B.1       Introduction

The schematic view of the writing set-up with the modified phase mask technique is presented in Fig. B-1. The cylindrical concave and convex lens should not be confounded with the lenses used for the beam reducer (aligned in the orthogonal direction). The parallel laser beam is 2h₀ wide before entering the convex lens. The focal length of the convex lens is f_x and the one for the concave lens is f_v. The distance between the lenses is d₁, the distance between the concave lens and the phase mask output is d₂, and the distance between the phase mask surface and the center of the fiber is d₃.

Fig. B-1 Principal parameters of the modified phase mask technique set-up