An optical switching apparatus and a method of efficiently switching optical signals are disclosed. Optical insertion loss may be reduced in a planar lightwave circuit by determining an optimal spacing between perturbations including using passive perturbations, having a three dimensional refractive index distribution, in an array of waveguides, or by adjusting parameters of existing perturbations e.g. their spacing. The perturbation and each waveguide have different three dimensional refractive index distributions. The perturbation may be positioned anywhere in the array of waveguides. The perturbation may be a trench, a region of refractive index different from that in each waveguide, a broken waveguide core, or a modification of the topography of the array of waveguides. In one embodiment, the perturbation is a periodic or quasiperiodic perturbation.