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Application of Optical Add-Drop Multiplexer

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What’s the Optical Add-drop Multiplexer?

An optical add-drop multiplexer (OADM) 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 (SMF). This is a type of optical node, which is generally used for the construction of optical telecommunications networks. An OADM may be considered to be a specific type of optical cross-connect.

A traditional OADM consists of three stages: an optical demultiplexer, and optical fiber multiplexer, and between them a method of reconfiguring the paths between the optical demultiplexer, the optical multiplexer and a set of ports for adding and dropping signals. The optical demultiplexer separates wavelengths in an input fiber onto ports. The reconfiguration can be achieved by a fiber patch panel or by optical switches which direct the wavelengths to the optical multiplexer or to drop ports. The optical multiplexer multiplexes the wavelength channels that are to continue on from demultiplexer ports with those from the add ports, onto a single output fiber.

Principles of OADM technology

General OADM node can use four port model (Figure 1) to represent, includes three basic functions: Drop required wavelength signal, Add rumored signal to other wavelengths pass through unaffected. OADM specific network process is as follows: WDM signal coming from the line contains mangy wavelength signals into OADM’s “MainInput” side, according to business required, from many wavelength signals to selectively retrieved from the end (Drop) output desired wavelength signal, relative to the end from the Add the wavelength of the input signal to be transmitted. While the other has nothing to do with the local wavelength channels directly through the OADM, and rumored signals multiplexed together, the line output from the OADM (Main Output) Output.


Figure 1 OADM basic model

OADM node technical classification

Optical drop multiplexer network technologies can be divided into two types, fixed optical drop multiplexer (Fixed OADM, FOADM) and reconfigurable optical drop multiplexer (Reconfigurable OADM, ROADM).

Fixed Optical Drop Multiplexer (FOADM)

FOADM to filter as the main component, and its function is fixed to join or retrieve certain light wavelengths. General common FOADM can be divided into three types, namely Thin Film Filter type (TFF type), Fiber Bragg Grating (FBG type) and integrated planar Arrayed Waveguide Gratings (AWG type).

Thin Film Filter (TFF FOADM)

* TFF FOADM using thin film between the filtering effect of the different refractive index.

Fiber Bragg Grating (FBG FOADM)

* FBG FOADM use of fiber Bragg grating filtering effect, with two circulator can become FOADM.

Arrayed Waveguide Gratings (AWG FOADM)

* AWG FOADM gererally used in semiconductor fabrication processes, the integration of different refractive index material is formed on a flat substrate in a planar waveguide, when different wavelength light source is incident through the couping after the import side, due to take a different path length, while the different phase delay caused by different wavelengths and thus produce certain wavelengths in the export side to form a constructive or destructive interference, making waves in the export side, the different wavelengths will follow the design on a different channel to reach, and thus achieve FOADM function.

Reconfigurable Optical Add/Drop Multiplexer (ROADM)

ROADM can always be adjusted with the distribution network to add and drop wavelength, which reconstruct the network resource allocation, the flexibility to meet the requires of modern urban network, so a flexible ROADM features, plus optical switch substantial advantage, making the current fastest growing ROADM based voa attenuator based ROADM (switch based OADM). ROADM mainly be the optical switch, multiplexer and demultiplexer composed, Switch-based OADM, mainly divided into Wavelength independent switch array and wavelength selection switch.


Type 1 Wavelength independent switch array

Type 2 Wavelength selective switch

All kinds of optical drop multiplexer performance comparison

OADM network applications

WDM ROADM optical fiber suitable for different network environments

OADM in the metropolitan network development tendency

1. Arbitrary choice must be retrieved, adding wavelength, the wavelength can take advantage of the limited resources, the node can be retrieved with the need to do to join the adjustment of the signal wavelength, and has a remote control functions. This can provide dynamic reconfiguration of optical communications network capable ROADM will be connected to the backbone network critical devices. And FOADM is used for wavelength demand network access will be smaller parts to reduce costs. Furthermore, ROADM use to all kinds of Tunable Laser, unable Filter, or wavelength selective optical switches and other components.

