October 2, 2014, Thursday, 274

SPIE 08 Nicolescu 1

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Conference Section
SPIE Optics and Photonics, Liquid Crystals Conference

Title
Polarization-independent tunable optical filters based on bilayer polarization gratings

Long Abstract
We report enhanced polarization-independent tunable optical filters based on liquid crystal (LC) and reactive mesogen (RM) polarization gratings (PGs). This new design achieves tunable passbands with significantly smaller bandwidth and allows for potential applications in spectroscopy and beyond. Analogous to Lyot and Solc filters, our filter is constructed of multiple bilayer polarization gratings (BPGs) of varying thicknesses, with the potential for highly compact implementation. BPGs are a hybrid of a switchable/tunable liquid crystal (LC) PG and a reactive mesogen (RM) PG. By adding the RM layer, the BPG provides a significant advantage over LCPGs for the filter application in that it allows very thick gratings to be created with thin active LC layers. As such, the difficulty in fabricating LCPGs with arbirtrarily large thicknesses is much less of a concern. BPGs exhibit the unique properties of PGs, including polarization independent zero-order transmittance, as well as diffraction at visible and infrared wavelengths. Furthermore, coupling between only the zero- and first- orders with nearly 100% efficiency has been demonstrated. Our unique design enables a high peak transmittance (~90%) as well as a significantly improved FWHM (~70% narrower peak in a simulated four-stage filter). Here, we present preliminary data, discuss the unique capabilities and compelling advantages of our filter, and provide comparison to our previously demonstrated LCPG tunable optical filter. We analyze performance in terms of finesse, 3dB bandwidth (full-width at half-maximum, FWHM), and free-spectral-range by comparison to theoretical simulation.

Short Abstract
We report enhanced polarization-independent tunable optical filters based on bilayer polarization gratings (PGs). This new design achieves tunable passbands with significantly smaller bandwidth and allows for potential applications in spectroscopy and beyond. Analogous to Lyot and Solc filters, our filter is constructed of multiple bilayer polarization gratings (BPGs) of varying thicknesses, with the potential for highly compact implementation. BPGs are a hybrid of a switchable/tunable liquid crystal (LC) PG and a reactive mesogen (RM) PG with the significant advantage of allowing very thick gratings to be created with thin active LC layers. In this work we present preliminary data, discuss the unique capabilities and compelling advantages of our filter, and provide comparison to our previously demonstrated LCPG tunable optical filter.

Authors
EN, MJE

Comments
[MJE] Suggestions are inserted above.