Abstract
Tunable diffraction gratings and phase filters are important functional devices in optical communication and sensing systems. Polarization gratings, in particular, capable of redirecting an incident light beam completely into the first diffraction orders may be successfully fabricated in liquid crystalline cells assembled from substrates coated with uniform transparent electrodes and orienting layers that force a specific molecular distribution. In this work, the diffraction properties of liquid crystal (LC) cells characterized by a continually rotating cycloidal director pattern at the cell substrates and in the bulk, are studied theoretically by solving a relevant set of the Euler-Lagrange equations. The electric tunability of the gratings is analyzed by estimating the changes in liquid crystalline molecular distribution and thus in effective birefringence, as a function of external voltage. To the best of our knowledge, such detailed numerical calculations have not been presented so far for liquid crystal polarization gratings showing a cycloidal director pattern. Our theoretical predictions may be easily achieved in experimental conditions when exploiting, for example, photo-orienting material, to induce a permanent LC alignment with high spatial resolution. The proposed design may be for example, used as a tunable passband filter with adjustable bandwidths, thus allowing for potential applications in optical spectroscopy, optical communication networks, remote sensing and beyond.
Highlights
Diffraction gratings are important optical components used in the field of spectroscopy by chemists, biologists and physicists [1,2,3]
We theoretically investigate the diffraction properties and electro-optical characteristics of liquid crystal (LC) polarization gratings formed by using typical nematic LC (NLC)
By analyzing analytically the proposed configuration and by solving numerically differential (Euler-Lagrange) equations, we demonstrate how the first order diffraction efficiency spectra are affected by the cell gap and LC birefringence at zero voltage, as well as how it changes when the LC cell is electrically biased
Summary
Diffraction gratings are important optical components used in the field of spectroscopy by chemists, biologists and physicists [1,2,3]. High-quality elements of this type require precise control over periodic surface modulation at the subwavelength scale and advanced technologies such as optical beam lithography, scanning beam holography, direct electron beam lithography or photo-lithography are involved in their fabrication When it comes to optical communication and information processing, gratings with controllable diffraction properties may serve as essential functional elements allowing for effective beam switching, steering, filtering, shaping, splitting or combining. From a practical point of view, when using diffraction gratings to redirect light beams and to change their paths in space, it is beneficial to eliminate the zeroth-order beam completely Various techniques, such as introduction of a third phase level to the original binary grating profile, inclusion of diffractive micro-prisms or Fresnel lens in the design, introduction of mechanical mask to block the optical signal at an intermediate image plane, application of double-sided diffraction elements or application of holographic gratings [12] may be used to complete this task. In principle, such proposed solutions allow for the signal in the zeroth diffraction order to be lowered to the null level, with the diffraction orders higher than the first one, present in most cases
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
