David M Benton

• PhD Physics
• Senior Researcher at Aston University

Photonic signal processing is used to implement common mode signal cancellation across a very wide bandwidth utilising phase modulation of radio frequency (RF) signals onto a narrow linewidth laser carrier. RF spectra were observed using narrow-band, tunable optical filtering using a scanning Fabry Perot etalon. Thus functions conventionally perfor...

Wavelength independent detection and discrimination of laser radiation has been performed by detecting the 'self coherence' of an incoming light source with photon sensitive detectors. The system successfully discriminates between coherent and incoherent sources. Detection of scattered light has been performed across the visible spectrum with filte...

Mode-division multiplexing has shown its ability to significantly increase the capacity of free-space optical communications. Accurate alignment of transmitter and receiver is crucial in maintaining performance, because a sub-optimal beam alignment will induce modal crosstalk. Conventionally, a beacon beam is necessary for system alignment due to m...

Mode-division multiplexing has shown its ability to significantly increase the capacity of free-space optical communications. An accurate alignment is crucial to enable such links due to possible performance degradation induced by mode crosstalk and narrow beam divergence. Conventionally, a beacon beam is necessary for system alignment due to multi...

Multi-plane light converters (MPLC) are a means of deconstructing a wavefront into constituent modes that are focused at specific spatial locations, and the reverse—that specific inputs result in controlled modal output. We have used a pair of MPLCs with 21 Hermite–Gaussian modes to represent a free-space optical connection. The effects of strong a...

We experimentally demonstrated, for, it is believed, the first time, high-capacity polarization- and mode-division multiplexing free-space optical transmission with adequate strong turbulence resiliency. A compact spatial light modulator–based polarization multiplexing multi-plane light conversion module was employed to emulate strong turbulent lin...

In this paper, to achieve higher robustness against atmospheric turbulence for high-capacity free-space optical (FSO) communications, an adaptive multi-modal FSO transceiver has been designed and experimentally demonstrated. We show that based on the dynamically estimated channel state information, modulation formats and power for different transmi...

We experimentally demonstrate the enhanced atmospheric turbulence resiliency in a 137.8 Gbit/s/mode mode-division multiplexing free-space optical communication link through the application of a successive interference cancellation digital signal processing algorithm. The turbulence resiliency is further enhanced through redundant receive channels i...

Emulated atmospheric turbulence effects constructed from a set of 22 Zernike modes have been written upon a DMD micromirror array operating as a binary amplitude spatial light modulator. Sequences of aberrated frames with controlled amounts of turbulence have been produced and can be operated at controlled rates that can exceed 1kHz rates which can...

We experimentally demonstrate the enhanced atmospheric turbulence resiliency in a 137.8 Gbit/s/mode mode-division multiplexing free-space optical communication link through the application of a successive interference cancellation digital signal processing algorithm. The turbulence resiliency is further enhanced through redundant receive channels i...

We employ commercial mode-selective photonic lanterns to implement mode multiplexing and demultiplexing for high-capacity free-space optical communications. Moreover, we design a time-division-multiplexed frame structure to efficiently emulate multiple independent transmitters with channelized precoding using only one transmitter. To maximize the t...

We experimentally demonstrate 10-channel mode-division multiplexed free-space optical transmission with five spatial modes, each carrying 19.6925-Gbaud dual-polarization quadrature phase shift keying signals. Strong inter-mode cross talk is observed in our commercially available photonic lantern based system when using a complete orthogonal mode se...

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Lasers can be identified by their relatively long coherence lengths using interferometry. A Mach Zehnder interferometer incorporating liquid crystal polarization modulators is demonstrated as a means of low cost, robust laser detection. Temporal modulations, as a signature of coherence can be induced by modulating polarization changes in liquid cry...

An unconventional encoding scheme called concurrent coding, has recently been demonstrated and shown to offer interesting features and benefits in comparison to conventional techniques, e.g. robustness against burst errors and improved efficiency of transmitted power. This concept has been demonstrated for the first time with optical communications...

Buildings, bridges, and aircrafts are frequently exposed to fluctuation loads which could start with a fine crack that instantly lead to unpredictable structure failures. The stationary strain sensors can be utilized, but they are costly and only detect limited deformations forms and sizes. Here, we fabricated photonic strain sensors on adhesive ta...

