How to Determin the Fiber Optical Cable Size

24 January, 2014 (08:55) | Fiber Optic Accessories | By: fiberopticis

Quick identification of the exact size and type of a given piece of optical fiber is a routine but necessary task. If one has access to the fiber itself, the first step in identification is to remove any outer jacket material that may exist and carefully remove the plastic buffer from the fiber. (Note: If you do not have access to the fiber itself and can only view the fiber end, then proceed to the section on Core Size.) To do this, use fiber strippers designed for the task, or use a razor blade. (It takes practice to remove the plastic with a razor blade, but it can be mastered after a few repetitions.) Always cut along the fiber axis towards the cut end of the fiber. Fiber has tremendous strength in tension but is very weak in all other directions. Always stroke the razor blade away from your body. Use the razor blade to remove a sliver of plastic, then rotate the fiber 90° and repeat the process until the fiber cladding is fully exposed. Once the bulk of the plastic coating is removed, carefully clean the bare fiber with a tissue soaked in alcohol. (Note: Use only industrial grade 99% pure isopropyl alcohol. Commercially available isopropyl alcohol, for medicinal use, is diluted with water and a light mineral oil. Industrial grade isopropyl alcohol should be used exclusively.) Always wipe along the fiber axis with continuous strokes to the end of the fiber.

Cladding Size
Once the fiber is clean, take a clean machinist micrometer, such as the one in Figure 1, and carefully measure the outer diameter of the fiber. This outer diameter is the cladding diameter of the fiber. Be certain that the metal faces of the micrometer are clean. Do not over tighten the micrometer as the fiber will fracture. Table 1 shows the possible results for the most common fiber sizes and the interpretation of the results.

 

Thus, if the fiber cladding diameter measures 5.38 mils, then the fiber is almost certainly multimode with a 140 µm cladding diameter. Cladding diameter is the most important parameter when selecting the fiber optic connector size. The cladding diameter determines the size of the hole in the fiber optic connector.

Core Size
Once the cladding diameter is determined, one must find the core size, unless the cladding diameter uniquely identified the fiber size. This step requires a microscope capable of about 50X magnification. A high intensity light or penlight is useful to light the fiber end. The idea is to get a good look at the end of the fiber, and judge the fiber size from what is seen. This technique works best if the fiber is in a connector so that the fiber end is polished and flat. If that is not the case, it may be necessary to cleave the fiber so that the end can be examined. Clamp the fiber end or fiber optic connector at the focal plane of the microscope and shine the light onto the fiber end. It is sometimes useful to light the far end of the fiber as well if it is accessible. Once focus is established, compare the view with the five drawings shown in Figure 2.

Fiber-core-size
Figure 2 – Relative Core/Cladding Size

This figure represents scale drawings of the relative size of the core and cladding on the six most popular fiber types for fiber optic communication. Of these six, the last two, PM single-mode 9/125 µm and single-mode 9/125 µm, are the most common and 110/125 µm is the least common of the six types. With a little practice, it is easy to quickly and accurately identify the fiber types. When looking through the microscope, the fiber core will be very dark if the fiber is illuminated only at the microscope side. If the distant end of the fiber is illuminated, then the fiber core will appear brightly lit. Simply compare the image in the microscope to the scale drawing to the left, and match the relative size of the core to cladding. With basically only five sizes of fiber to worry about, it becomes a relatively simple matter to judge the correct size. There is also a range of much larger fibers, but these have limited use in communications applications. Other large fiber sizes include 200/230 µm, 400/430 µm and 1000/1050 µm. The latter fiber is very nearly a glass rod. There are other imaginative ways of determining fiber size. For instance, if one has a multimode LED light source available (e.g. a fiber optic video transmitter), a simple light injection test can be performed to quickly determine the fiber size. A surface-emitting LED is best for this purpose since its light injection level varies most dramatically with fiber size. The LED should be powered at a fairly constant current and then attached to a few known size fiber optic cables. For more information on LEDs see Light-emitting Diodes. In each case, note the relationship between fiber size and launched power. Once a small database of results is available, then proceed to attach the unknown fiber optic cables. It is generally very easy to distinguish between fiber sizes. One possible drawback of this method is the possibility of high loss due to a bad fiber optic connector or a stressed or broken optical fiber. Launching the LED into both ends of the fiber optic cable will usually improve the chances of a correct result.

Design and Usage of Fiber Optic Return Path

20 January, 2014 (09:35) | Applications & Solutions | By: fiberopticis

The CATV industry has responded to the demand of interactive, real-time, two-way television programming with return path technology. Return path management allows the viewer to send information from a transmitter located within the set-top-box (STB) located in the viewer’s home to the headend with the touch of a few buttons on the television remote. This advancement came from the design of the hybrid fiber coax (HFC) networks that meet the demands of increased transmission distances required for today’s cable television. Return path management is prevalent in digital broadcast systems (DBS), such as Directv and Dish Network. Typical HFC networks, illustrated in Figure 1, use coaxial cable for shorter transmission lengths between video equipment and the transmitter, or the receiver and the cable customer’s television, while the path between the transmitter and the receiver uses single-mode (SM) fiber to extend transmission distances. Even in limited distance applications, this combination allows the system designer to use the lower cost solution for each portion of the network. In return path HFC networks, illustrated in Figure 2, the same system design principle applies, but now there is bidirectional transmission between the viewer location and the headend allowing for the interactive return path management. The signals from the headend are transported over SM fiber using either a 1310 nm or 1550 nm distributed feedback laser (DFB) or Fabry Perot (FP) transmitters. The receiver contains a return path laser that sends the viewer-sent signals back to the headend. Currently, wavelength-division multiplexing technologies, such as DWDM and CWDM, increase the transmission distance and system reliability.

