately in FIG. 72. For a
given value W3, the value for W2 could vary slightly due to the
variation of the thickness T of wafer (123) and undercut of the
masked edges by the etchant. For example, the hole clearance W2
could turn out to be anywhere between 124 and 130 microns
while the optical fiber diameter itself can vary between 123 to
127 microns. In the worst case the hole size W2 could be larger
than an optical fiber by seven microns, or the hole size W2 could
be smaller than the fiber diameter. In order to accommodate this
variations in the hole size and the fiber diameter, a number of
through-holes with varying dimensions can be fabricated, as
depicted in FIG. 73, which shows three through-holes (130), (131),
and (132), which have three different sizes of mask openings W3,
W3', and W3", and three corresponding sizes of the through-holes
W2, W2' and W2" (as examples, these three values could be 127,
125 and 123 microns, respectively) . One of these three through-
holes would match to a given optical fiber better than the other
holes . The number of holes may be more than three . The resulting
embodiment is shown in FIG. 74, which is a variation of the
surface layout shown in FIG. 61: each of the through-holes in FIG.
6 l is replaced by three through-holes in FIG. 74. There are also
three sets of the face-lock grooves 133, 134 and 135. The face-
lock grooves are used to align two connecting embodiments as
shown in FIG. 74. The matching grooves may be designed as
AMENDED Si. LT
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13
shown in FIG. 75 (a recess (120A) and a protrusion (120B)), or
FIG. 76 (recessed grooves (120A) and (120C) with a face-lock
insert (137)). In the either case, the selection of one through-hole
out of the three possibilities ((130), (131), or (132) in FIG. 74) can
be achieved by selecting the corresponding v-groove among the
three possible sets, namely (133), (134), or (135). The resulting
alignments are shown in FIGS. 77 and 78 as two possible
examples .
0 FIG. 75 shows a matched pair of an alignment groove (120A)
and an alignment ridge (120B). Each of the embodiments (123 A)
and (123B) represent the face-lock surface shown in FIG. 59, 61,
or 74. As indicated, the alignment ridge (120B) may be fabricated
by etching V-grooves on the both sides of the ridge (120B) on the
silicon surface
FIG. 76 shows two recessed alignment grooves (120A) and
(120C) and a cylindrical face-lock insert (137) in-between that
facilitates the face-locking.
FIG. 77 shows a matched pair of the three alignment grooves as
shown in FIG. 74, (133A) through (135A), and (133B) through
(135B). Each set of these grooves are supposed to belong to a face-
locking surface as shown in FIG. 74. By selecting the grooves to
lock via a face-lock insert (137), one may lock the two surfaces
either as shown in FIG. 77 or FIG. 78. In turn, this will determine
which through-holes are being used among the three choices,
(130) through (132), in FIG. 74.
FIG. 79 shows that the face-lock embodiment of the present
invention can be extended to align other optical components such
as a light source (138) and a lens (139). It shows a modular
approach, in which a number of face-lock embodiments (123),
(140), (141), and (142) are prepared separately and assembled
together using the self-alignment mechanism of the face-lock
features (120A) and (124B ), and the counterparts in the rest of
AIUIENOED S"L' r
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14
the stack. Photolithography ensures that the optical axis is at the
center within one-micron tolerance. The pre-determined thickness
of the individual face-lock embodiments (123), (140), (141), and
(142) ensures that the distances between the optical components,
(128), (139), (138), are accurate. FIG. 80 shows that a light (143)
is emerging from the light source (138) to be focused by the lens
(139) into the fiber core (144). The light source (138) may be a
light emitting diode (LED) or surface emitting laser diode (that are
energized by a voltage V as shown in FIG. 80), or a light delivered
0 to the spot (138) by a set of reflectors or/and deflectors. Micro-
machined silicon and other crystal (GaAs or InP) wafers would
preferred materials for such modular face-lock embodiments,
since, as described above in detail, the registration of the face-lock
features and through-holes can be fabricated with better than
one-micron accuracy on these wafers using the standard
integrated circuit lithography technology.
Even though the face-lock surface contours (120A), (120B) and
the likes reside on the surfaces that are mutually parallel in FIG.
79, they may be, by a simple extension, provided on other planes,
such as the one perpendicular to the face-lock surfaces shown in
FIG. 79.
(FIGS. 62, 63, 68, 69, 70, 71, 72, 73, 74, 79 and 80 contain an
important and distinct teaching that a through-hole may be tailor-
fabricated with better than one or two micron accuracy to
terminate and align an optical fiber, or other optical components
such as a lens, on a wafer with a preferential etching
characteristics. FIGS. 73 and 74 also teach a method how to
prepare a set of through-holes with incrementally varying hole
dimensions. Even though these embodiments and teachings are
described in this invention, they are not part of the face-lock
mechanism or features, which are the main subject of the present
invention. Accordingly these embodiments and teachings related
to the through-holes will be prepared separately as a divisional
patent application of the present (parent) patent application.)
AMENDEC ~t:'-ET
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It would be almost impossible to describe all the possible
variations that utilizes the basic teaching of the present invention.
Accordingly, it would be useful to conclude the detailed
description by clarifying again the essence of the teaching of this
invention using an optical fiber and a lens. Referring to FIG. 81, a
typical embodiment of the present invention comprises three
elements: an optical fiber (145) with its end terminated, a first
surface (146) residing on the plane coinciding with the end-facet
of the optical fiber (145), and a second surface (147), containing a
0 lens (148), to be mated with the first surface (146). The first
surface (146) has an unique contour on it, while the second
surface (147) have another unique contour that may be locked
with that of the first surface (146) in a stable position when
brought together.
The concept of choosing among the multiple grooves (133),
(134), and (137) in FIG. 74 through 77 may be slightly modified to
realize an optical switching embodiment. A number of optical
components (through-holes (168) through (173) for
accommodating optical fibers (174) through (179) in this
example), and a number of V-grooves (180) through (186) for
face-lock positioning are fabricated on one connector part (187) as
shown in FIG. 82. Side and front sectional views along the various
axes indicated are shown. The other connector part (188),
schematically illustrated in FIG. 83 using heavy lines, shows an
optical component (a through-hole (189) fo~ a fi~er (190) in this
example) and v-grooves (191), (192), and (193). FIG. 84 shows
one possible mating position between the two connector parts
(187) and (188), whereby the fiber (190) is aligned to the fiber
(177). FIG. 85 shows another possible mating position, in which
the fiber (190) is aligned to the fiber (174). FIG. 86 shows yet
another possible mating position, in which the fiber (190) is
connected to the fiber (175). In this way, one can select different
mating positions among periodically-located face-lock features,
accomplishing an optical switching from one fiber to another. A
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mechanical fiber optic switch can be manufactured by
mechanizing the switching described herein.
The face-lock V-grooves of FIG. 82 and 83 may be replaced by
sets of V-squares (194) and (195), as shown in FIG. 87, and by
sets of V-squares (203) and (204), as shown in FIG. 88. Matching
the fiber (202) to one of the fibers among (196) through (201) can
be accomplished in the same fashion, as depicted in FIGS. 89
through 90.
Obviously many modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims the invention may be practiced otherwise than as
specifically described.
AME~ID~D SHEET
