Sending the data with conventional electric data transfer, only one electric signal could be transmitted per cable. Using optical data transfer it is possible to send several different optical signals simultaneously in one glass fiber, without them interfering with one another. This technology is known as Dense Wavelength Division Multiplexing (DWDM). DWDM is the process by which multiple wavelengths carrying the data are simultaneously combined in a single optical fiber, and then separated again at the receiving end of the fiber. More wavelengths used mean more data transferred.
Passive optical components like multiplexers/demultiplexers based on Arrayed Waveguide Gratings (AWG), play a key role in DWDM systems. The AWG is a planar waveguide structure usually obtained on silicon wafer with a SiO2 lower cladding oxide obtained using thermal oxidation of Si substrate. Chemical vapor deposition (CVD) process creates GeSiO2 active layer with refractive index higher than the refractive index of the cladding layer. Optical lithography and dry etching define then AWG waveguide structure. The growth of the upper cladding (CVD process) with refractive index matching with lower cladding is the last technological step.
To design AWGs we use standard commercially available optical software tools together with our in-house developed software tool used to calculate the AWG component size parameters (which have a crucial influence on the AWG optical performance). Additionally, we use in-house developed software tool to evaluate transmission characteristics obtained from the simulations or/and from the measurements. The output of this software tool is a set of transmission parameters like non-uniformity, adjacent crosstalk, non-adjacent crosstalk, background crosstalk, insertion loss, Polarisation Dependent Loss (PDL).,etc.
For more information on AWGs please see PDF: AWG application note.