HFC
Figure 1 – Typical HFC Network

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Figure 2 – HFC Network with Return Path

Return Path Management Interactive Exchanges
Return path management supports the following interactive exchanges:

* Order and Payment Transactions: these orders could consist of purchasing a pay-per-view movie, merchandise from a home shopping network, or items from any store that may be available to the viewer on television channels.
* Obtaining Data from a Centralized Database: this action pertains to inquiring about local weather, television guides, and pay-per-view movie selections.
* Answer and survey information: the viewer can play along with interactive game shows, and vote in viewer integrated polls and surveys.
* Stand-alone games: the viewer can play games that relate to television shows. This exchange may consist of pay-per-play, high-score competitions, and pay-per-skill level.
* Enhanced Programming: the viewer can obtain more information on the subject of the television show. This interactivity especially pertains to nature, history, and technology based programming.
* Customizable Financial Reports: the viewer can customize a stock ticker to be displayed on the screen to watch the stock market.
* Email and chat: a viewer can chat with another viewer watching the same program, or send emails.
* Interactive Sports Channels: allows the viewers to watch two games simultaneously, choose camera angles, obtain game statistics, and score updates.
* Information Services: the viewer may get information on travel, sports, or education. These channels may be used for vacation promotions, and sporting events.
* Music Choices: the viewer may select a channel that plays streaming music of any genre. These channels may be free, pay-per-listen, or a pay channel. Also, included in these channels are information about the artist, album, and occasionally, how to purchase the album.

Return Path Management Signal Path
The return path signal, which typically ranges from five to 42 MHz, originates in the home and flows through the fiber plant toward the headend. The signal level in the plant is determined by the RF level produced by the transmitter contained within the STB, plug-in PC card, stand-alone modem, or a side-of-the-house box. However, when the signal leaves the viewer’s home it experiences losses from either the in-house cable, splitters, ground blocks, drop cables, tap ports, or feeder cables before it reaches the amplifier station port. Furthermore, each box has a different loss, but all signals coming from viewers’ homes should arrive at the amplifier at the same level. The design of the return path determines the signal level, and this requires a system designed to produce the correct level. Once the signal reaches the amplifier, it is transported through the span of cable with the correct unity gain so that the return path gain of every amplifier station matches the loss of the following cable. When the signal reaches the node station it is then transported over optical fiber to the headend. Once at the headend, the signals are converted to RF signals by the fiber optic receiver and fed to the demodulator designated for the service requested by the viewer.

Wavelength-division Multiplexed Schemes and Digitized Return Paths

Multiplexed Return Paths
As the popularity of return path management schemes increases, the ability to reliably transmit high-speed data in the five to 42 MHz bandwidth becomes more difficult. Currently, upgrades to HFC networks rely on dense wavelength-division multiplexing (DWDM) utilizing a frequency-stacking scheme. These upgrades, like most in the fiber optic industry, come from the demand for more bandwidth and better, more reliable transmission. This transmission scheme works by placing an uncooled distributed feedback laser (DFB) or Fabry-Perot (FP) laser transmitter operation at either 1310 nm or 1550 nm at the fiber node to transmit data to the secondary hub. At the secondary hub the data drives a directly modulated DWDM laser transmitter using time-division multiplexing (TDM) and frequency-stacking techniques. Figure 3 illustrates a return path HFC using DWDM and a frequency-stacking system (FSS). A reference pilot tone is generated at the frequency of 370 MHz in the block up-converter to synthesize the down-conversion; this technique removes frequency-offset errors. The composite RF signal drives each of the DWDM upstream laser transmitters at the secondary hub. The optical signal, using a 1 x 4 DWDM multiplexer, is transmitted over SM fiber to the headend. When the signal reaches the headend, an in-line erbium-doped fiber amplifier (EDFA) amplifies the optical signal. Once amplified, a demultiplexer demultiplexes the signal, and transmits the signal to four receivers. The composite RF signal gets transmitted from each receiver to the block-down converter unit, which extracts the four 5 to 42 MHz bands. The signals can then use different return path receivers to return to the viewer location.

return-path-dwdm
Figure 3 – HFC using DWDM

Digitized Return Path
Using an analog-to-digital (A/D) converter changes an analog return path into a digital return path. The analog-to-digital converter operating at 100 MHz with eight to 12 bits of resolution. The digitized signals are converted to serial bit stream with the appropriate synchronization at the fiber node to recover the signal at the optical receiver output in the local headend. At the node or secondary hub, several signals can be combined using TDM. Currently, cable television broadcasters use two 12-bit A/Ds to modulate the laser transmitter and produce approximately a 2.5 Gb/s TDM data stream. The data stream is then multiplexed at the hub. Once the data stream reaching the headend, it is demultiplexed and deserialized. In the final step, the data stream is transmitted to a digital-to-analog (D/A) converter and returned to the viewer location. The digitized return path offers a couple of advantages over an analog return path. The TDM digitized signals are transparent in a DWDM network, meaning that the signals can be transmitted throughout the network without degradation. Also, the techniques of processing digital signals reduces degradation before the A/D.

Fiber Optic Networks used in Intelligent Traffic Systems (ITS) Applications

17 January, 2014 (09:30) | Applications & Solutions | By: fiberopticis

Traffic control has been an issue since humans put the first wheels on the first cart. The modern world demands mobility. Cars represent the main method of mobility, but today’s congested highways and city streets don’t move fast, and sometimes they don’t move at all. Intelligent traffic systems (ITS), sometimes called intelligent transportation systems, apply communications and information technology to provide solutions to this congestion as well as other traffic control issues. Intelligent transportation systems offer many types of information.

traffic-jam

They may offer real-time information about traffic conditions, such as variable message signs (Figure 1) to warn of Amber Alerts, accidents, or other delays. ITS controls the flow of traffic via traffic signals, or by opening and closing special gated lanes that allow commuters to access additional traffic lanes in one direction or the other, depending on the time of day, and the direction of the heaviest commuter traffic flow. Some applications provide fog sensors that activate road lights in areas where heavy fog can occur and cause extremely hazardous driving conditions. These fog sensors may also be used to send a message to a variable message sign located before the foggy section to warn motorists of the upcoming hazard.Other forms of ITS include special radio channels for traffic updates, web sites that map driving routes or provide information on road construction. ITS features include “pay as you go” toll collections system that scan an electronic tag on the vehicle’s bumper and futuristic advanced vehicle control systems that act automatically to avoid collisions, improve vision in poor weather conditions, or wake up drowsy drivers who have fallen asleep behind the wheel.

