The dip-coating technique

The waveguide preparation by dip-coating technique may be divided in four stages:

·       Preparation or choice of substrate;

·       Thin layers deposition;

·       Film formation;

·       Densification throughout thermal treatment.

 
Figure 1: Stages of the dip-coating process.

Figure 1 shows the dip-coating process, which may be divided in five stages: immersion, start-up, deposition, evaporation and drainage. In the dip-coating method the substrate is slowly dipped into and withdrawn from a tank containing the sol, with a uniform velocity, in order to obtain a uniform coating.

The deposition operations were completely automated by computerised control system. The whole experimental set-up, entirely made in our laboratory, is isolated on a vibration damping table to ensure that the liquid surface remains completely undisturbed, thus granting the homogeneity of thickness at each deposition.