How to Make, Lay and Repair Submarine Cables?

Ninety-nine percent of international data is transmitted by submarine communication cables laid on the sea bed between land-based stations to carry telecommunication signals across stretches of ocean. These undersea cables are hundreds of thousands of miles long and can be as deep as Everest Is tall, as well as enable our globalized society by facilitating the transfer of digital information. This article will tell how to make, lay and repair submarine cables.

How to Make Submarine Cables?

The core of undersea cables is covered with brass tape which is impervious to the assault of the aqueous worm called teredo which is the greatest enemies of submarine cables. The completed core with the brass taping is fully wrapped by jute yarn, a coarse hemp, steeped in a tarry preservative. Wound around the core, this jute yarn serves as a bedding for the outer protecting wires. After several servings of the jute yarn have been applied to the core, the whole is then covered with galvanized iron wires which vary in number and thickness according to the depth of water the cables is to lay in.

Cables laid in deep water are lighter than those laid in shoaler water. Why? Because if the cables are too heavy in deep water, the strain of raising cables would be so great that it may be impossible to recover the cables for repair purposes. Moreover, there is very little to injure submarine cables in the deep water.

How to Lay Submarine Cables?

The laying of long submarine cables is not easy. The telecom engineers toil long and tedious hours to make this possible. Submarine cables are laid down by using specially modified ships. On reaching the place selected for the landing of the cable, the ship approaches as close to the shore as possible and, letting go anchor, prepares to land the shore end. Some companies use rafts to achieve this, while others use a couple of spider-sheaves, or large VV-shaped wheels in light iron frames are sent ashore and fixed by sand anchors some 60 yards apart. Hauling lines are paid out from the ship, reeved through the sheaves and brought back on board again. One end of this continuous lines is attached to the picking-up gear and the other to the cable. The engines are then set in motion, and the cable is dragged slowly out of the ship towards the shore. As it goes, large wooden casks or inflated India rubber buoys are lashed to it every 50 or 60 feet, to keep it afloat and prevent the damage which would result from it being dragged along the bottom.

When sufficient cable has been landed, the length on shore is laid in a trench which runs from low water mark to the cable landing station (CLS), and the end is inserted through a hole in the floor. Then there will be testing and speaking instruments set up in the CLS. For day and night, the testing goes on. The ship gets slowly under way when a satisfactory test has been taken.

How to Repair Submarine Cables?

The first indication that a cable is broken or faulty is the failure of the receiving apparatus to properly record incoming signals. When a break or a fault in the line is indicated by the receiving instruments, a test is immediately made from each end of the line. These tests are taken with very sensitive apparatus. Several methods of testing are employed in the localization of complete or partial interruptions of cables, with the most general being the Wheatstone Bridge balance.

The operation of repairing submarine cables is no child’s play. It is a kind of work which requires sturdy and fearless manhood as well as skillful seamanship. Most of the breaks happen during seasons of the year when the weather conditions at sea are most severe. It is common for a cable ship to spend months at sea waiting for suitable weather conditions to carry on operations.

Conclusion

By reading the above statements, have you got more knowledge about the submarine cables’ making, laying and repairing? It may not be rich in content, but submarine cables are indeed important members of fiber cables and do play an important role in international data transmission.

Article source: www.fiberopticshare.com/how-to-make-lay-and-repair-submarine-cables.html

Splice or Connector: Which to Choose for FTTH Drop Cable Installation?

When deploying a FTTH network, subscribers must choose the right drop cable interconnect solution. So they need to decide whether to use splices (permanent joint) or connectors (easily mated and unmated by hand) for the best solution. This is for both ends of the drop cable—the distribution point and at the home’s optical network terminal (ONT) or network interface device (NID). Splices and connectors are widely used at the distribution point, while at the ONT/NID, a field-terminated connector or a spliced-on factory-terminated connector is used. This paper discusses the available interconnect solutions (splices and connectors) for FTTH drop cables and their own pros and cons.

