A light control device is formed by ferroelectric material and N electrodes positioned adjacent thereto to define an N-sided regular polygonal region or circular region there between where N is a multiple of four

Choi, Sang H.

Elliott, Jr., James R.

Kim, Jae-Woo

King, Glen C.

Park, Yeonjoon

NASA Technical Reports Server

(12) United States Patent (io) Patent No.: US 7,379,231 B2 
Park et al. (45) Date of Patent: May 27,2008 
(54) FERROELECTRIC LIGHT CONTROL 
DEVICE 
(75) Inventors: Yeonjoon Park, Yorktown, VA (US); 
Sang H. Choi, Poquoson, VA (US); 
Glen C. King, Yorktown, VA (US); 
Jae-Woo Kim, Newport News, VA 
(US); James R. Elliott, Jr., Yorktown, 
VA (US) 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, DC (US) 
Subject to any disclaimer, the term of this 
patent is extended or adjusted under 35 
U.S.C. 154(b) by 64 days. 
(73) Assignee: The United States of America as 
( * ) Notice: 
(21) Appl. No.: 11/470,771 
(22) Filed: Sep. 7, 2006 
(65) Prior Publication Data 
US 200810074723 A1 Mar. 27, 2008 
(51) Int. C1. 
G02F 1/00 (2006.01) 
G02F 1/03 (2006.01) 
14A 
14C 
(52) U.S. C1. ....................................... 359/321; 3591245 
(58) Field of Classification Search ................ 3491133, 
3491171; 3591248, 251, 252, 254, 255, 256, 
3591321, 322; 38512, 140 
See application file for complete search history. 
References Cited 
U.S. PATENT DOCUMENTS 
(56) 
3,666,666 A * 511912 Haertling ............. 252162.9 PZ 
* cited by examiner 
Primary Examiner-David N Spector 
(74) Attorney, Agent, or Firm-Linda B. Blackburn; Barry 
V. Gibbens 
ABSTRACT (57) 
A light control device is formed by ferroelectric material and 
N electrodes positioned adjacent thereto to define an N-sided 
regular polygonal region or circular region therebetween 
where N is a multiple of four. 
13 Claims, 6 Drawing Sheets 
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dipole moment and the resulting re-orientation of its non- 
circular refractive index ellipsoid; 
FIG. 3A is a schematic view of the light control device of 
FIG. 1 coupled to an electrical energy source that applies 
5 voltage levels thereto in accordance with an embodiment of 
the present invention; 
FIG. 3B is a schematic view of the light control device of 
FIG. 1 coupled to an electrical energy source that applies 
voltage levels thereto in accordance with another embodi- 
FIG. 3C is a schematic view of the light control device of 
FIG. 1 coupled to an electrical energy source that applies 
voltage levels thereto in accordance with another embodi- 
ment of the present invention; 
FIG. 3D is a schematic view of the light control device of 
FIG. 1 coupled to an electrical energy source that applies 
voltage levels thereto in accordance with another embodi- 
ment of the present invention; 
FIG. 4 is a schematic view of an array of single-element 
20 light control devices in accordance with another embodi- 
ment of the present invention; 
FIG. 5 is a schematic view of a single-element light 
control device having an octagonal electrode arrangement in 
accordance with another embodiment of the present inven- 
FIG. 6 is a schematic view of a single-element light 
control device having a circular electrode arrangement in 
accordance with another embodiment of the present inven- 
tion. 
i o  ment of the present invention; 
15 
25 tion; and 
30 
DETAILED DESCRIPTION OF THE 
INVENTION 
1 
FERROELECTRIC LIGHT CONTROL 
DEVICE 
ORIGIN OF THE INVENTION 
The invention was made in part by employees of the 
United States Government and may be manufactured and 
used by or for the Government of the United States of 
America for governmental purposes without the payment of 
any royalties thereon or therefor. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to light control devices. More 
specifically, the invention is a solid-state light control device 
using ferroelectric material. 
2. Description of the Related Art 
Light control is conventionally achieved with one or more 
geometric optical components such as lenses, mirrors, polar- 
izers, beamsplitters, and gratings. Frequently, some type of 
motorized control is coupled to the optical components in 
order to adjust light control attributes of the optical com- 
ponents). Such motorized control can include conventional 
motoriactuators and “micro-electro-mechanical systems” 
(MEMS). However, motorized light control devices are 
sensitive to vibration and acceleration effects. Further, the 
