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Theory The direct far-field scanning technique measures the angular distribution of the far-field intensity distribution from the single mode fiber, F( p)2 .The variable aperture technique also measures power in the far-field but rather than making a continuous measurement of the intensity distribution, the total power passing through a set of circular apertures is measured. It is assumed that the far-field and therefore the fiber are rotationally symmetric. The apertures are centred on the optical axis of the fiber so that they are also centred on the axis of rotational symmetry of the far-field pattern. For a circular aperture of

The reason that fiber Ethernet ports can only transmit at one speed is that different light sources are utilized for each of the Ethernet configurations. 10Mbps Ethernet over fiber uses an 850nm LED (Light Emitting Diode), 100Mbps uses a 1300nm LED and 1000Mbps (1Gbps) uses a VCSEL (vertical Surface Emitting LASER). If a fiber port was capable of transmitting at all of these speeds each port would require three separate light sources which is not feasibly economic. Make sure that the port speeds are the same when connecting fiber switch ports. Also note it is recommended to always use LASER

The advantage of scanning the near-field intensity distribution of the test fiber directly is that there is no need for mathematical transformations of the measured data. If the intensity distribution of the aperture field, Ea(r)2,is measured then it can be input directly into equation 2-2 to give the effective area. The main difficulty with measuring the near-field is that it extends over very small area – typically 5-10-mm in diameter. Consequently, optics are required to produce a magnified image of the field that can be scanned radially using a detector with a pinhole in front or a fibre pigtail. The

Fiber optic cable provides a low loss medium for high-speed communications. While the continuous fiber cable itself is low loss, terminations at each access point provide a potential Achilles heel. The biggest cause of signal loss across fiber optic connectors is contamination. Poor installation practices in pathways and enclosures can also affect the signal loss of the fiber. The growing prevalence of fiber requires network technicians have a general understanding of fiber optic cable testing to enable them to troubleshoot or qualify cables. A majority of issues can be identified with two steps – cleaning/inspection of connector end-faces and loss

The line codes discussed in the previous lecture generally not the best line codes to be used because all of these line codes have the form of pulses. As it is known, pulses have spectrums of the form of sinc functions. So, in theory, channels with infinite bandwidths are required to transmit any of the line codes discussed previously. To study the performance of a line code we need to consider the Power Spectral Density (PSD) of line codes. The reason for not being able to use the Fourier transform to find the spectrum of a line code is that