WDM, Mux/Demux and OADM Over view

by http://www.fiber-mart.com

CWDM Mux/Demux
The Coarse Wavelength Division Multiplexing-CWDM Mux/Demux is often a flexible plug-and-play network solution, which helps insurers and enterprise companies to affordably implement denote point or ring based WDM optical networks. CWDM Mux/demux is perfectly created for transport PDH, SDH / SONET, ETHERNET services over WWDM, CWDM and DWDM in optical metro edge and access networks. CWDM products are popular in less precision optics and lower cost, un-cooled lasers with lower maintenance requirements. Weighed against DWDM and Conventional WDM, CWDM is much more economical and less power consumption of laser devices. CWDM Multiplexer Modules can be found in 4, 8 and 16 channel configurations. These modules passively multiplex the optical signal outputs from 4 too much electronic products, send on them someone optical fiber and after that de-multiplex the signals into separate, distinct signals for input into gadgets across the opposite end for your fiber optic link.

DWDM Mux/Demux
The Dense Wavelength Division Multiplexing-DWDM Mux/Demux Modules are made to multiplex multiple DWDM channels into one or two fibers. Based on type CWDM Mux/Demux unit, with optional expansion, can transmit and receive as much as 4, 8, 16 or 32 connections of various standards, data rates or protocols over one single fiber optic link without disturbing one another. DWDM MUX/DEMUX modules offers the most robust and low-cost bandwidth upgrade on your current fiber optic communication networks.

OADM Add/Drop Multiplexer

WDM OADM Add/Drop Multiplexer is designed to organize the signal output at a predetermined wavelength from an optical line in the WDM system. These devices are called Add/Drop modules — WDM OADM (Optical Add/Drop Multiplexer).

The OADM module, extracting the desired signal, passes the rest of the emission unchanged. OADM modules are passive devices. Single-sided and dual-sided modules have a fundamental difference. Single-sided OADM can seize and add a signal in the line towards one multiplexer. Dual-sided OADM can establish a connection with two multiplexers, and the line will have no idle channels.

What are polarization maintaining fibers?

In the most common an optical fiber in which the polarization of linearly polarized light waves launched into the fiber is maintained during propagation, with little or no cross-coupling of optical power between the polarization modes.


In the most common an optical fiber in which the polarization of linearly polarized light waves launched into the fiber is maintained during propagation, with little or no cross-coupling of optical power between the polarization modes. Such fiber is used in special applications where preserving polarization is essential.


 What is polarization maintaining(PM) fibers ? 


Polarization Maintaining (PM) optical fiber is a key component of Fiber Optic Gyroscopes, devices that measure rotation in missiles, aircraft, ships and satellites. They are a type of interferometric sensor in which the phase difference between two light paths is measured.The polarization of light propagating in the fiber gradually changes in an uncontrolled (and wavelength-dependent) way, which also depends on any bending of the fiber and on its temperature. Specialised fibers are required to achieve optical performances, which are affected by the polarization of the light travelling through the fiber.optical fibers always exhibit some degree of birefringence, even if they have a circularly symmetric design, because in practice there is always some amount of mechanical stress or other effect which breaks the symmetry. As a consequence, the polarization of light propagating in the fiber gradually changes in an uncontrolled (and wavelength-dependent) way, which also depends on any bending of the fiber and on its temperature.


 Principle of polarization maintaining(PM) fibers


The mentioned problem can be fixed by using a polarization-maintaining fiber, which is not a fiber without birefringence, but on the contrary a specialty fiber with a strong built-in birefringence (high-birefringence fiber or HIBI fiber, PM fiber). In general, optical fiber telecommunications applications, PM fiber is used to guide light in a linearly polarised state from one place to another. To achieve this result, several conditions must be met. Input light must be highly polarised to avoid launching both slow and fast axis modes, a condition in which the output polarization state is unpredictable.


