CWDM Coarse Wavelength Division Multiplexer

Coarse Wavelength Division Multiplexing (CWDM), abbreviated as CWDM, is a low-cost WDM transmission technology for MAN access layer. In principle, CWDM uses optical multiplexers to multiplex optical signals of different wavelengths into a single optical fiber for transmission, and at the receiving end of the link, the mixed signals in the optical fiber are decomposed into signals of different wavelengths with the help of an optical demultiplexer, which is connected to the corresponding receiving equipment.

WDM Dense Wavelength Division Multiplexer

Dense Wavelength Division Multiplexing (DWDM), abbreviated as DWDM, takes advantage of the bandwidth and low-loss characteristics of single-mode optical fibers to use multiple wavelengths as carriers, allowing simultaneous transmission of each carrier channel within the optical fiber. Compared with the general single-channel system, Dense Wavelength Division Multiplexing not only greatly improves the communication capacity of the network system, making full use of the bandwidth of the optical fiber, and it has many advantages such as simple expansion and reliable performance, in particular, it can directly access a variety of services makes it a very bright prospect for application.

Difference between CWDM and DWDM

1, CWDM has 18 bands, from 1270nm to 1610nm, the interval between each band is 20nm. DWDM has three kinds of intervals for each channel according to the needs: 0.4nm (50Ghz), 0.8nm (100Ghz) and 1.6nm (200Ghz), 100GHz (from C17 to C61, which is the most commonly used one, and it is applicable to the regular equipment); 50GHz (from C17 to C61, which is the most commonly used one, and it is applicable to the regular equipment); 50GHz (from C17 to C61, which is the most commonly used one); and 50GHz (from C17 to C61). ); 50GHz (from C17 to H61, for high-channel equipment), CWDM wavelengths 1470nm to 1610nm generally use DFB lasers, because the channel spacing is large, so CWDM devices as well as lasers are cheaper than DWDM devices, the CWDM lightwave channel spacing is wider, and the number of multiplexed optical wavelengths on the same fiber is less than that of DWDM. This is where the "coarse" and "dense" designations come from; the width of the spacing between each wavelength varies according to the design of the communication system. According to the different channel spacing, WDM can be subdivided into CWDM (Coarse Wavelength Division Multiplexing) and DWDM (Dense Wavelength Division Multiplexing). CWDM: Wavelength spacing ≥ 20nm, usually using eight bands of 1470~1610nm (one for each 20nm interval). DWDM: wavelength interval <10nm, the window is also in the vicinity of 1550nm, the optical device is more expensive, the optical terminal is not commonly used. The difference between CWDM and DWDM has two main points: one is that the CWDM carrier channel spacing is wider, so the same fiber can be multiplexed to about 10 wavelengths of light waves, while DWDM can multiplex more than 10 wavelengths of light waves; the second is that the CWDM modulation laser uses a non-cooling laser, while the DWDM adopts a cooling laser. Cooled lasers use temperature tuning and uncooled lasers use electronic tuning. Because the temperature distribution in a wide wavelength band is very uneven, so the temperature tuning is very difficult to realize, and the cost is also very high.CWDM avoids this difficulty, and thus significantly reduces the cost of the whole CWDM system cost is only 30% of DWDM.

2, DWDM system can provide 16/20 waves or 32/40 waves of single-fiber transmission capacity, up to 160 waves, with flexible expansion capabilities. Users can initially build 16/20-wave system, and then upgrade to 32/40-wave as needed, which can save the initial investment. The principle of the upgrade program: one is in the C-band red band 16-wave plus blue band 16-wave upgraded to 32-wave program; the other is the use of interleaver, in the C-band from 200GHz spacing 16/32-wave upgraded to 100GHz spacing 20/40-wave. For further capacity expansion, the C+L band expansion program can be provided to further expand the system transmission capacity to 160 waves.