What do optical communications, remote sensing, bio/chemical molecular analysis, and astronomy have in common? Each of these applications utilize photonics technologies to select desired information (be it telecommunication signals or images of cells or galaxies) from undesired background noise (be it other communication signal bands or ambient light) by maximizing transmission of light to the photodetector in the spectral band of interest while minimizing the amount of “out-of-band” light that reaches the same photodetector.
Signal to noise ratio (SNR or S/N) is a measure used in many disciplines but is most common in analyzing electrical signals, and is defined as the ratio of the power of signal (desired input) to the power of background noise (undesired input).
In an environment where the signal power “is what it is” (i.e. it can’t be controlled or increased) the path to improving this ratio, and thus the ability to better discriminate the desired information from the undesired background, is to reduce the power of the noise – less background.
Optical filters provide the wavelength selectivity that delivers “more signal, less background” to these, and many more, photonics applications.