Core fields in graded fibres with non-circular index contours

Fields in the cores of graded non-circular optical fibres are analysed using a new method. It is shown that the scalar wave equation in elliptical co-ordinates can be separated for many realistic non-circular profiles, thus allowing calculation of fields by a double WKB method, The boundaries separating oscillatory and evanescent regions are found by simple analysis of algebraic equations, This method supports and further explains previous analysis which used geometric optics.