Lecture 2 Optical Fiber Iksan Bukhori M Phil

Lecture 2: Optical Fiber Iksan Bukhori, M. Phil.

Light Theorem � Geometric optical approach � Light creeps straight � Speed in a vacuum � Speed in another medium v = c / n; n is the index of refractive of the medium �� air vacuum permit = � SNELL's law of reflection � The light comes, reflected light, and the normal line lies on the plane � Angle coming = reflected angle

Light Theorem - SNELL's law of refraction • Light continues to deflect close to normal • Light continues to deflect away from normal

Light Theorem � TIR (Total Internal Reflection) Light comes from a Medium with a higher index of refraction The angle is getting bigger, the light that keeps getting away from normal Continued angle = 900 This condition of the coming angle is called a critical angle When the angle comes > a critical angle occurs TIR

Light Theorem � Approximation of EM Waves - Light: Waves EM f ~ 1014 Hz

Light Theorem � Approximation of EM Waves - Polarization of EM waves

FRESNEL’S LAW (revision) Field coming: plane perpendicular to boundary plane and through direction of light propagation. The electric field vector is perpendicular to the propagation of light � The parallel polarization of the field comes: �

PERPENDICULAR POLARIZATION TO THE COMING PLANE

� Reflectance: Critical Angle: Anti reflection:

LIGHT THEOREM � A quantum theory approach - Light is a series of discrete quantized energies called quanta or photons - Light energy depends on frequency - Can explain the phenomenon of disperse, emission, and absorption

Fiber Optic

Optical fiber structure

Optical Fiber Materials � Terms: - Must be long - Must be translucent � efficient - Allows to have a small refractive index difference between the core and the skin � Eligible: - Glass Fiber - Halide Glass Fiber - Active Glass Fiber - Plastic Skin Glass Fiber - Plastic Fiber

GLASS FIBER Mixed fusion of metal oxides, sulfides / selenides.

Example of fiber composition

Halide Glass Fiber � Fluoride glass found by Universite de Rennes researchers in 1970 � It has very low losses at infrared middle frequency (0. 2 to 8 , lowest at 2. 55 ) � The main element is called ZBLAN � For a lower refractive index one part is replaced by making it a ZHBLAN for the skin � The low attenuation gain is 0. 001 to 0. 01 d. B / km � Losses difficult to make long because easy not to be glass (devitrification)

ZBLAN Key Element

ACTIVE GLASS FIBER

PLASTIC SKIN GLASS FIBER (PCS) � Silica nucleus � Plastic / polymeric skin (n = 1, 405 at 850 nm) or FEP (Ethylene Propylene Fluoride), n = 1, 338 � Higher NA � Only step index fiber � Advantage is cheap & coupling with source is good � Disadvantage is high attenuation, and low quality � Only suitable for short distance communication

PLASTIC FIBER � Core and plastic skin � Example: - Polystyrene core (n = 1. 60), methyl meta crylate skin (n = 1. 49) - Methyl meta crylate core, copolymer skin (n = 1. 40) � Advantages of large, cheap, easy to maintain, flexible angle acceptance large core size 110 s / d 1400 μm fit in LED � Only suitable for a very short distance of 100 m

OPTICAL FIBER �How does light propagate in optical fiber?

OPTICAL FIBER (TYPES OF OPTICAL FIBERS) �Single Mode Step Index

OPTICAL FIBER (TYPES OF OPTICAL FIBERS) �Step Index Multimode

OPTICAL FIBER (TYPES OF OPTICAL FIBERS) �Graded Index Multimode

GRADED-INDEX MULTIMODE (GI MM) FIBERS

OPTICAL FIBER CHARACTERISTICS �Numerical Aparture Numerical Aperture is a fiber optic ability to collect light

OPTICAL FIBER CHARACTERISTICS

OPTICAL FIBER CHARACTERISTICS � Bandwidth-distance product - A measure of fiber optic information capacity, otherwise in MHz. Km � Example: � BW 400 MHz. Km, meaning 400 MHz signal can be sent for 1 Km, or it can mean anyway

OPTICAL FIBER CHARACTERISTICS

MULTI-STEP SINGLE MODE FIBERS

FIBER PARAMETERS: SUMMARY

FIBER PARAMETERS: SUMMARY