Category Archives: Optical Solutions

The Latest Generation of PON – NG-PON2

To meet the large demand for high capacity transmission in optical access systems, 10G-PON (10G Passive Optical Network) has already been standardized by IEEE (Institute of Electrical and Electronics Engineers) and ITU (International Telecommunication Union). To enable the development of future optical access systems, the most recent version of PON known as NG-PON2 (Next-Generation Passive Optical Network 2) was approved recently, which provides a total throughput of 40 Gbps downstream and 10 Gbps upstream over a single fiber distributed to connected premises. The migration from GPON to 10G-PON and NG-PON2 is the maturity of technology and the need for higher bandwidth. This article will introduce the NG-PON2 technology to you.

GPON 10G-PON NG-PON2

What Is NG-PON2?
NG-PON2 is a 2015 telecommunications network standard for PON which was developed by ITU. NG-PON2 offers a fiber capacity of 40 Gbps by exploiting multiple wavelengths at dense wavelength division multiplexing (DWDM) channel spacing and tunable transceiver technology in the subscriber terminals (ONUs). Wavelength allocations include 1524 nm to 1544 nm in the upstream direction and 1596 nm to 1602 nm in the downstream direction. NG-PON2 was designed to coexist with previous architectures to ease deployment into existing optical distribution networks. Wavelengths were specifically chosen to avoid interference with GPON, 10G-PON, RF Video, and OTDR measurements, and thus NG-PON2 provides spectral flexibility to occupy reserved wavelengths in deployments devoid of legacy architectures.

How Does NG-PON2 Work?
If 24 premises are connected to a PON and the available throughput is equally shared then for GPON each connection receives 100 Mbps downstream and 40 Mbps upstream over a maximum of 20 km of fiber. For 10G-PON, which was the second PON revision, each of the 24 connections would receive about 400 Mbps downstream and 100 Mbps upstream. The recently approved NG-PON2 will provide a total throughput of 40 Gbps downstream and 10 Gbps upstream over a maximum of 40 km of fiber so each of the 24 connections would receive about 1.6 Gbps downstream and 410 Mbps upstream. NG-PON2 provides a greater range of connection speed options including 10/2.5 Gbps, 10/10 Gbps and 2.5/2.5 Gbps. NG-PON2 also includes backwards compatibility with GPON and 10G-PON to ensure that customers can upgrade when they’re ready.

NG-PON2 Work Principle

NG-PON2 Advantages
The NG-PON2 technology is expected to be about 60 to 80 percent cheaper to operate than a copper based access network and provides a clear undeniable performance, capacity and price advantage over any of the copper based access networks such as Fiber to the Node (FTTN) or Hybrid Fiber Coax (HFC). At present, three clear benefits of NG-PON2 have been proved. They are a 30 to 40 percent reduction in equipment and operating costs, improved connection speeds and symmetrical upstream and downstream capacity.

Reduced Costs
NG-PON2 can coexist with existing GPON and 10G-PON systems and is able to use existing PON-capable outside plant. Since the cost of PON FTTH (Fiber to the Home) roll out is 70 percent accounted for by the optical distribution network (ODN), this is significant. Operators have a clear upgrade path from where they are now, until well into the future.

Improved Connection Speeds
Initially NG-PON2 will provide a minimum of 40 Gbps downstream capacity, produced by four 10 Gbps signals on different wavelengths in the O-band multiplexed together in the central office with a 10 Gbps total upstream capacity. This capability can be doubled to provide 80 Gbps downstream and 20 Gbps upstream in the “extended” NG-PON2.

Symmetrical Upstream and Downstream Capacity
Both the basic and extended implementations are designed to appeal to domestic consumers where gigabit downstream speeds may be needed but more modest upstream needs prevail. For business users with data mirroring and similar requirements, a symmetric implementation will be provided giving 40/40 and 80/80 Gbps capacity respectively.

With the introduction of NG-PON2, there is now an obvious difference between optical access network and copper access network capabilities. Investment in NG-PON2 provides a far cheaper network to operate, significantly faster downstream and upstream speeds and a future-proof upgrade path all of which copper access networks do not provide, thus making them obsolete technologies. Telephone companies around the world have been carrying out trials of NG-PON2 and key telecommunication vendors have rushed NG-PON2 products to market.

Source: http://www.fs.com/blog/the-latest-generation-of-pon-ng-pon2.html

From O to L: the Evolution of Optical Wavelength Bands

In optical fiber communications system, several transmission bands have been defined and standardized, from the original O-band to the U/XL-band. The E- and U/XL-bands have typically been avoided because they have high transmission loss regions. The E-band represents the water peak region, while the U/XL-band resides at the very end of the transmission window for silica glass.

