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Custom Interference Bandpass Filters

Manufactured IF Bandpass Filters

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Find out more about our custom interference bandpass filters

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Interference bandpass filters are excellent for applications requiring specific spectral tolerances. The manufacturing process allows a high level of control on the transmission parameters.

Though we have an extensive stock range of interference bandpass filters, Knight Optical can also provide custom filters manufactured to your specification. We can tailor the spectral properties to meet your application demands including:

  • Peak transmission – either as a minimum value, or regulated to perform within a certain range.
  • Centre wavelength (CWL) within the UV, visible or infrared waveband.
  • Bandwidth or FWHM – we can supply narrowband (< 10nm), standard (10-50nm) and broadband filters (> 50nm).
  • Out-of-band blocking – Typically OD4 (T < 0.01%)

Knight Optical can also provide differing dimensions to fit into your application, including mounted and unmounted options. We typically supply 12.5mm, 12.7mm, 25mm, 25.4mm, 50mm, and 50.8mm diameter mounts, which can be etched with your unique batch number if required, however custom mount sizes can also be supplied.Our filters are:

  • CNC scribed which involves removing the outer diameter of coating and so enabling a glass-to-glass epoxy seal, rather than a glass-to-coating seal, which provides an excellent barrier against moisture.
  • If mounted, they are hermetically sealed to further protect against moisture and there increase the long-term stability.

You can find our typical manufacturing capabilities below, however, please enquire for further information. Please note, the spectral properties are dependent on factors such as the design wavelength and bandwidth size.

Explore the variety of filters Knight Optical provides:

Manufactured IF Bandpass Filters

Speak to our experts about your Custom Interference Bandpass Filters needs today

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    Optical Properties of Interference Bandpass Filters

    You can find our typical manufacturing capabilities below, however, please enquire for further information. Please note, the spectral properties are dependent on factors such as the design wavelength and bandwidth size.

    Diameter5mm to 100mm+
    Centre wavelength (CWL)200nm to 3000nm+
    Bandwidth (FWHM)3nm to 100nm+
    Temperature limits-50°C to 80°C
    Graph to depict the optical properties of Interference Band Pass filters, uncoated 1mm thick


    Frequently Asked Questions

    An interference bandpass filter is a type of optical filter that allows a specific range of wavelengths to pass through while blocking others outside this range. It operates on the principle of optical interference, using multiple layers of thin films to constructively and destructively interfere with incoming light. This process isolates a narrow band of wavelengths, making these filters ideal for applications requiring precise spectral selection, such as scientific research, telecommunications, and optical instrumentation.

    Infrared bandpass filters are designed to selectively transmit infrared wavelengths while blocking visible light and other parts of the spectrum. These filters are crucial in applications such as thermal imaging, night vision equipment, and infrared spectroscopy, where isolating specific infrared wavelengths enhances the performance of the system by providing clearer images or more accurate spectral data, allowing for detailed analysis and observation.

    Bandpass filters find extensive applications across various fields, including scientific research, particularly in spectroscopy and laser systems, to filter out unwanted wavelengths; and in photography and imaging, to enhance contrast or isolate specific light for creative effects. They’re also pivotal in medical imaging and diagnostics, where precise wavelength selection can lead to better imaging contrast and clarity.

    Bandpass filters and notch filters are opposites in their function. While a bandpass filter allows a specific range of wavelengths to pass and blocks those outside this range, a notch filter does the reverse by blocking a specific range of wavelengths and allowing those outside this range to pass. This makes bandpass filters ideal for applications requiring a narrow spectral window, whereas notch filters are used when a specific wavelength range needs to be eliminated, such as in laser protection or noise reduction in signals.

    Optical bandpass filters play a crucial role in imaging and spectroscopy by allowing only a selected range of wavelengths to reach the detector, thereby improving the quality of the image or the spectral data. In imaging, this can mean sharper, more defined images with reduced background noise. In spectroscopy, using bandpass filters can significantly enhance the detection of specific spectral lines or features by filtering out unwanted light, leading to more accurate and sensitive measurements.

    Interference bands are the result of the constructive and destructive interference of light waves when they reflect off the multiple thin-film layers of a bandpass filter. These bands define the specific wavelengths that the filter will transmit, based on the thickness and composition of the layers. By precisely controlling these parameters, manufacturers can design filters with very specific transmission properties, allowing for the creation of highly selective bandpass filters that can target very narrow ranges of wavelengths for various scientific, industrial, and technological applications.

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    We are ready and waiting to answer any queries you may have about interference bandpass filters.

    Additional Information

    Manufacturing Process

    Interference filters are manufactured by depositing layers of material (usually a metal or dielectric material), with differing refractive indices and thickness, on to a glass substrate.

    Customisable Behaviour

    The incident light will behave differently at each layer, due to interference, and ultimately only the desired wavelengths will exit the filter.

    Multiple Substrate Stacks

    Often multiple stacks of these coated substrates, separated by a dielectric spacer layer (filter cavity), are needed to get the desired wavelength and steep slope. One filter can often include 3-7 cavities.

    Bandwidth and Transmission

    Centre wavelength (CWL) is the midpoint of the bandwidth. Peak transmission is the maximum transmission achieved. Full width-half maximum (FWHM) defines the bandwidth of which the filter will transmit – half of the peak transmission will define the minimum and maximum limits of the bandwidth.

    Blocking Bands

    Either side of the transmission band there are blocking bands (or out-of-band blocking), usually specified as an OD value.

    Quality Assurance

    Transmission Verification

    Using our Agilent Cary 5000 spectrophotometer we verify the peak transmission, centre wavelength and FWHM, as well as the out-of-band blocking (OD). For infrared bandpass filters, we use our Agilent Cary 660 FTIR to check the transmission.

    Raw Transmission Data

    We are able to provide the transmission data as raw ASCII (.csv) files or present it as a graph.

    Verified Dimensions

    Dimensions are verified with handheld measuring devices, typically our micrometres.

    Visual Inspection

    All filters are visually inspected by our QA department prior to packaging.

    Typical Applications

    Interference Bandpass Filters for ANPR Cameras

    ANPR Cameras

    ANPR cameras where the centre wavelengths coincide with commonly used NIR LEDs – 740nm, 850nm, 870nm and 940nm. Knight Optical stock NIR ANPR filters with 25.5mm/30.5mm mounted options.

    Interference Gas Bandpass Filters

    Gas band filters

    NIR and IR bandpass filters are often used as gas band filters where the centre wavelength coincides with the absorption of a particular a gas molecule.

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    With our in-house state-of-the-art metrology laboratory you can be confident that your optical components will meet your requirements. You can find out more about our testing facilities here.

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