Replication Techniques for Digital Optics
The fabrication of diffractive optics makes sense in an industrial setting only if these elements can be cheaply mass-produced. This is the de facto condition for diffractive optics to emerge from the laboratory and address industrial needs in consumer electronics products and other fields of application, such as the automotive industry, factory automation, biomedical and telecom applications, and so on. In the previous chapters, we have emphasized the generation of master elements, by holographic recording, diamond machining or microlithography.
There are several methods available to the optical engineer to replicate these master elements in volume. These include roll embossing, hot embossing, UV casting, injection molding and the sol-gel process. These various techniques will be reviewed in the present chapter.
14.1 The LIGA Process
Historically, the LIGA process was the first replication process used for mass-production of microstructures. Originally, it was intended for the replication of high aspect ratio microstructures used in particle detectors for atomic energy research [1,2]. The term LIGA comes from the German ‘LIthografie’, ‘Galvanoformung’ and ‘Abformung’ (lithography + electroforming + molding). Most of this early research was done at the German Kern Forschungs Zenter (KFZ) (the German Atomic Agency).
This technology allows high aspect ratio structures to be defined in nickel. The process consists of exposing a sheet of ...