The first part of the present thesis brings optical setups based on optoelectronic oscillators for realization of key distribution, in optical networks, with security based on quantum physics and chaotic systems principles. Three optical setups are proposed: I) A setup for chaotic key distribution. II) A setup for quantum secured chaotic key distribution. III) A setup for quantum-chaotic key distribution, in which quantum and chaotic systems are integrated. In all cases the security analysis is realized. All three systems proved to be viable without the safest quantum-chaotic system. In the second part of the thesis, experimental aspects of photonic generation of microwave signals using fiber optical resonator are considered. Experiments for harmonic generation using amplitude and phase modulators in the optical loop were realized. It can be verified that the systems with phase modulators present a greater amount of harmonics generated.
The first part of the present thesis brings optical setups based on optoelectronic oscillators for realization of key distribution, in optical networks, with security based on quantum physics and chaotic systems principles. Three optical setups are proposed: I) A setup for chaotic key distribution. II) A setup for quantum secured chaotic key distribution. III) A setup for quantum-chaotic key distribution, in which quantum and chaotic systems are integrated. In all cases the security analysis is realized. All three systems proved to be viable without the safest quantum-chaotic system. In the second part of the thesis, experimental aspects of photonic generation of microwave signals using fiber optical resonator are considered. Experiments for harmonic generation using amplitude and phase modulators in the optical loop were realized. It can be verified that the systems with phase modulators present a greater amount of harmonics generated.
In this dissertation it is realized a study about quantum key distribution (QKD) in optical networks. Initially, a review of the theory of quantum key distribution and some of its implementations with strongly attenuated coherent states, as well a review of an optical system for physical encryptation using mesoscopic coherent states are realized. Following, it is analyzed the use of an error correction scheme in the physical encryptation system, and two new schemes for quantum key distribution are proposed. The first is a possible implementation of a hybrid system, that is, using weak and mesoscopic coherent states, for QKD and quantum authentication of classical messages. The second is an implementation of a QKD system based on relative phase modulation of sidebands frequency, using two RF carriers and an amplitude modulator in Alice and a phase modulator in Bob. After, an experimental realization of a simple QKD setup using polarization states of strongly attenuated coherent states for B92 protocol is presented. At last, it is realized an experimental characterization of an optical receiver for optical communication applications.
This thesis can be divided in three parts: I) Security analysis of quantum bit commitment (QBC). II) Quantum-chaotic key distribution (QCKD) using multiphoton pulses. III) Homodyne detection of weak coherent states. In respect to the security analysis of quantum bit commitment, it was shown that if one takes into account the spectral width of the light pulses and the frequency dependence of optical quantum gates, the QBC, contrary to what was previously considered, is not unconditionally insecure. In what concerns the QCKD, the usage of coherent states with continuous phase forces the eavesdropper to use an attack based on quantum homodyne tomography. In this case, it was shown that the transmitter can use coherent states with mean photon number much larger than the value traditionally used in quantum key distribution QKD, and the QCKD will still be secure. At last, in the homodyne detection part, an experiment was realized showing the detection, by an optical receiver based on PIN photodiode, of an analog modulating signal carried by a strongly attenuated coherent state.
In this dissertation it is realized a study about quantum key distribution (QKD) in optical networks. Initially, a review of the theory of quantum key distribution and some of its implementations with strongly attenuated coherent states, as well a review of an optical system for physical encryptation using mesoscopic coherent states are realized. Following, it is analyzed the use of an error correction scheme in the physical encryptation system, and two new schemes for quantum key distribution are proposed. The first is a possible implementation of a hybrid system, that is, using weak and mesoscopic coherent states, for QKD and quantum authentication of classical messages. The second is an implementation of a QKD system based on relative phase modulation of sidebands frequency, using two RF carriers and an amplitude modulator in Alice and a phase modulator in Bob. After, an experimental realization of a simple QKD setup using polarization states of strongly attenuated coherent states for B92 protocol is presented. At last, it is realized an experimental characterization of an optical receiver for optical communication applications.
An important issue in today’s information society is the security of data transmission against potential intruders, which always put at risk the confidentiality. Current methods to increase security require that the two parties wishing to transmit information, exchange or share one or more security keys. Once the key has been identified, the information can be transferred in a provable secure way using a one-time pad, i. e. the key length is as long as the plaintext. Therefore, the security of the information transmission is based exclusively on the security of the key exchange. Quantum cryptography, or more precisely quantum key distribution (QKD), guarantees absolutely secure key distribution based on the principles of quantum physics, according to which it is not possible to measure or reproduce a state (e.g. polarization or phase of a photon) without being detected. The key is generated out from the measurement of the information encoded into specific quantum states of a photon, named qubits. For example, a qubit can be created using properties such as the polarization or the phase of a photon. Achieved goals of this thesis are the development of a new class of high speed integrated photonic sources for applications in quantum key distribution systems, capable of producing unprecedented qubit rates (100 Mbps - 1 Gbps) and transmitting those over larger distances than those achieved so far (> 200 km). More specifically the work has been focused on developing faint pulse sources which can be used in very demanding environmental conditions, such as those in Space. For the development of these sources, apart from the optical design, essential is the opto-mechanical engineering as well as the integration with the electronics. One of the objectives was to achieve very high level of integration and power efficiency, e.g. volumes and power consumption between 10 and 100 times smaller than those typical of a laboratory experiment. Moreover, work in related parts of a whole QKD transmission system has been carried out. In particular, a new scheme for a compact, fast and simple random number generator has been demonstrated successfully achieving a random number generation rate of 1:1 Gbps. Also, during the course of this thesis, the development and engineering of a free-space QKD optical link has been initiated. This thesis makes use of novel ideas to alternatively demonstrate proof-of- concept experiments, which could then further develop into commercial products. To this end, close collaborations with world-wide leading companies in the field have been established. The Optoelectronics Group at ICFO has been involved in current European Space Agency (ESA) projects to develop a small footprint and low power consumption quantum transceiver and a high-flux entangled photon source.
This thesis presents experimental realizations of quantum key distribution (QKD) systems which are based on continuous variables. As such, polarization or amplitude and phase of a light field are used, in contrast to discrete variables like the photon number. One QKD-system examined in this work is based on the entanglement of intense light pulses in the amplitude and phase quadratures. A measurement system for these observables is built and characterized. The existing measurement procedures can be optimized in speed, such that a observation of entanglement at a rate of 100 kHz is possible. Future improvements of the measurement system to obtain a secure key generation are presented. The second group of experimentally investigated QKD-setups uses classical coherent states and homodyne detection. An absolute correspondence between the quantum mechanical description of the system and the state preparation and measurement apparatus is given. It is shown that quadrature variables can be substituted with polarization variables, providing significant technical advantages. A setup to generate arbitrary continuous variable polarization states is built and characterized, as well as a low noise, broadband and high efficiency homodyne polarization detection system. Its overall efficiency, including optical and photodiode loss, and interference visibility is up to 88%. Using these setups, different coding schemes for quantum key generation were implemented. Transmissions with pulse rates of 100 kHz and quantum channel losses up to 74% (-5.9 dB respectively) were experimentally simulated. By using the post selection method, correlated key pairs secure against beam splitting attacks could be obtained. A special detection setup, using simultaneous measurement of conjugate polarization observables, provides tomographical data (e.g. the Q-function) of the transmitted states. Thus, an advanced security analysis against more general attacks will be possible.