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Optical Filter Types

 

Filter types include Fluorescence, Bandpass (Narrow- and Multi-Band), Edge (Shortpass and Longpass), Notch, Dichroic, Neutral Density (ND) and Polarizing

 

Choose Mounted or Unmounted

 

Hard-Sputtered, Traditional Soft Coatings, and a Variety of Colored Glass and Plastic Options Available

 

Customization Options for Non-Stock Sizes and Wavelengths

Edmund Optics® manufactures and supplies optical filters to a wide variety of life science applications, including medical diagnostics and biotechnology, as well as industrial applications such as semiconductor, metrology, aerospace, automation, and robotics.

Precision optical filters are used to block, transmit, and reflect selected wavelengths, called wavebands, from light sources including lasers, LEDs, and broadband illumination sources. Precision optical filters enable such diverse applications as fluorescence microscopy, flow cytometry, factory automation, optical character recognition (OCR), and autonomous vehicles.

Types of Filters

Bandpass Filters

Optical bandpass filters are used to transmit a desired portion of the spectrum while rejecting all other wavelengths outside of the passband.

Figure 1 (right): Bandpass filters transmit specifically desired wavelengths or wavebands while rejecting all other wavelengths outside the passband.

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Bandpass Filters

Shortpass Filters

Optical shortpass edge filters are used to transmit wavelengths shorter than a specific cut-off wavelength.

Figure 2 (left): Shortpass filters, also known as shortpass egde filters, transmit wavelengths shorter than a specific cut-off wavelength.

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Shortpass Filters

Longpass Filters

Optical longpass edge filters are designed to transmit wavelengths greater than the specific cut-on wavelength of the filter.

Figure 3 (right): Longpass filters, also known as longpass egde filters, transmit wavelengths longer than a specific cut-on wavelength.

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Longpass Filters

Notch Filters

Notch filters selectively reject a spectrum of light wile transmitting all other wavelengths.

Figure 4 (right): Transmission profile of a notch filter

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Notch Filters

Dichroic Filters

Dichroic filters reflect unwanted wavelengths while transmitting the desired portion of the spectrum. This effect is desired for some applications because light can be separated by wavelength into two paths.

Figure 5 (right): Dichroic filters, also known as dichroic mirrors, reflect unwanted wavelengths and transmit desired portions of the spectrum. This effect is useful for applications where both the reflected and transmitted light will be used at a further point in a system.

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Dichroic Filters

Neutral Density (ND)

Neutral density filters are designed to reduce transmission evenly across a spectrum of light by absorbing or reflecting the portion of light not being transmitted.

Figure 6 (right): Transmission profile of a neutral density filter

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Neutral Density (ND)

Polarizing

Polarizers, or polarizing filters, preferentially transmit one polarization of light over the other.

Figure 7 (right): Transmission profile of a single polarizing filter and two parallel and crossed polarizing filters

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Polarizing

Colored Glass & Absorptive

Colored glass and absorptive filters function by using the material's inherent absorption properties.

Figure 8 (right): Colored glass filters consist of glass substrates of a given absorption and thickness

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Polarizing

Optical Filter Composition

3D printed mechanics used for prototyping
Figure 9: A traditional filter (left) and hard-sputtered filter (right).

Glossary

FAQ  Bandpass
Also referred to as waveband, passband, or bandwidth, bandpass is the wavelength range used to denote a specific part of the spectrum that passes incident energy through a filter. The first order is always at the design wavelength of the filter.

  See also Notch Filter , Filter , Full Width at Half Maximum (FWHM) , Cavity , Central Wavelength (CWL)

FAQ  Blocking
The blocking amount is the amount of light that is rejected, not passed, by a filter outside the passband. It is expressed as the ratio of total energy transmitted outside the passband to the total energy transmitted within the passband. Blocking values are given over a specified wavelength range.

  See also Cavity , Blocking Range , Optical Density (OD)

FAQ  Blocking Range
Also referred to as the stopband, blocking range is a wavelength range used to specify a spectral region of energy that is not transmitted by a filter. It is typically specified in terms of Optical Density (OD).
FAQ  Central Wavelength (CWL)
Used to denote the peak transmitting wavelength of a filter, it is the midpoint determined by the passband wavelengths where the transmittance is 50% of the peak (denoted by the Full-Width at Half Maximum).

  See also Filter , Bandwidth

FAQ  Cut-Off Wavelength
Cut-off wavelength is the wavelength at which transmission decreases to 50% in a shortpass filter.

  See also Filter , Cut-On Wavelength

FAQ  Cut-On Wavelength

In filter terminology, cut-on is the wavelength at which the transmission increases to 50% throughput in a longpass filter.

  See also Cut-Off Wavelength

FAQ  Filter
Filters are optical components that transmit, reflect, or absorb certain wavelengths or frequencies of light. Filter types include bandpass, longpass, shortpass, interference notch and rugate notch, color, dichroic, and neutral density.

