Scientific Publications

General framework for the analysis of imperfections in nonlinear systems

Title

General framework for the analysis of imperfections in nonlinear systems

Authors

Matteo Santandrea, Michael Stefszky, and Christine Silberhorn

Abstract

In this Letter, we derive a framework to understand the effect of imperfections on the phase-matching spectrum of a wide class of nonlinear systems. We show that this framework is applicable to many physical systems, such as waveguides or fibers. Furthermore, this treatment reveals that the product of the system length and magnitude of the imperfections completely determines the phase-matching properties of these systems, thus offering a general rule for system design. Additionally, our framework provides a simple method to compare the performance of a wide range of nonlinear systems.

Venue 

Optics Letters, 15 November 2019, Volume 44, Issue 22, pp. 5394-5649

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Characterisation of fabrication inhomogeneities in Ti:LiNbO3 waveguides

Title

Characterisation of fabrication inhomogeneities in Ti:LiNbO3 waveguides

Authors

Matteo Santandrea, Michael Stefszky, Ganaël Roeland and Christine Silberhorn

Abstract

Nonlinear processes in integrated, guiding systems are fundamental for both classical and quantum experiments. Integrated components allow for compact, modular and stable light-processing systems and as such their use in real-world systems continues to expand. In order to use these devices in the most demanding applications, where efficiency and/or spectral performance are critical, it is important that the devices are fully optimised. In order to achieve these optimisations, it is first necessary to gain a thorough understanding of current fabrication limits and their impact on the devices’ final performance. In this paper we investigate the current fabrication limits of titanium indiffused lithium niobate waveguides produced using a masked photolithographic method. By dicing a long (~8 cm) sample into smaller pieces and recording the resulting phase matching spectra, the fabrication error present in the UV photolithographic process is characterised. The retrieved imperfections fit well with theoretical expectations and from the measured imperfection profile it is shown that one can directly reconstruct the original distorted phase matching spectrum. Therefore, our measurements directly quantify the intrinsic limitations of the current standard UV photolitographically produced titanium-indiffused lithium niobate waveguides.

Venue

New Journal of PhysicsVolume 21December 2019

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Deployment Opportunities for DPS-QKD in the Co-Existence Regime of Lit GPON / NG-PON2 Access Networks

Title

Deployment Opportunities for DPS-QKD in the Co-Existence Regime of Lit GPON / NG-PON2 Access Networks

Authors

N. Vokic, D. Milovancev, B. Schrenk, M. Hentschel, and H. Hübel

Abstract 

We demonstrate cost-effective QKD integration for GPON and NG-PON2. Operation at 5.1×10-7 secure bits/pulse and a QBER of 3.28% is accomplished for a 13.5-km reach, 2:16-split PON, with 0.52% co-existence penalty for 19 classical channels.

Venue

The Optical Fiber Communication Conference & Exhibition (OFC 2020)

Place and Date

San Diego Convention Center, San Diego, California, USA, 8 – 12 March 2020

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Flexible Entanglement Distribution Overlay for Cloud/Edge DC Interconnect as Seed for IT-Secure Primitives

Title

Flexible Entanglement Distribution Overlay for Cloud/Edge DC Interconnect as Seed for IT-Secure Primitives

Authors

F. Laudenbach, B. Schrenk, M. Achleitner, N. Vokic, D. Milovancev, and H. Hübel

Abstract 

We leverage spectral assets of entanglement and spatial switching to realize a flexible distribution map for cloud-to-edge and edge-to-edge quantum pipes that seed IT-secure primitives. Dynamic bandwidth allocation and co-existence with classical control are demonstrated.

Venue

The Optical Fiber Communication Conference & Exhibition (OFC 2020)

Place and Date

San Diego Convention Center, San Diego, California, USA, 8 – 12 March 2020

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Compact Differential Phase-Shift Quantum Receiver Assisted by a SOI / BiCMOS Micro-Ring Resonator

Title

Compact Differential Phase-Shift Quantum Receiver Assisted by a SOI / BiCMOS Micro-Ring Resonator

Authors

N. Vokic, D. Milovancev, W. Boxleitner, H. Hübel, and B. Schrenk

Abstract 

We demonstrate a phase-selective and colorless quantum receiver assisted by a silicon-on-insulator microring, enabling a low 1.3% QBER at 5.3kb/s secure-key rate. No penalty incurs compared to a delay interferometer. BiCMOS 3D-integration is proven feasible.

Venue

The Optical Fiber Communication Conference & Exhibition (OFC 2020)

Place and Date

San Diego Convention Center, San Diego, California, USA, 8 – 12 March 2020

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On the Filter Issues in Multiplexing Classical and QKD Links through WSS-based Nodes

Title

On the Filter Issues in Multiplexing Classical and QKD Links through WSS-based Nodes

Authors

D. Zavitsanos (NTUA), G. Giannoulis (NTUA), A. Raptakis (NTUA), Ch. Kouloumentas (NTUA), and H. Avramopoulos (NTUA)

Abstract

We present an extensive study on the quantum link multiplexed with intense classical signal in a WSS-based node. Theoretical results on QBER and SKR performance revealed the dependence of BB84-QKD link on passband spectral response.

