This paper describes a numerical analysis of axially nonsymmetrical W-type optical fibers as optical-fiber-type broadband phase devices. Using these devices, phase difference between two orthogonal linear polarizations can be kept constant in a broad wavelength range. The propagation characteristics along a circular core with an elliptical cladding structure and an elliptical core with a circular cladding structure are numerically analyzed by the boundary-integral method. Using the numerical results, the performances of various broadband phase devices are theoretically compared.
Naoto Kishi and Eikichi Yamashita, "Optical Broadband Phase Devices Using Axially Nonsymmetrical W-Type Optical Fibers," J. Lightwave Technol. 16, 301- (1998)