Author: Fiber-MART.COM

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A fiber optic data link carries signals for communications, security, control and similar purposes by using transceivers and optical fibers. Designed to protect the fibers, an optical fiber cable should be installed, spliced and terminated with the proper hardware to mate the data link transceivers, and included in a fiber optic cable plant. This cable plant must be selected and installed to withstand the environment, and typically terminated at outlets or patch panels near the communications equipment. It’s connected to the transceiver by short fiber optic jumper. Last blog introduces fiber optic data links: parts, signals and power budget. Today’s blog details another device used in data links: fiber optic cable plant.

Cable Plant Basicst Basics

Since the fiber optic cable plant consists of the optical cable which is terminated with the transceiver, this cable plant must be compatible with the performance parameters of the transceivers for the link to operate properly. This includes types of fiber capped with different connectors (e.g. LC to SC fiber patch cable), optical loss and bandwidth of the cable plant. For the cable plant, a loss budget must be calculated to estimate its loss and a power budget to determine if the planned communications system will operate over the cable plant.

Cable Plant Performance Factors Factors

For a fiber optic data link performances, the parameters are those that define the communications signals to be carried on the link or bandwidth at which the link operates, the length of the link and the specifications (bandwidth and optical loss) of the fiber optic cable plant. These factors determine the types of transceivers and cable plant components that must be chosen for a communications system. (Among these factors, the loss of the cable plant and the bandwidth have effects on the link design and testing after installation.)

Cable Plant Lossant Loss

The loss of the cable plant is determined by the summation of the loss in the cable plant because of fiber attenuation, splice loss and connector loss. In some cases, the fiber attenuation may be increased due to improper installation of the cable. As a signal travels down the fiber, the signal will be attenuated by the optical fiber and reduced by the loss in connectors and splices.

Loss Budgets Budgets

For each cable plant designed, the loss budget must be calculated. Then according to the loss budget, the loss of the fiber in the cable plant can be estimated by multiplying the length (km) by the attenuation coefficient (dB/km), then adding the loss from connectors and/or splices determined by the number of connectors and/or splices times the estimated loss each to get the total estimated loss of the cable plant. The cable plant loss budget must be lower than the power budget of the link transceivers (see below) for the link to work properly.

Dispersionspersion

Dispersion or pulse spreading limits the bandwidth of the link. Transceivers have some dispersion caused by the limitations of the electronics and electro-optical components, but most of the dispersion results from the limited bandwidth of the fiber in the cable plant.

Dispersion in multi-mode fiber (MMF) occurs by modal dispersion or chromatic dispersion. Modal dispersion is caused by the different velocities of the various modes being transmitted in the fiber. Chromatic dispersion is caused by the different velocities of light at different wavelengths.

Single-mode fiber (SMF) also causes dispersion, but generally only in very long links. Chromatic dispersion has the same cause as MMF, the differences in the speed of light at different wavelengths. SMF may also suffer from polarization-mode dispersion causes by the different speeds of polarized light in the fibers.

The transceiver must be chosen to offer proper performance to the communications system’s requirements for bandwidth or bitrate, and to supply an optical transmitter output of sufficient power and receiver of adequate sensitivity to operate over the optical loss caused by the cable plant of the communications system. The difference in the transmitter output and receiver sensitivity defines the optical power budget of the link.

The cable plant components, optical fiber, splices and connectors, are chosen to allow sufficient distance and bandwidth performance with the transceivers to meet the communications system’s optical power budget requirements. The power budget of the link defines the maximum loss budget for the cable plant. The maximum link length will be determined by the power budget and loss budget for low bit rate links that will be derated for dispersion for higher bandwidth links.

Most communications systems with short links have options for both MMF and SMF, while longer links use only SMF. All networks may provide guidance as to the types or grades of fiber needed to support certain applications.

Every manufacturer of data links components and systems specifies their link for receiver sensitivity (perhaps a minimum power required) and minimum power coupled into the fiber from the source. In order for a manufacturer or system designer to test them properly, it is necessary to know the test conditions. For data link components, that includes input data frequency or bitrate and duty cycle, power supply voltages and the type of fiber coupled to the source. For systems, it will be the diagnostic software needed by the system.

