Know more CWDM and DWDM

 In recent years, with the development of metropolitan area networks ,there are a growing WDM technology investment for them due to cost-effective solution for telecommunication service providers,Generally, WDM technology is applied to an optical carrier which is typically described by its wavelength. WDM systems are divided into different wavelength patterns, Coarse (CWDM) and Dense(DWDM).

Introduction

CWDM stands for Coarse Wavelength Division Multiplexing, which is a wavelength multiplexing technology for city and access networks.CWDM allows a modest number of channels, typically eight or less, to be stacked in the 1550 nm region of the fiber called the C-Band. Transmission is realized using 18 channels with wavelengths between 1270 nm and 1610 nm. Due to the channel spacing of 20 nm cost-effective lasers can be used. The channel width itself is 13 nm. The remaining 7 nm is designed to secure the space to the next channel.

Feature

Up to 18 CWDM wavelength over one pair of fiber

CWDM channel spacing 20 nm, 1270 nm to 1610 nm

Distances up to 120 km

Cost-effective WDM solution

DWDM stands for Dense wavelength division multiplexing ,which refers originally to optical signals multiplexed within the 1550 nm band so as to leverage the capabilities of erbium doped fiber amplifiers (EDFAs), which are effective for wavelengths between approximately 1525–1565 nm (C band), or 1570–1610 nm (L band). Therefore EDFAs allow a single-channel optical link to be upgraded in bit rate by replacing only equipment at the ends of the link, while retaining the existing EDFA or series of EDFAs through a long haul route. Furthermore, single-wavelength links using EDFAs can similarly be upgraded to WDM links at reasonable cost. The EDFA's cost is leveraged across as many channels as can be multiplexed into the 1550 nm band.

Feature

Up to 96 DWDM wavelength over one pair of fiber

DWDM channel spacing 0.8 nm (100 GHz grid) or 0.4 nm (50 GHz grid)

Distances over 1,000 km can be achieved with the use of optical amplifier

DWDM wavelength: 1528 nm (channel 61) to 1563 nm (channel 17)

Differences between CWDM and DWDM system

1．Transmission Distance

CWDM is designed for short-range communications,which uses wide-range frequencies and spreads wavelengths far apart from each other.

DWDM is designed for long-haul transmission where wavelengths are packed tightly together.

2．Channel Spacing

CWDM channel spacing 20 nm, 1270 nm to 1610 nm

DWDM channel spacing 0.8 nm (100 GHz grid) or 0.4 nm (50 GHz grid)

3．Cost of design

Standardized channel spacing permits room for wavelength drift as lasers heat up and cool down during operation. CWDM equipment is compact and cost-effective as compared to DWDM designs.

High-precision filters are required to peel away one specific wavelength without interfering with neighboring wavelengths and precision lasers must keep channels exactly on target. That nearly always means such lasers must operate at a constant temperature. High-precision, high-stability lasers are expensive.

Summary

WDM systems are popular with telecommunications companies because they allow them to expand the capacity of the network without laying more fiber. By using WDM and optical amplifiers, they can accommodate several generations of technology development in their optical infrastructure without having to overhaul the backbone network.

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