Electrical and Computer Engineering ETDs

Publication Date



To meet the demands of the exponential growth in video, voice, data and mobile device traffic over the internet, the telecommunication industry has been moving toward higher speed protocols such as 40-Gb/s and 100-Gb/s. Operations at such high speeds require detectors with optimized internal gain (leading to high sensitivity) to reduce cost. Avalanche photodiodes (APDs) are commonly used photodetectors in many high-speed optical receivers due to their internal optoelectronic gain, which allows the photogenerated current to dominate the thermal noise without the need for optical pre-amplification of the received optical signal. However, the long avalanche buildup time associated with APDs, namely the time needed for all the impact ionizations to settle, has limited their speed and stopped them from meeting the expectations of 40-Gb/s systems. A new approach was proposed recently for operating APDs employing bit-synchronous and periodic dynamic biasing that is expected to reduce the buildup time dramatically. In this dissertation, we present an extensive theoretical modeling and analysis for the novel approach of dynamically biased APD. We develop the first theory for the joint buildup-time and gain statistics for avalanche multiplication under dynamic electric fields. We also develop a theory for filtered shot noise under dynamic biasing, which addresses rigorously the statistic of the dynamically biased APD photocurrent, such as the mean, variance, autocorrelation function, etc. This is used, in turn, to derive analytical expressions for the statistics of the output of the integrate-and-dump optical receiver output. The study is characterized by its ability to predict the performance of a dynamically biased APD-based receiver and to optimize the system parameters to achieve an optimal receiver performance. The exact expressions for the receiver bit-error rate and sensitivity in an on-off keying setting will be extracted using the photocurrent statistics. The sensitivity analysis of the dynamically biased APD-based receiver will specifically capture intersymbol interference (ISI) and dark current, as well as Johnson noise from the trans-impedance amplifier used in the pre-amplification stage of receivers. The results show that operating the APD under dynamic biasing improves the receiver performance beyond its traditional limits operating under static biasing.


Communication Theory, Optical Receivers, Avalanche Photodiodes, Dynamic biasing, Branching process, Intersymbol Interference, Bit error rate, Receiver sensitivity, Gaussian distribution, Stochastic process, Dead space, Dark current and tunneling


This work has been supported by Prof. Majeed M. Hayats projects supported in part by the Science and Technology Corporation (STC.UNM) GAP Funding and in part by the National Science Foundation under the Smart Lighting ERC.'

Document Type




Degree Name

Electrical Engineering

Level of Degree


Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

Krishna, Sanjay

Second Committee Member

Santhanam, Bal

Third Committee Member

Zarkesh-Ha, Payman

Fourth Committee Member

Zhang, Guoyi