Fiber Optic Cable Plant Link Loss Budget Analysis
Loss budget analysis is the calculation and verification of a fiber optic system’s operating characteristics. This encompasses items such as routing, electronics, wavelengths, fiber type, and circuit length. Attenuation and bandwidth are the key parameters for budget loss analysis.
Analyze Fiber Optic Link Loss In The Design Stage
Prior to designing or installing a fiber optic system, a loss budget analysis is reccommended to make certain the system will work over the proposed link. Both the passive and active components of the circuit have to be included in the budget loss calculation. Passive loss is made up of fiber loss, connector loss, and splice loss. Don’t forget any couplers or splitters in the link. Active components are system gain, wavelength, transmitter power, receiver sensitivity, and dynamic range. Prior to system turn up, test the circuit with a source and FO power meter to ensure that it is within the loss budget.
The idea of a loss budget is to insure the network equipment will work over the installed fiber optic link. It is normal to be conservative over the specifications! Don’t use the best possible specs for fiber attenuation or connector loss – give yourself some margin!
The best way to illustrate calculating a loss budget is to show how it’s done for a 2 km multimode link with 5 connections (2 connectors at each end and 3 connections at patch panels in the link) and one splice in the middle. See the drawings below of the link layout and the instantaneous power in the link at any point along it’s length, scaled exactly to the link drawing above it.
Fiber Optic Cable Plant Passive Component Loss
Step 1. Fiber loss at the operating wavelength
| Cable Length | 2.0 | 2.0 | ||
| Fiber Type | Multimode | Singlemode | ||
| Wavelength (nm) | 850 | 1300 | 1300 | 1550 |
| Fiber Atten. dB/km | 3 [3.5] | 1 [1.5] | 0.4 [1/0.5] | 0.3 [1/0.5] |
| Total Fiber Loss | 6.0 [7.0] | 2.0 [3.0] |
(All specs in brackets are maximum values per EIA/TIA 568 standard. For singlemode fiber, a higher loss is allowed for premises applications. )
Step 2. Connector Loss
Multimode connectors will have losses of 0.2-0.5 dB typically. Singlemode connectors, which are factory made and fusion spliced on will have losses of 0.1-0.2 dB. Field terminated singlemode connectors may have losses as high as 0.5-1.0 dB. Let’s calculate it at both typical and worst case values.
| Connector Loss | 0.3 dB (typical adhesive/polish conn) | 0.75 dB (TIA-568 max acceptable) |
| Total # of Connectors | 5 | 5 |
| Total Connector Loss | 1.5 dB | 3.75 dB |
(All connectors are allowed 0.75 max per EIA/TIA 568 standard)
Step 3. Splice Loss
Multimode splices are usually made with mechanical splices, although some fusion splicing is used. The larger core and multiple layers make fusion splicing abut the same loss as mechanical splicing, but fusion is more reliable in adverse environments. Figure 0.1-0.5 dB for multimode splices, 0.3 being a good average for an experienced installer. Fusion splicing of singlemode fiber will typically have less than 0.05 dB (that’s right, less than a tenth of a dB!)
| Typical Splice Loss | 0.3 dB |
| Total # splices | 1 |
| Total Splice Loss | 0.3 dB |
(All splices are allowed 0.3 max per EIA/TIA 568 standard)
Step 4. Total Passive System Attenuation
Add the fiber loss, connector and splice losses to get the link loss.
| Best Case | TIA 568 Max | |||
| 850 nm | 1300 nm | 850 nm | 1300 nm | |
| Total Fiber Loss (dB) | 6.0 | 2.0 | 7.0 | 3.0 |
| Total Connector Loss (dB) | 1.5 | 1.5 | 3.75 | 3.75 |
| Total Splice Loss (dB) | 0.3 | 0.3 | 0.3 | 0.3 |
| Other (dB) | 0 | 0 | 0 | 0 |
| Total Link Loss (dB) | 7.8 | 3.8 | 11.05 | 7.05 |
Remember these should be the criteria for testing. Allow +/- 0.2 -0.5 dB for measurement uncertainty and that becomes your pass/fail criterion.
Equipment Link Loss Budget Calculation: Link loss budget for network hardware depends on the dynamic range, the difference between the sensitivity of the receiver and the output of the source into the fiber. You need some margin for system degradation over time or environment, so subtract that margin (as much as 3dB) to get the loss budget for the link.
