Top 10 Filter Brand & Manufacturers

What is a Filter?

A filter is an optical device that can selectively transmit or block light within a specific wavelength range. Its main function is to change the spectral composition of light through absorption, reflection or scattering, etc., so that only light of specific wavelengths (or within a specific wavelength range) can pass through, while light of other wavelengths is attenuated or blocked. Filters play a crucial role in many fields such as optical instruments, photography, display technology, and spectral analysis.

History of the Filter

• Early Development: The origin of filters can be traced back to the early period of optical research. In the 19th century, with the development of optical experiments and optical instruments, scientists began to try to use materials like colored glass to achieve simple filtering functions. These early filters were mainly based on the addition of metal oxides and other components in the glass to absorb light of specific wavelengths. They were used in astronomical observations and early photography to help reduce stray light and improve image quality.
• Technological Advances: In the 20th century, with the progress of materials science and thin-film technology, the performance of filters has been significantly improved. Thin-film filters have gradually emerged. By depositing multiple layers of thin films on substrates, more precise wavelength selection can be achieved. This enables filters to be used in more complex optical systems, such as optical microscopes, spectrophotometers and other instruments, for the separation and detection of light of specific wavelengths. Meanwhile, plastic filters have also been developed. They have the advantages of low cost and easy processing and are used in some fields where high precision is not required.
• Modern Developments: Nowadays, filter technology is highly developed. There are products that can achieve high-precision filtering in a wide range of wavelengths including ultraviolet, visible and infrared. For example, in the field of optical communication, in order to meet the requirements of high-speed and large-capacity data transmission, ultra-narrowband filters are needed to accurately select light signals of specific wavelengths. In addition, through nanotechnology and micro-nano processing techniques, filters with special functions can be manufactured, such as adjustable filters and multi-layer composite filters, which are used in complex modern optical applications such as adaptive optical systems and laser processing.

Purposes of the Filter

• Optical Imaging: In the fields of photography and videography, filters are used to improve image quality. For example, using a polarizing filter can reduce the reflected light on the surfaces of water, glass, etc., making the underwater objects or the scenes behind glass photographed more clearly. In astronomical photography, by using filters of different wavelength bands, specific features of celestial bodies can be highlighted. For example, using an H-α filter to photograph the light of specific wavelengths emitted by nebulae can enhance the contrast of nebulae in images.
• Spectral Analysis: In scientific research and industrial testing, filters are key components of instruments such as spectrometers. They can separate light of specific wavelengths for the analysis of the spectral characteristics of substances. For example, in chemical analysis, by using a filter to select light of a specific wavelength to excite the molecules in a sample and then detecting its emission spectrum, the composition and structure of the substance can be determined.
• Display Technology: In display devices such as liquid crystal displays (LCDs) and organic light-emitting diode displays (OLEDs), filters are used to control the color and brightness of light. Color filters can decompose white light into basic colors such as red, green and blue, thus realizing color display. By optimizing the spectral characteristics of filters, the color saturation and contrast of displays can be improved.
• Optical Communication: In fiber-optic communication systems, filters are used to select and separate light signals of different wavelengths. Wavelength division multiplexing (WDM) technology relies on high-precision filters to enable multiple light signals to be transmitted simultaneously in the same fiber. At the receiving end, the different wavelength signals are separated by filters, which greatly increases the communication capacity of the fiber.

Principles of the Filter

• Absorption Filters: Such filters are mainly based on the absorption characteristics of materials for different wavelengths of light. They contain substances that can absorb light of specific wavelengths. When light passes through the filter, the atoms or molecules of these substances will absorb photons with specific energies (corresponding to specific wavelengths), so that light of these wavelengths will be attenuated. For example, in glass filters containing certain metal ions, the electron transitions of metal ions will absorb light of specific wavelengths, so that only light of other wavelengths can pass through.[!--empirenews.page--]
• Reflection Filters: Reflection filters utilize the interference principle of optical thin films. Multiple layers of thin films with different refractive indices are deposited on a substrate. When light shines on the filter, reflection and refraction will occur at the interfaces of each layer of thin films. By reasonably designing the thickness and refractive index of the thin films, the light of specific wavelengths can be enhanced through interference during the reflection process and thus be reflected back, while light of other wavelengths can pass through. Such filters are often used in situations where high reflectivity of specific wavelengths of light needs to be blocked.
• Interference Filters: Interference filters are also based on the interference principle of light. They consist of two reflective layers and an intervening spacer layer. When light enters the filter, multiple reflections and interferences will occur between the reflective layers. By precisely controlling the thickness of the spacer layer and the optical properties of the reflective layers, only light of wavelengths that meet specific interference conditions can be strengthened and pass through the filter after multiple reflections, while light of other wavelengths will be attenuated due to interference cancellation. Interference filters can achieve very narrow bandwidth filtering and are often used for high-precision spectral selection.

