Advantages of optical fiber communication

Let us see the advantages of optical fiber communication over conventional communication system 

Enormous bandwidth: the information carrying capacity of a transmission system is directly proportional to the carrier frequency of the transmitted signals. The optical carrier frequency is in the range of 10^14Hz while the radio frequency is about 10^6Hz. Thus the optical fibers have enormous transmission bandwidth and high data rate. Using wavelength division multiplexing operation, the data rate or information carrying capacity of optical fibers is enhanced to many orders of magnitude.

Low transmission loss: due to the usage of ultra low loss fibers and the erbium doped silica fibers as optical amplifiers, one can achieve almost loss less transmission. Hence for long distance communication fibers of 0.002dB/km are used. Thus the repeater spacing is more than 100km. 

Immunity to cross talk: since optical fibers are dielectric wave guides, they are free from any electromagnetic interference (EMI) and radio frequency interference (RFI). Since optical interference among different fibers is not possible, cross talk is negligible even many fibers are cabled together. 

Electrical isolation: optical fibers are made from silica which is an electrical insulator. Therefore they do not pick up any electromagnetic wave of any high current lightening. It is also suitable in explosive environment.

Small size and weight: the size of the fiber ranges from 10 micrometers to 50 micrometers which is very small. The space occupied by the fiber cable is negligibly small compared to conventional electrical cables. Optical fibers are light in weight. These advantages make them to use in aircrafts and satellites more effectively.

Signal security: the transmitted signal through the fiver does not radiate. Unlike in copper cables, a transmitted signal cannot be drawn from a fiber without tampering it. Thus, the optical fiber communication provides 100% signal security. 

Ruggedness and flexibility: the fiber cable can be easily bent or twisted without damaging it. Further the fiber cables are superior than the copper cables in terms of handling. Installation, storage, transportation, maintenance, strength and durability.

Low cost and availability: since the fibers are made of silica which is available in abundance. Hence, there is no shortage of material and optical fibers offer the potential for low cost communication.

Reliability: the optical fibers are made from silicon glass which does not undergo any chemical reaction or corrosion. Its quality is not affected by external radiation. Further due to its negligible attenuation and dispersion, optical fiber communication has high reliability. All the above factors also tend to reduce the expenditure on its maintenance.

Basic structure of optic fiber cable

Basic structure of optic fiber cable

                                               

An optical fiber can be called as a dielectric waveguide. This waveguide operates at optical frequencies.

The fiber consists of three parts namely

1.       Core

2.       Cladding and

3.       Buffer coating

The core of the fiber is cylindrical and has a radius a. its refractive index is represented by n1.

The core is surrounded by a solid dielectric cladding whose refractive index is n2. The refractive index of the core n1 is always greater than the refractive index of cladding n2. The cladding gives mechanical strength to the inner core.

The buffer coating gives additional strength and prevents any damage to the fiber.

Since the cladding that surrounds the core has lower refractive index than the core, the light is guided through the core due to total internal reflection.

Beverage antenna

Herold beverage discovered in 20 that an otherwise nearly bidirectional long wire antenna becomes uni-directional by placing it close to the lossy earth and by terminating one end of the wire with a non-inductive resistor with a resistance approximately matched to the characteristics or surge impedance of the antenna. This was the fundamental discovery in his 1921 patent. From the transmission line theory we know that the line terminated with load impedance equal to characteristic impedance (Z๐), there is only a traveling wave present on the line. Since there is no reflected wave, there is no standing wave on the line. Then the line is said to be non resonant.

   

It consists of a wire one or two wavelength long. Note that the length of 1 or 2λ is not a small length at LF or MF; it is hundreds of feet at MF to several kilometers for LF. The wire runs parallel to the earth’s surface from the receiver towards the direction of the desired signal. The wire is suspended by insulated supports approximately two meters above the ground. A non-inductive resistor of value equal to characteristic impedance is installed from the far end of the wire to the ground. As the wire is properly terminated, the structure becomes a non resonant antenna.

Emulator

An emulator is a piece of hardware that is placed into application circuit to run and observe that operation of the system without developing stimulus files.

Types of emulators 

Software emulators: 

A software emulator allows computer programs to run on a platform (computer architecture and/ or operating system) other than the one for which they were originally written. Unlike simulation, which only attempts to reproduce a program’s behavior, emulation attempts to model to various degrees the state of the device being emulated. High- level emulation uses a combination of the two approaches in an attempt to retain as much accuracy as possible while having the advantages of simplicity and speed provided by simulation. 

Hardware emulator:

A hardware emulator is an emulator which takes the form of a hardware device. Examples include printer emulators inside the ROM of the printer, and FPGA based emulators.

A popular use of emulators is to mimic the experience of running arcade games or console games on personal computers. Emulating these on modern desktop computers is usually less cumbersome and more reliable than relaying on the original machines, which are often old and hard to find. Emulation of arcade and console systems on home PCs usually includes the practice of illegally downloading software from various electronic distribution sources. 

In a theoretical sense, any operating environment can be emulated within any other. In practice, it can be quite difficult, particularly when the exact behavior of the system to be emulated is not documented and has to be deduced through reverse engineering. It also says nothing about timing constraints; if the emulator does not perform as quickly as the original hardware, the emulated software may run much more slowly than it would have on the original hardware, or it may run too fast to be usable.

Simulators

A simulator is a program that simulates the functioning of electronic circuits. Simulator allows the designer to determine the correctness and efficiency of a design before the system is actually constructed.

 

A stimulus file is used for simulating input from external hardware. The stimulus file provides a series of inputs to the simulator to observe the overall behavior of system. The stimulus file for micro controller process consists for cycle counter and pin states.

An important consideration while selecting a simulator is its execution speed i.e. how fast it can execute the application’s instructions. If the execution speed of simulator is less compare to the processor then the simulator may take hours in a simulated environment. The delay may be due to complex interactions within the system being simulated. Therefore the simulator’s result are deviated from the actual operation.