Background:
Patterned polarizers
have a variety of applications in polarimetry, interferometry, three dimensional
displays, and optical data storage. Linear micropolarizer arrays have been
fabricated using a variety of techniques including; etched dichroic polymers,
wire-grid polarizers, liquid crystal (LC) arrays, and photo aligned liquid
crystal polymers (LCP). Wire-grid polarizers are by far the most common
commercial products for infrared applications; however, micropatterned wire-grid
polarizers have limited spatial resolution and poor performance at visible
wavelengths, require complicated lithographic processing, are susceptible to
defects and cannot be easily extended to non-linear polarizations. An
alternative and potentially simpler technology to create patterned polarizers is
the photo alignment of absorbing materials which can produce micron sized
polarizers of high efficiency and extinction for ultra violet (UV), visible, and
near infrared (NIR) wavelengths.
Micropatterned LC
alignment has been demonstrated using atomic force microscopes, ion beams,
oblique angle gold deposition, and photo alignment using polarized laser light.
While smaller resolution alignment has been demonstrated using the first two
techniques, it is impractical for large areas. The use of linearly polarized
ultraviolet (LPUV) radiation to align linearly photopolymerizable polymers (LPP)
has been under intense research for many years as a noncontact replacement for
traditional mechanical buffing. Photo alignment of LCPs has been demonstrated
over large areas and with features as small as 2.5 microns. Many different LPP
materials have been explored including azodye and dye doped polymers, polyimide,
and cinnamoyl or coumarin side-chain polymers.
This invention
demonstrates the use of multiple layers of an LPP/LCP system to create more
complex polarization elements such as color circular
polarizers.
Invention:
The inventors have
developed a fabrication process to create patterned polarizers for various
visible wavelengths using dichroic dye in a liquid crystal polymer (LCP) host
directly on an array of optical sensors. Contact lithography is used to pattern
a thin alignment layer, which subsequently transfer the pattern to the LCP.
Waveplates of arbitrary retardance and linear and circular polarizers can be
fabricated using multiple layers of LCP. Examples of optical sensors include
charge-coupled device (CCD) and complementary metal-oxide semiconductor (CMOS).
The process is simple and inexpensive compared to other micropolarizer systems.
The main competitors are wire grid polarizers, which require sophisticated
lithography and etching toolsets for fabrication. In addition, circular
polarizer cannot be implemented using wire grid configurations. Dichroic liquid
crystal micro-polarizers use self-assembly to generate unique polarization
domains without metallization or etching.
Advantages:
- Waveplates
of arbitratry retardance and linear and circular polarizers can be fabricated
using multiple layers of LCP.
- The
process is simple and inexpensive compared to other micropolarizer systems.
The main competitors are wire grid polarizers, which require sophisticated
lithography and etching toolsets for fabrication.
- Circular
polarizers can be manufactured which cannot be implemented using wire grid
configurations.
Application:
- Fabricate
micro-polarizers and waveplates on optical filters and on sensor
arrays.
- Waveplates
and polarizers for optical array sensors include CCD and
CMOS.
- Three
dimensional displays, interferometry, optical storage, polarimeters,
cameras.
Status:
Inventors have
reduced this technology to practice and have demonstrated the ability to create
linear polarizers using a two layer liquid crystal system. The highest
extinction ratio measured for a blue polarizer was 40.1 at 633 nm. It is
expected that extinction ratios over 1000 can be achieved using higher dye
concentrations. The smallest feature resolved is 3.1 microns using contact
lithography. The demonstration of an integrated patterned circular polarizer
allows for new imaging polarimeters which can measure all four Stokes parameters
as well as other polarization or wavefront sensing applications. The patent
application has published on May 3, 2012 as Pub. No. US 2012/0105783
A1.
Lead
Inventor: Stanley Pau
UA ID:
UA11-058
