JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV Year OPTOELECTRONICS AND LASER INSTRUMENTATION Previous Question Paper (September - 2021 - R16)

Optical fibers are primarily classified based on their refractive index profile and the number of modes they support. The classification is as follows:

1. Classification based on the number of modes:

• Single-mode fiber: This fiber has a very small core diameter (typically 8-10 µm), allowing only a single mode of light to propagate. It eliminates modal dispersion, making it ideal for long-distance, high-bandwidth communication.
• Multi-mode fiber: This fiber has a larger core diameter (typically 50-62.5 µm), allowing multiple modes of light to propagate simultaneously. It is easier to couple with light sources but suffers from modal dispersion, limiting its use to shorter distances.

2. Classification based on refractive index profile:

• Step-index fiber: The refractive index of the core is uniform and changes abruptly to a lower value at the cladding interface. This creates a distinct 'step' in the refractive index profile.
• Graded-index fiber: The refractive index of the core decreases parabolically from the center toward the cladding. This design helps in equalizing the travel time of different modes, significantly reducing modal dispersion compared to step-index fibers.

Summary of common combinations:

3. Classification based on materials:

• Glass fibers: Made from high-purity silica (SiO2), these offer the lowest attenuation and are standard for telecommunications.
• Plastic Optical Fibers (POF): Made from polymers like PMMA, these are cheaper and more flexible but have higher attenuation, suitable for short-range consumer electronics or automotive applications.