PROCEEDINGS ARTICLE | April 12, 2005
Proc. SPIE. 5741, Emerging Liquid Crystal Technologies
KEYWORDS: Diffraction, Beam steering, Phase modulation, Electrodes, Dielectrics, Phase shift keying, Computer simulations, Liquid crystals, Binary data, Diffraction gratings
High diffraction efficiency and large diffraction angle are two major concerns in designing a liquid crystal (LC) phase grating for its applications in beam diffractive devices. High-spatial-frequency grating is capable of providing a large diffraction angle. However, fringing-field effect becomes more severe when the grating pitch size decreases, which imposes a limitation on the phase modulation depth and the diffraction efficiency of the LC grating. In this paper, a novel LC grating with striped electrodes patterned on both the top and bottom sides was proposed and fabricated. By using a specified biasing configuration, vertical electric fields are generated and well confined between the facing electrodes. Meanwhile, horizontal electrical fields are created between adjacent electrodes which help reducing the undesirable deformation of the LC director axis resulting from the fringing filed. Computer simulations show, in our novel structure, a maximum phase modulation depth of 4.15 rad (for 1.55 μm) can be achieved, which is large enough to satisfy the 1.17 π phase-shift requirement for maximum first order diffraction in sinusoidal phase gratings. Both the conventional single-sided and the novel double-sided LC gratings were fabricated and tested. Measurements showed, there was an efficiency enhancement of 77 times achieved by the double-sided structure comparing the conventional structure. A first order diffraction with diffraction angle at 14.5o and diffraction efficiency of ~31% is experimentally achieved, of which the efficiency approaches the theoretical upper limit at 33.8% for a sinusoidal phase grating.
