Tag Archives: EDFA

Brief Introduction to EDFA

In fiber optic communication systems, problems arise from the fact that no fiber material is perfectly transparent. The visible-light or infrared beams carried by a fiber are attenuated as they travel through the material. This necessitates the use of optical amplifiers. And EDFA (Erbium Doped Fiber Amplifier) is a representative one in the optical amplifier. There is one saying that EDFA is the most popular optical amplifier in optical network communications. Next, we will begin with the definition of EDFA.

The Definition of EDFA

An EDFA, also called optical amplifier or an erbium-doped fiber amplifier or erbium amplifier, is an optical or IR (Infrared Radiation) repeater that amplifies a modulated laser beam directly, without opto-electronic and electro-optical conversion. The device uses a short length of optical fiber doped with the rare-earth element erbium. When the signal-carrying laser beams pass through this fiber, external energy is applied, usually at IR wavelengths. This so-called pumping excites the atoms in the erbium-doped section of optical fiber, increasing the intensity of the laser beams passing through. The beams emerging from the EDFA retain all of their original modulation characteristics, but are brighter than the input beams.

Three Major Applications for Optical AmplifierThree Major Applications for Optical Amplifier

The above picture illustrates the three major applications for optical fiber amplifiers: booster, in-line amplifier, and pre-amplifier. These applications are described in more details below:

Booster Amplifier

Booster amplifiers are placed directly after the optical transmitter. In this application, booster amplifier is adopted to compensate for the losses of optical elements between the laser and optical fibers so that the increased transmitter power can be used to go further in the link.

In-line Amplifier

In-line amplifiers or in-line repeaters are placed along the transmission link to compensate for the losses incurred during propagation of optical signal. They take a small input signal and boost it for re-transmission down the fiber. Here it should also be pointed out that to control the signal performance and the noise added by the EDFA is important, because noise added by amplifier will limit the system length.

Pre-amplifier

Pre-amplifiers are placed just before the receiver to increase the signal level before the photodetection takes place in an ultra-long haul system so as to improve receiver sensitivity. By placing a pre-amplifier, a much larger signal can be presented to the receiver, thus easing the demands of the receiver design.

Top EDFA Products Overview

By now, you should have a basic idea of what an EDFA is and what it is used for, next I will introduce you some truly excellent EDFA products on the market.

Type
Description
22dBm Output Booster DWDM EDFA C-band 24dB Gain, 1U Rack Mount
16dBm Output Mid-stage DWDM EDFA C-band 26dB Gain, Plug-in Card for FMT Multi-Service Transport System
17dBm Output Mid-stage DWDM EDFA C-band 17dB Gain, Plug-in Card for FMT Multi-Service Transport System
Conclusion

Of the various technologies available for optical amplifiers, EDFA technology is the most advanced, and consequently the vast majority of optical amplifiers are designed based on this technology. In addition, the combination of reliable performance and relatively low cost allows EDFA to be widely deployed in modern optical networks.

Factors to Consider Before DWDM Network Design

DWDM network deployment usually requires a lot of preparation. There are many factors to be considered before DWDM network design. Even a professional team would take a long time to calculate the parameters over and over to ensure good network performance, let alone some customers who are not experienced. In many cases, customers just have a rough concept of what they need for a DWDM network. When it comes to specific parameters of products, they get no idea. This post offers the most important factors to be considered before DWDM networking. No matter you want to deploy a DWDM network all by your own team, or you want to customize one by other vendors. You will find this post helpful.

DWDM Network Design

What Kind of DWDM Network You Want to Build?

This question contains many details. Here offer several basic factors:

Simplex or Duplex: it is known that DWDM network multiplex different wavelengths together to transmit different ways of optical signals over optical fiber. These wavelengths can be transmitted over the same optical fiber or a pair of optical fibers. Duplex DWDM uses the same for both transmitting and receiving for a way of duplex optical signal over duplex optical fiber. However, the simplex DWDM network uses two different wavelengths for a way of duplex optical signal over a length of single fiber. Thus, the simplex DWDM network provides lower capacity than duplex DWDM network.

Distance: DWDM network gets the greatest returns on investment. It is usually deployed for long distance transmission. But long distance means large light loss. Distance of DWDM network and devices or points it passes should also be considered.

