Title: Solidifiable tunable liquid microlens
Abstract: A microlens of the present invention may include a liquid droplet whose position and/or surface curvature may be changed (tuned), e.g., by selectively biasing one or more electrodes configured to said droplet. The droplet may then be solidified to fix a desired configuration (e.g., focal length) of the microlens. In one embodiment, the droplet has an optically curable liquid adhesive that is polymerized under exposure to UV light. Microlenses of the present invention may be used, for example, in optical devices to obtain and then maintain optimal coupling between various optical components.
Patent Number: 6,936,196 Issued on 08/30/2005 to Chandross, et al.
| Inventors:
|
Chandross; Edwin A. (Murray, NJ);
Kroupenkine; Timofei N. (Warren, NJ);
Yang; Shu (North Plainfield, NJ)
|
| Assignee:
|
Lucent Technologies Inc. (Murray Hill, NJ)
|
| Appl. No.:
|
096199 |
| Filed:
|
March 12, 2002 |
| Current U.S. Class: |
264/1.36; 359/665; 425/174.4 |
| Intern'l Class: |
B29D 011/00 |
| Field of Search: |
264/11,136,17,484
425/174.4,808
359/665
|
References Cited [Referenced By]
U.S. Patent Documents
| 3454686 | Jul., 1969 | Jones.
| |
| 3670130 | Jun., 1972 | Greenwood.
| |
| 4030813 | Jun., 1977 | Kohashi et al.
| |
| 4569575 | Feb., 1986 | Le Pesant et al.
| |
| 5486337 | Jan., 1996 | Ohkawa.
| |
| 5659330 | Aug., 1997 | Sheridon.
| |
| 6014259 | Jan., 2000 | Wohlstadter.
| |
| 6369954 | Apr., 2002 | Berge et al.
| |
| 6538823 | Mar., 2003 | Kroupenkine et al.
| |
| 6545815 | Apr., 2003 | Kroupenkine et al.
| |
| 6545816 | Apr., 2003 | Kroupenkine et al.
| |
| Foreign Patent Documents |
| 196 23 270 | Jan., 1998 | DE.
| |
| 2 769 375 | Apr., 1999 | FR.
| |
| WO 99/1845/6 | Apr., 1999 | FR.
| |
Other References
"Electrostatically Actuation of Liquid Droplets for Microreactor Application,"
by Masao Washizu, IEEE Transactions on Industry Applications, vol. 34, No. 4, Jul./Aug.
1998, pp. 732-737.
"Surface Profiles of Reflow Microlenses Under the Influence of Surface Tension
and Gravity," by Andreas Schilling Andreas et al., Opt. Eng.39(8) pp. 2171-2176,
Society of Photo-Optical Instrumentation Engineers, Aug. 2000.
"Variable Focal Length Microlenses," by L.G. Commander et al., Optice Communications
177, Apr. 15, 2000,pp. 157-170.
"Potential-Dependent Wetting of Aqueous Solutions on Self-Assembled Monolayers
Formed from 15-(Ferrocenylcarbonyl) pentadecanethiol on Gold," by Nicholas L. Abbott
and George M. Whitesides, American Chemical Society, Langmuir, vol. 10, No. 5,
1994 , pp. 1493-1497.
|
Primary Examiner: Vargot; Mathieu D.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
The subject matter of this application is related to that of (i) U.S. patent
application Ser. No. 09/884,605, filed Jun. 19, 2001, and entitled "Tunable Liquid
Microlens" and (ii) U.S. patent application Ser. No. 09/951,637, filed Sep. 13,
2001, and entitled "Tunable Liquid Microlens with Lubrication Assisted Electrowetting,"
both of which are incorporated herein by reference.
Claims
1. A method of making a lens, comprising the steps of:
(A) tuning a droplet comprising a solidifiable liquid on a substrate to a desired
configuration, wherein the tuning includes:
biasing of two or more electrodes insulated from said droplet and adapted to
control the position of said droplet; and
controlling the position of said droplet, the position of said droplet being
variable; and
(B) at least partially solidifying the liquid.