HIWAY
Figure 1 — Variable Message Sign

Regardless of the exact function of the ITS, fiber optic links offer a valuable component in the overall traffic network. Modern ITS networks require ever-increasing data rates and payload carrying capabilities to facilitate real-time communications between a wide variety of field devices and traffic control centers (TCCs). Single-mode optical fiber-based ITS infrastructures are displacing twisted pair copper and coax for both data and video transmission requirements in urban and rural jurisdictions worldwide. Video transmission for surveillance of intersections, ramps and tunnels, incident detection or verification, and replacement of traffic signal loop sensors is an increasingly popular ITS tool. Lately, communities have been installing cameras on traffic signals to record the license plates of cars whose drivers run a red light. All of these applications require distance between the site where the information is collected and the location where the information gets stored. Video transmission that incorporates 2-way data has grown as an ITS application. This system transmits video to a control center as well as data. The control center sends data to the remote camera that allows a PTZ device to be custom positioned as needed by the person at the control center. Fiber optic links for point-to-point FM baseband transmission over single-mode fiber from fixed or PTZ-equipped roadside cameras are widely available for distances up to 90 km. Intelligent transportation systems, as with many fiber optic applications, require a network of nodes, controls and signal paths. “Fiber Optic Network Topologies” discusses the various forms this and other types of networks can take.

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Figure 2 — Traffic Sensor (left of center traffic signal) and Traffic Camera (right of center traffic signal).

Analog and Digital Video/Audio Fiber Optic Transport Systems

16 January, 2014 (09:26) | Fiber Optic Extenders | By: fiberopticis

Multi-format Analog and Digital Video/Audio Broadcast Fiber Optic Transport Systems described the system requirements of a multi-format analog and digital broadcast over fiber transport platform. In fact, many such transport platforms exist, though the types of video signals, the number of audio channels, and the ability to hot swap modules may vary from solution to solution. A state-of-the-art transport platform would allow for a number of video types and enough audio channels to support secondary audio programming (SAP) and surround sound in addition to standard television signals. This article discusses the various networks that can be configured in a multi-format analog and digital video/audio network. The elements of this transport platform include the following mix-and-match components:

* RS-250C video module with six audio inputs/outputs SDI (SMPTE 259M) video module that transports 16 embedded digital audio channels
* DVB-ASI/SMPTE 310M video module with pre-embedded audio
* Hot-swappable power supply module (universal 85-264 Volts AC)
* 1RU chassis with optics (1310 nm or 1550 nm, depending on system requirements)
* Optional CWDM, DWDM, and EDFA configurations
* Optional optical path redundancy via optical A/B switches

Using these basic components, broadcasters and cable providers can mix-and-match digitized analog video/audio with pure digital video and embedded audio, creating a uniquely flexible system.

Digitized Analog Transmission with Six Audio Inputs/Outputs
Most products on the market today that transport both analog and digital video utilize high-resolution uncompressed 12-bit A/D (analog-to-digital) conversion to transport broadcast quality signals. Employing a high signal-to-noise ratio (SNR) provides excellent broadcast quality video that surpasses the RS-250C short-haul video standard. Six channels of digitized audio, with 24-bit resolution, offers CD-quality sound allowing the end user to meet the FCC’s SAP requirements and additional audio channels required for surround sound programming. Figure 1 illustrates a point-to-point network that uses two digitized video/audio modules, each offering one video and six audio channels, for a total of two digitized analog video channels and 12 CD-quality audio channels on a single fiber.

2dig-ana-12cd
Figure 1 – Transport of Two Digitized Analog Video and 12 CD Quality Audio Channels.

SDI (SMPTE 259M) and DVB-ASI/SMPTE 310M Transmission with Pre-embedded Audio Signals
In general, most analog/digital transport platforms can carry SDI and DVB-ASI video at the same time. The products can transport SMPTE 259M compliant video at a data rate of 270 Mb/s. Using multiple interfaces, products can typically transport two SDI video streams on one fiber. Analog and digital transport platforms can also transmit either 19.4 to 40 Mb/s DVB-ASI or SMPTE 310M compliant digital signals. Figure 2 illustrates digital transmission of SDI and DVB-ASI/ SMPTE 310M. The units also support the transmission of pre-embedded digital audio channels.

Digitized Analog and DVB-ASI
Figure 3 illustrates a network with the ability to simultaneously transport a combination of analog and digital signals. For example, a studio may need to transport both a broadcast quality analog video and a SMPTE 259M SDI video to a remote location, such as an editing house or a duplication facility.

analog-and-digital
Figure 3 – Simultaneous Transport of Analog and Digital Signals

 

Bidirectional Analog and Digital fiber optic Transport

Increase Fiber Capacity with CWDM Technology
CWDM products are passive, bidirectional devices which allow individual wavelengths to be combined for transport over on single-mode optical fiber and separate into individual optical outputs at the receive end, increasing the fiber capacity. Configurations range from simple point-to-point and point-to-multipoint, to large scale video networks over numerous add/drop sites. Figure 4 illustrates the point-to-point configuration for four, eight, and 16 channel systems, ideal for applications such as studio-to-studio, studio-to-transmitter, studio-to-headend, and distance learning.

mult-ch-pnt-to-pnt
Figure 4 – Four, Eight, and 16 Channel Point-to-Point Configurations

By incorporating CWDM technology, bidirectional applications for transporting both analog and digital video and associated audio may be configured with ease. Figure 5 shows a bidirectional system that will transmit up to eight optical channels over a single fiber. Each transmission site contains both transmitters and receivers, ideal for headend-to-headend, interactive distance learning, return feeds, and studio-to-studio transmitter links.

bidir-tx-8ch
Figure 5 – Bidirectional Transmission of Eight Optical Channels

Optical Redundancy Increases System Reliability
Using an optical A/B switch, the analog and digital transport solutions can be configured for fail-safe redundant signal operation. The A/B switch monitors the optical level on the primary fiber. Should the optical level fall below the optical trip threshold, the switch automatically switches to the secondary fiber path without the intervention of the system operator. The unit returns to the primary path when the correct optical power is detected. This configuration allows the user assurance that this useful analog and digital transport technology will not fail. Figure 6 shows unidirectional transmission with optical path redundancy.

optical-redun
Figure 6 – Unidirectional Transmission with Optical Path Redundancy

Analog and Digital Transport Applications

Studio-to-Studio
Broadcasters are concerned with retaining the highest quality video and audio throughout the content creation and dissemination process. Fiber optic cable’s inherent EMI and RFI immunity ensures the broadcaster that the signal quality will suffer no degradation as a result of these effects. Fiber’s increased bandwidth increases transmission distance as well.

