Understanding Noise Figure in Amplifiers: Definition, Importance, and How to Reduce It

Technical 3 Mins Read

When working with amplifiers, grasping the concept of noise figure is essential. This article aims to elucidate noise figure, its significance, methods for its measurement and reduction in amplifier designs. Additionally, we’ll provide the correct formula for calculating noise figure and an illustrative example.

Noise figure is an indispensable factor in amplifier design, affecting signal quality and performance. By understanding and managing noise figure, amplifiers can be optimized for specific applications, ensuring minimal signal degradation over distances. Employing strategies like using LNAs and negative feedback can effectively minimize noise figure.

FAQs

What’s the difference between noise figure and noise temperature?
- Noise figure measures the noise added by an amplifier, while noise temperature represents the noise’s equivalent temperature.
Why is a low noise figure important in communication systems?
- A low noise figure ensures minimal signal degradation over long distances in communication systems.
How is noise figure measured?
- Noise figure is measured using a noise figure meter, which assesses the SNR at the amplifier’s input and output.
Can noise figure be negative?
- No, the noise figure is always greater than or equal to 0 dB.
How can I reduce the noise figure in my amplifier design?
- Reducing the noise figure can involve using a low-noise amplifier, implementing negative feedback, employing a balanced or differential amplifier, and minimizing the amplifier’s operating temperature.

25 Questions with Answers on EDFA Amplifiers

Interviews 10 Mins Read

EDFA stands for Erbium-doped fiber amplifier, and it is a type of optical amplifier used in optical communication systems

What is an EDFA amplifier?
How does an EDFA amplifier work?
What is the gain of an EDFA amplifier?
What is the noise figure of an EDFA amplifier?
What is the saturation power of an EDFA amplifier?
What is the output power of an EDFA amplifier?
What is the input power range of an EDFA amplifier?
What is the bandwidth of an EDFA amplifier?
What is the polarization-dependent gain of an EDFA amplifier?
What is the polarization mode dispersion of an EDFA amplifier?
What is the chromatic dispersion of an EDFA amplifier?
What is the pump power of an EDFA amplifier?
What are the types of pump sources used in EDFA amplifiers?
What is the lifetime of an EDFA amplifier?
What is the reliability of an EDFA amplifier?
What is the temperature range of an EDFA amplifier?
What are the applications of EDFA amplifiers?
How can EDFA amplifiers be used in long-haul optical networks?
How can EDFA amplifiers be used in metropolitan optical networks?
How can EDFA amplifiers be used in access optical networks?
What are the advantages of EDFA amplifiers over other types of optical amplifiers?
What are the disadvantages of EDFA amplifiers?
What are the challenges in designing EDFA amplifiers?
How can the performance of EDFA amplifiers be improved?
What is the future of EDFA amplifiers in optical networks?

What is an EDFA Amplifier?

An EDFA amplifier is a type of optical amplifier that uses a doped optical fiber to amplify optical signals. The doping material used in the fiber is erbium, which is added to the fiber core during the manufacturing process. The erbium ions in the fiber core absorb optical signals at a specific wavelength and emit them at a higher energy level, which results in amplification of the optical signal.

How Does an EDFA Amplifier Work?

An EDFA amplifier works on the principle of stimulated emission. When an optical signal enters the doped fiber core, the erbium ions in the fiber absorb the energy from the optical signal and get excited to a higher energy level. The excited erbium ions then emit photons at the same wavelength and in phase with the incoming photons, which results in amplification of the optical signal.

What is the Gain of an EDFA Amplifier?

The gain of an EDFA amplifier is the ratio of output power to input power, expressed in decibels (dB). The gain of an EDFA amplifier depends on the length of the doped fiber, the concentration of erbium ions in the fiber, and the pump power.

What is the Noise Figure of an EDFA Amplifier?

The noise figure of an EDFA amplifier is a measure of the additional noise introduced by the amplifier in the optical signal. It is expressed in decibels (dB) and is a function of the gain and the bandwidth of the amplifier.

What is the Saturation Power of an EDFA Amplifier?

The saturation power of an EDFA amplifier is the input power at which the gain of the amplifier saturates and does not increase further. It depends on the pump power and the length of the doped fiber.

What is the Output Power of an EDFA Amplifier?