Provided that the polarization of light launched into the fiber is aligned with one of the birefringent axes, this polarization state will be preserved even if the fiber is bent. The physical principle behind this can be understood in terms of coherent mode coupling. The propagation constants of the two polarization modes are different due to the strong birefringence, so that the relative phase of such copropagating modes rapidly drifts away. Therefore, any disturbance along the fiber can effectively couple both modes only if it has a significant spatial Fourier component with a wavenumber which matches the difference of the propagation constants of the two polarization modes. If this difference is large enough, the usual disturbances in the fiber are too slowly varying to do effective mode coupling.In addition, connectors must have been installed on the PM fibers in such a way that internal stresses do not cause the electric field to be projected onto the unintended axis of the fiber.




PM optical fibers are used in special applications, such as in fiber optic sensing, interferometry and quantum key distribution. They are also commonly used in telecommunications for the connection between a source laser and a modulator, since the modulator requires polarized light as input. They are rarely used for long-distance transmission, because PM fiber is expensive and has higher attenuation than singlemode fiber.Optical fibers may be applied in measurements of electrical current, particularly as so-called optical current transformers. Electric current sensors, in which optical fibers are used are small, light, cheap and safe. Their sensitivity is, however, due to the restricted magnetootpic properties of optical fibers, rather small. Moreover, these sensors are susceptible to deformations of the optical fiber. An increase of their sensitivity consists in lengthening the distance of optical fiber on which the magnetic field acts.PM fibers are applied in devices where the polarization state cannot be allowed to drift, e.g. as a result of temperature changes. Examples are fiber interferometers and certain fiber lasers. A disadvantage of using such fibers is that usually an exact alignment of the polarization direction is required, which makes production more cumbersome. Also, propagation losses are higher than for standard fiber, and not all kinds of fibers are easily obtained in polarization-preserving form.


Fiber-MART offer polarization components can be utilized in high power optical amplifiers and optical transmission system, test and measurement. the launch conditions at the optical fiber end face must be consistent with the direction of the transverse major axis of the fiber cross section. Fiber-Mart Polarizing Beam Combiner/Splitter (PBC/PBS) is a compact high performance light wave component that combines two orthogonal polarization signals into one output fiber, and also can split the incoming light into two orthogonal states. We also supply the Isolator type (IPBC/IPBS) which provides both polarization beam combining and optical isolation in one integrated component.for more information,you can visit www.fiber-mart.com.pls feel free to contact with us for any question . E-mail: service@fiber-mart.com

OTDRs Never Go Out of Style

by http://www.fiber-mart.com

The optical time domain reflectometer (OTDR) is now thirty-six years old and aging gracefully.

While fiber optic cables had been installed in North America since 1977, one major concern was and still is: how do we accurately locate a fault? This is the major reason that OTDRs exist. Fortunately, as the communications industry has matured, so has the OTDR.

Why Use It?

Today’s OTDRs address quality control (QC), quality assurance (QA) for optical fibers and cables as well as acceptance testing and troubleshooting installed links in the field. Fiber and cable manufacturers make use of the OTDR’s QC features to perform attenuation and length measurements at a variety of wavelengths based on the type of fiber being tested. These tests are more common in factory settings, often in conjunction with optical switches to allow quick and efficient testing of large numbers of optical fibers.

As fiber counts in cables have increased, the level of automation has paralleled this growth, providing opportunities to increase the OTDR’s value to service providers by incorporating optical switches to monitor live and dark fibers.

The OTDR’s dominant role for service providers and contractors is in QA roles — which is far more extensive and complex than QC testing. Modern OTDRs must address multiple tests and measurement tasks focused mostly around attenuation, but as the critical nature of reflections and their impact on system performance increase, the OTDR is essential for these measurements. It must also be able to perform length measurements for approximate physical locations of events such as splices, fiber stress points (macrobends and microbends), passive devices such as splitters and fiber breaks.

The OTDR is also the easiest instrument to use to measure component reflectance and span optical return loss (ORL) values. The importance of reflection testing cannot be overstated. Reflectance and ORL values are critical for achieving desired bit error rates, as Fresnel reflections from connectors can disrupt the efficient operation of the laser diodes in fiber optic transmitters.

