The Bit Error Performance and Information Transfer Rate of SPAD Array Optical Receivers

In this paper the photon counting characteristics, the information rate and the bit error performance of single-photon avalanche diode (SPAD) arrays are investigated. It is shown that for sufficiently large arrays, the photocount distribution is well approximated by a Gaussian distribution with dead-time-dependent mean and variance. Because of dead time, the SPAD array channel is subject to counting losses, part of which are due to inter-slot interference (ISI) distortions. Consequently, this channel has memory. The information rate of this channel is assessed. Two auxiliary discrete memoryless channels (DMCs) are proposed which provide upper and lower bounds on the SPAD array information rate. It is shown that in sufficiently large arrays, ISI is negligible and the bounds are tight. Under such conditions, the SPAD array channel is precisely modelled as a memoryless channel. A discrete-time Gaussian channel with input-dependent mean and variance is adopted and the properties of the capacity-achieving input distributions are studied. Using a numerical algorithm, the information rate and the capacity-achieving input distributions, subject to peak and average power constraints are obtained. Furthermore, the bit error performance of a SPAD-based system with on-off keying (OOK) is evaluated for various array sizes, dead times and background count levels

Statistical Modeling of Single-Photon Avalanche Diode Receivers for Optical Wireless Communications

In this paper, a comprehensive analytical approach is presented for modeling the counting statistics of active quenching and passive quenching single-photon avalanche diode (SPAD) detectors. It is shown that, unlike ideal photon counting receiver for which the detection process is described by a Poisson arrival process, photon counts in practical SPAD receivers do not follow a Poisson distribution and are highly affected by the dead time caused by the quenching circuit. Using the concepts of renewal theory, the exact expressions for the probability distribution and moments (mean and variance) of photocounts in the presence of dead time are derived for both active quenching and passive quenching SPADs. The derived probability distributions are validated through Monte Carlo simulations and it is demonstrated that the moments match with the existing empirical models for the moments of SPAD photocounts. Furthermore, an optical communication system with on-off keying and binary pulse position modulation is considered and the bit error performance of the system for different dead time values and background count levels is evaluated

Single-photon avalanche diode receivers for optical wireless communications

Single-photon avalanche diodes (SPADs) have been widely applied in many applications over the past few decades thanks to their high sensitivity, high photon detection efficiency and high timing resolution. Nowadays, they are drawing particular attention in the field of optical wireless communication (OWC), resulting in wider and deeper studies among the scientific research community. Compared with positive-intrinsic-negative (PIN) diodes and avalanche photodiodes (APDs), SPADs provide much higher internal gains and sensitivities, thereby easily overcoming the thermal noise and enabling the detection of individual photons without the need for transimpedance amplifiers (TIAs). However, upon detecting a photon, the SPAD is unable to respond to subsequent incident photons for a certain period of time, called dead time. This dead time is caused by the quenching circuit, which is of two principal modes: active quenching (AQ) and passive quenching (PQ). Depending on the structure of this circuit, the dead time can be constant or variable, in any case, it degrades the photon counting performance of the SPAD. In this thesis, a comprehensive analytical approach is presented for modelling the counting statistics of SPAD detectors in the presence of dead time. To the best of author’s knowledge, this is the first in-depth study of the impact of dead time in the context of OWC. Using the concepts of arrival processes and renewal theory, the exact photocount distributions and the count rate models are derived for AQ and PQ single SPADs. It is shown that, unlike ideal photon counting detectors, in AQ and PQ single SPADs, the photocounts do not follow a Poisson distribution. The results confirm that AQ single SPADs generally exhibit less counting losses and therefore, higher count rates compared to PQ single SPADs and the count rate gap in high photon rate regimes is substantial. It is also shown that the photocount distribution of a SPAD array can be well approximated by a Gaussian distribution, for which the mean and variance are dead time dependent. The numerical results suggest that as the size of the array increases, the gap between the photon counting performance of AQ and PQ SPAD arrays tends to vanish. Furthermore, in this thesis, the bit error performance of SPAD-based OWC systems with AQ single SPADs, PQ single SPADs and AQ SPAD arrays are evaluated. The results show that the SPAD dead time significantly degrades the bit error ratio (BER) of the systems. The system with an AQ single SPAD exhibits better BERs compared to the system with a PQ single SPAD. The effect of dead time is mitigated to some extent when an array is employed. The analytical and Monte Carlo simulation results are provided for various dead time values, background count levels and SPAD array sizes. From a communication theory point of view, the dead time also limits the achievable data rate of SPAD-based systems. In this thesis, the information transfer rate of SPAD detectors is also investigated. To this end, the SPAD is modelled as a communication channel. Using an information theoretic approach, the channel capacity and the capacity-achieving input distributions for AQ single SPADs and AQ SPAD arrays are obtained for various dead time values, background count levels, and array sizes