  See also Cold Mirror , Cavity , Central Wavelength (CWL) , Stopband , Longpass Filter , Neutral Density Filter (ND) , Rugate Notch Filter , Heat Absorbing Glass , Notch Filter , Peak Transmittance , Shortpass Filter , Full Width at Half Maximum (FWHM) , Bandwidth , Fluorescent Filter , Hot Mirror , Dichroic Filter , Cut-Off Wavelength , WRATTEN Filter , Cut-On Wavelength , Interference Filter , Dichroic Coating

FAQ  Full Width at Half Maximum (FWHM)

A specific wavelength region of the bandwidth of a filter defined by the two points of the passband where transmittance is 50% of the peak.

  See also Filter , Bandwidth , Central Wavelength (CWL)

FAQ  Longpass Filter

A type of filter in which the transmission band is a region of longer wavelengths as compared to the region blocked.

  See also Shortpass Filter

FAQ  Neutral Density Filter (ND)

A type of filter that yields a constant value for attenuation, or optical density, over a bandwidth (i.e. spectrally flat). It is useful for attenuating, or reducing, overall light in a system.

FAQ  Notch Filter

A type of filter designed to block a pre-selected bandwidth and transmitt all other wavelengths within the design range of the filter. Notch filters are manufactured using the dielectric stack method which involves using a series of thin layers of dielectric materials, of alternating refractive index.

FAQ  Optical Density (OD)

Optical density is a value that describes the amount of energy that can pass through an optical material. It is directly related to the transmittance of the material. The greater the OD, the more light being blocked.

  See also Continuously Variable Apodizing Filter , Blocking , Neutral Density Filter (ND)

FAQ  Peak Transmittance

The highest transmittance value for light being passed by a filter.

  See also Filter

FAQ  Peak Wavelength

The wavelength of light that has the highest transmittance value.

FAQ  Reflection

Radiation that changes direction, but not wavelength, after contact with a material surface.

  See also Transmission , Parity

FAQ  Shortpass Filter

A type of filter where the transmission band is a wavelength range of shorter wavelengths, typically lower than the region blocked.

  See also Filter , Longpass Filter

FAQ  Transmission

The amount of radiant energy that passes through an optical medium, not being absorbed, reflected, or scattered.

  See also Reflection

FAQ  Wavelength

The peak to peak distance covered by one cycle of an electromagnetic wave. It is inversely related to frequency. The longer the wavelength, the lower the frequency; conversely, the shorter the wavelength, the higher the frequency.

Optical Filter Applications

Optics are crucial to many advanced diagnostics techniques and technologies that are used to analyze blood. Beamsplitters and various types of filters, such as bandpass, dichroic, longpass, and shortpass filters, are only a few of the most prominently utilized.

Machine Vision

Because monochrome cameras are not able to differentiate different colors, the addition of a color filter can greatly improve contrast between objects. Color filters will generally lighten objects of the same color and darken objects of a different color (Figure 10).

To learn more about how to use optical filters to improve your machine vision application, visit our Filtering in Machine Vision application note.

Sample
Figure 10a: Contrast Enhancement: Sample under Inspection.
No Filter
Figure 10b: Contrast Enhancement: No Filter.
Red Filter
Figure 10c: Contrast Enhancement: Red Filter.
Green Filter
Figure 10d: Contrast Enhancement: Green Filter.

Fluorescence Microscopy

Fluorescence microscopy uses fluorescence, induced by fluorophores, rather than absorption, scatter, or reflection. Once a sample is dyed with a fluorophore, it absorbs energy of a specific wavelength range, called the excitation range, and then re-emits the energy in the form of light at a different wavelength range, called the emission range.

A typical fluorescence microscopy system must then require an excitation filter, a dichroic filter, and an emission filter, as well as a detector or sensor. For more information on how these components fit into the fluorescence microscopy system, visit our Optical Microscopy Application: Fluorescence application note.

Figure 11 (right): Fluorescence Image of Microspheres
Fluorescence Microscopy
Fluorescence Microscopy
Figure 12: A generalized fluorophore spectral curve. For more information on the importance of fluorophores in fluorescence microscopy, visit the Fluorophores and Optical Filters for Fluorescence Microscopy page.
Fluorescence Microscopy
Figure 13: The basic optical filtering arrangement for fluorescence microscopy. For more information on Fluorescence microscopy, visit the Optical Microscopy Application: Fluorescence page.

Flow Cytometry & Particle Analysis

Flow cytometry is an analytical technology used to count, inspect, and sort particles such as blood cells in a sample of blood. While these particles flow through a fluidics sub-system, lasers are focused onto the flowing fluid. Particles in the fluid then scatter the light depending on the size and shape of the particle, and this scattered light, after passing through a filter, is captured by detectors. Throughout this system, dichroic filters are additionally used to channel light of specific wavelengths to the correct detectors. Optical filters are critical for the accurate detection of particles flowing inside a flow cytometer. For more information on how Edmund Optics’ products power flow cytometry, visit our Advanced Diagnostics Blood page.

Flow Cytometry & Particle Analysis

Training Materials

 

Introduction to
Optical Filters

Read
 

Custom Bandpass Filter
using Shortpass and Longpass Filters

Read
 

Fluorophores and Optical
Filters for Fluorescence Microscopy

Read
 

Understanding Neutral
Density Filters

Read
 

Optics Enabling:
Advanced Diagnostics

Read

FAQs

Learn more about Optical Filters from our Frequently Asked Questions

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