Temperature-tuned ZnS etalon filters for WDM systems

A simple temperature-tunable (5 GHz/ degrees C) ZnS etalon filter for channel selection and noise filtering in amplified wavelength-division (WDM) systems is reported. It has a large free spectral range (30 nm), a narrow passband (4.6 AA), and a low insertion loss (1 dB). The filter has been used for channel selection in a WDM system without any degradation in the receiver sensitivity. When the filter was locked to a desired channel using a simple digital servoloop, it maintained a very stable transmission (maximum drift <3%) even when the wavelength of the transmitter laser was intentionally changed by as much as 1 nm.<
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