Showing papers in "Electronics Letters in 1998"
TL;DR: In this article, a monomode optical fiber with a core diameter equal to approximately 50 free-space wavelengths has been developed, which can guide only a single mode, no matter how large the fiber diameter.
Abstract: The authors report the realisation of a new design for a large mode area monomode optical fibre. This photonic crystal fibre will guide only a single mode, no matter how large the fibre diameter, provided the shape is kept constant. This is demonstrated with a fibre which has a core diameter equal to approximately 50 free-space wavelengths.
532 citations
TL;DR: In this paper, the characteristics of a rectangular microstrip antenna with an L-shaped probe are investigated and a foam layer with a thickness of around 10% of the wavelength is used as the supporting substrate.
Abstract: The characteristics of a rectangular microstrip antenna with an L-shaped probe are investigated. A foam layer with a thickness of around 10% of the wavelength is used as the supporting substrate. An impedance bandwidth of 35% and an average gain of 7.5 dBi can be achieved. The radiation pattern is stable across the passband.
455 citations
TL;DR: In this paper, a simple method of fabricating long-period fiber gratings by direct exposure of the fibre to focused 10.6 /spl mu/m wavelength CO/sub 2/ laser pulses is presented.
Abstract: A new, simple method of fabricating long-period fibre gratings by direct exposure of the fibre to focused 10.6 /spl mu/m wavelength CO/sub 2/ laser pulses is presented. No ultraviolet exposure is used. Hydrogen loading is found to enhance the writing sensitivity.
340 citations
TL;DR: The authors have accurately approximated the Rayleigh-lognormal distribution by the K distribution, which is simpler and thus more appropriate for analysis and design of wireless communication systems.
Abstract: The Rayleigh-lognormal distribution, which has proved useful for modelling fading-shadowing wireless channels, has a complicated integral form. The authors have accurately approximated it by the K distribution. This distribution is simpler and thus more appropriate for analysis and design of wireless communication systems.
310 citations
TL;DR: In this article, a Yagi-like printed dipole array antenna with broadband characteristics is presented, fed by a microstrip-to-coplanar strip transition, and uses the truncated microstrip ground plane as its reflecting element.
Abstract: A compact and uniplanar antenna with broadband characteristics is presented. The novel Yagi-like printed dipole array antenna is fed by a microstrip-to-coplanar strip transition, and uses the truncated microstrip ground plane as its reflecting element. An X-band prototype measures a bandwidth of 17%. With 6.5 dB gain, 18 dB front-to-back ratio, and lower than -15 dB cross-polarisation level at 10 GHz.
306 citations
TL;DR: In this article, an improved optical coherence tomography system is proposed to estimate the optical impulse response from the output interferometric signal of an interferometer according to the following steps: (a) acquiring auto-correlation data from the inter-ferometer system; (b) acquiring cross-correlated data from an inter-factory system having the biological tissue sample in the sample arm; and (c) processing the auto correlation data and the cross correlation data to produce an optical impulse reaction of the tissue.
Abstract: The present invention provides an improved optical coherence tomography system and involves estimating the impulse response (which is indicative of the actual reflecting and scattering sites within a tissue sample) from the output interferometric signal of an interferometer according to the following steps: (a) acquiring auto-correlation data from the interferometer system; (b) acquiring cross-correlation data from the interferometer system having the biological tissue sample in the sample arm; and (c) processing the auto-correlation data and the cross correlation data to produce an optical impulse response of the tissue The impulse response may be obtained from the cross-correlation and auto-correlation data by: (d) obtaining an auto-power spectrum from the auto-correlation data by performing a Fourier transform on the auto-correlation data; (e) obtaining a cross-power spectrum from the cross-correlation data by performing a Fourier transform on the cross-correlation data; (f) obtaining a transfer function of the LSI system by taking a ratio of the cross-power spectrum to the auto-power spectrum; and (g) obtaining the optical impulse response of the LSI system by performing an inverse-Fourier transform on the transfer function Preferably, coherent demodulation is used in combination with the above deconvolution technique to resolve closely-spaced reflecting sites in the sample By utilizing both the magnitude and phase data of the demodulated interferometric signals, the OCT system of the present invention is able to distinguish between closely spaced reflecting sites within the sample
304 citations
TL;DR: A new cluster validation index is presented which can be used to eliminate the montonically decreasing tendency when the number of clusters becomes very large and close to thenumber of data points.