Splices: Pros and Cons

Excellent optical performance is the most significant advantage of splices. And splicing can also eliminate the possibility of the interconnection point becoming dirty or damaged, potentially compromising signal integrity, as may happen to a connector end face when it is being handled while unmated. Contaminants will cause high optical loss or even permanently damage the connector end face. Splice enables a transition from 250µm drop cable to jacketed cable.

The major drawback of splice is its lack of operational flexibility. To reconfigure a drop at the distribution point (in the case of one subscriber dropping FTTH service and another one adding it) one splice must be removed, fibers rearranged, and two new fibers spliced. Then it requires the technician to carry special splicing tools for simple subscriber changes. Moreover, other customers’ service may be disrupted by the fiber-handling process. 250µm fiber cable is usually used at the distribution point, which is easily bent and then cause high optical loss or even break the fiber. If a splice is used at the ONT, a tray is needed to hold and protect the splice, which increase the ONT size and potentially the cost.

According to above description, splice is appropriate for drops where there is no need for future fiber rearrangement, typically in a greenfield or new construction application where all of the drop cables could be easily installed during the living unit construction.

Connectors: Pros and Cons

Due to the characteristic of being mated and unmated repeatedly, connectors can provide greater network flexibility. Without any tools, a technician can easily connect or disconnect subscribers. Connector could also provide an access point for networking testing.

Material cost is the connector’s most obvious downside. They cost more than splices, although network rearrangement is much cheaper. So providers need weight the connector’s material cost and its potential for contamination and damage against the greater flexibility and lower network management expense.

Connectors could be used to connect different subscribers as needed for distribution points. It must be installed at the ONT and then offers flexibility both at the curb and at the home.

Choose the Right Splice

Once the decision goes to splices, the type of splicing (fusion and mechanical) must be determined.

Fusion splicing has been the de facto standard for fiber feeder and distribution construction networks. Fusion splicer is used for FTTH drop splicing as it provides a high quality splice with low insertion loss and reflection (see the picture below). However, the initial capital expenditures, maintenance costs and slow installation speed of fusion splicing hinder its status as the preferred solution. Fusion splicing is best suited for companies which have invested in fusion splicing equipment and have no need to purchase additional splicing machines.

Mechanical splices are successfully deployed around the world in FTTH installation, but not popular in United States because the index matching gel inside the splices can yellow or dry out, resulting in service failures. Great strides have been made in improving gel performance and longevity over the last 20 years.

Choose the Right Connector

Once choosing to use a connector, a factory-terminated or field-terminated connector must be decided.

Factory-terminated drop cables provides high-performing and reliable connections with low optical loss. By reducing installation time, factory termination keeps labor costs low. However, factory-terminated cables are expensive compared to field-terminated alternatives. And they require a cable management system to store slack cable at the curb or in home.

The installation of field-terminated connectors can be customized by using a reel of cable and connectors. Fuse-on connectors use the same technology as fusion splicing to provide the highest level of optical performance in a field-terminated connector. Mechanical connectors provide alternatives to fuse-on connectors for field installation of drop cables.

Depending upon service provider requirements and living unit configurations, a hybrid solution of a field-terminated connector on one end of the drop cable and a factory-terminated connector on the other may be the optimal solution.

Summary

The drop cable interconnect solution is a key component of a FTTH network. Selecting the right connectivity product not only offers cost savings and efficient deployment but also provides reliable service to customers. Most FTTH drop cable installations have been field terminated on both ends of the cable with mechanical connectivity solutions.

Article source: www.fiberopticshare.com/splice-or-connector-which-to-choose-for-ftth-drop-cable-installation.html

How Much Do You Know About FTTH PON Testing?

Passive optical network (PON) is a cost-effective way to deliver high-bandwidth broadband services to users and widely deployed all over the world. FTTH uses PON technology and provides high bandwidth from the central office (CO) to subscribers. FTTH PON system achieves network reliability and makes network testing, monitoring and measuring easier. This article will tell about FTTH PON testing from the four aspects below.

