Editorial Feature

What is a Dichroic Filter?

Dichroic filters are optical filters that are placed at an angle of 45° to the light source, causing the light to split as some is reflected and some passes through. Dichroic is a Greek word meaning bicoloured - this is in reference to the fact that the transmitted light and the reflected light are two different colours.

Dichroic filters are glass plates that are made of a series of high refractive index dielectric layers that are equally spaced.

These filters are called dichroic mirrors, when their back layer is made totally reflective. Dichroic filters are named based on the color of light they transmit. This datasheet will elaborate on the working principle, construction and applications of dichroic filters.

Working Principle

Dichroic filters work on the principle of destructive interference. The different layers in the filter reflect light of a certain wavelength, leading to destructive interference. As a result the reflected light and transmitted light are of complementary colors.

Construction and Types of Dichroic filters

Dichroic filters are made of glass having a high refractive index. Different types of dichroic filters are classified based on the color of light that it transmits. The types of dichroic filters are as below:

  • Red filter – transmits red and reflects cyan
  • Yellow filter – transmits yellow and reflects blue
  • Green filter – transmits green and reflects magenta
  • Blue filter – transmits blue and reflects yellow.

Applications

Some of the typical applications of dichroic filters are given below:

  • Fluorescence microscopy
  • LCD projectors
  • Laser harmonics separators.

References

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