Optical Wavelength Bands

Intercity and metro ring fiber already carry signals on multiple wavelengths to increase bandwidth. Fibers entering the home will soon do the same. Now there are several types of optical telecom systems have been developed, some based on time division multiplexing (TDM) and others on wavelength division multiplexing (WDM), either dense wavelength division multiplexing (DWDM) or coarse wavelength division multiplexing (CWDM). This article may represent the evolution of optical wavelength bands mainly by describing these three high-performance systems.

Dense Wavelength Division Multiplexing
DWDM systems were developed to deal with the rising bandwidth needs of backbone optical networks. The narrow spacing (usually 0.2 nm) between wavelength bands increases the number of wavelengths and enables data rates of several Terabits per second (Tbps) in a single fiber.

These systems were first developed for laser-light wavelengths in the C-band, and later in the L-band, leveraging the wavelengths with the lowest attenuation rates in glass fiber as well as the possibility of optical amplification. Erbium-doped fiber amplifiers (EDFAs, which work at these wavelengths) are a key enabling technology for these systems. Because WDM systems use many wavelengths at the same time, which may lead to much attenuation. Therefore optical amplification technology is introduced. Raman amplification and erbium-doped fiber amplifiers are two common types used in WDM system.

DWDM

In order to meet the demand for “unlimited bandwidth,” it was believed that DWDM would have to be extended to more bands. In the future, however, the L-band will also prove to be useful. Because EDFAs are less efficient in the L-band, the use of Raman amplification technology will be re-addressed, with related pumping wavelengths close to 1485 nm.

Coarse Wave Division Multiplexing
CWDM is the low-cost version of WDM. Generally these systems are not amplified and therefore have limited range. They typically use less expensive light sources that are not temperaturestabilized. Larger gaps between wavelengths are necessary, usually 20 nm. Of course, this reduces the number of wavelengths that can be used and thus also reduces the total available bandwidth.

CWDM

Current systems use the S-, C- and L-bands because these bands inhabit the natural region for low optical losses in glass fiber. Although extension into the O and E-band (1310 nm to 1450 nm) is possible, system reach (the distance the light can travel in fiber and still provide good signal without amplification) will suffer as a result of losses incurred by use of the 1310 nm region in modern fibers.

Time Division Multiplexing
TDM systems use either one wavelength band or two (with one wavelength band allocated to each direction). TDM solutions are currently in the spotlight with the deployment of fiber-to-the-home (FTTH) technologies. Both EPON and GPON are TDM systems. The standard bandwidth allocation for GPON requires between 1260 and 1360 nm upstream, 1440 to 1500 nm downstream, and 1550 to 1560 nm for cable-TV video.

To meet the rise in bandwidth demand, these systems will require upgrading. Some predict that TDM and CWDM (or even DWDM) will have to coexist in the same installed network fibers. To achieve this, work is underway within the standardization bodies to define filters that block non-GPON wavelengths to currently installed customers. This will require the CWDM portion to use wavelength bands far away from those reserved for GPON. Consequently, they will have to use the L-band or the C- and L-bands and provided video is not used.

tdm

Conclusion
In each case, sufficient performance has been demonstrated to ensure high performance for today’s and tomorrow’s systems. From this article, we know that the original O-band hasn’t satisfied the rapid development of high bandwidth anymore. And the evolution of optical wavelength bands just means more and more bands will be called for. In the future, with the growth of FTTH applications, there is no doubt that C- and L-bands will play more and more important roles in optical transmission system. Fiberstore offer all kinds of products for WDM optical network, such as CWDM/DWDM MUX DEMUX and EDFA. For more information, please visit www.fs.com.

Erbium Doped Fiber Amplifier (EDFA) Used in WDM System

The capacity of fiber optical communication systems has undergone enormous growth during the last few years in response to huge capacity demand for data transmission. With the available wavelength division multiplexing (WDM) equipment, commercial system can transport more than 100 channels over a single fiber. However, increasing the number of channels in such systems will eventually result in the usage of optical signal demultiplexing components with greater values of optical attenuation. Besides, when transmitted over long distances, the optical signal is highly attenuated. Therefore, to restore the optical power budget, it is necessary to implement optical signal amplification. This article may mainly tell you why EDFA is used in WDM system and how does it work.

Why Use EDFA in WDM System?

EDFA stands for erbium-doped fiber amplifiers, which is an optical amplifier that uses a doped optical fiber as a gain medium to amplify an optical signal. EDFA has large gain bandwidth, which is typically tens of nanometers and thus actually it is enough to amplify data channels with the highest data rates. A single EDFA may be used for simultaneously amplifying many data channels at different wavelengths within the gain region. Before such fiber amplifiers were available, there was no practical method for amplifying all channels between long fiber spans of a fiber-optic link. There are practically two wavelength widows C-Band (1530nm-1560nm) and L-Band (1560nm-1600nm). EDFA can amplify a wide wavelength range (1500nm-1600nm) simultaneously, which just satisfies the DWDM application, hence it is very useful in WDM for amplification.