time required to adjust conventional optical components 
may be too slow for some applications. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to 
provide a light control device. 
Another object of the present invention is to provide a 
light control device that is insensitive to vibration andor 
acceleration effects. 
Another object of the present invention is to provide a 
light control device whose light control attributes are readily 
changed. 
Other objects and advantages of the present invention will 
become more obvious hereinafter in the specification and 
drawings. 
In accordance with the present invention, a light control 
device is formed by at least one multi-layer element defined 
by a layer of ferroelectric material and a layer of electrodes. 
The layer of electrodes comprises N electrodes electrically 
isolated from one another and positioned to define an 
N-sided regular polygonal region or circular region therebe- 
tween where N is a multiple of 4. The electrodes are used to 
establish an electric field orientation adjacent to the polygo- 
nal region. The electric field orientation and the thickness of 
the ferroelectric material define optical transmission prop- 
erties for the polygonal or circular region of the ferroelectric 
material. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a schematic view of a single-element light 
control device in accordance with an embodiment of the 
present invention; 
FIG. 2A is a graphic depiction of a ferroelectric material 
crystal structure and its non-circular refractive index ellip- 
soid; 
FIG. 2B is a graphic depiction of the ferroelectric material 
crystal structure in an electric field that changes the crystal’s 
Referring now to the drawings and more particularly to 
35 FIG. 1, a single-element light control device in accordance 
with an embodiment of the present invention is shown and 
is referred generally by numeral 10. Light control device 10 
is a solid state device with no moving parts that can be used 
in a wide variety of applications, the choice of which is not 
Light control device 10 is a multi-layer device with the 
primary optical element being a layer 12 of ferroelectric 
material. Typically, layer 12 is of constant thickness in at 
least the region thereof (e.g., region 18 in the illustrated 
45 example as will be explained further below) that will be 
exposed to light that is to be controlled. Suitable ferroelec- 
tric materials include, but are not limited to, barium titanate 
(BaTiO,), strontium barium titanate (SrBaTiO,), lithium 
niobate (LiNbO,), and potassium dihydrogen phosphate 
50 (KDP). These materials are suitable due to their relatively 
strong ferroelectricity where a permanent electric field 
polarization and hysteresis can be induced by an electric 
field. That is, when these materials are immediately adjacent 
to an electric field, the material’s crystal domain structure 
55 changes to become uniquely polarized with a permanent 
electric dipole moment. This situation will be explained with 
the aid of FIGS. 2A and 2B. 
FIG. 2A illustrates a crystal structure 100 of an exemplary 
ferroelectric material and its associated index of refraction 
60 ellipsoid 200. Crystal structure 100 has its electric dipole 
moment indicated by arrow 102. Since ferroelectric mate- 
rials have a similar crystal structure to that of anisotropic 
materials, ferroelectric materials exhibit birefringence in 
accordance with differing ordinary (no) and extraordinary 
65 (ne) indexes of refraction. In this example, the magnitude of 
these indexes define non-circular index ellipsoid 200 with 
the extraordinary axis 200A of ellipsoid 200 being aligned 
40 a limitation of the present invention. 
US 7,379,231 B2 
3 
with dipole moment 102 while the ordinary axes 2003 and 
200C are orthogonal to one another and extraordinary axis 
200A. In general, the direction and magnitude of the ordi- 
nary axis and extraordinary axis are determined by solving 
the electro-optic tensor of the ferroelectric material using the 
applied electric field’s strength and direction. 
When light enters a material with these properties, the 
light’s photons, whose polarization is parallel to ordinary 
axes 200B and 200C, are subject to refraction governed by 
index no, while the photons whose polarization is parallel to 
extraordinary axis 200A are subject to refraction governed 
by index ne. The photons with intermediate polarization 
directions are decomposed into two vector components 
