Optical coatings: Key to improving performance in sensor technology and photonics
1. Principles of action and benefits of optical coatings
Optical coatings consist of thin layers of dielectric or metallic materials that are applied to substrates such as glass or plastic. They specifically influence the interaction of light with the surface, for example through:
1.1 Anti-reflective coatings (AR) to improve transmission and reduce reflection
Anti-reflective coatings are applied to surfaces such as lenses and displays to minimize unwanted reflections. Through the precise design of thin-film systems with specific refractive indices and layer thicknesses, the reflectance of glass or plastic surfaces can be reduced from around 4.3% to as little as 0.5% across the visible spectrum. This means that more light penetrates the component, making images clearer and brighter and optimizing image contrast. At the same time, glare and ghost images are reduced. This is crucial for high-contrast imaging in cameras, microscopes, and displays.
1.2 Highly reflective coatings (HR) for increasing reflection and deflecting light rays
Surface mirrors are created by applying a metal layer or by coating with dielectric layer systems. The highly reflective layers produced in this way increase reflection in a specific wavelength range and reduce transmission. Optical mirrors are also used to select or deflect specific radiation components.
1.3 Filter coatings for adjusting spectral properties
Optical coatings can be designed as filters (such as bandpass, longpass, or shortpass filters) to transmit or block specific wavelengths. They precisely separate spectral ranges, e.g., for IR/NIR or color separation. This spectral separation is essential for applications such as detectors or other optical elements, for example in sensor technology or measuring instruments.
1.4 Beam splitters: Separate light beams into reflected and transmitted radiation components
Beam splitters are used to separate light of a defined wavelength or a specified spectral range into a reflected and a transmitted portion. They can also be used according to the reverse principle to combine two different beams into a single beam.
All of these functions are essential for applications such as distance sensors, laser scanners, optical quality control, material sorting, machine vision, environmental measurement technology, and many other applications.
2. Application examples and performance advantages
2.1 Sensors and Automation (BTE Born)
BTE Born offers coating solutions for sensors in the UV to IR range. Edge filters precisely separate laser light from ambient light, anti-reflective cover lenses maximize light transmission, and deflection mirrors optimize beam guidance in complex housings. The coatings increase measurement accuracy and signal quality and reduce interference such as extraneous light, for example in distance sensors, light barriers, or laser scanners.
2.2 High-precision filters and mirrors
The company also develops customer-specific filters, mirrors, and coating systems for applications in the automotive, automation technology, and defense industries.
2.3 ITO coatings
ITO coatings, which use indium tin oxide, are versatile and becoming increasingly important. ITO layers are transparent and electrically conductive, making them suitable for a wide range of applications. The electrically conductive surface with high transparency in the visible spectral range makes it suitable for preventing static charges (ESD/EMC shielding), as a heating resistor, or for contacting electrical panels. Due to its semiconductor properties, the material is also suitable for reflecting long-wave IR radiation. ITO is also suitable for the electrical activation of liquid crystals in microdisplays. Combining it with optical layers such as anti-reflective coatings further increases its range of applications. Combinations with filter layers are also possible, such as ITO layers and heat protection filters or heat regulation filters.
3. Conclusion: Improved performance through targeted coating
Optical coatings are a decisive factor in the performance of modern optical systems. They enable:
- Precise light guidance and control
- Precise separation of spectral ranges
- Advantages for applications:
- Reduced susceptibility to interference
- Higher measurement accuracy
- Improved signal quality
- Faster data acquisition in systems such as scanners
Developers and engineers would be well advised to work closely with specialized coating providers to implement customized solutions, whether for series products or highly specialized one-off items. Optical coatings are much more than just a technical detail: they are a strategic element for improving performance in sensor technology and photonics. Developers and engineers would do well to take a look at modern PVD coating technologies and their potential for optimizing existing and future systems.
Sources:
- Cheng-Chung Lee, “Optical interference coatings for optics and photonics,” Applied Optics 52, 73–81 (2012).
- Tatiana V. Amotchkina, Michael K. Trubetskov, Vladimir Pervak et al., “Design, production, and reverse engineering of two-octave antireflection coatings," Applied Optics 50, 6468–6475 (2011).