The output power of an EDFA amplifier depends on the input power, the gain, and the saturation power of the amplifier. The output power can be increased by increasing the input power or by using multiple stages of amplification.

What is the Input Power Range of an EDFA Amplifier?

The input power range of an EDFA amplifier is the range of input powers that can be amplified without significant distortion or damage to the amplifier. The input power range depends on the saturation power and the noise figure of the amplifier.

What is the Bandwidth of an EDFA Amplifier?

The bandwidth of an EDFA amplifier is the range of wavelengths over which the amplifier can amplify the optical signal. The bandwidth depends on the spectral characteristics of the erbium ions in the fiber and the optical filters used in the amplifier.

What is the Polarization-Dependent Gain of an EDFA Amplifier?

The polarization-dependent gain of an EDFA amplifier is the difference in gain between two orthogonal polarizations of the input signal. It is caused by the birefringence of the doped fiber and can be minimized by using polarization-maintaining fibers and components.

What is the Polarization Mode Dispersion of an EDFA Amplifier?

The polarization mode dispersion of an EDFA amplifier is the differential delay between the two orthogonal polarizations of the input signal. It is caused by the birefringence of the doped fiber and can lead to distortion and signal degradation.

What is the Chromatic Dispersion of an EDFA Amplifier?

The chromatic dispersion of an EDFA amplifier is the differential delay between different wavelengths of the input signal. It is caused by the dispersion of the fiber and can lead to signal distortion and inter-symbol interference.

What is the Pump Power of an EDFA Amplifier?

The pump power of an EDFA amplifier is the power of the pump laser used to excite the erbium ions in the fiber. The pump power is typically in the range of a few hundred milliwatts to a few watts.

What are the Types of Pump Sources Used in EDFA Amplifiers?

The two types of pump sources used in EDFA amplifiers are laser diodes and fiber-coupled laser diodes. Laser diodes are more compact and efficient but require precise temperature control, while fiber-coupled laser diodes are more robust but less efficient.

What is the Lifetime of an EDFA Amplifier?

The lifetime of an EDFA amplifier depends on the quality of the components used and the operating conditions. A well-designed and maintained EDFA amplifier can have a lifetime of several years.

What is the Reliability of an EDFA Amplifier?

The reliability of an EDFA amplifier depends on the quality of the components used and the operating conditions. A well-designed and maintained EDFA amplifier can have a high level of reliability.

What is the Temperature Range of an EDFA Amplifier?

The temperature range of an EDFA amplifier depends on the thermal properties of the components used and the design of the amplifier. Most EDFA amplifiers can operate over a temperature range of -5°C to 70°C.

What are the Applications of EDFA Amplifiers?

EDFA amplifiers are used in a wide range of applications, including long-haul optical networks, metropolitan optical networks, and access optical networks. They are also used in fiber-optic sensors, fiber lasers, and other applications that require optical amplification.

How can EDFA Amplifiers be Used in Long-Haul Optical Networks?

EDFA amplifiers can be used in long-haul optical networks to overcome the signal attenuation caused by the fiber loss. By amplifying the optical signal periodically along the fiber link, the signal can be transmitted over longer distances without the need for regeneration. EDFA amplifiers can also be used in conjunction with other types of optical amplifiers, such as Raman amplifiers, to improve the performance of the optical network.

How can EDFA Amplifiers be Used in Metropolitan Optical Networks?

EDFA amplifiers can be used in metropolitan optical networks to increase the reach and capacity of the network. They can be used to amplify the optical signal in the fiber links between the central office and the remote terminals, as well as in the access network. EDFA amplifiers can also be used to compensate for the loss in passive optical components, such as splitters and couplers.

How can EDFA Amplifiers be Used in Access Optical Networks?

EDFA amplifiers can be used in access optical networks to increase the reach and capacity of the network. They can be used to amplify the optical signal in the fiber links between the central office and the optical network terminals (ONTs), as well as in the distribution network. EDFA amplifiers can also be used to compensate for the loss in passive optical components, such as splitters and couplers.

What are the Advantages of EDFA Amplifiers over Other Types of Optical Amplifiers?

