What ‘s the AWG?

PublishTime： 2023-08-30 Article Source：T&S News

AWG, or Arrayed Waveguide Gratings are optical planar devices that are normally used as multiplexers/ demultiplexers. Layouts of those devices are primarily based on an array of waveguides with each imaging and dispersive properties. Although AWGs also are recognized by different names which include Phased Arrays (PHASARs), and Waveguide Grating Routers (WRGs), AWG is the term we use the most in the telecommunications industry. Light waves of different wavelengths intrude linearly with each other, for this reason, a couple of optical channels with barely different wavelengths are able to be transmitted over a single fiber with minimum crosstalk between adjacent channels, and based on which, AWGs, therefore, can be used to multiplex a couple of channels of different wavelengths on a single fiber on the transmitter and additionally be used to demultiplex them back into their channels of different wavelengths on the receiver end.

Due to their function of multiplexing big numbers of wavelengths right into a single fiber, AWGs are generally used as optical multiplexers and demultiplexers in a WDM system. There are different applications which include sign processing, measurement, and sensing. Silica-on-Silicon and Indium Phosphide (InP) primarily based totally semiconductors are the mostly seen technology in the AWG market. The mode field suits nicely with that of an optical fiber, for this reason making them smooth to couple with losses of much less than 0.1dB. In addition, there may be additionally a totally low propagation lack of much less than 0.05dB/cm. InP is the dominant solution in the telecom field.

Working Principle and Features of the Device

An AWG mainly consists of three parts, namely input/output optical fiber, Free Propagation Region (FPR), and grating waveguide. Light waves of different wavelengths enter the FPR through the input fiber. In FPR, light waves are no longer confined to the fiber and become divergent and enter the network of waveguides. The expanded light is then captured by the grating waveguide transmitting it toward the aperture of the output grating. The individual waveguides come in different lengths, with the inner tubes being shorter than the outer ones. The difference in the lengths of the adjacent waveguide is an integer multiple of the central wavelength of the DeMUX. The wavelengths arrive at the other end of the FPR at slightly offset times, with the signals from the inner waveguide coming last and the outer waveguide arriving last. The lengths of the array waveguides are chosen such that the optical path length difference between adjacent waveguides is multiple of the center wavelength of the demultiplexer. Therefore, the wavelengths from the individual arrayed waveguides to the output coupler input aperture are in different phases. Multiple beams of light structurally interfere and converge to a single focal point at the output of the output coupler.

There are also AWGs designed with multiple inputs and an equal number of outputs. Such an AWG has a cyclic behavior that a signal entering input 1 will reappear at output 1 if the frequency is increased by an amount equal to the channel spacing. This device is called a cyclic wavelength router. This AWG type acts as an add-on multiplexer and wavelength switch.

Based on the configuration of the AWG and wavelength switching, additional multiplexers can be fabricated. The most basic add-on multiplexer can be made using two 1xN AWGs with identical wavelength responses. By combining demultiplexers with switches, additional configurable multiplexers can be fabricated. This configuration allows adding and subtracting wavelengths by means of an external control signal. The more multiplexers/demultiplexers added to the configuration increase the insertion loss of the multiplexer. Additional multiplexers with lower insertion loss can be realized by combining a single (N+1) x (N+1) AWG with a wavelength router in a loopback configuration. The demultiplexed wavelengths can be fed into switches where they can be routed to the bypass port or loop back to the wavelength router, which will then multiplex them to the output.

AWG Technologies

Many technologies are used to develop AWG. The two main technologies used are silica-on-silicon technology and indium phosphide semiconductor technology.

Silica on Silicon (SoS) AWG

SoS AWG was introduced to the market in the early 1990s and holds the largest share of the AWG market. SoS is a type of planar lightwave circuit (PLC) fabricated on a flat substrate by placing layers of glass with high silicon content on a wafer. The composition of the glass layers is very similar to that of an optical fiber, which facilitates its coupling to the optical fiber due to its near-mode field conformance. This results in low splicing and low propagation attenuation. Another benefit of SoS AWG's PLC fabrication is its excellent heat dissipation properties that make it suitable for deployment in outdoor factory network environments.

Indium Phosphate-Based AWG (InP)

InP-based AWG is a semiconductor-based AWG that can be integrated with multiple active devices such as optical amplifiers and switches on a single chip. The InP-based AWG can be fabricated in a compact package due to the large index contrast of the InP-based waveguide. The optical attenuation, coupling loss, and crosstalk performance of InP-based AWG are not as good as that of silica-based AWG. Such a limitation is an obstacle for InP-based AWG to be more widely used. The potential of InP-based AWG to integrate into feature-rich circuits such as WDM transceivers and optical add-on multiplexers is a big advantage. This allows manufacturers to embed AWG functionality on active equipment to create InP-based photonic integrated circuits (PICs) to reduce network deployment costs. For example, add-drop multiplexing functions can be performed at the transceiver without the need for an external multiplexer. This reduces component and installation costs, as well as the optical attenuation of many connectors.

Applications

From complex telecommunications connections to very simple add-on multiplexers, there are many applications where AWG can be used. In the telecom industry, AWG is mainly used as a multiplexer/demultiplexer in the WDM network. This is often deployed in long-distance networks such as international networks, national networks, and regional transport networks. The majority of PONs deployed worldwide use wavelength-independent optical splitters for power division and time division multiplexing for upstream and downstream transmission. This reduces deployment costs and eliminates the need for wavelength management for individual connections behind the splitter. With the growing demand for higher bandwidth, AWG is starting to be used in access networks allowing multi-wavelength transmission from the central office to the end user without significant modification to the existing fiber optic network. WDM-PON is a technology in which multiple WDM channels are transmitted over the same optical network from an optical line terminal (OLT) located in an exchanger.

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