Experiment on Optical Fibre Transmission - Report Example

Laboratory Report of an Experiment on Optical Fibre Transmission The transmission of information through optical fibres is one of the most efficient techniques use in the communication sector today. In this system, electronic signals are converted into light and transferred across the optical cables. This lab exercise aims at determining the optical sources that are best suited for on and off keying. This will be achieved through various tests and observations that will be discussed in this paper. Contents Title Page Abstract 1 Contents 2 List of Figures 3 List of Tables 3 1. Introduction 4 2. Design 5 2.1 2.2 2.3 3. Results 8 3.1 3.2 3.3 3.4 4. Discussion 9 5. Conclusions 9 6. References 10 List of Figures Figure Number and Title Page Fig. 1 5 Fig. 2 6 Fig. 3 6 Fig. 4 8 List of Tables Table Number and Title Page Table 1 8 Table 2 8 Table 3 8 1. Introduction Write your Introduction in the space provided. Use only this space – any inserted sheets will be ignored for marking purposes. The Introduction should cover relevant background information that will help in the understanding of the report, but which cannot be included in the other sections. Fibre optics are usually long and thin strands of pure glass. They are normally arranged in bundles that are called optical cables and are used to transmit signals over long distances [1]. The fibre optic system for data transmission is used to send information over the fibre optic by converting electronic signals into light. The optical sources are the best suited for on-off keying for optical transmission [3]. An optical fibre communication system normally comprises of 3 basic elements which include: 1. A constant source of power 2. A low loss or dispersion optical fibre 3. A photo detector The basic requirement of for the light sources used in optical communication systems usually depends on the nature of the intended application. Both the light emitting diodes (LEDs) and the laser diodes are normally used as sources in the fibre optic communication systems. The laser diodes are usually characteristic of high power requirement, high speed in signal transmission and narrow spectral width [2]. They are however show a high degree of sensitivity to variations in temperatures. Light emitting diodes normally have a surface emitting and edge emitting structures [8]. The surface emitting diodes are characteristic of ruggedness on the surface, a high degree of reliability, lower cost of operation and simplicity in the design of the system [6]. The sensitivity of the receiver can be defined as the minimum power of the light that is received that is required in order to achieve a defined signal to noise ratio and this is subject to improvement by the use of photon numbers of the squeezed light [5]. The performance of the digital heterodyne receiver can therefore be determined using the amplitude and the phase modulations using the on-off key source. 2. Design 2.1: Equipment required The following equipment were used in this exercise: 1. SFH750V transmitter 2. SFH250V receiver 3. 8-inch length of plastic fibre 4. Bread-board, power supply 5. 330Ω and 470 kΩ resistors 6. A function generator(with fixed TTL output signal) 7. Oscilloscope 8. Assorted leads. The SFH750V transmitter can be said to be an LED device that emits about 650nm and it is capable of outputting about 20 uw of light. It has a spectral width of 35 nm and requires a current that is dependent on the required intensity of 10-45 mA. The transmitter is usually a four pin device is it is composed of an LED, a glass bead and a chamber into which the optical fibre can be inserted. SFH250V receiver is a photo diode receiver and it is designed to be much more sensitive at 850nm and normally detects a signal of about 650nm. When it is used to detect a signal, a photo diode must be used in reverse bias [7]. Figure 1: The pin-outs for both devices, looking from the bottom The A = anode C = cathode N/C = not connected 2.2: Set up and method The power supply was set to 5V and SFH750V which is the transmitter device was placed on the bread-board ensuring that the A and C terminals are not in the same bread-board column. The anode was connected to a 330Ω resistor. Figure 2: typical SFH750V transmitter The other end of the resistor was connected through the wire to the positive terminal of the power supply and the negative terminal was connected through the wire to the cathode of the transmitter. The LED should be on. The receiver SFH250V was placed on the bread-board, ensuring the A and C terminals are not shorted. The device must be reverse-biased, so connect the cathode to the 470kΩ resistor, and the other end of the resistor to the positive terminal of the power supply, via wire. Connect the negative terminal of the supply, via wire, to the anode of the receiver. Figure 3: The negative terminal of the supply connected via wire to the anode of the receiver. Connect. 