Four-Level Pulse Width Modulation for Fiber Optic Communications

• Published in: IEEE transactions on communications Vol. 30; no. 8; pp. 1958 - 1963
• Main Authors: Dai Xianda, Englefield, C., Goud, P., Razdan, R.
• Format: Journal Article
• Language: English
• Published: IEEE 01.08.1982
• Subjects: Bit error rate; Noise level; Optical fiber communication; Optical modulation; Optical noise; Optical pulses; Optical receivers; Pulse amplifiers; Pulse width modulation; Space vector pulse width modulation
• DOI: 10.1109/TCOM.1982.1095677
• ISSN: 0090-6778

The performance of a digital fiber optical system employing four-level pulse width modulation (PWM) is considered. It is shown that PWM may be an attractive alternative to pulse amplitude modulation (PAM), especially if a wide band channel is used. The probability density function (pdf) of the timing error is obtained in terms of the pdf of the noise amplitude, taking into account the thermal noise of the amplifier and the signal-dependent shot noise introduced by the photodiode detector. Near-Gaussian optical pulse edges at the receiver are assumed. Using typical system parameters, the variation of bit error rate (BER) with power level, and the effects of different bit rates, mean photodetector gain, and system bandwidths are calculated. It is observed that minimum BER's are achieved at moderate values of mean photodetector gain and that increased system bandwidth results in increased receiver sensitivity.