CWDM and DWDM analysis

WDM is a communication technology that combines a series of optical signals carrying information but with different wavelengths into one bundle and transmits them along a single optical fiber; the same technology is used at the receiving end to separate the optical signals of different wavelengths. This technology can transmit multiple signals on one optical fiber at the same time, and each signal is transmitted by light of a specific wavelength, and a wavelength is called a channel. Currently commonly used are CWDM (coarse wavelength division multiplexer) and DWMD (dense wavelength division multiplexer) two.

CWDM is the abbreviation of Coarse Wavelength Division Multiplexing. It has many advantages such as low cost, low power consumption, and small size. It is a low-cost WDM transmission technology for the access layer of the metropolitan area network.

DWDM is the abbreviation of Dense Wavelength Division Multiplexing (Dense Wavelength Division Multiplexing), 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.

The difference between CWDM and DWDM:

According to the ITU-T standard, the working band of CWDM is defined as 1270~1610nm (O, E, S, C, L bands), and 18 available wavelengths (18 channels) with a wavelength interval of 20nm are suggested; DWDM The working band is defined as 1525-1565nm (C-band) and 1570-1610nm (L-band), the channel spacing is 1.6/1.8/0.4nm (200GHz/100GHz/50GHz), and the number of channels can be as many as 40, 80 or even 160 channels .

This is why it is called coarse wavelength division multiplexing and dense wavelength division multiplexing. Due to the tight channel spacing of DWDM, more information can be carried on the same optical fiber, so the bandwidth and capacity of DWDM are larger.

In the DWDM system, due to the dense working wavelength, the general wavelength interval is only a few nanometers to a few tenths of a nanometer, so the wavelength of the laser used in the DWDM system must be accurate and have good stability. Due to the small wavelength shift, it must be Use costly cooled DFB lasers.

For CWDM using 20nm interval channels, the central wavelength drift does not exceed 6.5nm. Therefore, compared with the cooled DFB laser used in DWDM, the uncooled DFB laser used in CWDM has small size, low power consumption, and low cost. Advantage.