Experiment on Optical Fibre Transmission - Lab Report Example

Fibre Optic Communications Lab Report The rapid development in optical communications systems has created the need for the invention of better ways to modulate high bit rate links through fibre optics. This project is aimed at experimenting the signal modulation within a fibre channel with use of on-off keying or pulse position modulation. The fundamental modules entail a solid state function generator (with fixed TTL output signal), a plastic fibre, power supply, transmitter, two resistors, and a receiver, an oscilloscope and assorted heads. The results will be viewed on an oscilloscope screen showing the TTL signals generated from the output terminal that will show the outcome of changing the frequency of the signal information. The LED transmitters provide data source encoding for the fibre channel. The implications of this experiment will deliver and demonstrate the resultant effects of varying the intensity of the LED source. The transmission involves light of limited wavelength as low as between 400-700nm. The periodic signal generation is essential for implanting the on-off keying to deploy fibre optical communication. Table of Contents Title Page Abstract 1 List of Figures 3 List of Tables 3 1.Introduction 4 2. Design 5 2.1 The Experiment’s Setup 5 2.2 Inspection and Equipment Calibration 6 2.3 Recording Data Output 6 3. Results 7 3.1 Measured figures for a 10 kHz frequency 7 3.2 Measured figures for a 100 Hz frequency 7 3.3 Measured figures for a 1 kHz frequency 7 3.4 Graphical Results of the other frequencies 8 4. Discussion 10 5. Conclusions 10 6. References 11 List of Figures Figure Number and Title Page Fig. 1 Oscilloscope display at 100 Hz 6 Fig. 2 Oscilloscope display at 1 kHz 8 Fig. 3Oscilloscope display at 10 kHz 9 List of Tables Table Number and Title Page Table 1 The results at 10 kHz 7 Table 2 The results at 100 Hz 7 Table 3 The results at 1 kHz 7 1. Introduction Any typical optical fibre communication system contains a transmitter, an optic fibre cable, a receiver and a power supply balance between the source and destination. This project will study how the modulation of the signal frequency will affect the strength of the signal received and viewed on the oscilloscope. The internal of a fibre optic is usually made up of high quality silica glass meant to refract light information sent form a transmitter to a receiver for decoding. This wavelength properties of light transmitted are dependent on the fibre optic channel. The speed of the light within the optic fibre medium can be measured by looking at the refractive index of the fibre medium. This is represented in ratio formula by comparing the speed of light in the material over the speed of light in a vacuum environment (2). The equation utilized in calculating the refractive index is , where the Represent the angles of refraction and incidence at the boundary of the two materials while the n1 and n2 represent the refractive indices of the materials through which the light passes. Decisively, if light is propagated through a material that has a high refractive index to another that has a low refractive index, then the angle of refraction is usually 90º where the critical angle is - . This is shown This is the critical angle of incidence, beyond which if the light intensity exceeds between the two materials, then the light is totally internally reflected. Henceforth, the optical fibre communication channel is thin to facilitate the appropriate transmission by maintaining an incidence angle that is greater than that of the critical angle (1). Transmission of higher frequencies facilitates more information carriage capacity which makes it a viable option for fibre optic communication. The on-off keying scheme offers the simplest form of digital modulation performed by periodically switching on and off the carrier. This is achieved by using the TTL signal generator which provides a clear on-off signal. This is represented in a series of logical format od 1’s and ‘0’s. The resultant signal features for the optic communication also vary with the change in the fibre length. 2. Design 2.1 The Experiment’s Setup The equipment required to complete this experiment include: The SFH750V transmitter A Columnar breadboard A transmitter SFH250V photo-diode receiver A 5V power supply A 330 Ω and 470 Ω resistor Fibre optic cable Coaxial cable TTL signal generator – Digital oscilloscope 1. The power supply was set at 5V, and then the SFH750V transmitter was placed on the bread-board chamber while making sure that the anode and cathode terminals of the transmitter are not located on the same bread-board column. 2. The anode and cathode terminals of the transmitter was connected to the 5V power supply and then to a 330 Ω resistor. 3. Generally, the receiver which contains a SFH250V photo-diode connects in a reversed biased form where the cathode is connected to the 330 Ω resistor and its anode to the positive terminal of the same power supply 4. The fibre cable was the used to make the connection between the transmission and reception end. This was achieved by inserting the fibre cable ends into the threaded cavity of each component and gently tightening the holding nut. 5. The arrangements of the components on the bread-board were verified by cross referencing with the supplied laboratory script diagram. 6. The transmitting component was then connected to the TTL signal generator by using a coaxial cable which is earthed to the 5V power supply. The signal output from the generator was directed into channel 1 of the GW INSTEK digital oscilloscope 7. Channel 2 displayed the output from the photo diode receiver which made it easier to view both the received and output signal plus compare them. See Figure 2. 