Angle-dependent dip-coating technique (ADDC) an improved method for the production of optical filters

The production of high quality interference filters by a sol-gel coating process (e.g., dip-coating) with large areas of flat or shaped surfaces and with tubes has been developed. The angle dependent dip-coating process (ADDC) is an improved dip-coating technique method for the production of optical filters. In contrast to conventional dip-coating (DC), the substrate is withdrawn from the coating solution at an angle of inclination, that offers advantages for the production of optical interference tilters. Thereby, the two surfaces of the substrate are coated with different film thicknesses. To gain full control over the individual layer thicknesses, reaching from 20 nm to 160 nm, it is necessary to vary the following process parameters: lifting speed (upsilon) of the substrate, angle of inclination (phi) (Fig. 2c) and concentration of the dipping solution (c). An ADDC long pass filter produced in 10 coating steps reaches the same optical performance as a conventional DC filter made in Ih steps. The possibility to improve quality demonstrate a second example: a commercial DC beamsplitter can be improved with respect to the flatness of transmission and reflection curves when being produced in four steps by ADDC instead of right steps by DC. Furthermore, ADDC offers the possibility to fabricate even narrow band pass filters, which are naturally difficult to obtain by conventional DC. (C) 1997 Elsevier Science B.V.