The detection of laser radiation originating from space is a positive indicator of Extra Terrestrial Intelligence (ETI). Thus far the optical search for ETI (OSETI) has looked for enhanced brightness in the form of either narrow-band spectral emission or time correlated photons from laser pulses. In this paper it is proposed to look for coherence p...

Concurrent coding is an unconventional encoding technique that simultaneously provides protection against noise, burst errors and interference. This simple-to-understand concept is investigated by distinguishing 2 types of code, open and closed, with the majority of the investigation concentrating on closed codes. Concurrent coding is shown to poss...

Concurrent coding is an unconventional encoding technique that simultaneously provides protection against noise, burst errors and interference. This simple-to-understand concept is investigated by distinguishing 2 types of code open and closed with the majority of the investigation concentrating on closed codes. Concurrent coding is shown to posses...

A low-cost method of detecting lasers based on detecting coherence properties of received light is presented. The method uses an unbalanced Mach-Zehnder interferometer with a modulating piezo-mounted mirror in one arm to discriminate against incoherent background light and identify the presence of laser radiation at the nW level against much bright...

Nanofabrication through conventional methods such as electron beam writing and photolithography is time-consuming, high cost, complex, and limited in terms of the materials which can be processed. Here, we present the development of a nanosecond Nd:YAG laser (532 nm, 220 mJ) in holographic Denisyuk reflection mode method for creating ablative nanop...

Optically induced electron-hole plasmas in silicon are used to perform radiation pattern tuning. The antenna is a slot loaded microstrip patch and the effect of illumination is shown to produce beam switching in the radiation patterns of certain modes while other modes are left unaffected. The structure is specifically designed to make the best use...

Three dimensional laser beam steering has been demonstrated using a single optical device -a DMD micro-mirror array. Laser beam focus position is controlled using dynamically adjustable zone plates. These zone plates take the form of elliptical Fresnel zone plates or other variations such as binary Gabor zone plates. Active beam control can be real...

Three dimensional laser beam steering has been demonstrated using a single optical device -a DMD micro-mirror array. Laser beam focus position is controlled using dynamically adjustable zone plates. These zone plates take the form of elliptical Fresnel zone plates or other variations such as binary Gabor zone plates. Active beam control can be real...

Concurrent coding is an encoding scheme with holographic-type properties that are shown here to be robust against a significant amount of noise and signal loss. A simple and practical scheme has been tested that displays perfect decoding when the signal to noise ratio is of order -15dB. The same scheme also displays perfect reconstruction when a co...

Concurrent coding is an encoding scheme with "holographic" type properties that are shown here to be robust against a significant amount of noise and signal loss. This single encoding scheme is able to correct for random errors and burst errors simultaneously, but does not rely on cyclic codes. A simple and practical scheme has been tested that dis...

The optical illumination of a microstrip gap on a thick semiconductor substrate creates an inhomogeneous electron-hole plasma in the gap region. This allows the study of the propagation mechanism through the plasma region. This paper uses a multilayer plasma model to explain the origin of high losses in such structures. Measured results are shown u...

We present a fully automated method for the detection of changes within a scene between a reference and a sample image whose viewing angles differ by up to 30°. We also describe an extension to the SIFT technique that allows extracted feature points to be matched over wider viewing angles. Matched correspondences between reference and sample images...

This article proposes a frequency agile antenna whose operating frequency band can be switched. The design is based on a Vivaldi antenna. High-performance radio-frequency microelectromechanical system (RF-MEMS) switches are used to realize the 2.7 GHz and 3.9 GHz band switching. The low band starts from 2.33 GHz and works until 3.02 GHz and the hig...

A non-linear optical device includes a frequency-conversion waveguide and first and second input waveguides. The longitudinal axes of the input waveguides are inclined to that of the frequency-conversion waveguide such a first transverse mode is excited in the latter at the input frequency in operation of the device. The frequency-conversion wavegu...

The work of Manikas 1 highlighted the use of received signal strength in elements of an array of receivers to locate an emitting source. The technique relies upon sequential normalisation of each array element in relation to the other elements with subsequent use of eigenvector analysis to estimate the source position. The technique claims to be ro...