along the slow and fast optical axes according to their angles 
with the ordinary and extraordinary optical axes. For 
example, BaTiO, has an ordinary index of refraction 
n,=2.4727 and an extraordinary index of refraction 
n,=2.4114 when the light has a wavelength of 532 nanom- 
eters. 
FIG. 2B illustrates what happens to the crystal’s dipole 
moment 102 when exposed to an immediately adjacent 
electric field E (“E-field”). For example, when the E-field is 
provided as shown, the orientation of dipole moment 102 
and extraordinary axis 200A are re-oriented to be aligned 
with the E-field. As a result, the way that the material will 
refract incoming light photons will change accordingly. In 
general, the response of the index ellipsoid will be deter- 
mined by the components of the ferroelectric material’s 
electro-optic tensor. 
Referring again to FIG. 1, light control device 10 takes 
advantage of these properties of ferroelectric materials by 
providing a number of electrodes (i.e., four are shown in the 
illustrated example) 14A-14D adjacent to and typically on 
layer 12. More specifically, electrodes 14A-14D are posi- 
tioned on a planar surface 12A of two major opposing planar 
surfaces 12M12B of layer 12 as shown. Although not 
required (as evidenced by its dashed line inclusion in light 
control device lo), an optical material layer 16 can be 
positioned adjacent to the other major planar surface 12B. 
Optical material layer 16 could be a transparent material or 
a reflective material depending on the application require- 
ments. 
Electrodes 14A-14D can be coupled to layer 12 in ways 
that would be well understood in the art. In the illustrated 
embodiment, electrodes 14A-14D are (i) spaced apart from 
one another such that they are electrically isolated from one 
another, and (ii) shaped to define a square region (referred by 
dashed line box 18) therebetween. Region 18 forms the 
optical transmission region of light control device 10. Light 
impinging on region 18 is refracted in accordance with the 
established optical properties of layer 12. The refracted light 
can then be transmitted or reflected depending on the 
presence or type of layer 16. 
To establish or change the birefringence of layer 12, 
electrodes 14A-14D are coupled to an electric voltage 
source in a way that creates an electric field orientation 
between electrodes 14A-14D adjacent to layer 12 to thereby 
establishichange the ferroelectric material’s dipole moment 
orientation and its associated refractive index ellipsoid. 
Light control device 10 can retain its optical properties after 
the applied electric field has been removed due to the 
hysteresis of ferroelectric material layer 12. These properties 
can be renewed or changed as needed by application of the 
appropriate electric voltage. By way of example, several 
embodiments of possible electric field orientations are 
shown in FIGS. 3A-3D where an electric voltage source 20 
is coupled to electrodes 14A-14D in each embodiment. The 
4 
relative voltage levels are indicated on electrodes 14A-14D 
where V, indicates a positive voltage, V- indicates a nega- 
tive voltage, and V, indicates an intermediate voltage 
between V, and V-. The resulting F-field orientation is 
The advantages of the present invention are numerous. 
The solid-state light control device has no moving parts and 
is readily adjustable via application of electrical energy. The 
device can be sizedishaped for a variety of applications. The 
i o  thickness of the ferroelectric material layer can be matched 
to application requirements. For example, a quarter wave 
plate can be constructed by making the thickness of the 
ferroelectric material layer satisfy the relationship: 
5 shown in each example. 
Thickness=N*p(4* ( i z -nJ)]  
15 
where N is an odd number and h is the wavelength of light 
that will impinge on the light control device. 
Although the invention has been described relative to a 
specific embodiment thereof, there are numerous variations 
2o and modifications that will be readily apparent to those 
skilled in the art in light of the above teachings. For 
example, a number of the above-described single-element 
light control devices 10 can be arranged in a two-dimen- 
sional array as illustrated in FIG. 4. For clarity of illustra- 
25 tion, the electric voltage source(s) are not shown. However, 
it will be readily apparent to one of ordinary skill in the art 
