# Arrayed waveguide grating

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Optical multiplexer component

**Arrayed waveguide gratings** (**AWG**) are commonly used as [optical (de)multiplexers](/source/Optical_add-drop_multiplexer) in [wavelength division multiplexed](/source/Wavelength_division_multiplexing) (WDM) systems. These devices are capable of [multiplexing](/source/Multiplexing) many [wavelengths](/source/Wavelength) into a single [optical fiber](/source/Optical_fiber), thereby increasing the [transmission](/source/Transmission_(telecommunications)) capacity of [optical networks](/source/Optical_communication) considerably.[1]

The devices are based on a fundamental principle of [optics](/source/Optics), which states that [light waves](/source/Light_wave) of different wavelengths [do not interfere](/source/Interference_(wave_propagation)) linearly with each other. This means that, if each [channel](/source/Communication_channel) in an [optical communication](/source/Optical_communication) network makes use of [light](/source/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](/source/Crosstalk_(electronics)) 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](/source/Demultiplexer) to retrieve individual channels of different wavelengths at the receiving end of an optical communication network.[1]

## Operation of AWG devices

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](/source/Phase_(waves)) 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.

Conventional [silica](/source/Silica)-based AWGs, as illustrated in the figure above, are [planar](/source/Plane_(geometry)) lightwave circuits fabricated by depositing layers of [doped and undoped](/source/Doping_(semiconductor)) silica on a [silicon substrate](/source/Wafer_(electronics)).

The AWGs consist of a number of input *(1)* and output *(5)* couplers, a free space [propagation](/source/Wave_propagation) region *(2)* and *(4)* and the grating [waveguides](/source/Waveguide) *(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](/source/Diffraction) 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](/source/Normal_distribution).

- Each wavelength of light coupled to the grating waveguides *(3)* undergoes a constant change of [phase](/source/Phase_(waves)) attributed to the constant length increment in grating waveguides.

- The diffracted light from each waveguide within the grating undergoes [constructive interference](/source/Constructive_interference), resulting in a [refocusing](/source/Focus_(optics)) of the light at the output waveguides *(5).* The spatial position of the output channels is wavelength-dependent, determined by the array [phase shift](/source/Phase_shift) induced by the constant length increment in the grating waveguides.[2]

## References

1. ^ [***a***](#cite_ref-:0_1-0) [***b***](#cite_ref-:0_1-1) Paschotta, Dr Rüdiger (16 April 2005). ["Arrayed waveguide gratings"](https://www.rp-photonics.com/arrayed_waveguide_gratings.html). *RP Photonics AG*. Retrieved 2023-06-15.

1. **[^](#cite_ref-2)** Hecht, Jeff (2015). *Understanding Fiber Optics*.

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