Conclusionnclusion

Fiber optic cable plant is an integral part of a fiber optic data link, and it should be managed in the exact path that every fiber in each cable follows, including intermediate connections and every connector type.

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Optical fibers can be divided according to the material they are made of. As mentioned in previous post, optical fibers can be made of glass, but they can also be made of plastic. Both of the materials have their pros and cons.

The fibers made of glass are great for long-distance transmission, but are very expensive. They are divided into two different types: Single mode and Multimode. The main difference between both of them is the core diameter and the number of light bundles in the fiber. Single mode fibers allow only one beam of light to be transmitted, and Multimode fibers can transmit multiple light beams at a time.

As we already said, we also know optical fibers made of plastic, also called POF fibers (Polymer optic fiber). Plastic fibers are used at shorter distances and have a larger core diameter. Their transmission routes are less reliable than the ones of glass fibers, but their main gain is the low cost. Plastic fibers are, compared to the glass ones, really inexpensive.  So if we combine both, pros and cons, we can conclude that plastic fiber are mainly used on short distances (inside our homes etc.) to lower the cost. Most of the time, POFs at home are found in connecting audio devices. The attenuation for fiberglass is 0.2dB / Km, for POF this is 100dB / Km.

A huge part of human population has an access to the worldwide internet and if we are lucky enough to live in a bigger city, there is a good chance that our internet providers are not only able to offer us an internet connection through copper fibers, but through optical fiber as well.

According to the topology used by the ISP-Internet Service Provider, there is an optical fiber that leads to our houses. Mainly the fibers that lead to our homes are known as Single mode optical fibers (search above for an explanation) which are best suited for long distance transmissions. The connection is tailored to the economic and physical capacities, and most providers provide at least two optical fibers for security and faster debugging if some kind of error occurs. However, where economic or physical capacities do not allow the use of two fibers, the providers provide only one optical fiber through which the two-way communication is used.

Depending on the number of fibers, we have an adapted method of communication between the modem and the control panel. The simplest solution is if there are two optical fibers available. In this case one of the fibers represents the TX receiving fiber and the other optical fiber represents the transmitting fiber – RX.  Depending on the number of optical fibers that are available, the entire system, which includes the technology in the switchboard and the modem or the receiving side, must also be adapted.

In case we do not have enough (at least two) optical fibers, we use Bi-direction connection, which means that we use one optical fiber for the two-way communication and connection. The way this works is that the system uses two wavelengths. One wavelength is used for TX (Transmit) and the other one is used for RX (Receive).

Unlike Single mode optical fibers, Multi mode optical fibers are mainly represented in very old communication routes. They are most commonly encountered in older LAN extensions with Media Converters. The problem with these fibers is that they are harder to bond and have several different core diameters. Technology is older the support is poor.

We know two different ways to connect (splice) optical fibers. One way of connecting or splicing two fibers, is with the help of connector. If we chose to use this way of connecting the fibers, we have to be extra careful and pay attention to the kind of the connector we use. There are quite a few different types of connector, but the ones that are most commonly used are SC, LC, FC, E-2000 connectors. If choosing this way of connecting the fibers we also have to consider the surface areas of the fibers we are splicing. This means that wa have to pay special attention to the grinding angle.

Another way of splicing the optical fibers is the permanent welding of optical fibers. This way of splicing requires special equipment suitable for welding a particular type of optical fiber. The work itself is precise and demanding, and also includes the complex preparation of the optical fiber before splicing. Proper and quality preparation of the fiber and the joint is of paramount importance, since it later affects the quality of the transmission route itself. This way of splicing optical fibers is better than connecting the fibers with connectors, because the joints and routes are more reliable and the attenuation is lower.

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The electrical circuitry of the SFP transceiver modules is connected to copper or optical network. This type of transceivers is widely used for both data communications and telecommunication applications. Any official standards organization does not regularize the fiber optic SFP. The construction and specifications of this form-factor are specified by an MSA (multisource agreement) between competing manufacturers. SFP transceivers are readily available in a diverse range of options.

