What is Reconfigurable Optical Add-Drop Multiplexer

In the fiber optic network which uses wavelength division multiplexing (WDM), reconfigurable optical add-drop multiplexer (ROADM) is used to remotely add, block, pass or redirect modulated light emissions-infrared and visible-within a range of wavelengths.

With ROADM devices, signal switching doesn’t need optical-to-electric and electric-to-optical conversions. Instead, outgoing light beams can be generated, incoming beams could be terminated or beams could be passed through the device unmodified. This is achieved through wavelength-selective switch (WSS) components within the device.

A ROADM allows remote configuration and reconfiguration of emissions; bandwidth could be assigned when needed and without interrupting concurrent traffic, and power balancing is automatic. Most ROADM devices use technologies according to first-generation, wavelength blocking (WB) or second generation, planar light-wave circuit (PLC) technology. Whenever a wavelength change is required inside a specific channel, these technologies filter light emissions, extract data and impress data onto another emission. This method is more streamlined using PLC technology.

The different switching technologies in ROADM devices include microelectronic mirrors, live view screen, thermo-optic and beam-steering switches in planar waveguide circuits, and tunable optical filters.

ROADM devices were initially used in long-haul DWDM equipment. By 2005, metropolitan networks began using ROADMs in reaction to increased interest in Ethernet, as well as high-speed data, audio and video services. Within the ensuing years, ROADM devices have brought bandwidth flexibility and operational efficiency to networks. ROADM-based networks are enabling an automated optical layer with dynamic multipoint connectivity, independent wavelength add-drop, remote bandwidth allocation that has been enhanced power management capabilities.

Combined with the benefits of ROADM comes the inevitable need for fiber optic testing that safeguards function and helps to make sure performance. Here are common testing-related challenges to consider in ROADM-based networks.

1. Increases both in insertion loss per node and insertion loss per channel

2. The need to measure optical loss per channel for multiple ROADM configurations

3. The necessity to measure optical signal-to-noise ratios utilizing a precise and repeatable method

4. The impact of possible bandwidth thinning, other changes to bandwidth, and dispersion, that is of particular concern in multiple cascaded devices and 40 Gbit/s systems

5. Compliance using the optical transport network (OTN) standard-ITU-T G.709 standard

Unlike the optical add-drop multiplexer, Capabilities of ROADM test equipment should encompass optical spectrum analysis (OSA), and OTN performance qualifiers for newly commissioned links, along with the transport layer and all ROADM-supported interfaces. Major manufacturers of OSA and related electronic test equipment include, FiberStore, Anritsu, Digital Lightwave, Exfo and JDSU Test.

Source: http://www.fs.com/

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