Tag: Optical Amplifiers

Optical amplifier, with the introduction in 1990s, conquered the regenerator technology and opened doors to the WDM technology. It is mainly used to amplify an optical signal directly, without the need to first convert it to an electrical signal. There are many types of optical amplifiers, namely Raman amplifiers, erbium doped-fiber amplifiers (EDFAs), and semiconductor optical amplifier (SOA). This article will make a clearer introduction to SOA amplifier, and analyze its advantages and disadvantages.

The Basics of Semiconductor Optical Amplifier (SOA)

SOA optical amplifiers use the semiconductor as the gain medium, which are designed to be used in general applications to increase optical launch power to compensate for loss of other optical devices. Semiconductor optical amplifiers are often adopted in telecommunication systems in the form of fiber-pigtailed components, operating at signal wavelengths between 0.85 µm and 1.6 µm and generating gains of up to 30 dB. Semiconductor optical amplifier, available in 1310nm, 1400nm, 1500nm, 1600nm wavelength, can be used with singlemode or polarization maintaining fiber input/output.

Key Points of SOA Amplifier

1310 nm, 1400 nm, 1550 nm and 1610 nm wavelength selectable

High fiber-to-fiber gain of 20 dB

Up to 16 dBm output

1 MHz with 10 ns pulse width (optional)

PM Panda fiber input/output (optional)

Similar to lasers, but with non-reflecting ends and broad wavelength emission

Incoming optical signal stimulates emission of light at its own wavelength

Process continues through cavity to amplify signal

Working principle of SOA amplifier

The basic working principle of a SOA is the same as a semiconductor laser but without feedback. SOAs amplify incident light through simulated emission. When the light traveling through the active region, it causes these electrons to lose energy in the form of photons and get back to the ground state. Those stimulated photons have the same wavelength as the optical signal, thus amplifying the optical signal.

SOA Over EFDA in DWDM Networks

As the solution below, 120km Metro Networks by Using an SOA amplifier. You may wonder why not use EDFA in the above networks.

Theoretically, SOA optical amplifiers are not comparable with EDFA in the terms of performance. The noise figure of SOA optical amplifier is typically higher, the gain bandwidth can be similar, SOAs exhibit much stronger nonlinear distortions in the form of self-phase modulation and four-wave mixing. Yet, the semiconductor optical amplifier is of small size and electrical pumped, which is often less expensive than EDFA. Additionally, SOA can be run with a low power laser.

How to Choose SOA Optical Amplifier?

When selecting SOA amplifier, you have to check the every detailed parameter in the product data sheet. But, seriously, do you understand it? No, please read the following part.

The key parameters used to characterize a SOA amplifier are gain, gain bandwidth, saturation output power and noise.

Gain is the factor by which the input signal is amplified and is measured as the ratio of output power to input power (in dB). A higher gain results in higher output optical signal.

Gain bandwidth defines the range of bandwidth where the amplification functions. A wide gain bandwidth is desirable to amplify a wide range of signal wavelengths.

Saturation output power is the maximum output power attainable after amplification beyond which no amplification is reached. It is important that the SOA has a high power saturation level to remain in the linear working region and to have higher dynamic range.

Noise defines the undesired signal within the signal bandwidth which arises due to physical processing in the amplifier. A parameter called noise figure is used to measure the impact of noise which is typically around 5dB.

Network operators have the common basic target to produce cost-efficient telecommunication services. When considering operators from different nations including carriers operating worldwide, a variety of network architecture designs need to be considered. The suitable network design depends on the individual national properties with respect to the telecommunication services to be provided, such as the local population density distributions, the characteristic local residential consumer behavior, for example, the demand for voice telephony, internet protocol, or broadband TV, or the distribution and service level agreement (SLA) requirements of the business customers. The design of the network is governed by the topology. DWDM network for example, ring, star, mesh, by the purpose (access, aggregation, transport), by the mean and maximum link distance, and by the density and degree of switching or grooming nodes. All this has a direct impact on the choice of amplification in the optical multiplex section (OMS) of DWDM systems and on the local placement of DWDM optical amplifiers.

