A layer known as a buffer tube protects the cladding, and a jacket layer acts as the final protective layer for the individual strand.
If you look closely at a single optical fiber, you will see that it has the following parts:
• Core - Thin glass center of the fiber where the light travels.
• Cladding - Outer optical material surrounding the core that reflects the light into the core.
• Buffer coating - Plastic coating protects the fiber from damage and moisture.
Hundreds of thousands of these optical fibers are arranged in bundles in optical cables. The bundles are protected by the cable's outer covering, called a jacket.
Optical fibers come in two types
Single-mode fibers - Used to transmit one signal per fiber (used in telephones and cable TV)
Multi-mode fibers - Used to transmit many signals per fiber (used in computer networks, local area networks)
Some optical fibers can be made from plastic. These fibers have a large core (0.04 inches or 1 mm diameter) and transmit visible red light (wavelength = 650 nm) from LEDs.
Advantages of Fiber Optics
Compared to conventional metal wire (copper wire), optical fibers are:
- Less expensive - Several miles of optical cable can be made cheaper than equivalent lengths of copper wire. This saves your provider (cable TV, Internet) and your money.
- Thinner - Optical fibers can be drawn to smaller diameters than copper wire.
- Higher carrying capacity - Because optical fibers are thinner than copper wires, more fibers can be bundled into a given-diameter cable than copper wires. This allows more phone lines to go over the same cable or more channels to come through the cable into your cable TV box.
- Less signal degradation - The signal loss in optical fiber is less than in copper wire.
- Light signals - Unlike electrical signals in copper wires, light signals from one fiber do not interfere with those of other fibers in the same cable. This means more transparent phone conversations or TV reception.
- Low power - Because signals in optical fibers degrade less, lower-power transmitters can be used instead of the high-voltage electrical transmitters needed for copper wires. Again, this saves your provider and your money.
- Digital signals - Optical fibers are ideally suited for carrying digital information, which is especially useful in computer networks.
- Non-flammable - No electricity is passed through optical fibers, so there is no fire hazard.
- Lightweight - An optical cable weighs less than a copper wire cable. Fiber-optic cables take up less space in the ground.
Because of these advantages, you see fiber optics in many industries, including telecommunications and computer networks.
How fiber optics works
Fiber optics transmit data through light particles -- or photons -- that pulse through a fiber optic cable. The glass fiber core and the cladding each have a different refractive index that bends incoming light at a certain angle. When light signals are sent through the fiber optic cable, they reflect off the core and cladding in a series of zig-zag bounces, adhering to total internal reflection. The light signals do not travel at the speed of light because of the denser glass layers, instead traveling about 30% slower than the speed of light. To renew or boost the signal throughout its journey, fiber optics transmission sometimes requires repeaters at distant intervals to regenerate the optical signal by converting it to an electrical signal, processing that electrical signal, and retransmitting the optical signal.
Types of fiber optic cables
Multimode fiber and single-mode fiber are the two primary types of fiber optic cable. Single-mode fiber is used for longer distances due to the smaller diameter of the glass fiber core, which lessens the possibility for attenuation -- the reduction in signal strength. The smaller opening isolates the light into a single beam, which offers a more direct route and allows the signal to travel a longer distance. Single-mode fiber also has a considerably higher bandwidth than multimode fiber. The light source used for single-mode fiber is typically a laser. Single-mode fiber is usually more expensive because it requires precise calculations to produce the laser light in a smaller opening.
