Fiber Optic Video Transmission

The Complete Guide

David Goff

• Publisher: Routledge
• Year: 2013
• ISBN:
  9781136024894
• Edition: 1
• Topic: Languages & Linguistics
• Subtopic: Communication Studies
• Index: Languages & Linguistics

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.

Chapter 1

The Intersection of Two Cornerstone Technologies

This book discusses the convergence of two of the great technology forces of the last few decades: video transmission and fiber optic transmission. Video, like data and audio, represents an essential element in any modern communication system. However, fundamental differences set video transmission apart from data and audio transmission. Video signals require huge amounts of transmission capacity, or bandwidth, as well as one or more associated audio channels, and the system must transmit a continuous, uninterrupted signal in order to achieve proper reception. This contrasts sharply with data, where pauses in data reception are often only minor annoyances.

In its earliest incarnation, video signals traveled through the air – wireless using today's jargon. Video signal transmission used analog techniques and each channel consumed about 6 MHz of bandwidth. Over decades, the TV industry and technology evolved until more than 80 channels could be transported using the VHF and UHF bands. Audio shared a similar history, evolving into wireless AM and FM transmission formats, each requiring 10 kHz to 100 kHz of bandwidth per signal.

In parallel with the development of TV and radio, the telephone industry quietly advanced techniques for digitizing voice signals and then converting their copper-wired infrastructure to a fiber-based infrastructure. The telecommunications industry offered optical fiber its first large-scale application. In this process, an analog-to-digital (A/D) converter sampled 4 kHz analog voice channels 8,000 times per second, using an 8-bit format, to become 64 kb/s data channels. This 8-bit sampling format reduced the voice signals to 256 distinct levels, which proved adequate to reconstruct speech with little loss of clarity.

Broadcast quality digital audio soon followed, but in this application, the analog-to-digital conversion generated considerably more data. The initial CD format required sampling the audio signal 44,100 times per second using 16-bit words. The 16-bit words digitized the analog audio into 65,536 distinct levels providing much higher signal fidelity and higher bandwidth (20 kHz) as well. A stereo analog signal converted to the standard CD digital format generates a data rate of 1.411 Mb/s, 22 times higher than that required for voice telephone. New high-quality audio standards, such as DVD-audio, increase the sampling rate to 96 kHz using 24-bit words. This brings the number of distinct digitized levels to 16.8 million, increases the audio bandwidth to 48 kHz (well beyond the range of human hearing), and increases the digital data rate for a stereo audio signal to 4.6 Mb/s!

From Analog to Digital

As the demand for video increased, researchers considered ways to convert it to a digital format. This conversion presented some thorny issues compared to voice and audio; video required far more bandwidth. A typical uncompressed digitized video signal uses a minimum data rate of 270 Mb/s. In this case, the video is sampled at an effective rate of 27 million times per second using 10-bit words, giving 1,024 distinct digitized levels. (Actually, the brightness, or luminance, is sampled 13.5 million times each second and two additional color components are each sampled 6.75 million times per second, totalling 27 million samples per second.) The 270 Mb/s data stream also embeds audio and control signals.

Next generation HDTV video signals increase the serial data rate for a single uncompressed channel to 1,485 Mb/s, the equivalent bandwidth of 23,203 digitized telephone voice signals. Fiber provides the means to transmit more than one terabit of data per second. That enables fiber to transmit over 1,000 uncompressed HDTV signals and hundreds of thousands of MPEG compressed video signals at 19.4 Mb/s each. A few such signals would swamp even a gigabit data transport link.

In the late 1980s, Nicholas Negroponte of MIT's Media Lab developed a theory on the future of media that became known as the “Negroponte Switch.” This theory proposed that information once transmitted over the air – such as broadcast TV – would soon switch to wired architectures (fiber optic and copper). In contrast, wired services, chiefly voice telephony, would move to a predominantly wireless architecture, allowing for greater mobility. Despite numerous exceptions, communications and media have indeed made the “Negroponte Switch.” Most viewers receive today's television signals over wired architectures (cable TV), and a few minutes spent in any public place attests to the growing dominance of the cell phone in voice communications. Only the advance of fiber optic technology can support the “Negroponte Switch” because only fiber can provide the huge bandwidth needed.

