Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-05-01
2001-01-16
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S290000
Reexamination Certificate
active
06175443
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to adaptive optics. More particulary, the present invention relates to electrically-controlled deformable mirrors.
BACKGROUND OF THE INVENTION
Electrically-controlled, micro-machined “mirrors” can be used to alter the path of an optical signal. Such mirrors are usually implemented as metallized layer of polysilicon or as a dielectric stack. Among other applications, such mirrors can be used to create reconfigurable optical networks wherein one or more optical signals from one or more source fibers are directed to any one of several destination fibers via operation of the mirror. Such an arrangement, wherein an optical element (e.g., a mirror) is adjusted, typically in response to a sensed condition, is commonly referred to as “adaptive optics.”
In one conventional adaptive optics arrangement, a reflective layer having a uniform thickness is suspended above an electrode. As a voltage is applied across the reflective layer and the electrode (hereinafter “actuation”), the reflective layer deforms. An optical signal incident on the reflective layer is directed to a different destination on reflection as a function of the deformed or undeformed shape of the reflective layer.
A simplified schematic of such an arrangement is depicted
FIG. 1
, wherein reflective layer or mirror
102
is suspended, via supports
104
, over electrode
106
. Both mirror
102
and electrode
106
are substantially parallel to substrate surface
108
. Optical fibers
110
,
112
and
114
are in optical communication with mirror
102
.
In the arrangement depicted in
FIG. 1
, the path that an optical signal follows upon reflection from mirror
102
is dictated by the shape of the mirror. That relationship is illustrated in FIGS.
2
a
and
2
b
. In FIGS.
2
a
and
2
b
, optical fibers
110
and
112
deliver respective optical signals
116
and
118
to mirror
102
. When the mirror is undeformed such that it has a flat form, as depicted in FIG.
2
a
, optical signals
116
and
118
delivered to mirror
102
from respective optical fibers
110
and
112
are returned to those optical fibers upon reflection. On the other hand, when mirror
102
is deformed such that it has a curved form, as depicted in FIG.
2
b
, optical signals
116
and
118
delivered to the mirror are reflected to optical fiber
114
, rather than to the source fibers
110
and
112
.
Mirror
102
is deformed by applying a voltage across the mirror and electrode
106
. The applied voltage generates an electrostatic force that causes mirror
102
to move towards electrode
106
. Since the ends of mirror
102
are immobilized, the mirror deforms in a characteristically parabolic shape. When the voltage is removed, the electrostatic force diminishes, and mirror
102
substantially returns to its flat, undeformed shape.
As is clear from the foregoing description of the arrangement depicted in
FIG. 1
, the path that an optical signal follows upon reflection from mirror
102
is dictated by the shape of the mirror. And, the shape of mirror
102
depends upon the mechanical response of the uniform-thickness reflective layer serving as the mirror. Thus, the optical and mechanical response or properties of the mirror are disadvantageously coupled (i.e., they are not independent of one another). Moreover, the mechanical response of such a uniform layer is difficult to precisely control. In view of the extremely severe tolerances required for directing optical signals among fibers, particularly single-mode fibers (ie., about 1 micron tolerance), the utility of such a device is limited.
A second conventional adaptive optics arrangement is a mirror array comprising a plurality of individually-controlled discrete mirror elements. The optical behavior of the mirror array is dictated by its surface features, which is a function of the state (e.g., orientation, shape, etc.) of the plurality of individual mirror elements comprising the array. Thus, by individually controlling the mirror elements through the action their associated actuators, the surface features of the array can be varied to obtain a desired optical response.
A variety of actuators can be used in such an arrangement. One type of actuator is depicted in
FIG. 3
, which shows a single mirror element
322
connected to actuator
326
.
Actuator
326
is operable to tilt mirror element
322
. In particular, support members
340
and torsion members
342
suspend mirror element
322
above substrate surface
328
. Electrodes
344
a
and
344
b
are individually and separately charged (voltage source not shown) to attract mirror element
322
. Torsion members
342
allow mirror element
322
to move through an angle, ±&thgr;. The position of mirror element
322
depends upon which of electrodes
344
a
or
344
b
is charged at a given moment. An optical signal (not shown) that is received by mirror element
322
is reflected to a different destination as a function of the tilt of that mirror element.
The aforedescribed mirror array substantially avoids the problematic coupled optical/mechanical response characteristic of the first arrangement. But, in avoiding that problem, other problems result. In particular, in the prior art mirror array, an actuator is required for each element of the array. The multiplicity of actuators in such an array significantly adds to its complexity and cost.
The art would thus benefit from adaptive optics in the form of a micro-machined mirror that avoids the optical/mechanical interdependence of the uniform reflective layer, and also avoids the multiple actuators of the conventional mirror array.
SUMMARY OF THE INVENTION
An article comprising a segmented reflective layer operable to alter the path of optical signals is disclosed. The segmented reflective layer comprises a plurality of mirror elements that are mechanically and electrically linked to one another and controlled via a single actuator.
In a “quiescent” (i.e., unactuated) state, the reflective layer typically assumes a flat shape. Upon actuation, such as may be caused by applying a voltage across the mirror elements and a nearby fixed electrode, the mirror elements move towards the electrode to a greater or lesser degree, thereby deforming the reflective layer. In the “actuated” state, the reflective layer assumes a characteristically concave-upward shape (relative to optically communicating optical fibers). The change in shape of the reflective layer is used to alter the path of optical signals incident thereon.
Each mirror element is advantageously mechanically and electrically linked to an adjacent mirror element via a resilient, electrically-conductive linking member. During actuation, the linking members deform rather than the mirror elements. Upon such deformation, the linking members store energy. When the actuating force is removed, the linking members release the stored energy, the reflective layer is restored to a substantially flat form.
In some embodiments, the mechanical response of the linking members is isotropic; in other embodiments, the mechanical response of the linking members are directionally or regionally varied. As such, the reflective layer can be designed to assume virtually any shape upon deformation.
By virtue of its structure, the present invention provides an article that advantageously avoids the drawbacks of conventional adaptive optics devices. In particular, since it is the linking members rather than the mirror elements that deform on actuation, the optical behavior and the mechanical behavior of the reflective layer are decoupled. And, since the individual mirror elements comprising the reflective layer are mechanically linked to one another, only a single actuator is required for deforming the reflective layer.
REFERENCES:
patent: 5016997 (1991-05-01), Bliss et al.
patent: 5844711 (1998-12-01), Long, Jr.
Y. A. Peter, E. Rochat, and H.P. Herzig; Micro-Opto-Mechanical Systems: Application in Pulsed Fiber Lasers and Optical switching; in Microelectronic Structures and MEMS for Optical Processin
Aksyuk Vladimir A.
Barber Bradley Paul
Bishop David J.
Gammel Peter L.
Giles C. Randy
Breyer Wayne S.
DeMont Jason Paul
DeMont & Breyer
Epps Georgia
Lucent Technologies - Inc.
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