How Does EDFA Work ?

The basic configuration for incorporating the EDFA in an optical fiber link is shown in the picture below. The signals and pump are combined through a WDM coupler and launched into an erbium-doped fiber (EDF). The amplified output signals can be transmitted through 60-100km before further amplification is required.

Erbium-doped fiber is the core technology of EDFA, which is a conventional silica fiber doped with erbium ions as the gain medium. Erbium ions (Er3+) are having the optical fluorescent properties that are suitable for the optical amplification. When an optical signal such as 1550nm wavelength signal enters the EDFA from input, the signal is combined with a 980nm or 1480nm pump laser through a wavelength division multiplexer device. The input signal and pump laser signal pass through erbium-doped fiber. Here the 1550nm signal is amplified through interaction with doped erbium ions. This can be well understood by the energy level diagram of Er3+ ions given in the following figure.

Where to Buy EDFA for Your WDM System ?

To ensure the required level of amplification over the frequency band used for transmission, it is highly important to choose the optimal configuration of the EDFAs. Before you buy a EDFA, keep in mind that the flatness and the level of the obtained amplification, and the amount of EDFA produced noise are highly dependent on each of the many parameters of the amplifier. Fiberstore provide many kinds of EDFAs, especially the DWDM EDFAs (shown in the picture below), which have many output options (12dBm-35dBm). Besides, they are very professional in optical amplifiers. Whatever doubts you have, they can give a clear reply.

EDFA

Introduction of Media Converter

There is no doubt that Ethernet fiber-optic communications provide many advantages over copper based Ethernet communications. These include immunity to noise and further distance capabilities. Systems that require fiber-optic communication can use switches that contain built-in fiber optic ports. However, if your switch does not have built-in fiber optic ports or does not have enough fiber-optic ports, then a media converter will be needed to convert copper based communications to fiber-optic communications. This article will review the different types of media converters and provide information on the wide variety of applications for media converters.

What is a Media Converter?

Media converters are flexible and cost-effective devices for implementing and optimizing fiber links in all types of networks. Media converters enable you to connect different types of media, such as twisted pair, fiber, and coax, within a network. The most widely used converters are probably the ones used to convert computers UTP Ethernet ports to fiber. This enables you the ability extend your Ethernet network beyond the 100-meter limit imposed by copper cable. Besides, some other converters also convert multi-mode to single-mode, convert analog signals to digital, multiplex several signals over one fiber pair, or perform other signal processing. In a word, as a device to converter one media to another, media converters are really working.

Types of Media Converter

There are a wide variety of media converters available that support different network protocols, data rates, cabling and connector types. Two main kinds of media converters are copper-to-fiber media converter and fiber-to-fiber media converter.

Copper-to-Fiber Media Converters

The most common type of media converter is a device that functions as a transceiver, which is used to convert the electrical signal used in copper UTP network cabling into light waves used in fiber optic cabling. Fiber optic connectivity is necessary when the distance between two network devices exceeds the transmission distance of copper cabling. Copper-to-fiber conversion using media converters enables two network devices with copper ports to be connected over extended distances via fiber optic cabling.

Ethernet Copper-to-Fiber Media Converters
Supporting the IEEE 802.3 standard, Ethernet copper-to-fiber media converters are used to provide connectivity for Ethernet, Fast Ethernet, Gigabit and 10 Gigabit Ethernet devices. Hence these converters are also usually divided into Fast Ethernet media converter, Gigabit media converter and 10 Gigabit media converter. The diagram below shows a typical application where Ethernet Media Converters connect to Ethernet Switches by way of Multimode fiber and UTP copper cabling.

TDM Copper-to-Fiber Media Converters
The most common TDM copper-to-fiber converters are T1/E1 and T3/E3 converters, which provide a reliable and cost-effective method to extend traditional TDM (Time Division Multiplexing) telecom protocols copper connections using fiber optic cabling. T3/E3 and T1/E1 converters usually operate in pairs extending distances of TDM circuits over fiber, improving noise immunity, quality of service, intrusion protection and network security.
Serial-to-Fiber Media Converters
Serial-to-fiber converters provide fiber extension for serial protocol copper connections. They can automatically detect the signal baud rate of the connected Full-Duplex serial device, and support point-to-point and multi-point configurations.

Fiber-to-Fiber Media Converters

Fiber-to-fiber media converters can provide connectivity between multi-mode (MM) and single-mode (SM) fiber, between different power fiber sources and between dual fiber and single-fiber. In addition, they support conversion from one wavelength to another. Fiber-to-fiber media converters are normally protocol independent and available for Ethernet, and TDM applications.

