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

This artical is from: http://www.voscom.com/trainning/baseband-video-transmission.asp

Broadband Video Fiber Optic Transmission

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 Fiber Optic Video 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.

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.

This artical is from: http://www.voscom.com/trainning/broadband-video-transmission.asp

What are Fiber Optic Transmitters and Receivers?

Fiber Optic Transmitters

An fiber optic transmitter converts electrical input signals into modulated light for transmission over a fiber optic cable. Depending on the nature of the signal, the resulting modulated light may be turned on and off or may be linearly varied in intensity between two predetermined levels. Figure (2) shows a representation of these two basic schemes.

The devices used as the light sources in optical transmitters are Light Emitting Diode (LED) and Laser Diodes. LEDs and Lasers are semiconductors mounted in a TO style can or microlens package that focus the beam of light right into the optical fiber connector. In the case of analog FM transmission, the Laser is “pigtailed” directly onto the surface of the emitter in order to reduce or eliminate back reflection and noise.

LEDs have a wide spectral frequency, are suited for large aperture multimode fibers and are used for short to moderate transmission distances. Lasers, on the other hand, feature a narrow band of wavelengths and can couple many times more power into the fiber than LEDs and therefore are useful in applications that require high speed, high bandwidth over long distances. Lasers are not stable over wide operating temperatures, however, with well-designed feedback circuitry, continuous stable output can be achieved.

Analog modulation takes a number of forms – see figure (3). The simplest is intensity modulation (IM) where the brightness of an LED is varied in direct step with the variations of the transmitted signal. In other methods, an RF carrier is first frequency modulated (FM) with another signal or, in some cases, several RF carriers are separately modulated, then are combined and transmitted as one complex waveform.

Fiber Optic Receivers

The fiber optic receiver converts modulated light coming from an optical fiber back into the original electronic signal applied to the transmitter.

The detector is a photodiode of either the PIN or the Avalanche type and is mounted in a similar package to the one used for the LED or Laser. Sensitivity of the receiver is specified as the minimum signal that it can receive (in dBm). Dynamic Range is the difference between the minimum and maximum acceptance levels. Receivers usually employ high gain internal amplifiers and require special circuitry to avoid saturation or distortion. When the optical dynamic range of the system is equal to the optical power budget, no saturation of the receiver can occur. Quality of signal transmission is equally good at short or long distances.

As in the case of fiber optc transmitters, fiber optic receivers are available in both analog and digital versions. Figure (4) is a functional diagram of a simple analog optical receiver.

Fiber Optic CCTV Transmission System Implementations

Fiber optics for CCTV applications are predominantly used in extended local installations linking cameras back to monitors with dedicated fibres for each link. A typical fiber optic transmission system layout is shown in Fig. 6.

This example illustrates the main features of any fibre optic system, which are as follows:

1. The fibre optic link and its associated terminal equipment fit between the camera and the associated monitor/controller and provide a transparent signal path i.e. the camera and controller do not know that the signals have been transmitted over fiber.

2. The camera output is a 1V peak to peak composite video signal.

3. Movable cameras have a telemetry receiver is mounted near to the camera movement mechanism. This telemetry receiver connects to the system controller to provide control of the camera pan/tilt and zoom PTZ functions.

4. At the control end of the link camera selection and movement is looked after by the system controller and video signal outputs from the controller are displayed on a local monitor(s).

5. Electrical to optical and optical to electrical converters provides the interfaces to the optical fibre transmission fibre.

6. At the camera end of the link the E/O converter is usually a single channel unit packaged in a small enclosure which can be conveniently mounted near to the camera or telemetry receiver. These E/O converters are not usually environmentally sealed and so need to be protected from the elements often mounting them in the telemetry receiver enclosure. In their most cost effective form a PTZ cameras E/O converter will use two multimode fibres to give a uni-directional video connection plus a bi-directional control data channel.

7. As an alternative these control and video link functions can be carried over a single fibre using optical transmission at two wavelengths, WDM – wavelength division multiplexing. These WDM links are more expensive than single wavelength links but they do save on fibre usage and they also can make the best use of a previously installed fibre infrastructure.

8. The E/O converter data interface must be compatible with that used by the system controller; these are often non-standard.