The advantages of EDFA amplifiers over other types of optical amplifiers include high gain, low noise figure, wide bandwidth, and compatibility with other optical components. EDFA amplifiers also have a simple and robust design and are relatively easy to manufacture.

What are the Disadvantages of EDFA Amplifiers?

The disadvantages of EDFA amplifiers include polarization-dependent gain, polarization mode dispersion, and chromatic dispersion. EDFA amplifiers also require high pump powers and precise temperature control, which can increase the cost and complexity of the system.

What are the Challenges in Designing EDFA Amplifiers?

The challenges in designing EDFA amplifiers include minimizing the polarization-dependent gain and polarization mode dispersion, optimizing the pump power and wavelength, and reducing the noise figure and distortion. The design also needs to be robust and reliable, and compatible with other optical components.

How can the Performance of EDFA Amplifiers be Improved?

The performance of EDFA amplifiers can be improved by using polarization-maintaining fibers and components, optimizing the pump power and wavelength, using optical filters to reduce noise and distortion, and using multiple stages of amplification. The use of advanced materials, such as thulium-doped fibers, can also improve the performance of EDFA amplifiers.

What is the Future of EDFA Amplifiers in Optical Networks?

EDFA amplifiers will continue to play an important role in optical networks, especially in long-haul and high-capacity applications. However, new technologies, such as semiconductor optical amplifiers and hybrid amplifiers, are emerging that offer higher performance and lower cost. The future of EDFA amplifiers will depend on their ability to adapt to these new technologies and continue to provide value to the optical networking industry.

Conclusion

EDFA amplifiers are a key component of optical communication systems, providing high gain and low noise amplification of optical signals. Understanding the basics of EDFA amplifiers, including their gain, noise figure, bandwidth, and other characteristics, is essential for anyone interested in optical networking. By answering these 25 questions, we hope to have provided a comprehensive overview of EDFA amplifiers and their applications in optical networks.

FAQs

What is the difference between EDFA and SOA amplifiers?
How can I calculate the gain of an EDFA amplifier?
What is the effect of pump
power on the performance of an EDFA amplifier? 4. Can EDFA amplifiers be used in WDM systems?
How can I minimize the polarization mode dispersion of an EDFA amplifier?
FAQs Answers
The main difference between EDFA and SOA amplifiers is that EDFA amplifiers use a doped fiber to amplify the optical signal, while SOA amplifiers use a semiconductor material.
The gain of an EDFA amplifier can be calculated using the formula: G = 10*log10(Pout/Pin), where G is the gain in decibels, Pout is the output power, and Pin is the input power.
The pump power has a significant impact on the gain and noise figure of an EDFA amplifier. Increasing the pump power can increase the gain and reduce the noise figure, but also increases the risk of nonlinear effects and thermal damage.
Yes, EDFA amplifiers are commonly used in WDM systems to amplify the optical signals at multiple wavelengths simultaneously.
The polarization mode dispersion of an EDFA amplifier can be minimized by using polarization-maintaining fibers and components, and by optimizing the design of the amplifier to reduce birefringence effects.

A short discussion on 980nm and 1480nm pump based Erbium Doped Fiber Amplifiers (EDFA)

Technical 4 Mins Read

The 980nm pump needs three energy level for radiation while 1480nm pumps can excite the ions directly to the metastable level .

(a) Energy level scheme of ground and first two excited states of Er ions in a silica matrix. The sublevel splitting and the lengths of arrows representing absorption and emission transitions are not drawn to scale. In the case of the 4 I11/2 state, s is the lifetime for nonradiative decay to the I13/2 first excited state and ssp is the spontaneous lifetime of the 4 I13/2 first excited state. (b) Absorption coefficient, a, and emission coefficient, g*, spectra for a typical aluminum co-doped EDF.

.The most important feature of the level scheme is that the transition energy between the I15/2 ground state and the I13/2 first excited state corresponds to photon wavelengths (approximately 1530 to 1560 nm) for which the attenuation in silica fibers is lowest. Amplification is achieved by creating an inversion by pumping atoms into the first excited state, typically using either 980 nm or 1480 nm diode lasers. Because of the superior noise figure they provide and their superior wall plug efficiency, most EDFAs are built using 980 nm pump diodes. 1480 nm pump diodes are still often used in L-band EDFAs although here, too, 980 nm pumps are becoming more widely used.

