A fiber optic cable is a type of network cable which uses thin and flexible fibers made of glass for communication. It works on the optical properties of glass, hence the name fiber optic cable. The glass fiber used is the thickness of a hair and protected by an insulated casing. Fiber optic cables use the light of different wavelengths to transmit data. This light is generated by small lasers or light-emitting diodes (LEDs). They are designed for high performance regarding speed, reliability and data transmission over long distances. There are two types of fiber optic cable as single mode and muti-mode. Most of the world’s internet is now supported by fiber optic cables.
Composition and function of an optic fiber
Optical fiber works on the property of reflection. When light is passed through a medium, it either gets reflected or refracted (goes through the medium).
The amount of light reflected/refracted depends on the property of the medium called refractive index. The higher the refractive index of a medium, more light will pass through it.
Optical fibers are made of cylinders of glass. They can be viewed as two transparent glass cylinder, one surrounding the other. The inside cylinder is called the core of the fiber.
The optical fiber is designed in a way that the refractive index of the core is much higher than the outer glass cylinder. The outer cylinder is called the cladding.
When light is passed through the fiber, it gets transmitted through the core. However, when it tries to move to the outer cylinder, it gets reflected back due to the cladding’s low refractive index.
This prevents the loss of light and promotes transmission through bends while transmitting over long distances. The outer glass cylinder is covered with a polymer layer for protection and easy handling of the fiber. This protective layer is called the jacket.
For glass optical fibers, the diameter of the core has a range of 10-600 microns, the thickness of cladding is between 125-630 microns, and the jacket’s thickness varies from 250 microns to 1040 microns.
Types of optic fibers
Based on the thickness of the core and wavelength of light used, two types of optical fibers can be deployed as single mode fiber and multi-mode fiber. These two fibers have different advantages and can be used per the requirement.
In single mode optical fibers, the diameter of the glass strand that makes up the core is between 8.3 to 10 micron and allows only one mode of transmission.
The narrow core allows propagation of light with the wavelength ranging between 1310nm and 1550nm. For this, the source of light should have a very narrow spectral width. Lasers are typically used in this mode of transmission.
Single-mode fibers have many advantages. They can support a larger bandwidth, allowing a higher transmission rate. Since this mode uses a small core and very narrow wavelength band, this reduces distortions from overlapping light pulses.
This provides least signal attenuation and highest transmission speed of any fiber cable type.
Single mode fibers are more expensive than other types of fiber and primarily used in long-range transmission from kilometers to thousands of kilometers with right kind of single mode devices.
- 10 Gbps for distances of over 80 km (with commercially available transceivers)
- Hundreds of kilometers at 40 Gbps & thousands of kilometers at 10 Gbps (using optical amplifiers and dispersion-compensating devices)
In multi-mode fiber communication, the thickness of the glass core is kept between 50 and 100 microns. The most common size is 62.5 microns followed by 50 microns and 100 microns.
The cables are designed such that they can support a large band of wavelength. These fibers are cheaper to produce than single-mode fibers.
Multi-mode fibers offer high bandwidth and high speeds but only over medium distances. But the distance depends on the network speed.
- 100 Mbps for distances up to 2 km
- 1 Gbps up to 1000m (meter)
- 10 Gbps up to 550m (meter)
To get an idea of the distance, note that multi-mode fibers are deployed in universities and small process plants. When light is passed through the core, it disperses into numerous modes or paths as they travel through the cable.
This is not suitable for long-range transmission due to possible signal distortion resulting in incomplete data transmission.
POF or polymer optical fiber is a new alternative to glass optical fiber. They boast of the low cost of production and similar benefits as the multi-mode optical fibers.
Advantages of fiber optic cables
Fiber cables offer several benefits when compared to long-distance copper cables
When compared with copper wires with the same thickness, optic cables carry a much larger bandwidth. With optical cables, you can easily get data transfer rates of 10 Gbps, 40 Gbps and even 100 Gbps.
Data amplification is redundant
Since light can travel very long distances in the core of a fiber cable without losing its strength, it reduces the need to use signal boosters.
An optic fiber is less susceptible to interference. A copper cable requires special shielding to avoid electromagnetic interference.
However, when many cables are strung together in the proximity, the shielding is not able to prevent interference. The physical properties of the optic cables do not require any shielding and avoid most of these issues.
How to choose right kind of fiber optic cable?
These days, people prefer single mode over multi-mode fiber optic cable because of two important reasons. Firstly, a single mode fiber optic cable can help in longer distance network communication and secondly, it can carry the higher bandwidth of data.
But do you have such requirements all the time? Probably, No. Single mode fiber optic cables are cheaper than multi-mode fiber cables but the price of optics and equipment, which are used in a single mode fiber network, is 4 to 5 times of multi-mode equipment.
On the above, if your data transmission requirement in a few Mbps and distance requirement is in a few hundred meters, then multi-mode fiber optic will do more than sufficient.
In short, price, network speed and distance are the three most factors to be considered while making the selection between single mode and multi-mode fiber optic network.
Fiber optic deployment for household
Fiber optic cables are predominantly used in long-distance connections such as between cities or even countries. However, some residential ISP have started fiber cables for providing high-speed internet to the household as.
These installations are commonly referred to as “last mile” installations. Depending on how these cables are deployed, they can be categorized as one of the below:
- Fiber to the Household (FTTH): In this case, the fiber is laid till your house. Some known FTTH services in the market include Google Fiber and Verizon FIOS. These services can provide up to 1 Gbps internet speeds per household.
- Fiber to the Premises (FTTP): This is a low-cost package where the fiber is laid till the building.
- Fiber to the Building/Business/Block (FTTB): This is the same as FTTP.
- Direct fiber: In this case, the fiber leaves the central office and is directly attached to only one customer. This provides the greatest bandwidth but is more expensive.
- Shared fiber: This is a less expensive version of direct fiber. When the fiber gets close to the premises of nearby customers, it is split into multiple fibers, and each fiber is then provided to an individual customer
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