Multi-mode to Single-mode Converters
Enterprise networks often require conversion from MM to SM fiber, which supports longer distances than MM fiber. Mode conversion is typically required when lower cost legacy equipment uses MM ports but connectivity is required to SM equipment, a building has MM equipment, while the connection to the service provider is SM, and MM equipment is in a campus building but SM fiber is used between buildings.

Dual Fiber to Single-Fiber Converters
Enterprise networks may also require conversion between dual and single-fiber, depending on the type of equipment and the fiber installed in the facility. Single-fiber is single-mode and operates with bi-directional wavelengths, often referred to as BIDI. Typically BIDI single-fiber uses 1310nm and 1550nm wavelengths over the same fiber strand in opposite directions. The development of bi-directional wavelengths over the same fiber strand was the precursor to Wavelength Division Multiplexing.

Applications of Media Converter

Media converters do more than convert copper-to-fiber and convert between different fiber types. Media converters for Ethernet networks can support integrated switch technology, and provide the ability to perform 10/100 and 10/100/1000 rate switching. Additionally, media converters can support advanced bridge features which including VLAN, Quality of Service (QoS) prioritization, Port Access Control and Bandwidth Control and really facilitate the deployment of new data, voice and video to end users. Media converters can provide all these sophisticated switch capabilities in a small, cost-effective device.

Capacity Expansion and Flexibility—DWDM Network

DWDM increases the bandwidth of an optical fiber by multiplexing several wavelengths onto it. Even though it costs more than CWDM, it is currently the most popular WDM technology because it offers the most capacity. This article provides an overview of DWDM networks and its current applications.

Introduction of DWDM Technology
Dense wavelength-division multiplexing (DWDM) revolutionized data transmission technology by increasing the capacity signal of embedded fiber. This increase means that the incoming optical signals are assigned to specific wavelengths within a designated frequency band, then multiplexed onto one fiber. By providing channel spacings of 50 GHz (0.4 nm), 100 GHz (0.8 nm) or 200 GHz (1.6 nm), several hundreds of wavelengths can be placed on a single fiber. DWDM takes advantage of the operating window of the Erbium Doped Fibre Amplifier (EDFA) to amplify the optical channels and extend the operating range of the system to over 1500 kilometers. The following picture shows the operation of a DWDM system.

Components of DWDM System
Important components for DWDM systems are transmitters, receivers, optical amplifiers, transponders, DWDM multiplexers, and DWDM demultiplexer. These components, along with conforming to ITU channel standards, allow a DWDM system to interface with other equipment and to implement optical solutions throughout the network.

Optical transmitters/receivers

Transmitters are described as DWDM components since they provide the source signals which are then multiplexed. The characteristics of optical transmitters used in DWDM systems are highly important to system design. Multiple optical transmitters are used as the light sources in a DWDM system. Here we can ues a transceiver to replace transmitters and receivers, since it is the combiantion of them. Transceivers applied in DWDM network are often called the DWDM transceiver, of which the transmission distances can reach up to 120 km. The following picture shows the receivers and transmitters in DWDM systems.

Optical amplifiers

Optical amplifiers (OAs) boost the amplitude or add gain to optical signals passing on a fiber by directly stimulating the photons of the signal with extra energy. They are “in-fiber” devices. OAs amplify optical signals across a broad range of wavelengths. This is very important for DWDM system application. Erbium-doped fiber amplifiers (EDFAs) are the most commonly used type of in-fiber optical fibre. Following picture shows the operation of OA.

Transponders

Transponders convert optical signals from one incoming wavelength to another outgoing wavelength suitable for DWDM applications. Transponders are optical-electricaloptical (O-E-O) wavelength converters. A transponder performs an O-E-O operation to convert wavelengths of light. Within the DWDM system a transponder converts the client optical signal back to an electrical signal (O-E) and then performs either 2R (reamplify, reshape) or 3R (reamplify, reshape, and retime) functions. The following picture shows the operation of bidirectional transponder.

A transponder is located between a client device and a DWDM system. From left to right, the transponder receives an optical bit stream operating at one particular wavelength (1310 nm). The transponder converts the operating wavelength of the incoming bitstream to an ITU-compliant wavelength. It transmits its output into a DWDM system. On the receive side (right to left), the process is reversed. The transponder receives an ITU-compliant bit stream and converts the signals back to the wavelength used by the client device.

DWDM Multiplexers and Demultiplexers

Multiple wavelengths (all within the 1550 nm band) created by multiple transmitters and operating on different fibers are combined onto one fiber by way of an optical multiplexer. The output signal of an optical multiplexer is referred to as a composite signal. At the receiving end, a demultiplexer separates all of the individual wavelengths of the composite signal out to individual fibers. The individual fibers pass the demultiplexed wavelengths to as many optical receivers. Typically, mux and demux (transmit and receive) components are contained in a single enclosure. Optical mux/demux devices can be passive. Component signals are multiplexed and demultiplexed optically, not electronically, therefore no external power source is required. Following picture shows the operation of DWDM multiplexers and demultiplexers.