Features of the Filter

• Center Wavelength: A filter has a center wavelength (for a narrowband filter) or a center wavelength range (for a broadband filter), which is the main target wavelength for filtering. The accuracy and stability of the center wavelength are crucial for applications that require precise wavelength selection, such as optical communication and spectral analysis.
• Bandwidth: Bandwidth refers to the wavelength range that a filter can effectively transmit. A narrowband filter has a narrow bandwidth and can accurately select light of specific wavelengths, while a broadband filter can transmit light within a relatively wide wavelength range. The size of the bandwidth directly affects the filtering effect and application scenarios of the filter.
Transmittance: Transmittance refers to the ratio of the intensity of light passing through the filter to the intensity of incident light within the passband range of the filter. A filter with high transmittance can transmit the light of target wavelengths more effectively and reduce the loss of light energy. Transmittance is an important parameter in applications that have high requirements for light intensity, such as optical imaging and optical communication. Cut-off Depth: Cut-off depth is an indicator to measure the blocking ability of a filter for light of cut-off wavelengths (i.e., wavelengths that need to be blocked). A deeper cut-off depth means that the filter can attenuate light of unwanted wavelengths more effectively, thereby improving the quality of filtering. In applications that require strict separation of light of different wavelengths, such as spectral analysis and optical communication, a filter with high cut-off depth is essential. Incidence Angle Dependence: The filtering performance of a filter usually changes with the incidence angle of light. For some high-precision applications, such as optical instruments and optical communication, it is necessary to consider the performance changes of the filter at different incidence angles to ensure the stability and accuracy of the system.

Types of the Filter

• Absorption Filters: As mentioned above, these filters are based on the absorption characteristics of materials. Common ones include colored glass filters and plastic filters. Colored glass filters have good chemical stability and optical uniformity and are suitable for optical systems in harsh environments such as high temperature and high humidity. Plastic filters have low cost and light weight and can be made into various shapes and sizes. They are often used in consumer optical products where high precision is not particularly required.
• Interference Filters: They include dielectric interference filters and metal-dielectric interference filters. Dielectric interference filters are mainly composed of multiple layers of dielectric thin films and can achieve high-precision narrowband filtering. They are widely used in fields such as spectral analysis, laser technology and optical communication. Metal-dielectric interference filters combine the advantages of metal reflective layers and dielectric thin films and have advantages in some applications that require wide-angle incidence and high reflectivity.[!--empirenews.page--]
• Polarizing Filters: Polarizing filters can selectively transmit light of specific polarization directions. They are made based on the birefringence characteristics of crystals or the polarization-selective transmission characteristics of thin films. In photography, liquid crystal displays and optical instruments, polarizing filters are used to reduce reflected light, control the polarization state of light, etc., so as to improve image quality or the performance of optical systems.
• Neutral Density Filters: Such filters have a uniform attenuation effect on light in the entire visible light band without changing the color of light. They are mainly used to adjust the intensity of light. In photography, they can be used to control the exposure amount. In optical experiments, they can be used to adjust the light intensity to avoid detector saturation and other situations.

