Monolithically integrated selectable repetition-rate laser diode source of picosecond optical pulses.

We describe the characterization of a monolithically integrated photonic device for short pulse generation featuring a mode-locked laser diode, a Mach-Zehnder modulator (MZM), and a semiconductor optical amplifier (SOA). The integrated device is designed for fabrication by a generic foundry scheme with a view to ease of design, testing, and manufacture. Trains of 6.8 ps pulses are generated at repetition rates that are electronically switchable from 14 GHz to 109 MHz. The SOA boosts the peak power by 7.4 dB, and the pulses are compressible to 2.4 ps by dispersion compensation using single-mode telecommunications fiber.This research leading to these results has received support from the UK EPSRC COPOS award EP/H022384/1 and from the European Commission’s Seventh Framework Programme FP7/2007-2013 under grant agreement NMP 228839 EuroPIC.This is the author accepted manuscript. The final published version can be found on the publisher's website at: http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-14-414

Generic photonic integrated linear operator processor

Photonic integration platforms have been explored extensively for optical computing with the aim of breaking the speed and power efficiency limitations of traditional digital electronic computers. Current technologies typically focus on implementing a single computation iteration optically while leaving the intermediate processing in the electronic domain, which are still limited by the electronic bottlenecks. Few explorations have been made of all-optical recursive architectures for computations on integrated photonic platforms. Here we propose a generic photonic integrated linear operator processor based on an all-optical recursive system that supports linear operations ranging from matrix computations to solving equations. We demonstrate the first all-optical on-chip matrix inversion system and use this to solve integral and differential equations. The absence of electronic processing during multiple iterations indicates the potential for an orders-of-magnitudes speed enhancement of this all-optical computing approach compared to electronic computers. We realize matrix inversions, Fredholm integral equations of the second kind, 2^{nd} order ordinary differential equations, and Poisson equations using the generic photonic integrated linear operator processor

Experimental Demonstration of High Key Rate and Low Complexity CVQKD System with Local Local Oscillator

We experimentally demonstrate a 250MHz repetition rate Gaussian-modulated coherent-state CVQKD with local local oscillator implementation which is capable of realizing record 14.2 Mbps key generation in the asymptotic regime over 15km of optical fiber

Experimental demonstration of single-shot quantum and classical signal transmission on single wavelength optical pulse

Abstract: Advances in highly sensitive detection techniques for classical coherent communication systems have reduced the received signal power requirements to a few photons per bit. At this level one can take advantage of the quantum noise to create secure communication, using continuous variable quantum key distribution (CV-QKD). In this work therefore we embed CV-QKD signals within classical signals and transmit classical data and secure keys simultaneously over 25 km of optical fibre. This is achieved by using a novel coherent displacement state generator, which has the potential for being used in a wide range of quantum optical experiments. This approach removes the need for separate channels for quantum communication systems and allows reduced system bandwidth for a given communications specification. This demonstration therefore demonstrates a way of implementing direct quantum physical layer security within a conventional classical communications system, offering a major advance in term of practical and low cost implementation

Reference Pulse Attack on Continuous-Variable Quantum Key Distribution with Local Local Oscillator under trusted phase noise

We show that partially trusting the phase noise associated with estimation uncertainty in a LLO CVQKD system allows one to exchange higher secure key rates than in the case of untrusted phase noise. However, this opens a security loophole through the manipulation of the reference pulse amplitude. We label this as "reference pulse attack" which is applicable to all LLO-CVQKD systems if the phase noise is trusted. We show that, at the optimal reference pulse intensity level, Eve achieves unity attack efficiency at 23.8km and 32.0km while using lossless and 0.14dB/km loss channels, respectively, for her attack. However, in order to maintain the performance enhancement from partially trusting the phase noise, countermeasures have been proposed. As a result, the LLO-CVQKD system with partially trusted phase noise owns a superior key rate at 20km by an order 9.5, and extended transmission distance by 45%, than that of the phase noise untrusted system

Demonstration of high-speed and low-complexity continuous variable quantum key distribution system with local local oscillator

