Over the past seven years, WDM networks have evolved from simple point-to-point systems to single-ring networks to advanced interconnected mesh architectures. Reconfigurable Optical Add/Drop Multiplexers (ROADMs) are the key network element enabling these advanced networks, along with a key technology component called a Wavelength Selective Switch (WSS).

Fujitsu was the first vendor to develop and deploy ROADM technology in 2003, and the first to incorporate a WSS-based optical switch fabric. Fujitsu remains the global industry leader in metro/regional ROADM technology and solutions.

Prior to ROADMs, DWDM systems were commonly implemented using “fixed filters” in what is known as a “banded” DWDM architecture. A typical banded DWDM system provided 32 channels in eight groups of four channels in each group. Banded DWDM systems, like the Fujitsu FLASHWAVE 7420, remain popular for many access WDM and price-sensitive applications. ROADMs offer additional size, flexibility, and performance benefits, including:

  • Improved network utilization due to single-channel granularity
  • Non-block access to any lambda – improved network efficiency
  • Flexibility & service velocity – drop any channel and any number of channels at any site
  • Integrated auto-power balancing, eliminating costly & timely manual tuning
  • Full band tunable transponders
  • Support for interconnected ring and mesh architectures
  • A-Z end-to-end wavelength provisioning

The keys to any ROADM are the optical switch fabric and optical switching technology. Fujitsu employs an advanced Wavelength Selective Switch (WSS) module as our optical switching “engine.” The WSS provides wavelength selection, switching, power monitoring, and auto-power balancing all within a single device. In addition, the WSS allows Fujitsu ROADMs to support advanced network architectures such as multidegree hub nodes and mesh architectures.

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