The diameter of networks is one of the most obvious distinctions. Nationwide networks in the United States follow engineering rules different from those applicable to the national backbones in European countries, especially when the design of amplifier maps and the positioning of photonic cross connect (PXC)/ROADM based nodes are considered. The largest diameters within all optical transport is achieved in submarine cable networks that deploy lumped amplifier span designs with very short distance between adjacent DWDM EDFA and eventually supported by additional distributed Raman amplification.

Besides the distance, many other parameters influence decisions for special network layouts, such as the local distribution of population and industry to be connected, the traffic patterns and capacity evolution, the telecommunication service kinds and classes, and much more. Also, the deployment choice of lumped inline amplifiers . distributed Raman amplification or hybrid schemes, gain equalizing devices, electrical or optical inline regenerators, and electrical grooming nodes or optically amplified multi degree ROADM nodes is strongly dependent on these multiple factors.

The research shows that some network options with consequences for optical amplifier applications will be described against the background of European national network. Here a variety of requirements force operators to select many different network architectures for different local domains with suitable primary foci to meet optimum transport efficiency and operational performance. The present trend is to consolidate different network domains into a converged platform to simplify the overall network management process.

European networks cover many scenarios of possible architectures, for ultra long-haul (ULH) pan-European backbone to national European backbone, metro, and access networks. The typical distance characteristics of link lengths between major backbone nodes for North America and pan-European networks, but the distance are significantly shorter. The backbone links of national networks of the different European states like Germany reference network. Here the mean fiber link distance between major between major cities and thus backbone nodes is about 400 km which could be still called “metro”. However, as for the next generation architecture it is intended to intensively apply optically transparent transmit nodes （ROADM/PXC）, future national networks will also demand systems with a longer reach. In the following sub-sections we will focus on typical modern intranational European network architectures.

Future converged telecommunication platforms will comprise access, aggregation, and transport networks. Their design rules depend on their primary purpose: either traffic aggregation or distribution from and to customers, or the transport and routing of large amounts of combined capacity.

Network operators have the common basic target to produce cost-efficient telecommunication services. When considering operators from different nations including carriers operating worldwide, a variety of network architecture designs need to be considered. The suitable network design depends on the individual national properties with respect to the telecommunication services to be provided, such as the local population density distributions, the characteristic local residential consumer behavior, for example, the demand for voice telephony, internet protocol, or broadband TV, or the distribution and service level agreement (SLA) requirements of the business customers. The design of the network is governed by the topology. DWDM network for example, ring, star, mesh, by the purpose (access, aggregation, transport), by the mean and maximum link distance, and by the density and degree of switching or grooming nodes. All this has a direct impact on the choice of amplification in the optical multiplex section (OMS) of DWDM systems and on the local placement of DWDM optical amplifiers.

The diameter of networks is one of the most obvious distinctions. Nationwide networks in the United States follow engineering rules different from those applicable to the national backbones in European countries, especially when the design of amplifier maps and the positioning of photonic cross connect (PXC)/ROADM based nodes are considered. The largest diameters within all optical transport is achieved in submarine cable networks that deploy lumped amplifier span designs with very short distance between adjacent DWDM EDFA and eventually supported by additional distributed Raman amplification.

Besides the distance, many other parameters influence decisions for special network layouts, such as the local distribution of population and industry to be connected, the traffic patterns and capacity evolution, the telecommunication service kinds and classes, and much more. Also, the deployment choice of lumped inline amplifiers . distributed Raman amplification or hybrid schemes, gain equalizing devices, electrical or optical inline regenerators, and electrical grooming nodes or optically amplified multi degree ROADM nodes is strongly dependent on these multiple factors.

The research shows that some network options with consequences for optical amplifier applications will be described against the background of European national network. Here a variety of requirements force operators to select many different network architectures for different local domains with suitable primary foci to meet optimum transport efficiency and operational performance. The present trend is to consolidate different network domains into a converged platform to simplify the overall network management process.