9. Fixed cameras can use a miniature E/O transmitter, which can connect directly to the camera BNC signal output. This link requires only one fibre.

10. The camera end E/O converter is connected to the transmission fibre through a patch box. This patch box provides a point of termination for the transmission cable and so prevents strain and wear and tear being placed on the transmission cable when installing, servicing or moving the terminal equipment. Optical connections between the E/O converter and the patch box are made with duplex patchleads (which are short fibre cable lengths terminated at each end with an optical connector). The patch box will only be a relatively small enclosure because it will only need to provide connectivity for a few fibre cores.

11. At the control room end of the link fibres from a large number of cameras will be concentrated. Equipment must therefore be packaged accordingly and most often this means the use of 19” rack mount units. E/O converters are manufactured in modular card format, which enables multiple video channels to be accommodated in a 19” cage. Typically one 3 U high rack can accept plug-in E/O converters for up to 30 video only channels or 10 video/data channels (or a mixture of both).

12. The fibre transmission cables are also handled in 19” rack enclosures because now we will be organising many fibre cores. These enclosures are called patch panels and they again provide a physical buffer between the transmission cable and the terminal equipment. Here the cable will be bought into the rear of the patch panel via a compression gland and the fibre cores will be broken out into the secondary coated cores. These cores will then be terminated with connectors, which are then connected into in-line adaptors mounted through the front bulkhead of the patch panel enclosure. This termination may either be carried out by the direct attachment of connectors to the fibre tails or factory terminated connectors tails will be spliced to the transmission fibre cores. If splices are used then the splice enclosures will be mounted in clips on the patch panel base. Patchleads then connect the patch panel bulkhead connections to the E/O converter optical connections. Copper leads then complete the connections to the system
controller and monitors.

As part of the cable installation the installer will have measured the installed cable loss, a function of position using a piece of test equipment called an OTDR (Optical Time Domain Reflectometer). This measurement serves to finger print the system and provides a point of reference for future system maintenance. It also provides the value of the end to end loss of each optical fibre used. The total loss must not exceed the optical margin specified by the equipment manufacturer, otherwise the transmitted picture quality may be impaired. In a correctly installed multimode system link lengths of 4 km for 850nm products and 8 km for 1300nm products are readily achieved.

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 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.

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.

How Fiber Optics Works,Advantages,Transmission and Made.

Introduction to How Fiber Optics Work

You hear about fiber-optic cables whenever people talk about the telephone system, the cable TV system or the Internet. Fiber-optic lines are strands of optically pure glass as thin as a human hair that carry digital information over long distances. They are also used in medical imaging and mechanical engineering inspection.

In this article, we will show you how these tiny strands of glass transmit light and the fascinating way that these strands are made.

What are Fiber Optics?

Fiber optics (optical fibers) are long, thin strands of very pure glass about the diameter of a human hair. They are arranged in bundles called optical cables and used to transmit light signals over long distances.

If you look closely at a single optical fiber, you will see that it has the following parts:

• Core - Thin glass center of the fiber where the light travels
• Cladding - Outer optical material surrounding the core that reflects the light back into the core
• Buffer coating - Plastic coating that protects the fiber from damage and moisture

Hundreds or thousands of these optical fibers are arranged in bundles in optical cables. The bundles are protected by the cable's outer covering, called a jacket.

Optical fibers come in two types:

• Single-mode fibers
• Multi-mode fibers

See Tpub.com: Mode Theory for a good explanation.

Single-mode fibers have small cores (about 3.5 x 10^-4 inches or 9 microns in diameter) and transmit infrared laser light (wavelength = 1,300 to 1,550 nanometers). Multi-mode fibers have larger cores (about 2.5 x 10^-3 inches or 62.5 microns in diameter) and transmit infrared light (wavelength = 850 to 1,300 nm) from light-emitting diodes (LEDs).

Some optical fibers can be made from plastic. These fibers have a large core (0.04 inches or 1 mm diameter) and transmit visible red light (wavelength = 650 nm) from LEDs.

Let's look at how an optical fiber works.

How Does an Optical Fiber Transmit Light?