Applications for DWDM
As occurs with many new technologies, the potential ways in which DWDM can be used are only beginning to be explored. Already, however, the technology has proven to be particularly well suited for several vital applications.

DWDM is ready made for long-distance telecommunications operators that use either point–to–point or ring topologies. The sudden availability of 16 new transmission channels where there used to be one dramatically improves an operator’s ability to expand capacity and simultaneously set aside backup bandwidth without installing new fiber.
This large amount of capacity is critical to the development of self-healing rings, which characterize today’s most sophisticated telecom networks. By deploying DWDM terminals, an operator can construct a 100% protected, 40 Gb/s ring, with 16 separate communication signals using only two fibers.
Operators that are building or expanding their networks will also find DWDM to be an economical way to incrementally increase capacity, rapidly provision new equipment for needed expansion, and future–proof their infrastructure against unforeseen bandwidth demands.

Ultra-High-Power Optical Amplifier for FTTH – EYDFA

Background

While the Cable Modem, xDSL, and other forms of broadband access are booming in recent years, Fiber To The Home (FTTH) access is also gradually becoming a project that people are very interested in. The FTTH will eventually realize the “three networks in one” of Telephone, CATV and Internet, when the speed of data transmission can be more than 100 Mbps (200 times faster than the commonly used dial-up Internet access) and bring homes high-definition TV movies and fast online office, etc. FTTH can also solve the problem such as the quality of phone calls, the definition of television and so on.

From the perspective of the world’s situation, the FTTH’s promotion of South Korea and Japan has entered a rapid growth period; North America and Europe has begun to start which brings an optimistic outlook; China, Russia, India and South America is following and speeding up the development. From the perspective of FTTH, the optical communications industry market’s growth potential is still very large.

Applications of High-Power Optical Amplifiers

High-power optical amplifier as one of the basic devices of modern optical communications, is not only the premise of the existence of large-capacity and long-distance all-optical communication networks, but also plays a more and more important role in the process of fiber optic networks’ constantly extending and expanding. At present, in the central office, it usually needs to install more than one optical amplifiers in order to cover larger scope and more users. To take CATV for example, if a medium-sized county needs to send high-quality first-level TV signals to the villages and towns, it generally needs 4 to 8 sets of optical amplifiers. However, if high-power optical amplifiers are used, then only one is enough, which can greatly reduce the cost.

Solutions of High-Power Optical Amplifiers

Traditional Solution using EDFA Technology

One of the solutions for high-power optical amplifiers is to use the traditional general EDFA technology. As shown in the figure below, the signal is amplified at the first stage and then divided into several parts into several EDFAs at the second stage to realize the further ascension of power. The power enlarged in the end can be allocated.

Traditional High-Power Solution using EDFAs

Theare are mainly four problems of this solution:

The adoption of multilevel structure will make the optical structure very complex, and due to the adoption of multiple lasers in the internal part, the corresponding control scheme is very complicated.
As the multilevel structure has a WDM between the two stages of optical amplifiers, equivalent to bring more insertion loss to the optical path, the noise figure of EDFA amplifiers will deteriorate.
In addition, the traditional EDFAs use single mode fiber core pump technology, but high-power single-mode pumped lasers have been greatly restricted on technical and cost.
The whole sets of EDFA’s cost is very high and is very expensive.

Better Solution using EYDFA Technology

This ultra-high-power amplifier technology is a multimode cladding pump technology—EYDFA technology, a recently developed new technology that uses the Yb³⁺ and Er³⁺ ions doped double-clad fiber. The technology results to the combination of a series of new technologies, new processes and new materials. It is the core technology of ultra-high-power amplifiers and represents the development direction of optical amplifier technologies. While traditional EDFA use single-mode fiber core pump technology to achieve higher output power (which has been greatly limited on the technical and cost), the Er/Yb-Doped Fiber Amplifier (EYDFA) multimode cladding pump technology is the best choice for large output power optical amplifiers. Here is a typical optical structure of EYDFA.

EYDFA Structure

The main advantages of EYDFA are as following:

Compared with the single mode fiber core pump technology, multimode cladding pump technology has obvious advantages. The multimode cladding pump technology is to input the pump light to the multimode double-cladding fiber whose cross section are hundreds to thousands of times the single-mode fiber. As a result, at the same input optical density, multimode cladding pump can allow hundreds to thousands of times the single-mode pumped input, easily realizing the optical amplifiers’ high output power or ultra-high output power.
Can be realized using a simple optical structure, so the application form is very simple (as shown in the figure below).
The overall cost of the pumps can be greatly reduced.

