U.S. patent application number 09/960895 was filed with the patent office on 2002-02-14 for optical switching apparatus.
Invention is credited to Congdon, Philip A., Dewa, Andrew S., Forehand, David I., Laor, Herzel, Lin, Tsen-Hwang, Orcutt, John W., Sisco, James A..
Application Number | 20020018615 09/960895 |
Document ID | / |
Family ID | 22210195 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020018615 |
Kind Code |
A1 |
Laor, Herzel ; et
al. |
February 14, 2002 |
Optical switching apparatus
Abstract
An optical matrix switch station (1) is shown mounting a
plurality of optical switch units (15, 17), each of which includes
a mirror (29), moveable in two axes, for purpose of switching
optical beams from one optical fiber to another. A mirror assembly
(41) includes a single body of silicon comprising a frame portion
(43), gimbals (45), mirror portion (47), and related hinges (55).
Magnets (53, 54) and air coils (89) are utilized to position the
central mirror surface (29) to a selected orientation. The moveable
mirror and associated magnets along with control LED's (71) are
hermetically packaged in a header (81) and mounted with the air
coils on mounting bracket (85) to form a micromirror assembly
package (99) mounted in each optical switch unit.
Inventors: |
Laor, Herzel; (Boulder,
CO) ; Congdon, Philip A.; (Richardson, TX) ;
Dewa, Andrew S.; (Plano, TX) ; Forehand, David
I.; (Wylie, TX) ; Lin, Tsen-Hwang; (Dallas,
TX) ; Orcutt, John W.; (Richardson, TX) ;
Sisco, James A.; (Esmond, RI) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
|
Family ID: |
22210195 |
Appl. No.: |
09/960895 |
Filed: |
September 21, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09960895 |
Sep 21, 2001 |
|
|
|
09310284 |
May 12, 1999 |
|
|
|
6295154 |
|
|
|
|
60088239 |
Jun 5, 1998 |
|
|
|
Current U.S.
Class: |
385/18 |
Current CPC
Class: |
G02B 26/085 20130101;
G02B 6/3518 20130101; G02B 6/3558 20130101; G02B 6/359 20130101;
G02B 6/3548 20130101; G02B 6/3582 20130101; G02B 26/101 20130101;
G02B 6/358 20130101; G02B 6/3572 20130101; Y10S 359/904 20130101;
G02B 6/3512 20130101 |
Class at
Publication: |
385/18 |
International
Class: |
G02B 006/35 |
Claims
What is claimed:
1. Optical switching apparatus comprising, a header having a bottom
wall and upwardly extending side walls forming a recess, a platform
formed along the side walls spaced above the bottom wall, a
micromirror formed from a single piece of material having an outer
frame portion lying in a plane and supported on the platform, an
intermediate rotational gimbals portion hinged to the frame portion
and movable relative to the frame portion about a first axis and an
inner rotational mirror portion having a reflective, upper face
surface formed with a radius of curvature of at least 2 meters
hinged to the gimbals portion for movement of the mirror portion
relative to the gimbals portion about a second axis, at least one
magnet attached to one of the rotational portions, and at least one
electromagnetic coil assembly disposed in close proximity to the
mirror assembly for applying selected forces to the at least one
magnet for causing desired movement of the gimbals portion and the
mirror portion along the two axes to reflect an optical beam
directed to the mirror portion in a selected direction.
2. Optical switching apparatus according to claim 1 in which the
gimbals portion is hinged to the frame portion by a pair of hinges
spaced apart along the first axis and the mirror portion is hinged
to the gimbals portion by a pair of hinges spaced apart along the
second axis.
3. Optical switching apparatus according to claim 1 in which the
axes are disposed 90 degrees relative to one another.
4. Optical switching apparatus according to claim 1 further
comprising a plurality of light emitting diodes mounted on the
frame portion for providing control signals.
5. Optical switching apparatus according to claim 1 further
comprising a pair of magnets for driving movement of the gimbals
portion disposed on spaced apart locations of the gimbals portion
along the second axis and a pair of magnets for driving movement of
the mirror portion disposed on spaced apart locations of the mirror
portion along the first axis.
