Plastic Fiber Optics. III: Off-Axis Transmission Characteristics

Area of Science:

• Optics and Photonics
• Materials Science

Background:

• Plastic optical fibers (POFs) are widely used in various applications.
• Understanding light propagation and loss mechanisms in POFs is crucial for system design.

Purpose of the Study:

• To investigate the impact of input light direction on output intensity patterns and total throughput in plastic fiber optic systems.
• To analyze the causes of throughput decrease beyond geometrical predictions, focusing on interface reflection losses.

Main Methods:

• Experimental measurement of output intensity patterns and total throughput.
• Varying the input light direction from normal to oblique incidence.
• Analysis of reflection losses at the core-sheath interface using geometrical and physical optics principles.

Main Results:

• Output intensity patterns transform into a conical shell with increasing obliquity.
• Total throughput decreases significantly with oblique input, exceeding geometrical predictions.
• Reflection losses of the order of 10^-4 were observed for angles of incidence >= 70 degrees.
• Sheath penetration at internal reflection is identified as the primary loss mechanism for angles > critical angle.

Conclusions:

• The core-sheath interface is a significant source of loss in plastic optical fibers, particularly at higher angles of incidence.
• Sheath penetration during internal reflection contributes more to loss than bulk absorption.
• Interface quality is generally high, with imperfections playing a minor role except at near-grazing angles.