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Laser photolithography & UV exposure :
Photonics is to optics is what microelectronics is to electricity.
The basic functions of photonics are the optical wave-guide and the Bragg grating. These functions must be realised with extreme precision and must not have any structural defects over some tens of nanometres, because they are destined to transport electro-magnetic waves of a few hundred nanometres wave lengths
A wave-guide which the roughness would be some hundred nanometres can only guide the light on a few hundreds of microns before the power is dispersed out from the wave guide. Making waveguides with raster scan based writing technique is as a result not possible. It is therefore necessary to have a real vector writing mode. Furthermore, these integrated optical functions must generally be coupled to optical fibers, where the inner diameter is a minimum of 8µm.
To limit the coupling losses between the wave-guides and the optical fibers, the inner dimensions of the wave-guides must be of equal diameter. The production process must therefore offer a sufficient depth of focus to manufacture controlled structures on the whole thickness of the layer, namely about ten microns minimum.