6. Optical switching apparatus according to claim 5 in which each
magnet comprises a set of an upper magnet attached to an upper face
surface of the respective gimbals portion and mirror portion and a
lower magnet attached to a lower surface of the respective gimbals
portion and mirror portion, the respective upper and lower magnets
of a set being in alignment with each other.
7. Optical switching apparatus according to claim 1 in which the at
least one electromagnetic coil assembly is disposed in engagement
with the bottom wall of the header, a respective coil assembly
being in alignment with each spaced apart magnet location.
8. Optical switching apparatus according to claim 7 in which each
coil assembly comprises a bobbin having a spool on which a coil is
wound and an aluminum plate portion between the respective coil and
the bottom wall of the header, the bobbins having a massive heat
sink portion of heat conductive material relative to the respective
coils on a side of the coils remote from the plate portion.
9. Optical switching apparatus according to claim 8 further
comprising a flex circuit electrically connected to the coils and
to the LED's and a mounting bracket formed of heat conductive
material, the flex circuit received on the mounting bracket, the
mounting bracket being relatively massive relative to the coil
assemblies, the header mounted on the mounting bracket with the
coil assemblies therebetween and heat conductive potting material
disposed between the header on one side and the flex circuit and
the mounting bracket on another side.
10. Optical switching apparatus according to claim 5 further
comprising a push-pull drive for exciting the magnets.
11. Optical switching apparatus according to claim 1 further
comprising a single magnet mounted on a lower face surface of the
mirror portion.
12. Optical switching apparatus according to claim 11 further
comprising a plurality of electromagnetic coil assemblies spaced
apart adjacent to but out of alignment with the single magnet.
13. Optical switching apparatus according to claim 1 in which the
piece is formed of silicon.
14. Optical switching apparatus according to claim 13 in which the
mirror portion has a lower face surface and both the upper and
lower face surfaces are polished thereby providing improved surface
flatness.
15. Optical switching apparatus according to claim 2 in which the
frame portion has spaced apart, inwardly extending stop tabs on
either side of the first axis and the gimbals portion has an
extension along the first axis fitting closely between the stop
tabs to limit motion in the plane in which the gimbals portion
lies.
16. Optical switching apparatus to claim 2 in which the gimbals
portion has spaced apart, inwardly extending stop tabs on either
side of the second axis and the mirror portion has an extension
along the second axis fitting closely between the stop tabs to
limit motion in the plane in which the mirror portion lies.
17. Optical switching apparatus according to claim 15 further
comprising a projection formed on one of the stop tabs and the
extension and extending toward the other of the stop tabs and the
extension.
18. Optical switching apparatus according to claim 16 further
comprising a projection formed on one of the stop tabs and the
extension and extending toward the other of the stop tabs and the
extension.
19. Optical switching apparatus according to claim 1 in which the
header is ceramic and a glass window is attached to the header
covering the recess, the glass window being attached with indium
forming a hermetic seal with a selected atmosphere sealed in the
recess.
20. Optical switching apparatus according to claim 1 further
comprising a mounting bracket formed of heat conductive material,
the header mounted on the bracket, the bracket being formed with a
first portion having a pair of spaced apart surfaces lying in
respective planes which intersect each other, a package having a
bottom wall, the bottom wall having an upwardly extending mounting
pad formed with a second portion having a pair of complimentary,
spaced apart surfaces, one of the first and second portions forming
a concave cradle and the other of the first and second portions
forming a convex protrusion received in the cradle, the first and
second portions being fixed to one another.
21. Optical switching apparatus according to claim 19, in which a
bore is formed through the bracket intermediate to the spaced apart
surfaces of the first portion and a threaded bore is formed between
the pair of complementary, spaced apart surfaces of the second
portion and the portions are fixed together by a threaded member
received through the bore of the bracket and threaded into the
threaded bore.
