Interference

In terms of the spectral characteristics there are three basic types of filters:

• Band pass filters (BP) that transmit light only around a certain center wavelength.
   
  Standard band pass filters::
  BP 565 140 | BP 590 50 | BP 640 110
  BP 655 50 | BP 680 100 | BP 855 70
   
• Long pass filters (LP) that transmit light with wavelengths longer than a certain cut-on wavelength.
   
• Short pass filters (SP) that transmit light with wavelengths shorter than a certain cut-off wavelength.

Concerning the physical principle there are two basic types of filters:

• Absorption filters which suppress the undesired part of the spectral energy by transforming it into heat in the bulk of the filter material.
   
• Reflection filters which reflect the undesired part of the spectral energy back from the filter surface by interference (interference filters).

Reflection filters are made by depositing multiple layers of materials with differing refractive indices onto a glass substrate. The spectral characteristics of these filters depend upon the angle of incidence of light.

By designing a specific thin film layer system, nearly any desired transmission characteristic can be achieved. By combining both principles, i.e. using an absorptive glass as substrate for the multiple thin layers, special spectral characteristics can be achieved.

For OEM volumes, we offer the design and manufacture of an appropriate filter per special requested transmission characteristic. Please use the parameters listed below to specify your requirements.