Data Rate and Space Channel: a DWDM network can transmit optical signals of different data rates at the same time. Currently, DWDM network generally transmits 1G and 10G for each wavelength. 1G DWDM SFP, 10G DWDM SFP+ and 10G DWDM XFP modules are usually used. Space Channel of 50 GHz Grid and 100 GHz Grid is commonly applied.

Is There Any Wavelength Adding and Dropping?

The DWDM network needs DWDM MUX/DEMUX for wavelengths multiplexing and de-multiplexing. It is common that a DWDM network passing many places. And wavelengths are required to be added and dropped at some of these places. In this case, DWDM OADM should be used.

DWDM MUX insertion loss test

How to Calculate Light Loss of DWDM Network?

There is light loss in every DWDM network. Technicians should calculate the light loss to decide what devices to be added in the network to ensure good transmission quality. Light loss occurs at many place, the optical fiber for transmission, the DWDM MUX/DEMUX, the devices connected in the network and even the fiber optic splicers and connection points have light loss.

How to Ensure Good DWDM Network Transmission Quality?

There are a variety of factors that can affect the transmission quality. The light source, light loss, transmission distance, fault risks, etc. However, there are always methods to overcome problems. EDFA can be added in the network to ensure enough optical power. If optical power is too strong, fiber optic attenuator can be used. OEO offers conversion between grey wavelengths and DWDM wavelengths. DCM and OLP are separately used for light dispersion compensation and backup line building. These devices can be used properly for good transmission quality.

DWDM MUX

How to Satisfy the Requirements for Both Now and Future?

A DWDM network might only need to transmit several ways of optical signals. However, it might be required to transmission tens of ways optical signals. During the deployment, technician should considerate about the future application. If there is no limit in budget, it would be better to deploy DWDM MUX with more channel port. If not, you can try FS.COM FMU half-U plug-in DWDM MUX modules. You can buy one module for current use and expand the DWDM MUX with another module in the future easily via expansion port on the MUX. All the wavelengths on the DWDM MUX can be customized according to your application.

DWDM long haul

How to Get the Better Performance With Lowest Cost for DWDM Network?

To get the better performance with lowest cost for DWDM network, you need carefully calculate the wavelength, light loss, devices and so on. In practical application, the DWDM network could be really complex, many devices like EDFA, OEO and DCM might be added in the network. It costs a lot for the deployment and management of these devices. Now FS.COM has made these devices into small plug-in cards and offers 1/2/4U chassis to hold them. A free software is also provided for better management and monitoring. This is FS.COM new series of product for DWDM long haul transmission—FMT multi-service transmission platform, which is a cost-effect and high performance system for DWDM network.

Professional Team for DWDM Network Design and Customization

The above mentioned factors are just the basic information that you should consider before DWDM network design. For more professional service and tech support, you can visit FS.COM where you can find professional DWDM network design and customized one-stop solution team and services.

The Art of DWDM Wavelength-Case Study of DWDM Networking

DWDM network is widely accepted as the best solution to increase network capacity over long distance. Making full use of these DWDM wavelengths for transmission need to consider about both now and future. This makes the design of DWDM network complex. Here shares a true case of DWDM networking, which fulfills the requirement for now, but is also built for future.DWDM networking

DWDM Networking Requirement

Three duplex DWDM links (Link A, Link B and Link C) should be built between three different sites: Site 1, Site 2 and Site 3. The following table listed the distance and light loss of these three links.

Duplex DWDM Links Distance Light Loss
Link A: Site 1 – Site 2 31km 9dB
Link B: Site 2 – Site 3 31km 9dB
Link C: Site 1 – Site 3 59km 17dB

A backup link of Link C should be built as well. This backup link will use as length of dark fiber which passes Site 4. Thus, another two links—Link D and Link E work together as the backup for Link C. Meanwhile, Link D and Link E also work independently for 6 ways optical transmission. The following table lists the distance and the light loss of these links.

