What is WDM? WDM combines a series of information-laden but different wavelengths of light signals into a single beam that travels along a single fiber. Optical wavelength division multiplexing (WDM) is a technique in which two or more optical wavelength signals are simultaneously transmitted through different optical channels in the same fiber.

How does it work? The transmitter is fused by a MulTIplexer and coupled to the same fiber in the optical path for transmission. At the receiving end, optical signals of different wavelengths are separated by demultiplexer, and then further processed by the optical receiver to recover the original signal.

How many types of WDM are there? In WDM systems, there are two types of CWDM (coarse wavelength division multiplexing) and DWDM (dense wavelength division multiplexing).

CMDM
Coarse Wavelength Division Multiplexing (CWDM) is to reconstruct the optical fiber network by using the technology of Coarse Wavelength Division Multiplexing (CWDM). It has flexible and transparent access to a variety of speeds and services. It can effectively save optical fiber resources and networking costs. It solves the two problems of optical fiber shortage and multi-service transparent transmission. CWDM single fiber bidirectional equipment can transmit four waves through a single fiber bidirectional transmission Single-fiber unidirectional equipment can transmit 8-wave service unidirectionally through a single fiber, and dual-fiber bi-directional equipment can transmit 8-wave service bi-directionally through a pair of fibers. It is mainly used in metropolitan area network convergence and access layer, and can build network and carry out business in a short time.

DWDM
Dense wavelength division multiplexing (DWDM) is capable of combining a set of optical wavelengths with one optical fiber. This is a laser technology used to enhance bandwidth on existing optical backbone networks. The technique is to multiplex the tight spectral spacing of a single fiber carrier in a specified fiber to take advantage of achievable transmission performance (e.g., minimal dispersion or attenuation). Thus, under the given transmission capacity, the total number of optical fibers needed can be reduced.

What is the difference between CWDM and DWDM?
1. The spacing between optical channels. CWDM has 18 bands, ranging from 1270nm to 1610nm, with a 20nm interval between each band. There are three types of channel spacing for DWDM: 0.4 nm (50 Ghz), 0.8 nm (100 Ghz) and 1.6 nm (200 Ghz), 100 GHz (from C17 to C61), and 50 GHz (from C17 to H61, for high channel equipment). CWDM optical channel spacing is wider, the number of multiplexed optical wavelengths on the same fiber is less than DWDM, "thick" and "dense" is the reason for the title.

2, Modulation laser. CWDM light modulation uses uncooled laser, tuned electronically; DWDM uses cooled laser, tuned by temperature. But the power and physical size of the CWDM system are much smaller than that of the DWDM system.

3, Application. CWDM is used in short-distance, high-bandwidth, access-point-intensive communication applications, such as network communications within or between buildings; peer-to-peer, Ethernet, SDH, SONET ring, EPR (resilient packet ring) and other popular network structures. DWDM is suitable for long distance, large capacity trunk trunk network or super large capacity metropolitan area network core node.

4, Cost. CWDM wavelength 1470 nm ~ 1610 nm DFB laser is generally used, because the channel spacing is large, so CWDM devices and lasers are cheaper than DWDM devices. Temperature tuning is difficult and costly because the temperature distribution is very uneven in a very wide wavelength range. CWDM avoids this difficulty and thus greatly reduces the cost. At present, the cost of CWDM system is only 30% of that of DWDM.
 

Summary:
Although both CWDM and DWDM can achieve multiple wavelengths in a single optical fiber. When choosing CWDM / DWDM scheme, we should consider the demand and budget of the project comprehensively, and choose the best scheme according to their characteristics and differences. C-lght's WDM modules and Mux/Demux products are popular in the market.If interested.pls contact us by alisa@c-light.com.