In the field of telecommunications, data centre connectivity, video transport, fibre optic cabling is highly desirable for today’s communication needs due to the enormous bandwidth availability. As fibre cabling is sometimes expensive for people especially individuals to use, wavelength division multiplexing (WDM) is highly advisable for it can expand the capacity of fibres. This article will depict one kind of WDM: coarse wavelength division multiplexing (CWDM or Coarse WDM) which works efficiently with lower cost in short-haul networks in comparison with DWDM (Dense WDM).
CWDM is a method of combining multiple signals on laser beams at various wavelengths for transmission along fibre optic cables. Compared to DWDM which is a more tightly packed WDM system, CWDM has larger channel spacing, having fewer wavelengths be transported on the same fibre. For instance, CWDM typically has channels at wavelengths spaced 20 nanometres (nm) apart, compared with 0.4 nm spacing for DWDM. DWDM can typically transmit from 32 to 128 channels by using erbium-doped fibre amplifiers to boost the signal over long distances, which makes it ideal for long-haul networks. In contrast, CWDM can only transmit a maximum of 18 channels with large spacing between channels, making optical amplifiers not able to be used in CWDM system. So CWDM is typically deployed at short-haul networks.
Due to its broader channel spacing, CWDM has a cost advantage over DWDM. CWDM systems spread less precise lasers over a larger range of wavelengths with consuming less power with low losses. For example, both DWDM and CWDM utilise Distributed Feedback Lasers (DFB). However, DWDM requires the larger cooled DFB lasers because laser wavelengths drift about 0.08 nm/°C with temperature. CWDM uses DFB lasers that are not cooled because laser wavelengths drift about 6nm over the range of 0-70°C and the lasers’ tolerance (extent of wavelength imprecision or variability) in a CWDM is up to ±3 nm. The use of uncooled lasers causes lower power consume, which has positive financial implications for systems operators. For instance, the cost of battery is minimized with the decreasing of power consume, which reducing operating costs.
It is concluded that CWDM is the technology of choice for cost efficiently transporting data traffic in short-haul networks. And as the demand for bandwidth is pushed to the edge of the network, the need for low-cost transport systems is imperative.
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