Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-08-01
2003-11-11
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S572000, C359S573000, C359S231000
Reexamination Certificate
active
06646778
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an optical MEM device with movable ribbons for modulating light. More particularly, the present invention relates to an optical MEM device encapsulated within a dampening gas environment to reduce vibrations of the movable ribbons during operation.
BACKGROUND OF THE INVENTION
Optical MEM (micro-electro-mechanical) device have applications in display, print, optical and electrical technologies. One type of an optical MEM device is a grating light valve that is capable of modulating light by constructive and destructive interference of an incident light source. Exemplary grating light valves and methods for making grating light valves are disclosed in the U.S. Pat. Nos. 5,311,360, 5,841,579 and 5,808,797, issued to Bloom et al., the contents of which are hereby incorporated by reference.
SUMMARY OF THE INVENTION
Grating light valves of the instant invention generate the condition for constructive and destructive interference through a plurality of movable ribbons. The movable ribbons provide a first set of reflective surfaces that are movable relative to a second set of reflective surfaces. The second set of reflective surfaces are reflective surfaces on a substrate element or on a second set of ribbons. In operation, an incident light source having a wavelength &lgr; impinges on the first set of reflective surfaces and the second set of reflective surfaces. The movable ribbons are displaced towards or away from the second set of reflective surfaces by &lgr;/4, or a multiple thereof. The portion of light that is reflected from the first set of reflective surfaces and the portion of light that is reflected from the second set of reflective surfaces alternate between being in phase and being out of phase. Preferably, the first set of reflective surfaces and the second set of reflective surfaces are either in the same reflective plane or are separated &lgr;/2 for generating the condition for constructive interference.
FIG. 1
a
illustrates a grating light valve with plurality of movable ribbons
100
that are formed in a spatial relationship over a substrate
102
. Both the ribbons
100
and the regions of the substrate between the ribbons have reflective surfaces
104
and
106
. The reflective surfaces
104
and
106
are provided by coating the ribbons
100
and the substrate with a reflective material, such as an aluminum or silver. The height difference
103
between the reflective surfaces
104
and
106
on the ribbons
100
and the substrate
102
is n&lgr;/2 (where n is a whole number). When light having a wavelength &lgr; impinges on the complement of reflective surfaces
104
and
106
, the portion of light reflected from the surfaces
104
of the ribbons
100
will be in phase with the portion of light reflected from the surfaces
106
of the substrate
102
. This is because the portion of light which strikes the surfaces
104
of the substrate
102
will travel a distance &lgr;/2 farther than the portion of light striking the surfaces
104
of the ribbons
100
. Returning, the portion of light that is reflected from the surfaces
104
of the substrate
102
will travel an additional distance &lgr;/2 farther than the portion of light striking the surface
106
of the ribbons
100
, thus allowing the complement of reflective surfaces
104
to act as a mirror.
Referring to
FIG. 1
b,
in operation the ribbons
100
are displaced toward the substrate
102
by a distance
105
that is equal to &lgr;/4 or &lgr;/4 plus n&lgr;/2 (where n is a whole number) in order to switch from the conditions for constructive interference to the conditions for destructive interference. When light having a wavelength &lgr; impinges on the reflective surfaces
104
′ and
106
with the ribbons
100
′ in the down position, the portion of light reflected from the surfaces
104
′ will be out of phase, or partially out of phase, with the portion of light reflected from the surfaces
106
and some or all of the light will be diffracted. By alternating the ribbon between the positions shown in
FIG. 1
a
and
FIG. 1
b,
the light is modulated.
An alternative construction for a grating light valve is illustrated in the
FIGS. 2
a-b
. Referring to
FIG. 2
a,
the grating light valve has a plurality of ribbons
206
and
207
that are suspended by a distance
203
over a substrate element
202
. The ribbons
206
and
207
are provided with reflective surfaces
204
and
205
, respectively. The surface
208
of the substrate
202
may also be reflective. The first set of ribbons
206
and the second set of ribbons
207
are initially in the same reflective plane in the absence of an applied force. Preferably, the first set of ribbons
206
and the second set of ribbons
207
are suspended over the substrate by a distance
203
such that the distances
209
between the reflective surfaces
205
and
205
of the ribbons
206
and
207
and the reflective surface
208
of the substrate
202
corresponding to n &lgr;/2. Accordingly, the portions of light reflected from the surfaces
204
and
205
of the ribbons
206
and
207
and the reflective surface
208
of the substrate
202
with a wavelength &lgr; will all be in phase. The ribbons
206
and
207
are capable of being displaced relative to each other by a distance corresponding to a multiple of &lgr;/4 and thus switching between the conditions for constructive and destructive interference with an incident light source having a wavelength &lgr;.
In the
FIG. 2
b,
the second set of ribbons
207
is displaced by a distance
203
, corresponding to a multiple of &lgr;/4 of to the position
207
′. The portion of the light reflected from the surfaces
205
′ of the ribbons
207
will destructively interfere with the portion of the light reflected from the surfaces
204
of the ribbons
206
. While the
FIG. 1
b
and
FIG. 2
b
show ribbons touching the surface of the substrate, the instant invention is particularly useful in grating light valve designs where movable ribbons do not contact the substrate surface or where movable ribbons only partially contact the surface of the substrate. Accordingly,
FIGS. 1
a-b
and
FIGS. 2
a-b
are for illustrative purposes only and are not intended to limit the scope of the invention. Further, it is understood that the current invention is not limited to grating light valves and has applications for reducing vibrational oscillations in other micro machine devices with or without reflective surfaces.
FIG. 3
plots an idealized brightness response
107
of a grating light valve to an incident light source with a wavelength &lgr; when voltage
108
is applied across a selected set ribbons (active ribbons) and the underlying substrate of the grating light valve to alternate between the conditions for constructive and destructive interference. From the discussion above, the brightness will be at a maximum
111
when the ribbons are in the same reflective plane or separated by &lgr;/2, or a multiple of &lgr;/2, and the brightness will be at a minimum
111
when the ribbons are separated by &lgr;/4, or &lgr;/4 plus (n)&lgr;/2. Specifically, to operate the grating light valve, a voltage V
1
is applied across the active ribbons and the underlying substrate. At this point the active ribbons are in the constructive interference position and the maximum brightness
109
is observed. As the voltage is increased to V
2
, the active ribbons are moved to a destructive interference position and the minimum brightness
109
is observed. As the voltage is reduced, the active ribbons do return to their constructive interference position when V
1
is reached.
The rate (Volt/sec) at which voltage is applied to switch the ribbons of the grating light valve between the conditions for constructive and destructive interference is referred to as the switching rate, and is typically in the range of 4000 to 0.4 Volt
ano seconds. The frequency of at which the grating light valve is switched between the conditions for constructive and destructive interference is referre
Gudeman Chris
Shook James Gill
Dang Hung Xuan
Haverstock & Owens LLP
Silicon Light Machines
Tra Tuyen
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