Teresa K. Ewing

Advances in polarization-based liquid crystal optical filters

Liquid crystal tunable filters are gaining wide acceptance in such diverse areas as optical fiber communications, astronomy, remote sensing, pollution monitoring, color generation for display and medical diagnostics. The large aperture and imaging capability of liquid crystal tunable filters represent a distinct advantage over conventional dispersive spectral analysis techniques. Furthermore, benefits of liquid crystal tunable filters over acousto-optic tunable filters include low power consumption, low addressing voltage, excellent image quality and large clear aperture. We discuss polarization interference filters based on liquid crystal tuning elements. While liquid crystal tunable filters based nematic liquid crystal, using Fabry-Perot and polarization interference effects are commercially developed, only recently has the emphasis been on liquid crystal tunable filters to include current novel developments in high-speed, analog ferroelectric-liquid crystals (FLCs). Compared to nematic liquid crystal, FLC-based tunable optical filters offer fast response time and increased field-of-view.

New developments in high-resolution liquid crystal spatial light modulators for wavefront control

High resolution devices, using liquid crystal phase modulators, have the ability to correct large phase variations across the aperture. These phase variations are corrected using discrete (pixelated) modulo-2π phase shifts, which simplifies the control scheme by eliminating inter-actuator influence and decreases the response time of the phase modulator by reducing the required stroke. Even with these advantages, modulo-2π phase correction is generally not used if the source is broadband due to degradation from chromatic dispersion. This paper discusses techniques for reducing the angular dispersion using new modulators which are being developed.

Programmable 128 x 128 ferroelectric liquid crystal spatial light modulator compact correlator

This paper details a compact two-dimensional optical correlator based on 128 X 128 ferroelectric liquid crystal spatial light modulators in both the image and filter planes. A complete description of this compact correlator is given. The correlator is fully programmable and performs automatic pattern recognition functions at 500 frames per second. Key design parameters and results of performance analysis are presented.

Liquid crystal Fourier transform spectrometer

A new high throughput imaging spectrometer is described that utilizes a digitally switched polarizing interferometer to sample the complex autocorrelation of the input spectrum. Using a single filter stage and high speed digital liquid crystal switches, the spectrometer can provide rapid measurements of power spectra using a simple, easily driven, light efficient structure. The spectrometer is well suited to visible/near infrared operation, due to its use of path-length differences in crystals, rather than free space path length differences. The spectrometer provides accurate and stable steps in path length difference from zero to hundreds of waves.

Liquid crystal modulated optical CDMA in a fiber-based testbed

In recent years, optical CDMA systems have been proposed for multiple accesses to utilize the vast bandwidth available in optical fiber. Optical CDMA systems are believed to provide asynchronous access for each user in the system, which is especially suitable for usage in LAN. In this paper, we demonstrate a novel optical CDMA scheme in a fiber-based testbed. Using the liquid crystal spatial light modulator (SLM), we are able to construct a reconfigurable optical CDMA system suitable for fiber-optic networks. We address the code for each user in the spectrum domain by using a standard 4-f pulse shaping apparatus. Because of the low coherency of the light source we used in the system, we are able to modulate it in time domain without changing its frequency distribution significantly. We can reconfigure the network connection while keep the information bits un-influenced. Another merit of using analog liquid crystal device is that the transmissions of the different frequency components are analog controllable, we can get a uniform intensity distribution in frequency domain when the spectrum of the light source is not flat. Using the liquid crystal as a programmable optical modulator, the high polarization sensitivity of the components used in the system enables low crosstalk between different codes assigned to different users.

Development of a polarization hyperspectral image projector

This paper describes the development of a new instrument for calibrating satellite imaging sensors - the Polarization Hyperspectral Image Projector (PHIP). The PHIP instrument is capable of producing realistic standards-based satellite imagery, simultaneously projecting spectral, spatial and polarization scenes. The feasibility study outlined here demonstrates that liquid crystal devices are capable of producing arbitrary polarization states. Boulder Nonlinear Systems is currently developing a complete spectral/spatial/polarization instrument to be delivered to NASA in 2013.

Liquid crystal on silicon (LCOS) devices and their application to scene projection

Liquid Crystal on Silicon micro-displays are the enabling components on a variety of commercial consumer products including high-definition projection televisions, office projectors, camera view-finders, head-mounted displays and picoprojectors. The use and potential application of LCOS technology in calibrated scene projectors is just beginning to be explored. Calibrated LCOS displays and projectors have been built and demonstrated not only in the visible regime, but also in the SWIR, MWIR and LWIR. However, LCOS devices are not only capable of modulating the intensity of a broadband illumination source, but can also manipulate the polarization and/or phase of a laser source. This opens the possibility of both calibrated polarization displays and holographic projection displays.