Step 5. Data From Manufacturer’s Specification for Active Components (Typical 100 Mb/s link)
| Operating Wavelength (nm) | 1300 |
| Fiber Type | MM |
| Receiver Sens. (dBm@ required BER) | -31 |
| Average Transmitter Output (dBm) | -16 |
| Dynamic Range (dB) | 15 |
| Recommended Excess Margin (dB) | 3 |
Step 6. Loss Margin Calculation
| Dynamic Range (dB) (above) | 15 | 15 |
| Cable Plant Link Loss (dB) | 3.8 (Typ) | 7.05 (TIA) |
| Link Loss Margin (dB) | 11.2 | 7.95 |
As a general rule, the Link Loss Margin should be greater than approximately 3 dB to allow for link degradation over time. LEDs in the transmitter may age and lose power, connectors or splices may degrade or connectors may get dirty if opened for rerouting or testing. If cables are accidentally cut, excess margin will be needed to accommodate splices for restoration.
NOTE: Many techs forget when doing a loss budget that the connectors on the end of the cable plant must be included in the loss budget. When the cable plant is tested, the reference cables will mate with those connectors and their loss will be included in the measurements.
Types of Fiber Optic Cables – Singlemode, Multimode
Understanding the characteristics of different fiber types aides in understanding the applications for which they are used. Operating a fiber optic system properly relies on knowing what type of fiber is being used and why. There are two basic types of fiber: multimode fiber optic cable and single-mode fiber optic cable. Multimode fiber is best designed for short transmission distances, and is suited for use in LAN systems and video surveillance. Single-mode fiber is best designed for longer transmission distances, making it suitable for long-distance telephony and multichannel television broadcast systems.
Multimode Fiber
Multimode fiber, the first to be manufactured and commercialized, simply refers to the fact that numerous modes or light rays are carried simultaneously through the waveguide. Modes result from the fact that light will only propagate in the fiber core at discrete angles within the cone of acceptance. This fiber type has a much larger core diameter, compared to single-mode fiber, allowing for the larger number of modes, and multimode fiber is easier to couple than single-mode optical fiber. Multimode fiber may be categorized as step-index or graded-index fiber. Multimode Step-index Fiber Figure 2 shows how the principle of total internal reflection applies to multimode step-index fiber. Because the core’s index of refraction is higher than the cladding’s index of refraction, the light that enters at less than the critical angle is guided along the fiber.
Figure 2 – Total Internal Reflection in Multimode Step-index fiber
Three different lightwaves travel down the fiber. One mode travels straight down the center of the core. A second mode travels at a steep angle and bounces back and forth by total internal reflection. The third mode exceeds the critical angle and refracts into the cladding. Intuitively, it can be seen that the second mode travels a longer distance than the first mode, causing the two modes to arrive at separate times. This disparity between arrival times of the different light rays is known as dispersion, and the result is a muddied signal at the receiving end. For a more detailed discussion of dispersion, see “Dispersion in Fiber Optic Systems” however, it is important to note that high dispersion is an unavoidable characteristic of multimode step-index fiber. Multimode Graded-index Fiber Graded-index refers to the fact that the refractive index of the core gradually decreases farther from the center of the core. The increased refraction in the center of the core slows the speed of some light rays, allowing all the light rays to reach the receiving end at approximately the same time, reducing dispersion.Figure 3 shows the principle of multimode graded-index fiber. The core’s central refractive index, nA, is greater than that of the outer core’s refractive index, nB. As discussed earlier, the core’s refractive index is parabolic, being higher at the center. As Figure 3 shows, the light rays no longer follow straight lines; they follow a serpentine path being gradually bent back toward the center by the continuously declining refractive index. This reduces the arrival time disparity because all modes arrive at about the same time. The modes traveling in a straight line are in a higher refractive index, so they travel slower than the serpentine modes. These travel farther but move faster in the lower refractive index of the outer core region.
Figure 3 – Multimode Graded-index Fiber
Single-mode Fiber
Single-mode fiber allows for a higher capacity to transmit information because it can retain the fidelity of each light pulse over longer distances, and it exhibits no dispersion caused by multiple modes. Single-mode fiber also enjoys lower fiber attenuation than multimode fiber. Thus, more information can be transmitted per unit of time. Like multimode fiber, early single-mode fiber was generally characterized as step-index fiber meaning the refractive index of the fiber core is a step above that of the cladding rather than graduated as it is in graded-index fiber. Modern single-mode fibers have evolved into more complex designs such as matched clad, depressed clad and other exotic structures.
