Eye diagrams

Eye diagrams are used for the assessment of data handling ability of a digital transmission system. Since this method is best in the evaluation of performance of wire-line systems, we can employ this technique for optical fiber data links. The eye-pattern measurements are conducted in time domain and permit the effects of waveform distortion to be shown soon after the measurements on the monitor screen of standard BER (Bit Error Rate) test equipment. The width of the eye opening gives a measure of time interval over which the received signal can be sampled without error due to interference from adjacent pulses. In this experiment, ideal time to receive and sample the waveform is when the height of the eye opening is largest. The height of the eye opening also gives an idea about the noise level. Sensitivity of the whole system to timing errors is related to the rate of closing of eye. Edge jitter which is also known as timing jitter or phase distortion is a signal distortion occurring in optical fiber system due to the noise present in the receiver and pulse distortion introduced in the optical fiber.