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Introduction to Optical Wavelength Division Multiplexing Technology

Wavelength Division Multiplexing (Wavelength Division Multiplexing) is a method of combining a series of information-carrying optical signals with different wavelengths into one bundle and transmitting them along a single optical fiber; Communication technology that separates optical signals. This technology supports the transmission of multiple signals on an optical fiber, and each signal is transmitted by light of a specific wavelength, thus forming a wavelength channel.

  1. Introduction to Optical Wavelength Division Multiplexing Technology

Optical wavelength division multiplexing technology, referred to as WDM, refers to allowing two or more optical wavelength signals to transmit information through different optical channels in the same optical fiber at the same time. Optical wavelength division multiplexing is mainly divided into two types: frequency division multiplexing and wavelength division multiplexing. Optical frequency division multiplexing refers to the subdivision of optical frequency, and the optical channels are very dense; optical wavelength division multiplexing refers to the coarse division of optical frequency, and the optical channels are far apart, even in different windows of optical fibers. There is no obvious difference between optical frequency division multiplexing (FDM) technology and optical wavelength division multiplexing (WDM) technology. The main reason is that light waves are part of electromagnetic waves, and the frequency and wavelength of light have a single correspondence.

Optical wavelength division multiplexers are mainly divided into four types: fused tapered type, dielectric film type, grating type and planar type. It realizes the coupling and separation of different light waves by using wavelength division multiplexers and demultiplexers (also known as multiplexers/demultiplexers) placed at both ends of the optical fiber. Among them, insertion loss and isolation determine its main characteristic index. Insertion loss, that is, connection loss, refers to the loss of effective optical power of the link caused by the introduction of the connector; isolation refers to the difference between input power and output power.

There are mainly two types of products using WDM technology in the market: coarse wavelength division multiplexer (CWDM) and dense wavelength division multiplexer (DWDM).

  1. What is a coarse wavelength division multiplexer

Coarse Wavelength Division Multiplexing (CWDM) is a low-cost WDM transmission technology for the access layer of the metropolitan area network. In principle, CWDM is to use an optical multiplexer to multiplex optical signals of different wavelengths into a single optical fiber for transmission. signal, connect to the corresponding receiving equipment. Figure 1 below shows you the working principle of CWDM.

  1. What is DWDM

Dense Wavelength Division Multiplexing (DWDM) is abbreviated as DWDM, which utilizes the bandwidth and low loss characteristics of single-mode fiber, uses multiple wavelengths as carriers, and allows each carrier channel to transmit simultaneously in the fiber. Compared with the general single-channel system, the dense wavelength division multiplexer not only greatly improves the communication capacity of the network system, fully utilizes the bandwidth of the optical fiber, but also has many advantages such as simple expansion and reliable performance, especially it can directly Access to a variety of services makes its application prospects very bright.

  1. The main difference between coarse wavelength division multiplexer and dense wavelength division multiplexer
  2. Different band intervals:

① The coarse wavelength division multiplexer has 18 bands, from 1270nm to 1610nm, and the interval between each band is 20nm. CWDM devices and lasers are cheaper than DWDM devices because of the large channel spacing. CWDM wavelength 1470nm ~ 1610nm generally use DFB laser;

②Dense wavelength division multiplexer has three kinds of intervals for each channel according to needs: (50Ghz), (100Ghz) and (200Ghz). 100GHz (from C17 to C61, is commonly used, suitable for regular equipment); 50GHz (from C17 to H61, suitable for high channel equipment).

  1. Comparison of bands:

① CWDM optical channel spacing is wider, and the number of multiplexed optical wavelengths on the same fiber is less than that of DWDM. This is the reason for the titles “thick” and “dense”;

②CWDM optical modulation adopts uncooled laser, which is tuned electronically; while DWDM uses cooled laser, which is tuned by temperature. Since the temperature distribution is very uneven in a wide optical wavelength range, it is very difficult and expensive to realize temperature tuning. CWDM avoids this difficulty, thus greatly reducing the cost. At present, the cost of CWDM system is generally only 30% of DWDM;

③The power consumption and physical size of the CWDM system are much smaller than those of the DWDM system.

In short, technically speaking, coarse wavelength division multiplexing CWDM has obvious disadvantages compared with dense wavelength division multiplexing DWDM. Its transmission distance and the number of channels are far lower than DWDM. However, cost is also a very important factor. On the one hand, in the metropolitan area network, the user’s demand for broadband is limited; on the other hand, the metropolitan area network service provider cannot afford expensive DWDM equipment. As an optional expansion solution, CWDM can solve the urgent needs of suppliers. Coarse wavelength division multiplexing CWDM system is a wavelength division multiplexing system suitable for broadband metropolitan area network, and has a good development prospect. I hope that the introduction of the above knowledge will help you to have a better understanding. Flying Optical Fiber () is willing to learn and make progress together with you.