Duplex DWDM Links Distance Light Loss
Link D 24km 7dB
Link E 47km 13dB
Backup Link C (Link D+E) 71km (24km+47km) 20dB (7dB+13dB)
DWDM Networking Solution

As not all the links in this DWDM network are transmitting the same information, different wavelengths should be used. For instance, Link A and Link B only transmit 2 ways of optical signal, while Link C is required to transmit 10 ways of optical signal. And some of them are of different data rates. Assignment of the DWDM wavelengths in these links is very important. Considering about the future network expanding needs, Site 1, Site 2 and Site 3 are suggested to deploy 40-Channel DWDM MUX/DEMUXs. The following will offer the detailed solution for each links.2 Channel DWDM network

Link A: 2*10G Over 31km

Link A is from Site 1 to Site 2, which is 31 kilometers long with light loss of 9dB. It only needs to transmit two ways 10G optical signal. In this link, we use DWDM wavelength, C21 and C50 for transmission. DWDM SFP+ modules that support 80km is used. In this link, no other devices are required to booster the optical signals, as the light source from the 80km modules are powerful enough to support this link. The required products on Site 1 and Site 2 are listed in the following table:

Location Product Parameter
Site 1 DWDM MUX/DEMUX 40-Channel
10G 80km DWDM SFP+ C21,C50
Site 2 DWDM MUX/DEMUX 40-Channel
10G 80km DWDM SFP+ C21,C50

2 Channel DWDM network

Link B: 2*10G Over 31km

Link B is from Site 2 to Site 3. Just like Link A, it required to support two ways of 10G transmission over distance of 31km. For Link B, we use the same products as for Link A.

Location Product Parameter
Site 2 DWDM MUX/DEMUX 40-Channel
10G 80km DWDM SFP+ C21,C50
Site 3 DWDM MUX/DEMUX 40-Channel
10G 80km DWDM SFP+ C21,C50
Link C: 2*1G & 8*10G Over 57km

Link C is from Site 1 to Site 3. It is required to transmit 2 ways of 1G optical signal and 8 ways of 10G optical signal at the same time over a distance of 57km with light loss of 17dB. Compared with Link A and Link B, things are much different for Link C, as the distance, network capacity and power consumption are all increased. It means more device should be added.10 Channel DWDM network

Overcome Large Light Loss: To ensure that the optical signals are powerful enough to reach the distance, EDFA are suggested to be deployed. An 13dB output booster EDFA is suggested to be deployed after the DWDM MUX Tx end in both Site 1 and Site 3.

Overcome High Power Consumption: As the more wavelengths are used in Link C, more DWDM fiber optic modules should be used. As the power consumption of DWDM modules are higher than normal optical modules, install large sum of DWDM modules in one switch would increase the risk of fault caused by high power consumption. OEO converter which can support the optical wavelengths transmission between normal SMF & MMF wavelengths to DWDM wavelengths are suggested to be deployed between DWDM MUX/DEMUX and switch. This can reduce the fault risk caused by high power consumption effectively.

The product required for Link C are listed as following:

Location Product Parameter
Site 1 DWDM MUX/DEMUX 40-Channel
2*1G 80km DWDM SFP C23, C48
8*10G 80km DWDM SFP+ C21, C22, C30, C31, C49, C50, C59, C60
2*OEO 8-port
EDFA(OPM) 13dB
Site 3 DWDM MUX/DEMUX 40-Channel
2*1G 80km DWDM SFP C23, C48
8*10G 80km DWDM SFP+ C21, C22, C30, C31, C49, C50, C59, C60
2*OEO 8-port
EDFA(OPM) 13dB
Backup Link C = Link D + Link E

Link D and link E are working together as the backup Link C, so ten different wavelengths should be used as in Link C. Meanwhile, both Link D and Link E are working independently. Both of them are transmitting 6 ways of optical signal. Here we used two OAMDs at Site 4 to multiplex another 6 wavelengths into the existing network. Link D + Link E is 71 kilometers long, which is much longer than Link C. To support this backup link, except the devices used in Link C, 20dB optical booster EDFA is suggested to be added in both Site 1 and Site 3 at the DWDM Mux/DEMUX RX port.backup DWDM link

As Link D is only 24km and link E is 47km, for their independent working, DWDM SFP+ modules support 40km is suggested. The following listed the products for Link D + Link E in Site 1, Site3 and Site 4.