Abstract: A new cluster validation index is presented which can be used to eliminate the montonically decreasing tendency when the number of clusters becomes very large and close to the number of data points The limiting behaviour is described and numerical examples presented to show the effectiveness of the proposed cluster validity index
264 citations
TL;DR: In this article, a long wire fractal antenna based on the Koch curve is presented, which improves the features of a common linear monopole by increasing the radiation resistance and reducing the Q at each fractal iteration.
Abstract: A small but long wire fractal antenna based on the Koch curve is presented. Experimental and numerical results show that the antenna improves the features of a common linear monopole. The radiation resistance is increased and the Q is reduced at each fractal iteration, approaching the fundamental limit on small antennas.
256 citations
TL;DR: A carry select adder scheme using an add-one circuit to replace one carry-ripple adder requires 29.2% fewer transistors with a speed penalty for bit length n=64 and two of the original carry-select adder blocks can be substituted.
Abstract: Instead of using dual carry-ripple adders, a carry select adder scheme using an add-one circuit to replace one carry-ripple adder requires 29.2% fewer transistors with a speed penalty of 5.9% for bit length n=64. If speed is crucial for this 64 bit adder, then two of the original carry-select adder blocks can be substituted by the proposed scheme with a 6.3% area saving and the same speed.
237 citations
TL;DR: In this article, the authors examined the changes in wavelength and attenuation of long period fiber gratings subjected to bends with curvatures from 0 to 4.4 m/sup -1/.
Abstract: The authors examine the changes in wavelength and attenuation of long period fibre gratings subjected to bends with curvatures from 0 to 4.4 m/sup -1/. The wavelength change with curvature is nonlinear, with a projected minimum detectable curvature change of 2/spl times/10/sup -3/ m/sup -1/. The magnitude of the bend-induced wavelength shift depends on the rotation of the cylindrical fibre relative to the bending plane.
226 citations
TL;DR: Computer simulation results indicate that BICM-ID, with a few iterations, significantly outperforms conventional trellis coded modulation and is therefore another promising technique to achieve large coding gain without bandwidth expansion.
Abstract: A new iterative decoding (ID) scheme is suggested for bit-interleaved coded modulation (BICM). The bit-metric generation at the demodulator is optimised with the soft-output feedback from the convolutional decoder. Computer simulation results indicate that BICM-ID, with a few iterations, significantly outperforms conventional trellis coded modulation and is therefore another promising technique to achieve large coding gain without bandwidth expansion.
TL;DR: A new concept for analogue-to-digital (ADC) conversion is proposed and demonstrated where the analogue signal is stretched in time before sampling and quantisation.
Abstract: A new concept for analogue-to-digital (ADC) conversion is proposed and demonstrated. The analogue signal is stretched in time prior to sampling and quantisation. Time stretching increases the input bandwidth and sampling rate of the ADC and is best implemented using optoelectronic techniques.
TL;DR: In this article, a II-VI laser diode lifetime of >140 h at 40/spl deg/C, as well as /spl sim/400 h at 20/spl dc/C with a constant output power of 1 mW was achieved for a ZnCdSe-ZnSSe-znMgSSe separate-confinement heterostructure diode under continuous-wave operation.