22. Optical switching apparatus comprising, a header having a
bottom wall and upwardly extending side walls forming a recess, a
platform formed along the sidewalls spaced above the bottom wall, a
micromirror assembly formed from a single piece of material having
an outer frame portion lying in a plane and supported on the
platform, an intermediate rotational gimbals portion hinged to the
frame portion and movable relative to the frame portion about a
first axis and an inner rotational mirror portion having a
reflective, upper face surface hinged to the gimbals portion for
movement of the mirror portion relative to the gimbals portion
about a second axis, at least one magnet attached to one of the
rotational portions, and at least one electromagnetic coil assembly
disposed in close proximity to the mirror assembly for applying
selected forces to the at least one magnet for causing desired
movement of the gimbals portion and the mirror portion along the
two axes to reflect an optical beam directed to the mirror portion
in a selected direction.
23. A method for making a movable mirror comprising the steps of
taking a piece of silicon and forming an outer frame portion, an
intermediate gimbals portion connected by a hinge to the frame
portion and an inner mirror portion connected by a hinge to the
gimbals portion, attaching the mirror portion to the gimbals
portion at locations on both sides of the respective hinge,
attaching the gimbals portion to the frame portion at locations on
each side of the respective hinge to prevent movement of the
respective portions in a plane in which the piece lies and severing
the attachment at each location at any selected time prior to use.
Description
RELATED APPLICATIONS
[0001] Benefit is claimed from Provisional Application No.
60/088,239, filed Jun. 5, 1998.
FIELD OF INVENTION
[0002] This invention relates generally to a component for optical
switching systems and more particularly to a component for the
switching of optical signals directly, without first converting the
optical signals to electronic signals.
BACKGROUND OF THE INVENTION
[0003] In recent years optical fibers have come into wide spread
use in a wide variety of applications in which optical signals are
transmitted along such fibers and are switched from one fiber to
another by means of an optical switch. Conventional optical
switches generally include fiber positioning means, alignment
signal emitter means and interconnected computer control means. A
fiber positioning means is provided near the end of each fiber to
selectively point the end of a given fiber in one fiber group
toward the end of a given fiber in another fiber group for switched
optical transmission therebetween. An alignment signal emitter
means is provided near an end of and in predetermined spaced
relationship to the end of each fiber to emit an alignment signal
for receipt and use in controlling the fiber positioning means when
aligning the ends of selected fibers in the fiber groups for
switched optical transmission therebetween, for example as shown in
U.S. Pat. Nos. 4,512,036 and 5,177,348. This approach requires
considerable complexity and duplication of alignment means for each
alignable fiber. It would be very desirable to reduce this
complexity and duplication and to increase speed of switching,
reliability, as well as to reduce cost in implementation.
SUMMARY OF THE INVENTION
[0004] An object of the present invention is to provide an optical
switch that overcomes the limitations of the above noted prior art.
Another object of the invention is to provide an optical switching
unit which is relatively low in cost, has high speed and is
reliable in operation.
[0005] Briefly stated, an improved optical transmission switch made
in accordance with the invention employs a microelectromechanical
(hereinafter MEM) movable mirror assembly with associated
electromagnet coils mounted in a package and preferably including
control LED's with both drive and LED signals being supplied
through a wiring harness. The following described preferred
embodiments relate to a hermetic package using inorganic materials
in order to provide extended life, however, units can be made which
include organic materials for other shorter life applications.
[0006] The package comprises an LED lead frame of suitable material
such as ceramic, which mounts LED's used by the control system to
aim the movable mirror as well as circuitry to electrically connect
the LED's to their package terminations. The LED's are die and wire
bonded to the lead frame using conventional techniques. The LED's
are located so that lines drawn through diagnonal pairs would pass
through a selected location on the lead frame which is referenced
the movable mirror. A mirror assembly, described below, is attached
to the lead frame so that the center of the mirror portion
coincides with the selected location on the lead frame in order to
accurately locate the mirror for proper control of mirror movement.
The mirror assembly and lead frame are mounted in a header of
suitable material, such as ceramic which, along with driving means
and a wiring harness, are in turn mounted on a bracket. The package
is received in a housing in which an optical fiber is received and
in which another mirror is disposed in alignment with the fiber for
reflecting an optical signal from the fiber to the movable
mirror.