Location Product Parameter Function
Site 1 DWDM MUX/DEMUX 40-Channel Backup of Link C
2*1G 80km DWDM SFP C23, C48
8*10G 80km DWDM SFP+ C21, C22, C30, C31, C49, C50, C59, C60
2*OEO 8-port
EDFA(OPM) 13dB
EDFA(OBA) 20dB
6*10G 40km DWDM SFP+ C53, C54, C55, C56, C57, C58 Link D Works independently
Site 4 6*10G 40km DWDM SFP+ C53, C54, C55, C56, C57, C58
OADM 6-Channel: C53, C54, C55, C56, C57, C58
OADM 6-Channel: C53, C54, C55, C56, C57, C58 Link E Works independently
6*10G 80km DWDM SFP+ C53, C54, C55, C56, C57, C58
Site 3 6*10G 80km DWDM SFP+ C53, C54, C55, C56, C57, C58
DWDM MUX/DEMUX 40-Channel Backup of Link C
2*1G 80km DWDM SFP C23, C48
8*10G 80km DWDM SFP+ C21, C22, C30, C31, C49, C50, C59, C60
2*OEO 8-port
EDFA(OPM) 13dB
EDFA(OBA) 20dB
Products in this DWDM Networking Case

The products mentioned in the above case are all provided by FS.COM. Here offer the details for your reference. In FS.COM, you can offer your requirement for networking to the tech support team and get the suitable and reliable performance solutions for your projects.

DWDM MUX/DEMUX 40-CH DWDM MUX/DEMUX
DWDM OADM 6-CH DWDM OADM
DWDM SFP 80km DWDM SFP
DWDM SFP+ 80km DWDM SFP+
40km DWDM SFP+
EDFA 13dB EDFA (OPM)
20dB EDFA (OBA)
OEO 8-Port 3R OEO Converter

Guide to Fiber Optic Attenuator

Many components are used to enlarge the signals in today’s fiber optic transmission system, like EDFA (Erbium-Doped Fiber Amplifier). However, in some cases, the power level of an optical signal should be reduced. For example, in DWDM (dense wavelength division multiplexing) systems, multiple wavelength channels arriving at a node may pass though different paths and experience different losses, their powers need to be equalized before entering the optical amplifier to get flat gain since the gain of each channel depends on the power levels of the other channels. In this case, a point reduction in optical signal strength may be required. And a component is usually used which is known as fiber optic attenuator. This article is to give a basic introduction of fiber optic attenuator in details.

Introduction

A fiber optic attenuator, also known as an optical attenuator, is a passive component that is used to reduce the power level of an optical signal by a predetermined factor in fiber optic transmission system. The intensity of the signal is described in decibels (dB) over a specific distance the signal travels. Fiber optic attenuators are generally used in single-mode long-haul application.

Working Principles of Fiber Optic Attenuators

As technologies advanced, many principles are used in the operation of fiber optic attenuator to accomplish the desired power reduction. Several operation principles of fiber optic attenuators are being introduced here.

Gap-loss Principle: in attenuator using gap-loss principle, the reduction of the optical power level is accomplished by two fibers that are separated by air to yield the correct loss. The optical signal is attenuated when it passes a longitudinal gap between two optical fibers. This kind of attenuator is also called air gap attenuators which are susceptible to dust contamination and can be sensitive to moisture and temperature variations. In addition, this attenuator is very sensitive to modal distribution ahead of transmitter. Thus, it is recommended to be used very close to the optical transmitter. The farther the air gap attenuator is placed away from the transmitter, the less effective the attenuator is, and the desired loss will not be obtained. To attenuate a signal far down the fiber path, and optical attenuator using absorptive or reflective techniques should be used. Gap-loss principle is showed as following picture.

gap-loss principle

Absorptive Principle: as the fiber optic has the imperfection to absorb optical energy and convert it to heat. This absorptive principle is used in the design of fiber optic attenuator, using the material in optical path to absorb optical energy. This principle is very simple, however, it can be an effective way to reduce the optical signal power. The following picture shows the absorptive principle.

Absorptive Principle

Reflective Principle: another imperfection of fiber optic is also being used to reduce the signal power, which is reflection. The major power loss in optical fiber is caused by the reflection or scattering. The scattered light causes interference in the fiber, thereby reducing the signal power. Using reflective principle (shown in the picture below), fiber optic attenuator could be manufactured to reflect a known quantity of the signal, thus allowing only the desired portion of the signal to be propagated.

reflective principle

Various principles are being applied to reduce the power single. Also various types of attenuators are being manufactured to meet different applications. The following part is about the main types of the fiber optic attenuators.

