Silicon-based integrated multiplexers for WDM systems

Wavelength division multiplexing systems use multiplexers and demultiplexers to increase network capacity by allowing several information channels to be placed into one fiber. Depending on the application multiplexers and demultiplexers can have wide, coarse or dense channel spacing as well as different number of channels that they process. There are many techniques available today for realization of these passive, wavelength selective components including: thin film filters, Bragg gratings, arrayed waveguide gratings and echelle gratings. The last two solutions appear to be most suitable for wafer scale mass production. Silicon-based technology additionally allows for a high level of integration and compatibility with CMOS processing. Here we discuss issues related to different solutions and fabrication technologies and compare two of them based on planar lightwave circuits. We will illustrate with designed and fabricated components for different applications.