A Brief Introduction to PON

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Optical fiber is reliable and cost-effective, therefore FTTx (fiber to the x) is widely used as a new generation of broadband solutions. How to implement FTTx? PON, passive optical network, is generally considered to be the best approach. The text will provide a basic introduction to PON.
PON Technologies
A passive optical network is a single, shared optical fiber that uses unpowered optical splitters to enable a single optical fiber to serve multiple end-points. PON is a point to multipoint (P2M) network. Each customer is connected into the optical network via a passive optical splitter, therefore, no active electronics in the distribution network and bandwidth is shared from the feeder to the drop. Purely optical passive components in a PON architecture can withstand severe and demanding outside plant environment conditions without the need to consume energy between the central office exchange and the customer premises. The low maintenance requirements of these passive optical components will significantly reduce the cost of upgrades and operating expenditures. The picture below shows a PON architecture.
PON infrastructure
PON Standards
There are three main varieties of PON today: APON/BPON, GPON, EPON.
APON/BPON
ATM (asynchronous transfer mode) passive optical network (APON) was initiated in 1995 by ITU/FSAN and standardized as ITU-T G.983. APON was the first PON based technology developed for FTTH deployment. APON is renamed as broadband passive optical network (BPON). BPON is stable standard that re-uses ATM infrastructure. APON/BPON systems typically have downstream capacity of 155 Mbps or 622 Mbps. Upstream transmission is in the form of cell bursts at 155 Mbps.
GPON
While BPON may still be used in some systems, most current networks use Gigabit passive optical network (GPON) initiated by FSAN in the year 2001 for designing networks over 1Gbps. GPON architecture offers converged data and voice services at up to 2.5 Gbps, and enables transport of multiple services in their native format, specifically TDM and data. GPON uses generic framing procedure (GFP) protocol to provide support for both voice and data oriented services. A big advantage of GPON over other schemes is that interfaces to all the main services are provided and in GFP enabled networks packets belonging to different protocols can be transmitted in their native formats.
EPON
Ethernet passive optical network (EPON) is one of the solutions considered by new IEEE 802.3ah in September 2004, focusing on direct support of Ethernet services. EPON uses CWDM and TDM to provide bi-directional and point-to-point communications over a fiber and maintains frame structure for both upstream and downstream. EPON standards networking community renamed the term ‘last mile’ to ‘first mile’ to symbolize its importance and significance as part of the access network. The system architecture is the same as GPON but data protocols are different.
PON Components
A PON generally consists of an optical line terminal (OLT) at the service provider’s CO (central office), a number of optical network units (ONUs) or optical network terminals (ONTs) near end users, passive optical splitters and transceivers.
OLTOLT: The optical line terminal is the main element of the network and it is usually placed in the Local Exchange and it’s the engine that drives FTTH system. OLT has two float directions: one is upstream getting distributing different type of data and voice traffic from users, the other is downstream getting data, voice and video traffic from metro network or from a long-haul networkand sending it to all ONT modules on the optical distribution network (ODN). The picture on the left shows an OLT.
ONTONU/ONT: Optical network terminals or units are deployed at customer’s premises. ONTs are connected to the OLT by means of optical fiber and no active elements are present in the link. A single ONT can serve as point of access for one or multiple customers and be deployed either at customer’s premises or on the street in a cabinet. The ONU usually communicates with an ONT, which may be a separate box that connects the PON to TV sets, telephones, computers, or a wireless router. The ONU or ONT can be the same device. The picture on the right shows an ONT.
PON Splitter: Passive optical splitters divide a single optical signal into multiple equal but lower-power signals, and distribute the signals to users. The final splitting ratio can be achieved using a single splitter device.
PON Transceiver: PON transceiver is generally a bi-directional device that uses different wavelengths to transmit and receive signals between the OLT at the CO and the ONUs at the end users’ premises over a single fiber. PON transceiver can be divided into OLT transceiver module and ONU transceiver module. OLT transceiver is typically more complex than ONU transceiver.
PON splitter ＆ transceiver
PONs offer low cost connectivity for a large number of users with high security and relatively low management needs. Telecommunications companies use PONs to provide triple-play services including TV, VoIP phone, and Internet service to subscribers. A PON could also serve as a trunk between a larger system, such as a CATV system, and a neighborhood, building, or home Ethernet network on coaxial cable. As PONs grows into millions of homes, it can be seen that a new era of access networks is upon us. Fiberstore offers a series of high reliability and affordable fiber optical access devices for PONs, including OLT, ONU/ONT, PON splitters and transceivers, to meet customers’ fast growing demand of PON deployment.

