Introduction
This paper describes the application of a small digital computer
to automatically control the manufacture of multilayer thinfilm
optical-interference filters. These devices are an important feature
of many modern optical systems.1'4 Antireflectance coatings and cold
mirrors are two important examples. The development of control
systems to regulate various aspects of the manufacturing process has
been a subject of extensive study. Systems have ranged from simple
analogue feedback units2 to highly complex sequence and feedback
controllers that completely automate the process for particular
applications.3 Processes with the simple control systems require a
very skilled operator to achieve an acceptable product. Despite this,
the rejection rate because of inferior quality is usually high. The more
sophisticated controllers are restricted in application because of
limitations in the hardware. In addition, their complexity still requires
skilled operation. It is considered to be worthwhile, because of these
shortcomings, to investigate the feasibility of using a small digital
computer to supervise the manufacturing cycles.
For the purposes of this investigation, a minicomputer has been
interfaced to an Edwards High Vacuum 19E vacuum coating plant.
The objectives of the feasibility study are as follows:
(a) to demonstrate that a digital computer is capable of completely
automating the coating process
(b) to establish that the computer control permits devices to be
made with consistent accuracy and reliability
(c) to design an operating system with maximum flexibility so that
the computer is able to manufacture a wide variety of devices.
A computer control system has been developed to accept, within the
constraints of the manufacturing process, generalised designs for
optical interference systems. Design information is fed to the
computer which is then able to control the manufacture of the
appropriate device without a requirement for skilled manual supervision
of the operation of the plant.
The paper firstly defines the way in which the optical designs are
formulated. An outline of the process and the computer interfacing
is followed by a description of the computer control systems. Finally,
a particular case study is presented. This describes the manufacture of
a 5-layer antireflectance coating. It is demonstrated that computer
control is effective and consistent. Two consecutive runs on the
process are shown to