European networks cover many scenarios of possible architectures, for ultra long-haul (ULH) pan-European backbone to national European backbone, metro, and access networks. The typical distance characteristics of link lengths between major backbone nodes for North America and pan-European networks, but the distance are significantly shorter. The backbone links of national networks of the different European states like Germany reference network. Here the mean fiber link distance between major between major cities and thus backbone nodes is about 400 km which could be still called “metro”. However, as for the next generation architecture it is intended to intensively apply optically transparent transmit nodes （ROADM/PXC）, future national networks will also demand systems with a longer reach. In the following sub-sections we will focus on typical modern intranational European network architectures.

Future converged telecommunication platforms will comprise access, aggregation, and transport networks. Their design rules depend on their primary purpose: either traffic aggregation or distribution from and to customers, or the transport and routing of large amounts of combined capacity.

Optical amplifier is an important technology for optical communication networks. Without the need to first convert it to an electrical signal, the optical amplifiers are now used instead of repeaters. As we know, there are several types of optical amplifiers. Among them, the main amplifier technologies are Doped fiber amplifier (eg. EDFA), Semiconductor optical amplifier (SOA) and Fiber Raman amplifier. Today, we are going to study and compare different types of optical amplifiers in this paper.

Before the comparison of the different types of optical amplifiers, let’s take a closer look at fiber optic amplifier. In general, a repeater includes a receiver and transmitter combined in one package. The receiver converts the incoming optical energy into electrical energy. The electrical output of the receiver drives the electrical input of the transmitter. The optical output of the transmitter represents an amplified version of the optical input signal plus noise. Repeaters do not work for fiber-optic networks, where many transmitters send signals to many receivers at different bit rates and in different formats. However, unlike a repeater, an optical amplifier amplify optical signal directly without electric and electric optical transformation. In addition, an ideal optical amplifier could support multi-channel operation over as wide as possible a wavelength band, provide flat gain over a large dynamic gain range, have a high saturated output power, low noise, and effective transient suppression. Several benefits of optical amplifiers as the following:

Support any bit rate and signal format

Support the entire region of wavelengths

Increase the capacity of fiber-optic links by using WDM

Provide the capability of all-optical networks, not just point-to-point links

OK, after a brief introduction of the optical amplifiers, we formally begin today’s main topic. As we talk above, there are three main types of today’s amplifier technology. Each of them has their own working principle, features and applications. We will describe them one by one in the following paragraphs.

Doped fiber amplifier (The typical representative: EDFA)

Erbium-doped fiber amplifier (EDFA) is the most widely used fiber-optic amplifiers, mainly made of Erbium-doped fiber (EDF), pump light source, optical couplers, optical isolators, optical filters and other components. Among them, a trace impurity in the form of a trivalent erbium ion is inserted into the optical fiber’s silica core to alter its optical properties and permit signal amplification.

Working Principle

The working principle of the EDFA is to use the pump light sources, which most often has a wavelength around 980 nm and sometimes around 1450 nm, excites the erbium ions (Er3+) into the 4I13/2 state (in the case of 980-nm pumping via 4I11/2), from where they can amplify light in the 1.5-μm wavelength region via stimulated emission back to the ground-state manifold 4I15/2.

Advantages & Disadvantages of EDFA

Advantages

EDFA has high pump power utilization (>50%)

Directly and simultaneously amplify a wide wavelength band (>80nm) in the 1550nm region, with a relatively flat gain

Flatness can be improved by gain-flattening optical filters

Gain in excess of 50 dB

Low noise figure suitable for long haul applications

Disadvantages

Size of EDFA is not small

It can not be integrated with other semiconductor deviecs

Semiconductor optical amplifier (SOA)

Semiconductor optical amplifier is one type of optical amplifier which use a semiconductor to provide the gain medium. They have a similar structure to Fabry–Perot laser diodes but with anti-reflection design elements at the end faces. Unlike other optical amplifiers SOAs are pumped electronically (i.e. directly via an applied current), and a separate pump laser is not required.