WDM bearer schemes include coarse wavelength division multiplexing (CWDM), dense wavelength division multiplexing (DWDM), and medium wavelength division multiplexing (MWDM) and fine wavelength division multiplexing (LWDM).
CWDM coarse wavelength division multiplexer
CWDM (Coarse Wavelength Division Multiplexer) is a sparse wavelength division multiplexer, also known as coarse wavelength division multiplexer. CWDM has 18 different wavelength channels, each with different wavelengths separated by 20nm, using wavelengths from 1270 nm to 1610 nm. CWDM supports fewer channels than DWDM because it is compact and cost-effective, thus making it an ideal solution for short-range communications. The biggest advantage of the CWDM system is the low cost, and the device cost is mainly manifested in the filter and laser. The wide wavelength interval of 20nm also brings the advantages of low requirement of laser technical specifications and simplified structure of optical multiplexer/demultiplexer for CWDM. The structure is simplified, the yield is improved, so the cost is reduced.
DWDM dense wavelength division multiplexer
DWDM (Dense Wavelength Division Multiplexer) is a dense wavelength division multiplexer. The channel spacing of DWDM is 1.6/0.8/0.4 nm (200GHz/100 GHz/50 GHz), which is much smaller than that of CWDM. Compared with CWDM, DWDM with closer wavelength spacing can carry 8~160 wavelengths on one fiber, which is more suitable for long distance transmission. With the help of EDFA, DWDM systems can work over a range of thousands of kilometers.
FWDM filter type wave division multiplexer
FWDM (Filter Wavelength Division Multiplexing) filter type wavelength division multiplexing, is based on mature membrane filter technology. Filter-type wavelength division multiplexers (WDM) are widely used in Erbium-doped optical amplifiers, Raman amplifiers and WDM fiber networks because they can combine or separate different wavelengths of light in a wide wavelength range.
MWDM medium wavelength division multiplexing
MWDM reuses the first six waves of CWDM, compresses the wavelength interval of 20nm of CWDM to 7nm, and uses TEC (Thermal Electronic Cooler) temperature control technology to expand one wave to two waves. This allows for a capacity increase and further fiber savings. MWDM is based on CWDM 6 wave, The left and right shifts of 3.5nm spread into 12 waves (1267.5, 1274.5, 1287.5, 1294.5, 1307.5, 1314.5, 1327.5, 1334.5, 1347.5, 1354.5, 1367.5, 1374.5nm). MWDM is mainly proposed in the context of China's 5G fronthawall network.
LWDM
LWDM is the Ethernet channel-based WDM Lan-WDM technology, also known as fine WDM. Its channel spacing is 200 to 800GHz, which is between DWDM (100GHz, 50GHz) and CWDM (about 3THz). LWDM uses 12 wavelengths from 1269nm to 1332nm in the O-band (1260nm ~ 1360nm), The wavelength interval was 4nm (1269.23, 1273.54, 1277.89, 1282.26, 1286.66, 1291.1, 1295.56, 1300.05, 1304.58, 1309.14, 1313.73, 1318.35nm). The LWDM operating wavelength is characterized by being located near zero dispersion with small dispersion and good stability. At the same time, LWDM can support 12 waves of 25G, which improves the capacity and can further save fiber.
