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Optical filters are precision devices designed to selectively transmit or block specific wavelengths of light. They improve the performance of optical systems by allowing only desired wavelengths to pass while blocking unwanted light. This selective transmission is essential in a wide variety of scientific, medical, and industrial applications.

Our optical filters for the industry are used in a wide range of markets and applications, from manufacturing to medical, logistics, inspection and aerospace. If you would like to learn more about the wide range of our optical filters, please visit the following pages to find out, for example, how the filters can impact on production processes or entire logistics chains.

•    Reproducibility and Reliability: Rely on the consistent performance of our filters for precise results, even after years. •    Optical precision: Highest flatness and minimal wavefront deformation guarantee images without loss of quality. •    Wide selection: Choose from a variety of filter types and coatings to meet your specific needs. •    Flexible sizes: Our filters are available in a variety of diameters to suit your applications. •    Robust Mechanics: Rely on metal mounts for a durable and reliable filtration solution. •    Highest reproducibility, reliability and excellent image quality.

Optical filters improve the performance and accuracy of optical systems in many different applications. In fluorescence microscopy optical filters isolate specific fluorescent signals, in spectroscopy optical filters analyze the spectral properties of substances, in medical imaging optical filters improve image contrast and clarity, and in machine vision systems optical filters leverage quality control and inspection processes.

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Now that we have made the concept of coherence clear, we include a table with the characteristics of the 3 main light sources used in fiber optics: LED light sources, lasers and SLED light sources  (see our previous article about SLEDs). Notice that the temporal coherence automatically determines the bandwidth and the speckle, but we list all the three:

A neutral density filter, or gray filter, is an optical filter that uniformly reduces the intensity of light without affecting image quality.

A shortpass filter is an optical filter that passes only wavelengths below a certain cutoff wavelength and blocks longer wavelengths.

Keeping it simple:the higher the temporal coherence, the narrower the bandwidth of the light source and the other way round (a low temporal coherence implies a wide bandwidth). A high temporal coherence means that the light source can be used in an interferometric set-up with a higher distance between the light source and the target (due to a larger coherence length) and that there will be more problems related to speckle in imaging applications.

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Typically made of glass or plastic, optical filters are an integral part of many applications. Be it polarizing filters for life science applications or bandpass filters for biomedical applications, understanding the characteristics of the filters is essential: Dichroic filters, also known as interference filters, reflect unwanted wavelengths and transmit desired wavelengths, while absorptive filters absorb specific wavelengths.

A color filter is an optical absorption filter that absorbs certain colors of light, allowing only selected colors to pass.

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Schneider-Kreuznach is a leading manufacturer of optical filters for industrial applications. As the manufacturer of B+W filters, renowned among photographers worldwide, we bring decades of expertise in filter technology to a wide range of industries. Our filters are trusted for their precision, durability and performance in critical applications where optical clarity and reliability are essential. Whether you need standard filters or custom solutions tailored to your specific needs, Schneider-Kreuznach ensures high-quality optical filters that meet your requirements.

A narrowband filter is an interference filter that filters out only a very narrow spectrum of wavelengths from incident light, blocking the rest of the optical spectrum.

Coherence can be defined as the capability of a light source to produce interference. It has to be admitted that the definition isn’t very clear. Furthermore, talking about coherence is a bit ambiguous, as there are two types of coherence: spatial coherence and temporal coherence. In general, we will say a light source is coherent if it is both spatially and temporally coherent. But what does this really mean?

Optical filters require careful handling to avoid damaging their delicate surfaces. Begin by using a soft air blower to remove loose dust and debris. Next, apply a small amount of lens cleaning solution to a lint-free cloth or lens tissue. Gently wipe the filter surface in a circular motion, starting from the center and moving outward. Avoid using excessive force or abrasive materials that may scratch or damage the filter coating.

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A UV-blocking filter is an optical filter that blocks ultraviolet light and passes only visible light to reduce unwanted UV radiation, while an IR-blocking filter blocks infrared light and passes only visible light to minimize unwanted infrared radiation, improving image quality in optical applications such as cameras or optical sensors.

Keeping it simple: a high spatial coherence means a strong directionality of the light beam. If we consider a holographic display (display that employs light diffraction to create a virtual 3D image of an object), the higher the spatial coherence, the more detailed the reconstructed image will be.

A longpass filter is an optical filter that passes only wavelengths above a certain cutoff wavelength and blocks shorter wavelengths.

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where n is the refractive index of the medium, λ is the central wavelength and Δλ is the full width half maximum (FWHM). We can easily observe that a high Δλ (wide bandwidth) ⇔ low LC⇔ low temporal coherence, while a low Δλ (narrow bandwidth) ⇔ high LC ⇔ high temporal coherence.

In this article we are going to introduce the concept of coherence, as it plays a major role when selecting a light source for a certain application. It is always mentioned in the articles about light sources in the domain of fiber optics but it isn’t clearly explained most of the times. Although it isn’t an easy concept to grasp, we will try to make it as clear as possible.

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Optical filters improve the performance and accuracy of optical systems by selectively transmitting, reflecting or blocking specific wavelengths or ranges of wavelengths. The filters are critical components in several high-precision applications, including machine vision, spectroscopy, and medical imaging such as fluorescence microscopy.

A polarizing filter is an optical filter that selectively blocks or passes light waves based on their plane of vibration, allowing only light with a specific polarization direction to pass while other polarization directions are blocked.

At Schneider-Kreuznach, we design and manufacture both the mechanics and the coating of our high-quality optical filters. This enables us to produce customized optical filters that meet your exact requirements and guarantee the highest quality standards.

Deng, Y., & Chu, D. (2017).“Coherence properties of different light sources and their effect on the image sharpness and speckle of holographic displays” Scientific reports, 7(1), 5893. doi:10.1038/s41598-017-06215-x

where C is the new speckle contrast, C0 is the old speckle contrast, Δλ is the spectrum bandwidth and σ is the surface roughness. Combining this equation and the one for the coherence length, we reach the following conclusions: low temporal coherence ⇔ high Δλ⇔ low speckle, while high temporal coherence ⇔ low Δλ⇔ high speckle.

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Optical filters feature materials and coatings with specific transmission and reflection properties. These materials are designed to either transmit certain wavelengths while blocking others or reflect certain wavelengths while transmitting the rest. The design of these filters is based on the principles of interference and absorption, which determine how different wavelengths interact with the filter material.

A bandpass filter is an optical filter that blocks certain wavelengths or ranges of colors from incident light, allowing only certain ranges of the optical spectrum to pass.