[0007] MEM micromirrors are presently used to build digital
micromirror display (DMD) devices where the mirrors rotate about a
single axis by an electrostatic drive. The mirror of the present
invention provides two axes of motion and is preferably driven
magnetically. The micromirror is preferably made from a single
piece of crystal material such as silicon and has three portions
connected by two sets of hinges. An inner portion forms the mirror.
One of the hinge pairs, one hinge on each of two opposite sides of
the mirror portion, ties the mirror portion and the middle gimbals
portion, which surrounds the mirror portion. This allows the mirror
portion to rotate about the gimbals portion, providing the first
axis of rotation. The second set of hinges ties the gimbals portion
and the frame portion, one hinge on each of two opposite sides on a
line disposed, preferably 90 degrees relative to a line drawn
through the first set of hinges. This allows the gimbals portion,
which carries the mirror, to rotate about the frame portion,
providing a second axis of rotation.
[0008] In the first preferred embodiment, two pair of magnets, one
for each axis of rotation, are used to move the mirror portion and
are mounted on one face of the single piece to form a mirror
assembly. The first pair of magnets are attached by suitable means
to the mirror portion of the mirror assembly, one on each of two
opposite sides of a line, 90 degrees relative to a line through the
mirror/gimbals portions set of hinges. When magnetically
stimulated, the mirror portion rotates about the mirror/gimbals
portions set of hinges, providing the first axis of motion. The
second pair of magnets are suitably attached to the gimbals portion
of the mirror assembly, one on each of two opposite sides of a
line, 90 degrees relative to a line drawn through the gimbals/frame
portions set of hinges. When magnetically stimulated, the mirror
and gimbals portions rotate about the second set of axis, to
providing the second axis of rotation.
[0009] According to a feature of the invention, an additional
magnet is provided at each magnet location, with the poles in
opposing relationship to each other and disposed on the opposite
face of mirror assembly to balance the weight of the magnets
relative to the hinge centerlines of the mirror assembly,
minimizing undesirable oscillations under external shock or other
conditions.
[0010] According to a modified embodiment, a single magnet can be
utilized located in the center of the mirror portion, on the face
opposing the surface serving as the mirror.
[0011] According to another feature of the invention, motion stops,
disposed in a plane described by the two axes of rotation, are
added to the mirror assembly at each hinge location to limit motion
and thereby prevent failure of the hinge. Tabs are preferably
formed in the plane described by the two axes of rotation,
extending from the mirror portion to the gimbals portion and from
the gimbals portion to the frame portion, to prevent rotation
during initial manufacture. Sometime prior to final assembly, laser
or other suitable cutting means severs the tabs, preferably
perpendicular to each respective axis of the hinges, to allow free
rotation.
[0012] In order to obtain extended operation without degradation,
the mirror assembly is preferably hermetically assembled into a
cavity in the package to lock out moisture and allow the provision
of a benign atmosphere for micromirror operation. The cavity can be
filled with selected gases to provide improved heat transfer and,
if desired, exclude oxygen water vapor and other materials that
would adversely affect the micromirror over time. The hermetic
package comprises the header in which the cavity is formed and
which includes sealed pins for electrical LED connection pins. A
peripheral seal surface on the header extending around the cavity
is coated with indium or suitable non-organic seal materials, for
later attachment of a window over the cavity. The use of indium
allows the seal to be made at room temperature to avoid seal
temperature induced stresses and window distortions. Indium or
other non-organic attach materials are used exclusively to assembly
all items within the body cavity of the hermetic package, avoiding
any unwanted long term organic out gassing or other similar
problems.
[0013] According to another feature, the window is tilted at a
slight angle, such as 6 degrees, to deflect unwanted stray
radiation away from the desired optical path.
[0014] The lead frame assembly described above, containing LED's
and the mirror assembly, is placed in and attached to the body on a
platform within the cavity. The tabs preventing rotation of the
mirror and gimbals portions during assembly may now be released as
described above. The body cavity is sealed with a glass window that
preferably has been treated with anti-reflective coatings.