Suppose you want to shine a flashlight beam down a long, straight hallway. Just point the beam straight down the hallway -- light travels in straight lines, so it is no problem. What if the hallway has a bend in it? You could place a mirror at the bend to reflect the light beam around the corner. What if the hallway is very winding with multiple bends? You might line the walls with mirrors and angle the beam so that it bounces from side-to-side all along the hallway. This is exactly what happens in an optical fiber.

The light in a fiber-optic cable travels through the core (hallway) by constantly bouncing from the cladding (mirror-lined walls), a principle called total internal reflection. Because the cladding does not absorb any light from the core, the light wave can travel great distances.

However, some of the light signal degrades within the fiber, mostly due to impurities in the glass. The extent that the signal degrades depends on the purity of the glass and the wavelength of the transmitted light (for example, 850 nm = 60 to 75 percent/km; 1,300 nm = 50 to 60 percent/km; 1,550 nm is greater than 50 percent/km). Some premium optical fibers show much less signal degradation -- less than 10 percent/km at 1,550 nm.

A Fiber-Optic Relay System

To understand how optical fibers are used in communications systems, let's look at an example from a World War II movie or documentary where two naval ships in a fleet need to communicate with each other while maintaining radio silence or on stormy seas. One ship pulls up alongside the other. The captain of one ship sends a message to a sailor on deck. The sailor translates the message into Morse code (dots and dashes) and uses a signal light (floodlight with a venetian blind type shutter on it) to send the message to the other ship. A sailor on the deck of the other ship sees the Morse code message, decodes it into English and sends the message up to the captain.

Now, imagine doing this when the ships are on either side of the ocean separated by thousands of miles and you have a fiber-optic communication system in place between the two ships. Fiber-optic relay systems consist of the following:

• Transmitter - Produces and encodes the light signals
• Optical fiber - Conducts the light signals over a distance
• Optical regenerator - May be necessary to boost the light signal (for long distances)
• Optical receiver - Receives and decodes the light signals

Transmitter
The fiber optic transmitter is like the sailor on the deck of the sending ship. It receives and directs the optical device to turn the light "on" and "off" in the correct sequence, thereby generating a light signal.

The transmitter is physically close to the optical fiber and may even have a lens to focus the light into the fiber. Lasers have more power than LEDs, but vary more with changes in temperature and are more expensive. The most common wavelengths of light signals are 850 nm, 1,300 nm, and 1,550 nm (infrared, non-visible portions of the spectrum).

Optical Regenerator
As mentioned above, some signal loss occurs when the light is transmitted through the fiber, especially over long distances (more than a half mile, or about 1 km) such as with undersea cables. Therefore, one or more optical regenerators is spliced along the cable to boost the degraded light signals.

An optical regenerator consists of optical fibers with a special coating (doping). The doped portion is "pumped" with a laser. When the degraded signal comes into the doped coating, the energy from the laser allows the doped molecules to become lasers themselves. The doped molecules then emit a new, stronger light signal with the same characteristics as the incoming weak light signal. Basically, the regenerator is a laser amplifier for the incoming signal.

Optical Receiver
The fiber optic receiver is like the sailor on the deck of the receiving ship. It takes the incoming digital light signals, decodes them and sends the electrical signal to the other user's computer, TV or telephone (receiving ship's captain). The receiver uses a photocell or photodiode to detect the light.

Advantages of Fiber Optics

Why are fiber-optic systems revolutionizing telecommunications? Compared to conventional metal wire (copper wire), optical fibers are:

• Less expensive - Several miles of optical cable can be made cheaper than equivalent lengths of copper wire. This saves your provider (cable TV, Internet) and you money.

• Thinner - Optical fibers can be drawn to smaller diameters than copper wire.

• Higher carrying capacity - Because optical fibers are thinner than copper wires, more fibers can be bundled into a given-diameter cable than copper wires. This allows more phone lines to go over the same cable or more channels to come through the cable into your cable TV box.

• Less signal degradation - The loss of signal in optical fiber is less than in copper wire.

• Light signals - Unlike electrical signals in copper wires, light signals from one fiber do not interfere with those of other fibers in the same cable. This means clearer phone conversations or TV reception.

• Low power - Because signals in optical fibers degrade less, lower-power transmitters can be used instead of the high-voltage electrical transmitters needed for copper wires. Again, this saves your provider and you money.