2. The method of claim 1, wherein the tuning further includes biasing of the
two or more electrodes with respect to an electrode, which is in contact with said droplet.
3. The method of claim 2, wherein said at least partially solidifying step comprises
the step of changing one or more biasing voltages applied to the electrodes.
4. The method of claim 3, wherein said at least partially solidifying step comprises
the step of removing the biasing voltages.
5. The method of claim 1, wherein said at least partially solidifying step comprises
the step of fully solidifying the liquid.
6. The method of claim 5, wherein said at least partially solidifying step comprises
the step of solidifying a peripheral portion of the droplet to form an enclosure
for inner portions of said droplet.
7. The method of claim 5, wherein said at least partially solidifying step comprises
the step of solidifying the liquid to the consistency of a gel.
8. The method of claim 1, wherein said at least partially solidifying step is
performed by applying a stimulus to the droplet.
9. The method of claim 8, wherein the stimulus comprises at least one of a temperature
change, electromagnetic radiation, and corpuscular radiation.
10. The method of claim 8, wherein:
for said tuning step, the solidifiable liquid comprises a mixture of a photopolymerizable
liquid and molten salt; and
for said at least partially solidifying step, the stimulus is ultra-violet radiation.
11. The method of claim 1, wherein said at least partially solidifying step is
performed by waiting a period of time.
12. The method of claim 1, wherein said tuning step comprises the steps of:
changing the surface curvature of the droplet; and
moving the droplet along the substrate.
13. The method of claim 1, wherein said tuning step comprises the step of offsetting
one or more biasing voltages applied to the one or more electrodes to compensate
for a volume change of the droplet during said at least partially solidifying step.
14. The method of claim 1, wherein the lens is part of an optical device comprising
two or more optical components and said tuning step comprises the step of optimizing
optical coupling between said two or more optical components.
15. The method of claim 1, wherein said tuning step comprises (i) biasing four
electrodes configured underneath the substrate and (ii) biasing an electrode in
contact with the droplet, wherein:
the substrate is an insulating substrate; and
each electrode is connected to a voltage source configured to independently apply
different voltages to each electrode.
16. An apparatus for making a lens, comprising:
(A) means for tuning a droplet comprising a solidifiable liquid on a substrate
to a desired configuration; wherein the means for tuning includes:
means for biasing of two or more electrodes insulated from said droplet and adapted
to control the position of said droplet; and
means for controlling the position of said droplet, the position of said droplet
being variable; and
(B) means for at least partially solidifying the liquid.
17. The method of claim 1, wherein the tuning further includes biasing of the
electrodes to control the shape of said droplet.
18. The method of claim 1, wherein change in the position of said droplet results
directly from electrostatic attraction between said droplet and the electrodes.
19. The apparatus of claim 16, wherein change in the position of said droplet
results directly from electrostatic attraction between said droplet and the electrodes.
20. A method of making a lens, comprising the steps of:
(A) tuning a droplet comprising a solidiflable liquid on a substrate to a desired
configuration, wherein the tuning includes:
biasing of one or more electrodes insulated from said droplet and adapted to
control the position of said droplet; and
controlling the position of said droplet, the position of said droplet being
variable, wherein change in the position of said droplet results directly from
electrostatic attraction between said droplet and at least one of the one or more
electrodes; and
(B) at least partially solidifying the liquid.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optics, and more particularly to microlenses.
2. Description of the Related Art
Several approaches may be used for implementing a tunable microlens. For
example, one known approach is to control the refractive index of a lens using
an electrostatic potential applied to that lens. Such lenses are typically referred
to as gradient index (GRIN) lenses. The range of tunability (e.g., of the focal
length) for GRIN lenses is governed primarily by the electro-optic coefficient
of the lens material. Unfortunately, electro-optic coefficients associated with
the typical materials used in GRIN lenses are relatively small. This fact results
in small optical path modulation and, therefore, necessitates the use of relatively
thick lenses and/or high electrostatic potentials. In addition, many electro-optic
materials display strong birefringence causing the properties of a GRIN lens to
be polarization dependent.
