As we all known, WDM (wavelength division multiplexing) is a technology that can transmit multiple different wavelength lasers on a single optical fiber, and widely used in optical networks. CWDM (coarse wavelength division multiplexing), as one type of WDM technology, first came in the 1980s, mainly being used to transmit digital video signal in the multimode fiber. However, it did not interest telecommunication service providers much until now. In recent years, with the development of metropolitan area network which has short transmission distance and do not need optical amplifier, there is a growing technology investment for it because it is a cost-effective solution for telecommunication service providers. We could say this is the time that CWDM exists with great significance.
As we said above, CWDM is one type of WDM technology, oriented to metropolitan area network. According to ITU-T G.694.2 standard, it has three wavelength bands: O band, E band and S+C+L band. The wavelength of O band is about 1270 nm, 1290 nm, 1310 nm, 1330 nm and 1350 nm. The wavelength of E band is about 1370 nm, 1390 nm, 1410 nm, 1430 nm and 1450 nm. As to S+C+L band, the wavelength is about 1470 nm, 1490 nm , 1510 nm, 1530 nm, 1550 nm, 1570 nm, 1590 nm and 1610 nm. And the channel spacing in CWDM system is typically 20 nm as the picture shows below. So the number of its channels on the same link can be up to 18. And due to its wide channel spacing the temperature control could not be so rigid. Typically, its operating temperature is from 0 to 70°C. And the use of uncooled lasers brings a low cost.
One of the biggest advantage of CWDM is low cost. As we have mentioned before, CWDM with the wider channel spacing do not need rigid temperature stability control, so the construction of laser device could be simplified. This feature of it is of great help to reduce the cost.
Another advantage of CWDM is that it has small volume and low power consumption. The laser in CWDM system do not need semiconductor cooler and temperature controlling, so it can reduce the power consumption obviously. Its power consumption is only 0.5 W. And the laser module which is simplified in CWDM system can make the volume of optical transceiver module reduced so that it can save a lot of room space.
With these advantages, CWDM technology is applied in various areas now, such as enterprise LAN and SAN connection, central office to customer premise interconnection and so on. And one of the most commonly devices is CWDM SFP. CWDM SFP is the transceiver which made by CWDM technology. It is of great simplicity, flexibility and interoperability. Mostly there are eight center wavelengths available from 1470nm to 1610nm, with each step 20 nm. Of course, there are some other CWDM devices,too. But today we are not going to list the products.
In a word, because of its good capacity and low cost, CWDM provides a better solution for metropolitan area network. I believe it will be a hot spot in metropolitan area network construction in the next few years.