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SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC)

Deterministic State-of-Polarization Generation for Polarization-Encoded Optical Communications

Nelson Jesus Muga, Mariana F. Ramos, Sara T. Mantey, Nuno A. Silva, Armando N. Pinto

Published Nov 10, 2019• 1 citation
Publisher

Abstract

This work introduces a theoretical model for electronic polarization controllers (EPCs) based on fiber squeezing. First, a method to calculate the EPC configuration in order to transform between any two states of polarization (SOP) is presented. In a second stage, a technique to deterministically generate four SOPs in polarization-encoded quantum communication systems is proposed. Finally, the effectiveness of the proposed approach is experimentally assessed through the generation of two pairs of orthogonal SOPs. Results show that this polarization generation process is intrinsically stable, which evidences its potential for practical implementations of polarization-encoding quantum protocols, e.g. BB84 or B92 quantum key distribution protocols.

DOI
10.1109/imoc43827.2019.9317550

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This work introduces a theoretical model for electronic polarization controllers (EPCs) based on fiber squeezing. First, a method to calculate the EPC configuration in order to transform between any two states of polarization (SOP) is presented. In a second stage, a technique to deterministically generate four SOPs in polarization-encoded quantum communication systems is proposed. Finally, the effectiveness of the proposed approach is experimentally assessed through the generation of two pairs of orthogonal SOPs. Results show that this polarization generation process is intrinsically stable, which evidences its potential for practical implementations of polarization-encoding quantum protocols, e.g. BB84 or B92 quantum key distribution protocols.
This study presents a theoretical model for polarisation manipulation using electronic polarisation controllers (EPCs) based on fibre squeezing. A method to calculate the EPC configuration in order to transform between two arbitrary states of polarisation (SOP) is presented. After, a technique to deterministically generate four SOPs for use in polarisation‐encoded quantum communication systems is proposed. Moreover, the effectiveness of the proposed technique is experimentally assessed through the generation of two pairs of orthogonal SOPs. The experimental implementation used an field programmable gate array (FPGA) board to electrically control the four waveplates of the EPC, reaching a rate of 500 qubit/s. Results show that this polarisation generation process is intrinsically stable, demonstrating its potential for practical implementations of polarisation‐encoding quantum key distribution systems using the BB84 and B92 protocols.
In this paper we propose and validate an algorithm for the automatic and deterministic state of polarization (SOP) generation, with direct application in polarization-encoded quantum key distribution (QKD) systems. The proposed SOP generation algorithm uses an electronic polarization controller (EPC), whose active elements entail the concatenation of several fiber-squeezing-based waveplates. Initially, we carry out a characterization of the waveplates. After that, we present in detail the working principle of the proposed algorithm. Finally, the effectiveness of the algorithm is experimentally assessed through the calculation of the quantum bit error rate (QBER), where an Arduino Due is used to control the different waveplates of the EPC. The QBER was measured for periods of 4 hours and 10 hours when generating two or four SOPs, respectively, with an overall average QBER value of 2%. Results show the potential of the proposed method regarding the generation of automatic and deterministic SOPs, thus demonstrating viability for its practical implementation in polarization-encoding QKD systems.
Abstract We present the design and implementation of a state-of-polarization (SOP) management technique and two efficient synchronizing methods for quantum key distribution (QKD) systems. This is achieved following a wavelength-division multiplexing approach, where the classical synchronization signal and the quantum states are propagated in the same optical fiber. The employed frame synchronization method is based on the monitoring of the quantum bit error ratio (QBER) of the quantum channel, thus avoiding additional hardware and high computational resources. We evaluate the operation of SOP generation method through the assessment of the individual response of the waveplates that comprise the employed electronic polarization controller. Finally, the performance was assessed by computing the overall QBER and the QBER contributions of each of the four polarization states associated with the different qubits. The measurements, obtained during six hours, show a slight variation of the QBER values associated with the individual contributions, reaching an overall QBER of 0.75%. This demonstrates the capability of the presented methods to operate, stably, with very low QBER values, making its application in practical QKD systems reliable.
In this work, a fully functional polarization-encoding quantum key distribution system (QKD) is demonstrated. At the transmitter side, the polarization states are prepared using an algorithm to determine the voltages to be applied on the electronic polarization controller (EPC), to generate up to four polarization states. At the receiver, a second EPC is used to perform the basis alignment. The symbol synchronization is achieved using a reference optical signal that is wavelength division multiplexed with the quantum signal which carries the polarization-encoded qubit. Frame synchronization is achieved at a protocol level. The presented QKD system works at a repetition rate of 500 Hz, with an average quantum bit error rate of 1.35%.
The rapid increase on the information sharing around the world, leads to an utmost requirement for capacity and bandwidth. However, the need for security in the transmission and storage of information is also of major importance. The use of quantum technologies provides a practical solution for secure communications systems. Quantum key distribution (QKD) was the first practical application of quantum mechanics, and nowadays it is the most developed one. In order to share secret keys between two parties can be used several methods of encoding. Due to its simplicity, the encoding into polarization is one of the most used. However, when we use optical fibers as transmission channels, the polarization suffers random rotations that may change the state of polarization (SOP) of the light initially sent to the fiber to a new one at the output. Thus, in order to enable real-time communication using this encoding method it is required the use of a dynamic control system. We describe a scheme of transmission of quantum information, which is based in the polarization encoding, and that allows to share secret keys through optical fibers without interruption. The dynamic polarization control system used in such scheme is described, both theoretically and experimentally. Their advantages and limitations for the use in quantum communications are presented and discussed.
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.