Another approach for implementing a tunable microlens is to mechanically
control the shape of the microlens using flexible elastic materials, such as transparent
polymers, for making the lens. A typical mechanically adjustable, flexible lens
has a wider range of tunability than a GRIN lens. However for operation, mechanically
adjustable lenses require external actuation devices, such as mechanical pumps,
that may be laborious and expensive to implement. For example, integrating actuation
devices into a two-dimensional array of tunable microlenses is particularly difficult.
Yet another approach for implementing a tunable microlens is disclosed in U.S.
Pat. No. 6,014,259 to Wohlstadter, issued Jan. 11, 2000, the teachings of which
are incorporated herein by reference. Wohlstadter teaches a variable-focus liquid
lens controlled through self-assembled monolayers (SAMS) adsorbed on a substrate.
However, one problem with such lenses is the limited choice of complementary materials
that can be used for a SAM/substrate combination. Another problem is a strong hysteresis
typically exhibited by SAM-controlled lenses. The hysteresis may result, for example,
in failure of a lens to return to the original shape when the tuning voltage is
disconnected. Furthermore, none of the above-described microlenses, including GRIN
and mechanically adjustable lenses, allow for simultaneous lens position adjustment
and focal length tuning.
SUMMARY OF THE INVENTION
U.S. patent application Ser. No. 09/884,605, filed Jun. 19, 2001, and entitled
"Tunable Liquid Microlens," describes a tunable liquid microlens that may include
a liquid droplet whose position and/or surface curvature may be changed, e.g.,
by selectively biasing one or more electrodes configured to said droplet. U.S.
patent application Ser. No. 09/951,637, filed Sep. 13, 2001, and entitled "Tunable
Liquid Microlens with Lubrication Assisted Electrowetting," describes a method
of tuning a tunable microlens using a lubrication layer. The present invention
provides further improvements of the tunable microlens and methods of tuning and
making the same disclosed in those patent applications.
The present invention provide a solidifiable tunable liquid microlens. A microlens
of the present invention may include a liquid droplet whose position and/or surface
curvature may be changed, i.e., tuned, e.g., by selectively biasing one or more
electrodes configured to said droplet. The droplet may then be solidified to fix
a desired configuration, e.g., focal length and position, of the microlens. Solidification
may be induced or may occur through the passage of time. In one embodiment, the
droplet comprises an optically curable liquid adhesive that is polymerized under
exposure to UV light. Microlenses of the present invention may be used, for example,
in optical devices to obtain and then maintain optimal coupling between various
optical components.
According to one embodiment of the present invention, a lens may be made
by: (A) tuning a droplet including a solidifiable liquid on a substrate to a desired
configuration; and (B) at least partially solidifying the liquid.
According to another embodiment of the present invention, a microlens includes:
(a) a substrate; (b) an at least partially solidified droplet disposed on the substrate;
(c) at least one electrode configured to the substrate; and (d) at least one electrode
configured to the droplet.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 illustrates various parameters characterizing a liquid microlens;
FIG. 2 illustrates the electrowetting phenomenon;
FIGS. 3A-B show a side and top view of a tunable liquid microlens according
to one embodiment of the present invention;
FIGS. 4A-B illustrate exemplary shape changes of the tunable liquid microlens
of FIG. 3 due to the biasing of the electrodes;
FIG. 5 illustrates an exemplary optical system, in which a microlens of the
present invention may be used; and
FIG. 6 shows a method that may be used for fixing a desired configuration of
a tunable microlens of the present invention.
DETAILED DESCRIPTION
Reference herein to "one embodiment" or "an embodiment" means that a particular
feature, structure, or characteristic described in connection with the embodiment
can be included in at least one embodiment of the invention. The appearances of
the phrase "in one embodiment" in various places in the specification are not necessarily
all referring to the same embodiment, nor are separate or alternative embodiments
mutually exclusive of other embodiments.
Liquid Microlenses and the Electrowetting Phenomenon
Before embodiments of the present invention are described in detail, a brief
general description of liquid microlenses and the electrowetting phenomenon is provided.
