where \(\mathcal {K}=\mathcal {K}_{\mathrm {g}}+\mathcal {K}_{\mathrm {f}}\) . The
geometrical birefringence \(\mathcal {K}_{g}\)  is given by
[1]}, [2]}
\(\mathcal {K}_{\mathrm {g}}=\tau \left(\begin{array}[c]{cc}0 & -i\\i & 0\end{array}\right) \;,\) 

где \(\mathcal {K}=\mathcal {K}_{\mathrm {g}}+\mathcal {K}_{\mathrm {f}}\) . Геометрическая двуоказательность \(\mathcal {K}_{g}\) задается 

\(\mathcal {K}_{\mathrm {g}}=\tau \left(\begin{array}[c]{cc}0 & -i\\i & 0\end{array}\right) \;,\) [1]}, [2]}