2. Design (continued) In this continued section you should include any preparations you had to embark on in order for the experiment to go ahead. This would include things such as, but not limited to, calculations, equipment calibration and setup. You are only allowed three sub-sections here: 2.1, 2.2 and 2.3. Each sub-section number must have a title of your choice, and that title must be inserted into the Contents section, along with a page number. Any extra section numbers, or inserted sheets, will be ignored for marking purposes. If the transmitters threaded cavity can be seen, tighten up the threaded nut as before. The end of the 330Ω resistor that is connected to the 5V power supply is disconnected. The wave form is recorded at 100 Hz, 1KHZ and 10KHZ. 2.3 Calculations 3. Results 3.1 Tabular data recorded Table 1: results for the 100 Hz frequency Channel Y Gain (V/grid line) Peak to peak size (no. of grid lines) Peak to Peak Voltage (V) 1 20 1.5 30 2 10 1 10 Table 2: results for the 1KHz frequency Channel Y Gain (V/grid line) Peak to peak size (no. of grid lines) Peak to Peak Voltage (V) 1 20 1.5 30 2 10 1 10 Table 3: results for the 10 K Hz frequency Channel Y Gain (V/grid line) Peak to peak size (no. of grid lines) Peak to Peak Voltage (V) 1 20 1.5 30 2 10 1 10 3.2: Observations The waveform observed had the following shaped. Figure 4:Graph for 100 Hz, 1khz and 10 KHz 4. Discussion The results from the experiment show a measurement of the optical waveform that is a continuous and a bandwidth of between 100 Hz and 10000Hz. A voltage of 30 V to 10V is recorded. The measured bandwidth size can be approximated to be equal to the number of the slices multiplied by the bandwidth of each slice. Therefore, for a specific given bandwidth, there is a given maximum trade off that is obtained between the number of spectral slices and the size of each bandwidth [4]. In case a short pulse of light emanating from a particular source such as a light emitting diode or a laser is directed down an optical fibre, it results into degradation. It eventually emerges in a much weaker state and much more distorted [7]. This can be attributed to communication principles such as attenuation of the signal because the pulse of the signal becomes much weaker due to the fact that the glass absorbs light and also due to the maximum power that can be supported by the fibre optic [6]. Other reasons for this occurrence are polarisation and dispersion. Dispersion normally occurs if a pulse of light coming from a source is spread out during the process of transmission. It can be chromatic dispersion, non modal dispersion or waveguide dispersion. It is also important to point out that the voltage of the system increases with the increase in the frequency input. 5. Conclusions In conclusion, it can be noted that a number of communication principles are necessary in optic fibre communication and it is as a result of these principles that pulses of light are transferred through the optic cables in the form of light signals over long distances. This technology is very fast and efficient and it can be said to be the future of data transmission. 6. References [1] T. Li, ed.,(1991), Optical Fibre Data Transmission, Academic Press, Boston. [2] H. B. Killen, (1991), Fibre Optic Communications, Prentice Hall, Englewood Cliffs, NJ. [3] P. K. Cheo, (1990), Fibre Optics and Optoelectronics, Prentice Hall, Englewood Cliffs, NJ. [4] T. C. Edwards, (2001),Fibre-Optic Systems: Network Applications, Wiley, New York. [5] J. C. A. Chaimowicz, (1989),Lightwave Technology, Butterworths, Boston, 1989. C.Lin, ed., Optoelectronic Technology and Lightwave Communications Systems, Van Nostrand Reinhold, New York. [6] P. J. Winzer,(2002),“Optical transmitters, receivers, and noise,”inWiley Ency-clopedia of Telecommunications, J. G. Proakis, Ed. New York: Wiley, pp. 1824–1840. [7] W. Idler, A. Klekamp, R. Dischler, J. Lazaro, and A. Konczykowska,(2003),“System performance and tolerances of 43-Gb/s ASK and DPSK modu-lation formats,inProc. ECOC 2003, Rimini, Italy. [8] E. A. Swanson, J. C. Livas, and R. S. Bondurant,(1994),“High sensitivity opti-cally preamplified direct detection DPSK receiver with active delay-linestabilization,”IEEE Photon. Technol. Lett., vol. 6,pp. 263–265. Read More