Note: Descriptions are shown in the official language in which they were submitted.
~ 160~g
-- 1
OPTICAL FIBER SWITC~-I
Technical Field
.
The present invention relates to optical
transmission systems and, more particularly, to a switch
for switching an optical signal between optical fibers.
Background of the Invention
The use of optical fi~ers in telecommunications
applications requires the ability to switch an optical
signal between optical fibers Witll low loss over a varying
number of switch cycles. The optical fibers may be either
monomode or multimode fibers. ~onomode Eibers have a li~ht
transmitting core approximately one-tenth the diameter of
multimode fibers. Monomode fibers, however, exhibit lower
signal losses per unit distance than multimode fibers and
are, therefore, more desirable in long-haul op-tical
transmission systems. The number of switching cycles for
either type of optical fiber can vary from one or two to
several thousands in the switch service life. A high
degree of reliability is particularly important in many
applications, such as undersea fiber transmission systèms,
where the optical switch is not readily repaired or
replaced.
The switching function in optical fiber switches
is typically accomplished through the use of an optical
device and/or fiber movement. In switches utilizing an
optical device, such as a lens or mirror, the optical
signal is directed by the optical device between spatially
separated optical fiber. Such switches typically provide
satisfactory reliability but exhibit undesirable signal
losses and crosstalk levels due to the optical device and
the inherent separation between optical fibers. In moving
fiber switches, switching is accomplished by the
displacement and precise alignment of one fiber relative to
another. A nurnber of moving fiber switch designs exist
which can achieve low signal losses and crosstalk levels.
, . ",~.
~ 160~L89
- 2 ~
See, for example, U.S. Patent No. 4,033,669 to Hanson,
issued July 5, 1977 and U.S. Patent No. 4,220,396 to
Antell, issued September 2, 1980. The problem with moving
fiber switches, howeYer, is that the signal loss and
crosstalk level tend to increase significantly after many
switch operations. Moreover, most designs are not readily
adaptable for use with either multimode or monomode
optical fibers.
In light of the foregoing, a moving fiber switch
for either monomode or multimode fibers that exhibits low-
loss over thousands of switching cycles would be extremely
desirable.
Summary of the Invention
In accordance with an aspect of the invention
there is provided a switch for selectively aligning
discrete optical fibers characterized by first and second
housings having a number of fiber receiving channels
~* therethrough, the channels in the first and second
housings adapted to receive optical fibers, each housing
also having two parallel exterior surfaces with at least
one groove therein, the perpendicular distance between
- ~ said surfaces of said first housing being greater than the
perpendicular distance between said surfaces of said
second housing, a support assembly having a slot with
grooved and parallel surfaces serving to mate with the
grooved exterior housing surfaces, said first housing
being fixedly positioned in the slot by the mutual engage-
ment of the grooved exterior surfaces of the first housing
and the grooved slot surfaces, said second housing being
disposed in the slot adjacent said first housing with the
fiber receiving channels in each housing being parallel to
each other and means for displacing the second housing in
a direction substantially perpendicular to the exterior
surfaces to either of two positions, each position axially
aligning a predetermined number of fiber receiving channels
, . .
~ 1~0~89
~ 2a -
in said first and second housings, each position being
precisely determined by the mutual engagement of a grooved
exterior housing surface and a respective grooved slot
surface.
A feature of the present invention is that low
optical signal loss can be maintained over several hundred
thousand switching cycles.
Brief Description of the Drawing
A complete understanding of the present invention
may be gained from a consideration of the detailed
,.
l 16~89
-- 3 --
description presented hereinbelow in connection with the
accompanying figures in which:
~IG. 1 is a front view of an embodi~ent of the
present invention;
FIG. 2 is a side view of wafers used in the
embodiment of ~IG. l;
FIG. 3 is a cross-sectional view taken along line
3-3 of FIG. l;
E~IG. 4 is a cross-sectional view taken along line
4-4 of FIG. 1.
Detailed Description
As shown in FIGS. 1, 3 and 4, two housings 101
and 102 are disposed in slotted support member 103.
Housing 101, retaining planar arrays of optical fibers 104
and 105, is fixedly positioned in support member 103.
~ousing 102 retains a planar array of optical fibers 108
and is floatably mounted in support member 103 with optical
fiber arrays 104, 105 and 108 parallel to one another.
Array 108 passes through channel 113 in wall 114. Housing
102 is maintained in abutment with housing 101 by
longitudinal force F produced by coil spring 115. (For
purposes of clarity, housing 101 and 102 are shown in
FIG. 1 slightly displaced from one another.) Coil spring
115 surounds array 10~ and is positioned between wall 114
of support member 103 and end face 116 of housiny 102.
Displacement of housing 102, in a direction substantially
perpendicular to fiber arrays 10~, 105 and 1C8, to either
of two positions is provided by the actuation of either
solenoid 109 or 110. Both these solenoids e~tend through
support member 103. Coil springs 111 and 112 are
advantayeously disposed in each said solenoid to center
housing 102 within slotted member 103 when neither solenoid
is actuated.
Housings 101 and 102 are fabricated by the
stacking of thin wafer elements 201 shown in FIG. 2. Each
wafer 201 has two parallel surfaces 202 and 203 wi~h a
number of longitudinal and parallel grooves 204 and flat
~ ~60~
- peaks 209. Each groove has a uniform cross-section and a
maximum width g. Surfaces 202 and 203 are geometrically
identical as the grooves in each are in vertical alignment.
