Author: Fiber-MART.COM

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We know that fiber can carry more data over long distances than any other physical medium. That makes fiber a very precious material. And how to make the most use of your fiber plant becomes a question. So there comes Wavelength Division Multiplexing (WDM).

Why Should We Deploy WDM ?

WDM can multiply your fiber capacity by creating virtual fibers. The foundation of WDM lies in the ability to send different data types over fiber networks in the form of light. By allowing different light channels, each with a unique wavelength, to be sent simultaneously over an optical fiber network, a single virtual fiber network is created. Instead of using multiple fibers for each and every service, a single fiber can be shared for several services. In this way WDM increases the bandwidth and maximizes the usefulness of fiber. Since fiber rental or purchase accounts for a large share of networking costs, substantial costs can be saved through the application of WDM. Next I will introduce to you the basic four elements in the form of a WDM system.

The Core Technology of WDM System

Generally speaking, a WDM system consists of four elements, that are transceiver, multiplexer, patch cord and dark fiber. The following text will explain them to you respectively.

Fiber Optic Transceivers. Optical transceivers are wavelength-specific lasers that convert data signals from SAN or WAN to optical signals that can be transmitted into the fiber. Each data stream is converted into a signal with a light wavelength that is an unique color. Due to the physical properties of light, channels cannot interfere with each other. Therefore, all WDM wavelengths are independent. Creating virtual fiber channels in this way can reduce the number of fibers required. It also allows new channels to be connected as needed, without disrupting the existing traffic services.

Optical Multiplexers. The WDM multiplexer, sometimes referred to as the Mux, is the key to optimizing, or maximizing, the use of the fiber. The multiplexer is at the heart of the operation, gathering all the data streams together to be transported simultaneously over a single fiber. At the other end of the fiber the streams are demultiplexed and separated into different channels again.

Patch cord. The transceiver transmits the high-speed data protocols on narrow band wavelengths while the multiplexer is at the heart of the operation. The patch cable is the glue that joins these two key elements together. LC fiber patch cables are popular, which connect the output of the transceiver to the input on the multiplexer.

Dark fiber. A requisite for any WDM solution is access to a dark fiber network. The most common way of transporting optical traffic over an architecture is by using a fiber pair. One of the fibers is used for transmitting the data and the other is used for receiving the data. This allows the maximum amount of traffic to be transported. At times only a single fiber is available. Because different light colors travel on different wavelengths, a WDM system can be built regardless. One wavelength is used to send data and a second one to receive it.

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When DIY a home network, besides the common problems (written in the previous article “Do It Yourself for Your Home Network”), people often feel puzzled about what I should use for my jacks—inline coupler or punch down keystone jack. The first one is easy to install but adds an extra connection to the network. The last one is more cheaper and needs a punch down tool to complete the installation. Today’s article will continue to illustrate the technical differences between them, please read on.

What Is Inline Coupler?

Before we come to the comparison between inline couplers and keystone jacks, let’s have a brief overview of these two jacks. A small device for connecting two cables to make a linger cable, usually called an inline coupler or RJ45 coupler. Inline couplers do not provide any amplification or signal boost, and can cause attenuation and signal degradation unless they are of high quality. There are cat5e and cat6 RJ45 inline couplers available on the market.

What Is a Keystone Jack?

Keystone jacks are the standardized snap-in packages for mounting a variety of low-voltage electrical jacks or optical connectors into a keystone wall plate, faceplate, surface-mount box, or a patch panel. As displayed in the Figure 2, keystone jacks have a rectangular face of 14.5mm wide by 16.0mm high and are held in place with flexible tabs. This allows them to be snapped into a mounting plate with correspondingly-sized rectangular holes, called ports.

All keystones, regardless of the type of jack they carry, are interchangeable and replaceable. This provides much flexibility in arranging and mounting many different types of electrical jacks in one plate or panel without requiring customized manufacturing.

Some keystones use a pass-through type connector, where there is a jack on both the front face as well as the rear side. Others only have a jack on the front and employ a different mechanism for hard-wiring signal cables to the rear, such as a mini 110 block, an insulation-displacement connector, or a crimp or solder connection

Whether Should I Use Inline Coupler or Punch Down Keystone Jacks

If you go with inline couplers, you should be aware that they might work well but can turn flaky for a while owing to the plug oxidation or loose fit. RJ45 couplers are easy to install, but they probably will increase the line resistance of the whole total cable length slightly which would decrease the max length of the allowed run (from ~328 feet for 100mb and ~300 feet for gigabit on cat5e by 10-20ft per coupler/patch). However, this will not have any noticeable affect on network performance for a home network unless you are on the limits of the specs.

Note: If you have speed certified network (probably not at home, but possibly in a high-tech office) then you are not allowed to use couplers.