Though pumping with 1480 nm is used and has an optical power conversion efficiency which is higher than that for 980 nm pumping, the latter is preferred because of the following advantages it has over 1480 nm pumping.

It provides a wider separation between the laser wavelength and pump wavelength.
980 nm pumping gives less noise than 1480nm.
Unlike 1480 nm pumping, 980 nm pumping cannot stimulate back transition to the ground state.
980 nm pumping also gives a higher signal gain, the maximum gain coefficient being 11 dB/mW against 6.3 dB/mW for the 1.48
The reason for better performance of 980 nm pumping over the 1.48 m pumping is related to the fact that the former has a narrower absorption spectrum.
The inversion factor almost becomes 1 in case of 980 nm pumping whereas for 1480 nm pumping the best one gets is about 1.6.
Quantum mechanics puts a lower limit of 3 dB to the optical noise figure at high optical gain. 980 nm pimping provides a value of 3.1 dB, close to the quantum limit whereas 1.48 pumping gives a value of 4.2 dB.
1480nm pump needs more electrical power compare to 980nm.

Application

The 980 nm pumps EDFA’s are widely used in terrestrial systems while 1480nm pumps are used as Remote Optically Pumped Amplifiers (ROPA) in subsea links where it is difficult to put amplifiers.For submarine systems, remote pumping can be used in order not to have to electrically feed the amplifiers and remove electronic parts.Nowadays ,this is used in pumping up to 200km.

The erbium-doped fiber can be activated by a pump wavelength of 980 or 1480 nm but only the second one is used in repeaterless systems due to the lower fiber loss at 1.48 mm with respect to the loss at 0.98 mm. This allows the distance between the terminal and the remote amplifier to be increased.

In a typical configuration, the ROPA is comprised of a simple short length of erbium doped fiber in the transmission line placed a few tens of kilometers before a shore terminal or a conventional in-line EDFA. The remote EDF is backward pumped by a 1480 nm laser, from the terminal or in-line EDFA, thus providing signal gain

Vendors

Following are the vendors that manufactures 980nm and 1480nm EDFAs

Difference between EDFAs requirements for Terrestrial(Land) Systems and Submarine Systems.

Technical 3 Mins Read

Compared with requirements for EDFAs for terrestrial applications and for Submarine applications, there are major important differences making the two types of amplifiers definitely two different components.

Terrestrial(Land) system	Submarine System
•Reliability of land-based equipment is somewhat relaxed, corresponding to a 15-year required lifetime.	• Submarine systems are designed for a 25-year lifetime and a minimum of ship repair that imply reliability and redundancy of all the critical components.
• Terrestrial equipment should enable operation over a wide temperature range of −5, +70°C (and −40, +85°C in storage conditions). This wide temperature range makes it necessary to implement cooling means for the highest temperatures and compensation means for temperature-sensitive devices.	• In submarine amplifiers, heat is dissipated from the outer side of the repeater container into the sea. Such a container is designed in order to make the heat go through the box from the pump device to the outer side, ensuring moderate temperature in all points. Temperature of the deep sea is indeed around +5°C. Specific care is taken for repeaters located at the coast or in shallow water, in order to guarantee no pump failure while avoiding Peltier cooling. For reliability reasons, no glue is used on the optical path. The constant temperature of the devices and the doped fiber incorporated in the amplifier makes it possible to perfectly tailor the gain spectrum of the submerged EDFAs, owing to very accurate equalizing filters and to concatenating hundreds of amplifiers. This would not be possible for land-based amplifiers whose gain cannot be guaranteed below 1 dB for a 30-nm bandwidth partly due to such temperature changes (while a few tenths of dB of gain excursion is reached for submarine amplifiers).
• The infrastructure itself of terrestrial systems determines the actual characteristics of the amplifier that needs to cope with important variations of the span loss between two amplifier sites. In addition, for economical reasons, the amplifiers cannot be tailored to cope with this nonuniform link.	• In submarine systems, the link is manufactured at the same time as the amplifiers and much attention is paid to guarantee constant attenuation loss between amplifier values, while the amplifier has been designed to perfectly adapt to the link characteristics.
• There are high gain range (20 to 35 dB) of the amplifiers incorporated in land-based systems and allowed by the margins given on the OSNR due to the reduced total link length. Gain equalizers therefore compensate for much larger gain excursion values than in submarine amplifiers and should therefore be located at amplifier midstage in order not to impact their equalizing loss on the amplifier output power.	• On the contrary, such filters can be placed after the single section of doped fiber that composes the amplifier in the case of submarine applications.

