Common DWDM optical devices
Dense wavelength division multiplexing (DWDM) can combine a group of optical wavelengths and transmit them with one optical fiber. This is a laser technology used to improve the bandwidth of the existing optical fiber backbone network. DWDM technology is an extension of optical network. The main advantage of DWDM is that it is independent of protocol and transmission rate. The network based on DWDM can transmit data in IP, ATM, SONET, SDH and Ethernet.
This paper introduces the optical devices commonly used in DWDM and the combined solutions of these optical devices.
DWDM system usually has the following optical devices: DWDM optical module, DWDM MUX / demux, DWDM OADM and optical amplifier.
DWDM optical module
As a kind of optical module, DWDM optical module, like ordinary optical module, is an important device for photoelectric signal conversion. Dwmd optical module needs the cooperation of DWDM wavelength division multiplexer. The corresponding band realizes high-capacity long-distance communication transmission in one core or a pair of optical fibers through combining and dividing waves. Each DWDM optical module has its own specific wavelength. Using DWDM technology can greatly save optical fiber resources, but ordinary optical modules can’t. In today’s market, most of them are DWDM optical modules (DWDM SFP, DWDM SFP +, DWDM XFP, etc.) working at 100GHz and 50GHz.
DWDM Mux/Demux
DWDM multiplexer (MUX) combines the output optical signals from multiple transmitters to transmit on a single optical fiber. At the receiving end, another DWDM demultiplexer (demux) separates the combined optical signal. Only one optical fiber is used between DWDM multiplexers (in each transmission direction). DWDM does not need to use one optical fiber in each pair of optical modules, but allows multiple optical channels to occupy one optical cable.
AAWG
Aawg is a kind of DWDM multiplexer. In the optical fiber communication system, the earliest commercial DWDM multiplexer is composed of multiple three port dielectric film filters (TFF) in series. However, when the number of channels is greater than 16, the DWDM module based on TFF technology can not meet the application requirements because of its large loss. However, a typical DWDM system usually transmits more than 40 or 48 wavelengths in a single fiber, so a multiplexer / demultiplexer with a larger number of ports is required. WDM module with series structure will accumulate too much power loss at the back port, so it needs to adopt parallel structure to multiplex / demultiplex ten wavelengths at one time. Arrayed waveguide grating AWG is such an optical device. Aawg is a heatless AWG, which mainly realizes the functions of wave combination and wave division of more than 16 channels.
DWDM OADM
On some optical network transmission contacts, it is often necessary to separate some signal streams from the transmission system or insert some signal streams into the system, that is, “add and drop”. The following figure shows a 1-channel DWDM OADM, which is designed to separate or insert only optical signals of a specific wavelength. From left to right, the input composite signal is divided into two components: through and separation. OADM only separates the blue optical signal flow. The separated signal stream is passed to the receiver of the client device. The remaining optical signals passing through the OADM are multiplexed with the new insertion signal stream. OADM adds a new blue optical signal flow, which is combined with the through signal to form a new composite signal.
optical amplifier
In the previous tweet, we introduced EDFA optical amplifier in detail, which is a fiber amplifier using erbium ion as gain medium. Optical amplifier can amplify optical signal in a wide wavelength range, which is very important for DWDM system application. Compared with the EDFA used in CATV or SDH system, the EDFA used in DWDM system is sometimes called DWDM EDFA. In order to extend the transmission distance of DWDM system, you can choose from different types of optical amplifiers, including DWDM EDFA, CATV EDFA, SDH EDFA, EDFA and Raman amplifier.
DWDM optical transmission network solution
As shown in the figure, it is a complete DWDM system solution:
DWDM optical modules with different wavelengths convert electrical signals into optical signals, which are multiplexed into an optical fiber by DWDM MUX for transmission;
. the post amplifier improves the intensity of the optical signal after the optical signal leaves the DWDM MUX;
. using DWDM OADM to separate and insert optical signals of specific wavelengths at remote locations;
. relay amplifiers can be used on the optical fiber span as needed;
The preamplifier amplifies the optical signal before it enters DWDM demux;
The input optical signal is decomposed into separate DWDM wavelengths by DWDM demux.
. each DWDM optical module converts the optical signal into an electrical signal and transmits it to the client equipment.
Using DWDM system can provide bandwidth for a large amount of data. With the development of technology, the capacity of DWDM system is growing, which can allow shorter spacing and more wavelengths. However, DWDM is also going beyond the field of transmission and becoming the basis of all-optical network with wavelength supply and mesh protection. With the development of technology, DWDM system may need more advanced components to play a greater advantage.