Precautions for Using the Filter

• Wavelength Matching: Ensure that the filtering wavelength range of the filter matches the wavelength required by the application. If the center wavelength or bandwidth of the filter does not meet the requirements, it may lead to ineffective light filtering or excessive filtering, which will affect the performance of the system. When selecting a filter, carefully refer to its spectral characteristic curve to ensure that it can meet the optical wavelength requirements of the application.
• Light Intensity Limitation: A filter has a maximum light intensity limit that it can withstand. Excessive light intensity may cause damage to the filter. For example, an absorption filter may be damaged due to excessive absorption of light energy and heat generation, and an interference filter may have its thin film structure damaged due to the impact of high-energy light. When using a filter, it is necessary to understand its light intensity tolerance and ensure that the light intensity in the application is within a safe range.
• Incidence Angle Control: As mentioned before, the performance of a filter is related to the incidence angle of light. When designing an optical system, try to control the incidence angle of light within the range where the filter performance is stable. If the incidence angle changes greatly, it may be necessary to compensate for the performance changes of the filter or choose a filter with wider incidence angle adaptability.
• Cleaning and Maintenance: Keeping the filter clean is crucial for its performance. Contaminants such as dust and oil stains may affect the transmittance and filtering effect of the filter. When cleaning the filter, use appropriate cleaning tools and methods to avoid scratching the surface of the filter. Generally, clean compressed air, special optical cleaning solutions and soft lens paper can be used for cleaning.

Things to Consider When Purchasing a Filter

• Application Requirements: Clearly define the specific requirements of the application, including the wavelength range to be filtered, bandwidth, transmittance, cut-off depth and other parameters. For example, if it is used in a wavelength division multiplexing system in optical communication, it is necessary to purchase a high-precision narrowband interference filter, and there are relatively high requirements for the accuracy and stability of its center wavelength.
• Filter Type: Select the appropriate filter type according to the application requirements. For example, in photography, polarizing filters, neutral density filters or specific color absorption filters may need to be selected according to different shooting scenes. Consider the advantages and disadvantages of different types of filters. For example, interference filters have high precision but are relatively expensive, while absorption filters have lower cost but may not have precise enough bandwidth control.
• Performance Parameters: Carefully check the performance parameters of the filter, including the accuracy of the center wavelength, the stability of the bandwidth, transmittance, cut-off depth, etc. These parameters should be able to meet the optical requirements of the application. For example, for a spectral analysis instrument, the filter needs to have high accuracy of the center wavelength and deep cut-off depth to ensure accurate spectral separation.
• Size and Shape: Consider whether the physical size and shape of the filter meet the installation requirements of the optical system. The size of the filter should match that of other optical elements in the optical path, and its shape (such as circular, square, etc.) should be convenient for installation in optical equipment. In some optical systems with limited space, miniaturized filters need to be selected.[!--empirenews.page--]
• Cost and Budget: Determine the budget for purchasing the filter. The price of filters varies depending on factors such as type, performance and brand. Consider not only the purchase cost but also the long-term use cost, such as possible replacement cost and maintenance cost. In some applications where extremely high performance is not required, cost-effective filters can be selected.
• Manufacturer Support and Training: Select a reputable manufacturer that can provide technical support and training. Correct use of filters may require certain optical knowledge. The resources provided by the manufacturer, such as user manuals, online tutorials and customer support, can help users better use the filters and solve possible problems.

Related Terms of the Filter

• Center Wavelength (λ₀): For a narrowband filter, it refers to the wavelength with the highest transmittance; for a broadband filter, it refers to the wavelength corresponding to the center position of the main transmission wavelength range. It is the main target wavelength for filtering by the filter, and the unit is usually nanometer (nm).
• Bandwidth (Δλ): It refers to the wavelength range that a filter can effectively transmit light through, which is an indicator to measure the width of the filtering range of the filter, and the unit is nanometer (nm). The bandwidth of a narrowband filter is relatively narrow, usually between a few nanometers and dozens of nanometers, while that of a broadband filter is relatively wide.
• Transmittance (T): It refers to the ratio of the intensity of light passing through the filter to the intensity of incident light within the passband range of the filter, usually expressed as a percentage. The higher the transmittance, the higher the transmission efficiency of the filter for the light of target wavelengths.
• Cut-off Depth (D): It is used to measure the blocking ability of a filter for light of cut-off wavelengths. It is usually expressed in terms of optical density (OD). The larger the optical density, the deeper the cut-off depth, and the more severely the light at the cut-off wavelength is attenuated.
• Incidence Angle (θ): It refers to the angle between the light and the normal of the filter surface. The performance of a filter (such as transmittance, center wavelength, etc.) usually changes with the incidence angle.