Advantages of SFP Transceivers

SFP Transceiver Module can be considered as the improved version of GBIC, and it is also called mini-GBIC. However, it allows better port density as its physical attributes are much compact than the GBIC. These transceivers are designed to offer data rates of up to 5 gigabits per second and even higher. With SFP transceiver, the up-gradation and maintenance of fiber optic network become more convenient than it has been with soldered-in modules. A single module SFP module can be replaced or repaired easily as it is hot-pluggable, and you won’t need to replace the entire board with multiple modules on it. This benefit can bring significant savings in terms of both; up-gradation and maintenance. The SFP form-factor is designed to support Fiber Channel, Gigabit Ethernet, SONET, and various other communication standards. Today`s SFP transceivers come with DDM and DOM functions. These functions offer real-time monitoring of various important networking parameters such as optical input and output power, laser-bias current, temperature, and transceiver supply voltage.

Availability in Various Types and Capacities

The availability of fiber-optic SFP in a broad range of types allows users to choose the best suitable transceiver according to their existing network requirements. Different types of SFP transceivers are available to operate over different wavelengths. Moreover, you can also choose an SFP transceiver based on the required link distance, please check the following summary:

Transmission rates: 100 Mbps to 4 Gbps

Possible Wavelengths: 850 nm, 1310nm, 1550ns, CWDM

Working Distance: 500 meters to 100 kilometers

What is Bending Radii or Bend Radius?

Following types of SFP modules are available at CBO – one of the finest networking equipment vendors:

It is essential to understand that the Copper SFP transceivers offer communication between optical fiber compatible host devices over twisted pair networking cables.

SFP Duplex

SFP Bidi

SFP Copper

SFP CWDM

SFP CWDM-Bidi

SFP DWDM

SFP PON

SFP Applications

Fiber optic SFP transceivers provide interference between network devices such as media converters, routers, switches, and a copper or fiber optic networking cable. These transceivers are designed to support a broad range of networking and communications standards. SFP transceivers allow the transmission of gigabit ethernet and fast ethernet LAN packets over WANs. Besides this, the transmission of E1/T1 streams is also possible over packet-switched networks with SFP transceivers.

Electrodes are the most essential consumable of fusion splicing machine. In general, after a period of use, it needs to be replaced. This is the basic maintenance of fusion splicing machine. Thus, users of fusion splicing machines should have the ability to judge when to replace electrodes and master the maintenance knowledge of replacing electrodes. This post will guide you how to judge when to replace the electrodes and explain the replacing steps by taking example of the latest Fujikura fusion splicing machine FSM-80S.

 
When to Replace Electrodes of Your Fusion Splicing Machine
What’s the best time to replace the electrodes of your fusion splicing machine, and how do you know when to replace it? Different users have different methods according to their working experiences. But the most basic method to judge when to replace the electrodes will be introduced here. Generally, there are two basic ways to judge whether the fusion splicing machine needs to be replaced its electrodes.

There is a function of a fusion splicing machine called arc discharge count. Electrodes should be replaced after reaching the manufactures recommended arc discharges. In general, the fusion splicing machine will alarm to remind users to replace the electrodes in that case. You should replace the electrodes of your fusion splicing machine when you see this alarm. Otherwise, splicing loss and quality will be effected.

Users can confirm whether the electrodes need to be replaced through some abnormal conditions during using. For example, if you find that your fusion splicing machine often prompt discharge not stable during the splicing, or discharge correction can not pass normally, or even the tip of the electrodes are oxidate severely and bald, you should replace the electrodes in those cases.
How to Replace Electrodes of Fusion Splicing Machine

Electrodes Replacing Steps
We can see the electrodes replacing steps in the following picture. It shows us the electrodes replacing steps of the Fujikura latest FSM-80S fusion splicing machine.

Tips for Replacing Electrodes
Ensure to use the appropriate sized screwdriver to remove the fixing screws of the electrodes fixture. Because long-term use of an unsuitable screwdriver to remove the screw may cause the screw to be stripped which may affect the later disassembly.
Avoid excessive pressure when locking the screw, otherwise screw also will be stripped so that the later disassembly is inconvenience.