Connector Inspection

Connector inspection/cleaning plays an important role in network installation and maintenance. Typically an optical microscope is used for connector inspection. To prevent accidental eye damage when inspecting fibers potentially carrying live traffic, a video microscope images the connector end-face and displays the magnified image on a handheld display. In this way, the dirt, debris or damage on the connector could be easily detected. According to the study by NTT-Advanced Technology, connector contamination and damage are the key reason for poor optical network performance.

Insertion Loss Test

In telecommunications, the term “insertion loss” expressed in dB, refers to the loss of signal power resulting from the insertion of a device in a transmission line or in an optical fiber. An insertion loss test measures the end-to-end loss of the installed link by injecting light with a known power level and wavelength at one end, and then measures the received power level output from the other end. The measured difference between the transmitted and received power levels exactly indicates the very optical loss through the network. In some occasions, insertion loss is allowed and considered acceptable when the measured loss level is lower than the budget loss level.

Optical Return Loss Test

In telecommunications, return loss expressed in dB, means the loss of power in the signal returned or reflected by a discontinuity in a transmission line which can be a mismatch with the terminating load or with a device inserted in the line. The optical return loss test injects light with known wavelength and power level into one end and measures the power level returned to that same end. Then the return loss is the difference between the injected power level and the measured return level. When the return loss is higher than the budgeted return loss target, it is considered acceptable.

Typically insertion loss test and return loss test are performed by using wavelengths at those which will be used during network operation. For FTTH PON system, 1310nm wavelength is used in the upstream direction, while 1490nm and 1550nm wavelengths are used in the downstream direction. So it is essential to have insertion and return loss testing at 1310nm, 1490nm and 1550nm wavelengths. The optical network is considered ready for activation when the insertion loss and return loss measured at each wavelength are within the budgeted levels for the link. However, in some cases, the network operator uses an optical time domain reflectometry (OTDR) as the following picture shows for more fully documented network.

Optical Time Domain Reflectometry (OTDR)

OTDR scans a fiber from one end to measure the length, loss and optical return loss of an optical network. And it also locates and measures reflective or non-reflective events in the network caused by splices, connectors, splitters, faults, etc. OTDR operates like a radar by injecting narrow pulses of light into the fiber under test. As each pulse travels down the fiber, imperfections in the fiber scatter some of the light, with some of this Rayleigh-scattered light being guided back up the fiber.

Summary

From the above description, four tests are commonly used to verify optical links. Proper testing is critical for FTTH PON installing, activating and maintaining, because excess loss or reflectance can result in poor network performance if not detected and corrected. And over time, transmission errors will occur before the need for any maintenance activity.

Article source: www.fiberopticshare.com/how-much-do-you-know-about-ftth-pon-testing.html

FTTH Access Network Based on GPON

Growing demand for high speed internet drives the new access technologies which enable experiencing true broadband. This leads telecommunication operators to seriously consider the high volume roll-out of optical fiber based access networks. In order to allow faster connections, the optical fiber gets closer and closer to the subscriber. Then FTTH (Fiber To The Home) appears the most suitable choice for a long term objective because it will be easier to increase the bandwidth in the future if the clients are wholly served by optical fibers. FTTH is a future-proof solution for providing broadband services.

Passive optical network (PON) based FTTH access network is a point-to-multipoint, fiber to the premises network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 32-128. The GPON FTTH access network is highly emphasized in this article.

Components of GPON FTTH Access Network

Taking advantages of WDM (wavelength division multiplexing), PON uses one wavelength for downstream traffic and another for upstream traffic on a single fiber. The OLT (Optical Line Terminal) is the main element of the network. Placed in the Local Exchange, OLT is the engine that drives FTTH system. OLT performs the function of traffic scheduling, buffer control and bandwidth allocation. The optical splitter splits the power of the signal and enables sharing of each fiber by many users. ONT (Optical Network Terminal) is deployed at customer’s premises and connected to the OLT through optical fiber and no active elements are present in the link.

