Category Archives: WDM Optical Network

EDFA — the Most Popular Optical Amplifier in Optical Communications

There will be attenuation losses in the fiber when the signals transmit over long distances. To compensate for the attenuation losses, optical amplifier which could restore the optical signal to its original power level without E-O and O-E (electrical to optical and optical to electrical) conversions is needed. Optical amplifier is an important enabling technology for optical communication networks. There are three common optical amplifiers which include erbium-doped fiber amplifier (EDFA), the semiconductor optical amplifier (SOA), and the Raman amplifier. Among them EDFA is most often applied in optical communications.

Definition

EDFA uses a short length of optical fiber doped with the rare-earth element erbium that has the appropriate energy levels in the atomic structures for amplifying optical signal. It’s designed to amplify light at wavelengths around 1550 nm and make wavelengths suffer minimum attenuation in optical fibers. EDFA often uses a 980nm or 1480nm pump laser to inject energy into the doped fiber. The 980nm band has a higher absorption cross-section and is generally used for low-noise performance. The 1480nm band has a lower but broader absorption cross-section and is generally used for high power amplifiers.

Principle of EDFA

The principle of EDFA is shown as the following picture. EDFA usually consists of a length of EDF (erbium-doped fiber), a pump laser, and a component (often known as a WDM coupler) for combining the signal and pump wavelength and an isolator. The pump laser, known as pumping bands, inserts dopants into the silica fiber and makes erbium enter into an excited state. When the weak signals at 1310 nm or 1550 nm travel through the fiber, the lights will stimulate the excited atoms of erbium so that the atoms can release energy in the form of photons. The emitted light photons which have the same wavelength with input signals amplify the optical signals. The signals passing by the fiber will grow stronger and stronger. And the function of the isolator usually placed at the output is to prevent reflections returning from the attached fiber. Because the reflections can disrupt amplifier operation. Thus, EDFA is a high gain amplifier.

Applications

EDFA has many useful functions in telecom systems for fiber communications. For instance, it can boost the power of a data transmitter before entering a long fiber span. It could also be used in front of a data receiver if the arriving signal is weak. What’s more, an EDFA can be used to maintain extended spans of passive transmission fiber. So that the transmission losses through the long distance fiber could be compensated. EDFA is oftern applied in DWDM, CATV, SDH. In addition, an EDFA could be used as the equipment for testing transmission hardware.

Conclusion

In long distance communications, the signals should be amplified to avoid the attenuation losses. There are many kinds of optical amplifiers could be used to amplify the signal but some of them are not very often applied because of certain obvious disadvantages. For example, SOA will add noise to the signal. While EDFA has some interesting properties for fiber optics communications due to its rare-earth element. EDFA is a low-noise amplifier which can simultaneously amplify many data channels at different wavelengths with flat gain, high saturation output power and stable operation. So these advantages make EDFA the most popular in optical communication applications.

Related atricle: Optical Amplifiers-a Way to Improve the Signal Quality

The Essential Mux/Demux Device in CWDM system

CWDM is short for coarse wavelength division multiplexing. CWDM technology is a method of combining multiple signals on laser beams at various wavelengths for transmission along a single fiber optic cable. CWDM system provides channels like 4, 8, 12 and 16 with the spacing of 20nm. The spectrum grid can remain from 1270nm to 1610nm when multiple wavelengths added to one fiber. It’s a cost effective choice for transporting large amounts of data traffic in telecoms or enterprise networks. Because CWDM can increase a fiber network capacity without deploying more fiber cables thus avoid fiber exhaust.

As mentioned above, CWDM is used to increase the amount of information that can be transmitted over a single fiber. Then the optical wavelength multiplexer (MUX) and the de-multiplexer (DEMUX) are indispensable components to deal with small numbers of wavelengths in this system.

What is CWDM Mux/Demux? The CWDM Mux/Demux is a device designed to allow multiple optical signals with different wavelengths to pass through a single optical fiber strand and split the multi-wavelength optical signals. For example, with a multiplexer at the beginning of the network, a typical 4 channel CWDM will be used to multiplex four different wavelengths onto one fiber. This means four different networks/systems can be transmitted over the same fiber simultaneously. At the opposite end of the network, a CWDM demultiplexer to demultiplex the wavelengths to allow them to be directed to the correct receivers. But usually CWDM Mux and Demux are integrated in an entirety. So the optical transmission is done by dual fibers where one fiber is transporting data from east to weat and vice-versa. With highly reliable passive optics certified for environmentally hardened applications, the CWDM Mux/Demux lets operators make full use of available fiber bandwidth in local loop and enterprise architectures. It’s a flexible, low cost solution that enables the expansion of existing fiber capacity.

CWDM Dux and Demux

The followings are the features of CWDM Mux/Demux:

  • Long distance coverage of multiple signals on a single fiber strand
  • Good flexibility and expansibility
  • Low end-to-end insertion loss
  • Extended operating temperature range suitable for remote office environments
  • High optical fiber transmission capacity
  • Simple to install, requires no configuration or maintenance
  • Passive CWDM optical Mux/Demux design
  • Low content delivery costs where dark fiber is available

Based on these features, CWDM Mux/Demux module can be applied in broad fields: enterprises and carriers with fiber optic infrastructure, transmitting additional applications with existing fiber cables, connecting buildings to CWDM campus ring, connecting field offices to cental office, ideal solution for metro-core, metro-access and enterprises.

Fiberstore supplies passive CWDM Mux/Demux with all channels except the common 4, 8, 16, 18 channel. All CWDM Mux/Demux modules suit Gigabit & 10G Ethernet, SDH/SONET, ATM, ESCON, Fibre Channel, FTTx and CATV, etc. And various optional port configurations are available such as Express Port, Monitor Port, 1310nm passband port and 1550nm port for these multiplexers according to your choice.