Physical-layer key distribution using synchronous complex dynamics of DBR semiconductor lasers

Common-signal-induced synchronization of semiconductor lasers with optical feedback inspired a promising physical key distribution with information-theoretic security and potential in high rate. A significant challenge is the requirement to shorten the synchronization recovery time for increasing key rate without sacrificing operation parameter space for security. Here, open-loop synchronization of wavelength-tunable multi-section distributed Bragg reflector (DBR) lasers is proposed as a solution for physical-layer key distribution. Experiments show that the synchronization is sensitive to two operation parameters, i.e., currents of grating section and phase section. Furthermore, fast wavelength-shift keying synchronization can be achieved by direct modulation on one of the two currents. The synchronization recovery time is shortened by one order of magnitude compared to close-loop synchronization. An experimental implementation is demonstrated with a final key rate of 5.98 Mbit/s over 160 km optical fiber distance. It is thus believed that fast-tunable multi-section semiconductor lasers opens a new avenue of high-rate physical-layer key distribution using laser synchronization.Comment: 13 pages, 5 figure

Exploiting nonlinearity and noise in optical tweezers and semiconductor lasers : from resonant damping to stochastic logic gates and extreme pulses

This thesis is focused on the study of stochastic and nonlinear dynamics in optical systems. First, we study experimentally the dynamics of a Brownian nanometer particle in an optical trap subjected to an external forcing. Specifically, we consider the effects of parametric noise added to a monostable or bistable optical trap and discovered a new effect which we named stochastic resonant damping (SRD). SRD concerns the minimization of the output variance position of a particle held in a harmonic trap, when an external parametric noise was added to the position trap. We compared the classical stochastic resonance (SR) with SRD and found that they are two phenomena which coexist in the same system but in different regimes. The experimentally studied monostable system showed a maximum in the signal to noise ratio, a clear signature of a resonance. We also developed a new technique to increase 10-fold the detection range of the quadrant photodiode that we used in this study, which exploits the channel crosstalk. Second, we study the stochastic dynamics of a type of semiconductor laser (SCL), known as vertical-cavity surface-emitting laser (VCSEL), that exhibits polarization bistability and hysteresis, either when the injection current or when the optically injected power are varied. We have shown how these properties can be exploited for logic operations due to the effect of the spontaneous emission noise. Two logical input signals have been encoded in three levels of optically injected power from a master laser, and the logical output response was decoded from the emitted polarization of the injected VCSEL. Correct and robust operation was obtained when the three levels of injected power were adjusted to favor one polarization at two levels and to favor the orthogonal polarization at the third level. We numerically demonstrated that the VCSEL-based logic operator allows to reproduce the truth table for the OR and NOR logic operators, while the extension to AND and NAND is straightforward. With this all-optical configuration we have been able to reduce the minimum bit time required for correct operation from 30 ns, obtained in a previous work with an optoelectronic configuration, to 5 ns. The third focus of this thesis is the study of the chaotic nonlinear dynamics of a SCL optically injected, in the regime where it can display sporadic huge intensities pulses, referred to as Rogue Waves (RWs). We found that, when adding optical noise, the region where RWs appear becomes wider. This behavior is observed for high enough noise; however, on the contrary, for very weak noise we found that noise diminishes the number of RW events in certain regions. In order to suppress or induce extreme pulses, we investigated the effects of an external periodic modulation of the laser current. We found that the modulation at specific frequencies modifies the dynamics from chaotic to periodic. Depending on the parameter region, current modulation can contribute to an increased threshold for RWs. Therefore, we concluded that the modulation can be effective for suppressing the RWs dynamics

Semiconductor Laser Dynamics

This is a collection of 18 papers, two of which are reviews and seven are invited feature papers, that together form the Photonics Special Issue “Semiconductor Laser Dynamics: Fundamentals and Applications”, published in 2020. This collection is edited by Daan Lenstra, an internationally recognized specialist in the field for 40 years

Optical Communication

Optical communication is very much useful in telecommunication systems, data processing and networking. It consists of a transmitter that encodes a message into an optical signal, a channel that carries the signal to its desired destination, and a receiver that reproduces the message from the received optical signal. It presents up to date results on communication systems, along with the explanations of their relevance, from leading researchers in this field. The chapters cover general concepts of optical communication, components, systems, networks, signal processing and MIMO systems. In recent years, optical components and other enhanced signal processing functions are also considered in depth for optical communications systems. The researcher has also concentrated on optical devices, networking, signal processing, and MIMO systems and other enhanced functions for optical communication. This book is targeted at research, development and design engineers from the teams in manufacturing industry, academia and telecommunication industries

Data security in photonic information systems using quantum based approaches

The last two decades has seen a revolution in how information is stored and transmitted across the world. In this digital age, it is vital for banking systems, governments and businesses that this information can be transmitted to authorised receivers quickly and efficiently. Current classical cryptosystems rely on the computational difficulty of calculating certain mathematical functions but with the advent of quantum computers, implementing efficient quantum algorithms, these systems could be rendered insecure overnight. Quantum mechanics thankfully also provides the solution, in which information is transmitted on single-photons called qubits and any attempt by an adversary to gain information on these qubits is limited by the laws of quantum mechanics. This thesis looks at three distinct different quantum information experiments. Two of the systems describe the implementation of distributing quantum keys, in which the presence of an eavesdropper introduces unavoidable errors by the laws of quantum mechanics. The first scheme used a quantum dot in a micropillar cavity as a singlephoton source. A polarisation encoding scheme was used for implementing the BB84, quantum cryptographic protocol, which operated at a wavelength of 905 nm and a clock frequency of 40 MHz. A second system implemented phase encoding using asymmetric unbalanced Mach-Zehnder interferometers, with a weak coherent source, operating at a wavelength of 850 nm and pulsed at a clock rate of 1 GHz. The system used depolarised light propagating in the fibre quantum channel. This helps to eliminate the random evolution of the state of polarisation of photons, as a result of stress induced changes in the intrinsic birefringence of the fibre. The system operated completely autonomously, using custom software to compensate for path length fluctuations in the arms of the interferometer and used a variety of different single-photon detector technologies. The final quantum information scheme looked at quantum digital signatures, which allows a sender, Alice, to distribute quantum signatures to two parties, Bob and Charlie, such that they are able to authenticate that the message originated from Alice and that the message was not altered in transmission