Abstract

Kerr-type nonlinear optical devices working in a self-phase modulation (SPM) regime, such as tapered nonlinear fibers, appear to be very promising for the design of all-fiber optical switches [1]. Crucially important for devices based on nonlinear tapered fibers is the waist diameter to maximize the magnitude of the nonlinear Kerr effect. To determine the optimal diameter, we computed the nonlinear propagation constant β^NL as a function of the guided power P. In the range of diameters of interest for nonlinear applications, the field is guided by the air-cladding interface. Due to the strongly guiding conditions, the scalar theory is expected not to provide the exact modal characteristics. In this paper, four different numerical methods are used to investigate the nonlinear modal properties of tapered fibers: (1) a first-order scalar perturbation method; (2) a first-order vectorial perturbation method; (3) an exact numerical solution of the scalar (Helmholtz) equation; (4) an exact numerical solution of the Maxwell's equations. A comparison of the results obtained by the scalar approaches and by their vectorial counterparts is presented.

© 1995 Optical Society of America