Maximum number of erbium-doped fiber amplifiers in a DWDM lin

Technical 3 Mins Read

The maximum number of erbium-doped fiber amplifiers (EDFAs) in a fiber chain is about four to six.

Explanation

The rule is based on the following rationales:

1. About 80 km exists between each in-line EDFA, because this is the approximate distance at which the signal needs to be amplified.

2. One booster is used after the transmitter.

3. One preamplifier is used before the receiver.

4. Approximately 400 km is used before an amplified spontaneous emission (ASE) has approached the signal (resulting in a loss of optical signal-to-noise ratio [OSNR]) and regeneration needs to be used.

An EDFA amplifies all the wavelengths and modulated as well as unmodulated light. Thus, every time it is used, the noise floor from stimulated emissions rises. Since the amplification actually adds power to each band (rather than multiplying it), the signal-to-noise ratio is decreased at each amplification. EDFAs also work only on the C and L bands and are typically pumped with a 980- or 1480-nm laser to excite the erbium electrons. About 100 m of fiber is needed for a 30-dB gain, but the gain curve doesn’t have a flat distribution, so a filter is usually included to ensure equal gains across the C and L bands.

For example, assume that the modulated power was 0.5 mW, and the noise from stimulated emission was 0.01 mW. The signal-to-noise ratio is 0.5/0.01 or 50. If an EDFA adds a 0.5 mW to both the modulated signal and the noise, then the modulated signal becomes 1 mW, and the noise becomes 0.501 mW, and the SNR is reduced to 2. After many amplifications,even if the total power is high, the optical signal-to-noise ratio becomes too low. This typically occurs after four to six amplifications.

Another reason to limit the number of chained EDFAs is the nonuniform nature of the gain. Generally, the gain peaks at 1555 nm and falls off on each side, and it is a function of the inversion of Er+3. When a large number of EDFAs are cascaded, the sloped of the gain becomes multiplied and sharp, as indicated in Fig. 6.3. This results is too little gain-bandwidth for a system. To help alleviate this effect, a gain flattening device often is used, such as a Mach–Zehnder or a long-period grating filter.

Reference

1. A. Willner and Y. Xie, “Wavelength Domain Multiplexed (WDM) Fiber-optic Communications Networks,” in Handbook of Optics, Vol. 4., M. Bass, Ed.,McGraw-Hill, New York, pp. 13–19, 2001.

2.http://www.pandacomdirekt.com/en/technologies/wdm/optical-amplifiers.html

3.http://blog.cubeoptics.com/index.php/2015/03/what-edfa-a-noise-source

Source: Optical Communications Rules of Thumb

Note:I have heard many times among optical folks discussing maximum number of amplifiers in a link;so thought of posting this.

A short discussion on 980nm and 1480nm pump based EDFA

Technical 4 Mins Read

A short discussion on 980nm and 1480nm pump based EDFA

Introduction

The 980nm pump needs three energy level for radiation while 1480nm pumps can excite the ions directly to the metastable level .

(a) Energy level scheme of ground and first two excited states of Er ions in a silica matrix. The sublevel splitting and the lengths of arrows representing absorption and emission transitions are not drawn to scale. In the case of the 4 I11/2 state, s is the lifetime for nonradiative decay to the I13/2 first excited state and ssp is the spontaneous lifetime of the 4 I13/2 first excited state. (b) Absorption coefficient, a, and emission coefficient, g*, spectra for a typical aluminum co-doped EDF.

The most important feature of the level scheme is that the transition energy between the I15/2 ground state and the I13/2 first excited state corresponds to photon wavelengths (approximately 1530 to 1560 nm) for which the attenuation in silica fibers is lowest. Amplification is achieved by creating an inversion by pumping atoms into the first excited state, typically using either 980 nm or 1480 nm diode lasers. Because of the superior noise figure they provide and their superior wall plug efficiency, most EDFAs are built using 980 nm pump diodes. 1480 nm pump diodes are still often used in L-band EDFAs although here, too, 980 nm pumps are becoming more widely used.