Venue

Asia Communications and Photonics Conference (ACP) 2019

Place and date

Chengdu, China, Nov. 2-5, 2019

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Photon-Pair Sources and Quantum Cryptography using Continuous Variables

Title

Photon-Pair Sources and Quantum Cryptography using Continuous Variables

Authors

Fabian Laudenbach (AIT Austrian Institute of Technology)

Abstract 

The counter-intuitive phenomena of quantum mechanics are currently leaping from their mere exploration to their deployment in real-life applications. Quantum superposition, the uncertainty principle, the no-cloning theorem and, most prominently, quantum entanglement are proven to allow for computing and cryptography algorithms, simulation of complex physical phenomena and sensing of physical quantities in new and beneficial ways which are unparalleled by classical devices. In particular, quantum technologies based on photons offer a straightforward way to protect quantum states from decoherence and, if necessary, transmit them from one place to another reliably. Most applications in the realm of optical quantum technology have successfully been demonstrated in proof-of-principle experiments. However, in order for quantum technologies to unleash their full potential and establish in the shape of wide-spread applications with a true advantage over their classical counterparts, they need to become scalable in size, quantity, performance and cost. This thesis is divided into two parts dealing with different aspects of quantum optics: The first part discusses ways to generate photon pairs with high brightness and, at the same time, high quality in terms of their performance in quantum experiments. The second part provides a theoretical discussion and experimental demonstration of quantum cryptography based on continuous variables — a promising concept to make the striking advantages of quantum communication compatible with off-the-shelf telecom hardware and fibre networks. As I hope, the research presented in both parts of this thesis will, in one way or another, make a contribution to the scalability of quantum technologies and thereby help to enforce the breakthrough of the so-called quantum revolution.

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Flexible entanglement distribution based on WDM and active switching technology

Title
Flexible entanglement distribution based on WDM and active switching technology

Authors
Hannes Hübel, Bernhard Schrenk, Sophie Zeiger, Fabian Laudenbach and Michael Hentschel.

Abstract
In future, the distribution of single or entangled photons inside optical networks will be a prerequisite for a general roll-out and adoption of quantum communication technologies. In particular, on-demand routing and active wavelength allocation will be needed to meet the demand of complex network architectures. In the last years several attempts have been made, based either on passive optical WDM technology or active switching of channels. Here we present a novel approach whereby we combine spectral slicing of the emission spectrum of SPDC sources together with space-switches to generate a reconfigurable distribution node for entanglement.  The increased switching complexity offered by our hybrid solution allows us to realise quantum ROADMs with up to three degrees.

Venue
21st International Conference on Transparent Optical Networks ICTON 2019 (http://www.icton2019.com/)

Place and Date
Angers, France, July 9-13, 2019

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Modelling Weak-Coherent CV-QKD Systems Using a Classical Simulation Framework

Title
Modelling Weak-Coherent CV-QKD Systems Using a Classical Simulation Framework

Authors
Sören Kreinberg, Igor Koltchanov, Piotr Novik, Saleem Alreesh, Fabian Laudenbach, Christoph Pacher, Hannes Hübel, André Richter.

Abstract
Due to their compatibility to existing telecom technology, continuous variable (CV) weak coherent state protocols are promising candidates for a broad deployment of quantum key distribution (QKD) technology. We demonstrate how an existing simulation framework for modelling classical optical systems can be utilized for simulations of weak-coherent CV-QKD links. The quantum uncertainties for the measured characteristics of coherent signals are modelled in the electrical domain by shot noise, while a coherent signal in the optical domain is described by its quadrature components. We simulate various degradation effects such as attenuation, laser RIN, Raman noise (from classical channels in the same fibre), and device imperfections and compare the outcome with analytical theory. Having complemented the physical simulation layer by the post-processing layer (reconciliation and privacy amplification), we are able to estimate secure key rates from simulations, greatly boosting the development speed of practical CV-QKD schemes and implementations.

Venue
21st International Conference on Transparent Optical Networks ICTON 2019 (http://www.icton2019.com/)

Place and Date
Angers, France, July 9-13, 2019

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Coexistence of discrete-variable QKD with WDM classical signals in the C-band for fiber access environments

Title
Coexistence of discrete-variable QKD with WDM classical signals in the C-band for fiber access environments

Authors
D. Zavitsanos, G. Giannoulis, A. Raptakis, C. Papananos, F. Setaki, E. Theodoropoulou, G. Lyberopoulos, Ch. Kouloumentas, and H. Avramopoulos.

Abstract
In this paper, a coexistence scheme between a Discrete-Variable Quantum Key Distribution (DV-QKD) and four bidirectional classical channels in a Passive Optical Network (PON) topology is theoretically investigated. The study aims to explore the imposed limitations considering the coexistence of weak quantum channels with realistic traffic flows of classical streams through shared fiber infrastructures. Based on a ‘plug and play’ phase coding DV-QKD implementation, we conducted numerical simulations of the QBER and the secure key rate for fiber distances up to 10km. The reported results suggest that in a fixed C-band grid, the spectral isolation between classical and quantum channels is essential at dense grids. By removing the leakage noise through stronger spectral isolation, the photons linked with the Raman scattering becomes the dominant noise source, since this mechanism covers an ultra-broadband window and gets stronger as the propagation distance increases.

Venue
21st International Conference on Transparent Optical Networks ICTON 2019 (http://www.icton2019.com/)

Place and Date
Angers, France, July 9-13, 2019

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