For an efficient analysis of the coupling characteristic of a multimode fiber device using a GRIN-rod lens, a skew ray path in radial gradient suitable for an investigation of the third-order property of a GRIN-rod lens is derived by greatly modifying the first-order asymptotic solution found by Paxton and Streifer. Then, using the derived skew ray path, a coupling characteristic is analyzed on the multimode fiber directional coupler developed by Minemura et al. The result is shown as a contour map of coupling efficiency when the influences of defocus and the third-order aberrations of the GRIN-rod lens and of the lateral shifts of the optical fiber are taken into account. The validity of the ray trace analysis is also examined from the point of view of the far-field pattern of a multimode fiber.
© 1986 Optical Society of America
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