Figure 4
Single-mode fiber has disadvantages. The smaller core diameter makes coupling light into the core more difficult. The tolerances for single-mode connectors and splices are also much more demanding. Single-mode fiber has gone through a continuing evolution for several decades now. As a result, there are three basic classes of single-mode fiber used in modern telecommunications systems. The oldest and most widely deployed type is non dispersion-shifted fiber(NDSF). These fibers were initially intended for use near 1310 nm. Later, 1550 nm systems made NDSF fiber undesirable due to its very high dispersion at the 1550 nm wavelength. To address this shortcoming, fiber manufacturers developed, dispersion-shifted fiber(DSF), that moved the zero-dispersion point to the 1550 nm region. Years later, scientists would discover that while DSF worked extremely well with a single 1550 nm wavelength, it exhibits serious nonlinearities when multiple, closely-spaced wavelengths in the 1550 nm were transmitted in DWDM systems. Recently, to address the problem of nonlinearities, a new class of fibers were introduced. These are classified as non zero-dispersion-shifted fibers (NZ-DSF). The fiber is available in both positive and negative dispersion varieties and is rapidly becoming the fiber of choice in new fiber deployment. For more information on this loss mechanism, see the article “Fiber Dispersion.”
Figure 6 – Dispersion for Alternating 20 km Lengths of (+D) NZ-DSF and (-D) NZ-DSF Fiber
One additional important variety of single-mode fiber is polarization-maintaining (PM) fiber. All other single-mode fibers discussed so far have been capable of carrying randomly polarized light. PM fiber is designed to propagate only one polarization of the input light. This is important for components such as external modulators that require a polarized light input. Figure 7 shows the cross-section of a type of PM fiber. This fiber contains a feature not seen in other fiber types. Besides the core, there are two additional circles called stress rods. As their name implies, these stress rods create stress in the core of the fiber such that the transmission of only one polarization plane of light is favored. Single-mode fibers experience nonlinearities that can greatly affect system performance. For complete information, see “Fiber Nonlinearities.”
Figure 7
This artical is from: http://www.voscom.com/trainning/fiber-optic-cable.asp
What componets you need in a fiber optic CCTV transmission system
The sole purpose of the fibre optic link in a CCTV fibre optic transmission systems is to transfer electrical signals between two remotely separated points, A and B, with no degradation in the transmitted signal quality. In this way the fibre optic link becomes transparent to the user. An analogous situation is with a telephone call where you want to be able to talk to another person anywhere as though they were standing next to you.
The basic components of a CCTV fibre optic transmission system are as follows:
· Electrical to Optical Converter (Transmitter) at the camera end of the link. This unit takes the analogue 1 v peak to peak signal from the surveillance camera and converts it into a light signal that varies in proportion to the camera output signal. The light signal is generated by an LED (light emitting diode) or laser transmitter which is designed to couple a maximum of the generated light into an optical fibre.
· The optical transmission fiber and fiber optic cable. The optical fibre guides the light from the LED or laser transmitter with a minimum of loss to the monitor or matrix controller end of the link. The optical fibre itself is protected by a variety of sheathing materials to provide a cable construction appropriate to the specific application. The fibre cable is connected to the terminal equipment using de-mountable screw or bayonet fixing connectors.
· Optical to Electrical Converter (Receiver) at the monitor end of the link. This unit takes the optical signal from the optical fibre and converts it into an analogue electrical signal that is compatible with the monitor input requirements. The light to electrical conversion is carried out by a semiconductor detector which is called a photodiode, or an avalanche photodiode. Subsequent electronic circuitry regenerates the output signal. Products from the better quality manufacturers compensate for optical fibre losses and transmitter output intensity variation with time and temperature by providing automatic gain control to give a standard 1 v peak to peak output format as generated at the camera output.
· Control data and audio connections. Cameras in CCTV installations are either fixed, viewing a specific scene, or movable, so that different scenes can be viewed under the direction of the operator who would be sited in the remote control room. In the case of fixed cameras then the fibre optic link is required to transmit video only information from the camera to monitor, this requires only a single fibre link for each camera to monitor path. In the case of a movable camera then a return signal must be provided from the control room to the camera usually over a second optical fibre. It is usual for these return control links to provide remote control of the camera PTZ – pan, tilt and zoom functions plus
camera enclosure wash/wipe activation.