[0015] An air coil drive assembly is used and preferably employs a
push and pull arrangement for driving the mirror magnets to rotate
the mirror portion to the desired orientation in its two axes. Four
air coil assemblies, comprising copper wire coiled on a bobbin, are
attached to a mounting bracket, trapping a flex circuit harness and
are aligned with the mirror assembly. The air coil leads are
soldered to the flex circuit harness to allow system electrical
control of the air coils and their push pull arrangement to drive
the mirror assembly. The air coil bobbins are made of aluminum or
other eddy current generating material, and sufficient amounts of
aluminum are provided at the top and bottom of the bobbins to allow
eddy current dampening of the movable portions of the mirror
assembly, to prevent unwanted oscillations. In order to prevent
overheating and loss of mirror position control, the air coil
bobbins are made of high heat transfer material, such as aluminum,
and the bobbins are massive relative to the air coils. The mounting
bracket is massive relative to the bobbins and is also made of a
high heat transfer material, such as aluminum. The bracket is in
intimate contact with the optical unit housing, which in turn is in
intimate contact with the ultimate heat sinking of the customer's
system.
[0016] According to yet another feature, the air coil bobbins trap
the flex circuit harness to the bracket when the air coil bobbins
are attached to the bracket to facilitate later location and
assembly of the flex circuit to the bracket. The LED pins of the
header assembly are soldered to the appropriate pads on the flex
circuit harness. The micromirror can fully be tested at this point.
The header assembly is then rotated and aligned with the mounting
bracket and joined by fixing the header assembly to the mounting
bracket. The open area around the air coils is then potted with
heat conductive material to ensure optimum assembly rigidity and
improved heat transfer.
[0017] Other objects and advantages of the present invention will
be apparent from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] For a more complete understanding of the present invention
and further advantages thereof, reference is now made to the
following detailed description of the preferred embodiments taken
in conjunction with the drawings in which:
[0019] FIG. 1 is a schematic view of an optical switching station
showing two optical switching units;
[0020] FIG. 2 is a schematic view of one of the optical switching
units shown in FIG. 1;
[0021] FIG. 3 is a plan view of a mirror assembly used in the FIG.
2 switch unit;
[0022] FIG. 3a is a cross sectional view taken on line A-A of FIG.
3;
[0023] FIG. 3b is a view similar to FIG. 3a but showing rotation of
the mirror portion of the mirror assembly;
[0024] FIG. 3c is a cross sectional view taken on line B-B of FIG.
1;
[0025] FIG. 3d is a view similar to FIG. 3c but showing rotations
of the gimbals portion of the mirror assembly;
[0026] FIG. 4 is an enlarged cross sectional plan view taken on
line E-E of 3a showing a hinge and an in-plane motion stop;
[0027] FIG. 5 is an enlarged, broken away portion of FIG. 4 showing
a portion of the in-plane stop;
[0028] FIG. 6 is a cross sectional plan view taken on line E-E of
FIG. 3a, showing a hinge with an optional lock down tab to stop
rotation used during manufacture;
[0029] FIG. 6a is a view similar to FIG. 6 showing the lock down
tab severed to allow rotation;
[0030] FIG. 7 is a top plan view of an optical switch package made
in accordance with the invention;
[0031] FIG. 7a is a cross sectional view taken on line C-C of FIG.
7;
[0032] FIG. 7b is a view similar to FIG. 7 showing rotation of the
mirror portion of the mirror assembly;
[0033] FIG. 7c is a cross sectional view taken on line D-D of FIG.