studio-to-studio
Figure 7 – Studio-to-Studio Transport

Studio-to-Tower
Many broadcasters are making the transition from analog to digital transmission from their towers. Utilizing analog video and DVB-ASI/SMPTE 310M modules, the broadcasters can send content from their broadcast studio directly to the transmission tower over fiber optic cable. At the tower site, and ATSC encoder compresses the signal before transmitting over the air.

studio-to-tower
Figure 8 – Studio-to-Tower Transport

Studio-to-Headend over fiber
Cable providers offer several level or “tiers” of service to their customers, ranging from local and public access television stations at the low tier, up to digital cable and VOD (Video on Demand) at the high tier. Much of this programming arrives at the cable providers CATV headend in DVB-ASI or analog formats. The digital and analog transport products transmit either analog or DVB-ASI, or both at the same time.

studio-to-headend
Figure 9 – Studio-to-Headend Transport

Distance Learning
Analog and digital transport can be used to create a large scale video/audio distance learning transport networks capable of supporting an area of many kilometers from headend routing systems to multiple remote school/classroom sites. Using CWDM technology, each remote site can operate on a single wavelength, allowing up to eight sites to be networked. Multiplexed signals from the headend get added or dropped via a CWDM, allowing full two-way interactive video/stereo audio transmission of high quality digital signals. Each remote classroom contains a television and a microphone and camera for receiving and transmitting distance learning programming. This will allow school systems to broadcast lessons from one classroom to many other classrooms while still providing feedback and interaction between the teacher and the students. Figure 10 illustrates a four-channel distance learning/videoconferencing network.

distance-lrn-3762
Figure 10 – Four-channel Distance Learning/Video conferencing Network

Fiber Optical Communication Networks overview

16 January, 2014 (09:04) | Applications & Solutions | By: fiberopticis

All fiber optic networks involve the same basic principle: information can be sent to, shared with, passed on, or bypassed within a number of computer stations (nodes) and a master computer (server). In addition to various topologies for networks, a number of standards and protocols have been developed, each with their own advantages, topologies, and medium requirements. This article discusses these standards and protocols, including: ATM, Ethernet, FDDI, Fibre Channel, ISDN, and SONET.

Asynchronous Transfer Mode (ATM over Fiber)
Asynchronous transfer mode (ATM) is widely deployed as a network backbone technology. This technology integrates easily with other technologies, and offers sophisticated network management features that allow signal carriers to guarantee quality of service (QOS). ATM may also be referred to as cell relay because the network uses short, fixed length packets or cells for data transport. The information is divided into different cells, transmitted, and re-assembled at the receive end. Each cell contains 48 bytes of data payload as well as a 5-byte cell header. This fixed size ensures that time critical voice or video data will not be adversely affected by long data frames or packets. ATM organizes different types of data into separate cells, allowing network users and the network itself to determine how bandwidth is allocated. This approach works especially well with networks handling burst data transmissions. Data streams are then multiplexed and transmitted between end user and network server and between network switches. These data streams can be transmitted to many different destinations, reducing the requirement for network interfaces and network facilities, and ultimately, overall cost of the network itself. Connections for ATM networks include virtual path connections (VPCs), which contain multiple virtual circuit connections (VCCs). Virtual circuits are nothing more than end-to-end connections with defined endpoints and routes, but no defined bandwidth allocation. Bandwidth is allocated on demand as required by the network. VCCs carry a single stream of contiguous data cells from user to user. VCCs may be configured as static, permanent virtual connections (PVCs) or as dynamically controlled switched virtual circuits (SVCs). When VCCs are combined into VPCs, all cells in the VPC are routed the same way, allowing for faster recovery of the network in the event of a major failure. While ATM still dominates WAN backbone configurations, an emerging technology, gigabit Ethernet, may soon replace ATM in some network scenarios, especially in LAN and desktop scenarios. A discussion of Ethernet follows.

Ethernet over Fiber
Ethernet began as a laboratory experiment for Xerox Corporation in the 1970′s. Designers intended Ethernet to become a part of the “office of the future” which would include personal computer workstations. By 1980, formal Ethernet specifications had been devised by a multi-vendor consortium. Widely used in today’s LANs, Ethernet transmits at 10 Mb/s using twisted-pair coax cable and/or optical fiber. Fast Ethernet, transmits at 100 Mb/s, and the latest developing standard, gigabit Ethernet, transmits at 1,000 Mb/s or 1 Gb/s. Figure 1 illustrates the basic layout of an Ethernet network.

ethernet-01
Figure 1 — Basic Layout of an Ethernet Network

The formal Ethernet standard known as IEEE.802.3 uses a protocol called carrier sense multiple access with collision detection (CSMA/CD). This protocol describes the function of the three basic parts of an Ethernet system: the physical medium that carries the signal, the medium access control rules, and the Ethernet frame, which consists of a standardized set of bits used to carry the signal. Ethernet, fast Ethernet, and gigabit Ethernet all use the same platform and frame structure. Ethernet users have three choices for physical medium. At 1 to 10 Mb/s, the network may transmit over thick coaxial cable, twisted-pair coax cable or optical fiber. Fast 100 Mb/s Ethernet will not transmit over thick coax, but can use twisted pair or optical fiber as well. Gigabit Ethernet, with greater data rate and longer transmission distance, uses optical fiber links for the long spans, but can also use twisted-pair for short connections. CSMA/CD represents the second element, the access control rules. In this protocol, all stations must remain quiet for a time to verify no station in the network is transmitting before beginning a transmission. If another station begins to signal, the remaining stations will sense the presence of the signal carrier and remain quiet. All stations share this multiple access protocol. However, because not all stations will receive a transmission simultaneously, it is possible for a station to begin signaling at the same time another station does. This causes a collision of signals, which is detected by the station speaking out of turn, causing the station to become quiet until access is awarded, at which time the data frame is resent over the network. The final element, the Ethernet frame, delivers data between workstations based on a 48-bit source and destination address field. The Ethernet frame also includes a data field, which varies in size depending on the transmission, and an error-checking field which verifies the integrity of the received data. As a frame is sent, each workstation Ethernet interface reads enough of the frame to learn the 48-bit address field and compares it with its own address. If the addresses match, the workstation reads the entire frame, but if the addresses do not match, the interface stops reading the frame. Ethernet at all data rates has become a widely installed networks for LAN, MAN, and WAN applications. Its ability to interface with SONET and ATM networks will continue to support this popular network. In LANs, Ethernet links offer a scalable backbone, and a high speed campus data center backbone with inter-switch extensions. As a metro backbone in MANs, gigabit Ethernet will interface in DWDM systems, allowing long-haul, high speed broadband communications networks. Finally, Ethernet supports all types of data traffic including data, voice, and video over IP. Figure 2 illustrates a typical Ethernet deployment scenario.