GPON FTTH Access Network Architecture

With a tree topology, GPON is able to maximize the coverage with minimum network splits, thus reducing optical power. A FTTH access network comprises five areas, namely a core network area, a central office area, a feeder area, a distribution area and a user area as shown in the following diagram.

The core network includes the ISP (internet service provider) equipment, PSTN (packet switched or the legacy circuit switched) and cable TV provider equipment. The main function of the central office is to host the OLT and ODF and provide the necessary powering. The feeder area extends from ODF (optical distribution frames) in the CO (central office) to the distribution points. Distribution cable connects level-1 splitter with level-2 splitter. Level-2 splitter is usually hosted in a pole mounted box placed at the entrance of the neighborhood. In the user area, drop cables are used to connect the level-2 splitter to the subscriber premises.

Traffic Flow in GPON FTTH Access Network

The data is transmitted from OLT to ONT in downstream as a broadcast manner and as a time division multiplexing (TDM) in upstream. The wavelength of the downstream data is 1490 nm. Core network data services transported over the optical network reaches the OLT and then distributed to the ONTs through the FTTH network by dint of power splitting. Every home receives the packets intended to it through its ONT. The upstream represents the data transmission from the ONT to OLT and the wavelength is 1310 nm. If the signals from different ONTs arrive at the splitter input at the same time and at the wavelength 1310 nm, it will lead to superposition of different ONT signals when it reaches OLT. Thus TDMA is adopted to avoid the interference of signals from ONTs. In TDMA time slots will be provided to each user on demand for transmission of their packets. At the optical splitter packets arrive in order and they are combined and transmitted to OLT.

Conclusion

This paper presents the components, architecture, and traffic flow in GPON FTTH access network. The content may not be detailed, but GPON FTTH network architecture is indeed reliable, scalable, and secure. It is a passive network, so there are no active components from the CO to the end user, which dramatically minimizes the network maintenance cost and requirements. It is a future-proof architecture.

Article source: www.fiberopticshare.com/ftth-access-network-based-on-gpon-2.html

Introduction to PON Technologies

Passive optical network (PON) is a very significant class of fiber access system in the world and it enjoys a dominant position in the access market. GPON and EPON are the two classifications of PON. The primary differences between the GPON and EPON lie in the protocols used for upstream and downstream communications. This article will introduce PON, GPON and EPON sequentially.

Passive Optical Networks (PON)

 

A PON is a fiber network that only uses fiber and passive components like PON splitters and combiners rather than active components like amplifiers, repeaters, or shaping circuits. Thus PON network costs significantly less than those using active components, but it has a shorter range of coverage limited by signal strength. An active optical network (AON) is able to cover a range to about 100 km (62 miles), while a PON is typically limited to fiber cable runs of up to 20 km (12 miles). PON is also called FTTH (fiber to the home) network.

The typical PON arrangement is a point to multi-point (P2MP) network where a central optical line terminal (OLT) at the service provider’s facility distributes TV or Internet service to as many as 16 to 128 customers per fiber line. Dividing a single optical signal into multiple equal but lower-power signals, the optical splitters distribute the signals to users. An ONU (optical network unit) terminates the PON at the customer’s home. Usually, ONU communicates with ONT (optical network terminal). The ONU/ONT may be one device.

Gigabit Passive Optical Networks (GPON)

 

GPON utilizes optical wavelength division multiplexing (WDM) so a single fiber could be used for both upstream and downstream data. A laser on a wavelength of 1490 nm transmits downstream data, while upstream data transmits on a wavelength of 1310 nm.