7;
[0034] FIG. 7d is a view similar to FIG. 7c but showing rotation of
the gimbals portion of the mirror assembly;
[0035] FIG. 8 is an exploded view of a cross sectional, broken away
portion of the bottom wall of the housing of an optical switching
unit package and the mounting bracket;
[0036] FIG. 9 is a top plan view of a modified embodiment of an
optical switch unit with certain parts removed for purposes of
illustration;
[0037] FIG. 9a is a cross sectional view of the top portion of an
optical switch unit taken on line F-F of FIG. 9; and
[0038] FIG. 9b is a view similar to FIG. 9a but showing rotation of
the mirror portion of the modified mirror assembly.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0039] FIG. 1 shows the layout of a matrix optical switch station
comprising a plurality of parallelly extending optical switch units
5 and 15, two being shown for purposes of illustration, but any
number can be provided as desired. These switch units are mounted
in a frame 3 such that they are aligned with optical switch mirror
11 fixedly mounted in housing 1. An end portion of fiber optics
cable 17 is mounted in a selected fixed position within housing 1
and fiber optics cable 7 is similarly affixed into the housing of
optical switch 5. An optical signal 13 is transmitted in cable 17
and is directed by optical switch unit 15, by reflecting optical
signal 13 from optical switch mirror 11 to another selected optical
switch unit, such as optical switch 5, which directs optical signal
13 into cable 7.
[0040] The optical signal is optimized to minimize transmission
losses by the optical units. As seen in FIG. 2, optical beam 13
carried by optical cable 17 is focused by lens 14 and is reflected
by a fixed mirror 25 mounted within optical switch 15 to a moveable
mirror 29, shown in a solid line in its middle or neutral unpowered
position. Mirror 29 is moveable between two opposite extremes, 29',
29", with optical beam 13 correspondingly reflected to 13', 13",
respectively. Although the movement of the mirror shown in FIG. 2
illustrates movement in one plane, mirror movement in a second
plane is also included in the operation of the switch and will be
described below.
[0041] Mirror assembly 41, FIG. 3, includes a frame portion, an
intermediate gimbals portion and an inner mirror portion preferably
formed from one piece of crystal material such as silicon. The
silicon is etched to provide outer frame portion 43 forming an
opening in which intermediate annular gimbals portion 45 is
attached at opposing hinge locations 55 along first axis 31. Inner,
centrally disposed mirror portion 47, having a mirror 29 centrally
located thereon, is attached to gimbals portion 45 at hinge
portions 55 on a second axis 35, 90 degrees from the first axis.
Mirror 29, which is on the order of 100 microns in thickness, is
suitably polished on its upper surface to provide a specular
surface. In order to provide necessary flatness, the mirror is
formed with a radius of curvature greater than approximately 2
meters, with increasing optical path lengths requiring increasing
radius of curvature. The radius of curvature can be controlled by
known stress control techniques such as, by polishing on both
opposite faces and deposition techniques for stress controlled thin
films. If desired, a coating of suitable material can be placed on
the mirror portion to enhance its reflectivity for specific
radiation wavelengths.
[0042] Mirror assembly 41 also comprises a first pair of permanent
magnets 53 mounted on gimbals portion 45 along the second axis and
a second pair of permanent magnets 53 is mounted on extensions 51,
which extend outwardly from mirror portion 47 along the first axis.
In order to symmetrically distribute mass about the two axes of
rotation to thereby minimize oscillation under shock and vibration,
each permanent magnet 53 preferably comprises a set of an upper
magnet 53a mounted on the top surface of the mirror assembly 41
using conventional attachment techniques such as indium bonding,
and an aligned lower magnet 53b similarly attached to the lower
surface of the mirror assembly as shown in FIGS. 3a-3d. The magnets
of each set are arranged serially such as the north/south pole
arrangement indicated in FIG. 3c. There are several possible
arrangements of the four sets of magnets which may be used, such as
all like poles up, or two sets of like poles up, two sets of like
poles down; or three sets of like poles up, one set of like pole
down, depending upon magnetic characteristics desired.
[0043] By mounting gimbals portion 45 to frame portion 43 by means
of hinges 55, motion of the gimbals portion 45 about the first axis
31 is provided and by mounting mirror portion 47 to gimbals portion
45 via hinges 55, motion of the mirror portion relative to the
gimbals portion is obtained about the second axis 35, thereby
allowing independent, selected movement of the mirror portion 47
along two different axes.
[0044] The middle or neutral position of mirror assembly 41 is
shown in FIG. 3a, which is a section taken through the assembly
along line A-A of FIG. 3. Rotation of mirror portion 47 about axis
35 independent of gimbals portion 45 and/or frame portion 43 is
shown in FIG. 3b as indicated by the arrow. FIG. 3c shows the
middle position of the mirror assembly 41, similar to that shown in
FIG. 3a, but taken along line B-B of FIG. 3. Rotation off the
gimbals portion 45 and mirror portion 47 about axis 31 independent
of frame portion 43 is shown in FIG. 3d as indicated by the arrow.