FIG. 1 shows a liquid microlens
100, comprising a small droplet
112
of a liquid, such as water, typically (but not necessarily) with a diameter from
several micrometers to several millimeters. Droplet
112 is disposed on a
substrate
114. Substrate
114 is typically hydrophobic or has a hydrophobic
coating. Depending on the application, the liquid and substrate might only be transparent
to light having wavelengths within a selected range. A beam of light
116
impinging onto microlens
100 is focused at a focal point
118 that
is a focal length "ƒ" away from the contact plane between droplet
112
and substrate
114.
The contact angle "θ" between droplet
112 and substrate
114
is determined by interfacial tension forces (or the interfacial energy associated
with these forces) characterized by surface tension coefficients "γ", typically
measured in milli-Newtons per meter (mN/m). As used herein, γ
S-V
is the surface tension coefficient between substrate
114 and the air, gas,
or liquid (hereafter referred to as "vapor") that surrounds microlens
100;
γ
L-V is the surface tension coefficient between droplet
112
and the vapor, and γ
S-L is the surface tension coefficient between
substrate
114 and droplet
112. Then angle θ may be determined
using Equation (1):
##EQU1##
Angle θ and the volume of droplet
112 (Volume) determine the radius
(R) of surface curvature of droplet
112 according to Equation (2) as follows:
##EQU2##
The focal length ƒ of droplet
112 is a function of R and the refractive
indices, n
L and n
v, of droplet
112 and the vapor,
respectively. Said focal length ƒ may be calculated using Equation (3):
Since substrate
114 has little effect on the focal length of microlens
100 (due to the substrate's substantially planar geometry), Equation (3)
may also be used to calculate the focal length of microlens
100. As is clear
from Equations (2) and (3), the focal length of microlens
100 is a function
of θ.
FIG. 2 demonstrates how the electrowetting phenomenon may be used to reversibly
change angle θ and, therefore, the focal length of a liquid microlens. FIG.
2 shows a tunable liquid microlens
200 comprising a droplet
212 of
a conducting liquid disposed on an insulating layer
214, which layer has
a thickness "d" and dielectric constant "ε
r". Microlens
200
further comprises (i) an electrode
216 positioned below layer
214
and insulated from droplet
212 by said layer and (ii) an electrode
218
immersed into droplet
212. Electrodes
216 and
218 are connected
to a variable voltage source
220. Droplet
212, substrate
214,
and electrodes
216 and
218 may be, for example, a water droplet,
a teflon/parylene slide, a copper film, and a platinum wire, respectively.
When no voltage difference is applied to electrodes
216 and
218,
droplet
212 maintains the shape shown by solid line
212-
1
in FIG.
2. Shape
212-
1 is defined by the volume of droplet
212 and contact angle θ
1, where θ
1, in
turn, is determined by the surface tension coefficients as explained above. The
shape shown by dashed line
212-
2 illustrates that droplet
212
spreads over layer
214 when a voltage "V" is applied by source
220
to electrodes
216 and
218. Depending on the thickness of layer
214
and the materials involved, the applied voltage may range from several volts to
several hundred volts. In the example shown in FIG. 2, the value of θ decreases
from θ
1 to θ
2. The degree of spreading (e.g.,
characterized by the contact angle) is a function of V (i.e., θ(V)) and can
be calculated using Equation (4):
##EQU3##
where θ(V=0) is the contact angle between layer
214 and droplet
212 when no voltage is applied between electrodes
216 and
218
(i.e., θ
1) and ε
0=8.85×10
-12 F/m
is the permittivity of vacuum. It is clear from Equation (4) that the degree of
spreading depends on the absolute value of V and does not depend on the polarity.
Tunable Liquid Microlens
FIGS. 3A and 3B show side and top views, respectively, of a tunable liquid
microlens
300 according to one embodiment of the present invention. Microlens
300 comprises a droplet
312 of a conductive liquid disposed on a
first surface of a dielectric insulating layer
314. In one embodiment, layer
314 may be, for example, a polyimide layer coated with a fluorinated polymer
(e.g., a highly fluorinated hydrocarbon). Layer
314 preferably provides
a desired value of the contact angle, low contact angle hysteresis, and has a dielectric
breakdown strength appropriate for the intended application of voltages.
