Introduction

Wavelength Division Multiplexing (WDM) technology has brought unprecedented bandwidth capacity upgrade, improve bandwidth while also saving costs, as an ideal solution for the modern communication network. WDM has a wide range of terms, to find out is really a headache. Today, we will come to these "WDM terminology".

WDM

WDM is a kind of technology which combines two or more different wavelengths of optical carrier signals (carrying a variety of information) at the sender by the multiplexer (also known as the multiplexer, multiplexer) together, and coupled to the same optical line Fiber transmission. This is estimated that you are still confused, in fact, this like the principle of the light sunshine the mirror and appears a rainbow , there are a variety of colors of light in a bunch of white light, WDM separated the spectrum of all colors of light, so that they are in the same fiber transmission, the color (wavelength) of the light are carrying different signals, and do not interfere with each other.

Coarse wavelength division multiplexing (CWDM)

CWDM is a special WDM technology defined by the ITU-T G.694.2 spectrum grid by the International Telecommunication Union (ITU), which uses wavelengths between 1270 nm and 1610 nm with a channel spacing of 20 Nm. CWDM is a cost-effective technology for transmitting large amounts of data in telecommunications or enterprise networks.

Dense wavelength division multiplexing (DWDM)

DWDM is also a special WDM technology defined by the ITU in the ITU-T G.694.1 spectrum grid. Its grid is calculated in terms of frequency, the unit is MHz (THz), DWDM spectrum grid fixed at 193.1THz, channel spacing from 12.5 GHz (GHz) to 200 GHz range, the common channel spacing is 100 GHz. In practice, DWDM frequency is usually converted to wavelength, in the C-band spectrum can transmit up to 80 channels (wavelength), and the 80 channels at the same time can be 1550 nm wavelength transmission.

When it comes to WDM fiber transmission systems, you must know the following terms:

Single fiber bidirectional transmission

Single-fiber bi-directional transmission is that is on a two-way communication in a fiber. It uses two groups of the same wavelength in a fiber on the two-way transmission. In a single-wire bi-directional transmission system, each channel can be the bi-directional transmission.

Two-fiber unidirectional transmission

Two-fiber unidirectional transmission refers to the communication in two fibers, one fiber for the transmission, another fiber for receiving. In a dual-fiber unidirectional transmission system, the same wavelength is usually used both for the transmission direction and for the receiving direction. In a redundant system, the second fiber can be used as a backup fiber, or as an optical path in the opposite direction.

Uplink/Downlink

The transmission direction of the transmission signal can be expressed by up and down. Downstream refers to the direction in which the communication is sent from the service provider to the service user, and the reverse is the opposite.