2. Must be able to convert incompatible wavelength suitable for the backbone network will be transmitted wavelengths. Therefore, OADM be combined with wavelength conversioin Transponder or other functional components.

3. Must be able to compensate for the node to make acquisistion, adding such action energy loss. Therefore, OADM optical amplifiers must be combined with functional components.

4. Wavelength signals related specifications, such as: the signal to noise ratio (S/N), the energy balance between the signal wavelength, etc., are required to meet network requirements. Therefore must be combined OADM Variable Optical Attenuator (VOA), dispersion compensation module (DCM) and other components.

Noun Explanation of Several Common Optical Passive Devices

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Noun Explanation of Several Common Optical Passive Devices

1) What is the PON?

PON is the English abbreviation of Passive Optical Network. Because of its large transmission capacity, low maintenance cost and fiber dosage saving, PON has now become the main optical access technology in the world, and is widely used mainly by the fiber to the home (FTTH) network construction. PON is mainly comprised of OLT, optical splitter and ONU. According to the agreement, PON can be divided into EPON, GPON, WDM-PON and so on.

2) What is the optical passive device?

Optical passive device is a kind of optical components which does not rely on any outside optical or electrical energy, and can do some optical functions by their own, such as coupler, filter and so on. Its working principle complies with the physical and geometrical optics theory, while laser transceiver device based on photoelectric energy conversion is called active devices.

3) How is the optical passive device classified?

Optical passive devices can be classified according to their production process and functions. According to the different production process, optical passive devices can be divided into fiber optical passive devices and integrated optical passive devices. According to the different functions, they can be divided into optical connection devices, optical attenuator, optical splitter, optical wavelength distribution devices, optical isolation devices, optical switch, optical modem devices and so on.

4) What is the main technical indicators to evaluate optical passive devices?

The main technical indicators to evaluate optical passive devices are: insertion loss, return loss, bandwidth, with ups and downs, power allocation error, the wavelength isolation, channel isolation, channel width, extinction ratio, switching speed, speed and so on. Different devices have different requirements of technical indicators, but most of the optical passive devices need the requirements of low insertion loss, high reflection loss, and wide working bandwidth.

5) What is the PLC?

PLC is the English abbreviation of Planar Lightwave Circuit, namely the planar optical waveguide. The optical passive device and traditional vertical difference, PLC devices are used by semiconductor fabrication, which can integrate the optical components with different functions into one chip. PLC is the basic technology of photoelectric device integration, modularization, miniaturization. The devices those are used PLC technology include: optical splitter, arrayed waveguide grating (AWG), variable optical attenuator (VOA), variable optical attenuation combiner (VMUX), reconfigurable optical add-drop multiplexer (ROADM) and so on.

6) What are the advantages of PLC splitter compared to FBT optical splitter?
Compared with the traditional device FBT splitter used of FBT(Fused Biconical Taper) processing, PLC splitter has wide work wavelength channel loss, good uniformity, small volume, wide working temperature range, high reliability, is currently the preferred connection of OLT and ONU and the realization of optical signal power distribution PON the access network.

7) What is the difference between Full-band PLC splitter and three FBT window splitter?

Due to the working principle and the limit of process, traditional FBT splitter can generally meet the transfer at most three different wavelength, which is called the three window splitter. While the loss of PLC splitter is very low in a very wide wavelength range (1260-1650nm), so in addition to meet the three a window outside the commonly used, PLC splitter can also be used for transmission and management more work wavelength. So PLC splitter is called full-band splitter. The wavelength requirements of EPON and GPON standards were 13101490 and 1550nm, the next generation PON standard (such as WDM-PON) will require more work wavelength. The use of PLC optical branch devices can better adapt to the needs of future network upgrade and development.