Fiber Optic Tap Couplers for FTTx Systems

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

Maximizing the efficiency of optical line terminal (OLT) cards in passive optical networks (PON) in low-density and rural FTTx installations can be a major challenge. In most PON designs, it is considered ideal to connect 32 subscribers to a single OLT for maximum cost efficiency.

In rural installations, however, the density can range from a home every mile or two, to 20-30 homes scattered in random patterns. In these instances, connecting 32 users to a single OLT may be not be economical using standard optical splitters. Fortunately, tap splitters provide an easy method of maximizing OLT usage without being penalized by the number of subscribers connected.

Most PON networks use one of three physical topologies when using optical splitters.

  • The home run topology places the splitter within a service provider’s facility and is recommended for high density, short distance designs.
  • The centralized topology places a single 1:32 splitter in the OSP inside cabinet, pedestal, or even a splice closure.
  • The distributed topology has two or more splitters that are cascaded off one another, i.e., 1:2 x 1:4 x 1:4 = 32 subscribers.  It is this topology that provides the best solution.

A single 1:32 splitter adds an average of 15.8 dB of loss to the span, on top of the attenuation added by the fiber, splices, and connectors. In a standard distributed design, each 1:2 optical splitter would have a loss of 3.4 dB.  After the sixth 1:2 splitter, the total attenuation would be 20.4 dB.  After adding the fiber, splice, and connector attenuation values, the total loss would limit the number of subscribers to six or seven. Therefore, the OLT’s utilization rate would be only 20% rather than the desired optimum 100%.

For this reason, tap splitters offer a unique solution for low-density installations. These products can taper the split percentages in increments ranging from as low as 1/99 percent up to the standard 1:2 (50/50) types.  With a tap splitter in place, the cable near the first subscriber would have a drop cable spliced to the 1% leg of the splitter, and the other 99% of the optical power would be transmitted down the span.

As each subscriber would have different attenuation levels due to the splitter and span variations, a loss budget would need to be calculated for each subscriber between the OLT and their ONT. The maximum loss allowed per subscriber would vary as the distance from the OLT increases.  This — along with splitter attenuation differences based on the split percentage — requires attention to detail when planning the system.

This first subscribers on each fiber would use the 1/99 tap splitters until the loss budget required a larger split percentage such as a 2/98 splitter. The percentages would continue to increase to maintain the optical power level at the ONT until the last splitter is installed, which would normally be a 1:2 (50/50) split.

This technique helps to provide greater OLT utilization while still making use of standard OSP cables and closure products. Since tap splitters are the same size as most heat shrink protectors used to protect fusion splices, they can fit into standard splice trays, offering a cost effective technique for fiber access in low-density rural applications.