Fiberstore’s high-power optical amplifier module type products—FTTH-EYDFA series are featured with high output power (17–26 dBm), low noise figure (less than 6 dB @ 1550 nm, 5 dBm input power), wide range of working wavelength (1540–1565 nm), flexible control, high reliability, etc. The output power of high-power optical amplifier is nearing 32 dBm in the laboratory.

Conclusion

Predictably, the widely applications of the ultra-high-power optical amplifiers (EYDFA) will have a profound impact on the development of optical communication, and its market prospect and effectiveness to economic and social present a good trend.

Wavelength Selective Couplers and Splitters

Wavelength Selective Couplers (or Splitters) are used to either combine or split light of different wavelengths with minimal loss. Light of two different wavelengths on different input fibers can be merged (combined) onto the same output fiber. In the reverse direction light of two different wavelengths on the same fiber can be split so that one wavelength goes to one output fiber and the other wavelength is output onto the other output fiber. The process can be performed with very little loss.

As the coupling length is wavelength dependent, the shifting of power between the two parallel waveguides will take place at different places along the coupler for different wavelengths. All we need to do is choose the coupling length carefully and we can arrange for loss free wavelength combining or splitting. These functions are shown in the figure below. The graph of power transfer shows how power input on one of the fibers shifts back and forth between the two waveguides. The period of the shift is different for the two different wavelengths. Thus in the left-hand section of the diagram (combining wavelengths) there will be a place down the coupler where all of the light is in only one waveguide. If we make the coupler exactly this length then the signals have been combined. On the right-hand side of the diagram the reverse process is shown where two different wavelengths arrive on the same input fiber. At a particular point down the coupler the wavelengths will be in different waveguides so if we make this the coupling length then we have separated the wavelengths exactly. In fact both the processes described above are performed in the same coupler—the process is Bi-Directional (BiDi). Thus the coupler on the left can operate in the opposite direction and become a splitter and the splitter on the right can operate in the opposite direction and become a coupler (combiner). Note that each coupler or splitter must be designed for the particular wavelengths to be used.

Wavelength Selective Coupling and Splitting

Commercial devices of this kind are commonly available and are very efficient. The quoted insertion loss is usually between 1.2 and 1.5 dB and the channel separation is quoted as better than 40 dB. “Wavelength flattened” couplers or splitters of this kind operate over quite a wide band of wavelengths. That is a given device may allow input over a range of wavelengths in the 1310 nm band up to 50 nm wide and a range of wavelengths in the 1550 nm band also up to 50 nm wide.

Power Input to an EDFA

On the left-hand side of the figure we see an example of coupling two different wavelengths into the same output fiber. At the input of an EDFA you want to mix the (low level) incoming signal light with (high level) light from the pump. Typically the signal light will be around 1550 nm and the pump will be 980 nm. In this case it is possible to choose a coupling length such that 100% of the signal light and 100% of the pump light leaves on the same fiber. A major advantage of this is that there is very little loss of signal power in this process.

Splitting Wavelengths for CWDM Systems

On the right-hand side of the figure we show an example of CWDM demultiplexing. A mixed wavelength stream with one signal in each of the 1300 and 1550 nm bands is separated into its two component wavelengths. A CWDM system like this might be used in a system for distributing CATV and advanced VOD services to people in their homes. One signal stream might be carried at 1310 nm and the other at 1550 nm. A resonant coupler is shown here operating as a splitter separating the two wavelengths. Note that an identical splitter could also be used to combine the two wavelengths with very little loss.

Adding the Management Channel in DWDM Systems

In DWDM systems where many channels are carried in the 1550 nm band there is often a requirement to carry an additional relatively slow rate channel for management purposes. A convenient way to do this is to send the management information in the 1310 nm band and the mixed DWDM stream in the 1550 band. Wavelength selective couplers are commonly used for this purpose. A management signal (a single wavelength) in the 1310 band is coupled onto a fiber carrying many wavelengths between 1540 nm and 1560 nm. Another similar device (wavelength selective splitter) is used to separate the signals at the other end of the link.

Article Source: http://www.fiberopticshare.com/wavelength-selective-couplers-and-splitters.html

Advanced Optical Components – Optical Isolator

Connectors and other types of optical devices on the output of the transmitter may cause reflection, absorption, or scattering of the optical signal. These effects on the light beam may cause light energy to be reflected back at the source and interfere with source operation. To reduce the effects of the interference, an Optical Isolator is used. Many laser-based transmitters and Optical Amplifiers use an optical isolator because the components that make up the optical circuit are not perfect.

The optical isolator comprises elements that will permit only forward transmission of the light; it does not allow for any return beams in the fiber transmission routes or in the optical amplifiers. There are a variety of optical isolator types, such as Polarized (dependent and independent), Composite, and Magnetic.