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Figure 2 — Switched, Routed Gigabit Ethernet Network

Gigabit Ethernet has emerged as a cost-effective alternative to ATM network structures. ATM has a greater cost, and he standards and products used to transmit ATM are still in flux, unlike the proven paradigm of Ethernet. In addition, system complexity is reduced in gigabit Ethernet, and because it works with existing Ethernet formats, the system does not require emulation software to act as a gateway between an Ethernet LAN and an ATM network. Table 1 outlines how Ethernet and gigabit Ethernet offer the same benefits of ATM.

ATM-and-Ethernet

Fiber Distributed Data Interface (FDDI)
FDDI usually finds placement as a high-speed backbone for mission-critical or high traffic LANs, MANs or WANs. Operating at a data rate of 100 Mb/s, FDDI was originally designed for optical fiber transmission. An unbroken FDDI network can run to 100 km with nodes up to 2 km apart on multimode fiber, and 10 km apart on single-mode fiber. However, a copper standard exists, known as a copper distributed data interface, or CDDI, although it is restricted to distances of only 100 m. Any one ring, copper or fiber, may contain as many as 500 nodes. FDDI’s niche is high reliability, the result of its counter-rotating ring topology illustrated in Figure 3. A dual-attached station connects the two paths via Port A, the primary path, and Port B, the secondary path. Port A may also have a number of M ports which attach to single-attached stations such as computer workstations. Information is passed around the FDDI ring via a token generated by the main station. The token moves around the ring until a requires access to the network. When a station needs to transmit information, it takes control of the token, and transmits in an FDDI frame, after which it releases the token, signaling that it has completed its transmission. Each FDDI frame contains the address of the station or stations that need to receive this frame. All nodes read the frame, but only to verify this address. If the node address and the FDDI frame address match, the station extracts the data from the frame and then retransmits it to the next node on the ring. When the frame returns to the originating station, that station strips the frame, and the network remains quiet until a node captures the token. A second generation network, FDDI-2 currently under development, supports the transmission of voice and video information as well as data. It uses a circuit-switched configuration in which a physical path is obtained for and dedicated to a single connection between two end-points in the network for the duration of the connection. In addition, another variation of FDDI, called FDDI full duplex technology (FFDT) uses the same network infrastructure but can potentially double data rates. If the secondary ring is not needed for backup, it can also carry data, extending the network’s capacity to 200 Mb/s. Work is underway to connect FDDI networks to the developing synchronous optical network (SONET).

Counter-rotating
Figure 3 — Dual Counter-rotating Ring Topology

Fibre Channel
Fibre channel, originally developed in the United Kingdom, was designed to provide high bandwidth (100 Mb/s), long distance connectivity (over several kilometers), and flexible topologies that allow the use of the same physical interface and media as existing channel and networking protocols. In fact, fibre channel was an attempt to combine the benefits of both channel and network topologies. Channels are closed, direct, structured and predictable mechanisms for data transmission. No decision making is required, allowing for a high speed, hardware intensive environment. Channels connect peripheral devices such as disk drives and printers, to a work station using protocols such as HIPPI or SCSI. By contrast, networks are unstructured and unpredictable in that much decision making is required to correctly route the data from one point to another.Fibre channel’s biggest impact has been made on storage devices, using an upper layer SCSI protocol. This gives fiber channel the ability to access mass storage devices more quickly and from a greater distance. Three main topologies include a point-to-point configurations, an arbitrated loop topology or a fabric topology. As a result, the most common of these three is the arbitrated loop, illustrated in Figure 4. In a fibre channel arbitrated loop (FC-AL), when a device is ready to transmit to the rest of the network, it first arbitrate for control of the loop. This is done via an arbitrate primitive signal (APBx), and each device in the network has its own APBx. It submits the signal to the network control, and the signal is looped around until the originating device receives its APBx, its signal that it has control and may begin transmitting. An open primitive signal allows the device to communicate with other devices in the loop by creating, essentially, a point-to-point connection between the two devices. All other devices in the loop simply repeat the data. A fabric topology represents the costliest configuration, because it requires a cross-point switch to connect multiple devices in a switched configuration. The benefit of this topology is that many devices can communicate at the same time; the media is not shared.

arbitrated-loop
Figure 4 — Arbitrated Loop

Integrated Services Digital Network (ISDN)
ISDN has been designed to replace the standard telephone system and provide greater numbers of digital services to telephone customers, such as digital audio, interactive information services, fax, e-mail, and digital video. ISDN uses asynchronous transfer mode which can handle data transmission in both connection-oriented and packet schemes. As with regular telephone lines, the user must pay a fee for use of the line. Basic rate ISDN or BRI offers two simultaneous 64 kb/s data channels as well as a 16 kb/s carrier channel for signaling and control information. The combined data rate, 128 kb/s, allows for videoconferencing capabilities. Multiple ISDN-B connections further increase the data rate and the transmission quality. Primary rate ISDN (PRI) offers 30 channels (of 64 kb/s each), giving a total of 1920 kb/s. As with BRI, each channel can be connected to a different destination, or they can be combined to give a larger bandwidth. These channels, known as “bearer” or “B” channels, give ISDN tremendous flexibility. The original version of ISDN employs baseband transmission. Another version, called B-ISDN, uses broadband transmission and is able to support transmission rates of 1.5 Mb/s. B-ISDN requires fiber optic cables and is not yet widely available.

