Fraunhofer Institute for Applied Optics and Precision Engineering IOF
Fraunhofer Institute for Applied Optics and Precision Engineering IOF

Materials for Micro- and Nanooptical Elements

The selection of a suitable material is a decisive step on the way to the optimum system. Fraunhofer IOF has extensive experience in the evaluation and qualification of optical materials and can therefore make an optimal decision for each specific application during the design process. Non-optical properties often also play a role here, in particular fine optical machinability, coatability, thermal suitability, vacuum behavior, etc. A holistic design approach that takes your project requirements into account is therefore required for realization.

The structuring of surfaces in wavelength dimensions also enables the targeted manipulation of the optical properties of a material so that effective-medium materials and Metastructures can be realized.

Lithography as a Technological Prerequisite

Whether electron beam, photo or nano-imprint lithography, these technologies enable micro- and nanostructures of very high quality in the respective optimal resist materials. However, these are usually not the materials of the finished optical element, but represent the masking for the etch transfer process or the original form (master) for replication. Only the subsequent processes lead to the application-specific optical materials, coatings and material systems.

The available infrastructure at IOF is designed to process optically relevant materials and produce high-quality optical structures. Our expertise covers both lithography materials and optical functional materials. The application-related choice together with you is the key to success.

Our Services and Competencies

We can process a wide range of substrate dimensions in our process chain. From wafer to mask blank, dimensions up to a diameter of 300mm are possible, thicknesses from 100µm to 15mm. In some cases the substrates are used as carriers and in other applications the substrate is structured or a silicone-on-glass molding is used. This allows us to make many applications possible.

With structured materials, the focus is on silicon-based materials (silica glass, silicon, silicon nitride) and highly refractive oxides. In the field of replication, single-component acrylates and epoxies are mostly used. In addition to fused silica, all types of borosilicate, crown and flint glass in wafer or plate form are also used as carrier substrates.

Examples of structured materials (not exhaustive):

  • Transmissive pulse compressor gratings: Fused Silica SiO2
  • Reflective pulse compressor gratings and highly efficient spectrometer gratings: Designed layer stacks of dielectric, high and low refractive index layers
  • Reflection structures: coatings or nanostructured, UV to FIR
  • Echelle gratings and transmission optics SWIR - MIR: Silicon
  • Waveguide structures: Silicon nitride Si3N4, lithium niobate LiNbO3
  • Spectral purity filters for EUV and soft-X-ray in reflection: silicon
  • Transmission optics MIR: germanium, silicon, diamond (DLC)
  • Microlenses: Silicon (SWIR-MIR), silica glass (UV-SWIR), borosilicate glass (VIS-NIR)
  • Optical aperture materials: metals, black chrome (wet chemical)
  • Transparent conductive layers: Indium tin oxide (ITO) (wet chemical)

The material of your choice is not on the list? Feel free to contact us, we are constantly expanding our portfolio.

Materials for the replication processes

Commercially available polymers are used for replication processes, with Fraunhofer IOF also testing experimental samples. Materials for replication with UV molding (not complete):

  • Acrylates
  • Epoxides
  • Ormocers
  • Silicone

Flexible material selection & platform development for hybrid PICs

Commercially available polymers are used for replication processes, with Fraunhofer IOF also testing experimental samples. Materials for replication with UV molding (not complete):

  • Platforms with high TRL:
    LiNbO3 (LNO) and SiN offer mature technologies with stable processing and high reliability. Our highlight: low-loss LNOI single-mode waveguides with <2 db/m.
  • Platforms under development:
    Materials such as BaTiO3 (BTO) open up new degrees of freedom in nonlinear and electro-optical functionality.
  • Hybrid approaches:
    Combination of linear, electro-optically active and non-linear materials as well as integration of (single) emitters enable extended (quantum) optical functionalities.
  • Advanced material integration:
    Ion implantation for targeted defect generation, integration of non-linear van der Waals materials (e.g. 3R-MoS2, NbOI2) and electro-optically active layers for novel device designs.
© Fraunhofer IOF

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