When installing the electrodes, tighten screws no more than finger tight while pushing the electrode collars against the electrode fixtures, Incorrect installation of the electrodes may result in greater splice loss or damage to the circuit.
Be careful not to damage the electrodes shaft or tips. Any damaged electrodes should be discarded
Always replace fusion splicer electrodes as a pair.
 
After replacing the electrodes, it’s necessary to stabilize the electrode and conduct discharge correction in order to make sure that the new electrodes perform well. These can usually be done through instructions of the fusion splicing machine. In addition, we should use the discharge correction feature to get the best discharge power of the machine in daily use.

There are many fiber tools available for testing at different stages of the network, to meet various test requirements. These tests are used to reveal the total loss, optical return loss (ORL) and fiber length, can be in a single fiber or a complete network. In addition, the test may require further examination of the different elements of the measured link. Whether identify the characteristics of each component in the link, locate potential problems for a fiber, or find fault in the network, all will inevitably have to use optical time domain reflectometer (OTDR) – from commissioning to the optical network troubleshooting and maintenance, OTDR is the ideal choice. This article will describe the basic principles of an otdr test, for you better understanding the instrument specifications.

What Is An OTDR?

OTDR shows the link condition by reading the light level sent back from the optical pulse. Note that there are two types of reflected light: a continuous low-level light produced by fiber is called Rayleigh backcattering light, high reflection peak at the connection point is called the Fresnel reflection. Rayleigh backscattering is used as a distance function to calculate the attenuation level in fiber optic (unit of dB/km), shown as the linear slope of OTDR trajectory. This phenomenon comes from reflection and absorption of the fiber impurities inside the inherent. When light hits on some impurities, impurity particles will redirect light in different directions, while generating a signal attenuation and backscattering. The longer wavelength, the less the attenuation. Therefore, transmit the same distance in the standard fiber requires smaller power. The below picture illustrates the Rayleigh backscattering.

The second reflection (Fresnel reflection) OTDR uses can detect the physical events along the link. When the light reaches the refractive index mutated position (such as from glass to air), a large part of the light is reflected back, resulting Fresnel reflection, it may be thousands of times stronger than the Rayleigh backscattering. Fresnel reflection can be identified through the OTDR track peak. Examples of such reflection are fast connectors, mechanical splices, optical fiber, fiber breaks or open connectors.

What Is The Blind Zone?
Fresnel reflection leads to an important specification of OTDR, namely blind spot. There are two types of blind spots: events and attenuation. Both are generated by the Fresnel reflection, with the changing distance (meters) depends on the different changes in the reflected power to represent. Blind spot is defined as the duration time, in the meantime detector by high intensity reflected light effects of temporary “blindness”, until it returns to normal can re-read the light signal, imagine, when you night driving with the oncoming cars encounter, your eyes will be short-term blindness. In the OTDR field, time is converted to distance, therefore, the more reflective the detector longer recovery time, leading to longer blind. Most manufacturers are available in the shortest possible pulse width, and single mode fiber -45 dB, -35 dB multimode fiber reflection to specify blind. Therefore, reading the table footnote of specifications is very important because manufacturers use different test conditions for measuring blind area, with particular attention to the pulse width and reflectance values. For example, single-mode fiber -55 dB reflection provides shorter blind specifications than that of -45 dB, just because -55 dB is a lower reflection, the detector recovery faster. In addition, the use of different methods to calculate the distance will be a shorter blind zone than that of the actual value.

Event Blind Zone
Event blind zone is the minimum distance of another event OTDR can detect after Fresnel reflection. In other words, is the minimum fiber length needed between the two reflection events. Still the diving mentioned before as an example, for example, when your eyes can not open because the glare stimulation from the opposite car, after a few seconds, you will find that there is an object on the road, but you can not identify it correctly. Turned to OTDR, can be detected by continuous event, but can not measure the loss. OTDR merging successive events, and returns to a global reflection and loss on all the combined events. To establish specifications, the most common industrial way is to measure the distance between each side of the -1.5 dB of peaks.You can also use another method, measure the distance from the event starts until the reflection level from the peak down to -1.5 dB. This method returns to a longer blind, manufacturers use less.