The above independent rotation of mirror 29 of mirror portion 47
about the two axes allows direction of optical beam 13 as needed by
the optical switch units.
[0045] In order to protect hinges 55 from in-plane shock during
handling and shipping, stops 57 are provided according to an
optional feature of the invention as best shown in FIGS. 4 and 5,
which are enlarged sectional views taken on line E-E of FIG. 3a. At
this point it should be noted that the mirror assembly is on the
order of 100 microns thick, whereas hinge 55 of the same thickness
is on the order of 10 microns wide, thereby providing robust
strength in directions normal to the surface of the assembly. In
order to provide protection against excess in-plane motion 90
degrees to the axis of the hinge, i.e., axis 31, cooperating
surfaces 61 on gimbals portion 45 and 63 on frame portion 43 are
formed on either side of each hinge 55 and extend generally
parallel to axis 31. Surfaces 61 and 63 are spaced apart a selected
distance such as 10 microns by way of example. In order to provide
less in-plane motion, projection 65, extending from surface 63
towards surface 61, is formed to any selected distance such as 5
microns. It will be understood that such projection could be
provided on surface 61 instead of 63 if desired. Similar stops are
provided on the mirror and gimbals portions to provide protection
against in-plane motion of hinges 55 relative to axis 35.
[0046] According to another optional feature of the invention, lock
down tabs associated with each hinge are provided. As seen in FIG.
6, an example showing one such hinge 55, bridge portion 67 extends
from gimbals portion 45 to frame portion 43 and locks the two
portions together isolating hinge 55 from all normal manufacturing
stresses. At the appropriate manufacturing step, the bridge portion
67 is cut providing gap 69 as shown in FIG. 6a, which allows normal
rotation of gimbals portion 45 relative to frame portion 43 about
the hinge 55. This provides suitable stress protection for all
hinges and significantly improves manufacturing yields.
[0047] With reference to FIG. 3, extensions 51 are preferably
provided with laterally extending tabs 51a which can be used to
clamp down the mirror portion during assembly to thereby provide
additional stress protection.
[0048] The movable mirror assembly 41 is received in a cavity 81a
of a header 81 which forms part of the mirror assembly package
shown in FIGS. 7-7d. Header 81 is formed of any suitable material,
such as ceramic in the case of a hermetic package and plastic where
hermeticity is not required, and has a circumferentially extending
shelf 81b formed within cavity 81a on which frame portion 43 of
mirror assembly 41 is received. Bottom wall 81c is spaced from
shelf 81b to provide clearance for movement of gimbals portion 45
and mirror portion 47. Recesses 81d are formed in bottom wall 81c
aligned with each set of magnets 53 to provide motion clearance for
lower magnets 53b. The size of the opening of recesses 81d is
maintained as small as possible, allowing suitable motion of the
magnets, to facilitate making wall 81e as thin as practicable, for
example 125 microns.
[0049] The magnet drive for the magnets comprise four air coils 89
(two shown in FIGS. 7c-7d) each wound on a bobbin in turn mounted
on mounting bracket 85 and aligned with respective recesses 81d and
magnets 53. The bobbin and bracket are made of suitable material
for good heat transfer, magnetic dampening, and strength such as
aluminum. The air coils are wound using high electrical
conductivity materials such as copper. The bobbin has an air coil
disposed proximate to top end 89a of bobbin 89 such that the air
coil is as close to magnets 53 as possible, for example, 200
microns, to provide full mirror rotation using minimum power.
