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Questions and Answers
What is the maximum operating temperature of plastic made fibers?
Which type of optical fiber is characterized by having a relatively small core that guides a single mode?
What is a key disadvantage of plastic made optical fibers?
Which characteristic is TRUE for glass made fibers?
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What material is typically used as the core in glass made fibers?
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What type of light sources are generally used for launching light into single-mode fibers?
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Which of the following statements is accurate regarding multimode optical fibers?
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Which of the following is NOT a feature of plastic made fibers?
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What characteristic distinguishes multimode optical fibers from single mode optical fibers?
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Which of the following is a characteristic of step index single mode optical fibers?
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What is the typical refractive index of silica fibers used in multimode optical fibers?
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What happens to light waves that meet the core-cladding interface at an angle below the critical angle in multimode fibers?
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Which type of optical fiber is primarily used for long-distance communication due to its high bandwidth?
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The core diameter of which type of optical fibers must be on the order of the wavelength of light to achieve single mode?
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What is a common application for step index multimode optical fibers?
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Which class of optical fibers has the consequences of having multiple paths for light rays due to varying angles of incidence?
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Study Notes
Material Based Optical Fibers
-
Plastic Optical Fibers:
- Manufactured from polymers, drawn into fibers.
- High losses, around 100s of dB.
- Low operating temperature (up to 125°C).
- Employed in sensors, process control, and short-distance communication.
- Features include high light-gathering capacity, large core area, low-cost components, compatibility with visible LEDs, and ease of connection.
- Examples:
- Core: Polymethyl methacrylate or Polystyrene
- Cladding: Co-polymer or Methyl methacrylate
-
Glass Optical Fibers:
- "Plastic Clad Silica" (PCS) fibers have a glass core and plastic cladding.
- Characteristics include high numerical aperture, large core diameter, high attenuation, and low bandwidth.
- Large core facilitates greater power coupling.
- High numerical aperture allows for less expensive surface emitting LEDs.
- Disadvantages include poor mechanical strength, low maximum operating temperature, and high attenuation.
- Example:
- Core: SiO2
- Cladding: P2O3 - SiO2
Modes of Light Propagation
-
Single Mode Fibers:
- Have a small core (few micrometers in diameter).
- Guide only one spatial mode, with a roughly Gaussian shape.
- Launch conditions affect power but not the spatial distribution of exiting light.
- Efficient light launch requires lasers and precise optical alignment for mode matching.
- Mode radius is typically 5 μm, with larger mode area fibers also existing.
- Larger mode area fibers have relaxed positioning tolerances but stricter angular requirements.
-
Multimode Fibers:
- Have dimensions much larger than the wavelength of the input signal.
- Guide a large number of modes.
- Multiple reflections at the core-cladding interface result in constructive interference.
- Circular dielectric waveguides with core diameters significantly larger than the wavelength are commonly multimode.
- Silica fiber core diameters are typically between 50 and 200 µm, while plastic fibers range from 0.5 to 1 mm.
- Mode propagation can be studied using geometric optics.
- All modes operate at the same wavelength.
Refractive Index-Based Classification
-
Step Index Fibers:
- Have a sharp change in refractive index from the core to the cladding.
- Single-mode step-index fibers have a tiny core, low numerical aperture, low attenuation, and high bandwidth.
- Core diameter must satisfy a specific formula for single-mode operation:
- Core Diameter <= 2.405 * Wavelength / (Numerical Aperture)
- Multimode step-index fibers:
- Core (n1) has a higher refractive index than the surrounding cladding (n2).
- Light travels along multiple paths with different angles of incidence.
- Light exceeding the critical angle θc is totally reflected and propagates along the core.
-
Graded Index Fibers:
- Refractive index gradually decreases from the core to the cladding.
- Light follows curved paths, reducing modal dispersion and allowing wider bandwidths.
- Typically used for longer distances compared to step index fibers.
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Description
Explore the characteristics and applications of both plastic and glass optical fibers. This quiz covers the materials used, their properties, and their roles in various technologies like sensors and communication. Test your knowledge on the advantages and disadvantages of these optical fibers.