To form housings 101 and 102, wafers 201 are staclced with
grooves 204 in adjacent wafers aligned to form fiber
receiving channels. Two wafers 205, each having parallel
surfaces 206 and 207, are affixed to support member 103.
Surface 206, containing grooves 20~, and peaks 210 is the
mating opposite of surfaces 202 and 203 in wafer 201. The
minimum peak width is designated as p. Two wafers 205,
along with the outermost grooved surfaces of housings 101
and 102 are not used for optical fiber retention but, as
will be discussed, are used to precisely control the
relative position of each housing over thousands of
switching cycles.
Refer now to FIGS. 1 and 3. Housiny 101
comprises three stacked wafers 201 which interleave fiber
arrays 104 and 105. Housing 101 is fabricated by inserting
each fiber in an array into a groove in one surface of
wafer 201. A second wafer is then stacked on top the first
wafer with the bottom grooves in the second wafer aligned
with the top grooves in the Eirst wafer to form fiber
receiving channels 301. The fibers in the second array are
then inserted into the top grooves in the second waEer
followed by the alignment of a third wafer on top the
second wafer to for~ additional fiber receiving channels
301. After stacking, epoxy is introduced between the
wafers and each optional fiber end face is lapped and
polished to be substantially flush with the stacked wafer
end faces.
A housing support structure is assembled by
bonding surface 207 of one wafer 205 to wall 305 and
bonding surface 207 of a second wafer 205 to screw 105.
This forms a slot with grooved and paralle] sidewalls into
which housing 101 is inserted. Precise positioning of
housing 101 is provided by the mutual engage~ent of the
outermost grooved surfaces of housing 101 with the mating
1 ~6~9
-- 5 --
- grooved slot sidewalls~ Screw 106 e~tends through support
member 103 to assure this mutual engagement is maintained
and to prevent longitudinal displacement of housing 101.
Referring to FIGS. 1 and 4, housiny 102 comprises
two wafers 201 which interleave fiber array 108. The two
wafers 201 are stacked, as in housing 101, with the grooves
in adjacent surfaces aligned to form fiber receiving
channels 301. ~s illustrated, the fibers in array 108 are
precisely axially aligned and a substantial abutment with
the fibers in array 105. Precise alignment is provided by
the mutual engagement of the grooves in the e~terior
surface of the bottommost wafer 201 of housing 102 with the
mating grooves in lower wafer 205 of support member 103.
I'hese two grooved surfaces are brought into contac~ with
one another by the actuation of solenoid 109.
~lternatively, solenoid 110 may be actuated thereby
aligning the fiber in array 108 with the fibers in array
104 by the mutual engagement of the grooves in the exterior
surface of the topmost wafer in housing 102 with the mating
grooves in the upper wafer 205 of support member 103. To
maintain precise axially alignment of fiber array 108 to
either Eiber array 104 or 105, the difference between the
depth d of the slot in support member 103 and the width w
of wafer 201 is judiciously selected to be less than the
maximum groove width g minus the minimum peak width p. The
support housing 103 was also fit-ted with a cover plate 308
(shown in phantom lines in FIGS. 3 and 4). This use of a
cover pla-te along with the aforementioned difference
between slot depth and wafer width assures self-centering
and complete intermeshing of the outermost grooved surfaces
of housing 102 and the grooved slot side walls.
In stackin~ wafers 201 to form housing 101 or 102
a yap 302 exists between fiber receiving channels 301
formed by adjacently disposed grooved wafer surfaces. The
groove geometry preEerably is selected ~o maintain a gap
302 between adjacent wafers. Typically, this gap was about
38 microns (~m). Consequently~ the wafers ride upon the
- ~ -
enveloped optical fiber without coming into contact with
another. If gap 302 was eliminated, some fiber would
likely have leeway to move out of alignment and increase
switching losses.
Switches have been constructed for optical fibers
haviny a diameter of 110 microns (~m). Multimode fiber
switches maintained an optical signal loss of less than
.2ds over 250,000 cycles with crosstalk levels less than
-70dB. Monomode optical fibers have also been switched
with an optical signal loss of less than .5dB. The switch
models utilized .51 millimeter (mm) thick silicon wafers.
The switches were extremely compact as wafers 201 and 205
were 6.30 rnm and 12~70 mm, respectively. Preferential
etching o~ the silicon was used to produce .050 mm deep
grooves on a center-to-center spacing of .23 mm. The angle
forlned by opposing groove walls was approximately 70.5
degrees. Finally, to reduce Fresnel reflections, index
matching fluid was applied to the fiber end Eaces during
assembly.
It should, of course, be understood that while
housings 101 and 102 were fabricated using three and two
wafers, respectively, the housing size is adjustable. For
example, the number of wafers and the number of yrooves in
each wafer can be adjusted to accommodate a varying number
of fiber arrays as well as a varying number of optical
fibers in each array. Moreover, the fabrication of each
housing is not limited to the stacking of waEers. For
example, precision apertures could be formeci in a block of
metal or plastic having two grooved and parallel exterior
surfaces. In similar fashion, wafers 205 could be
eliminated by the formation of grooves directly in support
member 103.