Though pumping with 1480 nm is used and has an optical power conversion efficiency which is higher than that for 980 nm pumping, the latter is preferred because of the following advantages it has over 1480 nm pumping.

It provides a wider separation between the laser wavelength and pump wavelength.
980 nm pumping gives less noise than 1480nm.
Unlike 1480 nm pumping, 980 nm pumping cannot stimulate back transition to the ground state.
980 nm pumping also gives a higher signal gain, the maximum gain coefficient being 11 dB/mW against 6.3 dB/mW for the 1.48
The reason for better performance of 980 nm pumping over the 1.48 m pumping is related to the fact that the former has a narrower absorption spectrum.
The inversion factor almost becomes 1 in case of 980 nm pumping whereas for 1480 nm pumping the best one gets is about 1.6.
Quantum mechanics puts a lower limit of 3 dB to the optical noise figure at high optical gain. 980 nm pimping provides a value of 3.1 dB, close to the quantum limit whereas 1.48 pumping gives a value of 4.2 dB.
1480nm pump needs more electrical power compare to 980nm.

Application

The 980 nm pumps EDFA’s are widely used in terrestrial systems while 1480nm pumps are used as Remote Optically Pumped Amplifiers (ROPA) in subsea links where it is difficult to put amplifiers.For submarine systems, remote pumping can be used in order not to have to electrically feed the amplifiers and remove electronic parts.Nowadays ,this is used in pumping up to 200km.

The erbium-doped fiber can be activated by a pump wavelength of 980 or 1480 nm but only the second one is used in repeaterless systems due to the lower fiber loss at 1.48 mm with respect to the loss at 0.98 mm. This allows the distance between the terminal and the remote amplifier to be increased.

In a typical configuration, the ROPA is comprised of a simple short length of erbium doped fiber in the transmission line placed a few tens of kilometers before a shore terminal or a conventional in-line EDFA. The remote EDF is backward pumped by a 1480 nm laser, from the terminal or in-line EDFA, thus providing signal gain

Vendors

Following are the vendors that manufactures 980nm and 1480nm EDFAs

edfa

Table of Contents

What is Noise Figure in Amplifiers?

Why is Noise Figure Important in Amplifiers?

How to Measure Noise Figure in Amplifiers

Factors Affecting Noise Figure in Amplifiers

How to Reduce Noise Figure in Amplifier Design

Formula for Calculating Noise Figure

Example of Calculating Noise Figure

Conclusion

FAQs

What is an EDFA Amplifier?

How Does an EDFA Amplifier Work?

What is the Gain of an EDFA Amplifier?

What is the Noise Figure of an EDFA Amplifier?

What is the Saturation Power of an EDFA Amplifier?

What is the Output Power of an EDFA Amplifier?

What is the Input Power Range of an EDFA Amplifier?

What is the Bandwidth of an EDFA Amplifier?

What is the Polarization-Dependent Gain of an EDFA Amplifier?

What is the Polarization Mode Dispersion of an EDFA Amplifier?

What is the Chromatic Dispersion of an EDFA Amplifier?

What is the Pump Power of an EDFA Amplifier?

What are the Types of Pump Sources Used in EDFA Amplifiers?

What is the Lifetime of an EDFA Amplifier?

What is the Reliability of an EDFA Amplifier?

What is the Temperature Range of an EDFA Amplifier?

What are the Applications of EDFA Amplifiers?

How can EDFA Amplifiers be Used in Long-Haul Optical Networks?

How can EDFA Amplifiers be Used in Metropolitan Optical Networks?

How can EDFA Amplifiers be Used in Access Optical Networks?

What are the Advantages of EDFA Amplifiers over Other Types of Optical Amplifiers?

What are the Disadvantages of EDFA Amplifiers?

What are the Challenges in Designing EDFA Amplifiers?

How can the Performance of EDFA Amplifiers be Improved?

What is the Future of EDFA Amplifiers in Optical Networks?

Conclusion

FAQs

Application

Vendors

A short discussion on 980nm and 1480nm pump based EDFA

Introduction

Application

Vendors