Today, video transmission and fiber optic technology are intertwined and interdependent. Each technology supports and benefits from the other. Fiber provides the bandwidth needed to transport a multitude of video signals, which at the same time increases the demand for fiber. Today there exist literally dozens of ways to transport video over fiber. And despite the battle cries of the digitizers, the industry still uses amplitude modulation (AM) and frequency modulation (FM) to transport video over fiber. Why? Because, in many cases, these solutions still cost less than digital schemes. Still, fiber carries digitized video in numerous digital formats, ranging from nearly 1.5 Gb/s for a single digitized HDTV signal down to 9,600 Baud for highly compressed, low-resolution, low frame rate video signals.

Key Applications for Fiber Optic Video Transmission

Broadcast: Digital Video and High Definition Video

As the broadcast industry moves to digitized video and HDTV (high-definition television), or enhanced NTSC (National Television Standards Committee), the use of fiber optic technology becomes inevitable. This technology will revolutionize broadcast video in the same way that CD technology changed the audio industry. Figure 1.1 shows a typical HDTV transmitter.

Figure 1.1 – High Definition Serial Digital Component Video Transmitter

(Photo courtesy of Force, Inc.)

Fiber optic links can support both video and audio broadcast transmissions as well as data transmission. Video transport signal types include multichannel (4, 8, 12, 16, 40, 60, 80, and 110 channels are common), point-to-point RS-250, and digitized video (NTSC, CCIR 656, EU95, SMPTE 259). Audio transport signal types include the multichannel audio snake, point-to-point CD quality (stereo), and digitized audio.

The critical fiber parameters for broadcast are light weight, lightning immunity, high bandwidth, long distance, and excellent signal quality. Actual applications include: electronic news gathering (ENG), signals to TV camera pan/tilt/zoom pedestals, multimedia distribution systems, campus video distribution systems, intra-studio broadcasting, and inter-studio broadcasting. A studio-to-transmitter link (STL) represents one example of a inter-studio broadcast link. This application could utilize equipment such as the transmitter shown in Figure 1.1. Figure 1.2 illustrates a typical studio-to-transmitter link. The ATSC encoder implements the digital compression essential to making HDTV transmission practical.

Figure 1.2 – Studio-to-Transmitter Link

Broadband CATV Transport

Once dominated by such transmission media as twisted pair, copper coaxial cable, satellite, and microwave transmission, broadband CATV networks now look to fiber for the transmission of radio frequency (RF) signals. This transition results from an increased consumer demand for new services, speed, bandwidth, and cost-containment.

While all-digital systems may ultimately prevail, they are still prohibitively expensive to install and operate for many applications. Recently, hybrid fiber/coax cable (HFC) CATV networks have gained acceptance as an alternative to coppe...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Chapter 1: The Intersection of Two Cornerstone Technologies
• Chapter 2: A Brief History of Video and Video Transmission
• Chapter 3: A Brief History of Fiber Optics
• Chapter 4: Overview of Fiber Optic Transmission Methods
• Chapter 5: Characteristics of Optical Fiber
• Chapter 6: Fiber Limits
• Chapter 7: Electro-optic and Opto-electronic Devices
• Chapter 8: Basic Optical Components
• Chapter 9: Important Advanced Optical Concepts
• Chapter 10: Transmitters, Receivers, and Transceivers
• Chapter 11: The Nature of Video Signals
• Chapter 12: Video Over Fiber Using AM Techniques
• Chapter 13: Video Over Fiber Using FM Techniques
• Chapter 14: Video Over Fiber Using Digital Techniques
• Chapter 15: High Linearity CATV Fiber Optic Systems
• Chapter 16: Advanced Optical Components
• Chapter 17: End-to-End Systems
• Chapter 18: The Future of Fiber Optic Video Transmission
• Appendix A: Glossary of Terms
• Appendix B: Bibliography
• Appendix C: Fiber Optic Symbols
• Appendix D: Television Standards
• Appendix E: Societies, Conference Sponsors, and Trade Journals
• Appendix F: General Reference Material
• Appendix G: Optical and RF Conversions
• Index