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Nano-optical Structures

Nano-optical Structures on Widely Tunable MEMS Fabry-Pérot Filters


This project investigates nano-optical structures, such as photonic crystals or sub-wavelength gratings. Ideally, they should be designed to optimize the features of optical filters to the effect that they can be tailored toward each individual application.

 

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Micro-mechanical tunable Fabry–Pérot filters, that are based on the semiconductor material Indium Phosphide (InP), can be used from a wavelength of 1μm up. Integrated into optical detection systems, they can improve the systems’ performance in the near infrared range decisively. This applies in particular to spectroscopic devices.

Once the filter surfaces are furnished with nano-optical structures, it is possible to adjust their polarization properties with the help of photonic band diagrams and symmetry analysis. This extends the range of possible applications considerably. They could, for instance, be used in polarization selective spectroscopy.
The cavity wavelength of the filters is tuned electro-statically. Since the properties of nano-optical structures, such as their birefringence, also depend on the wavelength, it is possible to adjust them accordingly within the tuning range.

Model calculations serve to determine the properties of the structures,  singularly and as parts of the filters. The size of these nano-structures lies in the range of 100 nm. They are manufactured with Focused Ion Beam (FIB) lithography or, alternatively, with electron beam lithography and ensuing dry etching. Thinking ahead, nano-imprint lithography might offer a cost effective solution for their production.

In measurement systems, the selective and tunable filter components can be used as sensors, either to determine  gas concentrations in chemical and medical processes, or to measure birefringence in material analysis. In addition, these tiny MEMS structures can be mounted on smallest surfaces, like the end of glass fibers.

 

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