Thin Film Coating: Enabling Technology Right Before Our Eyes

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Optical components are an integral part of modern society. They are used almost everywhere. As long as there are optical systems, optical coatings will be required. And it is thin film technology that allows these optical systems to realize their incredible potential.

Thin-film technology is key to the ultimate performance of many optical systems, which play a key role in applications ranging from biomedical and analytical instrumentation to advanced laser systems.

Its production dates back to 1817 when the anti-reflective effect of a single layer on glass was first discovered by the German scientist and optician Joseph von Fraunhofer. Today, supercharged by an unlimited number of applications and an unquenchable thirst for market, their sophistication has advanced as rapidly as most other consumer technical products.

Optical thin films involve the interaction of electromagnetic radiation, at different wavelengths, with a deposited functional layer. And filters are usually made of several alternating layers of high and low refractive index material deposited on a glass substrate. They work on the basis of wavelength-dependent interference from reflected or transmitted light with many interferences between the layers.

In the late 1970s and early 1980s, Dense Wavelength Division Multiplexing (DWDM) brought about substantial improvements in virtually every aspect of thin-film optical coating design, manufacturing, and performance. . The later capabilities thus unlocked, particularly in the field of telecommunications, were astounding.

The ability to tailor film properties through variation of microstructure via deposition parameters and deposition technique has facilitated their use for the simplest to most advanced wear and corrosion protection coatings. technologically such as microelectronics and biomedicine.

A novel approach

For a thin film intended for use in optics, each layer of different materials ranges from a fraction of a nanometer to several micrometers. Their synthesis is controlled by deposition, with one or more layers of material deposited on the substrate, generally by vapor phase deposition.

Umicore manufactures thin film optical coating solutions in wavelengths from 2 µm to 14 µm on a variety of substrates, and its coatings offer exceptional spectral and environmental performance that can be used on lenses to combat aberrations or defaults.

Take a camera lens for example. These are often covered with thin transparent multi-layers of metals such as titanium dioxide, silicon nitride or silicon oxide, to combat defects or aberrations. These thin layers are deposited on a lens and change the way the optic reflects and transmits light. Each application requires different optical filter characteristics.

Improvements in cost, performance and availability of key components have led to the diversification of lidar systems, a method of remote sensing that uses light in the form of a pulsed laser to measure distances (variable distances) to Earth in areas such as autonomous vehicles, atmospheric science, terrain mapping and oceanography. Optical filters are used either as a receiver to isolate the signal from background light or as an emitter to clean up the spectral characteristics of the laser.

These unassuming thin films are used in many different fields and optical applications are an important class, where they excel in terms of efficiency, scalability and added product value. They can be used to make filters, mirrors, and anti-reflective coatings, all of which are applied in different industrial fields such as automotive, biomedical, and optoelectronics.

The production of advanced optical coatings with complex spectral characteristics and high performance is directly dependent on the stability of the deposition process and the accuracy of the monitoring system used to control layer thickness.

Continuous improvements in these techniques, materials, better process controls and innovative work like ours means we are continually developing new understanding in design, expertise and practical production. As we innovate, we enable many other industries to do the same.

The science is well documented and widely known. The possibilities and limits of light control, equipment operation, selection of the most suitable materials, as well as control techniques, process development, practical knowledge and precision engineering are where true mastery is achieved.

By choosing to work with a thin film coatings specialist, you remove much more than finished products. Satisfied customers also tap into our wealth of practical knowledge; be it design optimization methods, the latest spectral measurement equipment, new substrates or optical monitoring techniques.

From Holy Grail to Commodity

The growth of computer technology has made high-density storage systems mandatory, and this has led to rampant research and development, especially on the optoelectronic, magnetic and optical properties of thin films.

With the ability to enhance substrate material properties through a range of deposition materials, the right fabricator can meet the exact needs of a host of highly specialized applications. Device miniaturization continues to drive its growing commercialization while reducing costs associated with equipment and processes.

Areas such as engineering, magnets and energy, as well as applications such as neurological sensors, optical memories and friction reduction, continue to demand innovation from our industry.

There is no doubt that we are in the midst of a bold new period of advancement in new applications for the benefit of society. Developments in different areas of nanotechnology, LEDs, photovoltaics and solar cells, as well as environmental and medical diagnostics continue, with many keen observers watching with fascination their contribution to areas such as spectral imaging, time-correlated single photon counting, chemical reaction rate kinetics, non-invasive optical biopsy and visual implants.

The same technological advances that have been spurred by optical communications systems can be applied to a wide variety of other established and emerging markets. There is great potential in the availability of high performance optical filters and if coordinated evolution continues, this article would read very differently five or 10 years from now.

Written by Mark Naples, Managing Director, Umicore Coating Services

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