Punch down keystone jack is usually cheaper than the RJ45 coupler, but more difficult to install. As the punch down is more prone to human error, so not only is it hard to install, but if you have issues, it’ll also be hard to reinstall. Therefore, the toolless keystone jacks have been introduced on the market, which make for a simple installation without the need for a punch down tool. Of course, the price is much higher than that of the Punch down keystone jack.

To sum up, if all the connectors are done right, there are really no any obvious differences in signal whether you use the Inline couplers or punch down keystone jacks for connection. It’s all a question of how reliable the physical connections can be. However, sometimes the couplers can have issues inside the cube where they just stop working over time. You’d then have to replace it, which indeed will be a faster replacement than a punch down. But after its replaced, things should be back to normal.

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

The Basics of Semiconductor Optical Amplifier (SOA)

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

Key Points of SOA Amplifier

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

High fiber-to-fiber gain of 20 dB

Up to 16 dBm output

1 MHz with 10 ns pulse width (optional)

PM Panda fiber input/output (optional)

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

Incoming optical signal stimulates emission of light at its own wavelength

Process continues through cavity to amplify signal

Working principle of SOA amplifier

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

SOA Over EFDA in DWDM Networks

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

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

How to Choose SOA Optical Amplifier?

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

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

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

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

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

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

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Today’s high-performance computing environments featuring by switching and routing, cloud computing and virtualization require higher network speeds, greater scalability, and higher levels of performance and reliability in data centers. Some bandwidth-hungry applications, like video streaming applications, also drive data rates to higher points. These all boost the need for a migration to 40G and 100G interfaces as 1 and 10G can’t meet the bandwidth needs well. 40G interface is QSFP (Quad Small Form-factor Pluggable) which has several standards requiring different connectors to fit cabling infrastructure, so as to achieve network connectivity. Do you know what cabling infrastructure is needed to support 40G applications? MPO/MTP cable, direct attach cable (DAC), or LC fiber patch cable? Have any ideas? Follow this article and find the answer.

MTP/MPO Cable

MTP is a registered trademark of US Conec used to describe the connector, and MPO stands for multi-fiber push-on or also multi-path push-on. Actually, the former product is 100% compatible with the latter. Thus, only MTP is written for simplicity in the following paragraphs. In 2010, the IEEE 802.3ba standard specifies MTP connectors for standard-length multi-mode fiber (MMF) connectivity. Its small, high-density form factor makes MTP cable ideal for higher-speed 40G networks in data centers.

To support 40G applications, a 12-fiber MPO connector is needed. The typical implementations of MTP plug-and-play systems split a 12-fiber trunk into six channels that run up to 10 Gigabit Ethernet (depending on the length of the cable). 40G system uses 12-fiber trunk to create a Tx/Rx link, dedicating 4 fibers for 10G each of upstream transmit, and 4 fibers for 10G each of downstream receive, leaving the middle 4 fibers unused. The upgrade path for this type of system entails simply replacing the cassette with an MTP-to-MTP adapter module.

Direct Attach Cable

Besides MTP cable, many data centers also like to choose DACs for 40G cabling infrastructure. DAC, a kind of optical transceiver assembly, is a form of high speed cable with “transceivers” on either end used to connect switches to routers or servers. The “transceivers” on both ends of DACs are not real optics and their components are without optical lasers, thus DACs are much cheaper, preferable for 40G data center applications. As such, the fiber connectivity cost is significantly reduced by using either direct attach copper cables or active optical cables (AOCs) instead of costly fiber transceivers and optical cables.

Direct Attach Copper Cable

Direct attach copper cables are designed in either active or passive versions for short-reaches in data center. Compared with active optical cables, these copper cables are less expensive. Nowadays, there are many twinaxial cables available to support 40G (10G x four channels), in QSFP+ to QSFP+ (ie. EX-QSFP-40GE-DAC-50CM) version or in QSFP to 4 SFP+ cable assembly (eg. QSFP-4SFP10G-CU5M).

The issue is that copper cable is stiff and bulky, thus consuming precious rack space and blocking critical airflow. But with the advancing technology, manufactures produce a thinner, uniquely shielded ribbon-style twinaxial cable that can support speeds of 10G per channel while addressing many of the concerns associated with round, bundled cable. And the ribbon-style twinaxial cable is significantly slimmer than its round counterparts. Even better, the cable can be folded multiple times and still maintain signal integrity, allowing for higher density racks and space savings.

Active Optical Cable

Being a form of DAC, AOC integrates single-mode fiber (SMF) or MMF cable terminated with a connector and embedded with transceivers. It uses electrical-to-optical conversion on the cable ends to improve speed and distance performance of the cable. AOCs can reach a longer distance copper cables, and use the same interfaces as copper cables, typically used in data center. Similar to direct attach copper cables, AOCs are also available in QSFP+ to QSFP+ (eg. QSFP-4X10G-AOC20M) and QSFP+ to 4 SFP+ cabling (ie. QSFP-4X10G-AOC10M) versions.

