Arrayed waveguide grating
Encyclopedia
Arrayed waveguide gratings (AWG) are commonly used as optical (de)multiplexer
s in wavelength division multiplexed (WDM) systems. These devices are capable of multiplexing
a large number of wavelength
s into a single optical fiber
, thereby increasing the transmission
capacity of optical networks
considerably.
The devices are based on a fundamental principle of optics
that light waves of different wavelengths 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 a large number 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.
Conventional silica-based AWGs schematically shown in the above figure, are planar lightwave circuits fabricated by depositing doped and undoped
layers of silica on a silicon substrate
. The AWGs consist of a number of input (1) / output (5) couplers, a free space propagation
region (2) and (4) and the grating waveguide
s (3). The grating consists of a large number of waveguides with 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. Light diffracted from each waveguide of the grating interferes
constructively and gets refocused
at the output waveguides (5), with the spatial position, the output channels, being wavelength dependent on the array phase shift.
Optical add-drop multiplexer
An optical add-drop multiplexer is a device used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of a single mode fiber . This is a type of optical node, which is generally used for the construction of optical telecommunications...
s in wavelength division multiplexed (WDM) systems. These devices are capable of multiplexing
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
a large number of wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s into a single optical fiber
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...
, thereby increasing the transmission
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
capacity of optical networks
Optical communication
Optical communication is any form of telecommunication that uses light as the transmission medium.An optical communication system consists of a transmitter, which encodes a message into an optical signal, a channel, which carries the signal to its destination, and a receiver, which reproduces the...
considerably.
The devices are based on a fundamental principle of optics
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
that light waves of different wavelengths interfere
Interference
In physics, interference is a phenomenon in which two waves superpose to form a resultant wave of greater or lower amplitude. Interference usually refers to the interaction of waves that are correlated or coherent with each other, either because they come from the same source or because they have...
linearly with each other. This means that, if each channel
Channel (communications)
In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel...
in an optical communication
Optical communication
Optical communication is any form of telecommunication that uses light as the transmission medium.An optical communication system consists of a transmitter, which encodes a message into an optical signal, a channel, which carries the signal to its destination, and a receiver, which reproduces the...
network makes use of light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
of a slightly different wavelength, then the light from a large number of these channels can be carried by a single optical fiber with negligible crosstalk
Crosstalk (electronics)
In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel...
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.
Operation of AWG devices
Doping (semiconductor)
In semiconductor production, doping intentionally introduces impurities into an extremely pure semiconductor for the purpose of modulating its electrical properties. The impurities are dependent upon the type of semiconductor. Lightly and moderately doped semiconductors are referred to as extrinsic...
layers of silica on a silicon substrate
Wafer (electronics)
A wafer is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices...
. The AWGs consist of a number of input (1) / output (5) couplers, a free space propagation
Wave propagation
Wave propagation is any of the ways in which waves travel.With respect to the direction of the oscillation relative to the propagation direction, we can distinguish between longitudinal wave and transverse waves....
region (2) and (4) and the grating waveguide
Waveguide
A waveguide is a structure which guides waves, such as electromagnetic waves or sound waves. There are different types of waveguides for each type of wave...
s (3). The grating consists of a large number of waveguides with a constant length increment (ΔL). Light is coupled into the device via an optical fiber (1) connected to the input port. Light diffracting
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
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
Phase (waves)
Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...
attributed to the constant length increment in grating waveguides. Light diffracted from each waveguide of the grating interferes
Interference
In physics, interference is a phenomenon in which two waves superpose to form a resultant wave of greater or lower amplitude. Interference usually refers to the interaction of waves that are correlated or coherent with each other, either because they come from the same source or because they have...
constructively and gets refocused
Focus (optics)
In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by...
at the output waveguides (5), with the spatial position, the output channels, being wavelength dependent on the array phase shift.