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European Conference on Networks and Optical Communications

Fiber-optical communication system using polarization-encoding photons

Álvaro J. Almeida, Nuno A. Silva, Nelson Jesus Muga, Armando N. Pinto

Published Jun 8, 2010• 1 citation
OpenAlex

Abstract

We present a single-photon source based on the stimulated four-wave mixing process with adjustable linear state of polarization. This source allowed us to generate non-orthogonal states of polarization, that can be used for quantum key distribution experiments. The average number of photon counts as a function of the angle of the analyzer was obtained for two non-orthogonal linear states of polarization. The results show an accurate detection after propagation through a standard single-mode optical fiber with a length equal to 20 km. We also employed a master/slave configuration between two avalanche photodiodes, in order to check the probability of our single-photon source to emit pulses with more than one photon, for an average number of photons per pulse, μ ∼ 0.2, and consequently the probability of a photon to choose one of the paths. Results show that our experimental scheme is suitable for polarization-encoding experiments.

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This thesis begins by proposing the implementation of a probabilistic photon source based on the stimulated four-wave mixing (FWM) process. This source was implemented experimentally and characterized in terms of its statistical distribution. Next, the impact of the stimulated FWM process in a co-propagating quantum signal was studied experimentally. Finally, the violation of Clauser-Horne-Shimony-Holt (CHSH) inequality was experimentally verified using polarization-entangled photon pairs, which were obtained from the spontaneous FWM process in a Sagnac loop. The experimental evolution of the quantum-bit error rate (QBER) in a system without control of polarization, using this degree of freedom to encode information, was studied. It was found out that the QBER increases with the length of the transmission fiber. It was also verified that the increase in the QBER was due to the random rotation of photon’s polarization. A model for the rigorous estimation of the QBER was derived and developed an automatic method to compensate the random rotations of polarization. The method was validated numerically and experimentally, in a transmission system with 40km, showing that it can compensate for the rotations that photons suffer during propagation in optical fibers. Finally, a quantum bit commitment (QBC) protocol between two untrusted entities was implemented. The encoding was performed using two nonorthogonal states of polarization (SOPs). As quantum channel between the two entities, it was first assumed that the transmitter and the receiver were side by side, and after that, they were separated by 8 km and finally, that they were 16km from each other. The implementation of the protocol was performed with a success rate in measurements exceeding 93%, well above the theoretical security limit of 85%. The best strategy for deceiving the commitment was also implemented, and its security experimentally confirmed with a confidence of 7 standard deviations.

•Mar 4, 2016•0 citations
We present a single-photon source based on the stimulated four-wave mixing process with adjustable linear state of polarization. This source allowed us to generate non-orthogonal states of polarization, that can be used for quantum key distribution experiments. The average number of photon counts as a function of the angle of the analyzer was obtained for two non-orthogonal linear states of polarization. The results show an accurate detection after propagation through a standard single-mode optical fiber with a length equal to 20 km. We also employed a master/slave configuration between two avalanche photodiodes, in order to check the probability of our single-photon source to emit pulses with more than one photon, for an average number of photons per pulse, μ ∼ 0.2, and consequently the probability of a photon to choose one of the paths. Results show that our experimental scheme is suitable for polarization-encoding experiments.
A single-photon source based on the stimulated four-wave mixing (SFWM) process in optical fibers is presented. At the output of the source, the state of polarization (SOP) of the photons can be adjusted in order to obtain any linear polarization. A theoretical model to describe the average photon counts recorded in the avalanche photodiodes (APDs) is presented. The experimental results show an accurate detection of two non-orthogonal linear SOPs after propagation through a 60 km quantum channel, and good agreement with theory. This source, operating in a low power regime, can be used for quantum key distribution (QKD) using polarization-encoding in quantum communications.
This paper gives experimental results of quantum key distribution on a fiber-optic setup at a telecom wavelength of 1555 nm. A self-compensated two-channel optical circuit is used. Quantum key distribution was performed by coding the phase states of single photons radiated by a pulsed semiconductor laser in two alternative nonorthogonal bases. Specially developed single photon counters based on InGaAs: InP avalanche photodiodes were employed as high-sensitivity photodetectors. The results of investigation of the quantum efficiency, probability of afterpulses, and noise level for various operating modes of the detectors at temperatures from −40 to −60°C are given. A key distribution rate of 450 bit/s was obtained for a single-mode fiber-optic quantum communication channel between the receiver and sender 25 km long at a laser pulse clock frequency of 5 MHz and an average number of photons per pulse of about 0.2. For the achieved photodetector characteristics, the average number of errors in the quantum key did not exceed 3.7%.
We report a proof-of-principle quantum key distribution experiment using a one-way optical scheme with polarization encoding implementing the BB84 protocol. LiNbO 3 phase modulators are used for generating polarization states for Alice and active basis selection for Bob. This allows the former to use a single laser source, while the latter needs only two single-photon detectors. The presented optical scheme is simple and consists of standard fiber components. Calibration algorithm for three polarization controllers used in the scheme has been developed. The experiment was carried with 10 MHz repetition frequency laser pulses over a distance of 50 km of standard telecom optical fiber.
This thesis begins by proposing the implementation of a probabilistic photon source based on the stimulated four-wave mixing (FWM) process. This source was implemented experimentally and characterized in terms of its statistical distribution. Next, the impact of the stimulated FWM process in a co-propagating quantum signal was studied experimentally. Finally, the violation of Clauser-Horne-Shimony-Holt (CHSH) inequality was experimentally verified using polarization-entangled photon pairs, which were obtained from the spontaneous FWM process in a Sagnac loop. The experimental evolution of the quantum-bit error rate (QBER) in a system without control of polarization, using this degree of freedom to encode information, was studied. It was found out that the QBER increases with the length of the transmission fiber. It was also verified that the increase in the QBER was due to the random rotation of photon’s polarization. A model for the rigorous estimation of the QBER was derived and developed an automatic method to compensate the random rotations of polarization. The method was validated numerically and experimentally, in a transmission system with 40km, showing that it can compensate for the rotations that photons suffer during propagation in optical fibers. Finally, a quantum bit commitment (QBC) protocol between two untrusted entities was implemented. The encoding was performed using two nonorthogonal states of polarization (SOPs). As quantum channel between the two entities, it was first assumed that the transmitter and the receiver were side by side, and after that, they were separated by 8 km and finally, that they were 16km from each other. The implementation of the protocol was performed with a success rate in measurements exceeding 93%, well above the theoretical security limit of 85%. The best strategy for deceiving the commitment was also implemented, and its security experimentally confirmed with a confidence of 7 standard deviations.