HOW POINT-TO-POINT AND PASSIVE OPTICAL FIBER NETWORKS ARE DIFFERENT

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Every broadband installer should know about the different types of fiber networks. The two main ones are: point-to-point and passive optical network (PON).
Think of how a phone call works and you’ll get the gist of a point-to-point network. There’s a direct connection between two phones, or nodes, and the other phone only hears the call.
A PON, in contrast, is a point-to-multipoint network where a signal is shared.
In the case of fiber optic networks, the point-to-point architecture would involve a switch at the central office of the Internet Service Provider (ISP) connected by multi-fiber cable to an aggregation switch in a cabinet on the street.
These switches have multiple optical ports – each of which is connected by fiber to an optical network termination or ONT in an enclosure somewhere on or near the building. These connections are dedicated and full duplex, meaning that the download and upload speed and bandwidth are the same.
As the point-to-point architecture features dedicated fiber, it’s also able to deal with higher capacity and technology changes down the road.
HOW NETWORK TYPES AFFECT FIBER PRICING
Guess why a PON is a cheaper option? There’s a lot less fiber needed than a point-to-point network. The central office would have an optical line terminal (OLT), which connects by multi-fiber to a series of passive optical splitters that divide the signal up to 64 times! This reduces costs by sharing components including an expensive laser with multiple premises. The return data can be sent using a cheaper laser as the bandwidth is less and the splitter is bidirectional.
Sounds great, but there’s a drawback with this type of network: the bandwidth is shared so speed is limited. Also, download speeds are much higher than upload speeds, which can be a problem with video conferencing and file sharing.
The optical line terminal converts the signal from the ISP’s fiber backbone and also receives the uploaded data from the customer. The passive splitter divides the light signal into two or more signals. It is usually located somewhere fairly close to the customer so as to reduce the amount of fiber required. A 1 to 64 split ratio is common and can be achieved by combining different combinations of splitter. For example, a four way splitter can connect to another splitter located closer to the premises that splits the signal again into sixteen feeds. This saves running so much fiber back to the first splitter.
As fiber continues to be rolled out to cities across North America, it’s a good idea get familiar with the different types of PONs.
-Broadcast PON or BPON was the original method and used the standard telephone network protocol ATM or asynchronous transfer mode.
-Ethernet PON or EPON uses the IEEE Ethernet standard and is capable of 1 Gbps.
-Gigabit capable PON or GPON uses Internet protocol or IP and handles data up to 2.5 Gbps downstream and 1.5 Gbps upstream. It is also triple play, which means it can handle voice, data and video. It is the system most planned fiber to the premises (FTTP) will use. However, bandwidth requirements have already exceeded this standard so work is being done to improve it.
-A new standard NGPON2 is being developed that will be capable of 40 Gbps downstream and 10 Gbps upstream with the potential of those being doubled.

Fiber Optic Fusion Splicers and How They Work

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A fiber optic fusion splicer is a device that uses an electric arc to melt two optical fibers together at their end faces, to form a single long fiber. The resulting joint, or fusion splice, permanently joins the two glass fibers end to end, so that optical light signals can pass from one fiber into the other with very little loss.
How does a fusion splicer work?
Before optical fibers can be successfully fusion-spliced, they need to be carefully stripped of their outer jackets and polymer coating, thoroughly cleaned, and then precisely cleaved to form smooth, perpendicular end faces. Once all of this has been completed, each fiber is placed into a holder in the splicer’s enclosure. From this point on, the fiber optic fusion splicer takes over the rest of the process, which involves 3 steps:
Alignment: Using small, precise motors, the fusion splicer makes minute adjustments to the fibers’ positions until they’re properly aligned, so the finished splice will be as seamless and attenuation-free as possible. During the alignment process, the fiber optic technician is able to view the fiber alignment, thanks to magnification by optical power meter, video camera, or viewing scope.
Impurity Burn-Off: Since the slightest trace of dust or other impurities can wreak havoc on a splice’s ability to transmit optical signals, you can never be too clean when it comes to fusion splicing. Even though fibers are hand-cleaned before being inserted into the splicing device, many fusion splicers incorporate an extra precautionary cleaning step into the process: prior to fusing, they generate a small spark between the fiber ends to burn off any remaining dust or moisture.
Fusion: After fibers have been properly positioned and any remaining moisture and dust have been burned off, it’s time to fuse the fibers ends together to form a permanent splice. The splicer emits a second, larger spark that melts the optical fiber end faces without causing the fibers’ cladding and molten glass core to run together (keeping the cladding and core separate is vital for a good splice – it minimizes optical loss). The melted fiber tips are then joined together, forming the final fusion splice. Estimated splice-loss tests are then performed, with most fiber fusion splices showing a typical optical loss of 0.1 dB or less.

