Optical Bandpass filters are used for transmitting the desired portion of wavelength from the total spectrum. It transmits the necessary wavelength and rejects all other unwanted wavelengths. They have wide usage in spectroscopy, clinical chemistry, blood chemistry analysis, fluorescence microscopy, paint-color formulation, and traffic control system.
How Optical Bandpass Filters are made?
Bandpass filters are usually made of colored glass. Bandpass filter create by depositing ways of material on the surface of substratum. There are many dielectric stacks that are later separated by spacer layers. The dielectric stack has many alternating layers of low and high index dielectric material. The thickness of dielectric stacks depends upon the central wavelength of the bandpass filter which is the fourth portion of the central wavelength. The thickness of the spacer layers is half of the central wavelength of the bandpass filter. The spacer layers are usually formed from epoxy, dyes, and colored glass. At last, the filter is fixed with a metal ring for protection and easy handling.
How does an Optical Bandpass Filter work?
A bandpass filter is a combination of longpass filter and shortpass filter. Longpass filters reflect shorter wavelengths when they transmit longer wavelengths. On the other hand, shortpass filters reflect longer wavelengths when they transmit shorter wavelengths. Both filters work together for making a customized bandpass filter. They provide a custom solution for selecting a specific bandpass according to need.
Characteristics of Optical Bandpass Filters
Some important characteristics of Optical bandpass filters are as follows:
CW: Central Wave, specifies the wavelength of transmission profile at the center.
FWHM: Full Width at Half Maximum, it specifies the bandwidth between which filter passes light at half or more of its peak frequency.
Peak Transmission: it measures how much the incident light is transmitted through the filter at the CW.
Blocking Range: It specifies how many wavelengths outside FWHM bandwidth are blocked by the filter.
Types of Optical Bandpass Filters:
Optical bandpass filters are categorized into two types on the basis of the range of wavelength they pass.
Narrowband filters pass less than 1% of incident wavelengths, and they give output light that is specific to a particular frequency.
Wideband filters pass 10% or more than 10% of incident wavelengths, and they give an output of wider range wavelengths.
Difference between Barrier filters and Bandpass filters in terms of fluorescence screen?
Barrier filters are designed to block unwanted wavelengths and they only permit desired wavelengths to pass towards the screen. The role of any barrier filter in fluorescence application is to increase the visual contrast of what you want to see.
Longpass and bandpass are good for blocking the excitation light. The bandpass transmits only green wavelengths, while the long pass transmits green, yellow, orange, and red.
Applications of Bandpass filters
Bandpass filters are frequently used in wireless transmitters . They prevent the transmitters from interfering with more platforms. Bandpass filters are used in audio processing. They have wide use in the medical and research field. They have a usage in SONAR and seismology applications.