Abstract: A II-VI laser diode lifetime of >140 h at 40/spl deg/C, as well as /spl sim/400 h at 20/spl deg/C, has been achieved for a ZnCdSe-ZnSSe-ZnMgSSe separate-confinement heterostructure laser diode under continuous-wave operation with a constant output power of 1 mW. Progress has been made towards increasing the basic reliability of ZnMgSSe-based wide bandgap laser diodes by reducing point defects.
TL;DR: In this paper, an iterative decoding scheme for quadrature phase shift keying (QPSK) modulation with anti-gray mapping is presented, where a soft demapper accepting a priori information and a convolutional decoder are applied in a serial concatenation.
Abstract: The authors present an iterative decoding scheme which is particularly suited for quadrature phase shift keying (QPSK) modulation with anti-Gray mapping. At the receiver, a soft demapper accepting a priori information and a convolutional decoder are applied in a serial concatenation. Numerical results are presented for QPSK in additive white Gaussian noise and Rayleigh-fading channels. The iterated system applying anti-Gray mapping outperforms the conventional system using Gray mapping after only one iteration.
TL;DR: Division-free duplex is proposed for future wireless systems, thus providing simultaneous duplex radio transmission on a division-free basis, and results from an experimental RF system yielding some 72 dB duplex isolation at 1.8 GHz for 200 kHz channelisation.
Abstract: Division-free duplex is proposed for future wireless systems, thus providing simultaneous duplex radio transmission on a division-free basis. The required duplex isolation can be achieved by electronic interference cancellation operating at both RF and baseband, with results from an experimental RF system yielding some 72 dB duplex isolation at 1.8 GHz for 200 kHz channelisation.
TL;DR: In this paper, a 640 Gbit/s TDM signal was successfully demultiplexed to 10 Gbps with a walk-off free, ultrafast, 450 m long nonlinear optical loop mirror (NOLM).
Abstract: A 640 Gbit/s TDM signal has been successfully demultiplexed to 10 Gbit/s with a walk-off free, ultrafast, 450 m long nonlinear optical loop mirror (NOLM). The NOLM consists of nine 50 m long sections of dispersion flattened fibre (DFF) with different group delay characteristics. The walk-off between the signal and control pulses for each of the nine fibres was within /spl plusmn/400 fs. By properly connecting them, a total walk-off of <100 fs has been achieved.
TL;DR: In this article, a rectangular microstrip antenna with two U-shaped slots on the patch is described, and an impedance bandwidth of 44% is achieved using a foam layer of thickness /spl sim/8% wavelength as the supporting substate.
Abstract: A rectangular microstrip antenna with two U-shaped slots on the patch is described. Using a foam layer of thickness /spl sim/8% wavelength as the supporting substate, an impedance bandwidth of 44% is achieved. The radiation patterns are stable across the passband.
TL;DR: An image watermarking scheme in a DCT domain is proposed that is adaptive in that a different strength of watermark is applied to different blocks according to their block classification.
Abstract: An image watermarking scheme in a DCT domain is proposed. It is adaptive in that a different strength of watermark is applied to different blocks according to their block classification. For the classification, visual masking (both luminance and texture masking) is taken into account. Consequently, the watermarks thus generated are robust and invisible.
TL;DR: In this paper, an improved plug-and-play interferometric system for quantum key distribution is presented, where self-alignment and compensation of birefringence remain, while limitations due to reflections are overcome.
