Application of Optical Add-Drop Multiplexer

What’s the Optical Add-drop Multiplexer?

The optical add-drop multiplexers (OADM) are 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 cross connect cabinet.

A traditional OADM consists of three stages: an optical demultiplexer, and optical multiplexers, 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.

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).

TFF FOADM

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 optical switches 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.

Wavelength independent switch array

Type 1: Wavelength independent switch array

Wavelength selective switch

Type 2: Wavelength selective switch

All kinds of optical drop multiplexer performance comparison

optical drop multiplexer performance

OADM network applications

WDM ROADM optical fiber suitable for different network environments

OADM network applications

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 attenuators (VOA), dispersion compensation module (DCM) and other components.

Tutorial- How To Assemble a Fiber Optic Connector

Because there are many different types of fiber optic connectors have been developed, we will talk about fiber optic connectors in fairly general terms.

Most popular connectors in use today have some common elements. Let’s examine it below:

The most critical part, fiber is installed, is the ferrule. Ferrule is long, thin cylinder with the fiber mounted in the center hole. The size of the center hole is set to match the cladding of the fiber is usually 125 microns in diameter.

Fiber connector ferrules are made from several types of materials including ceramic (Zirconia), stainless steel and plastic.

The ferrule’s work is the center and align the fiber and protects it from mechanical damage. Finally at the end of the fiber ring and fiber end is polished smooth either flat or curvature.

The ferrule is mounted in the connector body and then the connector body is attached to the fiber optical cable structure. Finally, a strain-relief rubber boot protects the connector cable junction.

Unlike most electronic connectors, fiber optic connectors usually do not have the male-female polarity. Most fiber connectors are male only. Instead, fiber optic connectors to mate in the fiber optic adapter, it is often referred to as mating sleeves or coupling socket. Fiber optic adapter connector types used in different partners such as FC SC connector connector is called hybrid adapters.

Although this method needs to use a separate adapter, fiber optic connector it otherwise to reduce inventory requirements because now you only need to stock a type connector. Another advantage is that fiber optic adapters can be designed to mate one type of connector to another, which is a big plus compared to electronic connectors.

The fiber’s plastic coating is stripped first before the fiber is inserted in the ferrule. The center hole through the ferrule is large enough to fit the fiber cladding (which is usually 125um after fiber coating stripped off) but tight enough to hold the fiber in a fixed position without any further moving.

Standard bore diameters are 126 +1/-0 um for single mode connectors and 127 +2/-0 um for multimode connectors. Because of fiber cladding diameter’s variation from manufacturing, some fiber connector manufacturers also supply a range of ferrule bore sizes such as 124um, 125um, 126um and 127um.

Fiber optic epoxy or adhesive is inkected into the ferrule hole before the fiber is pushed in to hold the fiber in place. The epoxy or adhesive is then cured with high temperature oven according to adhesive manufacturer’s instruction. Finally the fiber end is polished to a smooth face on polishing films.

The ferrule is then slipped inside another hollow cylinder before it is mounted in the connector body. The connector body includes one or more pieces that are assembled to hold the cable and fiber in place. Connector body is made of metal or plastic.

The ferrule end protrudes beyond the connector body so it can slip into the mating sleeves (fiber adapters). A stain relief rubber boot is finally slipped over the cable end of the connector to protect the cable connector junction point.

In fiber optical cross connect boxes or fiber patch panels, an array of connector adpators are mounted inside, ready for you to plug an input fiber cable in one side and an output cable in the other. Fiber connector adapters are also mounted in wall outlets, just like standard phone jacket.