SUBMITTED BY- PROJECT GUIDE-

Aim of ProjectThe objective of this project is to replace all the

modulation units required for digital communication with a single unit where one can visualize all the working strategies as well as respective waveforms of all subunits like source encoder, channel coder and modulation units .

To achieve this goal we include introductory treatments on the subjects of OPTICAL FIBER COMMUNICATION SYSTEMS. This project is primarily meant for educational purposes, especially designed keeping in mind to showcase various communication units for electronics and electrical students. The encouragement, patience, technical support, enthusiasm provided by our esteemed institution, has been crucial in making this project a reality.

OPTICAL FIBER

An optical fiber is a thin, flexible, transparent fiber that acts as a waveguide, or "light pipe", to transmit light between the two ends of the fiber.

Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference.

Optical Fiber Cable

PRINCIPLE OF OPERATION

An optical fiber is a cylindrical dielectric waveguide (nonconducting waveguide) that transmits light along its axis, by the process of total internal reflection.

The fiber consists of a core surrounded by a cladding layer, both of which are made of dielectric materials.

To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding.

The most commonly-used optical transmitters are semiconductor devices such as light-emitting diodes (LEDs) and laser diodes. The difference between LEDs and laser diodes is that LEDs produce incoherent light, while laser diodes produce coherent light. For use in optical communications, semiconductor optical transmitters must be designed to be compact, efficient, and reliable, while operating in an optimal wavelength range, and directly modulated at high frequencies.

LIGHT EMITTING DIODEA light-emitting diode (LED) is a

semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.

LASER DIODEThe laser diode is a laser where the active medium is a

semiconductor similar to that found in a light-emitting diode. The most common type of laser diode is formed from a p-n junction and powered by injected electric current. The former devices are sometimes referred to as injection laser diodes to distinguish them from optically pumped laser diodes.

RECEIVERSThe main component of an optical receiver is a photodetector,

which converts light into electricity using the photoelectric effect. The photodetector is typically a semiconductor-based photodiode. Several types of photodiodes include p-n photodiodes, a p-i-n photodiodes, and avalanche photodiodes. Metal-semiconductor-metal (MSM) photodetectors are also used due to their suitability for circuit integration in regenerators and wavelength-division multiplexers.

AMPLIFIERSAn optical amplifier is a device that amplifies an optical signal

directly, without the need to first convert it to an electrical signal. An optical amplifier may be thought of as a laser without an optical cavity, or one in which feedback from the cavity is suppressed. Optical amplifiers are important in optical communication and laser physics.

WAVELENGTH-DIVISION MULTIPLEXING

Wavelength-division multiplexing (WDM) is the practice of multiplying the available capacity of an optical fiber by adding new channels, each channel on a new wavelength of light. This requires a wavelength division multiplexer in the transmitting equipment and a demultiplexer (essentially a spectrometer) in the receiving equipment. Arrayed waveguide gratings are commonly used for multiplexing and demultiplexing in WDM.

Optical Fiber

Optical Fiber

THE STRUCTURE OF A TYPICAL OPTICAL FIBER

AUDIO COMMUNICATION

A new, simple and efficient fiber audio transmission method for the long distance secure communication.

It performs signal modulation by the strain optic effects and the signal demodulation by the all fiber interferometer.

Interferometer is truly path matched device which eliminates much of the undesirable noise by combining the reference and the sensing arms within the same optical fiber.

The sinesoidal signals adopted in the experiment are in the frequency range of 300 hz. To 3400 hz. and of the multi frequency.

The device may be applicable in the field of point to point secure communicatuion of the 40 km. long transmission range.

SOME BASIC CONCEPTS OF OPTICAL FIBER AUDIO

COMMUNICATION

MODULATION TECHNIQUES The optical signal used for the optical communication

network can be generated with different modulation techniques. Their are four basic physical attributes that can be modulated to optically transmit information: intensity, phase, frequency, and polarization. The electrical signal is modulated by the carrier signal. Depending on depending on which parameter of signal is modulated, the modulation techniques can be divided into amplitude shift keying (ASK), frequency shift keying (FSK), phase shift keying (PSK) and polarization shift keying (PolSK).

Principle of optical signal modulation

AMPLITUDE SHIFT KEYING

Amplitude-Shift-Keying (ASK) known as”On-Off”-keying (OOK) is the technique of modulating the intensity of the carrier signal is shown in figure. In the simplest form, a source is switched between on and off states. The ASK modulation is characterized b y the relation between the signal levels in on and off states called extinction ratio (ER).

FREQUENCY SHIFT KEYING Frequency Shift Keying (FSK) is realized by switching the

laser light frequency between two frequency values as shown in figure (1.1). In FSK, the optical signal envelope remains unchanged and the complexity of signal generation and detection increases compared to ASK modulation. FSK modulation is characterized by the modulation index.

