厚い異方性格子における偏光回折特性の結合波解析

摘要

Diffraction properties of thick anisotropic gratings, recorded by vector holography in photoreactive liquid crystals, were characterized with the use of a simple coupled-wave theory. Two eigen polarizations in the gratings were determined based on the dielectric perturbation, and diffraction efficiencies were formulated by considering the coupling between both the polarizations. The obtained diffraction properties were in good agreement with that calculated by the finite-difference time-domain (FDTD) method. In addition, by comparative studies using the FDTD method, we confirmed that the coupled wave analysis (CWA) provides reasonable accuracy for relatively large perturbation in the case of Bragg incidence with eigen polarization.%光反応性液晶材料中へのベクトルホログラム記録により形成可能となる厚い異方性格子の特性解析へ，結合波理論の適用を試みた．誘電率テンソルの摂動成分から格子内部での二つの固有偏光を明らかにし，両偏光間での結合を考えることで格子の回折効率を定式化した．回折特性の解析結果は，回折光の偏光状態も含め，時間領域差分（finite-diffbrence time-domain；FDTD）法による計算結果とよく一致するものであった．また，結合波理論の適用条件についても言及し，Bragg条件下における固有偏光の入射に対してであれば，摂動が比較的大きい場合においても高確度での解析が可能となることを示した．