While each ONU gets the full downstream rate of 2.488 Gbits/s, GPON uses a time division multiple access (TDMA) format to allocate a specific timeslot to each user. It divides the bandwidth, so each user gets a fraction such as 100 Mbits/s depending on the way the service provider allocates it. The upstream rate is less than the maximum as it is shared with other ONUs in a TDMA scheme. The distance and time delay of each subscriber are determined by the OLT. Then software provides a way to allot timeslots to upstream data for each user. The typical split of a single fiber is 1:32 or 1:64, which means each fiber can serve up to 32 or 64 subscribers. Split ratios up to 1:128 are possible in some systems.

Ethernet Passive Optical Networks (EPON)

 

Based on the Ethernet standard 802.3, EPON 802.3ah specifies a similar passive optical network with a range up to 20 km. EPON uses WDM with the same optical frequencies as GPON and TDMA. The raw line data rate is 1.25 Gbits/s in both the upstream and downstream directions.

EPON technology provides bidirectional 1Gb/s links using 1490nm wavelength for downstream and 1310nm wavelength for upstream, with 1550nm wavelength reserved for future extensions or additional services. EPON is fully compatible with other Ethernet standards, so no encapsulation or conversion is necessary when connecting to Ethernet-based networks on either end. The same Ethernet frame is used with a payload for up to 1518 bytes. As Ethernet is the primary networking technology utilized in local area networks (LAN) and now in metro area networks (MAN), no protocol conversion is needed.

Summary

 

PONs are used to provide triple-play services including TV, and Internet service to subscribers. The lower cost of passive components means simpler systems with fewer components failing or requiring maintenance. The primary disadvantage is shorter range possible, commonly no more than 12 miles or 20 kilometers. As the demand for faster Internet service and more video grows, PONs are growing in popularity. The age of PON has begun. It is a new era of access network upon us.

Article source: www.fiberopticshare.com/introduction-to-pon-technologies.html

Things You Should Know about Fiber Optic Connector Polishing

Optical fiber is utilized for high-speed and error-free data transmission across connector assemblies. So the connector end faces need to be polished to optimize performance. And also the connectors must follow acceptance criteria related to insertion and back reflection loss as well as end-face geometry specifications. This article will talk about the fiber optic connectors polishing.

Polishing Process 

 

Early physical contact connectors required spherical forming of their flat end faces as part of the polishing procedure. It involved a four-step process: epoxy removal, ferrule forming, and preliminary and final polishing. These steps utilized aggressive materials for epoxy removal and ferrule forming, generally accomplished with diamond polishing films. Now the polishing process has developed into a sequence of epoxy removal, followed by rough, intermediate and final polishing cycles because almost all connectors are manufactured with a pre-radiused end face. One goal is to avoid excessive disruption of the spherical surface, while still producing a good mating surface.

Polishing Specifications

 

Polishing specifications for fiber connectors fall into two categories related to performance and end-face geometry. Back reflection and insertion loss specifications are the most critical measures of polished end functionality. The insertion loss is the amount of optical power lost at the interface between the connectors caused by fiber misalignment, separation between connections (the air gap) and the finish quality of each connector end. The current standard loss specification is less than 0.5 dB, but less than 0.3 dB is increasingly specified. Back reflection is the light reflected back through the fiber toward the source. High back reflection can translate to signal distortion and, therefore, bit errors in systems with high data transfer rates.

Polishing Material

 

Today several types of connectorized fibers are available, the most common of which are 2.5 mm, 1.25 mm and multifiber. Connector end faces must first be air-polished to ensure a proper mating surface. This will be followed by a sequence of polishing steps depending on the type of connector, the back reflection and the insertion loss specifications. Regardless of the connector type, most polishing sequences begin with aggressive materials, including silicon carbide to remove epoxy and diamond lapping films for beginning and intermediate polishing. These remove both surrounding material and fiber at the same rate. But the last polishing step needs a less aggressive material to attack only the fiber, such as silicon dioxide. Using a material for final polishing that is too aggressive could result in excessive undercut. The wrong final-polish material can cause excessive protrusion, leading to fiber chipping and cracking during the connector mating process.

