Optical Filters Information

Optical Filters Information

Optical filters are used to attenuate light across a certain portion of the spectrum. Common types of optical filters include bandpass or interference filters, cold or hot mirrors, color filters, diachronic filters, long or short pass filters, neutral density filters, and spectral filters.

Types of Optical Filters

Bandpass or interference optical filters are designed to transmit a specific waveband. These optical filters are a combination of long pass and short pass filters, although bandpass filters typically have lower transmittance values than long or short pass filters. Bandpass optical filters are composed of many thin layers of dielectric materials that have differing refractive indices to produce constructive and destructive interference in the transmitted light.

Cold mirror optical filters are heat transmitting mirrors / filters that are designed to reflect visible wavelengths while transmitting near-infrared wavelengths. Similarly, hot mirror optical filters are heat reflecting mirrors that are designed to transmit visible wavelengths while reflecting near-infrared, heat generating wavelengths.

Other types of optical filters include color filters and dichroic filters. Color optical filters include a wide range of filter types that are distinguished by specific color spectrums and wavelengths, in addition to their Schott glass compositions. Dichroic optical filters are accurate color filters that are used to pass selected wavelengths of light, while reflecting all other colors and wavelengths. Dichroic mirrors are often used to reflect desired colors or wavelengths. 

Long or short pass optical filters are also commonly available. Long pass filters transmit a wide spectral band of long wavelength radiation while blocking short wavelength radiation. Short pass optical filters transmit a wide spectral band of short wavelength radiation while blocking long wave radiation.

Optical filters are also available for neutral density and spectral specificity. Neutral density optical filters are designed to reduce transmission evenly across a portion of the spectrum. They are slightly sensitive to angles, but are more forgiving than interference filters. Spectral optical filters are used to selectively transmit light according to its wavelength. Spectral filters should not be mistaken for color filters, which can be differentiated by their associated Schott glass number.

Choosing Optical Filters

Optical filters should be chosen based on their specific application use and whether it is to be used in the infrared (IR), visible (VIS), or ultraviolet (UV) ranges. Other considerations for optical filters include filter shape and filter surface quality. Filters may be commonly available in circular, square, and rectangular shapes; other shapes for optical filters may also be available.

• Optical Filter Guide
  In the high technology work of constant change, one element, the "High Precision Optical Interference Filter" has remained essentially unchanged for almost 40 years. These extremely compact optical elements offer a number of advantages over the other types of elements designed to isolate discreet...
• Optical Filter Specifications (.pdf)
  Following is a short review of filter specifications to assist you in formulating requirements for your particular application....
• Optical Filter Specifications