Plasma- or ion-assisted coating processes represent the state of the art for the production of high quality interference coatings. To meet the special filter demands of the telecom industry, special types of coating equipment have been developed with outstanding capabilities for producing complex layer systems. However, their limited productivity makes them unsuitable for cost-effective filter production on traditional sized substrates. Therefore, the challenge for future coating equipment is to achieve the same order of accuracy in process control on large substrate areas together with short production cycles and superb layer properties. The existing plasma and ion sources are one limitation for achieving short production cycles. It is their limited performance that restricts the obtainable coating rate for dense, shift-free interference coatings. The direct optical monitoring is, together with the applied coating technology, the key for the production of complex layer systems. This has been shown in many applications, but is still a challenge on large scale.