OTDR event blind zone as short as possible is very important, so that it can detect the closely spaced events in the link. For example, testing requirements of OTDR event blind zone is very short in the building network, because the fiber jumper connecting various data centers is very short. If the blind area is too long, some connectors may be missed, the technicians can’t identify them, which makes the job of positioning potential problems become more difficult.

Attenuation Blind Zone
Attenuation blind zone is after the Fresnel reflection, OTDR can accurately measure the minimum distance of successive events loss. Also use the example above, after a longer period of time, your eyes are fully restored, the ability to identify and analyze possible attributes of objects on the way. Shown below, the detector has enough time to recover, so that it can detect and measure the loss of successive events. The minimum distance required from the beginning of reflection events, until the reflection is reduced to the fiber backscattering level of 0.5 dB.

The Importance Of Blind Zone
The short attenuation zone makes the OTDR can not only detect the continuous events, but also can return to the close event loss. For example, you can now learn the loss of short fiber jumpers in network, which can help technicans to understand the situation within the link.

Blind zone also affected by other factors: pulse width. Specifications using the shortest pulse width in order to provide the shortest blind zone. However, the blind zone is not always the same length, as the pulse wider, blind spots will be stretched. Use the longest possible pulse broadband will lead to blind particularly long, but it has a different purpose.

Conclusion
On the market, there are many types of OTDR – from based fault locator to advanced equipment, can meet the different test and measurement requirements. To buy the right OTDR, you must consider the basic parameters. Because if the selected model is not suitable for the application, only based on the overall performance and price to choose equipment will appear problems. OTDR with complex specifications, the vast majority are a result of compromise. A deep understanding of these parameters and know how to verify these parameters can help buyers to make the right choice meeting their demand, maximizing productivity and cost effectiveness.

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25G Ethernet has been hitting the web world at a sudden rate and may eventually become the fastest IEEE Ethernet standard ever completed.

25G cable is divided into 25G SFP28 direct attach cable and 25G SFP28 active optical cable, both of them can transmit data at 25Gbps. What are the differences between them?

In this article, fiber-mart.com will focus on the differences between the two cables.

What is a 25G Direct Attach Cable?

25G DAC cable using silver conductor and foam insulation core, it has good attenuation performance and low delay performance, which make the signal transmission is correct, and can increase the transmission speed, is a short connection solution instead of the optical transceiver, the price is much cheaper than the same type of optical transceiver, in short distance connection applications has been widely welcomed.

What is a 25G Active Optical Cable?

25G AOC cable can be overcome the bandwidth limitation of traditional high-speed cable, and the 25G active optical cable can provide an ideal alternative solution for high-speed cable and short-distance SFP28 optical module, and the signal is more complete and higher performance. It is widely used in high-speed, high-density, and low-power data center networks.

What is difference in structure between 25G Direct Attach Cable and 25G Active Optical Cable?

The 25G DAC is made up of a copper cable and a fiber-optic transceivers at both ends. The connector is similar to the interface of the optical transceiver.But the connector modules on high-speed cables do not have expensive lasers, which greatly reduces the cost of short-range applications.

The 25G AOC consists of optical transceiver devices at both ends and composed of different length of OM3 or OM4 multimode optical fibers.The transceiver devices at both ends can provide the function of photoelectric conversion and optical transmission. This function ensures data transmission stability and application flexibility.

Compares to the 25G DAC, What are the advantages of 25G AOC?

1. The volume of 25G active optical cable is one-half of 25G high-speed cable, the weight is a quarter of it, so 25G active optical cable is much lighter than 25G high-speed cable;

2. 25G active optical cable also has better transmission performance and bit error rate, and the BER can reach 10-15;

3. 25G active optical cable has lower transmission power on the system link.

The 25G technology is the foundation of the 100G(4*25Gbps) Ethernet standard. Compared with the 40G technology, the 25G technology can provide higher port density and reduce cost, so the 25G technology has a promising prospect.

With the rapid development of 25G Ethernet technology, fiber-mart.com has introduced two types of cables, 25G SFP28 DAC and 25G SFP28 AOC to meet the 25G network needs of customers. You can also select our 25G DAC cable or 25G AOC cable customized service according to your needs.