Arrayed Waveguide Gratings
An arrayed waveguide grating is a (typically fiber-coupled) device which can separate or combine signals with different wavelengths. It is usually built as part of a planar lightwave circuit (or photonic integrated circuit), where the light coming from an input fiber first enters a multimode waveguide section, then propagates through several single-mode waveguides to a second multimode section, and finally into the output ports. Wavelength filtering is based on an interference effect and the different optical path lengths in the single-mode waveguides: any frequency component of the input propagates through all single-mode waveguides, and the output in any channel results from the superposition (interference) of all these contributions. The wavelength-dependent phase shifts lead to a wavelength-dependent overall throughput for any combination of an input port and an output port.
Particularly for AWGs with large numbers of channels, a high precision of the fabrication is required for achieving a low channel cross-talk.
AWGs can be realized with different material systems, e.g. based on fused silica (SiO2), indium phosphide (InP), or silicon (Si).
Arrayed waveguide gratings are mainly applied in optical fiber communication systems, in particular in those based on multi-channel transmission with wavelength division multiplexing (WDM), where individual wavelength channels must be combined or separated. They can be part of more complex photonic integrated circuits, functioning e.g. as WDM data transmitters. An arrayed waveguide grating may also be used for separating the lines in the optical spectrum of a supercontinuum source, or in a pulse shaper for ultrashort pulses.
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