Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2003-10-22
2004-12-28
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S298000, C359S230000
Reexamination Certificate
active
06836352
ABSTRACT:
TECHNICAL FIELD
The invention relates to the modulation of light beams and in particular, to modulating light using a light valve.
BACKGROUND
Spatial light modulators, also commonly referred to as light valves, can be applied in many different fields. One particular field in which these devices have made an impact is the printing industry. Light valves are used in computer-to-plate imaging devices for modulating the illumination produced by a laser in order to imagewise expose a printing plate. In the imagewise exposure of printing plates pixel size and resolution are important parameters. Computer-to-plate systems make great demands upon the performance of light valves. The limits on optical power handling, switching speed and resolution are continually under pressure due to the operational demands of the printing industry. The most common lasers used for plate imaging have near-infrared wavelengths.
Light valves, or linear and two-dimensional arrays of light valves, are typically employed to produce a large number of individually modulated light beams.
Another field that stands to benefit from this technology is that of optical communications where there is a need for devices that may be used to switch, modulate, or process light signals.
One particular subset of light valves operate by controlling the reflection of an incident light beam from a micro-miniature (MEMS) deformable mirror. The term MEMS (Micro-Electro-Mechanical Systems) describes technology that forms mechanical devices such as mirrors, actuators or sensors in a substrate. MEMS devices are typically formed by selectively etching a semiconductor substrate such as a silicon wafer. Prior art MEMS light valves can be generally divided into three types:
a. cantilever or hinged mirror type light valves which re-direct a light beam when the mirror is tilted. A well-known example in this category is the Digital Micromirror Device (DMD) developed by Texas Instruments of Dallas, Tex.;
b. membrane light valves where a flat membrane is deformed into a concave or spherical mirror, thus changing the focal properties of the light beam; and,
c. grating light valves which diffract the light by forming a periodic physical grating pattern in a reflective or transparent light valve substrate. A well-known example in this category is the Grating Light Valve developed by Silicon Light Machines of Sunnyvale, Calif. and described in Bloom, Proc. SPIE—Int. Soc. Opt. Eng. (USA) vol.3013 p.165-p.171.
Considerable effort has been invested in the development of MEMS light valves. Significant technical advances have been made, particularly in improving the fabrication processes to obtain better yields. However, a number of central limitations remain in respect of MEMS devices.
A major disadvantage of the hinged or cantilevered mirror type devices is the comparatively slow response time for mirrors any larger than a few square &mgr;m in area. These devices operate by tilting a small mirror to deflect an incident beam. Typically, response times are of the order of 10 microseconds. This is due to the low natural frequency of a cantilever mirror and the large deflection required to provide sufficient spatial separation between a deflected and un-deflected beam. Typical cantilever mirrors are between 5 and 10 microns long and require the tip to move between 1 and 5 microns in order to deflect the light through an angle of 10 degrees.
U.S. Pat. No. 4,441,791 to Hornbeck describes a membrane light valve. Membrane light valves have the advantage of somewhat faster response times. However, they are difficult to fabricate. The membrane is supported around its periphery making it difficult to form the cavity under the membrane by micromachining which is the most cost effective fabrication method for light valves.
FIGS. 1
a
,
1
b
and
1
c
schematically depict three prior art modes of operation of deformable mirror devices of the deflection type.
FIG. 1
a
hows a tilting mirror device having a rigid mirror
10
which remains essentially planar while it tilts about axis
12
, typically on torsion hinges (not shown).
FIG. 1
b
shows the simple cantilever type of elongate ribbon
14
, which has considerably greater length than width and flexes about a transverse axis
16
. Ribbon
14
is attached at one end to fixture
18
.
FIG. 1
c
shows a deformable mirror device of the type described in U.S. Pat. No. 5,311,360 to Bloom. This device has a ribbon
20
attached to fixtures
24
at ends
26
(one fixture not shown for the sake of clarity). Ribbon
20
can be flexed into a concave shape about axis
22
.
All of the movable mirror elements depicted in
FIGS. 1
a
,
1
b
and
1
c
share the problem of relatively low natural frequencies. This results in poor response times. The natural frequency of the element shown in
FIG. 1
c
may be improved by making the ribbon shorter but this makes the element more sensitive to the alignment of the incident light and requires increasingly higher voltage to actuate.
There remains a need for light valves that have faster response times.
SUMMARY OF INVENTION
The invention provides elongate deformable mirror elements. A deformable mirror element has a support pedestal and a one or more reflective wings extending laterally from the pedestal.
Further aspects of the invention and factors of specific embodiments of the invention are described below.
REFERENCES:
patent: 4229732 (1980-10-01), Hartstein et al.
patent: 4441791 (1984-04-01), Hornbeck
patent: 5172262 (1992-12-01), Hornbeck
patent: 5311360 (1994-05-01), Bloom et al.
patent: 5517359 (1996-05-01), Gelbart
patent: 5610757 (1997-03-01), Ji et al.
patent: 5661592 (1997-08-01), Bornstein et al.
patent: 5748172 (1998-05-01), Song et al.
patent: 5768009 (1998-06-01), Little
patent: 5867302 (1999-02-01), Fleming
patent: 5926309 (1999-07-01), Little
patent: 5999303 (1999-12-01), Drake
patent: 6025951 (2000-02-01), Swart et al.
patent: 6028689 (2000-02-01), Michalicek et al.
patent: 6307663 (2001-10-01), Kowarz
patent: 6445502 (2002-09-01), Islam et al.
patent: 2001/0028756 (2001-10-01), Flanders et al.
patent: 2002/0031305 (2002-03-01), Ticknor et al.
patent: 2003/0142383 (2003-07-01), Nanjyo et al.
Fitzpatrick Glen Arthur
Gelbart Daniel
Choi William
Creo Inc.
Epps Georgia
Owen Wiggs Green & Mutala
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