Synchronous Optical Network (SONET)
SONET is the American National Standards Institute (ANSI) standard for synchronous data transmission on optical media. The international equivalent of SONET is synchronous digital hierarchy (SDH). SONET provides standards for a number of line rates up to the maximum line rate of 39.808 gigabits per second and beyond. SONET is considered to be the foundation for the physical layer of the broadband ISDN (B-ISDN). Asynchronous transfer mode runs as a layer on top of SONET as well as on top of other technologies. The network defines optical carrier levels and their electrical equivalents, called synchronous transport signals (STS) for fiber optic transmission. The first step in the process involves multiplexing multiple signals by generating the lowest level or base signal, called STS-1. Its optical carrier counterpart is called OC-1, and it transmits at 51,480 Mb/s. Other levels operate from 155 Mb/s up to 40 Gb/s. The basic network elements include the terminal multiplexer (PTE), a regenerator (as needed for long distance transmissions), an add-drop multiplexer (ADM), for use in point-to-multipoint configurations, wideband digital cross-connects (W-DCS), broadband digital cross-connects, and the digital loop carrier. Together, these elements may be used in a point-to-point, point-to-multipoint (hub), or ring network configuration. Figure 5 illustrates a typical hub network configuration.

sonet-hub
Figure 5 — SONET Hub Network

SONET provides a number of benefits over asynchronous systems. Its multiplexing technique allows simplified synchronous clocking and reduced back-to-back multiplexing, which reduces circuit complexity and cost. SONET’s optical interconnections meet a number of vendor requirements. The hub configuration adds greater flexibility to the system, allowing the convergence of a number of types of network protocols, ATM, Internet protocol, etc.

Broadband Video Fiber Optic Transmission

10 January, 2014 (04:29) | Applications & Solutions | By: fiberopticis

Broadband has become synonymous with “always on” Internet connections and digital high-definition television (HDTV). It describes the digital technologies that provide consumers with integrated access to voice, high-speed data services, video-on-demand (VOD), and interactive delivery services. This transmission concept developed slowly, and carried many of promises along the way. Today, most of these promises are being realized. It is estimated that 21.2 million households will have broadband access by 2003. The FCC’s Telecommunications Act of 1996 mandating that any communications business be allowed to compete in any market by 2006, affectively raising the performance bar, acts as a driving force to bring homes and industries into the broadband realm. The numerous advantages of broadband, in addition to its speed, include enhanced picture quality, reliable transmission, and convenience. The convenience covers both television and computer use in the sense that the “always on” digital connection allows for video-on-demand and real-time interactions that before were not possible or severely limited in either media.

Broadband Video Fiber Optic Transmission Applications
Broadband, a blanket term, describes an application that utilizes high speed, high bandwidth transmission. In the simplest description, broadband is merely a broader band through which information can pass; it is sometimes referred to as the “fat pipe.” This means that multiple channels and can be transmitted digitally over a hybrid fiber coax or optical fiber at one time. The FCC requires that the quality of broadband, as an information service, carries a capacity of 200 kbps upstream, direction opposite the data flow or information from computer to the Internet, and downstream, direction of the data flow or information for the Internet to the computer. This carrying capacity accommodates the fiber optic converter of audio, video, and data services in an interactive format. Internet connections like DSL and cable modems all use the broadband scheme. Table 1 illustrates the amount of time it takes to download a 30 second video clip from the Internet based on connection speed. The disparity among the different connection speeds makes it apparent that broadband allows for more advanced and demanding Internet applications.

broadband

Video-on-demand applications, allow viewers to digitally record programs for viewing at a later time. This makes television viewing more convenient by permitting the viewer to watch virtually whatever whenever from the comfort home. This technology operates through connecting the television set to the source (a set-top box, also known as digital video recorders, or DVRs) and recording to a hard drive. In addition to recording shows, other options for video-on-demand include searching for upcoming features and control over live television.

Baseband Video Fiber Optic Transmission Systems

8 January, 2014 (04:19) | Applications & Solutions | By: fiberopticis

Baseband Video Fiber Optic Transmission Systems consists of one video picture being sent point-to-point, such as the video output of a VCR to the video input of a monitor. Figure 1 illustrates simple point-to-point transmission. There exist two levels of service for baseband video: broadcast studio and consumer. These types describe, primarily, the quality of the signal. Broadcast studio quality requires a much higher signal fidelity, while consumer quality baseband requires is less demanding. In addition to the difference in signal fidelity, there is also a difference in the connectors typically used for the transmission of these signals. The broadcast baseband applications typically use a BNC connector and the consumer baseband applications typically uses an RCA connector.

fiber-optic-link
Figure 1 – Point-to-Point Transmission

bnc-connector
rca-connectors
Figure 2 – BNC and RCA Connectors

Baseband Video Signals
The most basic form of a television signal is a baseband video signal, also referred to as a composite video signal. In an AM baseband system, the input signal directly modulates the strength of the transmitter output, in this case light. The baseband signal contains information relative to creating the television picture only. The following information is carried on a baseband signal:

• Scanning: drawing the television picture
• Luminance: the brightness of the picture
• Chrominance: the color of the picture

The creation of the baseband signal produces a range of frequency components. The highest frequency in a baseband signal is also its bandwidth. The lowest frequency ranges close to zero Hz or DC. The video output of a television camera or video tape recorder has its highest frequency, therefore, its bandwidth, at either 4.2 or 6 MHz, depending on the type of TV format used. Looking at an actual baseband signal, illustrated in Figure 3, we can see that the camera and the video display are scanned horizontally and vertically. The horizontal lines on the screen are scanned alternately, with the odd numbered lines first and the even numbered lines second, or vice versa. (Figure 3B depicts the initial scan of the odd numbered lines.) This method is known as an interlacing system. The second method is to scan the lines sequentially; this is known as progressive Scanning. The camera and receiver must be synchronized when scanning and reproducing an image. The horizontal and vertical sync pulses regulate the synchronization of the camera and receiver, illustrated in both 3B and 3C, and starts a horizontal trace. As seen in Figure 3A, during the horizontal blanking interval, the beam returns to the left side of the screen and waits for the horizontal sync pulse before tracing another line. The dotted line illustrated the horizontal retrace. When the beam reaches the bottom of the screen, it must return to the top to begin the next field. This is called the vertical retrace, which is signaled by the vertical sync pulse illustrated in Figure 3C. The vertical retrace takes much longer than the horizontal retrace, therefore, a vertical blanking interval ensues to synchronize the two signals. During both the horizontal or vertical blanking intervals no information appears on the screen.

baseband-vid-sig
Figure 3 – Baseband Composite Video Signals

Baseband Video Applications
Figure 4 illustrates a multimedia baseband fiber optic transmission systems.multimedia-baseband-trans

Figure 4 – Multimedia baseband transmission

Analog Fiber Optic Transmission VS Digital Fiber Optic Transmission

7 January, 2014 (03:33) | Applications & Solutions | By: fiberopticis

There are three predominant methods of encoding a transmission signal. Amplitude modulation(AM), and frequency modulation(FM) are both analog modulation schemes. The third method is digital modulation. The Table 1 outlines the basic characteristics of the three modulation schemes.

