How to Optimize Amplification and Dispersion in Optical Networks
Mar 18, 20251 min read
Two critical factors that impact the efficiency of optical networks are signal amplification and dispersion management. In short-distance and low-data-rate transmissions, the power budget of an optical transceiver can often compensate for signal loss, and the accumulated dispersion may not be significant enough to cause noticeable distortion. Therefore, the WDM networks can be deployed with relative ease. However, as the demand for bandwidth continues to grow, amplification and dispersion compensation are needed to extend the transmission distance between two sites.
Manage Signal Amplification in Optical Networks
Optical amplifiers counteract the attenuation of light signals as they travel through fiber optic cables. One of the most widely used technologies for signal amplification is the Erbium-Doped Fiber Amplifier (EDFA).
EDFAs are optical amplifiers that use erbium-doped fiber to boost the intensity of light signals in optical networks. EDFAs offer several advantages, including high gain, low noise, and the ability to amplify multiple wavelengths simultaneously, making them ideal for dense wavelength-division multiplexing (DWDM) systems.
Select Right EDFA Optical Amplifier for Your WDM Network
EDFAs are categorized into three main types based on their placement and function within the network: Pre-Amplifiers (PA), Booster Amplifiers (BA), and Line Amplifiers (LA).
Pre-Amplifiers (PA)
Pre-amplifiers are placed at the receiving end of an optical link. They amplify weak incoming signals to a level that can be accurately detected and processed by the receiver. PAs are designed to have a low noise figure (typically 4–5 dB) to minimize the addition of noise to already weak signals, and provide moderate gain (around 20–30 dB) to ensure the signal is strong enough for detection without introducing excessive noise. PAs are primarily used in long-haul networks.
Booster-Amplifiers (BA)
Booster amplifiers amplify signal just after it transmits. They increase the power of the outgoing signal to ensure it can travel long distances without significant degradation. BAs are designed to provide high output power to launch strong signals into the fiber without intermediate amplification.
In-Line Amplifiers (LA)
In-line amplifiers are deployed at intermediate points along the optical link to boost the signal as it travels through fiber. They are commonly used to maintain signal strength over extended distances.
In ultra-long distance transmission or network with high loss, PA and BA may not be enough to compensate the loss of the whole link. So, LA needs to be inserted in the middle to compensate the attenuation in sections to ensure that the signal still has enough signal-to-noise ratio when it reaches the receiving end.
In addition, the influence of noise needs to be considered. Each amplifier will introduce extra noise, and too many amplifiers may accumulate noise and affect system performance. Therefore, the position and number of amplifiers matters. PA and BA may be responsible for the amplification of the endpoint, while LA compensates at the intermediate node to ensure that the signal remains stable during the whole transmission process.
Best Practices for EDFA Deployment
Proper deployment of EDFA optical amplifier can ensure optimal performance in optical networking. Below are detailed best practices for EDFA deployment.
Proper Gain Setting
The gain of an EDFA must be carefully calibrated to match the signal loss between amplifiers. If the gain is set too high (over-amplification), it may distort the signal and introduce errors, and VOA (Variable Optical Attenuator) is needed to increase the attenuation. Conversely, if the gain is too low (under-amplification), the signal may become too weak to be detected accurately at the receiver, resulting in a high bit error rate. It is practical to use optical power meters and spectrum analyzers to measure signal loss between amplifiers and adjust the EDFA gain accordingly.
Noise Management
EDFAs introduce amplified spontaneous emission (ASE) noise, which accumulates with each amplification stage. Excessive noise can degrade the optical signal-to-noise ratio (OSNR), leading to poor signal quality and higher BER. It is recommended to use EDFAs with low noise figures to minimize ASE noise.
Monitoring and Maintenance
EDFA amplifiers experiencing gain drift due to aging components might gradually reduce their output power, causing signal degradation over time. Regular monitoring can detect this issue early, allowing for timely maintenance or replacement. OPM (optical performance monitoring) tracks key parameters such as gain, noise figure, and output power, and is widely deployed in long-haul networks.
Managing Dispersion in Optical Networks
While EDFA amplifier addresses signal attenuation, dispersion threatens your optical networks. Dispersion refers to the spreading of light pulses as they travel through fiber, which can cause signal overlap and degrade data integrity. DCM and TDCM are commonly used to compensate dispersion in DWDM Networks.
Choose Proper DCM for Your WDM Network
Dispersion Compensation Module
DCM generally refers to a module with a fixed dispersion compensation value. It is a completely passive device with negative dispersion to overcome the signal pulse distortion in long-distance transmission.
