Thomas E. Chapuran

Optical networking for quantum key distribution and quantum communications

Modern optical networking techniques have the potential to greatly extend the applicability of quantum communications by moving beyond simple point-to-point optical links and by leveraging existing fibre infrastructures. We experimentally demonstrate many of the fundamental capabilities that are required. These include optical-layer multiplexing, switching and routing of quantum signals; quantum key distribution (QKD) in a dynamically reconfigured optical network; and coexistence of quantum signals with strong conventional telecom traffic on the same fibre. We successfully operate QKD at 1310 nm over a fibre shared with four optically amplified data channels near 1550 nm. We identify the dominant impairment as spontaneous anti-Stokes Raman scattering of the strong signals, quantify its impact, and measure and model its propagation through fibre. We describe a quantum networking architecture which can provide the flexibility and scalability likely to be critical for supporting widespread deployment of quantum applications.

Dense wavelength multiplexing of 1550 nm QKD with strong classical channels in reconfigurable networking environments

To move beyond dedicated links and networks, quantum communications signals must be integrated into networks carrying classical optical channels at power levels many orders of magnitude higher than the quantum signals themselves. We demonstrate the transmission of a 1550 nm quantum channel with up to two simultaneous 200 GHz spaced classical telecom channels, using reconfigurable optical add drop multiplexer (ROADM) technology for multiplexing and routing quantum and classical signals. The quantum channel is used to perform quantum key distribution (QKD) in the presence of noise generated as a by-product of the co-propagation of classical channels. We demonstrate that the dominant noise mechanism can arise from either four-wave mixing or spontaneous Raman scattering, depending on the optical path characteristics as well as the classical channel parameters. We quantify these impairments and discuss mitigation strategies.

Fast wavelength-switching of laser transmitters and amplifiers

The authors discuss system aspects and describe experimental demonstrations of nanosecond wavelength tuning in laser diode structures. Both tunable transmitters and tunable filters are considered. The dependence of the refractive index on the carrier density in semiconductors is exploited to obtain fast wavelength tuning. Experimentally, switching times of >

Experimental investigation of quantum key distribution through transparent optical switch elements

Quantum key distribution (QKD) enables unconditional physical layer security for the distribution of cryptographic key material. However, most experimental demonstrations have relied on simple point-to-point optical links. In this paper we investigate the compatibility of QKD with reconfigurable optical networks. By performing the first tests of QKD transmission through optical switches, we study if there are impairment mechanisms other than switch insertion loss that impact the sifted and error corrected secret bit yield. Three types of transparent optical switch elements are investigated including lithium niobate (LiNbO/sub 3/), microelectromechanical systems (MEMS), and optomechanical. We show that QKD can be extended beyond point-to-point links to switched multinode architectures including protected ring networks to enhance quantum channel availability.

Demonstration of 1550 nm QKD with ROADM-based DWDM Networking and the Impact of Fiber FWM

We demonstrate compatibility of 1550 nm QKD with a MEMS-based ROADM and also show that four-wave mixing resulting from copropagating DWDM signals can become the dominant source of background noise within the QKD channel passband.

Experimental characterization of the separation between wavelength-multiplexed quantum and classical communication channels

Quantum key distribution (QKD) is a new technique for secure key distribution based on the laws of physics rather than mathematical or algorithmic computational complexity used by current systems. Understanding the compatibility of QKD at 1310 nm with the existing commercial optical networks bearing classical wavelength-division-multiplexed (WDM) channels at 1550 nm is important to advance the deployment of QKD systems in such networks. The minimum wavelength separation for multiplexing QKD and WDM channels on a shared fiber is experimentally determined for impairment-free QKD+WDM transmission.

Impact of spontaneous anti-Stokes Raman scattering on QKD+DWDM networking

This study presents an experimental demonstration of 1310 nm QKD multiplexing and transmission with amplified DWDM signals over a shared 10 km fiber span. This work identifies anti-Stokes Raman scattering generated during fiber propagation as the primary contributor of crosstalk noise at the QKD receiver. New results are presented on the characterization of spontaneous anti-Stokes Raman noise (SASRN), generated within the fiber by the high-power DWDM signals, and implications for QKD+DWDM networking architectures are also discussed.

Progress toward quantum communications networks: opportunities and challenges

Quantum communications is fast becoming an important component of many applications in quantum information science. Sharing quantum information over a distance among geographically separated nodes using photonic qubits requires a reconfigurable transparent networking infrastructure that can support quantum information services. Using quantum key distribution (QKD) as an example of a quantum communications service, we investigate the ability of fiber networks to support both conventional optical traffic and single-photon quantum communications signals on a shared infrastructure. The effect of Raman scattering from conventional channels on the quantum bit error rate (QBER) of a QKD system is analyzed. Additionally, the potential impact and mitigation strategies of other transmission impairments such as four-wave mixing, cross-phase modulation, and noise from mid-span optical amplifiers are discussed. We also review recent trends toward the development of automated and integrated QKD systems which are important steps toward reliable and manufacturable quantum communications systems.

Digital transmission over in-home coaxial wiring

The wiring of a customers premises network (CPN) may be the weakest link in the end-to-end transport of residential broadband digital services such as digital video. Detailed knowledge of how such premises wiring will affect digital service delivery is critical to the cost-effective deployment and robust operation of digital technologies. This paper reports selected results from a series of experimental and analytical studies of coaxial-cable premises-wiring impairments for digital broadband signals. The investigations included return loss, isolation and attenuation measurements of a wide variety of components, as well as measurements and simulations of bit-error-rate performance for several inside-wiring test-bed configurations. The components showed a broader range of performance, and in some cases considerably worse performance, than indicated in previous studies. The premises wiring generated signal reflections which can severely degrade digital transmission. Some reflections can cause destructive interference that effectively decreases the received signal power by 10 dB more than the nominal attenuation, and this decrease is not mitigated by set-top or cable-modem adaptive equalization.

Broadband multichannel WDM transmission with superluminescent diodes and LEDs

The authors investigate the use of superluminescent diodes (SLDs) and light emitting diodes (LEDs) in broadband multichannel WDM (wavelength division multiplexing) transmission. This technique, known as spectral slicing, may afford important advantages over traditional laser-based WDM in many network applications. The authors describe three system demonstrations using combinations of SLDs, LEDs, and erbium-doped fiber amplifiers to achieve spectrally sliced transmission over 4 to 16 WDM channels at bit rates up to 155 Mb/s per channel. A generalized power-budget analysis of spectrally sliced transmission is then presented and compared with experimental results. The investigation quantifies key trade-offs in the design of spectrally sliced WDM networks, and identifies opportunities for extension and optimization of system performance.<<ETX>>