A micromechanical optical switch (30). A reflective surface with two angled reflective surfaces (32,34) positioned opposite a micromechanical device (12). The micromechanical device is positioned such that light input along a path (36) to a first (32) of the two angled reflective surfaces is reflected to the micromechanical device. The micromechanical device then reflects the light to the second (34) of the angled surfaces to be output along another path (38a, 38b). The path (38a, 38b) that the second angled surface (34) outputs the light along is selected depending upon the position of the micromechanical device's reflective member (14). The reflective member (14) deflects from at least one hinge (22) to one of several positions. The number of positions available to the reflective member (14) depends upon the voltage applied to the electrodes (27a, 27b, 27c, 27d). The reflective member (14) makes no contact with any other surfaces, and thereby always returns to a know position upon loss of power.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to optical switching, more particularly to 
micromechanical optical switches. 
2. Background of the Invention 
Micromechanical devices have certain advantages in the optical switching 
area. They are compact, have fast response times and can achieve stable 
states which allow them to switch light in consistent directions. However, 
depending upon the states assumed by the micromechanical element of the 
switch, it can leave the optical system in an unknown state at loss of 
power. 
One example of these type of devices is shown in U.S. Pat. No. 5,226,099. 
In this patent a micromechanical device referred to as a digital 
micromirror device or deformable mirror device is adapted to include a 
small vertical flap off the mirror. When the mirror deflects, the small 
vertical flap slides into a slit in a waveguide, thereby switching the 
light OFF. 
This type of device has an advantage in that it can achieve one of three 
stable states: deflected to one side; deflected to the other side; or 
undeflected (flat). The mirror achieves a stable state when deflected 
because it comes into contact with a landing electrode. However, a 
disadvantage of this landing is that when power is lost, there is no way 
of determining quickly what state the structure is in. It could be in any 
one of the three states. 
Another type of micromechanical device that has a known state upon loss of 
power is shown in U.S. Pat. No. 4,954,789. This type of device comprises a 
mirrored surface suspended over an activating electrode by four hinges. 
When the electrode is activated, the mirror moves down in a piston-like 
motion towards the electrode, due to electrostatic attraction. The voltage 
on the electrode are controlled such that the mirror is deflected to a 
stable, known state each time. When power is lost, the attractive forces 
between the electrode and the mirror cease to exist and the mirror returns 
to its undeflected state. 
However, a disadvantage of this type of non-contacting element is that it 
can only achieve two positions, deflected or undeflected. This limits its 
applicability as an optical routing switch. Therefore, an optical switch 
is needed that can achieve more than one stable state, yet returns to a 
known state upon loss of power. 
SUMMARY OF THE INVENTION 
One aspect of the invention is a micromechanical device which acts as an 
optical switch. The device comprises of a reflective member suspended over 
at least one activation electrode such that when the electrode or 
electrodes are activated, the member deflects towards the electrode but 
does not make contact. 
The device is positioned directly opposite a surface that has two 
reflective surfaces. Incoming light is reflected by the first surface to 
the reflective member. Depending upon the position of the reflective 
member, it directs light to one of several points on the second reflective 
surface, which then reflects the light into an outgoing optical fiber or 
waveguide. The position of the reflective member is controlled by the 
voltage on the electrode or electrodes. The electrode can be segmented to 
allow for fine-tuning of the position of the reflected light. 
It is an advantage of the invention in that it allows multiple input and 
output paths for optical switching. 
It is a further advantage of the invention in that it does not make contact 
with any surfaces and thereby always returns to a known state upon loss of 
power. 
It is a further advantage of the invention in that it allows for 
fine-tuning of the reflective member's position to provide maximum optical 
throughput.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
One example of a prior art, contacting micromechanical device is shown in 
FIG. 1a. The reflective member 14 is supported by a post 16. The post 16 
in turn rests upon an active yoke 21. Yoke 21 is supported by hinges 22, 
which are supported by posts 23. Post 25 support landing surface 24. 
Underneath the landing surface and yoke lies the control circuitry for the 
device. When the electrodes 27 are activated, the yoke 21 is attracted to 
them and rotates about the hinges 22 until the yoke 21 comes into contact 
with the lower landing surface 26. As the yoke 21 deflects, the reflective 
member 14 also deflects and touches down onto landing surface. 24. The 
yoke 21 can go to either side, allowing two stable deflected positions, 
and one stable undeflected or flat position. 
The problems with using this type of device for optical switching lies in 
its contacting of other surfaces. When it makes contact, the position is 
stable. If power is lost, it is uncertain whether or not enough sticking 
forces have accrued that would cause the yoke 21 to remain deflected. In 
some situations, depending upon the operating environment of the device, 
it may remain deflected or it may return to it undeflected state. There is 
no way of determining the actual position of the switch in a loss of power 
situation, short of visual inspection or testing after power has been 
regained. 