Statistical modeling of single-photon avalanche diode receivers for optical wireless communications

In this paper, a comprehensive analytical approach is presented for modeling the counting statistics of active quenching and passive quenching single-photon avalanche diode (SPAD) detectors. It is shown that, unlike ideal photon counting receiver for which the detection process is described by a Poisson arrival process, photon counts in practical SPAD receivers do not follow a Poisson distribution and are highly affected by the dead time caused by the quenching circuit. Using the concepts of renewal theory, the exact expressions for the probability distribution and moments (mean and variance) of photocounts in the presence of dead time are derived for both active quenching and passive quenching SPADs. The derived probability distributions are validated through Monte Carlo simulations and it is demonstrated that the moments match with the existing empirical models for the moments of SPAD photocounts. Furthermore, an optical communication system with on-off keying and binary pulse position modulation is considered and the bit error performance of the system for different dead time values and background count levels is evaluated

Photon Detection Characteristics and Error Performance of SPAD Array Optical Receivers

In this paper a novel photon counting receiver for optical communication applications is proposed. The proposed receiver is a single photon avalanche diode (SPAD) array which can provide a significantly improved detection sensitivity compared to conventional photodiodes. First, the detection statistics and main characteristics of a single SPAD receiver is presented, and the effects of the SPAD dead time, which is introduced by the quenching process, on the counting probability and effective count rate are studied. The approach is then extended to account for SPAD arrays. Using a Gaussian approximation, the counting distribution of a large size SPAD array is derived and effective count rate of arrays with different sizes is evaluated and compared. It is found that even in SPAD arrays, dead time still has a significant role in the maximum achievable count rate, and the fill factor of the array greatly affects the performance and count rate and has to be carefully dealt with. The impact of SPAD background counts and fill factor on the error performance of an on-off keying (OOK) modulation optical communication system is also investigated. It is shown that the bit error rate (BER) depends critically on back ground counts and improves with increasing fill factor

Advances in Quantum Nonlinear Optics: a nonclassical journey from the optimization of silicon photomultipliers for Quantum Optics to quantum second-harmonic generation

openIn this thesis, we present our experimental and theoretical work on modern and old topics of Nonlinear Quantum Optics. The thesis is structured as follows. In the first chapter, we provide a general introduction about the basis of this field, in particular about the main concepts and results that will be needed in the following. In the second and third chapters, we explain our research on the role of silicon photomultipliers in Quantum Optics experiments. After a specific characterization of the sensors, we used them to detect nonclassical states of light. Different strategies for the estimation of experimental quantities are suggested. In the fourth chapter, we propose our quantum description for the second-harmonic-generation process, based on well-known perturbative methods. After a general introduction on the state of the art, we immediately dive into the problem by explaining the employed methods and showing our analytical results. Finally, we resume the essence of our achievements and draw our conclusions.openFisica e astrofisicaChesi, GiovanniChesi, Giovann

Advances in Quantum Nonlinear Optics: a nonclassical journey from the optimization of silicon photomultipliers for Quantum Optics to quantum second-harmonic generation

In this thesis, we present our experimental and theoretical work on modern and old topics of Nonlinear Quantum Optics. The thesis is structured as follows. In the first chapter, we provide a general introduction about the basis of this field, in particular about the main concepts and results that will be needed in the following. In the second and third chapters, we explain our research on the role of silicon photomultipliers in Quantum Optics experiments. After a specific characterization of the sensors, we used them to detect nonclassical states of light. Different strategies for the estimation of experimental quantities are suggested. In the fourth chapter, we propose our quantum description for the second-harmonic-generation process, based on well-known perturbative methods. After a general introduction on the state of the art, we immediately dive into the problem by explaining the employed methods and showing our analytical results. Finally, we resume the essence of our achievements and draw our conclusions