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Papers by keith blow

Optical fibres are being employed in telecommunications systems because of their significant adva... more Optical fibres are being employed in telecommunications systems because of their significant advantages over other transmission media. Data has been transmitted at rates up to 2 Gbits/sec1 and over distances in excess of 100 km without repeaters2. Although impressive, these figures are far from the ultimate obtainable. Present day systems transmit data in the form of an encoded train of optical noise bursts. In concept this is as primitive as radio engineering was in the days of Hertz and Marconi. It is only within the last 2–3 years that serious effort has been directed to exploit the coherence properties of lasers for optical communications. In the laboratory, narrowband single-frequency lasers and coherent detection are being used to increase both transmission range and data rate. An alternative is to harness the nonlinear properties of fibres by using high peak power (>1 W), short duration (~1ps), transform limited pulses. In low loss fibres, high intensities can be maintaine...

Proceedings of the IEEE 6th Circuits and Systems Symposium on Emerging Technologies: Frontiers of Mobile and Wireless Communication (IEEE Cat. No.04EX710)

We combine a simple energy model of radio transceivers with analysis of ad-hoc routing to optimiz... more We combine a simple energy model of radio transceivers with analysis of ad-hoc routing to optimize system performance. A simple example of a linear wireless ad hoc sensor network is used to deduce the relationship between traffic load and optimal radio range of topology management schemes. We find that half of the power can be saved if the radio range is adjusted appropriately compared with the best case where equal radio ranges are used.

Optical Fiber Communication, 1983

Recently techniques for optical pulse compression have received both theoretical and experimental... more Recently techniques for optical pulse compression have received both theoretical and experimental attention.1,2 This involves the generation of an enhanced frequency chirped pulse using a nonlinear normal dispersive medium followed by a medium with anomalous group velocity dispersion. Two systems have been reported at 619 nm. One involves a nonlinear optical fiber followed by a grating pair.1

Optics Letters, 1985

ABSTRACT We have constructed a pulse compressor using two different optical fibers. By adjusting ... more ABSTRACT We have constructed a pulse compressor using two different optical fibers. By adjusting the waveguide dispersion it has been possible to produce fibers with positive and negative dispersion at 1.32 microm. We have demonstrated the compression of 130-psec pulses down to our photodiode limit of 70 psec. This is supported by our calculations, which give a theoretical pulse width of 50 psec. This is the first reported demonstration of both an all-fiber pulse compressor and optical pulse compression at 1.32 microm.

IETE Journal of Research, 2016

We present experimental results for wavelength-division multiplexed (WDM) transmission performanc... more We present experimental results for wavelength-division multiplexed (WDM) transmission performance using unbalanced proportions of 1s and 0s in pseudo-random bit sequence (PRBS) data. This investigation simulates the effect of local, in time, data unbalancing which occurs in some coding systems such as forward error correction when extra bits are added to the WDM data stream. We show that such local unbalancing, which would practically give a time-dependent error-rate, can be employed to improve the legacy long-haul WDM system performance if the system is allowed to operate in the nonlinear power region. We use a recirculating loop to simulate a long-haul fibre system.

Quantum cryptography has been shown to be an effective technique for the secure distribution of c... more Quantum cryptography has been shown to be an effective technique for the secure distribution of cryptographic keys on point-to-point communication links. Here, we describe adaptations of the existing quantum cryptography protocols and equipment configurations that allow secure key distribution to be performed on a variety of multiuser passive optical network (PON) architectures. These adaptations enable the network controller on the PON to distribute individual secret keys to each user on the network, and hence to securely encrypt subsequent data transmissions broadcast on the network. 2 Introduction: The concept of quantum cryptography, a theoretically secure technique for distributing cryptographic keys, was developed in the 1980s by Bennett, Brassard, Weisner and coworkers [1]. Their work culminated in a remarkable proof-of-principle demonstration of secure quantum key exchange over short distances of free space [2]. Since this original experiment progress towards practical appli...