Fiber Optic Technology In Security Applications

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This paper explores using fiber optic cabling and sensors to achieve cost-effective, long-distance intrusion monitoring.  Also covered are the advantages of these non-electric, spark-free fiber optic sensors, which enable their use in chemical plants, underground installations and other environments where explosive gases may be present.
Background
The telecommunications industry has long known the advantages of using optical fiber to send information over great distances. Now the security industry has the opportunity to use the same technology to achieve long distance intrusion monitoring using the same technology and components as that used in a telecommunications network.
It must be recognized that using fiber optics in security applications is not a new idea. Security systems exist that use specialized, highly sensitive optical fiber involving doped fiber cladding and interferomic sensing equipment.
These highly sensitive security systems are not the subject of this paper. These systems are excellent for monitoring small areas, but they are not usually deployed to monitor distances greater than 1000 feet, such as the perimeter around an airport or large factory complex.  These systems are too expensive for such large-scale deployment, and they are so sensitive they can be subject to frequent nuisance alarms caused by environmental factors when monitoring large areas.
Instead, this paper focuses a new technique of applying common, low-cost optical fiber to monitor large-scale facilities.
A Cost-Effective Approach
This new approach takes advantage of optical fiber’s sensitivity to optical losses resulting from “macrobending,” i.e. bending fiber to a radius of curvature that is tight enough to produce measurable light loss.  Because this approach uses standard communication optical fiber, the tools, installation and maintenance of this type of security system is no different than that required for a standard fiber optic telecommunications link.
Actually, this technology has been used in communication closets for years to signal an alert if a fiber optic cable in a large network becomes broken, severely bent, or is otherwise damaged.
  For example, if a backhoe operator were to accidentally break a buried fiber optic telecommunications cable, repair personnel are alerted. They then use a device called an Optical Time Domain Reflectometer (OTDR) to identify the type of problem and pinpoint exactly where it occurred along many miles of cable.
  An OTDR is required to average thousands of reflections at intervals along the fiber to identify this break point, typically requiring 10 seconds or more to complete the process.
This inherent ability of fiber optic technology to pinpoint the location of a bent or broken cable makes this same technology ideal for pinpointing the location of an intruder. For example, if an intruder breaks or bends an optical fiber that has been installed around the perimeter of a facility, the location of their intrusion attempt can be pinpointed with an OTDR that is built into the system.
  One minor problem in using this approach in a security application is that for an OTDR to detect a measurable amount of optical loss, the optical fiber must either be broken or bent at a relatively sharp angle.  In most cases, an intruder would likely bend the cable only slightly to gain access to a protected facility; the light loss produced by this slight bend would not be enough to be detected by the OTDR.
  Fortunately, the solution is straightforward.  It involves installing simple spring-loaded triggering devices along the cable route that can sense a slight disturbance to the perimeter cable, and then magnify that disturbance by creating a much more pronounced bend in the cable. This tighter bend produces enough light loss to be detected by the OTDR.
  Example # 1 – Perimeter Security
In this first example, standard fiber optic cable (with a U.V. resistant jacket) is attached to the existing fencing around a perimeter of a large facility, such as a military base. The fiber is held in place by a number of triggering devices installed on the fencing at intervals around the perimeter.