If camera control is used then the fibre optic link interface electronics must be compatible with the protocols used by the controller manufacturer. These functions are transmitted over the return fibre link using a standard digital transmission format such as RS232, RS485/422, 20 mA current loop and most recently Echelon Lonworks FTT10A. In addition some controller manufacturers require a return data channel from the camera to confirm camera movement. This return data is usually encoded by the camera optical transmitter electronics and sent over the same fibre as the video signal.
Help point and door entry installations require the transmission of two-way audio signals over the fibre link. Again optical transmitter and receiver units are available to provide this facility in addition to the video and control data links all over the same two fibres. It is also possible to provide all of these video, data and audio transmission functions over one fibre using different wavelength (colour) lights sources to transmit light in each direction. This technique is known as wavelength division multiplexing; it maximises the use of installed fibre cores but at the expense of more costly fiber optic transmitters and fiber optic receivers.
Use fiber optics to transmission CCTV camera video singal
The principle reasons for using optical fiber as the transmission media in CCTV applications are:
· The maintenance of picture quality and control data integrity over extended distances:
This is the major reason for using fibre optics which have superior signal amplitude loss characteristics than copper cable. Typically co-axial cable attenuation at a signal frequency of 5 MHz can be 20 dB/km. In comparison fiber attenuation is between 0.3 and 3 dB/km meaning that fiber optic transmitter distances of 60 km+ can be achieved, depending on the precise details of the application. In addition this low fibre signal attenuation is achieved over a very wide signal frequency range so that optical fiber can be used for the transmission of multiple video signals over long distances.
· Immunity to electromagnetic interference:
Optical fibre transmits signals as light pulses rather than electrical pulses. This light transmission is unaffected by the presence of electro-magnetic fields. As a consequence fiber optic transmission can be used in applications where links are routed near electrical conductors and electrical machines. This includes applications such as railways, tramways, power generation and vehicle manufacture with welding machinery. In addition the fibre cable usually has a metal free construction so that there are no ground loop problems between terminal equipment and the cable will not transmit lightning pulses. This elimination of ground loops makes fibre cable the media of choice for inter building links of whatever distance.
· Security of Information and Operational Safety
Unlike copper cables fiber cables do not radiate any signals as a consequence fiber optical cables are virtually immune from “tapping” and so the signal content is difficult to access for unauthorised parties. As there are no emissions from optical fibre cable there is no risk that a fibre installation will act as a ignition source. This means that fibre can be used in explosive atmospheres such as chemical and petro-chemical sites providing a truly “Intrinsically Safe” transmission path. Note however, that this Intrinsic Safety, would not extend to the electro-optic termination modems which would need to be safety certified and protected the same as any other electrical equipment.
· Efficient use of duct space.
Optical fibre itself is very small, each glass fibre being only 0.125mm diameter. Protective sheathing is then applied in stages, depending on the application area, to make up the fibre into a usable cable. Typically resulting cable would have a diameter of 3mm for a single fibre core patchlead or 8mm for a 8 fibre cable suitable for internal or external use. In contrast 75 Ohm CT100 coaxial copper cable has a diameter of 6.5 mm. It can therefore be seen that the small size of fibre cable gives significant savings over copper where installation space is in short supply or where duct space is limited. Along with the small fibre cable size comes a weight saving both of which give savings in storage and transportation costs prior to installation.
· Multi-channel capability and “Future Proofing”.
While most CCTV fibers today will be used to transmit one video signal and perhaps a control data signal, the user may wish to upgrade the system to support more camera and control channels. Any glass optical fiber used today is able to transmit multiple optical channels either by using different optical carrier “colours” i.e. wavelength division multiplexing or by increasing the signal frequency using electrical multiplexing techniques. The transmission media is hence “future proofed” and the link will need only additional fiber optic converter equipment to expand the link capacity.
VOSCOM’S VOS-1000 FIBER OPTIC TRANSMISSION SYSTEMS MAKES THE CONNECTION FOR CBS NEWS CREWS
For political conventions of news was live from Super Bowl VOSCOM’S VOS-1000 on the grounds of the fiber optic transmission systems, has contributed to CBS News Top Stories provide viewers at home. VOSCOM, a leading provider of fiber optic converter for audio and video routing solutions for the delivery of broadcasting and Pro A / V applications YOUR-winning CBS News in 1000 as part of their equipment for the transmission of video from multiple locations in the diffusion of various new programs.