We present a design of a fast all-optical core-node processor that performs packet-forwarding in ... more We present a design of a fast all-optical core-node processor that performs packet-forwarding in optical networks without header-modification. The design is based on bit-serial architecture using TOADs as logic-gates that perform modulo-arithmetic to forward packets.

EFTA 2003. 2003 IEEE Conference on Emerging Technologies and Factory Automation. Proceedings (Cat. No.03TH8696)

This paper considers the design of wireless sensor networks in which a set of smart battery-power... more This paper considers the design of wireless sensor networks in which a set of smart battery-powered sensor nodes cooperatively form an ad hoc communications network for monitoring and control applications. The paper examines ways of extending the life of such networks by introducing a 'sleep mode' in the sensor node. Quantitative analysis is used to show that although there is a complex relationship between 'sleeping' and energy conservation, it is possible to make significant energy savings while incurring only modest degradation in performance. An optimum energy saving curve is derived which provides a basis for the design of extended-life ad hoc wireless sensor networks.

Wireless Sensor Network, 2011

Wireless sensor networks have been identified as one of the key technologies for the 21 st centur... more Wireless sensor networks have been identified as one of the key technologies for the 21 st century. In order to overcome their limitations such as fault tolerance and conservation of energy, we propose a middleware solution, In-Motes. In-Motes stands as a fault tolerant platform for deploying and monitoring applications in real time offers a number of possibilities for the end user giving him in parallel the freedom to experiment with various parameters, in an effort the deployed applications to run in an energy efficient manner inside the network. The proposed scheme is evaluated through the In-Motes EYE application, aiming to test its merits under real time conditions. In-Motes EYE application which is an agent based real time In-Motes application developed for sensing acceleration variations in an environment. The application was tested in a prototype area, road alike, for a period of four months.

Wireless Sensor Network, 2009

Sensor networks are dense wireless networks of small, low-cost sensors, which collect and dissemi... more Sensor networks are dense wireless networks of small, low-cost sensors, which collect and disseminate environmental data. Wireless sensor networks facilitate monitoring and controlling of physical environments from remote locations with better accuracy. They have applications in a variety of fields such as environmental monitoring; military purposes and gathering sensing information in inhospitable locations. Sensor nodes have various energy and computational constraints because of their inexpensive nature and adhoc method of deployment. Considerable research has been focused at overcoming these deficiencies through more energy efficient routing, localization algorithms and system design. Our survey presents the fundamentals of wireless sensor network, thus providing the necessary background required for understanding the organization, functionality and limitations of those networks. The middleware solution is also investigated through a critical presentation and analysis of some of the most well established approaches.

Wireless Networks, 2005

In this paper we use the Erlang theory to quantitatively analyse the trade offs between energy co... more In this paper we use the Erlang theory to quantitatively analyse the trade offs between energy conservation and quality of service in an ad-hoc wireless sensor network. Nodes can be either sleeping, where no transmission or reception can occur, or awake where traffic is processed. Increasing the proportion of time spent in the sleeping state will decrease throughput and increase packet loss and delivery delay. However there is a complex relationship between sleeping time and energy consumption. Increasing the sleeping time does not always lead to an increase in the energy saved. We identify the energy consumption profile for various levels of sensor network activity and derive an optimum energy saving curve that provides a basis for the design of extended-life ad hoc wireless sensor networks.

Physical Review A, 1992

When subpicosecond solitons propagate in an optical fiber the soliton self-frequency shift occurs... more When subpicosecond solitons propagate in an optical fiber the soliton self-frequency shift occurs. We have made observations of this effect in standard telecommunication fiber, which show a strong departure from the predicted behavior. This difference is shown to be due to the residual birefringence in the standard fiber. Results are also presented on the power and length dependence and detailed comparisons with numerical simulations are made.