Abstract: We present an experimental demonstration of the feasibility of the first 20 + Mb/s Gaussian modulated coherent state continuous variable quantum key distribution system with a locally generated local oscillator at the receiver (LLO-CVQKD). To increase the signal repetition rate, and hence the potential secure key rate, we equip our system with high-performance, wideband devices and design the components to support high repetition rate operation. We have successfully trialed the signal repetition rate as high as 500 MHz. To reduce the system complexity and correct for any phase shift during transmission, reference pulses are interleaved with quantum signals at Alice. Customized monitoring software has been developed, allowing all parameters to be controlled in real-time without any physical setup modification. We introduce a system-level noise model analysis at high bandwidth and propose a new ‘combined-optimization’ technique to optimize system parameters simultaneously to high precision. We use the measured excess noise, to predict that the system is capable of realizing a record 26.9 Mb/s key generation in the asymptotic regime over a 15 km signal mode fibre. We further demonstrate the potential for an even faster implementation

16-user OFDM-CDMA optical access network

We demonstrate a 16×2.5 Gb/s (40 Gb/s aggregate) OFDM-CDMA PON for next-generation access applications. Four-channel error-free transmission over 25 km SMF shows 6 dB coding gain, with 0.1 dB dispersion and 0.9 dB crosstalk penalties

Reference Pulse Attack on Continuous-Variable Quantum Key Distribution with Local Local Oscillator

We reveal a security loophole in the current state-of-art phase reference pulse sharing scheme for Continuous Variable Quantum Key Distribution using a Local Local Oscillator (LLO-CVQKD). The loophole is associated with the amplitude of the phase reference pulses which Eve can manipulate to extract information which cannot be discovered by legitimate users. We call this new attack as the reference pulse attack. We have demonstrated the efficiency of our attack for different LLO-CVQKD transmission distances. Unity attack efficiency can be achieved at a transmission distance greater than 21.2 km in the case of a zero loss channel. The distance extends to 24.3 km where hollow-core fibre channels are used. We also propose possible countermeasures

Experimental demonstration of confidential communication with quantum security monitoring

Abstract: Security issues and attack management of optical communication have come increasingly important. Quantum techniques are explored to secure or protect classical communication. In this paper, we present a method for in-service optical physical layer security monitoring that has vacuum-noise level sensitivity without classical security loopholes. This quantum-based method of eavesdropping detection, similar to that used in conventional pilot tone systems, is achieved by sending quantum signals, here comprised of continuous variable quantum states, i.e. weak coherent states modulated at the quantum level. An experimental demonstration of attack detection using the technique was presented for an ideal fibre tapping attack that taps 1% of the ongoing light in a 10 dB channel, and also an ideal correlated jamming attack in the same channel that maintains the light power with excess noise increased by 0.5 shot noise unit. The quantum monitoring system monitors suspicious changes in the quantum signal with the help of advanced data processing algorithms. In addition, unlike the CV-QKD system which is very sensitive to channel excess noise and receiver system noise, the quantum monitoring is potentially more compatible with current optical infrastructure, as it lowers the system requirements and potentially allows much higher classical data rate communication with links length up to 100 s km

Secure optical communication using a quantum alarm

Abstract: Optical fibre networks are advancing rapidly to meet growing traffic demands. Security issues, including attack management, have become increasingly important for optical communication networks because of the vulnerabilities associated with tapping light from optical fibre links. Physical layer security often requires restricting access to channels and periodic inspections of link performance. In this paper, we report how quantum communication techniques can be utilized to detect a physical layer attack. We present an efficient method for monitoring the physical layer security of a high-data-rate classical optical communication network using a modulated continuous-variable quantum signal. We describe the theoretical and experimental underpinnings of this monitoring system and the monitoring accuracy for different monitored parameters. We analyse its performance for both unamplified and amplified optical links. The technique represents a novel approach for applying quantum signal processing to practical optical communication networks and compares well with classical monitoring methods. We conclude by discussing the challenges facing its practical application, its differences with respect to existing quantum key distribution methods, and its usage in future secure optical transport network planning