Fiber Optics Continue to Connect Us to the Future
By Bob Hult, Bishop & Associates Inc.

The concept of transmitting information via optical signals has been in existence for many years. Alexander Graham Bell broke new ground when he invented the photophone in 1880. Bell’s system used a modulating beam of sunlight through free space to send his voice about 700 feet. In essence, this experiment was the world’s first wireless phone. Although it never became a commercial success, it opened another potential technology by which people could communicate between distant points.

Over the next 60 years, a series of incremental advances enhanced the ability to capture and retain light within flexible glass fibers, ultimately leading to the high-speed, long distance communication links that span the globe today.

Fiber optic links offer an enticing blend of exceptional bandwidth, resistance to crosstalk, electrical isolation, and ability to transmit over long distances with minimal distortion, as well as provide significant weight and size advantages over copper conductors.

A single optic fiber can convey the same number of high-speed signals as a copper bundle of twisted pair conductors many times its size. Improved signal fidelity and reduced installed cable maintenance are also very attractive features of optic transmission.

Fiber optic cables, fabricated in glass and plastic, have evolved to include a wide variety of constructions, including multimode step and graded index, as well as single-mode. In order to propagate pulses of light over long distances, fiber optic cables utilize the principal of total internal reflection. Light that enters one end of the fiber reflects off the boundary between the core and the cladding, which results in minimal loss and distortion to the signal.

In order to protect the fragile fiber, a series of protective layers surround the optical fiber. Cables may contain one or more fibers in bundled or planar configurations. 

The fact that our computing and telecom equipment infrastructure is currently based on the processing of electronic signals mandates that a conversion process is required before signals can be transmitted via optic ports.

A fiber optic link, as typically used in modern equipment, consists of a series of components required to convert electrical signals into pulses of light at the transmit end, and back into electronic signals at the receiver. Light emitting diodes (LEDs) or lasers inject light into the fiber, while photo detectors at the far end sense the incoming light stream and convert it back to electronic signals.

This conversion process requires power and generates heat, both factors that add headaches to system designers who do everything they can to reduce these effects. The need for conversion devices also adds cost to the system, which has been a major reason why optics have been limited to relatively long distance connections where copper is simply not practical or capable of providing the needed performance.

The logarithmic growth of the Internet raised concerns about the ability of the telecom infrastructure to support such a rapid adoption of this new media. Fiber optics was identified as a groundbreaking technology in the ‘90s, and a great amount of research and development work was invested in developing practical fiber optic components to replace copper interconnects. Engineers interviewed during this period predicted that copper would reach performance limits at three to five gigabits per second, and that a replacement technology was needed. Major advances were achieved in producing more powerful and efficient lasers, as well as connectors with significantly reduced loss characteristics. Even the venerable copper backplane became a target for migration to optic alternatives. Concepts were proposed for integrating optical waveguides within the traditional copper laminations. Several solutions for creating 90 degree bends within the board were prototyped. Many miles of fiber optic cables were laid in anticipation that only fiber would be able to provide the bandwidth pipe necessary to maintain the projected growth rate.

A number of events put a screeching halt on this market. A serious case of “irrational exuberance” finally collapsed in 2000, drastically adjusting the expectations of the entire electronics industry. A second factor was the continuous development of signal conditioning technology that enabled copper conductors to perform well in excess of what engineers had anticipated just a few years before. The promised fiber optic revolution has repeatedly been delayed, causing frustration and disappointment within the industry.

In some cases, the availability of large-capacity and long-distance fiber optic links has created highly successful business opportunities. The huge investment in buried long distance fibers drastically reduced the cost of telephone and Internet access on a global basis. According to American journalist Thomas Friedman, the availability of low-cost high-speed communication channels leveled the global business playing field, and enabled the rise in off-shore customer service functions, as well as competitive manufacturing to remote locations. Fiber optic links today are common in data center backbone and campus applications that demand high bandwidth links.

Fiber optic connectors have proliferated over the past 30 years into many different configurations, as the technology evolved and applications demanded.

Today’s fiber optic connectors can be organized in many ways.

• Single-mode/Multimode

• Plastic/Ceramic Ferrule

• Glass Fiber/Plastic Fiber

• Single Fiber/Multi-fiber

• Physical Contact (PC)/Expanded Beam

• Standard/Harsh Environment

• Commercial/Mil–Aero

• Industry Standard/Proprietary

• Standard/Small Form Factor

One solution to solving the copper vs. fiber optic link question is the use of pluggable small form factor interfaces. A printed circuit board mounted cage assembly is designed to accept either electronic or fiber optic adapter modules. Daughtercards are assembled with a common cage assembly, and then populated with a copper or optic module, depending on the application. Users have the advantage of easily converting the interface at a future time as requirements change.

In addition to these separable interfaces, the passive fiber optic hardware market includes permanent splices, splitters, combiners, attenuators, adapters, and fan-out assemblies.

A collection of both large and small manufacturers has sprung up to provide fiber optic interconnection products to the market. Connector industry recognized-leaders, such as Molex, Tyco Electronics, and Amphenol, offer a wide range of fiber optic interconnects, but a host of additional suppliers have carved out profitable niches with custom interfaces that are often application specific. At this point, the three major fiber optic product segments include industry standard connectors, which have largely migrated to Asian manufacturers due to commodity pricing; custom connectors, often designed to address specific user needs; and cable assemblies, which compete with advanced high-speed copper assemblies. Adding to the mix are fiber optic cable manufacturers, such as Corning, who offer a wide variety of cable assemblies that are primarily marketed to the equipment installer/user rather than equipment OEMs.

Fiber optic links are becoming more economical in shorter runs and offer additional advantages. Large server and data center applications are experiencing problems with huge bundles of copper cabling. Fiber optic assemblies offer a significant improvement in cable bulk, which in some applications may tip the scale to the advantage of fiber. A key question remains about when and if copper interconnect systems may ultimately reach a technical performance limitation, making fiber optics a cost-effective alternative, and enabling the continuing march to ever-higher system speed and performance.

Bishop & Associates Comments:

• Fiber optic links offer dramatic increases in bandwidth, speed, distance, as well as reduction in cable diameter.

• Fiber optics have been successfully implemented in long distance applications and are making inroads in shorter lengths. They remain a more costly alternative in very short and internal applications.

• The fiber optic market is highly fragmented, with many suppliers providing a huge array of both standard and custom interfaces.

• Some providers in this market have chosen to manufacture only fiber optic cable assemblies, rather than offer components.

•  Pluggable small form factor assemblies offer the ability to utilize copper or fiber I/O by simply changing a pluggable module, either at the OEM or later in the field. SFP+ and QSFP are examples of new products in this segment.

• Major advances have been made in the ability of advanced cable construction and chips to compensate for noise and signal distortion in copper interconnects. Copper cables, as well as backplane connectors, have demonstrated capability of 20+ Gb/s using these techniques. Few engineers are willing to predict an ultimate limit to the bandwidth of copper interconnects.

Several recently introduced fiber optic products combine the advantages of a standard electronic interface with reduced cable bulk.

Robert Hult
Director of Product Technology, Bishop & Associates, Inc.
Robert Hult has been in the connector industry for over 36 years. Hult began his career as a sales engineer for Amphenol. He joined AMP in 1972 and served in several management positions through 1996. In 1997, Hult joined Foxconn as group marketing manager for Intel, Chandler, Arizona, U.S.A. Prior to joining Bishop & Associates, Hult was the regional application engineering manager for Tyco Electronics.

Hult graduated in 1968 from Bradley University with a Bachelor of Science degree in electronics technology and a minor in business.