• Digital signals - Optical fibers are ideally suited for carrying digital information, which is especially useful in computer networks.

• Non-flammable - Because no electricity is passed through optical fibers, there is no fire hazard.

• Lightweight - An optical cable weighs less than a comparable copper wire cable. Fiber-optic cables take up less space in the ground.

• Flexible - Because fiber optics are so flexible and can transmit and receive light, they are used in many flexible digital cameras for the following purposes:
  • Medical imaging - in bronchoscopes, endoscopes, laparoscopes
  • Mechanical imaging - inspecting mechanical welds in pipes and engines (in airplanes, rockets, space shuttles, cars)
  • Plumbing - to inspect sewer lines

Because of these advantages, you see fiber optics in many industries, most notably telecommunications and computer networks. For example, if you telephone Europe from the United States (or vice versa) and the signal is bounced off a communications satellite, you often hear an echo on the line. But with transatlantic fiber-optic cables, you have a direct connection with no echoes.

How Are Optical Fibers Made?

Now that we know how fiber-optic systems work and why they are useful -- how do they make them? Optical fibers are made of extremely pure optical glass. We think of a glass window as transparent, but the thicker the glass gets, the less transparent it becomes due to impurities in the glass. However, the glass in an optical fiber has far fewer impurities than window-pane glass. One company's description of the quality of glass is as follows: If you were on top of an ocean that is miles of solid core optical fiber glass, you could see the bottom clearly.

Making optical fibers requires the following steps:

1. Making a preform glass cylinder
2. Drawing the fibers from the preform
3. Testing the fibers

Making the Preform Blank
The glass for the preform is made by a process called modified chemical vapor deposition (MCVD).

In MCVD, oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) and/or other chemicals. The precise mixture governs the various physical and optical properties (index of refraction, coefficient of expansion, melting point, etc.). The gas vapors are then conducted to the inside of a synthetic silica or quartz tube (cladding) in a special lathe. As the lathe turns, a torch is moved up and down the outside of the tube. The extreme heat from the torch causes two things to happen:

• The silicon and germanium react with oxygen, forming silicon dioxide (SiO2) and germanium dioxide (GeO2).
• The silicon dioxide and germanium dioxide deposit on the inside of the tube and fuse together to form glass.

The lathe turns continuously to make an even coating and consistent blank. The purity of the glass is maintained by using corrosion-resistant plastic in the gas delivery system (valve blocks, pipes, seals) and by precisely controlling the flow and composition of the mixture. The process of making the preform blank is highly automated and takes several hours. After the preform blank cools, it is tested for quality control.

Drawing Fibers from the Preform Blank
Once the preform blank has been tested, it gets loaded into a fiber drawing tower.

The blank gets lowered into a graphite furnace (3,452 to 3,992 degrees Fahrenheit or 1,900 to 2,200 degrees Celsius) and the tip gets melted until a molten glob falls down by gravity. As it drops, it cools and forms a thread.

The operator threads the strand through a series of coating cups (buffer coatings) and ultraviolet light curing ovens onto a tractor-controlled spool. The tractor mechanism slowly pulls the fiber from the heated preform blank and is precisely controlled by using a laser micrometer to measure the diameter of the fiber and feed the information back to the tractor mechanism. Fibers are pulled from the blank at a rate of 33 to 66 ft/s (10 to 20 m/s) and the finished product is wound onto the spool. It is not uncommon for spools to contain more than 1.4 miles (2.2 km) of optical fiber.

Testing the Finished Optical Fiber
The finished optical fiber is tested for the following:

• Tensile strength - Must withstand 100,000 lb/in² or more
• Refractive index profile - Determine numerical aperture as well as screen for optical defects
• Fiber geometry - Core diameter, cladding dimensions and coating diameter are uniform
• Attenuation - Determine the extent that light signals of various wavelengths degrade over distance
• Information carrying capacity (bandwidth) - Number of signals that can be carried at one time (multi-mode fibers)
• Chromatic dispersion - Spread of various wavelengths of light through the core (important for bandwidth)
• Operating temperature/humidity range
• Temperature dependence of attenuation
• Ability to conduct light underwater - Important for undersea cables

Once t­he fibers have passed the quality control, they are sold to telephone companies, cable companies and network providers. Many companies are currently replacing their old copper-wire-based systems with new fiber-optic-based systems to improve speed, capacity and clarity.

