Calcite Frequency Splitter for High-Density Wavelength-Division-Multiplexing Transmission

In this work we present a frequency demultiplexing device, inserted in a multimode transmitting stage for High Density WDM systems. It is based on bulk Calcite single crystals and represents a valuable and costeffective alternative solution to dispersive gratings and Fahry-Perot filters in separating closely spaced optical channels. The device has been designed as a componenf of a transmitter based on a Er:YbGlass laser source. where optical channels must be spatially separated to be indipendently modulated. It operates in free space and it is built up of three basic modules, each of which makes use of one Calcite crystal. It separates the 4 central modes of the source, IOKhz-wide and 39Ghz-spaced. In order to demultiplex N channels, N-1 modules can be assembled.The only requirement set on the Sate of Polarization of the source beam is stability. A precision of 0.1" in thermal control guarantees tunability and crosstalk performance. More than 28 dB of rejection between channels are. measured, and insertion losses amount to less than I dB.