Tunable Dispersion Compensation Module
TDCM features adjustable dispersion. It offers dynamic compensation capabilities, and is normally applied in higher data rates (40G/100G) that requires accurate dispersion compensation.
Best Practices for DCM Deployment
Optimize DCM Placement
The placement of DCMs within the network significantly impacts their effectiveness. There are two primary strategies for DCM placement: pre-compensation and post-compensation.
Pre-Compensation means that DCMs are placed at the transmitting end to introduce negative dispersion before the signal enters the fiber. This approach is useful for reducing nonlinear effects in the early stages of transmission.
Post-Compensation means that DCMs are placed at the receiving end to correct dispersion after the signal has traveled through the fiber. This is the most common approach and is effective for long-haul networks.
Hybrid Approach combines pre- and post-compensation can provide better performance, especially in networks with complex topologies or varying fiber types.
Match DCM Dispersion to Fiber And Network Characteristics
The dispersion value of the DCM should match the dispersion requirement of the fiber span and network to ensure effective compensation. The dispersion value should be:
Total Dispersion = Dispersion Coefficient (ps/(nm·km)) x Fiber Length (km)
In 10G network, a small amount of under-compensation (20km) should be considered to avoid potential issues caused by over-compensation. But in 40G/100G networks, the tolerance to dispersion is limited. Dispersion accuracy must be strictly adhered to and even a small error can affect signal quality.
User-Friendly FMT Series Optimize Amplification and Dispersion
Designed for ease of use, the FMT Series integrates EDFA and DCM cards, providing precise signal amplification and dispersion compensation in a compact platform. The gain, output power, input power, compensation length, housing and more can be tailored to various network demands. The OnlineMonitor System provides user-friendly management and operation. With low noise figures, high gain accuracy, the FMT Series simplifies network management, reduces operational costs, and enhances signal integrity, which is a good choice for DWDM networks.
Product List
EDFA Optical Amplifier
Types | FS P/N | Product Description | Operation Wavelength | Housing | Application |
C-band EDFA | FMT26PA-EDFA, 26dB Gain C-band DWDM EDFA Pre-amplifier, 16dBm Output | 1528nm~1564nm | Plug-in Module | DWDM Network | |
FMT20PA-EDFA, 20dB Gain C-band DWDM EDFA Pre-amplifier, 13dBm Output | 1528nm~1564nm | Plug-in Module | DWDM Network | ||
Customized Pre-Amplifier EDFA for DWDM Solution | 1528nm-1564nm | Plug-in Module 1U 19" Rack Mount | DWDM Network | ||
FMT17BA-EDFA, 17dB Gain C-band DWDM EDFA Booster Amplifier, 17dBm Output | 1528nm-1564nm | Plug-in Module | DWDM Network | ||
Customized Booster EDFA for DWDM Solution | 1528nm-1564nm | Plug-in Module 1U 19" Rack Mount | DWDM Network | ||
Customized In-Line EDFA for DWDM Solution | 1528nm-1564nm | Plug-in Module 1U 19" Rack Mount | DWDM Network | ||
Extended C-band EDFA | FMT26PA-51EDFA, 26dB Gain Extended C-Band DWDM EDFA Pre-amplifier, 20dBm Output | 1528nm~1568nm | Plug-in Module | DWDM Network | |
FMT17BA-51EDFA, 17dB Gain Extended C-Band DWDM EDFA Booster Amplifier, 20dBm Output | 1528nm~1568nm | Plug-in Module | DWDM Network | ||
Arrayed EDFA | Customized Multiports DWDM Array EDFA Pre-amplifier | 1528nm~1568nm | Plug-in Module 1U 19" Rack Mount | DWDM Network ROADM System | |
Customized Multiports DWDM Array EDFA Booster Amplifier | 1528nm~1568nm | Plug-in Module 1U 19" Rack Mount | DWDM Network ROADM System |
Dispersion Compensation Module
Types | FS P/N | Product Description | Compensation Length | Dispersion Compensation |
DCM | FMT40-DCM, C-Band 40km DCF-based Passive Dispersion Compensation Module | 40km | -680ps/nm±3% | |
FMT80-DCM, C-Band 80km DCF-based Passive Dispersion Compensation Module | 80km | -1360ps/nm±3% | ||
Customized C-Band DCF-based Dispersion Compensation Module | 20/40/60/80/100km | -340/-680/-1020/-1360/-1700ps/nm | ||
TDCM | Customized C-band Tunable Dispersion Compensation Module (TDCM) | -20~+20km -40~+40km | ±400 ps/nm ±800 ps/nm |