Abstract: An improved « plug & play » interferometric system for quantum key distribution is presented. Self-alignment and compensation of birefringence remain, while limitations due to reflections are overcome. Original electronics implementing the BB84 protocol makes adjustment simple. Key creation with 0.1 photon per pulse at a rate of 325 Hz with a 2.9% QBER – corresponding to a net rate of 210Hz - over a 23 Km installed cable was performed. Quantum key distribution allows two remote parties, Alice and Bob, to generate a secret key, with privacy guaranteed by quantum mechanics. It has been demonstrated in optical fibers by several groups [1,2,3]. However continuous active adjustment, either of polarization or path length in the setups was necessary. Our group introduced in 1997 an interferomete r with Faraday mirrors featuring self-alignment. A key creation rate of the order of 1Hz with the B92 two states protocol was achieved [5]. In this letter, we present a modification of this set-up, allowing a higher key creation rate, with implementation of the BB84 four states protocol. Moreover, this system uses InGaAs/InP avalanche photodiodes cooled to only 173K as photon counters, and electronics allowing automatic timing. We then discuss results of experiments in the laboratory over a 4.9km optical fiber spool and in the field, over 23km of installed fibers. The 97 system was operated at a frequency of 1 kHz. At this low repetition rate, there is never more than one pulse in the optical fiber. When increasing the frequency, the quantum bit error rate QBER rises because of false counts arising from reflected photons and from afterpulses. To get round this difficulty, we developed the system depicted in Fig. 1. Bob sends a light pulse through a circulator. This pulse splits at the coupler C1. The first half travels through the short arm. A polarization controller is set so that this pulse is completely transmitted at the polarizing beam splitter PBS. It then propagates to Alice, where it splits again at coupler C2 to provide a timing signal. It then travels through Alice's equipment and is reflected back to Bob. Thanks to the Faraday mirror, the birefringence of the optical link is compensated, and the pulse comes back orthogonally polarized. It is then reflected by the PBS and takes the long arm, where Bob applies a phase shift φB with its modulator PMB. The second pulse propagates through both arms in reverse order. Alice applies to it a phase shift φA. Since both pulses travel exactly the same optical path, they reach the coupler C1 simultaneously with identical polarization, giving rise to interference. Thanks to this improved interferometer, reflections directly into the detectors are suppressed. According to the phase applied by Alice and Bob, the pulse
TL;DR: In this paper, the first error free operation of 100 Gbit/s wavelength conversion employing cross-gain modulation in a semiconductor optical amplifier was demonstrated, and a near transform limited non-return-to-zero data stream was generated at the device output.
Abstract: The authors demonstrate the first error free operation of 100 Gbit/s wavelength conversion employing cross-gain modulation in a semiconductor optical amplifier. A near transform limited non-return-to-zero data stream is generated at the device output.
TL;DR: In this paper, the nonlinear process of two-photon absorption in a commercial laser diode may be used for all-optical demultiplexing in terabit per second optical time division multiplexing networks.
Abstract: The authors describe how the nonlinear process of two-photon absorption in a commercial laser diode may be used for all-optical demultiplexing in terabit per second optical time division multiplexing networks. Switching windows of 650 fs in duration have been observed, with corresponding switching energies of a few picojoules.
TL;DR: In this article, a half symmetric cavity structure was proposed for a tunable filter with a 3 dB linewidth of 0.27 nm, more than 70 nm tuning range under a voltage swing of 14 V and less than 0.9 dB insertion loss.
Abstract: A novel microelectromechanical tunable filter with a half symmetric cavity structure is described. The device exhibits a 3 dB linewidth of 0.27 nm, more than 70 nm tuning range under a voltage swing of 14 V and less than 0.9 dB insertion loss. The parameters of the optical cavity were tailored to efficiently couple 1550 nm light in and out of the devices using a singlemode fibre without any lenses. The structure exhibits a frequency response of 150 kHz at the 3 dB cutoff point.
TL;DR: In this paper, a folded reflectarray antenna is presented, which combines a twist and focusing reflector concept in a single printed structure, together with a printed grid, a low profile and high gain antenna results.
Abstract: A novel folded reflectarray antenna is presented. This antenna combines a twist and focusing reflector concept in a single printed structure. Together with a printed grid, a low profile and high gain antenna results. A test antenna in the 20 GHz range was designed, fabricated and tested.
TL;DR: A new high-speed and low power design of the 3-2 counter and 4-2 compressor of a parallel array multiplier has better speed and power performance than other recently proposed approaches.
