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. This means that, if each
channel in an
optical communication network makes use of
light of a slightly different wavelength, then the light from many of these channels can be carried by a single optical fiber with negligible
crosstalk between the channels. 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]
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 grating waveguides consists of many waveguides, each having a constant length increment (ΔL).
Light is coupled into the device via an optical fiber (1) connected to the input port.
Light
diffracting out of the input waveguide at the coupler/slab interface propagates through the free-space region (2) and illuminates the grating with a
Gaussian distribution.
Each wavelength of light coupled to the grating waveguides (3) undergoes a constant change of
phase attributed to the constant length increment in grating waveguides.
The diffracted light from each waveguide within the grating undergoes
constructive interference, resulting in a
refocusing of the light at the output waveguides (5). The spatial position of the output channels is wavelength-dependent, determined by the array
phase shift induced by the constant length increment in the grating waveguides.[2]