Optical filter is used to allow one wavelength to pass through meanwhile block all other wavelengths. Optical filter is an important component in WDM fiber optic systems, where each wavelength is associated with a data channel. Optical filter help select individual wavelength thus the individual WDM information channel is selected.
There are two types of optical filters, one is called fixed optical filter, which allow a fixed, predetermined wavelength to pass through. The other type is called tunable filter, this device dynamically turn the selected wavelength. In many places, WDM MUX/DEMUX and WDM filter is interchangeable, because their function is just the same. Major characteristics of the fiber filters include center frequencies; pass bandwidth, stop bandwidth, isolation and ripple.
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