Polarization-Independent Modulation & Simplified Spectropolarimetry Using LC Polarization Gratings Michael J. Escuti 1, W.M. Jones 1, C. Oh 1, R. Komanduri 1, C. Sanchez 2, C. Bastiaansen 3, D.J. Broer 3 contact: 1) NC State Univ, 2) Univ de Zaragoza, 3) Eindhoven Univ of Technology O pto-Electronics and L ightwave E ngineering G roup ( OLEG ) E lectrical & C omputer E ngineering Step 2: Hologram ExposureStep 3: Fill w/ LC + careful optimization of material choices and critical thickness design Similar to method in Eakin et al, Appl Phys Lett 85 (2004)  OBJECTIVE: NEW LIQUID CRYSTAL DEVICE MODES POLARIZATION INDEPENDENT liquid crystal microdisplays HYPERSPECTRAL POLARIMETER designs enabling high-speed detection  MOTIVATION: Capitalize on Adv Polarization Control Techniques Achieve ultra-efficient, portable, projection displays, with low-cost potential LCoS Simplified spectropolarimeter for easier wavelength-parallel polarization detection  APPROACH: Surface-directed Holograms in Bulk Liquid Crystals These optical elements are technically “Liquid Crystal Polarization Gratings” or (LCPG) First reported by Crawford and coworkers (Eakin et al, Appl Phys Lett 85, 2004) We improve on prior work by achieving high quality optical elements for 1 st time Summary & Motivation LCPG Properties  Construction & Properties Hologram w/ continuous in-plane profile Splay-bend nematic LC texture Bulk liquid crystals Photo-alignment layers capture pattern  Fabrication Used standard MERCK liquid crystals and ROLIC photo- alignment materials  =11μm d =2μm  n =0.2 Side View (0V) Top View Diffraction Efficiency Voltage Threshold: Switching Times: (V>V th )  Transmittance Spectra Basic Operation (monochromatic light) Reactive-Mesogen Polarization Gratings  Diffractive Modulator Directs optical power between 0 th and ±1 st diffraction orders (Floquet modes) Polarization independent! Controlled by applied voltage Threshold voltage = ~1.65 V (2  m thickness) Modest operating voltages Very low scattering (< 0.3%) High contrast for monochromatic light Experiment Specifications Magnification = 15X, Throw = 0.6m I +1 + I –1 I incident  Transmittance vs Voltage Zero V, Linear Polzn Full (30) V, All Polarizations (633 nm laser light)  Switching Times Wavelength-Parallel Spectropolarimeter For More SID Symposium Digest 2006: paper # 39.4, posters P-209, SPIE Optics & Photonics (San Jose, CA, 2006): three entries Manuscripts in preparation/submission (2006): Nat. Photonics, etc. Modulation of Unpolarized LED Light (first results)  Bright-Field Schlieren (BFS) Projection System Maximum Contrast Ratios Color Red Green Blue Contrast 144:1 73:1 82:1 * Potentially as high as 600:1 given higher voltages & dark-field Features High efficiency (~100%), low scattering (< 0.3%) Single substrate, robust polymer films Grating periods as small as 1  m Rolic Photo-alignment, Merck reactive mesogens Features Full spectral polarization information w/o active tuning elements Simultaneous measurement of six intensities only needed Simple light-weight construction Proof-of-concept shows very good accuracy!