Microlens
300 further comprises a plurality of electrodes
306,
e.g., electrodes
306a-
306d, and a droplet electrode
308. Electrodes
306 are electrically insulated from droplet
312
by layer
314, whereas electrode
308 is in contact with droplet
312.
In one embodiment, electrodes
306 may be deposited onto a second surface
of layer
314. Each electrode
306 and
308 is coupled to a variable
voltage source (not shown) configured to apply respective voltages V
1-V
4
and V
0 to said electrodes. Microlens
300 may also include an
optional supporting substrate
310 configured to support electrodes
306
and layer
314.
FIG. 3B illustrates an exemplary configuration for electrodes
306 according
to one embodiment of the present invention. In the embodiment shown in FIG. 3B,
four electrodes
306a-
306d are used. In different embodiments,
a different number, as well as pattern and/or shape, of electrodes
306 and
308 may be utilized in microlens
300. Furthermore, in one embodiment,
electrodes
306 and
308 and substrate
310 may be, for example,
gold, platinum, and glass, respectively. In other embodiments, other suitable materials
may be used. Additional embodiments for a tunable liquid microlens are disclosed
in related U.S. patent application Ser. No. 09/884,605, filed Jun. 19, 2001, and
entitled "Tunable Liquid Microlens."
FIGS. 4A and 4B illustrate how the shape and/or position of droplet
312
of microlens
300 can be changed (tuned) using biasing of electrodes
306
and
308. When no or equal voltages (i.e., V
1=V
2=V
3=V
4are
applied to electrodes
306 and
308, droplet
312 is centered
relative to electrodes
306, e.g., as shown in FIG.
3B. As explained
above, the volume of droplet
312 and contact angle θ determine the
droplet's shape in accordance with Equations (1)-(3). Referring now to FIG. 4A,
if equal voltages are applied to electrodes
306 and a different voltage
is applied to electrode
308 (i.e., V
1=V
2=V
3=V
4V≠V
0),
then droplet
312 spreads equally within quadrants I-IV as shown by the dashed
line in FIG.
4A. In so doing, the value of angle θ is reduced whereas
the focal length of microlens
300 is increased.
FIG. 4B illustrates that the lateral position of droplet
312 along the
X- and Y-axes can be changed (tuned) using differential biasing of electrodes
306
and
308. For example, by applying the following exemplary pattern of voltages:
V
1=V
3=V
042, droplet
312 is moved toward the higher voltage electrode 306b in quadrant
II as shown by the dashed line in FIG. 4B. By applying a different pattern
of voltages to the electrodes, droplet 312 can be steered to different positions
and/or shapes within quadrants I-IV. Change in the position of droplet 312
results in a corresponding movement of the focal point of microlens 300.
It should be apparent from the above examples that one can change any one of
or
both the contact angle and position of droplet 312 by applying various combinations
of voltages to electrodes 306 and 308. Therefore, microlens 300
is tunable such that its focal point can move in three dimensions, i.e., along
the Z-axis by changing the contact angle (and therefore the focal length) and along
the X- and Y-axes by laterally steering the droplet within quadrants I-IV.
FIG. 5 illustrates an exemplary optical system 500, in which microlens
300 may be used. In addition to microlens 300, system 500
comprises an optical signal transmitter 502 and an optical signal receiver
504. In one embodiment, transmitter 502 and receiver 504 may
be a laser and photodetector, respectively. Microlens 300 is configured
between transmitter 502 and receiver 504 to achieve optimal optical
coupling between the two. In the example shown in FIG. 5, a beam of light emitted
from transmitter 502 is diverging and, as such, will be focused behind focal
plane 506 of microlens 300. To obtain optimal coupling, focal point
508 of microlens 300 is moved along the X-, Y-, and/or Z-axes as
described above, e.g., by selectively biasing the electrodes of microlens 300
until maximum power is detected at receiver 504.