An example of a micromechanical device 12 that returns to a known state 
upon loss of power is shown in FIG. 1b. The mirror or reflective surface 
14 is suspended by four flexure hinges 22 and posts 23 over an electrode 
27. When the electrode 27 is activated, the mirror deflects towards the 
electrode until it reaches the limits of the hinges 22. This causes the 
mirror to assume a stable state. Since there is no contact between the 
mirror and the electrodes or any other surface, no other forces except 
electrostatic attraction come into play. When power is lost, and the 
electrostatic forces dissipate, the mirror returns to it undeflected 
position. While the device is shown as being supported by four hinges, it 
could be supported by as few as one or as many as desired, so long as the 
mirror returns to a known position upon loss of power. The term digital 
micromirror device is often used to refer to these type of devices as 
well, even though they can be operated in an analog fashion, with the 
depth of deflection being determined by the amount of voltage applied. 
However, this switch only has two states, deflected or undeflected. It is 
not very useful in a crossbar or routing switch embodiment. The control 
circuitry and the electrodes can be adapted to allow finer control of the 
mirror's stable deflected states. 
One example of a device used in this invention is shown in FIG. 2. The 
mirror 14 has been cut away from the device and is represented by the 
dashed lines. The electrode 27 has been divided or segmented into four 
electrodes 27a-27d. These electrodes are activated with a known analog 
voltage. The different levels of voltage available in the analog domain 
determine which of several deflected states the member assumes. Once a 
known analog voltage is applied, the segmented electrodes allow 
fine-tuning of the member's position. 
For example; the reflective member may be deflected to a position 
corresponding to 5 volts being applied to the electrodes. In order to fine 
tune the position of the reflected light, the voltage on electrode 1 may 
be adjusted to 4.8 volts, electrode 2 to 5.1 volts, and electrode 3 to 5.2 
volts, with electrode 4 remaining at 5 volts. The nonuniform field 
underneath the member is small enough that the member will not change its 
depth, but some slight torqueing of its surface will occur. This torqueing 
of the surface is what causes the position of the reflected light to be 
positioned in a slightly different place. 
Alternate embodiments of the segmented electrodes are shown in FIGS. 3a-3b. 
The electrodes could be patterned as four triangles as shown in FIG. 3a, 
which may have an advantage of increasing surface area. Instead of 
patterning four electrodes, only two electrodes could be used as shown in 
FIG. 3b. These two electrodes are shown as triangular, but could be 
rectangular as well. Finally, four strip electrodes are shown in FIG. 3c. 
One embodiment of an optical switch 30 using a non-contacting 
micromechanical device is shown in FIG. 4. Opposite the non-contacting 
micromechanical device is a reflective surface that has two angled 
surfaces 32 and 34. The incoming light along path 36 reflects down to the 
reflective member or mirror 14. If the mirror 14 is in its undeflected 
position, shown with the solid lines, the light is reflected back up to 
the angled reflective surface 34 and output along path 38b. If the mirror 
is in a deflected position, shown by the dashed lines, the light is 
reflected back up to the angled reflective surface 34 and output along 
path 38a. Again, the voltages on each electrode could be adjusted to 
maximize the amount of light in path 38a that enters an output fiber or 
waveguide. 
The embodiment shown has a mirror with only two stable positions indicated. 
However, the electrodes 27a-d of FIG. 3a could allow a third stable 
position. For example, the position of mirror 14 shown by the dashed line 
could be due to a different voltage being applied. There could be a third 
state, lower than that state shown by the dashed line, where the applied 
voltage is higher. That position would lie between the solid line position 
and the dashed line position of mirror 14. 
Finally, the embodiment shown shows only one input light path. If fibers 
were vertically stacked coming into the switch, it could have two light 
paths passing light onto reflective surface 32. The light could then be 
switched for one path or the other or both into one of four output paths 
for the two positions shown, or one of six output paths if there were a 
third position. 
In this manner, the use of grazing angles increases the possible input and 
output configurations of the non-contacting micromechanical optical 
switch. This increases its usefulness while allowing the switch to 
continue to return to a known position upon loss of power. 
While the above embodiments discuss structures which may be interpreted as 
limited to those referred to a digital micromirror devices, this in no way 
is intended to limit this invention to those structures. Any 
micromechanical device which allows deflection of a reflective member upon 
activation of electrodes, such that the member returns to a known position 
may be used. 
Thus, although there has been described to this point a particular 
embodiment for a method and structure for a micromechanical optical 
switch, it is not intended that such specific references be considered as 
limitations upon the scope of this invention except in-so-far as set forth 
in the following claims.