A laser injects infrared light into one end of the fiber optic cable and the light is continually monitored with the system’s built-in OTDR to determine if there has been any change in light output. If the fiber optic cable is broken, or one of the trigger devices is activated by a slight disturbance to the cable, the system triggers an alarm.
The triggering devices installed along the perimeter can include mechanical adjustments to control their level of sensitivity. System sensitivity can also be adjusted by varying the wavelength of the injected infrared light.
Example # 2 – Security for Underground Facilities
In a similar example, the fiber optic cable is attached beneath a number of manhole covers, to protect against unauthorized access to underground utilities.
An opto-magnetic triggering device is installed beneath each manhole cover.  When one of these devices sense that a manhole cover has been removed, it triggers an internal mechanism that creates a tight bend in the fiber. As in the first example, the OTDR at the head end of the system senses the resulting loss of light, triggers an alert, and pinpoints the exact location of the event.
Problems Solved
This new approach provides solutions to some of the classic challenges faced by security system designers, such as:
How to monitor very large distances in a cost-effective manner?
Fiber carries signals over a much greater distance than copper wire without requiring re-amplification of the signal. With fiber, no electrical source is required to power the sensors. This makes fiber optics a cost-effective security solution for monitoring very large perimeters, such as those around military bases, large factory complexes, and so forth.
How to reduce the greater incidence of nuisance alarms that result when monitoring large areas?
The perimeter monitoring approach discussed here involves using opto-mechanical sensors that include mechanisms that allow for tension adjustments of the fiber optic sensing cable. The sensors can be adjusted to resist wind, snow and other environmental factors to reduce or even eliminate nuisance alarms. Varying the wavelength of the light injected into the cable can also adjust the sensitivity of the system.
How to guard against someone defeating the security system?
A unique attribute of a fiber optic security system is that, unlike copper wire,  optical fiber cannot be cut, spliced into, or jumped without being detected.
How to monitor environments subject to explosive gases? Fiber optics use infrared light, not electricity, to transmit signals.  Unlike copper wire, optical fiber cannot arc or produce a spark that could trigger an explosion. This makes fiber optic sensors ideal for monitoring chemical plants, underground installations, storage tanks and many other areas where combustible gases may be present.
How to monitor environments where there are conductive or corrosive liquids or gases?
Optical fiber is made of glass, which is inert.  Unlike metallic wire, optical fiber will not corrode when subject to chemicals, and it cannot short out, even when exposed to water.
How to design a system that can survive electrical storms?
A security system that covers a wide area is more subject to damage or destruction caused by lightning storms. Optical fiber, which is glass, does not conduct electricity or lightning.  If one sensor is destroyed by a lightning strike, the lightning cannot travel over the optical cable to destroy other sensors and components within the system.
Installation Considerations
As one might conclude, security systems that use light (photons) instead of electricity (electrons) require a different skill set as far as security installers are concerned. The handling of fiber optics is not necessarily more difficult, but it does require some new knowledge and tools.
Fiber optic security systems as described above would also require a user-friendly software program to integrate the system’s OTDR with a display monitor to show tripped sensors along the cable run. Carefully labeled visual maps, showing the attenuation locations, would enable the security guard to quickly locate an intrusion attempt and provide a quick response.
As mentioned earlier, there are different types of fiber optic security systems. Installers must be familiar with the particular type of fiber optic system specified by the end user as well as the installation specifications required by the manufacturer of the system.  Only factory trained and authorized installers should attempt installation of fiber optic security systems.