[0050] An electrical wiring harness 87 is provided for required
electrical connections to the micromirror assembly package 99 and
comprises an elongated flex circuit 87 mounting a connector 95 at
one end thereof for connection to a control system (indicated at
100, FIG. 7a). An opening 87b is formed at an opposite end which
receives therein bobbins 89. Coil leads 97 are attached to
appropriate traces on the flex circuit as shown in 7c-7d. A
plurality of diode pins 79 are mounted in bores provided in shelf
81b and extend above and below the shelf. The upper portion of the
diode pins are connected by leads 77 to respective conductive pads
75a-75h (see FIG. 7) and on the lower end are connected to
respective traces on electrical harness 87. LED's 71a-71d are
assembled to board 75 in according to conventional semiconductor
techniques and are powered by the traces on the harness discussed
above. The LED's 71a-71d are positioned so that they can be used to
direct the optical beam 13 using the optic unit's sensing control
system 100.
[0051] Once the electrical connections are made to the diode pins
79, window 83 is attached to the open side of header 81, closing
cavity 81a. The closing of cavity 81a can be made to be a hermetic
seal by using known techniques such as employing indium as the
window seal material and glass sealing or the like sealing of the
diode pins 79 to the header 81. If desired, a protective atmosphere
such as nitrogen can be trapped within the cavity. The window is of
suitable material and anti-reflective coatings to allow
transmission of optical signal 13 with minimum losses and is
preferably tilted approximately 6 degrees relative to the plane in
which mirror assembly lies, to deflect unwanted stray radiation. In
this respect, the spacing between gimbals portion 45 and mirror
portion 47 is maintained sufficiently large to avoid unwanted stray
radiation.
[0052] After the electrical connections are made between diode pins
79 and harness 87 completing all electrical connections, header 81
with all of its internal components described above, are aligned
with mounting bracket 85 and its components and potted in place
with thermally conductive, strong potting material 93 to complete
the micromirror assembly package 99.
[0053] With particular reference to FIG. 8, micromirror assembly
package 99 is precisely mounted and orientated in optical switch
unit 15 utilizing cooperating registration surfaces of mounting
bracket 85 and a portion of wall 16 of switch unit 15. First
opposing inclined surfaces 107 and 105 forming a somewhat convex
configuration on mounting bracket 85 cooperate with respective
second opposing inclined surfaces 103 and 101, forming a somewhat
concave, or cradle configuration, respectively, on bottom wall 16
of the switch unit. Mounting bolt 113 is received through bore 111
in bracket 85 and threaded bore 16a in the cradle in bottom wall 16
to secure micromirror assembly package 99 within optical switch
unit 15. The cooperating opposed surfaces provide a precise
registration in two planes while bolt 113 and its corresponding
bore 111 in bracket 85 and threaded bore 16a in wall 16 provides
registration in a third plane. It will be realized that the convex
and concave configurations can be reversed if desired and further,
that the surfaces can be fixed to one another by means other than a
bolt, eg, welding.
[0054] An alternate embodiment is shown in FIG. 9 in which a single
permanent magnet 54 is centrally located on the lower side of the
mirror portion 47. Air coils 89a-89d are shown located in the same
positions as in the FIGS. 3-7 embodiment and can be independently
excited so that the interaction of the magnetic field of the
permanent magnet and the coils cooperate to produce the appropriate
magnetic field to cause movement of the mirror portion along each
axis 31 and 35, as desired. Although four air coils are shown, if
desired, three air coils could be used to produce the desired
magnetic field.
[0055] A micromirror assembly package made in accordance with the
invention included a mirror portion which measured approximately 3
mm.times.4 mm in width and length and had approximately 8 degrees
of rotation about each of axes 31 and 35.
[0056] Although the invention has been described with regards to
specific preferred embodiments thereof, variations and
modifications will become apparent to those skilled in the art. For
example, magnet and air coil locations other than those described
above can be employed as long as appropriate currents can be
applied by means of control 100 to the air coils to move the
gimbaled mirror to a desired orientation. In this respect, with
reference to the four coil arrangement shown, a push-pull drive in
control 100 is preferred. Further, although permanent magnets are
shown attached to the movable mirror assembly, it will be
appreciated that, if desired, magnetic material could be added to
the assembly instead of the permanent magnets and polarized
perpendicular to the mirror surface. It is therefore the intention
that the appended claims be interpreted as broadly as possible in
view of the prior art to include all such variations and
modifications.
* * * * *