How Are Fiber Optic Cables Constructed?
Due to their delicate nature, fiber optic strands are protected by multiple layers of shielding, tailored to the type of cable:
1. Indoor Cable
Used inside buildings and structures, indoor fiber optic cables typically consist of:
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An outer flexible plastic jacket that protects the inner layers.
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Silk-like threads to prevent stretching.
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A small plastic casing containing the optical fiber.
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An internal rubber sheath to protect against bending and pressure.
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A central core made of ultra-pure glass, often as thin as a human hair (or even thinner).
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A reflective cladding layer around the core to guide the light internally.
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Additional protective layers made from specialized plastics.
2. Outdoor Cable
Designed for harsh external environments — whether buried underground or submerged deep in oceans — these cables share a similar internal structure to indoor cables but feature:
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A more durable outer jacket.
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Metal layers to resist moisture and environmental exposure.
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Steel armor or protective tubes to withstand high pressure.
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In undersea cables, diameters can reach up to 150 mm due to extensive protective layers.
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Higher fiber counts, ranging from 4 to 6912 individual fibers.
Two Main Types of Optical Fibers
1. Single-Mode Fiber
Designed for long-distance transmission, capable of sending signals up to 50 kilometers or more without needing repeaters.
Features an extremely narrow glass core (about 9 microns), allowing only one mode of light to pass.
Widely used in long-haul communications and backbone infrastructure.
2. Multimode Fiber
Allows multiple modes of light to travel simultaneously.
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Best suited for shorter distances, usually up to 2 kilometers.
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Has a larger core diameter (typically between 50 and 62.5 microns).
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Offers high-speed data transfer over short ranges, commonly used in local networks.
How Is Data Converted Into Light Signals?
In fiber optic systems, data isn't transmitted in its original electrical form. Instead, it's first converted into light pulses:
1. On the Transmitter Side
Data such as voice, images, or digital information arrives at a device called a transmitter .
The transmitter contains a laser diode or LED that rapidly turns on and off based on the data stream.
This process "chops" the light into pulses representing binary digits (0s and 1s).
2. Inside the Fiber
These light pulses travel through the glass core using the principle of total internal reflection, bouncing repeatedly with minimal loss.
3. On the Receiver Side
A receiver detects the incoming light pulses.
It then converts them back into electrical signals that electronic devices can interpret.
Why Fiber Optics Revolutionized Modern Communication
Compared to traditional copper cables, fiber optics offer significant competitive advantages:
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Huge bandwidth capacity : Terabytes of data can be transmitted per second.
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Low signal attenuation : Signals remain strong over long distances.
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Immunity to electromagnetic interference : Not affected by nearby electrical or magnetic fields.
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Cost-effective in the long run : Although installation costs are higher, maintenance and performance make them more sustainable.
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High security : Nearly impossible to tap remotely, as they emit no electromagnetic radiation.
How Analog Images and Videos Are Transmitted via Fiber Optics
Analog video and image signals can also be sent through fiber optics with ease:
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A camera sends an electrical signal representing the image.
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The transmitter converts this signal into light pulses.
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These pulses travel through the fiber to a remote location.
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Upon arrival, the receiver converts the light back into an electrical signal that can be displayed on a screen or stored digitally.
A single fiber can carry signals from multiple cameras simultaneously using advanced multiplexing techniques like Time Division Multiplexing (TDM) or Wavelength Division Multiplexing (WDM).
Main Transmission Modes in Fiber Optic Systems
1. Point-to-Point Mode
Direct connection between two devices.
Example: A camera or group of cameras sends signals directly to a recording device located elsewhere.
2. Node System Network
Devices have both input and output ports, enabling signal processing or retransmission.
Ideal for complex networks requiring data redistribution.
Can Cameras Be Controlled Over Fiber Optics?
Yes, certain types of switches and intermediate devices allow the transmission of both video and control signals for Pan-Tilt-Zoom (PTZ) cameras:
You can control camera rotation, zoom, focus, and other functions remotely.
Some advanced systems even support simultaneous transmission of audio, video, and control signals over the same fiber.
Written By Faisal Otari
First published in 2007