Physics of Total Internal Reflection

When light passes from a medium with one index of refraction (m1) to another medium with a lower index of refraction (m2), it bends or refracts away from an imaginary line perpendicular to the surface (normal line). As the angle of the beam through m1 becomes greater with respect to the normal line, the refracted light through m2 bends further away from the line.

At one particular angle (critical angle), the refracted light will not go into m2, but instead will travel along the surface between the two media (sine [critical angle] = n2/n1 where n1 and n2 are the indices of refraction [n1 is greater than n2]). If the beam through m1 is greater than the critical angle, then the refracted beam will be reflected entirely back into m1 (total internal reflection), even though m2 may be transparent!

In physics, the critical angle is described with respect to the normal line. In fiber optics, the critical angle is described with respect to the parallel axis running down the middle of the fiber. Therefore, the fiber-optic critical angle = (90 degrees - physics critical angle).

In an optical fiber, the light travels through the core (m1, high index of refraction) by constantly reflecting from the cladding (m2, lower index of refraction) because the angle of the light is always greater than the critical angle. Light reflects from the cladding no matter what angle the fiber itself gets bent at, even if it's a full circle!

Because the cladding does not absorb any light from the core, the light wave can travel great distances. However, some of the light signal degrades within the fiber, mostly due to impurities in the glass. The extent that the signal degrades depends upon the purity of the glass and the wavelength of the transmitted light (for example, 850 nm = 60 to 75 percent/km; 1,300 nm = 50 to 60 percent/km; 1,550 nm is greater than 50 percent/km). Some premium optical fibers show much less signal degradation -- less than 10 percent/km at 1,550 nm.

For more information on fiber optics and fiber optic transmission systems related topics, check out the links on the training categories.

Excellent Book Recommended "Fiber Optic Video Transmission: The Complete Guide - David R. Goff"

Synopses & Reviews

Publisher Comments:

Fiber Optic Video Transmission: The Complete Guide is the only comprehensive reference to the techniques and hardware required to transmit video signals over optical fiber. As the broadcast industry moves to HDTV and enhanced television standards become the norm, fiber will become the medium of choice for video transmission, and this book is the essential guide to transmitting video over fiber optic cables.

From the most basic video signal to complex multi-channel high definition video, this book details the methods of encoding video signals (including AM, FM, and digital encoding), the advantages and disadvantages of all encoding methods, and the expected performance of each method. A discussion of the the fiber optic components — such as lasers, LEDs, detectors, connectors, and other components — that are best for video transmission applications is also included. A glossary of terms, appendices of standards and publications, and a complete index round out this comprehensive guide.

*A detailed guide to the techniques and hardware required to transmit video over optical fiber

*Covers broad range of applications: cable T.V., studio-to-studio transmissions, medical imaging, distance learning, security and surveillance, and intelligent traffic systems

'Fiber Optic Video Transmission' Contents:

Introduction;

A Brief History of Video Transmission;

Brief History of Fiber Optics;

Convergence of Video & Fiber;

Basband Video Transmission;

CATV Applications; Digitized Video:

Uncompressed; Digitized Video: Compressed;

Transmitting Video: Copper vs. Fiber;

Characteristics of Optical Fiber;

Designing Fiber Optic Baseband Video Systems;

Designing Fiber Optic CATV Systems;

Designing Fiber Optic Digitized Video Systems;

Fiber Optic Baseband Video Links;

Fiber Optic CATV Video Links;

Fiber Optic Digitized Video Links;

Pushing the Limit: Long-haul Transmission;

Limitations due to Nonlinearities;

The Future for Video and Fiber;

Glossary of Terms;

Bibliography;

Index

Product Details

ISBN: 9780240804880

Subtitle:The Complete Guide

Author:Goff, David R.

Author:Goff, David

Publisher:Focal Press

Location:Oxford

Subject:General

Subject:Television & Video

Subject:Telecommunications

Subject:Fiber Optics

Subject:Optical communications

Series Volume:no. 37

Publication Date:December 2002

Binding:Hardcover

Language:English

Illustrations:yes

Pages:400

Dimensions:9.21 x 6.5 in.

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.