Introduction<br />Anoptical fiberis aglassorplasticfiber that carrieslightalong its length. <br />Fiber opticsis the overlap ofapplied scienceand engineeringconcerned with the design and application of optical fibers.<br /> Optical fibers are widely used infiber-optic communications.<br />Fibers are also used for illumination, and are wrapped in bundles so they can be used to carry images, thus allowing viewing in tight spaces.<br /> Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers. <br />
Classification Of Optical Fiber<br /> Multi-mode fibers (MMS):<br /> generally have a larger core diameter, and are used for short-distance communication links and for applications where high power must be transmitted .<br />Single-mode fibers(SMF):<br />They are using for most communication links longer than 550 meters (1,800 ft) .<br />
Advantages<br />Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communications.<br />Fibers are used instead of metal wires because signals travel along them with lessloss, and they are also immune toelectromagnetic interference.<br />
Objectives of our project:<br /> The well known advantages of optical fiber as :<br />Take advantage of optical fiber for obtaining more data rate.<br />Multiple access of users at same time & channel frequency distinguish between them by using PN codes.<br />Low cost, low loss, light weight.<br />Large bandwidth characteristics.<br />In addition to its transmission properties, the insensitivity of fiber optic cables to electromagnetic radiation .<br />
CDMA<br />CDMA is a spread spectrum technology that uses digital code division ,not frequency or time division, to realize multiple access.<br /> It is a multiple access technique that allow multiple user to share the same bandwidth channel by give every user a unique code .<br />
Clock Function<br />In a digital computer or controller, the device or circuit that supplies timing pulses to pace the operation of the system.<br />Clock signal in digital circuit is responsible for synchronizing the transfer to the data between processing elements.<br />
Frequency Divider<br />Divides the circuit input Frequency <br />The lower waveform is the generated signal from the clock circuit with a frequency (4 MHz) .<br /> The upper waveform is the output signal from divider circuit with a frequency (1MHz) .<br />
<ul><li> The lower waveform is the generated signal from the clock circuit with a frequency (4 MHz) .
The upper waveform is the output signal from divider circuit with a frequency ( 250KHz) .</li></li></ul><li>Frequency Divider Schematic:<br />
Function of PN Code: <br />We use sequence of random like noise to spread the signal and make it like noise level .<br />This techniques called CDMA . <br />Method of PN Code Generations:<br />LFSRs sequence through L=(2N - 1) states, where N is the number of registers in the LFSR<br />
Figure 1. Direct Sequence Spread Spectrum System<br />
An active filters offers the following advantages over a passive filters:<br />Gain and frequency adjustment flexibility.<br />No loading problem.<br />Active low pass filter<br />Passive low pass filter<br />
Low pass filter (LPF)<br />Definition:<br />A low-pass filter is a filter that passes low-frequency signals but attenuates (reduces the amplitude of) signals with frequencies higher than the<br /> cutoff frequency.<br />
Filter Design :<br />1- Choose a value of high cutoff frequency fH<br />2- select a value of C<br />3- Calculate the value of R using<br /> R= <br />4- select value of R1 and Rf dependent on the desired passband gain Af using <br /> Af =1+ <br />
: (500KHz) <br />LPFExperiment of<br />LPF for 500KHZ<br />
Band pass filter (BPF)<br />Definition:<br />A band-pass filter is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range.<br />
Filter Design:<br />1- Choose a value of high cutoff frequency fH<br />and low cutoff frequency fL<br />2- select a value of C<br />3- Calculate the value of R for LPF and R for HPF using<br /> for LPF R=<br /> for HPF R= <br />4- select value of R1 and Rf dependent on the desired passband gain Af using <br />1+ Af=<br />
Experiment of BPF: (500KHz)<br />BPF for 500KHZ<br />
Driver circuit schematic:<br /><ul><li>In our project we used the common-emitter amplifier to drive the optical source and convert the signal from theelectrical forminto optical formusing the intensity modulation. </li></li></ul><li>The Transmission Over Optical Fiber Test:<br />
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