Fiber Optic and Cable Experiment Report

This report summarizes key fiber optic experiments, including bending loss, numerical aperture, splice loss, and signal transmission over optical fibers, highlighting both theoretical and practical aspects.Objective

The primary objectives of the fiber optic experiments are to:

1. Study the relationship between input and received signals in fiber optic links.
2. Measure bending loss and understand its effect on signal attenuation.
3. Determine the numerical aperture (NA) of optical fibers.
4. Evaluate splice loss and overall attenuation using the fiber cut-back method.
5. Compare signal transmission characteristics between fiber optic and conventional cable systems .

Theory

Fiber optic communication relies on transmitting light signals through a core surrounded by cladding, using total internal reflection to guide light. The main components include a transmitter (LED or laser), the optical fiber, and a receiver (photodiode or PIN detector). Light signals carry information in analog or digital form, and losses can occur due to bending, impurities, or improper splicing .

• Bending Loss: Occurs when the fiber is flexed, causing light to escape the core. Smaller bend radii increase loss.
• Numerical Aperture (NA): Defines the acceptance angle for light entering the fiber and is calculated as the sine of the maximum acceptance angle.
• Splice Loss: Loss of signal at fiber joints due to misalignment or core diameter mismatch.
• Attenuation: Reduction in signal power along the fiber, measured using the cut-back method by comparing output power before and after shortening the fiber .

Materials and Equipment

• Optical fibers (plastic and glass) of various lengths
• Fiber optic connectors (ST, SC)
• LED or laser diode transmitter
• PIN photodiode receiver
• Optical power meter
• Function generator and CRO
• Epoxy and mechanical crimping tools for connector termination

Procedure

1. Signal Transmission: Connect the transmitter to the fiber and the receiver to measure input and output signals. Record amplitude and waveform characteristics.
2. Bending Loss Measurement: Flex the fiber at different radii and measure the corresponding power loss at the receiver.
3. Numerical Aperture Determination: Shine light at varying angles into the fiber and measure the maximum angle that allows light propagation.
4. Splice Loss Measurement: Join two fiber segments using a splice and measure the power loss.
5. Attenuation Measurement (Cut-Back Method): Measure output power for a long fiber, then cut it to a shorter length and measure again to calculate attenuation per unit length .

Observations

• Signal amplitude decreases with increased bending, confirming bending loss.
• NA measurements indicate the fiber's light acceptance capability.
• Splice loss varies depending on alignment and connector quality.
• Attenuation is higher in plastic fibers compared to glass fibers, consistent with theoretical expectations.
• Fiber optic links show lower signal degradation over long distances compared to conventional copper cables .

Conclusion

Fiber optic experiments demonstrate the advantages of optical communication, including high bandwidth, low attenuation, and immunity to electromagnetic interference. Bending and splice losses are critical factors affecting performance, and proper connector installation is essential for reliable operation. Numerical aperture and attenuation measurements provide insight into fiber characteristics, enabling optimized design and deployment of fiber optic networks .

References

• Optical Fiber Communication ECE Practical File
• Fiber Optics Lab Manual, The Fiber Optic Association
• EE 420 - Optical Fiber Communications Lab Manual
• Fiber Optic Experiment Report, Academia.edu
• Laboratory Manual Communication Systems Lab, CET