Polarized Optical Isolator

As mentioned, the Polarized Optical Isolator transmits light in one direction only. This is accomplished by using the polarization axis of the linearly polarized light. The incident light is transformed to linearly polarized light by traveling through the first polarizer. The light then goes through a Faraday rotator; this takes the linearly polarized light and rotates the polarization 45 degrees, then the light passes through the exit polarizer. The exit polarizer is oriented at the same 45 degrees relative to the first polarizer as the Faraday rotator is. With this technique, the light is passed through the second polarizer without any attenuation. This technique allows the light to propagate forward with no changes, but any light traveling backward is extinguished entirely.

The loss of backward-traveling light occurs because when the backward light passes through the second polarizer, it is shifted again by 45 degrees. The light then passes through the rotator and again is rotated by 45 degrees in the same direction as the initial tilt. So when the light reaches the first polarizer, it is polarized at 90 degrees. And when light is polarized by 90 degrees, it will be “shut out.” The figures below show the forward- and reverse-transmitted light in a dependent polarized optical isolator.

Forward-Transmitted Light through a Polarized Optical Isolator

Reverse-Transmitted Light through a Polarized Optical Isolator

It should be noted that these figures depict the dependent type of polarized optical isolator. There is also an independent polarized optical isolator. The independent device allows all polarized light to pass through, not just the light polarized in a specific direction. The principle of operation is roughly the same as the dependent type, just slightly more complicated. Tips: The Independent Optical Isolators are frequently used in EDFA Optical Amplifiers.

Composite Optical Isolator

In fact, Composite Optical Isolator is a type of polarization independent isolator used in the EDFA optical amplifier. The EDFA optical amplifier is comprised of Erbium-Doped Fiber, Wavelength-Division Multiplexer, Pumping Diode Laser, Polarization Independent Isolator, and other passive components. Because the polarization independent isolator is composited with the others components into a single EDFA module, it is called a Composite Optical Isolator.

Magnetic Optical Isolator

Magnetic Optical Isolator is another name for polarized optical isolator. The magnetic portion of any isolator is of great importance. As mentioned, there is a Faraday rotator in the optical isolators. The Faraday rotator is a rod composed of a magnetic crystal having a Faraday effect and operated in a very strong magnetic field. The Faraday rotator ensures that the polarized light is in the correctly polarized plane, thus ensuring that there will be no power loss. Here is a figure that shows a basic magnetic optical isolator.

Magnetic Optical Isolator

Optical isolators are used to ensure stabilization of laser transmitters and optical amplifiers as well as to maintain good transmission performance. Ultra speed and large capacity optical fiber trunk systems are expanding as a result of the development of optical amplifiers. In parallel, the demand for optical isolators is increasing. Demand is also expected to increase as LAN and other subscriber fiber optic networks expand. It is therefore imperative that optical isolators be further improved to achieve higher performance, smaller size, and lower price. Luckily, you can now find the best optical isolators solution in Fiberstore, a Manufacturer & Supplier of Fiber Optic Network Solutions focus on Professional Customization.

The Basic Parameters of Passive Optical Network Devices

There are many devices elementary but necessary for the Passive Optical Network (PON) applications that require the transmission, combining, or distribution of optical signals. These passive devices include the Optical Splitter/Coupler, Optical Switch, Optical Attenuator, Optical Isolator, Optical Amplifier, and WDM Filters (CWDM/DWDM Multiplexer) etc. Tips: The passive devices are components that do not require an external energy source.

When working with these passive devices it is important to have a basic understanding of common parameters. Some of the basic parameters that apply to each device are Optical Fiber Type, Connector Type, Center Wavelength, Bandwidth, Insertion Loss (IL), Excess Loss (EL), Polarization-Dependent Loss (PDL), Return Loss (RL), CrossTalk (XT), Uniformity, Power Handling, and Operating Temperature.

Connector Type and Optical Fiber Type

Many passive devices are available with receptacles or fiber optic pigtails. The pigtails may or may not be terminated with a fiber optic connector. If the device is available with a receptacle or connector, the type of receptacle or connector needs to be specified when ordered. You should also note the type of optical fiber used by the manufacturer of the device to ensure it is compatible with the optical fiber used for your application.

Center Wavelength and Bandwidth

Center Wavelength is the nominal operating wavelength of the passive device.

Bandwidth (or bandpass) is the range of wavelengths over which the manufacturer guarantees the performance of the device. Some manufacturers will list an operating wavelength range instead.

Types of Loss

IL is the optical power loss caused by the insertion of a component into the fiber optic system. When working with passive devices, you need to be aware of the IL for the device and the IL for an interconnection. IL as stated by the manufacturer typically takes into account all other losses, including EL and PDL. IL is the most useful parameter when designing a system.
EL may or may not be defined by the manufacturer. EL associated with fiber optic couplers, is the amount of light lost in the coupler in excess of the light lost from splitting the signal. In other words, when a coupler splits a signal, the sum of the power at the output ports does not equal the power at the input port; some optical energy is lost in the coupler. EL is the amount of optical energy lost in the coupler. This loss is typically measured at the specified center wavelength for the device.
PDL is only a concern for Single-Mode passive devices. It is often the smallest value loss, and it varies as the polarization state of the propagating light wave changes. Manufacturers typically provide a range for PDL or define a not-to-exceed number.
RL, short for Return Loss or Reflection Loss, is typically described as this: when a passive device is inserted, some of the optical energy from the source is going to be reflected back toward the source. RL is the negative quotient of the power received divided by the power transmitted.