Digital_Transmission

AM, FM, and digital modulation are described in detail in other sections of this web site. One key difference between analog and digital fiber optic transmission involves the bandwidth, or transmission capacity required for both schemes. Analog signals require much less bandwidth, only about 4.5 MHz with a 143.2 Mb/s data rate. for the average NTSC video signal. By comparison, some digital video transmission standards require as much as 74.25 MHz with a data rate of 1485 Mb/s. Advances in single-mode optical fiber make these higher rates more accessible for longer distances. Copper coax fails to perform at these data rates. Another difference between analog and digital transmission deals with the hardware’s ability to recover the transmitted signal. Analog modulation, which is continuously variable by nature, can often require adjustment at the receiver end in order to reconstruct the transmitted signal. Digital transmission, however, because it uses only 1′s and 0′s to encode the signal, offers a simpler means of reconstructing the signal. Both types of modulation can incorporate error detecting and error correcting information to the transmitted signal. However, the latest trend in signal transmission is forward error correcting (FEC). This scheme, which uses binary numbers, is suited to digital transmission. Extra bits of information are incorporated into the digital signal, allowing any transmission errors to be corrected at the receive end. A third important difference relates to the cost of analog transmission links compared to digital transmission links. Because the circuitry required for digital transmission is more complex, the cost is often much higher. In short distance applications, analog modulation will almost always be the most cost-effective system to specify. However, today’s demand for high speed Internet, video-on-demand, video conferencing, and “pushed” data directly to our home computers requires moderate to long-distance fiber optic transmission systems to specify digital equipment. And as is the case with any form of technology, greater demand will lead to mass production, inevitably driving the cost of digital systems down. However, it will always be true that the decision to specify one type of modulation over the other involves the same system design considerations.

How to test the fiber optic transmitter and receiver?

30 December, 2013 (16:50) | Fiber Optic Extenders | By: fiberopticis

Introduction
Most fiber optic transmitter is designed to be as simple as the application will allow. However, due to the complexity of some of the applications, things go wrong. In many cases, resolving a troubleshooting challenge can be as simple as properly cleaning the optical connectors. See article “Fiber Optic Connectors” for more information on cleaning optical connectors. In more complex scenarios, additional troubleshooting will be required. This article describes some of the more common problems that have been encountered.

Fiber Optic Problems and Comments

1. PROBLEM: No optical power out of the transmitter or transceiver.
A) Check the fiber optic transmitter or fiber optic transceiver power connection. If there is less than the specified supply voltage between power pins, a higher current power supply may be required. Be sure the power supply polarity is correct.
B) Be sure that data input is present. Many data links put out no light if a logic “0″ is input. Be sure that the input data is alternating between 0′s and 1′s, otherwise no output light may be present.

2. PROBLEM: No optical power out of the fiber at the optical input port.
A) Check power at optical output port of the transmitter or transceiver. If optical power is present at optical output port, ensure that the proper fiber is connected at optical input port. Verify the integrity of the fiber.

3. PROBLEM: Receiver output electrical signal is noisy or intermittent.
A) Check that optical loss does not exceed the rated value between transceivers or between the fiber optic transmitter and fiber optic receiver. If the loss is too high, reduce optical loss, or insert a repeater between transceivers or the transmitter and receiver. High loss may be caused by bad connectors, improperly seated connectors, or bad splices. See Fiber Optic Connectors for information on the proper use of connectors.
B) Check the wavelength of the transceivers or transmitter and receiver. Detectors are typically optimized for one wavelength. Mixing 850 nm units and 1310 nm units, for instance, may result in poor or no performance.
C) Be sure that the transmitter and receiver enclosures are grounded. It should be noted that 850 nm FM video links are generally bandwidth-limited at distances over 1.5 km. When this occurs, the receiver output will not be usable even when sufficient optical power is received.

4. PROBLEM: No signal out of the receiver.
A) Verify signal input at transmitter. Be sure that an electrical input signal is present at the transmitter input. Also verify that the signal has proper amplitude, frequency, and impedance. For instance, a video signal must be 1.0 Volt peak-to-peak. Several high-speed data links can be configured for positive or negative ECL levels. Be sure that the power supply voltages and connections are correct.
B) Check receiver power connection. If there is less than the specified voltage between the power supply pins, a higher current power supply may be required. Be sure that the power supply polarity is correct.

5. PROBLEM: Signal amplitude out of the fiber optic receiver is too large.
A) Verify that the receiver output is terminated into the proper impedance. Many data links and most audio and video links require that a terminating resistor be added to the receiver output. If this resistor is omitted, the amplitude will be two times too large. If the value is incorrect, the receiver output level may be too large or too small depending on the value of the resistor. Video links typically require a 75 Ohm terminating resistor. Audio links typically require a 600 Ohm or 10 kOhm terminating resistor. Low-speed data links such as RS-422 and RS-485 typically require a 120 Ohm terminating resistor and high-speed ECL data links typically require a 50 Ohm terminating resistor.

6. PROBLEM: Signal out of the receiver is distorted.
A) Verify the input signal at the transmitter. Must be 1.0 Volt peak-to-peak or less. A larger signal will cause distortion.
B) Verify the fiber size. See Determining Fiber Size details. Fibers with larger core sizes may overload the receiver. Verify that receiver power is within specifications.

7. PROBLEM: Data errors occur.
A) Be sure that the power supply voltage is correct and clean for both the transmitter and receiver or transceivers.
B) Be sure that the enclosures are properly grounded, especially when using a wall-mount power supply.
C)
Be sure that the data inputs and outputs are properly terminated.