Transmitter manufacturers define the quality of signal based on the level of attenuation and the ORL values for fiber spans. A single contaminated connector can affect the component reflectance, which in turn affects the span’s ORL value. Component reflectance and ORL testing should be requirements for all end-to-end OTDR tests on single-mode fibers.

New Challenges

As system data rates increase, the need for fiber characterization (FC) continues to challenge the industry. In some cases where optical amplifiers are installed, identifying, locating and re-terminating high-loss connectors and splices is required due to higher reflection and attenuation issues with legacy terminations. Older terminations were limited by two issues: fiber tolerances and the type of polish on the connectors. Single-mode fiber tolerances for core, cladding dimensions, ovality and concentricity continue to improve. Older fibers simply have more opportunity for higher loss connections.

Many legacy connectors had either flat polishes or original physical contact (PC) polishes with reflectance levels of 30-40 dB. Even the improved super PC (SPC) polishes of the late 1990s with most ST and SC connectors have much greater reflectance levels (45 dB) than the 50-65 dB reflectance levels for today’s ultra physical contact (UPC) and angled physical contact (APC) polishes.

Identifying high loss splices and connectors as well as high reflectance connectors can easily be performed by the OTDR. However if the readings are too high to meet today’s standards or system performance levels, these older terminations may have to be replaced with UPC or APC connectors.

The Chicken and the Egg Question

Is the technology driving the development of improved OTDRs? Or are the users driving their needs? Each group will have their own perspectives. The manufacturers have done a great job at developing smaller, lighter, less costly instruments. They have done so while improving technical requirements: greater dynamic range options, shorter and longer laser pulse widths, increased waveform and data storage, longer battery life, and interfaces for exporting data via Bluetooth or Wi-Fi. At the same time maintaining an instrument that is easy to operate.

OTDRs have also grown from AC powered mainframe OTDRs to handheld mini OTDRs.

The development of modular OTDR platforms allows for greater flexibility to add various optical tools such as power meters, visual fault locators, inspection scopes or other modules for advanced fiber testing, wifi or copper testing.


In the communications market,  Wavelength Division Multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light.

In the communications market,  Wavelength Division Multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light. This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity.

The WDM is divided into three types (WDM, CWDM and DWDM) on the basis of wavelength difference among the three.

CWDM Mux/Demux

Dense Wavelength Division Multiplexing (CWDM) networks need multiplexer/demultiplexer (MUX/DEMUX) modules to combine and split wavelength channels at standard ITU grid. These modules are generally called CWDM MUX/DEMUX.

The CWDM Mux/Demux is a universal device capable of combining nine optical signals into a fiber pair. It is designed to support a broad range of architectures, ranging from scalable point-to-point links to two fiber-protected rings. The market-standard LGX™ packaging of the CWDM Mux/Demux enables easy deployment in existing LGX-compatible frames or WaveReady 3500F shelves.

The CWDM Mux/Demux is designed to interoperate with both the WaveReady line of transponder and optical regenerator solutions as well as CWDM transponders and small form-factor pluggables (SFPs) used in widely available transmission equipment. With billions of field operating hours, the industry leading Lumentum optical multiplexing technology offers unparalleled reliability and leading-edge performance.

CWDM Mux/Demux is a flexible network solution for WDM optical networks. At most 18 full-duplex wavelengths can be added over a single fiber trunk which greatly alleviates fiber exhaustion. With low insertion loss and high stability, CWDM Mux/Demux is applied to many operations, such as CATV links, WDM systems, test and measurement, metro and access networks, FTTH networks, etc. The deployment of CWDM Mux/Demux is transparent and clear. Its compact form factor enables a much easier manipulation. Only coarse wavelengths can be transmitted over the fiber which reduces the WDM system cost.