Tips: IL, EL, PDL, RL are all measured in decibels(dB).

CrossTalk (XT)

XT in an optical device describes the amount of light energy that leaks from one optical conductor to another. XT is not a concern in a device where there is a single input and multiple outputs. However, it is a concern with a device that has multiple inputs and a single output, such as an optical switch. XT is also expressed in dB, where the value defines the difference between the optical power of one conductor and the amount of leakage into another conductor. In an optical switch with a minimum XT of 60 dB, there is a 60 dB difference between the optical power of one conductor and the amount of light that leaked from that conductor into another conductor.

Uniformity

Uniformity is a measure of how evenly optical power is distributed within the device, expressed in dB as well as XT. For example, if a device is splitting an optical signal evenly into four outputs, how much those outputs could vary from one another is defined by uniformity. Uniformity is typically defined over the operating wavelength range for the device.

Power Handing

Power Handling describes the maximum optical power at which the device can operate while meeting all the performance specifications defined by the manufacturer. Power handling may be defined in mW(milliwatt) or dB, where 0 dBm is equal to 1 mW.

Operating Temperature

Operating Temperature describes the range of temperatures that the device is designed to operate in. This can vary significantly between devices, because some devices are only intended for indoor applications while others may be used outdoors or in other harsh environments.

Article Source: http://www.fiberopticshare.com/the-basic-parameters-of-passive-optical-network-devices.html

Some Developments that May Occur in the Fiber Amplifier

This page will focus on fiber optic amplifiers?application, and obviously, the introduction of EDFA in a long distance network has been the first, application identified by several telecom’s operators. I just think EDFA’s advantage is that using the existing cable from 565 Mbit/s systems. Into a 2400 Mbit/s without any additional electronic requirement, maybe this is one of the cost/performance ratio advantage of the optical amplifier versus the conventional technologies. Other applications arise from those countries where the telecommunication network infrastructures are poor, or even non existing. In such a situation the possibility to reach a distance in the order of 200km at 140 or 565 Mbit/s makes the use of EDFA more competitive.

Optical amplification has been already successfully tested in various laboratories and field trials in Europe, North America and Japan. Worldwide standards authority is still working on the standardization of EDFA optical amplifier. Major telecom manufactures already supply line terminals with integrated optical amplifier functions. As far as the future submarine links are concerned, it is expected that in a few years, because of optical amplification, the electronical of today submerged repeaters, will be amended by replacing all optical amplifiers.

Well, an example of the power budget calculations at 2400 Mbit/s is given in the annex, where an EDFA system composed by a power amplifier and a pre-amplifier has been considered. In combination with a dispersion shifted submarine fiber optic cable, it belongs to outdoor fiber optic cable. Junction Networks. The massive introduction of SDH systems, and the forecast use of it on the existing cables, has made the use of EDFA technologies achievable also in the junction networks area. In Europe, North America and Japan, this possibility will be limited to the intercity applications.

In connection with the subscriber loop network design, a similar range of products is drawn up by the worldwide industry for the next generation of CATV systems. It is CATV amplifier. In a near future optical transmitters with Booster Amplifier? integrated in the same equipment, will need to be able to transmit up to 60/80 television channels simultaneously, in a cluster of 200/300 subscribers each. The figure showed a?Booster EDFA Optical Amplifier.

Although CATV amplifier housing employed in current CATV networks is designed to accommodate a return path amplifier, most of today’s CATV system have unactivated return channels. Roughly 20 percent of today’s CATV systems use some fiber optic links to bypass slow amplifier chains in the trunk portion of the network. Service is typically provided to residences and apartments, with relatively limited business locations connected to CATV networks. Similar applications product has WDM amplifier. In-line amplifier, just differ in the range of applications. There is usually only a single CATV operator in a given service area, with nascent competition from microwave and direct broadcast satellite service providers. Television receives only background antennas that are 1 to 2 meters in diameter are used by a small fraction of residential customers. With the fast developments of fiber optical amplifiers, I am very bullish on the trend of it, hope it can be dragged out more widely features and bring more benefits to people.

Fiber Optic Cabling Solutions

The largest solutions of pre-terminated fiber optics, including multimode and single-mode patch cords, MTP/MPO fiber trunks and harnesses, plug-n-play modules/cassettes and fiber enclosures.