Hello Mi Fans,
Welcome back to Mi Community Tech Class Session. In the previous Tech Class, you got all the information about SPDIF Connections. In today's Tech Class, you will learn about Fiber Optics.
Fiber optics are used as a data transmission method whereby data is converted into modulated waves of light to be sent over optical fiber cable. Fiber optics are an alternative to traditional copper-based data transmission cables over which they possess several advantages such as extremely high bandwidth, low losses even over great distances and inherent resistance to EMI.
It would take thousands of metal-based wires to replace one single fiber optic wire
How it Works?
Light is transmitted through the core of a fiber optical cable by bouncing off the walls of the cladding by the principle of total internal reflection allowing the fiber to act as a light waveguide. Because the cladding does not absorb light from the core, signals can travel great distances with only slight losses occurring from impurities in the glass. Fiber cable can be made to support a single propagation path (single-mode fiber) or multiple propagation paths (multi-mode fiber).
History of Fiber Optics
The birth of fiber optics dates back to the first demonstration of guiding light by refraction by Daniel Colladon and Jacques Babinet in early 1840s France. The first practical applications of optical fiber appeared early last century when it was used for internal illumination during dentistry procedures. It was not until 1965 though that fiber finally hit its potential when Charles K. Kao [Info: Nobel Prize recipient in Physics 2009] and George A. Hockham, of the firm Standard Telephones and Cables, proposed that optical fiber could be effectively used for telecommunications by removing impurities within the optical glass to reduce the signal attenuation to below the threshold of 20 dB/km. By the mid-seventies, doped optical glass produced by Corning yielded attenuation levels of just 4 dB/km.
Multi-mode Optical Fiber Detail
The first generation of deployed fiber came about in 1977 using GaAs semiconductor lasers to achieve a bit rate of 45 Mbps with repeater spacing of up to 10 km. A major milestone for fiber occurred in 1988 when the first transatlantic telephone cable to use optical fiber, the TAT-8, went into operation. Since then, the use of fiber has exploded to encompass virtually all long-distance telecommunications within the United States. In fact, the Internet as we know it today would not have been possible without a massive fiber optic infrastructure to carry the burden of such high data through fare.
Construction of Optical Fiber
Optical fiber cable is constructed by two dielectric layers: a core which is surrounded by cladding. In order to confine the light signal within the core, the core's refractive index must be greater than the cladding's. The physical boundary between the core and cladding is an abrupt change in step-index fiber and a gradual change for graded-index fiber. Both the core and cladding are fabricated from silica glass which has a typical refractive index of 1.5 [Info: The refractive indexes of the core and cladding typically differ by a mere 1%]. Surrounding the cladding is a buffer coating comprised of UV-cured urethane acrylate composite. Finally, a cable jacket layer acts as the last form of protection for the fiber cable from the environment.
Unlike metal-based electrical connections, combining lengths of fiber optic cable is a complex and delicate process. Care and special tools are needed to cleave the ends at the appropriate angle which is followed by either a mechanical connection or by fusing the ends with an electrical arc. For mechanical connections, special removable connectors are available exclusively for this purpose.
Civilian Fiber Optic Jacket Color Chart
Fiber Optics vs Copper Based Signal Transmission
Fiber Optic Bandwidth per Cable Size
Types of Fiber
Step-Index Multi-mode Fiber
Graded-Index Multi-mode Fiber
Step-Index Single-mode Fiber
Single-mode fiber cable is a thin, 9 μm core of glass doped with the element Germanium surrounded by a thicker layer of pure glass. While it can be used for nearly any application, single-mode fiber is optimized for near-infrared light transmission at wavelengths between 1,300 and 1,550 μm from lasers. This type of cable provides the backbone for the telecommunications industry in the United States.
Single-mode fiber is designed to transmit only a single mode of light which travels down the length of the cable core. Single-mode fiber optics exhibit a much narrower modal dispersion than their multi-mode cousins which makes them better suited for long-distance transmission and higher bandwidths than the latter. Single-mode cables are only deployed to non-local environments due to their requiring powerful and expensive lasers for operation.
Multi-mode fibers have large cores (typically 62.5 μm in diameter) and transmit infrared light (850 nm ≤ λ ≤ 1,300 nm) from LEDs. Multi-mode fiber is designed for transmission over small distances ( 1 km) such as within a building or a complex.
Multi-mode fiber's larger core size allows for the transmission of multiple paths of light. As each mode travels at its own propagation velocity, multi-mode fiber suffers from modal dispersion which limits the maximum length a signal can be transmitted through it. This shortcoming is made up for by multi-modes superior light gathering which allows signals to be driven with less powerful light sources such as light emitting diodes or vertical-cavity-surface-emitting lasers.
10 Gig Multi-mode Fiber
Society's ever-increasing data consumption has led to the development of high-bandwidth multi-mode optical fiber. Otherwise known as "aqua" fiber due to their aqua colored jacketing, these 10 Gig Multi-mode 50/125 μm cables use VCSELs as light sources. Because VCSELs emit fewer modes than their LED counterparts, bandwidth limitations due to modal dispersion are lessened in 10 Gig fiber optic cables. In fact, Data rates up to a theoretical 10 Gbps are possible with this type of fiber which also provides for full backward compatibility with older LED-based 50/125 multi-mode networks (but at slower speeds).
Fiber Optic Connectors
Mixing and Matching Fiber Types and Sizes
Without the proper equipment, you cannot mix fiber types or sizes. Connecting multi-mode to single-mode fiber cables will result in 20 dB signal losses which translate to a whopping 99% power loss. Even connecting 50/125 to 62.5/125 cables will result in a 3 dB signal loss which is 50% of the original power. However, by using mode conditioning cables which avert losses due to differential mode delay, single-mode fiber connections can be run over existing multi-mode networks without significant signal losses.
Care and Feeding of Fiber Optics
Unlike copper-based cables, fiber optic connections are rarely lost due to cable damage or breakage. However, dust, dirt and other contaminants each have the potential for disrupting or even severing an optical signal. Because fiber cables have such a small core (especially single-mode cables at 9 μm), even a 1-2 μm dust particle will cause significant optical signal loss. Oil too, such as from fingerprints while handling a cable, has the potential to ruin a fiber connection.
Fiber connections can be cleaned with either a wet or a dry cleaning method. For wet cleaning, fold a piece of lens paper a few times and lay it on a flat surface. After this, apply a couple of drops of isopropyl alcohol (rubbing alcohol) to the paper at which point it is ready for cleaning. To clean the fiber core, hold the connector in a vertical manner and lightly press the end against the lens paper while moving it in a figure-eight pattern. Repeat this motion a few times and follow this by removing any solvent build-up with a lint-free wipe or air dusting.
Dry cleaning a fiber connection is similar to wet cleaning and involves either a lint-free wipe (without adding solvent) or a reel-based fiber connector cleaner. As dry cleaning methods are abrasive in nature, the latter device is recommended as it effectively removes the potential for damaging the core's face by scratching due to a layer of padding below the cleaning surface.
In Case You Missed Previous Chapters:
Chapter 69: All About S/PDIF
In order to fulfill the basic functions of our service, the user hereby agrees to allow Xiaomi to collect, process and use personal information which shall include but not be limited to written threads, pictures, comments, replies in the Mi Community, and relevant data types listed in Xiaomi's Private Policy. By selecting "Agree", you agree to Xiaomi's Private Policy and Content Policy .