An introduction to fiber cable pushing machines

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

Since they were first introduced in the 1980s, optical fiber cables have dramatically shrunk in size. A 96 fiber cable can now weigh 30kg/km (down from 300kg/km) and have a diameter of 7mm, compared to 20mm for first generation cables.
Similarly, 12 fiber drop cables used to connect individual FTTH customers now weigh less than 10kg/km and have a diameter of 1-3mm. These are normally installed into microducts, which typically range in outside diameter size from 3-18mm.
This leads to new challenges for installers when it comes to equipment. Previously cables would have been installed with heavy equipment, such as winches and capstans, or heavy compressors and blowing heads. However, this has four big disadvantages in the last drop:
1. People
It requires multiple operators, pushing up costs.
2. Disruption and mess
Customers don’t want bulky equipment in their buildings or apartments, particularly if it damages their homes.
3. Equipment cost
Operators need to invest in buying or hiring expensive machines to carry out installations.
4. Time
While the cable install itself may not take long, setting up (and dismantling machines) is time-consuming, limiting the number of installs that can be completed in a day.
What is a handheld pushing machine?
What is needed is a single operator, a self-contained installation head and low-cost, lightweight ancillary apparatus. For example, this handheld pushing machine caters for cables from 2 to 5.5m diameter and microducts from 5 to 12.7mm outer diameter.
It’s necessary to understand a little of the science behind “pushing” to see how it can be used. When pushing there is no cable tension, meaning that, unlike pulling, the challenge is not one of over-straining the cable, but in forcing the cable to buckle by over-pushing. Buckling the cable effectively locks it into the duct and can cause permanent damage.
This can be controlled by controlling and optimizing the cable stiffness and by reducing the coefficient of friction between the duct and cable. While low friction is always beneficial, stiffness is a compromise. It needs to be sufficient high to tolerate the push force exerted by the head, but low enough to enable to cable to flex around curves in the route.
Cable pushing machines typically exert around 40 to 50N of push force at the drive system, which can be a belt or driven wheels. Provided that the microduct’s internal diameter is a relatively close fit (for example no larger than a 6mm bore for a 3-4mm cable) there is no danger of the cable kinking at these force levels. This means that, for a low friction duct, a push distance of 100 to 200m is possible, depending on the degree of bend in the route.
In practice, this enables installers to deploy the majority of drop cable connections by using pushing machines.To meet these contrasting needs you need a cable designed specifically for pushing. The relatively hard polymer used as a jacket confers low friction properties when used with optimally lined microducts, providing the right level of stiffness to avoid the risk of buckling – while still having the flexibility to push around corners.
Of course, even a pushing machine requires a power source and in the interests of simplicity and cost many use a standard 10.8V Euro/12V Li-ion US unit.
Adding air assistance
Despite the optimization of pushable cables, there will always be instances where pushing alone is insufficient to deliver the required installation. For example, the route may curve unexpectedly or the actual install length may be longer than planned. In these situations air assistance will be required.
For this reason, most high quality pushing machines provide an optional inlet for compressed air sources of up to around 12-15 bar. Whereas pushing puts the cable into mild compression, the use of a high speed air flow brings a distributed force to bear on the cable, which eases it around any significant bends, meaning that the install length can be extended to over 1km. The good news is that the same ultra-low friction duct used for cable pushing provides the same excellent properties when used for air assisted deployments.
When adding air, it is important to use the right type of source. Large, wheeled and towed petrol compressors provide ample air but aren’t necessarily appropriate quality for installation.
The user needs to determine the air pressure and volume needed, although pushing equipment manufacturers can advise on this. Additionally, they need to set the degree of filtering and contaminant removal. This is because it is vital to remove moisture from the air supply using an after-cooler and water filter and to take out any residual hydrocarbons, since both of these contaminants interfere with effective blowing. One way to achieve this is to use an air cylinder which contains clean air under high pressure (alternatively a compressed nitrogen tank will work).
However, for those users who want to avoid the logistical issues associated with obtaining and returning a large number of cylinders, a small compressor remains the best option. Historically 10 bar and 15 bar compressors have provided relatively large air outputs (measured in cubic feet per minute (CFM) or cubic meters per minute (m3/min)). A substantial compressor will generate in excess of 1 m3/min but will weigh around 100kg. Such a size rules out single operator working and necessitates specialized vehicles to transport the compressor.
Coping with leakage
In the past, one of the reasons that users tended to opt for these large machines was that older style blowing heads lost a large volume of air through leakage. This meant that a modest air supply wouldn’t let cables be pushed “hard” enough to ensure they reached their destination.
However, recent work has led to the availability of one-person portable compressors. These weigh around 25kg in weight, meaning that the pushing machine and its ancillary compressor can be handled and transported by a single person in a standard commercial vehicle. This further brings down staff costs and makes pushing available for a wider range of installs.
Pushing to the future
Installers have three options when it comes to last drop deployments – blowing, pulling or pushing cables. Given the relatively short runs and often complex routes of the last drop, pushing cables is becoming much more common as an option. Using a pushing machine extends the usefulness and range of this technique, helping to bring down last drop install costs and speed up deployments. Particularly when used in combination with cable and microduct designed for pushing, they deliver major budgetary and time benefits. This means they should now be a standard part of every operator’s toolbox when carrying out FTTH deployments.