“For the live broadcast of our regular news broadcasts in several places, the sand on the south beach, Sun Life asked Stadium during the Super Bowl, that the material must be very portable,” says Mel Olinsky, Director of the Office Operations, CBS News. “Working on-site, we also need to transport HD signals over long distances, which was impossible with copper. The VOS-1000 field optics fiber transmission provided that the all of our cable connectivity over a fiber strand multi without restrictions on duration. ”
CBS VOS-1000 widely used, several major events including political conventions and the last Super Bowl. During the week before Super Bowl VOSCOM Use VOS-1000 video transport for several new programs, including “The CBS Early Show,” CBS Weekend Evening News “and” Face the Nation “, all live in different places, including South Miami and Miami Beach Gardens Sun Life stage. For these shows, CBS News needed the ability to supervise both HD and SD video signals and wanted to and fro transportation from various locations in South Florida’s network OB truck, often parked near the place . A battery, bi-directional HD designed the fiber transmission system for field use and harsh environment applications, the VOS-1000 is the ideal portable solution for transmitting signals over distances ranging up three football fields away from turning over any local transport.
Frank Xu, Director General, VOSCOM, said: “The Place-ENG and production can be very hectic, especially in advance of important events.” He concluded: “The VOSCOM takes some of the stress of live shooting distance, as it is very easy, quite robust to any state in the field and transported extremely reliable. We are very pleased that our VOS-1000 plays a role, ensuring that emissions go up CBS News smoothly. “
CBS News continued to units VOS-1000 for remote broadcast. For more information on the VOS-1000, please visit http://www.voscom.com
CCTV PTZ Cameras Video Transmission over Fiber Optics Application
Single CCTV PTZ Camera Video Transmission over fiber optics, support 8-bit digitally encoded broadcast quality video, data and 10M/100M IP Ehternet over one multi-mode or single-mode optical fiber. The modules are directly compatible with NTSC, PAL, and SECAM camera systems and support RS-485, RS-232, and RS-422 data protocols. These Transmitter and Receiver are typically used in applications with PTZ cameras for security surveillance, CCTV, ITS, CIQ, etc.
Application:
Remote PTZ analog camera with fiber optical connection to be viewed on a video monitor.
EXAMPLE: Owner of building needs to view and control an PTZ Dome Camera from Monitor Center.
Solution:
Standard PTZ equipped CCTV camera is connected to the VOSCOM Fiber Optic Video & Data Transmitter using standard coax cable. The transmitter digitally compresses the signal for transmission across the Fiber Optical Cable.
At the Monitor Center, the receiver can receive the signal and the user can view the video image and control the camera movement using a standard Keyboard.
more information please find in the website: www.voscom.com
Notes:
1) VOSCOM Fiber Optic Transmitter can transmit 1~64 channels video signals and data support RS485, RS232, RS422. you can choose our fiber optic products according to your needs.
2) If you just need to control the PTZ cameras, one return data is enough, in theory, one channel data can control 1~128 PTZ cameras, the detail connection information you can refer to your PTZ camera’s manual.
Fixed CCTV Cameras Video over Fiber Transmission Application
Single Fixed Camera to Video Monitor Transmission over Fiber Optical Cable. The camera video transmission over fiber that delivers a sharper image with better color quantification and faster, more efficient codecs. The video over one multi-mode or single-mode optical fiber. The modules are directly compatible with NTSC, PAL, and SECAM camera systems.
Application:
Remote fixed analog camera with fiber optical connection to be viewed on a video monitor.
EXAMPLE: Apartment residents need to view the main entrance camera via the Fiber Optics.
Solution:
Standard CCTV camera is connected to VOSCOM Fiber Optic Video Transmitter using standard coax cable. The transmitter digitally compresses the signal for optical transmission across the fiber optical cable.
At the Monitor Center, the receiver can receive the signal and user can view the video image using a monitor.
Notes:
1) While this will also work for viewing a PTZ camera additional wiring is necessary in order to PTZ control the camera (see Single PTZ to Monitor).
2) VOSCOM Fiber Optic Video Transmitter and Receiver can transmit 1~64 channels video signals, you can choose our fiber optic products according to your needs.
Baseband Video Fiber Optic Transmission
Baseband video 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.
Figure 1 – Point-to-Point Transmission
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.
Figure 3 – Baseband Composite Video Signals
Baseband Video Applications
Figure 4 illustrates a multimedia baseband fiber optic transmission systems.