Optics Communications, 1982

ABSTRACT Calculations are presented on the non-linear Schrödinger equation in the presence of los... more ABSTRACT Calculations are presented on the non-linear Schrödinger equation in the presence of loss. This equation describes the propagation of optical pulses in a non-linear waveguide in the anomalous dispersion regime. The calculations are performed for realistic fibre parameters over 15 km. The results indicate that it is necessary to generate higher order solitons in order to obtain any advantage from the non-linear effects in the material. We also show that including loss as a perturbation is only valid for short fibre lengths or very low losses and that the conclusions of Hasegawa and Kodama (1981) are not necessarily appropriate for all fibre systems.

Optics Communications, 1985

We monitor the time evolution of the temperature of phononic collective modes in a one-dimensiona... more We monitor the time evolution of the temperature of phononic collective modes in a one-dimensional quasicondensate submitted to losses. At long times the ratio between the temperature and the energy scale mc 2 , where m is the atomic mass and c the sound velocity takes, within a precision of 20%, an asymptotic value. This asymptotic value is observed while mc 2 decreases in time by a factor as large as 2.5. Moreover this ratio is shown to be independent on the loss rate and on the strength of interactions. These results confirm theoretical predictions and the measured stationary ratio is in quantitative agreement with the theoretical calculations.

Optics Communications, 1995

We advance the average so&on concept to include averaging of the pulse shape in addition to the p... more We advance the average so&on concept to include averaging of the pulse shape in addition to the pulse energy. A simple prescription is presented for the optimum launch position of a bandwidth-limited sech(t) pulse, relative to the periodic cycle. We identify how this result can also be obtained from the Lie algebra approach by Hasegawa and Kodama (Optics Lett. 15 (1990) 1443). Improved stability and reduced pulse distortion is demonstrated in a numerical example. Application of this result will enhance the performance of some strongly perturbed, soliton-based, amplified optical communication systems.

Optics Communications, 2008

A new improved design of an all-optical processor that performs modular arithmetic is presented. ... more A new improved design of an all-optical processor that performs modular arithmetic is presented. The modulo-processor is based on all-optical circuit of interconnected semiconductor optical amplifier logic gates. The design allows processing times of less than 1s for 16-bit operation at 10Gb/s and up to 32-bit operation at 100Gb/s.

Journal of the Optical Society of America B, 1991

We discuss the quantum theory of self-phase modulation as applied to optical fibers. We use a for... more We discuss the quantum theory of self-phase modulation as applied to optical fibers. We use a formalism that does not rely on a cavity and thereby resolves some anomalous length dependences present in earlier studies. We show that the exact expectation values and variances can be evaluated without the need for linearizing about a classical pump wave. The standard quantum equations for self-phase modulation are generalized in order to remove singularities in some expectation values whose origin is the instantaneous response time approximation.

Journal of Lightwave Technology, 1983

The possible use of Bragg fibers for long-distance low-loss optical communications is investigate... more The possible use of Bragg fibers for long-distance low-loss optical communications is investigated, structures calculated, and their limitations established. It is found that the original design of Bragg fibers offers no possibility of low-loss propagation.

IET Communications, 2013

The recent explosive growth of voice over IP (VoIP) solutions calls for accurate modelling of VoI... more The recent explosive growth of voice over IP (VoIP) solutions calls for accurate modelling of VoIP traffic. This paper presents measurements of ON and OFF periods of VoIP activity from a significantly large database of VoIP call recordings consisting of native speakers speaking in some of the world's most widely spoken languages. The impact of the languages and the varying dynamics of caller interaction on the ON and OFF period statistics are assessed. It is observed that speaker interactions dominate over language dependence which makes monologue based data unreliable for traffic modelling. The authors derive a semi-Markov model which accurately reproduces the statistics of composite dialogue measurements.

IEEE Journal of Quantum Electronics, 1983

In this paper we have calculated the effects of loss on the propagation of soliton solutions of t... more In this paper we have calculated the effects of loss on the propagation of soliton solutions of the nonlinear Schrodinger equation. Since we are interested in the application of these results to optical communications, it is necessary to go beyond perturbative results. This is due to the fact that propagation distances in optical fibers are significantly greater than the decay length of the energy in the pulses. Some conclusions are drawn about the application of solitons in long-distance communications.