8. The transmission was tested for three different frequencies generated by the TTL signal generator. These included: 100 Hz, 1 kHz and 10 kHz. Figure 1. Oscilloscope display at 100 Hz 2.2 Inspecting and Calibrating Equipment The configuration of the oscilloscope made it easy to view the signal outputs. The LED transmission is confirmed using the setting of the fibre cable. This aids in confirming there is an actual signal transmission. The y-gain displayed on the screen is recognized before inspecting the signal output reading on the oscilloscope display. 2.3 Recording Output Data The data or information collected from the experimental outputs was then recorded in organized format for each of the attenuated frequencies used to test the transmission. The tabulated figures were or both the transmitted and received peak to peak voltage signal amplitudes. Snapshots of the oscilloscope demonstration for all the tested frequencies were taken. The amplitude shift for the transmitted and received signals was also noted. The resultant figures are represented below. 3. Results 3.1 Measured figures for a 10 kHz frequency Following the modulation of the frequency at 10 kHz, the following resultant figures were recorded. The subsequent power frequencies via channel 1 and 2 were noted and listed in the table below. Channel Y Gain (V/grid line) Peak to peak size (no. of grid lines) 1 2 V 2.2 2 100 mV 2 Table 3 The results at 10 kHz 3.2 Measured figures for a 100 Hz frequency Following the modulation of the frequency at 100 Hz, the following resultant figures were recorded. The subsequent power frequencies via channel 1 and 2 were noted and listed in the table below. Channel Y Gain (V/grid line) Peak to peak size (no. of grid lines) 1 2 V 2.2 2 200 mV 1.8 Table 1 The results at 100 Hz 3.3 Measured figures for a 1 kHz frequency Following the modulation of the frequency at 1 kHz, the following resultant figures were recorded. The subsequent power frequencies via channel 1 and 2 were noted and listed in the table below. Channel Y Gain (V/grid line) Peak to peak size (no. of grid lines) 1 2 V 2 2 50 mV 2.6 Table 2 The results at 1 kHz 3.4 Graphical Results of the other frequencies Figure 1 above shows the oscilloscope display at 100 Hz. The Channel and Channel 2 waveform displayed an asymmetrical shape that is closely the same. The upper waveform display well-formed square angles while the on Channel 2 waveform displays the received signal that can be differentiated form the first one because it has slight rounding on the edges. The Figure 2 below highlights the findings of the frequency range of 1 kHz. The generated signal is then compared for both the Channel 1 and 2 outputs. Notably, there is a well formed square wave for both but the channel 2 signal showcases increased rounding of the signal at the corners of the waveform. Figure 2 Oscilloscope display at 1 kHz Implementing a higher frequency range of 10 kHz transmitted via the circuit output a well formed square wave for the Channel 1 signal but the received signal (on Channel 2) was marked with saw tooth like features in shape. The Figure 3 below shows a reproduction Figure 3. Oscilloscope display at 10 kHz 4. Discussion Comparing all the waveforms produced for the different frequency signals. This experimental project aims to prove the need for signal optimisation and recovery to prevent data loss at different modulation occurrences. This can be seen by relating the figures presented in this report. Even the most slanted waveform in the setup depicts viable features for information transmission. The governing factors in the project also involved the consideration of the fibre length. Increasing its length would affect the dispersion rate of the signal since the signal loss directly varies with distance. The waveform sequence is caused by dispersion and increased bandwidth, or the strength of the signal. Other factors would be the rate of light absorption by the fibre material. Fibre optics communication networks offer fast and excellent ways for information transmission since it uses light (3). The prevention of information loss can be achieved by implementing cladding which guards against loss of internal reflection. The utilization of on-off keying facilitates the transmission of the information over a relatively long distance. 5. Conclusions Notably, the signal distortion of the waveform was high at higher frequencies. The transmission of binary information which is easily readable by computers via using an on-off keying scheme maintains a superior performance. Additionally, it is advantageous for use on deployed fibre since the attenuation or change in bit rate does not require sophisticated equipment configuration. The only setback noticed in this form of information transmission medium is exemplified by the distortion of the received signal waveform which is dependent on the frequency of the transmitted signal. 6. References 1. NAKAZAWA, M., KIKUCHI, K., & MIYAZAKI, T. (2010). High spectral density optical communication technologies. Berlin, Springer. http://public.eblib.com/choice/publicfullrecord.aspx?p=603114 2. NOÉ, R. (2010). Essentials of modern optical fiber communication. Berlin, Springer-Verlag. http://site.ebrary.com/id/10375207 3. PARKER, J. (2010). Communication. New York, Weigl Publishers. 4. SELVARAJAN, A. (2006). Optical fibre communication: principles and systems, p.17, Tata McGraw-Hill 5. WILLEBRAND, H., & GHUMAN, B. S. (2002). Free space optics: enabling optical connectivity in todays networks. 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