I. Definition
Coarse Wavelength Division Multiplexing (CWDM)
Coarse Wavelength Division Multiplexing (CWDM) allows multiple signals to be transmitted simultaneously over a single optical fiber by using a different wavelength of light to carry each signal. CWDM operates in the wavelength range of 1270nm to 1610nm, with each CWDM channel typically spaced 20nm apart.
CWDM has a total of 18 channels - the technology was initially developed for 9 (1470-1610) channels, and was later expanded to 18 channels, including channels with shorter wavelengths and lower effective attenuation. The following table shows the standard channel pairings in a CWDM setup.
Dense Wavelength Division Multiplexing (DWDM)
Dense Wavelength Division Multiplexing (DWDM) enables the simultaneous transmission of multiple data signals over a single optical fiber by dividing the available bandwidth into multiple wavelengths or channels.
II. Main differences between CWDM and DWDM
(1) Applications
CWDM is typically used in short-distance applications, such as metropolitan area networks (MANs) or campus networks, where transmission distances are limited. It uses a wider channel spacing, allowing a smaller number of wavelengths to be multiplexed. On the other hand, DWDM is more advantageous in long-distance applications, such as backbone networks or submarine cables, where the transmission distance is longer.
(2) Transmission capacity
Due to the difference in channel spacing, DWDM supports significantly more channels than CWDM, resulting in higher transmission capacity. DWDM systems can support up to 96 channels, while CWDM systems typically support up to 18 channels.
(3) Transmission distance
CWDM has a shorter operating distance, typically up to 80 kilometers. On the other hand, DWDM has amplification and dispersion compensation capabilities, which can provide longer transmission distances, exceeding hundreds of kilometers after amplification.
(4) Channel spacing
CWDM uses a wider channel spacing, typically around 20 nanometers, while DWDM uses a much narrower channel spacing, typically ranging from 50 GHz (96 channels) to 100 GHz (48 channels). CWDM operates in the 1270-1610 nm range, while DWDM operates around 1550 nm. These wavelengths ensure efficient operation due to the lower attenuation of optical fibers near these wavelengths. Typical attenuation at 1550 nm is 0.25-0.35 dB/km, while the attenuation at the commonly used 1310 nm spectrum is 0.35-0.45 dB/km.
III. Advantages and Disadvantages of CWDM and DWDM
CWDM: CWDM technology is cost-effective as long as the number of channels is small. Furthermore, CWDM is compatible with a variety of protocols and data rates, making it versatile and adaptable to different network needs. However, its coverage is limited, and its maximum distance cannot be increased.
DWDM: Compared to CWDM (coarse wavelength division multiplexing), DWDM offers more channels, significantly increasing network capacity. It also offers long-distance transmission capabilities, allowing data transmission over hundreds or even thousands of kilometers. Furthermore, its flexible wavelength allocation makes the network easy to expand and future-proof. However, CWDM solutions are more cost-effective for shorter distances.
The choice between CWDM and DWDM depends on the specific needs of the optical communications infrastructure, budget, and project circumstances. CWDM is cost-effective and suitable for short- to medium-haul transmission, offering fewer wavelengths, making it suitable for metropolitan area networks. In contrast, DWDM is well-suited for high-capacity, long-haul applications, supporting more and narrower wavelength spacing, making it ideal for long-haul and data-intensive networks.