Impact Factor

 

Issues to be examined include the polishing films used, the type of epoxy and lubrication. Films are the most significant impact because the gradations and quality vary from supplier to supplier. End users should pay attention on selecting film type. Excessively aggressive films can destroy a 125-μm fiber and the end-face radius. Epoxy removal is also essential to contamination-free polishing. Some types of epoxies can be removed more easily with specific grades of silicon-carbide polishing films. The films to use in this step depend on the size of the epoxy bead mounted on the connector end face and the epoxy type. Epoxies have different varieties. Some will be tacky, some firm. In all, a contamination-free environment is essential to optimizing connector polishing.

Polishing may be an old art form, but for the immediate future, it’s here to stay. Undoubtedly inspection criteria will increase. Polishing procedures will be driven to change, and new connector style will also make us continuously strive to reinvent our approach to polishing. Fiberstore has various products about fiber optic polishing. For more details, please visit FS.COM.

Article source: www.fiber-optic-components.com/things-your-should-know-about-fiber-optic-connector-polishing.html

Evolution of Flat, PC, UPC and APC Fiber Connectors

When a connector is installed on the fiber end, loss will be incurred. Some light loss would be reflected back directly down the fiber towards the light source that generated it. These back reflections, or Optical Return Loss (ORL) will damage the laser light sources and also disrupt the transmitted signal. Fiber connectors with different polishing types have different back reflections (see the picture below). With the development of technology, four polishing types are available: flat-surface, Physical Contact (PC), Ultra Physical Contact (UPC), and Angled Physical Contact (APC). How one evolves into another? This article will tell the answer.

Flat Fiber Connector

The original fiber connector is a flat-surface connection, or a flat fiber connector. The primary issue of it is that a small air gap between the two ferrules is naturally left when mated. This is partly because the relatively large end-face of the connector allows for numerous slight but significant imperfections to gather on the surface. The flat fiber connector is not suitable for single-mode fiber cables with a 9µm core size, thus it is essential to evolve into Physical Contact (PC) connectors.

PC Fiber Connector

The Physical Contact is polished with a slight spherical design to reduce the overall size of the end-face, which helps to decrease the air gap issue faced by Flat Fiber connectors. It results in lower Optical Return Loss (ORL) with less light being sent back towards the power source.

UPC Fiber Connector

Building on the convex end-face attributes of the PC, but utilizing an extended polishing method creates an even finer fiber surface finish: Ultra Physical Contact (UPC) connector. It has a lower back reflection (ORL) than a standard PC connector and allows more reliable signals in digital TV, telephony and data systems. UPC fiber connector could be used with both single-mode fiber and multimode fiber. Usually the UPC single-mode fiber connector is blue, but the UPC multimode fiber connector is beige. (Note: 10G UPC multimode fiber connector is aqua.)

PC and UPC connectors do have a low insertion loss, but the back reflection (ORL) depends on the the surface finish of the fiber. The finer the fiber grain structure, the lower the back reflection. When PC and UPC connectors are continually mated and unmated, the back reflection will begin to degrade. So there is a need for a connector with low back reflection and it could sustain repeated matings/unmatings without ORL degradation.

APC Fiber Connector

The end faces of Angled Physical Contact connectors are still curved but are angled at an industry standard eight degrees, which allows for even tighter connections and smaller end-face radii. Combined with that, any light that is redirected back towards the source is actually reflected out into the fiber cladding, again by the virtue of the 8°angled end-face. APC connector back reflection does not degrade with repeated matings/unmatings. APC fiber connector can only be used with single-mode fiber and it is green.

It is clear that all of the connector end-face options mentioned above take a place in the market. And it is hard to claim that one connector beats the others when your specification needs to consider cost and simplicity not just optical performance. Your particular need decides which one to choose. For those applications calling for high precision optical fiber signaling, APC should be the first consideration, but less sensitive digital systems will perform equally well using UPC. For various connector options, please visit FS.COM.

Article source: www.fiber-optic-components.com/evolution-of-flat-pc-upc-and-apc-fiber-connectors.html