Using a tunable microlens, such as microlens 300, in an optical device
that requires alignment may be advantageous compared to other alignment/tuning
techniques. For example, one commonly used method of alignment is to physically
move optical components until optimal coupling is achieved. This method may be
slow and expensive as it involves manual labor of a qualified technician. By including
one or more tunable liquid microlenses of the present invention into an optical
device that needs to be aligned, the amount of such labor may be significantly
reduced or, in some instances, eliminated.
One of ordinary skill in the art will realize that tunable microlenses, such
as microlens 300, may be utilized in various optical and/or optoelectronic
applications. However, in many such applications, it is preferable to maintain
an optimal configuration for a long period of time or, quite often, for the entire
application life of the device. In such cases, it may be advantageous to "disable"
the tunability feature of a tunable microlens after the optimal configuration for
the device has been obtained.
A desired configuration of microlens 300 can be fixed, e.g., by maintaining
the voltages applied to electrodes 306 and 308. However, in some
applications, it may not be feasible to incorporate a suitable voltage source to
maintain the voltages, e.g., due to size constraints. Therefore, other approaches
to fixing different configurations of a tunable microlens are desirable. Embodiments
of the present invention described hereafter are directed, e.g., to a method of
fixing a configuration of a tunable liquid microlens, such as microlens 300,
without continuous application of voltages.
Solidifiable Tunable Liquid Microlens
Different conductive liquids may be used in a tunable liquid microlens,
such as microlens 300. In one embodiment, droplet 312 of microlens
300 may be an inherently conductive liquid, such as organic molten salts
(e.g., 1-ethyl-3-methyl-1H imidazolium tetrafluoroborate or 1-ethyl 3-methyl-1H-imi
trifluoromethanesulfonate). In a different embodiment, the liquid of droplet 312
may be made conductive, e.g., through the use of various additives. Typical examples
of the latter liquids are aqueous solutions of inorganic salts (e.g., K2SO4,
NaCl, KClO4, etc.) or organic solutions of (i) organic molten salts
(e.g., those given above) or (ii) other soluble organic salts (e.g., tetralkylammonium
salts of various acids, such as toluenesulfonic acid, fluorinated aliphatic or
aromatic acids, etc.). Other examples of usable liquids can be found in related
U.S. patent application Nos. 09/884,605, filed Jun. 19, 2001, and 09/951,637, filed
Sep. 13, 2001.
In general, liquids used in tunable microlenses may remain liquid throughout
the
life of the lens. Therefore, a droplet (e.g., droplet 212 of microlens 200
of FIG. 2) will typically revert to its initial shape (e.g., shape 212-1)
once the voltage source (e.g., source 220) is disconnected. According to
the embodiments of the present invention described hereafter, a tunable liquid
microlens, e.g., microlens 300, can be configured to fix its configuration
(e.g., a focal length and/or lateral position of droplet 312) using solidifiable liquids.
In one embodiment of the present invention, droplet 312 of microlens 300
comprises a photopolymerizable liquid. Such liquid can be obtained, e.g., by mixing
a Norland Optical Adhesive "NOA-61" (manufactured and distributed by Norland Products
Inc. of Cranbury, N.J.) with 0.01 wt. % of molten salt (e.g., 1-ethyl-3-methyl-1H
imidazolium tetrafluoroborate, available from Sigma-Aldrich Corporation of St.
Louis, Mo.). Different suitable optically curable liquids optionally mixed with
different conductive additives in different proportions may also be used in droplet
312 of microlens 300. In a preferred embodiment, such optically curable
liquid transmits light within a selected range of wavelengths in both the liquid
and solidified form.
For example, in one embodiment of the present invention, an optically curable
liquid may be obtained using a liquid epoxy monomer (or a mixture of such monomers)
and an "onium salt" photo-acid generator. Epoxy monomers may be chosen such that
they can undergo acid-catalyzed polymerization. The onium salt confers electrical
conductivity to the liquid and serves as an initiator for the polymerization. In
another embodiment, an optically curable liquid may comprise a vinyl monomer (or
a mixture of such monomers) and a corresponding initiator. The onium salt may serve
as an initiator for vinyl polymerization because it also facilitates free radical
formation. Therefore, mixtures of epoxy and vinyl monomers may be co-polymerized
using the dual (acid and free radical) initiating action of the onium salt. A programmed
temperature treatment may be used to enhance the degree of polymerization (which
is advantageous for long-term material stability) after a desirable shape of the
microlens has been fixed by initial solidification.