PHASE SHIFT KEYING

Phase Shift Keying (PSK) uses the phase of the signal to encode information. Optical PSK signals posses a narrow spectrum and a constant signal envelope as shown in figure, which enables improved nonlinear tolerance, but on the other hand the PSK signals are sensitive to a phase modulation induced by multi-channel effects, which can result in decoding errors at the receiver side.

POLARIZATION SHIFT KEY

Polarization Shift Keying (PolSK) is the most exotic modulation format among all already presented. The optical PolSK signals are generated by switching the signal polarization between two orthogonal states of polarization. T he PolSK is characterized by a constant signal envelope enabling an improved nonlinear tolerance, an improved sensitivity (3 dB) [6] compared to ASK-based modulation, and enable a better utilization of the system bandwidth by the use of orthogonal polarization as an additional degree of freedom.

COMPONENTS USED PARTS (COMPONENTS) LIST [TX] R1 3K3 R2 4K7 R3, R4 10K R5 100E R6 1K P1 1M/3006 TRIMOT C1 1000UF/16V C2 22UF/16V C3 47KPF DISC C4 10UF/25V D1-D4 4007 DIODE (4 NOS) U1 LM7809 U2, U3 LM741 Q1 BC547 TX1 FBO TRANSMITTER 2 NOS 8 PIN IC SOCKET 1 NOS CON.MICE 1NOS 0-2 / 250 ma X’MER

PART (COMPONENTS) LIST [RX] R1 100K R2 1M R3 1K R4 100K R5 100K/3006 TRIMPOTE R6 10K LOG VOLUME CONTROL R7 220L R8 100K R9 10K R10 4.7E C1, C2, C3, C4, C5 0.1UF DISC (104) C8, C9 C2 1000/16V C6 10UF/25V C10 10UF/25V C11 47KPF DISC D1-D4 4007 DIODE (4NOS) U1 LM 7805 U2 LM 358 U3 LM 386 RX1 FIBER OPTIC RECEIVER 2 NOS 8 PIN IC SOCKET 1 NOS 0-12/250 ma X” MER

CIRCUIT EXPLANATION This project allows you to send sound through 1mm plastic

fibre optic (FO) cable. On the transmitter (TX) circuit board there is a microphone and a circuit to modulate the light emitted from an LED. The LED is contained in a plastic case, which allows easy connection of the FO cable. On the receiver (RX) board there is the photo-darlington receiver unit, a speaker and a circuit to convert and amplify the detected signal back into a sound wave. Because the signal travels in the FO cable as a light wave, it is unaffected by any electric or magnetic fields that it travels through. The voice signal begins as a sound wave. It is converted to an electrical signal by a microphone in the TX circuit. This signal is amplified by the LM741 audio amplifier and converted to an optical signal by switching.

Circuit Diagram

The voltage to the optical fiber is transmitted via a signal transistor. This optical signal is fed into the plastic fiber optic cable . At the other end of the cable,the optical signal is directed at a photo darlington in to receiver, which converts it to an electrical signal again. The signal is amplified and fed into a speaker where it become a sound wave. A voltage regulator has been used in the circuit to overcome feedback in the circuit. The voice signal begins as a sound wave. It is converted to an electrical signal by a microphone in the TX circuit. This signal is amplified by the LM741 audio amplifier and converted to an optical signal by switching. The voltage to the optical fiber is transmitted via a signal transistor. This optical signal is fed into the plastic fiber optic cable. At the other end of the cable, the optical signal is directed at a photo Darlington in to receiver, which converts it to an electrical signal again. The signal is amplified and fed into a speaker where it becomes a sound wave. A voltage regulator has been used in the circuit to overcome feedback in the circuit.

CONCLUSION

Fiber optic transmission has found a vast array of applications in computer systems. Some design considerations depend largely on the application. For certain terminal to terminal application, crucial factors including maximising transmission speed and distance and minimising fiber and splice loss. By contrast, connector loss becomes important in local area networks that operate within buildings. In other systems, it is important to minimise the cost of cable, with the intention of reducing the cost of terminal equipment. These system considerations make design and construction of practical fiber optic systems a difficult task. Guidelines appropriate for one system is usually not suitable for another system.

References and BibliographyG. P. Agrawal, Fiber-Optic Communication Systems, 3rd

edition (Wiley, Hoboken, NJ, 2002)R. Ramaswami and K. Sivarajan, Optical Networks 2nd edition

(Morgan, San Francisco, 2002).G. E. Keiser, Optical Fiber Communications, 3rd ed. (McGraw-

Hill, New York, 2000). www.wikipedia.com/optical fiber.html www.wikipedia.com/optical fiber commmunication

system.html www.wikipedia.com/optical fiber transmitters.html www.wikipedia.com/optical fiber receivers.html

THANK YOU