that each light control device 10 could be uniquely designed 
and controlled to tailor the output of the array. 
Furthermore, the present invention is not limited to the 
30 construction of light control devices having square optically 
operative regions (i.e., region 18). In general, the optically 
operative region of the ferroelectric material should be a 
regular polygonal region having N equal sides where N is a 
multiple of four. Accordingly, FIG. 5 illustrates another light 
35 device 30 having ferroelectric material layer 32 and eight 
electrodes 34A-34H arranged to define an octagonal region 
38. The precision of the E-field orientation increases with N. 
Still further, the optically operative region of the ferro- 
electric material could be circular as governed by the shapes 
40 of the spatially-separated electrodes. Accordingly, FIG. 6 
illustrates another light device 40 having ferroelectric mate- 
rial layer 42 and, for example, eight electrodes 44A-44H 
arranged to define a circular region 48. It is therefore to be 
understood that, within the scope of the appended claims, 
45 the invention may be practiced other than as specifically 
described. 
What is claimed as new and desired to be secured by 
Letters Patent of the United States is: 
5o The invention claimed is: 
1. A light control device, comprising: 
a layer of ferroelectric material having first and second 
a plurality of electrodes positioned adjacent to said first 
55 planar surface and electrically isolated from one 
another to define an N-sided region therebetween 
where N is a multiple of 4. 
2. A light control device as in claim 1 further comprising 
a layer of transparent material adjacent to said second planar 
3. A light control device as in claim 1 further comprising 
a layer of reflective material adjacent to said second planar 
surface. 
4. A light control device as in claim 1 further comprising 
65 means for applying electrical energy to said electrodes in 
order to establish a dipole moment orientation for said 
region of said ferroelectric material. 
planar surfaces opposing one another; and 
60 surface. 
US 7,379,231 B2 
5 6 
5. A light control device as in claim 1 wherein said layer 
of ferroelectric material is of constant thickness. 
6. A light control device as in claim 1 wherein said region 
comprises a regularly-shaped polygon. 
7. A light control device comprising at least one multi- 5 
layer element defined by a layer of ferroelectric material and 
material, said laver of electrodes comm-isine N electrodes 
N electrodes to control dipole moment orientation in said 
region of said ferroelectric material. 
11, A light control device as in claim 7 wherein said layer 
of ferroelectric material is of constant thickness. 
12. A light wherein said device as in 
a layer of electrodes coupled to said layer of ferroelectric region is from the group consisting Of a re!darlY- 
shaped polygon and a 
- I  
electrically isolated from one another and positioned to 
define a regularly-shaped region therebetween where N is a i o  
multiple of 4. 
8. A light control device as in claim 7 wherein each said 
element further comprises a layer of transparent material 
adjacent to said ferroelectric material and aligned with said 
region wherein light passing through said region subse- 15 
quently passes through said transparent material. 
9. A light control device as in claim 7 wherein each said 
element further comprises a layer of reflective material 
adjacent to said ferroelectric material and aligned with said 
region wherein light passing through said region is subse- 20 
quently reflected by said reflective material. 
10. A light control device as in claim 7 further comprising 
means for applying electrical energy to selected ones of said 
13. A light control device comprising: 
a layer of ferroelectric material of constant thickness 
having first and second planar surfaces opposing one 
another; 
means coupled to said first planar surface for establishing 
an electric field orientation adjacent to an exposed 
region of said ferroelectric material wherein said elec- 
tric field orientation and said constant thickness of said 
ferroelectric material define optical transmission prop- 
erties for said exposed region; and 
a layer of reflective material adjacent to said second 
planar surface and aligned with said exposed region. 
* * * * *  


Ferroelectric Light Control Device

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