Figure 4 – Multimedia baseband transmission
How Fibre Optic Surveillance Systems Work
Protection With Fiber Optic Surveillance Systems
Security has become a word that is taken very seriously in the twenty-first century. Optical surveillance systems are security set-ups that utilize cameras which are able to monitor surrounding areas in various lighted (or non lighted) environments. The cameras are able to adjust to day or night conditions and allow clear imaging of an area. Many different locations are using optical surveillance systems to achieve security goals.
These include:
• Transportation such as airports, and public transportation terminals
• Manufacturing facilities, particularly large ones that have a high risk threat such as petroleum processing and military sites.
• Military and Armed Services, including defense facilities that rely heavily upon optical surveillance, even in the battlefield.
Optical surveillance systems are able to transmit images by different means such as fiber optic technology. To understand how fibre optic transmission systems work, you will need to understand the basics of fiber optics.
How Fibre Optic Surveillance Systems Work
Digital images are transmitted through a camera via a fiber optic cable. Fiber optic cable consists of strands of pure glass that are thinner than human hair. The strands carry digital information (such as images) over distance and deliver the information to a receiver. The strands are arranged in bundles that have an outer jacket (covering).
The light (image) is transferred along the fiber optic cable by bouncing along the mirror lined walls of the cable. The purity of the glass used in the fiber optic strands affects the clarity of the image transmitted to the receiver. This is an important factor to keep in mind if you are looking to purchase any fiber optic products.
Fibre optic surveillance systems allow wireless surveillance camera systems to function and transmit images. The system is comprised of these components:
1. A fiber optic transmitter is used to feed data into. The transmitter transforms the information into coded light.
2. The optical fiber conducts the light signals over a distance.
3. An optical booster may be used to amplify the light if it is traveling a long distance.
4. An optical receiver decodes the light signal back into the original data format.
This method is how information is transferred from wireless surveillance camera systems. The camera takes the image, its transmitter sends the image signal (via fiber optic light) to the receiver. The receiver translates it into an image that can be viewed.
This technology has proven very beneficial for most communications. It has profoundly affected military communications on the battlefield. Troops in combat areas are able to communicate over extremely long distances without being detected.
Many tactile missions must be done in darkness to have the winning advantage. Optical surveillance systems and fiber optic transmission technology allow this to happen. The same technology that helps our military protect us is also available to protect our homes as well. Lower cost versions of the same systems are being used by many people to protect and monitor their belongings and loved ones. Businesses depend on these types of business surveillance systems for security in retail stores, industrial manufacturing facilities and many others.
The History of Fiber Optic Technologies
Fiber Optic Technology in The Nineteenth Century
In 1870, John Tyndall, using a jet of water that flowed from one container to another and a beam of light, demonstrated that light used internal reflection to follow a specific path. As water poured out through the spout of the first container, Tyndall directed a beam of sunlight at the path of the water. The light, as seen by the audience, followed a zigzag path inside the curved path of the water. This simple experiment, illustrated in Figure 1, marked the first research into the guided transmission of light.
William Wheeling, in 1880, patented a method of light transfer called “piping light”. Wheeling believed that by using mirrored pipes branching off from a single source of illumination, i.e. a bright electric arc, he could send the light to many different rooms in the same way that water, through plumbing, is carried throughout buildings today. Due to the ineffectiveness of Wheeling’s idea and to the concurrent introduction of Edison’s highly successful incandescent light bulb, the concept of piping light never took off.
That same year, Alexander Graham Bell developed an optical voice transmission system he called the photophone. The photophone used free-space light to carry the human voice 200 meters. Specially placed mirrors reflected sunlight onto a diaphragm attached within the mouthpiece of the photophone. At the other end, mounted within a parabolic reflector, was a light-sensitive selenium resistor. This resistor was connected to a battery that was, in turn, wired to a telephone receiver. As one spoke into the photophone, the illuminated diaphragm vibrated, casting various intensities of light onto the selenium resistor. The changing intensity of light altered the current that passed through the telephone receiver which then converted the light back into speech. Bell believed this invention was superior to the telephone because it did not need wires to connect the transmitter and receiver. Today, free-space optical links find extensive use in metropolitan applications.