Three kinds of CWDM Mux/Demux are widely used in the application. They are 1RU 19″ rack chassis CWDM Mux/Demux, half 19″/1RU CWDM Mux/Demux and splice/pigtailed CWDM Mux/Demux. CWDM Mux/Demux in 19 inch rack mount package is often used for CWDM, EPON and CATV network. Half 19″/1RU CWDM Mux/Demux is packed in LGX box using thing film coating and non-flux metal bonding micro optics packaging. Splice/pigtailed CWDM Mux/Demux is packed in the ABS box package based on standard thin film filter (TFF) technology.

DWDM Mux/Demux

Dense Wavelength Division Multiplexing (DWDM) networks need multiplexer/demultiplexer (MUX/DEMUX) modules to combine and split wavelength channels at standard ITU grid. These modules are generally called DWDM MUX/DEMUX.

DWDM Mux/Demux conveys optical signals in a more dense wavelength. It is especially used for long distance transmission where wavelengths are highly-packed together. The maximum delivered wavelengths can reach up to 48 channels in 100GHz grid (0.8nm) and 96 channels in 50GHz grid (0.4nm). DWDM Mux/Demux uses a reliable passive WDM technology that achieves low insertion loss. And it provides a solution for adding WDM technology to any existing network device. Applications like point-to-point DWDM fiber optimization, linear add/drop DWDM fiber optimization, external optical monitoring are typically using DWDM Mux/Demux module.

The functionality of DWDM (Dense Wavelength Division Multiplexing) resembles to the one of CWDM. The DWDM channel spacing is 0.8/0.4 nm (100 GHz/50 GHz grid). This small channel spacing allows to transmit simultaneously more information. Currently a restriction on wavelengths between 1530 nm and 1625 nm exists which corresponds to the C and L band. DWDM wavelengths are more expensive compared to CWDM caused by the need of more sophisticated transceivers.

Likewise, 1RU 19″ rack chassis DWDM Mux/Demux, Half 19″/1RU DWDM Mux/Demux and splice/pigtailed DWDM Mux/Demux are three divisions of DWDM Mux/Demux modules. The first type is in 19 inch rack mount package used for long-haul transmission over C-band range of wavelengths. The second one is in LGX package used for PDH, SDH/SONET, Ethernet services transmission. The last one is in ABS box package and its pigtails are labeled with wavelengths.

Comparison Between CWDM and DWDM System

The difference between CWDM and DWDM lies in the channel spacing between neighbored wavelengths, for CWDM 20 nm and for DWDM 0.8/0.4 nm (using 100 GHz/50 GHz grid). this advantage for an efficient CWDM/DWDMintegration. Thereby up to sixteen DWDM channels are transmitted simultaneously in only one CWDM channel (1530 nm and 1550 nm). Thus an easy-to-realize channel extension can be achieved under continued use of existing CWDM components.

Price differenceCWDM system carries less data, but the cabling used to run is less expensive and less complex. A DWDM system has much denser cabling and can carry a significantly larger amount of data, but it can be cost prohibitive, especially where there is a need for a large amount of cabling in an application.

Transmission distanceDWDM system is designed for longer distance transmission as stated above. They can transmit more data over a significantly larger run of cable with less interference than a comparable CWDM system. If there is a need for transmitting the data over a long range, DWDM system will likely be the best in terms of functionality of the data transmittal and the lessened interference over the longer distances that the wavelengths must travel.

CWDM system cannot transmit over long distances because the wavelengths are not amplified, and therefore CWDM is limited in its functionality over longer distances. Typically, CWDM can travel anywhere up to about 100 miles (160 km), while an amplified DWDM system can go much further as the signal strength is boosted periodically throughout the run. As a result of the additional cost required to provide signal amplification, the CWDM solution is best for short runs that do not have mission critical data.

