Arrayed waveguide grating
Arrayed Waveguide Grating (AWG) is multiplexers / demultiplexers are planar waveguide devices.Image and dispersive properties are based on an array of waveguides. They imaging
the field in an input and output waveguide on to array waveguides in such a way that the different wavelength signals presented.
Arrayed Waveguide Grating (AWG) was first discovered by Smit in 1988 and later by Takahashi in 1990 and after that Dragone in 1991. They are known by under different names: Phased Arrays (PHASARs), Arrayed Waveguide Gratings (AWGs), and the Waveguide Grating Routers (WGRs). The acronym AWG introduced by Takahashi is the most frequently used name today. Thin-Film Filters and Fibre Bragg Gratings, AWGs are the most important filter type applied in WDM networks. They are expected to become the most important advance of Photonic Integrated Circuits technology.
Modern world the most important technologies are used for AWGs.
Indiumphosphide (InP) based semiconductor technology.
In addition to that they research on silicon-based polymer technology and on lithium niobate have been reported as well. Silica-on-silicon (SoS) AWGs have been introduced to the market in 1994 and currently hold the largest share about the AWG market.
This modal matches with fibre and therefore it relatively easy to couple them to fibres. Low propagation loss (< 0.05 dB/cm) and high fibre-coupling efficiency of (losses in the order of 0.1 dB) with they combined.
The major disadvantage is, they are relatively large due to their fibre matched waveguide properties. They are prohibiting the use of short bends. This is for the present being improved by using higher index disparity and the spot-size converters to maintenance fibre coupling low losses.
Array Waveguide Grating
This is a new technology uses an integrated array of waveguides as a grating and interleaving. The arrayed waveguide grating (AWG) is a planar waveguide device. And the light going through a device grating will produce an interference pattern, suggesting the light is diffracted only at certain angles. The spatial intensity of distribution is a function of the grating, the wavelength and the angle of occurrence. In here different wavelengths will be diffracted in the different angles (spatially separated). Arrayed waveguide grating (AWG) is producing a tiny grating with lithographic technology and with low losses.
Functions in AWG:-
Ttransmissive diffraction and grating in bulk of optics
Diffracting light at angles- that depend on the wavelengths
The primary application of arrayed waveguide gratings is WDM. By developing AWG, used for WDM wavelength-division multiplexing (WDM) and demultiplexing. Initially, developers are found that AWGs can be integrated with other planar waveguide components. And a variety of other functions like,
- Including dynamic gain
- Reconfigurable optical add/drop multiplexers
- Wavelength-selectable lasers.
The arrayed waveguide grating base interleaver is consists of an array of narrow waveguides. The signals running closed each other between a pair of mixing regions or coupling zones. The input signals first enter the mixing region and where they are coupled in to the several cyclic waveguides running up to the second mixing region.
After that the light transmitted to the second mixing region .I that region the wave signal diffraction and spreads different wavelengths at different angles, it is like a diffraction grating.
The mixing region acts like a lens to focus the diffracted light onto a series of output ports on the opposite side. Beneficent interference focuses light of a peculiar wavelength at only one point on the opposite side, with the ports arranged to collect light at the expected wavelength ranges, such as standard optical channel slots for WDM.
The number of output ports and the number of channels are separated, with the free spectral range of the device equalling the channel spacing multiplied by the number of channels. The number of waveguides running between the two mixing regions is greater than the number of channels.
AWG is a planar-waveguide devise execution of high-order transmission gratings. Arrayed waveguides fabricated in silica, plastic, silicon, or III-V semiconductor materials such as indium phosphates. AWG as a planar waveguide device, it can be fabricated monolithically and integrated with other components
Arrayed waveguide gratings have gained acceptance for WDM with high channel counts because their composition allows lower cost per channel than the systems based on discrete optics. When in the laboratory versions have achieved extremely high channel counts and the spacing, with channel spacing to 10 GHz and hundreds of channels in a single device.
The main application for AWGs is for demultiplexing, with using a single input carrying a WDM signal and that is demultiplexed and the output of the optical channels are separated among many output waveguides. For multiplexing in AWGs , the device can be reversed with signals at separate wavelengths. And entering separate port combined inside of the AWG.
Standard AWGs have pass bands. That is closely in Gaussian shape. They are powerful attenuate light from the adjacent pass bands. However, the ideal pass band for WDM has a flat top conversely than the curved Gaussian peak. The simplest channel to flattening the peak is spatial filtering by adjusting way light is delivered to the input port, or by adjusting the lengths of the array arms of the AWG. One alternative is to add an interleaver to split signals between pair of AWGs. One receiving the odd channels and the other even channels. Another AWG or waveguide component for additional filtering.