Abstract: A 3-2 counter and a 4-2 compressor are the basic components in the partial product summation tree of a parallel array multiplier. A new high-speed and low power design of these components is presented. Owing to the reduction of the internal load capacitance, the counter and compressor have better speed and power performance than other recently proposed approaches.
TL;DR: In this article, a new edge detection filter is presented, based on a new type of image convolution in which colour images are convolved with a pair of quaternion-valued (hypercomplex) masks.
Abstract: A new type of edge-detecting filter is presented, based on a new type of image convolution in which colour images are convolved with a pair of quaternion-valued (hypercomplex) masks. When applied to a colour image, the new filter converts areas of smoothly-varying colour to shades of grey, and generates colours in regions where colour (but not intensity) edges occur in the image. The result may be easily thresholded for chromaticity to produce an edge image exhibiting colour only where the original image exhibited a sharp change of colour.
TL;DR: In this article, a single-feed compact dual-frequency design is proposed, which consists of a rectangular patch loaded with two parallel slots close to the radiating edges and meandered with slits at the non-radiating edges.
Abstract: A novel single-feed compact dual-frequency design is demonstrated. The proposed design consists of a rectangular patch loaded with two parallel slots close to the radiating edges and meandered with slits at the non-radiating edges. The two operating frequencies have parallel polarisation planes and, by varying the insetting slit length, the frequency ratio of the two frequencies is tunable in the range of /spl sim/1.8-2.4. In addition, with the insetting slit, the two frequencies can be greatly lowered, which results in a large antenna size reduction for fixed dual-frequency operation.
TL;DR: The authors propose an algorithm based on a class of perturbance to solve the short cycle problem for chaotic cryptography systems, and the lower bound of the extended cycle length can be specified theoretically and the original good statistical properties of chaotic dynamics can be maintained.
Abstract: The authors propose an algorithm based on a class of perturbance to solve the short cycle problem for chaotic cryptography systems. The lower bound of the extended cycle length can be specified theoretically, and the original good statistical properties of chaotic dynamics can be maintained.
TL;DR: A simplification of the MAP decoder for use in turbo decoders is presented, which eliminates the need for a ROM or multiplexor-tree lookup table and replaces it with a constant value.
Abstract: A simplification of the MAP decoder for use in turbo decoders is presented. The simplification eliminates the need for a ROM or multiplexor-tree lookup table and replaces it with a constant value. Simulations show that the performance of turbo decoders is not adversely affected by this simplification.
TL;DR: In this paper, a single channel, time domain multiplexed 640 Gbit/s data signal has been successfully transmitted over 60 km using a walk-off free, dispersion flattened nonlinear loop mirror.
Abstract: A single channel, time domain multiplexed 640 Gbit/s data signal has been successfully transmitted over 60 km. The width of the input pulse train was as little as 400 fs and a walk-off free, dispersion flattened nonlinear loop mirror was used to demultiplex the signal to 10 Gbit/s. The maximum transmission distance was mainly determined by the polarisation mode dispersion as well as the third order dispersion.
TL;DR: In this paper, a simple circular polarisation (CP) design of microstrip antennas using a tuning stub is proposed and studied, and it is also demonstrated that, by applying this CP design method to a circular microstrip patch with a cross slot having equal slot lengths, a compact circularly-polarised microstrip antenna can easily be implemented, with much more relaxed manufacturing tolerances as compared to the case of using a cross-slot of unequal slot lengths.
Abstract: A simple circular polarisation (CP) design of microstrip antennas using a tuning stub is proposed and studied. It is also demonstrated that, by applying this CP design method to a circular microstrip patch with a cross slot having equal slot lengths, a compact circularly-polarised microstrip antenna can easily be implemented, with much more relaxed manufacturing tolerances as compared to the case of using a cross slot of unequal slot lengths. Details of the antenna designs are described, and experimental results are presented and discussed.