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Topological defects of optical indicatrix orientation in optically biaxial crystals. The case of light propagation in the directions close to the optic axes

Krupych O., Vasylkiv Yu., Kryvyy T., Skab I. and Vlokh R.
 

Vlokh Institute of Physical Optics, 23 Dragomanov Street, 79005 Lviv, Ukraine

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Abstract. We have developed analytical approach to determine the orientations of cross sections of optical indicatrix (OI) around the optic axes (OAs) in biaxial crystals. It has been found that the angular distribution of cross sections of the OI by the planes perpendicular to the directions close to the OA reveals a topological defect of OI orientations with the strength equal to ½. When a conical circularly polarized wave with cone’s axis coinciding with the OA in a biaxial crystal propagates through a sample, a singly charged optical vortex is generated. We have shown that splitting of a single OA in optically uniaxial crystals into two OAs due to electrooptic effect is accompanied by the topological reaction that involves dividing a single defect with the unit strength into two defects with the strengths equal to ½. We have experimentally discovered topological dipoles that consist of topological defects with the strengths of each defect within the pair equal to +½ and –½.

Keywords: topological defects, optical indicatrix of biaxial crystals, optical vortices, topological reactions

PACS: 42.55.Zz 
UDC: 538.958+681.7.069.24
Ukr. J. Phys. Opt. 18 131-138
doi: 10.3116/16091833/18/3/131/2017
Received: 09.06.2017

Анотація. У роботі представлено аналітичний підхід до опису орієнтації перетинів оптичних індикатрис за умови просвічуванні оптично двовісного кристала в довільному напрямку. Виявлено, що кутовий розподіл перетинів оптичних індикатрис площинами, перпендикулярними до напрямків, близьких до оптичної осі двовісного кристала, містить топологічний дефект орієнтації оптичних індикатрис із силою ½. При поширенні конічної циркулярно поляризованої хвилі вздовж оптичних осей у двовісних кристалах буде генеруватися вихор одиничного заряду. Показано, що розщеплення єдиної оптичної осі в одновісному кристалі внаслідок електрооптичного ефекту і відповідна поява двох оптичних осей супроводжується топологічною реакцією розпаду дефекту з силою 1 на два дефекти з силою ½. Експериментально виявлено топологічні диполі, які складаються з пари топологічних дефектів із силами +½ і –½.
 
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