Arrayed waveguide grating

Arrayed waveguide gratings (AWG) are commonly used as optical (de)multiplexers in wavelength division multiplexed (WDM) systems.

[1] The devices are based on a fundamental principle of optics, which states that light waves of different wavelengths do not interfere linearly with each other.

The AWGs are used to multiplex channels of several wavelengths onto a single optical fiber at the transmission end and are also used as demultiplexers to retrieve individual channels of different wavelengths at the receiving end of an optical communication network.

[1] Conventional silica-based AWGs, as illustrated in the figure above, are planar lightwave circuits fabricated by depositing layers of doped and undoped silica on a silicon substrate.

The AWGs consist of a number of input (1) and output (5) couplers, a free space propagation region (2) and (4) and the grating waveguides (3).

The incoming light (1) traverses a free space (2) and enters a bundle of optical fibers or channel waveguides (3) . The fibers have different length and thus apply a different phase shift at the exit of the fibers. The light then traverses another free space (4) and interferes at the entries of the output waveguides (5) in such a way that each output channel receives only light of a certain wavelength. The orange lines only illustrate the light path. The light path from (1) to (5) is a demultiplexer, from (5) to (1) a multiplexer.