First, we should know what the WDM is.
WDM (Wavelength Division Multiplexing) combines a series of optical signals with different information but different wavelengths into one bundle and transmits them along a single fiber. At the transmitting end, they are combined by a multiplexer (also known as a combiner, MulTIplexer) and coupled to the light, a technique for transmitting in the same fiber of a line; at the receiving end, a demultiplexer (also called a demultiplexer) separates optical signals of different wavelengths, and then is separated by an optical receiver. Further processing to restore the original signal. In the same fiber, two or more optical wavelength signals are simultaneously transmitted through different optical channels, which is called optical wavelength division multiplexing (WDM).
Is it difficult to understand?
Example:
The Christmas is coming. Peter is ready to drive home. However, the traffic is busy and the road can’t widen more and more cars. (Peter is like a light signal. The main road is like the backbone fiber laid in optical communication. Because of the limited number, the single fiber transmission signal can no longer satisfy the growing communication needs).
Peter thinks that everyone can go to the high-speed rail together, it is fast and convenient (the high-speed rail originating station is like the combined wave in the WDM wavelength division multiplexing technology, the optical signals are together and coupled into the same light transmission). After the high-speed rail ran for a certain distance, the supply was insufficient. After stopping to increase the supply, the vehicle was driven again. Soon after, it arrived at the destination, and all the passengers were diverted to each home. (The replenishment in the middle is equivalent to the signal being weakened after long-distance transmission of the optical signal; increasing the replenishment is equivalent to enhancing the optical signal after the weakening of the EDFA; the terminal of the high-speed rail is equivalent to the partial wave in the WDM wavelength division multiplexing technique. Separate various optical signals)
What are the CWDM and DWDM?
CWDM (Coarse Wavelength Division Multiplexer) is a sparse wavelength division multiplexer, also called a coarse wavelength division multiplexer. DWDM (Dense Wavelength Division Multiplexer) is a Dense Wavelength Division Multiplexer.
Table 1. CWDM vs. DWDM
| Type | CWDM | DWDM |
| Wavelength Band | 1270 – 1610nm O, E, S+C+L | 1525 – 1565nm (C)
1570 – 1610nm (L) |
| Channels | 18 | 40 – 160 |
| Cost | Low | High |
| Application | Metropolitan area network Access layer,
Telecommunication, Business network, Campus network |
Long-distance and large-capacity trunk networks,
Large-capacity metropolitan area network core nodes, 5G Telecommunications, Metropolitan area networks, Backbone networks, data centers, etc. |
CWDM and DWDM have a big difference in the channel spacing between the two. Channel spacing refers to the difference between the nominal carrier frequencies of two adjacent channels and can be used to prevent inter-channel interference. The wavelength spacing between CWDM channels is 20 nm, while the channel spacing of DWDM is 1.6/0.8/0.4 nm (200 GHz/100 GHz/50 GHz), which is much smaller than CWDM. The difference in channel spacing is also the difference in bandwidth and capacity that can be carried by CWDM and DWDM. The DWDM module further increases system bandwidth and capacity by using more closely spaced wavelengths to carry more signals on the same fiber.
How to choose CWDM, DWDM, CCWDM?
The biggest advantage of CWDM systems is the low cost, and the device cost is mainly reflected in filters and lasers. The wide wavelength spacing of 20 nm also gives CWDM the advantage of low specification of the laser and simplified structure of the optical multiplexer/demultiplexer. The structure is simplified, the yield is improved, and the cost is lowered. The cost increase of DWDM is mainly due to the high cost of laser diodes and the cooling laser technology used to maintain wavelength stability.
What is the CCWDM?
CCWDM is a mini-wavelength division multiplexer and is a mini version of CWDM. A wavelength division multiplexing technology based on TFF (Thin Film Filter), which works in the same way as CWDM. The difference is that CCWDM uses free space technology, and its package size is greatly reduced compared with CWDM modules, and insertion loss. Lower and more consistent. It can replace CWDM products in telecommunications, enterprise networks, PON networks, TV and other fields.
We should choose the right WDM according to our transmission needs.
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