Since 40G AOC connectors are factory pre-terminated, 40G AOC is easier for installation and thus less affected by the repeating plug during daily use than MTP cable. In case there was a fault in the interconnection, for AOC, you can just replace it with another AOC.

LC Fiber Cable

Certainly, LC fiber cable can also be the cabling solution for the long-reach 40G QSFP+ modules (40GBASE-LR4). That is, 40GBASE-LR4 QSFP+ uses a duplex LC connector as the optical interface, able to support transmission distance up to 10km over single-mode fiber (SMF).

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In this technological world filled by fiber optic systems everywhere, one won’t fail to enjoy the benefits brought by fiber optics in daily life. In a whole fiber optic system, the most essential part should be the fiber optic cable. This cable is made up of incredibly thin strands of glass or plastic capped with the same (eg. ST ST fiber cable) or different connector types (LC ST patch cable) on the ends, used as the medium to carry information from one point to another with light-based technology. Just like electricity that can power many types of machines, beams of light can carry many types of information, so fiber optics do great to people in many ways, like broadcasting, transportation, medicine, etc..Along with the heavy use of fiber optic cables, testing the installed cables also gains importance in practical use. Since there are many standards available for testing, some people may get confused. But don’t worry. This text is written with an attempt to clear off this confusion.

Testing Principles

Generally speaking, five ways are listed in various international standards from the EIA/TIA and ISO/IEC to test installed cable plants. First three of them use test sources and power meters to make the measurement, while the last two use an optical time domain reflectometer (OTDR). Let’s first see the different results from these methods, and then delve into each one.

The use of source and power meter method, also known as “insertion loss”, simulates the way the actual network uses the cable plant. The test source mimics the transmitter, and the power meter the receiver. But insertion loss testing requires reference cables attached to the source and meter to connect to the cable under test. This insertion loss test can use 1, 2 or 3 reference cables to set the “zero dB loss” reference for testing. Each way of setting the reference gives a different loss. While OTDR is an indirect method, using backscattered light to imply the loss in the cable plant, which can have large deviations from insertion loss tests. OTDRs are more often used to verify splice loss or find damage to cables.

Source/Power Meter Method

In source and power meter method, all the three tests share the same setup (shown below), but the reference power can be set with one, two or three cables as explained next. In general, the 1 reference cable loss method is preferred, but it requires that the test equipment uses the same fiber optic connector types as the cables under test. If the cable (ST ST fiber cable) has different connectors from the test equipment (SC-SC on the tester), it may be necessary to use a 2 or 3 cable reference, which will give a lower loss since connector loss is included in the reference and will be subtracted from the total loss measurement.

Reference per TIA Ofiber-martTP-14 (1 Cable Reference)

This method, formerly called method B, uses only one reference cable. The meter, which has a large area detector that measures all the light coming out of the fiber, effectively has no loss, and therefore measures the total light coming out of the launch reference cable. When the cable is tested as below, the measured loss will include the loss of the reference cable connection to the cable plant under test, the loss of the fiber and all the connections and splices in the cable plant and the loss of the connection to the reference cable attached to the meter.

Reference per TIA Ofiber-martTP-14 (2 Cable Reference)

This one, formerly called method A, uses two reference cables with one launch cable attached to the source, and the other receive one attached to the meter. (The two cables are mated to set the reference.) Setting the reference this way includes one connection loss (the mating of the two reference cables) in the reference value. When one separates the reference cables and attaches them to the cable under test, the dB loss measured will be less by the connection loss included in the reference setting step. This method gives a loss that’s less than the 1 cable reference.

Reference per TIA Ofiber-martTP-14 (3 Cable Reference)

Reference cables are often patch cords with plugs, while the cable under test has jacks on either end. The only way to get a valid reference is to use a short and good cable as a “stand-in” for the cable to be tested to set the reference. To test a cable, replace the reference cable with the cable to test and make a relative measurement. Obviously this method includes two connection losses in setting the reference, so the measured loss will be less by the two connection losses and have greater uncertainty. Finally, here goes the picture showing the testing case with one, two, three reference cables.

Reference per TIA Ofiber-martTP-14 (1 Cable Reference)

This method, formerly called method B, uses only one reference cable. The meter, which has a large area detector that measures all the light coming out of the fiber, effectively has no loss, and therefore measures the total light coming out of the launch reference cable. When the cable is tested as below, the measured loss will include the loss of the reference cable connection to the cable plant under test, the loss of the fiber and all the connections and splices in the cable plant and the loss of the connection to the reference cable attached to the meter.