Fiber Optic Technology in The Twentieth Century
Fiber optic technology experienced a phenomenal rate of progress in the second half of the twentieth century. Early success came during the 1950’s with the development of the fiberscope. This image-transmitting device, which used the first practical all-glass fiber, was concurrently devised by Brian O’Brien at the American Optical Company and Narinder Kapany (who first coined the term ‘fiber optics’ in 1956) and colleagues at the Imperial College of Science and Technology in London. Early all-glass fibers experienced excessive optical loss, the loss of the light signal as it traveled the fiber, limiting transmission distances.
This motivated scientists to develop glass fibers that included a separate glass coating. The innermost region of the fiber, or core, was used to transmit the light, while the glass coating, or cladding, prevented the light from leaking out of the core by reflecting the light within the boundaries of the core. This concept is explained by Snell’s Law which states that the angle at which light is reflected is dependent on the refractive indices of the two materials ‘ in this case, the core and the cladding. The lower refractive index of the cladding (with respect to the core) causes the light to be angled back into the core as illustrated in
The fiberscope quickly found application inspecting welds inside reactor vessels and combustion chambers of jet aircraft engines as well as in the medical field. Fiberscope technology has evolved over the years to make laparoscopic surgery one of the great medical advances of the twentieth century.
The development of laser technology was the next important step in the establishment of the industry of fiber optics. Only the laser diode (LD) or its lower-power cousin, the light-emitting diode (LED), had the potential to generate large amounts of light in a spot tiny enough to be useful for fiber optics. In 1957, Gordon Gould popularized the idea of using lasers when, as a graduate student at Columbia University, he described the laser as an intense light source. Shortly after, Charles Townes and Arthur Schawlow at Bell Laboratories supported the laser in scientific circles. Lasers went through several generations including the development of the ruby laser and the helium-neon laser in 1960. Semiconductor lasers were first realized in 1962; these lasers are the type most widely used in fiber optics today.
Because of their higher modulation frequency capability, the importance of lasers as a means of carrying information did not go unnoticed by communications engineers. Light has an information-carrying capacity 10,000 times that of the highest radio frequencies being used. However, the laser is unsuited for open-air transmission because it is adversely affected by environmental conditions such as rain, snow, hail, and smog. Faced with the challenge of finding a transmission medium other than air, Charles Kao and Charles Hockham, working at the Standard Telecommunication Laboratory in England in 1966, published a landmark paper proposing that optical fiber might be a suitable transmission medium if its attenuation could be kept under 20 decibels per kilometer (dB/km). At the time of this proposal, optical fibers exhibited losses of 1,000 dB/ km or more. At a loss of only 20 dB/km, 99% of the light would be lost over only 3,300 feet. In other words, only 1/100th of the optical power that was transmitted reached the receiver. Intuitively, researchers postulated that the current, higher optical losses were the result of impurities in the glass and not the glass itself. An optical loss of 20 dB/km was within the capability of the electronics and opto-electronic components of the day.
Intrigued by Kao and Hockham’s proposal, glass researchers began to work on the problem of purifying glass. In 1970, Drs. Robert Maurer, Donald Keck, and Peter Schultz of Corning succeeded in developing a glass fiber that exhibited attenuation at less than 20 dB/km, the threshold for making fiber optics a viable technology. It was the purest glass ever made.
The early work on fiber optic light source and detector was slow and often had to borrow technology developed for other reasons. For example, the first fiber optic light sources were derived from visible indicator LEDs. As demand grew, light sources were developed for fiber optics that offered higher switching speed, more appropriate wavelengths, and higher output power. For more information on light emitters see Laser Diodes and LEDs.
Fiber optics developed over the years in a series of generations that can be closely tied to wavelength. Figure 3 shows three curves. The top, dashed, curve corresponds to early 1980’s fiber, the middle, dotted, curve corresponds to late 1980’s fiber, and the bottom, solid, curve corresponds to modern optical fiber. The earliest fiber optic systems were developed at an operating wavelength of about 850 nm. This wavelength corresponds to the so-called ‘first window’ in a silica-based optical fiber. This window refers to a wavelength region that offers low optical loss. It sits between several large absorption peaks caused primarily by moisture in the fiber and Rayleigh scattering.
The 850 nm region was initially attractive because the technology for light emitters at this wavelength had already been perfected in visible indicator LEDs. Low-cost silicon detectors could also be used at the 850 nm wavelength. As technology progressed, the first window became less attractive because of its relatively high 3 dB/km loss limit.
Most companies jumped to the ‘second window’ at 1310 nm with lower attenuation of about 0.5 dB/km. In late 1977, Nippon Telegraph and Telephone (NTT) developed the ‘third window’ at 1550 nm. It offered the theoretical minimum optical loss for silica-based fibers, about 0.2 dB/km.
