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 NanavatySource: Warren HiokiTelecommunications, 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 θ1 = n2 sin θ2

n1 and n2 = Refractive index of material 1 and 2

θ1=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 θ1 = n2 sin θ2

Θ2 = sin -1 (n1 sin θ1/n2) = sin -1(1.00 sin 52˚/1.33)

= 36.3˚

Source: Warren HiokiTelecommunications, 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 fiberIndex 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 HiokiTelecommunications, Fourth Edition

Instructor: Sam Nanavaty

Acceptance angle or numerical aperture (NA) measures the range of acceptance of light into a fiber.

NA = sin θA = SQRT (n12 – n2

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 NanavatySource: Warren HiokiTelecommunications, 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

http://www.corning.com/opticalfiber/

http://www.corning.com/opticalfiber/discovery_center/index.aspx

http://www.jdsu.com

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.