OPTICAL WAVEGUIDES
IS A PHYSICAL STRUCTURE THAT GUIDES ELECTROMAGNETIC WAVES IN THE OPTICAL SPECTRUM
COMMON TYPES OF OPTICAL WAVEGUIDES INCLUDE OPTICAL FIBER AND RECTANGULAR WAVEGUIDES
CAN BE CLASSIFIED ACCORDING TO THEIR
GEOMETRY
MODE STRUCTURE
REFRACTIVE INDEX DISTRIBUTION
MATERIAL
PLANAR WAVEGUIDE
WAVEGUIDE STRUCTURES GUIDING LIGHT ONLY IN ONE DIMENSION
STRIP WAVEGUIDE
BASICALLY A STRIP OF THE LAYER CONFINED BETWEEN CLADDING LAYERS -TWO DIMENSIONAL WAVEGUIDES
PRINCIPLES OF PLANAR AND STRIP WAVEGUIDES
TRANSVERSE RESONANCE CREATES MODES
LIGHTWAVE GUIDING CAN ONLY OCCUR AT ANGLES AT WHICH THE TRANSVERSE RESONANCE CONDITION IS FULFILLED
LIGHT PULSE ENTERING THE WAVEGUIDE BREAKS UP INTO VARIOUS MODES WHICH THEN PROPAGATE AT DIFFERENT GROUP VELOCITIES DOWN THE GUIDE
BECAUSE OF DIFFERENT GROUP VELOCITIED , EACH MODE WILL REACH THE OTHER END OF THE WAVEGUIDE AT DIFFERENT TIME
AT THE END OF THE GUIDE, THE MODES COMBINE TO CONSTITUTE THE OUTPUT LIGHT PULSE WHICH IS BROADER THAN THE INPUT LIGHT PULSE
MODAL DISPERSION LIMITS THE BANDWIDTH OF THE SIGNAL CARRIED DOWN IN THE WAVEGUIDE
OPTICAL FIBER WAVEGUIDE
STEP INDEX FIBER
A FIBER IN WHICH THE CORE IS OF A UNIFORM REFRACTIVE INDEX AND THERE IS A SHARP DECREASE IN THE INDEX OF REFRACTION AT THE CLADDING
GRADED INDEX FIBER
A TYPE OF FIBER WHERE THE REFRACTIVE INDEX OF THE CORE IS LOWER TOWARD THE OUTSIDE OF THE FIBER. IT BENDS THE RAYS INWARD AND ALSO ALLOWS THEM TO TRAVEL FASTER IN THE LOWER INDEX OF REFRACTION REGION. THIS TYPE OF FIBER PROVIDES HIGH BANDWIDTH CAPABILITIES
REFRACTIVE INDEX
THE RATIO OF LIGHT VELOCITY IN A VACUUM TO ITS VELOCITY IN THE TRANSMITTING MEDIUM
THE REFRACTIVE INDEX OF THE CORE IS UNIFORM AND STEP OR ABRUPT CHANGE IN REFRACTIVE INDEX TAKES PLACE AT THE INTERFACE OF CORE AND CLADDING IN STEP INDEX FIBERS
THE LIGHT RAYS PROPAGATE IN ZIG-ZAG MANNER INSIDE THE CORE. THE RAYS TRAVEL IN THE FIBER AS MERIDIONAL RAYS AND THEY CROSS THE FIBER AXIS FOR EVERY REFLECTION
STEP INDEX FIBER IS OF TWO TYPES VIZ; MONO MODE FIBER AND MULTI MODE FIBER
THE REFRACTIVE INDEX OF THE CORE OF STEP INDEX FIBER IS CONSTANT THROUGHOUT THE CORE
MODAL DISPERSION AFFECTS SIGNAL QUALITY IN STEP INDEX FIBER
THE REFRACTIVE INDEX OF CORE IS NON-UNIFORM , THE REFRACTIVE INDEX OF CORE DECREASES PARABOLICALLY FROM THE AXIS OF THE FIBER TO ITS SURFACE
THE LIGHT RAYS PROPAGATE IN THE FORM OF SKEW RAYS OR HELICAL RAYS. THEY WILL NOT CROSS THE FIBER AXIS
GRADED INDEX FIBER IS OF ONLY ONE TYPE, THAT IS MULTI MODE FIBER
THE REFRACTIVE INDEX OF THE CORE OF THE GRADED INDEX FIBER IS MAXIMUM AT CENTER, CORE AND THEN IT DECREASES TOWARDS CORE-CLADDING INTERFACE
GRADED INDEX FIBER PROVIDES ZERO DISPERSION AS THE VELOCITY OF MODES IS CHANGED BY CHANGING R.I SUCH THAT TIME TAKEN BY ALL MODES IS SAME
MERIDIONAL RAY
ENTERS THE FIBER THROUGH THE FIBER AXIS AND HENCE ALSO CROSSES THE FIBER AXIS ON EACH REFLECTION AS IT ZIGZAGS DOWN THE FIBER. IT TRAVELS IN A PLANE THAT CONTAINS THE FIBER AXIS
SKEW RAY
ENTERS THE FIBER OFF THE FIBER AXIS AND ZIGZAGS DOWN THE FIBER WITHOUT CROSSING THE AXIS
