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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Fast polarization QKD scheme based on LiNbO3 phase modulators

Alexander Duplinskiy, Vasily E. Ustimchik, A. A. Kanapin, Yury Kurochkin

Published Dec 30, 2016• 3 citations
Publisher

Abstract

An optical scheme for polarization encoding BB84 protocol is described. Fiber electro-optical LiNbO3 phase modulators based on Pockels cells provide both polarization states generation for Alice and basis choosing for Bob at high frequency, requiring low operation voltages (Vπ < 5V). Proposed scheme uses only one laser source, which guarantee the indistinguishability of the pulses and active basis choosing allows the system to have two single photon detectors in contrast to the four in the standard polarization encoding schemes. Two phase modulators compensate each others’ polarization mode dispersion, caused by the natural birefringence of the lithium niobate crystal. The system consists of standard components and has simple configuration. The principle of operation is experimentally demonstrated.

DOI
10.1117/12.2266517

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Acta Physica Sinica•Jan 1, 2007•1 citation
An optical scheme for polarization encoding BB84 protocol is described. Fiber electro-optical LiNbO3 phase modulators based on Pockels cells provide both polarization states generation for Alice and basis choosing for Bob at high frequency, requiring low operation voltages (Vπ < 5V). Proposed scheme uses only one laser source, which guarantee the indistinguishability of the pulses and active basis choosing allows the system to have two single photon detectors in contrast to the four in the standard polarization encoding schemes. Two phase modulators compensate each others’ polarization mode dispersion, caused by the natural birefringence of the lithium niobate crystal. The system consists of standard components and has simple configuration. The principle of operation is experimentally demonstrated.
We present a new optical scheme for BB84 protocol quantum key distribution (QKD). The proposed setup consists of a compact all-fiber polarization encoding optical scheme based on LiNbO3 phase modulators, single laser source and two single-photon detectors. Optical scheme consists of standard telecommunication components and is suitable for both fiber and free-space quantum communication channels. Low losses (~2dB) in Bob's device increase both the key generation rate and distance limit. A new technique for solving polarization mode dispersion (PMD) issue in LiNbO3 is implemented, allowing two crystals to neutralize the effect of each other. Several proof-of-concept experiments have been conducted at 10 MHz repetition frequency over 50 km of standard optical fiber under laboratory conditions and over 30 km of urban fiber with high losses (13dB), which is a link within a QKD network. To achieve this, calibration algorithms have been developed, allowing the system to work autonomously and making it promising for practical applications.
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.
Abstract The BB84 quantum key distribution (QKD) protocol sets the foundation for achieving secure communication against quantum threats. Since its inception, significant advancements have aimed towards frugal experimental implementations with enhanced security. In this paper, we report a passive polarization encoded BB84 protocol. By passively and randomly encoding the polarization states, the setup avoids active modulation and simplifies design with security standards analogous to entanglement-based QKD. The heralding of a probabilistic single-photon source ensures an extremely low probability of multi-photon emissions evading photon number-splitting attacks. The quality of the single-photon source and thus, the QKD setup is certified by the second-order correlation function, g (2) (0) = 0.006 ± 0.0002. Our protocol provides an optimisation trade-off between the conventional BB84 and the BBM92 protocol. The advantage relies on using fewer detectors (compared to the BBM92 protocol) and no reliance on active quantum random number generators (compared to the standard BB84) to drive Alice’s encoding scheme. Our implementation achieves a quantum bit error rate of 7% and a secure key rate of 5 kbps.
Efficient detection of quantum states underpins advanced device-independent quantum-information protocols that provide the ultimate level of security for tasks including quantum random number generation and quantum key distribution (QKD). High-dimensional encoding is a natural route to boost the performance of such protocols, offering enhanced noise resilience and higher information capacity, yet their practical implementation remains challenging. A key experimental bottleneck in higher dimensions is the typical need of active modulators for basis selection, which incur substantial optical losses and polarization-sensitive operation. Poled optical fiber phase modulators (PFPMs) are a fiber-native electro-optic technology that naturally addresses these challenges, combining sub-dB insertion loss, intrinsic polarization independence, and direct compatibility with standard telecommunications fiber. Here we report the first use of a PFPM for active quantum-state measurements in a fully fiber-integrated platform. Basis selection in our receiver for four-dimensional qudits is achieved using a single PFPM, substantially simplifying the receiver architecture. As a benchmark, we perform a four-dimensional QKD session and obtain a finite secret-key rate per pulse that, to the best of our knowledge, surpasses all previously reported QKD demonstrations. Our results establish poled-fiber electro-optic modulation as a broadly applicable platform for high-efficiency detection in fiber-integrated quantum information processing.
The experimental implementation of the polarization encoding system is presented using weak coherent pulses at a low enough frequency. The optical pulses are generated through intensity modulation at the repetition rate of 101010 pulses/sec with the intensity of 7μW7μW7μW, whose polarization is modulated by the Pockel cell. For a $ 5$ km long fiber link, the key rate is thus limited to $ 10$ bits/sec accompanied by temporal synchronization among the Intensity Modulator (IM), Pockel cell, and the gate of the detector. The system was continuously operated for 555 minutes, and 300030003000 binary bits were distributed between two nodes with an error rate less than unity. We have used only a single polarization basis, i.e., horizontal and vertical polarizations, as the objective of this experiment is to validate the feasibility of the setup under simplified conditions, intended primarily for the laboratory-scale demonstrations.
An improved DPS-QKD scheme is proposed and demonstrated in this paper. At Alice's site，we use a M-Z interferometer to produce two coherent pulses. At Bob's site，a Faraday-mirrors-based Michelson interferometer is used instead of a M-Z interferometer to auto-compensate for the phase drifts and polarization mode dispersions in the fiber. It enhances the security of the whole system to use the two quantum cryptography protocols (namely the two pulse DPS-QKD scheme associated with the BB84 scheme). It is shown in our experiment that such a system features perfect stability with a quantum bit error rate less than 5% and high key generation rate. This scheme has been implemented successfully during the 80km fiber transmission.