Instructor: Sam Nanavaty Fiber Optics-1

Instructor: Sam Nanavaty Advantages of Fiber Optics Bandwidth Low attenuation (few tenths of dB/Km) Immune to crosstalk and EMI Does not emit electric noise Substantially lighter than copper Occupies significantly less volume than copper Difficult to tap in to Flexible Resistant to corrosion

Instructor: Sam Nanavaty Issues with Fiber optics Requires special end units (transmitters, receivers, couplers etc.) Requires special test equipment Requires strengthening material surrounding it. Unable to remotely power a device using fiber as fiber carries no current. New cables include additional metallic conductors for this very reason.

Instructor: Sam Nanavaty Source: Warren Hioki Telecommunications, Fourth Edition Silicone coating protects fiber from moisture. Buffer jacket provides protection from abrasion and shock Strengthening members are steel, fiberglass, Kevlar and Flame Retardant PVC

Instructor: Sam Nanavaty Snell’s law It is a fundamental law in optics that predicts the path of light rays as they travel between media. It is based on their indices of refraction. Mathematically, the Snell’s law may be stated as: n1 sin θ 1 = n2 sin θ 2 n1 and n2 = Refractive index of material 1 and 2 θ 1 =Angle of incidence θ 2 = Angle of refraction

Instructor: Sam Nanavaty A light ray is incident on the surface of water at an angle of 52° with respect to the normal. The light ray refracts toward the normal as it enters the more dense medium of water. To compute the angle of refraction for the light ray entering water from air medium, one must apply Snell’s law: n1 sin θ 1 = n2 sin θ 2 Θ 2 = sin -1 (n1 sin θ 1 /n2) = sin -1 (1.00 sin 52˚/1.33) = 36.3˚ Source: Warren Hioki Telecommunications, Fourth Edition

Instructor: Sam Nanavaty When travelling from glass media to air the ray of light bends away from the normal. When angle of incidence θ1 becomes large enough to cause the sine of refracted angle θ2 to exceed the value of 1, a total internal reflection occurs. This angle is called critical angle, θc

Instructor: Sam Nanavaty Internal Reflection within the optical fiber Index of refraction of cladding is about 1% lower than that of the core. The critical angle is approx 82˚ in this case Core is the center of the optical fiber made of ultra pure glass Source: Warren Hioki Telecommunications, Fourth Edition

Instructor: Sam Nanavaty Acceptance angle or numerical aperture (NA) measures the range of acceptance of light into a fiber. NA = sin θ A = SQRT (n 1 2 – n 2 2 )

Instructor: Sam Nanavaty Modes of transmission within fiber Single-mode fibers have small cores (approx 10 microns in diameter). They use laser diodes as transmission source (wavelength = 1,300 to 1,550 nanometers). Multi-mode fibers have larger cores ( approx 62.5 microns in diameter) They use LEDs as transmission source (wavelength = 850 to 1,300 nm).

Instructor: Sam Nanavaty Source: Warren Hioki Telecommunications, Fourth Edition

Instructor: Sam Nanavaty Laying new fiber is the traditional means used by carriers to expand their networks. Deploying new fiber, however, is a costly proposition ( This includes the cost of permits and construction as well) Laying new fiber may make sense only when it is desirable to expand the embedded base.

Instructor: Sam Nanavaty Increasing the effective capacity of existing fiber can be accomplished in two ways: Increase the bit rate of existing systems. Increase the number of wavelengths on a fiber

Instructor: Sam Nanavaty Wave Division Multiplexing

Instructor: Sam Nanavaty TDM WDM Single fiber / one wavelength Single fiber/ multiple wavelengths

Instructor: Sam Nanavaty Wavelength Division Multiplexing (WDM) Many wavelengths are combined onto a single fiber. Using wavelength division multiplexing (WDM) technology, several wavelengths, or light colors, can simultaneously multiplex signals of 2.5 to 40 Gbps each over a strand of fiber. Without having to lay new fiber, the effective capacity of existing fiber plant can routinely be increased by a factor of 16 to 128. The resulting capacity is an aggregate of the input signals, but WDM carries each input signal independently of the others. All signals arrive at the same time, rather than being broken up and carried in time slots (as in TDM).

Instructor: Sam Nanavaty WDM and DWDM use single-mode fiber to carry multiple lightwaves of differing frequencies. The difference between WDM and dense wavelength division multiplexing (DWDM) is DWDM spaces the wavelengths more closely than does WDM, and therefore has a greater overall capacity DO NOT CONFUSE THIS WITH transmission over multimode fiber, where the light is launched into the fiber at different angles, resulting in different "modes" of light. A multimode transmission only uses a single wavelength

Instructor: Sam Nanavaty Interesting links y_center/index.aspx

Instructor: Sam Nanavaty Assignment Companies involved in the manufacture of the Optical Fiber Additional components that are needed to activate the fiber optic link between two locations. Cost comparison between single mode,multimode fiber and CAT5 cable.