Category Archives: Optical Amplifiers

Using EDFA Amplifier for Long-Haul CATV Systems

With Laser technology combining with fiber optic technology, CATV systems in the field of optical communication have demonstrated unprecedented and irreplaceable achievements in the past few decades. When transmitting optical signals with fibers, fiber attenuation is the main factor that limits the transmission distance. EDFA (Erbium-Doped Fiber Amplifier) designed for CATV long-haul transmission avoids the conversion of optic-electric-optic in CATV long-haul transmission. It amplifies low signal power into high signal power, thus extending transmission distance. This post analyzes EDFA configurations and the utilization in long-haul CATV systems.

EDFA Leading Position in CATV Systems

EDFA is one of the most prominent achievements in fiber optic transmission technology over the past decade. Because it cleverly combined the laser technology and optical fiber manufacturing technology in the CATV systems and its applications were then rapidly expanded. Originally PDFA and EDFA amplifiers were equally used for CATV systems, but today, EDFA has completely replaced PDFA and become the primary device for fiber optic transmission systems. Why EDFA has leading position on CATV systems? Because EDFA noise and distortion characteristics are better, and its superior characteristics can be clearly seen in the following:

  • Operates at wavelength of 1550nm, consistent with C-band where fiber has the lowest loss
  • Has higher saturation output power, useful in systems requiring transmission up to 100 km or systems requiring the optical signal to be split to multiple fiber optic receivers
  • The signal gain spectrum is wide up to 30nm or more, can be used for broadband signal amplification, especially for WDM (wavelength division multiplexing) system, ideal for radio and data services networks
  • Has user friendly interface RS232, easy to control and monitor with computers
  • Low noise figure with high stability
EDFA Configurations

The configuration of a co-propagating EDFA is shown in Figure 1. The optical pump is combined with the optical signal into the erbium-doped fiber with a wavelength division multiplexer. A second multiplexer removes residual pump light from the fiber. An in-line optical filter provides additional insurance that pump light does not reach the output of the optical amplifier. An optical isolator is used to prevent reflected light from other portions of the optical system from entering the amplifier.

EDFA Configuration-1

An EDFA with a counter propagating pump is pictured in Figure 2. The copropagating geometry produces an amplifier with less noise and less output power. The counter propagating geometry produces a noisier amplifier with high output power. A compromise can be made by combining the co- and counter-propagating geometries in a bi-directional configuration.

EDFA Configuration-2

A Typical CATV System Using EDFA

Figure 3 illustrates a basic long-haul CATV transmission system designed to carry 77 channels of CATV signals for 100 km in a basic point-to-point configuration.


As you can see in Figure 3, the local CATV provider sends 77 channels of CATV signals at the transmitting side. After processing and RF combining, those multiple signals are combined into one channel of CATV signal with the wavelengths of 1550 nm. It transmits over a single-mode optical fiber to 50 km. An EDFA amplifier is used at the middle point to amplify the signals to a certain power level, continuing to transmit over a single mode fiber to 100 km. At the receiving side, the 1550nm CATV channel is split into multiple channels of 1550nm CATV signals, serving multiple hotel cable TV users.

FS.COM CATV EDFA Optical Amplifiers List

EDFA has undoubtedly received wide interest for CATV applications because of its high output power, low distortion and low noise capability. FS.COM supplies optical amplifiers including CATV EDFA, SDH EDFA, DWDM amplifier, etc. The following table lists FS.COM CATV EDFA amplifiers which are available with range of output power from 13 dBm to 24 dBm to meet the requirements of a high-density solution for the large-scale distribution of broadband CATV video and data signals to video overlay receivers in a FTTH/FTTP or PON system.

Product ID Part Number Description
17467 CEDFA-O13 New 13dBm 1550nm CATV EDFA Fiber Optic Amplifier
17489 CEDFA-O17 New 17dBm 1550nm CATV EDFA Fiber Optic Amplifier
17495 CEDFA-O23 New 23dBm 1550nm CATV EDFA Fiber Optic Amplifier
36458 CEDFA-BA Customized 1550nm CATV EDFA Fiber Optic Amplifierr

Knowledge About ROADM

Over the past decades, the use of bandwidth in transport networks increases dramatically. This resulted in the generation of wave division multiplexing (WDM) which could introduce more bandwidths on a single fiber. The need for more bandwidth flexibilities, operational efficiencies, and technology advances brought the optical add/drop multiplexer (OADM) to add or drop wavelengths at a node point. FOADM, an initial type of OADM, which uses fixed lasers for fixed wavelengths has emerged. But it can’t meet the needs of bandwidth. So this drives the emergence of the other kind of OADM – ROADM.

ROADM (reconfigurable optical add/drop multiplexer) adds the ability to remotely switch traffic from a WDM system at the wavelength layer. It avoids the unnecessary optical-electrical-optical conversion. And it’s bit-rate/protocol transparent, so future upgrades of bit-rate/protocol can be accommodated without upgrading the switch. ROADM technology has revolutionized optical network and offered huge bandwidth for data transport.

ROADM is an integral part of WDM networks due to its advantages. ROADM allows for remote configuration and reconfiguration. The planning of entire bandwidth assignment does not need to be carried out during initial deployment of a system. The configuration can be done as required without affecting traffic already passing the ROADM. It provides full flexibility of delivering any wavelength to any node throughout the ring infrastructure. It automates the optical layer to remove error-prone service provisioning, and equalizes signal loss across all wavelengths, reducing the need for expensive signal boosting equipment. What’s more, it can reduce the costs of networks.

ROADM functionality firstly appeared in long-haul equipment. By 2005, it started to appear in metro optical systems because of the network traffic driven by the increasing demand for packet-based services such as Ethernet, high-speed data, audio and video services. ROADM equipment is used to build a versatile, agile and quickly provisioned optical transport network. This transport network can scale in both distance and number of nodes.

As the continuous development of technology, it brings three generations of ROADM. The 1st generation was to solve fiber exhaust problems caused by inflexibility in the long haul networks. Compared with the 1st generation, the 2nd generation ROADM is typified by wavelength blocker technology. And the structure design of the 2nd generation is simple with a tap (a splitter and filter array) used to drop any number of selected wavelengths. But if all wavelengths enter the blocker, the pass-through wavelengths will not be blocked. The 3rd generation is the wavelength selective switch (WSS) (see the following picture). It’s more versatile, smaller, consuming less power and cheaper than 2nd generation ROADM.


Common advantages of ROADM like automatic performance monitoring and equalization make WDM systems more useful. However, the current ROADM technology is not perfect and still needs to be upgraded. The development of the advanced ROADM depends on the growth of supporting optical components maturity, progress of integrated optics technology, improved capability of the equipment and new algorithms. Whatever, the new design should concern those factors such as the future broadband communication network service needs, fewer components, fewer devices in network, effective interoperability and the flawless service evolution with considerable decrease in the operational costs.