FIG. 6 shows an exemplary method 600 that may be used to fix a configuration
of a tunable liquid microlens, e.g., microlens 300, according to one embodiment
of the present invention. In step 602 of method 600, microlens 300
is configured with droplet 312 of a solidifiable liquid, e.g., an NOA-61/molten
salt mixture. In step 604, microlens 300 is tuned to a desired configuration,
e.g., using the voltages applied to electrodes 306 and 308. If microlens
300 is part of an optical device, such as system 500 of FIG. 5, step
604 may be performed by interactively monitoring the performance of that
optical device, e.g., the coupling efficiency between transmitter 502 and
receiver 504. In step 606, the desired configuration of the microlens
is fixed by solidifying the liquid in droplet 312. In one implementation
in which microlens 300 is configured with the mentioned NOA-61/molten salt
mixture, step 606 may be accomplished by subjecting droplet 312 to
UV radiation, e.g., the 365-nm spectral line of a mercury lamp. In other implementations,
different stimuli may be applied to droplet 312 to solidify it. After droplet
312 has been solidified, the voltages are removed from electrodes 306
and 308 in step 608 and microlens 300 may be used as a regular
solid lens.
Depending on the particular liquid used in droplet 312, the stimulus
applied to the droplet in step 606 of method 600 may be one or more
of the following: (1) change of temperature (heating and/or cooling); (2) electromagnetic
radiation (e.g., microwave, UV, or IR); (3) corpuscular radiation (e.g., β-
or neutron); and/or (4) time. For example in one embodiment, the material of droplet
312 may be such that it undergoes a liquid-to-solid phase transition in
a suitable temperature range. Then steps 602 and 604 of method 600
may be performed at an elevated temperature, while step 606 is accomplished
by dropping the temperature to below the phase transition point to solidify droplet
312. In a different embodiment, the material of droplet 312 may be
a relatively slow-curing epoxy resin. Then steps 602 and 604 of method
600 may be performed while the resin is in a liquid state, while step 606
is accomplished by simply waiting a sufficient amount of time for the resin to polymerize.
In addition, the solidification of droplet 312 carried in step 606
of method 600 does not need to be complete or uniform. For example in one
embodiment, only the periphery of droplet 312 is solidified to form a shell-like
enclosure for the inner regions of the droplet, which regions may include a fluid.
In other embodiments, after step 606, the material of droplet 312
may have the consistency of a gel.
In some embodiments of the present invention, droplet 312 may change its
volume, e.g., shrink by about 10-20%, during step 606 of method 600.
To compensate for the shrinkage, step 604 of method 600 may further
include a step of offsetting the voltages applied to electrodes 306 and
308 by appropriate values. In a preferred implementation, the offset values
are chosen in such a manner as to have the resulting configuration of microlens
300 (e.g., the focal length and/or lateral position of droplet 312
after the shrinkage in step 606) to correspond to the desired configuration.
Furthermore, the voltages at electrodes 306 and/or 308
need not be kept constant during step 606 of method 600. For example,
one or more voltages may be changed during step 606. Alternatively, step
608 may be performed after partially solidifying the liquid in step 606.
Then step 606 may be carried out to completion.
While this invention has been described with reference to illustrative embodiments,
this description is not intended to be construed in a limiting sense. Various modifications
of the described embodiments, as well as other embodiments of the invention, which
are apparent to persons skilled in the art to which the invention pertains are
deemed to lie within the principle and scope of the invention as expressed in the
following claims.
Although the steps in the following method claims, if any, are recited in
a particular sequence with corresponding labeling, unless the claim recitations
otherwise imply a particular sequence for implementing some or all of those steps,
those steps are not necessarily intended to be limited to being implemented in
that particular sequence.
*
