DWDM Today - How Deployment Issues Are Being Resolved - Sponsored Whitepaper

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Dense Wavelength Division Multiplex (DWDM) systems are multi-wavelength systems that provide economical capacity relief on fiber optic spans. DWDM systems can multiplex up to 160 wavelengths on a single fiber with 16, 32, 40, and 80 channel systems being most typical. They are deployed over distances of 500 to 600 km in regional networks. More sophisticated (and expensive) long-haul systems take advantage of Erbium-doped fiber amplifier (EDFA) and dispersion compensation technologies to achieve distances of 1000 km or more. ITU Compatibility

ITU recommendation (Standard) G.694.1 specifies a standard grid of 160 wavelengths ranging from 1530 to 1565 nm. This narrow 35 nm range, as compared to the 340 nm range of CWDM systems, is because of the operational range of the EDFA. Vendors and carriers use this standard grid to develop their own specific channel plans at wavelength separation distances of 200, 100 and 50 Ghz. ITU-T Recommendation G.696.1 provides physical layer specifications for inter-vendor compatibility. This allows one vendor’s transponders to interoperate with another vendor’s DWDM filters and optical fiber amplifiers (or vice versa). These recommendations provide the groundwork for inter-vendor interoperability and the resulting flexibility to the service provider in designing DWDM systems. DWDM Building Blocks

DWDM systems are made of four primary building blocks: 1. DWDM filters that perform the wavelength multiplexing function 2. Transponders that perform the wavelength conversion to the desired ITU grid wavelength 3. EDFAs that provide optical signal gain to all wavelengths 4. Dispersion compensation modules that counter the negative effects of chromatic dispersion inherent in the fiber. A fifth item, although not dealt with in detail in this paper, is the optical add/drop multiplexer (OADM). DWDM filters or multiplexers (see Figure 1 below) are passive devices typically using array waveguide grating (AWG) or thin film filter technology to combine wavelengths onto a single fiber. DWDM filter losses at both transmit and receive ends of the fiber link (typically 6 dB) must be accounted for in the overall system design.

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