Types of Fiber Optic Attenuators

Fixed and variable attenuators are the main types that are being provided in today’s market. Their characteristics are being introduced.

Fixed Attenuator, as the name implies, has a fixed attenuation level. Fixed attenuator can theoretically be designed to provide any amount of attenuation that is desired and be set to deliver a precise power output. Fixed attenuators are typically used for single-mode applications. They mate to regular connectors of the identical type for example FC, ST, SC and LC.

Variable attenuators allow a range of adjustability, delivering a precise power output at multiple decibel loss levels. Variable attenuators can be divided into two types. One is stepwise variable attenuator which can change the attenuation of the single in known steps such as 0.1dB, 0.5dB, or 1 dB. The other one is continuously variable attenuator. This kind of fiber optic attenuator produces precise level of attenuation, with flexible adjustments. It allows the operators to adjust the attenuator to accommodate the changes required quickly and precisely without any interruption to the circuit. They are also available with various fiber optic connectors.

Fiber optic attenuator, an important device to control the power level of optical signal precisely, are being designed to different operation principles and types. Getting the basic knowledge about its working principle and types could help to select the fiber optic attenuator to the required applications.

Comparison Of Different Optical Amplifiers

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 them in this paper.

Before the comparison of the different optical amplifiers, let’s take a closer look at fiber optic amplifer. 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.

the components of EDFA

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.

EDFA

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.

design of SOA

Working Principle
1.Stimulated emission to amplify an optical signal.
2.Active region of the semiconductor.
3.Injection current to pump electrons at the conduction band.
4.The input signal stimulates the transition of electrons down to the valence band to acquire an amplification.

SOA

Advantages & Disadvantages of SOA
Advantages

  • The semiconductor optical amplifier is of small size and electrically pumped.
  • It can be potentially less expensive than the EDFA and can be integrated with semiconductor lasers, modulators, etc.
  • All four types of nonlinear operations (cross gain modulation, cross phase modulation, wavelength conversion and four wave mixing) can beconducted.
  • SOA can be run with a low power laser. This originates from the short nanosecond or less upper state lifetime, so that the gain reacts rapidly tochanges of pump or signal power and the changes of gain also cause phase changes which can distort the signals.

Disadvantages
The performance of SOA is still not comparable with the EDFA. The SOA has higher noise, lower gain, moderate polarization dependence and high nonlinearity with fast transient time.

Fiber Raman amplifier (FRA)
Fiber Raman Amplifier (FRA) is also a relatively mature optical amplifier. In a FRA, the optical signal is amplified due to stimulated Raman scattering (SRS). In general, FRA can is divided into lumped type called LRA and distributed type called DRA. The fiber gain media of the former is generally within 10 km. In addition, it requires on higher pump power, generally in a few to a dozen watts that can produce 40 dB or even over gains. It is mainly used to amplify the optical signal band of which EDFA cannot satisfy. The fiber gain media of DRA is usually longer than LRA, generally for dozens of kilometers while pump source power is down to hundreds of megawatts. It is mainly used in DWDM communication system, auxiliarying EDFA to improve the performance of the system, inhibiting nonlinear effect, reducing the incidence of signal power, improving the signal to noise ratio and amplifing online.

Working Principle
The principle of FRA is based on the Stimulated Raman Scattering (SRS) effect. The gain medium is undoped optical fiber. Power is transferred to the optical signal by a nonlinear optical process known as the Raman effect. An incident photon excites an electron to the virtual state and the stimulated emission occurs when the electron de-excites down to the vibrational state of glass molecule. The Stokes shift corresponding to the eigen-energy of a phonon is approximately 13.2 THz for all optical fibers.

FRA

Advantages & Disadvantages of FRA
Advantages

  • Variable wavelength amplification possible
  • Compatible with installed SM fiber
  • Can be used to extend EDFAs
  • Can result in a lower average power over a span, good for lower crosstalk
  • Very broadband operation may be possible

Disadvantages

  • High pump power requirements, high pump power lasers have only recently arrived
  • Sophisticated gain control needed
  • Noise is also an issue

Summary
After talking about these three types of optical amplifiers, we make a comparison of them as the following table.

Optical amplifier Comparison