Today, 850 nm, 1310 nm, and 1550 nm systems are all manufactured and deployed along with very low-end, short distance, systems using visible wavelengths near 660 nm. Each wavelength has its advantage. Longer wavelengths offer higher performance, but always come with higher cost. The shortest link lengths can be handled with wavelengths of 660 nm or 850 nm. The longest link lengths require 1550 nm wavelength systems. A ‘fourth window,’ near 1625 nm, is being developed. While it is not lower loss than the 1550 nm window, the loss is comparable, and it might simplify some of the complexities of long-length, multiple-wavelength communications systems.
Fiber Optic Applications in the Real World
The U.S. military moved quickly to use fiber optics for improved communications and tactical systems. In the early 1970’s, the U.S. Navy installed a fiber optic telephone link aboard the U.S.S. Little Rock. The Air Force followed suit by developing its Airborne Light Optical Fiber Technology (ALOFT) program in 1976. Encouraged by the success of these applications, military R&D programs were funded to develop stronger fibers, tactical cables, ruggedized, high-performance components, and numerous demonstration systems ranging from aircraft to undersea applications.
Commercial applications followed soon after. In 1977, both AT&T and GTE installed fiber optic telephone systems in Chicago and Boston respectively. These successful applications led to the increase of fiber optic telephone networks. By the early 1980’s, single-mode fiber operating in the 1310 nm and later the 1550 nm wavelength windows became the standard fiber installed for these networks. Initially, computers, information networks, and data communications were slower to embrace fiber, but today they too find use for a transmission system that has lighter weight cable, resists lightning strikes, and carries more information faster and over longer distances.
The broadcast industry also embraced fiber optic transmission. In 1980, broadcasters of the Winter Olympics, in Lake Placid, New York, requested a fiber optic video transmission system for backup video feeds. The fiber optic feed, because of its quality and reliability, soon became the primary video feed, making the 1980 Winter Olympics the first fiber optic television transmission. Later, at the 1994 Winter Olympics in Lillehammer, Norway, fiber optics transmitted the first ever digital video signal, an application that continues to evolve today.
In the mid-1980’s the United States government deregulated telephone service, allowing small telephone companies to compete with the giant, AT&T. Companies like MCI and Sprint quickly went to work installing regional fiber optic telecommunications networks and fiber optic transmission systems throughout the world. Taking advantage of railroad lines, gas pipes, and other natural rights of way, these companies laid miles fiber optic cable, allowing the deployment of these networks to continue throughout the 1980’s. However, this created the need to expand fiber’s transmission capabilities.
In 1990, Bell Labs transmitted a 2.5 Gb/s signal over 7,500 km without regeneration. The system used a soliton laser and an erbium-doped fiber amplifier (EDFA) that allowed the light wave to maintain its shape and density. In 1998, they went one better as researchers transmitted 100 simultaneous optical signals, each at a data rate of 10 gigabits (giga means billion) per second for a distance of nearly 250 miles (400 km). In this experiment, dense wavelength-division multiplexing (DWDM technology, which allows multiple wavelengths to be combined into one optical signal, increased the total data rate on one fiber to one terabit per second (1012 bits per second).
Fiber Optic Technology in The Twenty-First Century and Beyond
Today, DWDM technology continues to develop. As the demand for data bandwidth increases, driven by the phenomenal growth of the Internet, the move to optical networking is the focus of new technologies. At this writing, nearly half a billion people have Internet access and use it regularly. Some 40 million or more households are ‘wired.’ The world wide web already hosts over 2 billion web pages, and according to estimates people upload more than 3.5 million new web pages everyday.
The important factor in these developments is the increase in fiber transmission capacity, which has grown by a factor of 200 in the last decade. Figure 5 illustrates this trend.
Because of fiber optic technology’s immense potential bandwidth, 50 THz or greater, there are extraordinary possibilities for future fiber optic applications. Already, the push to bring broadband services, including data, audio, and especially video, into the home is well underway.
Broadband service available to a mass market opens up a wide variety of interactive communications for both consumers and businesses, bringing to reality interactive video networks, interactive banking and shopping from the home, and interactive distance learning. The ‘last mile’ for optical fiber goes from the curb to the television set top, known as fiber-to-the-home (FTTH) and fiber-to-the-curb (FTTC), allowing video on demand to become a reality.
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