O pto-Electronics and L ightwave E ngineering G roup ( OLEG )

1. + careful optimization of material choices and critical thickness design Similar to method in Eakin et al, Appl Phys Lett85 (2004) I+1+ I–1 Iincident Step 2: Hologram Exposure Step 3: Fill w/ LC Zero V, Linear Polzn Full (30) V, All Polarizations Polarization-Independent Modulation & Simplified SpectropolarimetryUsing LC Polarization Gratings Michael J. Escuti1, W.M. Jones1, C. Oh1, R. Komanduri1, C. Sanchez2,C. Bastiaansen3, D.J. Broer3 contact: mjescuti@ncsu.edu, 1) NC State Univ, 2) Univ de Zaragoza, 3) Eindhoven Univ of Technology Opto-Electronics and Lightwave Engineering Group (OLEG) Electrical & Computer Engineering Basic Operation (monochromatic light) Summary & Motivation • 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 Lett85, 2004) • We improve on prior work by achieving high quality optical elements for 1st time • Diffractive Modulator • Directs optical power between 0th and ±1st 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 LCPG Properties • Construction & Properties • Hologram w/ continuous in-plane profile • Splay-bend nematic LC texture • Bulk liquid crystals • Photo-alignment layers capture pattern • Transmittance vs Voltage • Switching Times Top View • Diffraction Efficiency • Voltage Threshold: • Switching Times: Side View (0V) (633 nm laser light) (V>Vth) 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 • Transmittance Spectra • * Potentially as high as 600:1 given higher voltages & dark-field • Experiment Specifications • Magnification = 15X, Throw = 0.6m • Fabrication • Used standard MERCK liquid crystals and ROLIC photo-alignment materials • =11μm d=2μmn=0.2 Wavelength-Parallel Spectropolarimeter Reactive-Mesogen Polarization Gratings • 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! For More Information: mjescuti@ncsu.edu • @ SID Symposium Digest 2006: paper # 39.4, posters P-209, P-167 • @ SPIE Optics & Photonics (San Jose, CA, 2006): three entries • Manuscripts in preparation/submission (2006): Nat. Photonics, etc.