To sum up, before buying We should first understand the differences between them,Fiber-Mart provides a series of CWDM DWDM MUX/DEMUX modules with as more as 18 channels (20nm spaced) in simplex or duplex configurations. All the CWDM  DWDM modules are available with three types of packaging: ABS Pigtailed Box, Rack Chassis and LGX Cassette. For more details, please visit www.fiber-mart.com. Please not hesitate to contact us for any question. E-mail: service@fiber-mart.com

The introduction to EDFA(Erbium-Doped Fiber Amplifier)

EDFA is an optical repeater device that is used to boost the intensity of optical signals being carried through a fiber optic communications system.It was invented in 1987, EDFA exhibits its gain in the C-band and L-band

EDFA is an optical repeater device that is used to boost the intensity of optical signals being carried through a fiber optic communications system.It was invented in 1987, EDFA exhibits its gain in the C-band and L-band, where telecomputer optical fibers show its lowest loss in the entire optical telecommunication wavelength bands.

What does Erbium-Doped Fiber Amplifier (EDFA) mean?

EDFAs are used as a booster, inline, and pre-amplifier in an optical transmission line, as schematically shown in Figure 1. The booster amplifier is placed just after the transmitter to increase the optical power launched to the transmission line. The inline amplifiers are placed in the transmission line, compensating the attenuation induced by the optical fiber. The pre-amplifier is placed just before the receiver, such that sufficient optical power is launched to the receiver.

Figure 1

It is used in the telecommunications field and in various types of research fields .An EDFA is “doped” with a material called erbium. The term “doping” refers to the process of using chemical elements to facilitate results through the manipulation of electrons.

How it Works

An optical fiber is doped with the rare earth element erbium so that the glass fiber can absorb light at one frequency and emit light at another frequency. An external semiconductor laser couples light into the fiber at infrared wavelengths of either 980 or 1480 nanometers. This action excites the erbium atoms. Additional optical signals at wavelengths between 1530 and 1620 nanometers enter the fiber and stimulate the excited erbium atoms to emit photons at the same wavelength as the incoming signal. This action amplifies a weak optical signal to a higher power, effecting a boost in the signal strength.

Before the invention of EDFA, a long optical fiber transmission line required a complicated optical-to-electrical (O-E) and E-O converter for signal regeneration. The use of EDFA has eliminated the need for such O-E and E-O conversion, significantly simplifying the system. This is especially of use in a submarine optical transmission, where more than a hundred repeaters may be needed to construct one link. The TPC-5CN (Trans-Pacific Cable 5 Cable Network), started its operation in 1996, is the first submarine optical fiber network which employed EDFA.

The EDFA rate, or amplification window, is based on the optical wavelength range of amplification and is determined by the dopant ions’ spectroscopic properties, the optical fiber glass structure and the pump laser wavelength and power. As ions are sent into the optical fiber glass, energy levels broaden, which results in amplification window broadening and a light spectrum with a broad gain bandwidth of fiber optic amplifiers used for wavelength division multiplex communications. This single amplifier may be used with all optic fiber channel signals when signal wavelengths are in the amplification window. Optical isolator devices are placed on either side of the EDFA and serve as diodes, which prevent signals from traveling in more than one direction.

EDFAs are usually limited to no more than 10 spans covering a maximum distance of approximately 800 kilometers (km). Longer distances require an intermediate line repeater to retime and reshape the signal and filter accumulated noise from various light dispersion forms from bends in the optical fiber. In addition, EDFAs cannot amplify wavelengths shorter than 1525 nanometers (nm).

Fiber-MART Optical Amplifier & EDFA

Optical Amplifiers provided by Fiber-Mart are designed for all network segments (access, metro, regional and long haul) and applications (telecom, cable and enterprise). We have a series of Erbium-Doped Fiber Amplifier (EDFA) optical amplifiers, including DWDM EDFA for DWDM systems, CATV EDFA for CATV applications, SDH EDFA for SDH networks. In addition, we can also provide Raman Fiber Amplifiers, DCM EDFA with mid-stage access, and high power amplifiers such as EYDFA.

In a word , Optical Amplifier & EDFA enables the optical transmission over long distance by amplifying signals. For more information, please visit Fiber-MART.COM .pls not hesitate to contact us for any requirements : service@fiber-mart.com


Optical Amplifier & EDFA
Optical Amplifier & EDFA
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