Reference per TIA Ofiber-martTP-14 (2 Cable Reference)

This one, formerly called method A, uses two reference cables with one launch cable attached to the source, and the other receive one attached to the meter. (The two cables are mated to set the reference.) Setting the reference this way includes one connection loss (the mating of the two reference cables) in the reference value. When one separates the reference cables and attaches them to the cable under test, the dB loss measured will be less by the connection loss included in the reference setting step. This method gives a loss that’s less than the 1 cable reference.

Reference per TIA Ofiber-martTP-14 (3 Cable Reference)

Reference cables are often patch cords with plugs, while the cable under test has jacks on either end. The only way to get a valid reference is to use a short and good cable as a “stand-in” for the cable to be tested to set the reference. To test a cable, replace the reference cable with the cable to test and make a relative measurement. Obviously this method includes two connection losses in setting the reference, so the measured loss will be less by the two connection losses and have greater uncertainty. Finally, here goes the picture showing the testing case with one, two, three reference cables.

If a receive cable is used on the far end of the cable under test, the OTDR can measure the loss of both connectors on the cable under test as well as the fiber in the cable, and any other connections or splices in the cable under test. The placement of the B marker after the connection to the receive cable means some of the fiber in the receive cable will be included in the loss measured.

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There is no doubt that fiber optic cables play an integral role in telecommunication industry. Applications like data centers, local area networks, telecommunication networks, industrial Ethernet, and wireless network are all needing fiber optics to ensure smooth connectivity. Each application requires a specific cable design based on performance requirements, environmental conditions, and installation type. The common fiber optic cables like LC to LC patch cord cannot adapt to the harsh environment (e.g. moisture environment or underground deployment), thus water-resistant fiber optic cables are highly demanded on the market due to their water proof nature. Here is what you should know about the water-resistant fiber optic cable.

Overview of Water-resistant Fiber Optic Cables

Water-resistant fiber optic cable refers to the special type of fiber optic cable that are designed and specified for installations where the cable will come in contact with water or moisture, such as aerial, direct buried, or in conduit. The cables in these applications are exposed to or can be temporarily submerged in water, so they contain either a water-resistant gel-filled or gel-free (dry gel) polymer.

Generally, fiber optic cables can be divided into three types—outside plant cable (OSP), indoor/outdoor, and indoor, which are specified based on the environment and location where they are installed. With the exception of indoor cables, all cables contain water-resistant gel-filled or gel-free material to protect them from water and moisture. Before the use of gel-filled and gel-free materials, flooded core was another water-blocking method that is rarely used today (it has been replaced with gel-filled). The following image shows the gel-filled cables.

The gel is a gooey substance that must be removed when accessing and installing the cable. Gel-free cables, which are now more widely used, contain a super-absorbent polymer powder that is activated when it comes in contact with water or moisture. This blocks the water from penetrating the cable and allows for some expansion and contraction with temperature changes. Indoor cables do not contain water-resistant material since they are not typically exposed to water. Indoor (and indoor/outdoor) cables must meet additional flammability requirements dictated by local codes, such as the National Electrical Code.

Tight-Buffered & Loose Tube Cable Construction Provides Excellent Moisture Resistance

Water-resistant materials and cables are included in many industry specifications and standards. Generally, there are two basic water-resistant cable designs: Tight-buffer cables (primarily used inside buildings), Loose tube cables (used for OSP and indoor/outdoor).

It is known to all that most tight-buffered cable designs (seen in image below) are specified for indoor use, but some of them are designed with water-resistant powder and yarn, making them suitable for some indoor/outdoor applications. This tight-buffered cable utilizes an different design approach to deal with the moisture issue. Buffer materials are low-porosity plastics with excellent moisture resistance. This construction very effectively minimises the water molecule and OH-ion concentration level at the glass surface and virtually eliminates the stress corrosion phenomenon.

In loose tube cables (seen in image below), in order to prevent the water from reaching the 250Ľm coated fibers, the tubes surrounding the fibers must be filled with water-absorbent powder or gel that withstands high-moisture conditions, making them excellent for outside plant applications. This approach is especially made to waterproof the cable by filling the empty spaces in the cable with gel. The gel-filled tubes can also expand and contract with temperature changes, which makes loose-tube cable great for harsh, high-humidity environments where water or condensation can be a problem. However, gels can move, flow, and settle, leaves an uncertainty of the filled level of any particular point of a loose-tube gel-filled cable. Because loose-tube cable is typically 250 microns, you’ll need a fan-out kit to build up the individual fiber strands to 900 microns when making the transition at the entrance point from outdoor loose-tube to indoor to tight-buffered cable.

The same level of protection remains in place all along the fiber, regardless of installation conditions, environment, or time. The balance of the tight-buffered, tight bound cable designs is such that it minimizes the open spaces available in the cable structure in which water can reside. Even if an outer cable jacket is cut, or water otherwise enters the cable structure, only a very small percentage of the cross-sectional area is open to water.