Durable, Front Surface Hard Optical Coatings For Replacing Laminated Soft Coatings
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Durable, Front Surface Hard Optical Coatings for Replacing Laminated Soft Coatings Alluxa Engineering Staff

Alluxa’s proprietary high speed plasma deposition technology for the first time delivers the optical performance and durability of hard coated optical filters at laminated soft coating pricing. Overview Soft coatings, also known as laminated coatings are well known to possess poor environmental durability, poor temperature stability, low transmission, high optical scatter and low blocking levels, yet they are still widely used due to their low cost, ready availability and legacy status. Alluxa’s proprietary high speed plasma deposition technology for the first time delivers the optical...

Coating optionally removed Float glass substrate Epoxy Float glass substrate Fig. 1 A typical soft coating has three structures laminated together to help provide moisture resistance. The structure is typically 2-5mm in thickness and mounted in a ring to further try to restrict humidity ingress. Soft coatings have large optical losses from both scatter and absorption in the visible and near infra-red, which further increases in the UV and blue. Figure 2 shows the spectral function of a series of typical commercially available dielectric (no silver) laminated soft coatings across the visible...

Fig. 2 Soft coating designed for high transmission that contains no silver layers. The transmission can rise above 80% in the green/red, but drops to less than 50% in the UV blue. Also note the severe ripple in the pass-band attributable to the lack of computer controlled deposition control. Alluxa Plasma Deposition of Hard Coatings Hard dielectric films produced by Alluxa’s advanced high speed plasma deposition process are nearly lossless, with extinction coefficients in the low ppm range from the UV to the IR. They are made using sophisticated computer control algorithms that control...

which means for the instrument design the filter must be controlled to +/- 15C for a lnm filter tolerance. For telecom applications, Alluxa routinely builds filters to less than 1 picometer per degree Celsius at 1550m, well less than 1 part per million change in wavelength. Transmitted Wavefront Error (TWE) Alluxa can provide filters with TWE values of less than V* wave peak to valley as show in Fig. 4 if the user requires. For most designs, the TWE of the finished filter is essentially identical to that of the uncoated substrate. Soft coatings with their laminated structure would have to...

Fig. 5 Ultra-narrow band filter built using Alluxa’s pulsed plasma deposition technology. The bandwidth is approximately 0.3 nm in bandwidth at 1570nm.

Fig. 6 Consecutive runs of an ultra-narrow band filter at 632.8nm built using Alluxa’s plasma deposition technology. The bandwidth is approx. 2nm wide. Cost Comparisons While soft coatings are manufactured in inherently lower cost bell jar evaporation chambers, they also have much smaller batch sizes and are almost exclusively manual in operation, which adds cost and variability while decreasing yield. Alluxa processes are fully automated ensuring repeatability, continuous operation, and low direct labor cost. For OEM applications, Alluxa’s hard coatings have much larger load sizes than...

Table 1. Cost comparison ofAlluxa hard coatings against soft coatings.

Summary Soft coatings possess poor environmental durability, poor temperature stability and low transmission, high optical scatter, yet they are still used mostly due to low cost. Alluxa’s advanced high speed deposition technology has finally enabled hard coatings to compete on price with soft coatings, even in small batch sizes. Alluxa’s filters offer dramatically improved transmission, spectral shape, and lifetime. Alluxa Alluxa designs and manufactures next generation hard coated optical filters using a proprietary plasma deposition process in Santa Rosa, California. Alluxa’s unique,...