FIBER OPTICS

Principle and propagation of light in optical fibers

Total internal reflection

Numerical aperture and Acceptance angle

• Numerical aperture / Light collecting capacity NA = ( n1

2 - n22 ) ½

• Acceptance angle = Sin -1 (NA)

Types of optical fibers

• Material • Mode• Refractive index profile

Material

• Glass fiber• Plastic fiber

• Glass fiberCore Cladding

SiO2 B2O3-SiO2

GeO2-SiO2 SiO2

P2O5-SiO2 SiO2

• Plastic fiber core cladding

polyurethene methyl metha crylatePoly methyl metha co-polymer crylate

Mode

• Single mode • Multi mode

Multimode

Refractive index profile

• Step index • Graded index

Double crucible technique of fiber drawing

Platinum crucible

Fiber manufacture

Splicing

connector

Loss in optical fiber

• Attenuation coefficient

Po is the power emitted from the source fiber

Pi is the power accepted by the connected fiber

Dispersion

• Dispersion chromatic intermodal dispersion

Bending loss

Fiber optical communication system (Block diagram)

Light sources

• LED• LASER

LED

LASER

Detectors

• PHOTO-DIODE• P-I-N DIODE

Photo diode• When a photon of sufficient energy strikes the

diode, it excites an electron, thereby creating a mobile electron and a positively charged electron hole.

Photodiode

P-I-N diode• The intrinsic "i" region is flooded with charge

carriers from the "p" and "n" regions.• Its function is similar to filling up a water

bucket with a hole on the side. If,water reaches the hole's level it will begin to pour out.

• Similarly the Pin diode will conduct where the number of electrons is equal to the number of holes in the intrinsic region

Fiber optic sensors – temperature & displacement

Endoscope