Wavelength routing is the same principles as the AWG demultiplexer. The diffraction angle of the arrayed waveguide greetings depends on the angle of the incidence as well as the geometry of the grating technology. All the optical channels are enter through the single fibres, they all have to the same angle of incidence. However, If the light enters to the input mixer through the two or more input ports, those inputs signals have different incidence angles, so they are diffracted at the different angles as they emerge from the arrayed waveguides gratings in the output of the mixer. This effect can be used to be reroute and the rearrange to optical channels carried by multiple inputs of fibres. According to that the routing pattern is fixed, but the passive device is ensures that the channels with the same wavelength won't interfere with the each other or to be routed in out of the same waveguide.
Operation of AWG
An arrayed waveguide grating having a waveguide configuration formed on a substrate. The waveguide configuration including these options:
- one or more optical input waveguides arranged to the first slab, waveguide connected to an output side of the one or more optical output waveguides(an arrayed waveguides),that waveguides connected to the input side of the second slab.
- Receiving light from the first slab waveguide to propagate the light there through, the arrayed waveguide having a plurality of waveguides of different lengths.
- The second slab waveguide connected to an output side of the arrayed waveguide; and one or more optical output waveguides arranged.
- The arrayed waveguide grating of claim (fibre optics) where different in length from each other. And fibre optics is (sliding) construct in mutually-different materials.
- In thearrayed waveguide grating, fibers are separate from each other.
In the optical communication field, there is used an arrayed waveguide grating as specified. The present invention relates to an arrayed waveguide grating handling the function of wavelength multiplexing and the demultiplexing of optical signals of plural wavelengths.
The arrayed waveguide grating has one or more optical input waveguides arranged .The first slab waveguide connected to output sides of the optical input waveguides, arrayed waveguide connected to the output side of the first slab waveguide. The second slab waveguide connected to the output side of the arrayed waveguide and one or more optical output waveguides arranged.
The arrayed waveguide is provided for propagating light output from the first slab waveguide and has a plurality of waveguides (channel waveguides) arranged. Adjacent channel waveguides are different in length by a predetermined length and the arrayed waveguide gives each signal a phase difference in the arrayed waveguide grating.
Typically, the arrayed waveguide includes a large number of channel waveguides or, for example, 100 waveguides, however in the figure; a small number of waveguides are only shown for easy illustration.
In the arrayed waveguide grating, for example, when a wavelength division multiplexed optical signal comprising signals having wavelengths λ1, λ2, λ3. . . λn enters one optical input waveguide , this signal passes through the optical input waveguide into the first slab waveguide . Then, the signal is diffracted and spread by the first slab waveguide and is transmitted to the arrayed waveguide to propagate there through.
After passing through the arrayed waveguide, the signals enter the second slab waveguide, converge on and then are output from optical output waveguides . As the channel waveguides of the arrayed waveguide are all different in length, a phase difference appears in each of the signals that have passed through the arrayed waveguide . Due to this phase difference, the wave fronts of the signals tilt and this tilt angle determines focal points of the signals.
For this reason, the focal points of the signals having different wavelengths differ from each other and accordingly the optical output waveguides are formed at the respective focal points. With this configuration, the signals of different wavelengths are extracted by the optical output waveguides, respectively, thereby completing the function as a wavelength-division demultiplexer of the arrayed waveguide grating.
And the arrayed waveguide grating takes advantage of the principle of reversibility of the optical circuit, the arrayed waveguide grating also handles the function as a wavelength-division multiplexer as well as a wavelength-division demultiplexer. That is, reversing the above-described procedure, when signals having differing wavelengths λ1, λ2, λ3. . . λn enter respective optical output waveguides , the signals passes through the above-mentioned propagation path in reverse, the signals are multiplexed by the second slab waveguide , the arrayed waveguide and the first slab waveguide and output from one optical input waveguide .
Generally, as the arrayed waveguide grating is made of silica-based glass.
In the laboratory experiment I used to Optisystem software to analysing proformens of Array Waveguid Based Interleaver. In here I used to AWG N x N multiplexer.
Mainly in AWG can be configure as,
Size - with N inputs between 2 and 1000
Configuration - Mux and De-mux
Frequency - Between 30 and 300000 THz.
Bandwidth - Numeric value between 0 and 1e+100 GHz.
Frequency Spacing - Numeric value between -10000 and 10000 GHz.
To the AWG can be input in N frequencies. According to frequency, each channel will exit through a different output, according to its wavelengths. AWG input with an appropriate design, the channels will be separated and exit through different outputs.
A basic 2 x 2 AWG is shown in Figure. There are two input ports, each with two channels. The channels are separated, and the switches control the routing of the channels to the outputs.
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