D) Be sure that the input data levels are correct.
E)
Be sure that the optical input level to the receiver is within valid limits.

8. PROBLEM: Signal out of diplexer/demultiplexer is noisy.
A) Check the copper or fiber optic link between the diplexer mux/demux pair. Ensure that the losses in the optical path do not exceed the loss budget of the transmitter/receiver pair used.

9. PROBLEM: Audio signal amplitude out of diplexer demultiplexer is too large or distorted.
A) Verify the signal input at the multiplexer.
B)
Verify that the demultiplexer audio output has been properly terminated into the required impedance, usually 600 Ohm or 10 kOhm terminations.

C) The audio input to the multiplexer must be 1.0 Volt RMS maximum. This translates to about 4 Volts peak-to-peak maximum.

What is Fiber Optic Couplers & Fiber Optic Splitters

29 December, 2013 (16:38) | Fiber Optic Accessories | By: fiberopticis

Fiber, connectors, and splices rank as the most important passive devices. However, closely following are tap ports, switches, wavelength-division multiplexers, bandwidth couplers and splitters. These devices divide, route, or combine multiple optical signals. Some of the most common applications for couplers and splitters include:
* Local monitoring of a light source output (usually for control purposes).
* Distributing a common signal to several locations simultaneously. An 8-port coupler allows a single transmitter to drive eight receivers.
* Making a linear, tapped fiber optic bus. Here, each splitter would be a 95%-5% device that allows a small portion of the energy to be tapped while the bulk of the energy continues down the main trunk.
For more information on switches and wavelength-division multiplexers see Fiber Optic Components.

Fiber Optic Couplers
Fiber optic couplers either split optical signals into multiple paths or combine multiple signals on one path. Optical signals are more complex than electrical signals, making optical couplers trickier to design than their electrical counterparts. Like electrical currents, a flow of signal carriers, in this case photons, comprise the optical signal. However, an optical signal does not flow through the receiver to the ground. Rather, at the receiver, a detector absorbs the signal flow. Multiple receivers, connected in a series, would receive no signal past the first receiver which would absorb the entire signal. Thus, multiple parallel optical output ports must divide the signal between the ports, reducing its magnitude. The number of input and output ports, expressed as an N x M configuration, characterizes a coupler. The letter N represents the number of input fibers, and M represents the number of output fibers. Fused couplers can be made in any configuration, but they commonly use multiples of two (2 x 2, 4 x 4, 8 x 8, etc.).

Fiber Optic Splitters
The simplest couplers are fiber optic splitters. These devices possess at least three ports but may have more than 32 for more complex devices. Figure 1 illustrates a simple 3-port device, also called a tee coupler. It can be thought of as a directional coupler directional coupler. One fiber is called the common fiber, while the other two fibers may be called input or output ports. The coupler manufacturer determines the ratio of the distribution of light between the two output legs. Popular splitting ratios include 50%-50%, 90%-10%, 95%-5% and 99%-1%; however, almost any custom value can be achieved. (These values are sometimes specified in dB values.) For example, using a 90%-10% splitter with a 50 µW light source, the outputs would equal 45 µW and 5 µW. However, excess loss hinders that performance. All couplers and splitters share this parameter. Excess loss assures that the total output is never as high as the input. Loss figures range from 0.05 dB to 2 dB for different coupler types. An interesting, and unexpected, property of splitters is that they are symmetrical. For instance, if the same coupler injected 50 µW into the 10% output leg, only 5 µW would reach the common port. Click here to view the table of typical insertion losses for modern single-mode couplers.

tee-coupler
Figure 1 – Typical Tee Coupler

Coupler and Splitter Applications
In applications that require links other than point-to-point links, optical couplers find the widest use. This includes bidirectional links and local area network (LAN). In LAN applications, either a star network topology or a bus topology incorporate couplers. Figure 2 illustrates a star topology, notice that stations branch off from a central hub, much like the spokes on a wheel. The allows easy expansion of the number of workstations; changing from a 4 x 4 to an 8 x 8 doubles the system capacity. The star coupler divides all outputs allowing every station to hear every other station. Star couplers have many ports (usually a power of two), and couplers with 32 or 64 ports are not uncommon. One use of a star coupler creates a large party-line circuit. Many transceivers connect to the star coupler and can communicate with all other transceivers, assuming the network adopts a protocol which prevent two or more transceivers from communicating simultaneously. Large insertion loss, (20 dB typically for a 64-port device) creates the biggest disadvantage of the star coupler, as is the need for a complex collision-prevention protocol.

star-network
Figure 2 – Star Topology

Bus topology utilizes a tee coupler to connect a series of stations that listen to a single backbone of cable. In a typical bus network, a coupler at each node splits off part of the power from the bus and carries it to a transceiver in the attached equipment. In a system with N terminals, a signal must pass through N-1 couplers before arriving at the receiver. Loss increases linearly as N increases. A bus topology may operate in a single direction or a bidirectional or duplex transmission configuration. In a one way, unidirectional setup, a transmitter at one end of the bus communicates with a receiver at the other end. Each terminal also contains a receiver. Duplex networks add a second fiber bus or use an additional directional coupler at each end and at each terminal. In this way, signals flow in both directions. By far the most popular type of coupler in use today is a fused coupler fused fiber coupler. In this type of coupler, two or more fibers are twisted together and melted in a flame. Figure 3 shows the basic construction.

FUSEDCOUP
Figure 3 – Fused Fiber Coupler

This construction technique can be used to make 50%-50% couplers, 99%-1% couplers and even WDMs. The length of the coupling region (the fused region) as well as the amount of twisting and pulling done on the fiber while it is melted, determines the result. This coupler has grown in popularity because of the low cost of the basic materials needed for its construction: a few meters of fiber, a bit of potting compound, and a metal tube. The magic is knowing how to melt, twist, and pull the fiber. The most interesting type of fused fiber coupler is the WDM. It is only possible with single-mode fiber. An interferometric action forms the WDM within the fused mixing region. Like an interferometer, this causes a sinusoidal response as the length increases. WDMs operate at two specific wavelengths. Adjusting the minimum of the sinusoid to correspond to the first wavelength of interest and the maximum of the sinusoid to correspond to the second wavelength of interest forms a WDM. For More Information See “WDMs.”