This paper examines a method for locating within a scene a distribution of an absorbing gas using a passive imaging technique. An oscillatory modulation of the angle of a narrowband dielectric filter located in front of a camera imaging a scene, gives rise to an intensity modulation that differs in regions occupied by the absorbing gas. A prelimina...

Laser-induced breakdown spectroscopy has been performed on isolated samples of six types of asbestos—Chrysotile, Crocidolite, Amosite, Anthophyllite, Actinolite, and Tremolite—with analysis of optical emission in the visible region of the spectrum. The principal elements of Mg, Fe, Si, Na, and Ca have all been identified. By examining peak intensit...

This paper investigates the use of photoconductive plasmas for controlling microwave circuits and antennas on semiconductor substrates. Initial experiments show that significant changes in the reflection coefficient characteristics can be obtained by varying the length of a photo-illuminated plasma region from 0 to 2mm. The resulting structure form...

This paper presents an investigation into the use of photoconductive silicon for controlling microwave circuits. Initial experiments show that significant changes in the S21 characteristics of a 9 GHz silicon end coupled filter can be implemented. The results are compared against an equivalent copper conductivity.

new approach to locating gas and vapor plumes is proposed that is entirely passive. By modulating the transmission waveband of a narrow-band filter, an intensity modulation is established that allows regions of an image to be identified as containing a specific gas with absorption characteristics aligned with the filter. A system built from readily...

A free space quantum key distribution system has been demonstrated. Consideration has been given to factors such as field of view and spectral width, to cut down the deleterious effect from background light levels. Suitable optical sources such as lasers and RCLEDs have been investigated as well as optimal wavelength choices, always with a view to...

This paper presents a slide presentation on practical quantum key distribution. The transmitter, random number generator, receiver, and software are presented.

We describe a free space Quantum cryptography system which is designed to allow continuous unattended key exchanges for periods of several days, and over ranges of a few kilometres. The system uses a four laser faint pulse transmission system running at a pulse rate of 10MHz to generate the required four alternative polarization states. The receive...

The remote detection and identification of liquid chemical contamination is a difficult problem for which no satisfactory solution has yet been found. We have investigated a new technique, pulsed indirect photoacoustic spectroscopy (PIPAS), and made an assessment of its potential for operation at stand-off ranges of order 10m. The method involves o...

When a laser plasma is produced on a target, various electromagnetic phenomena can occur. These can produce substantial currents and voltages in nearby structures. The effects depend on the target material and morphology, the pressure and species of the atmosphere, and the nature of the laser pulse. The following mechanisms are known to make a majo...

An adaptive optics system usually has three basic elements, a wavefront sensor, a deformable element, and a feedback scheme. Typically these components are a Shack-Hartmann sensor, a bimorph or segmented mirror, and a DSP solution for performing the necessary calculations. These components are expensive, and give rise to a complex optical and compu...

We report on the progress of the collinear laser spectroscopy programme at the IGISOL isotope separator in Jyväskylä. The sensitivity of the photon-ion coincidence tecnique has been sufficient to measure isotope shifts and hyperfine structures of light hafnium isotopes produced in 175Lu(p,xn) reactions. A gas-filled RF quadrupole has recently been...

At the Jyväskylä IGISOL facility, different ion guide designs are used for different types of reactions. The performance of these ion guides is summarized. The limitations for performing nuclear decay studies and collinear laser spectroscopy due to the large beam energy spread and the presence of isobars will be removed after the installation of an...

The method of positron emission particle tracking (PEPT) has been adapted for use during extrusion. A particle 2 mm in diameter was tracked through a 45° conical die geometry using ram speeds of 5 and 10 mm min−1. The particle was placed at different points across the diameter of the barrel in order to determine the dependence of the speed and stra...

The first fully on-line isotope shift measurement of a radioactive refractory element is reported. Collinear laser-induced fluorescence measurements were made on the radioactive isotopes 170,172,173,174Hf produced with a flux of 2-3×103 ions per second from an ion-guide fed isotope separator. The method may be applied to all elements and isomers wi...

High-resolution crossed beam laser spectroscopy has been performed on an atomic beam of natural vanadium. The hyperfine structure was measured in highly resolved spectra for 25 transitions from the first metastable states, , to two high-lying multiplets, and . This yielded the hyperfine A(J) and B(J) coefficients of 16 fine structure states, includ...

Isotope shifts between and have been measured for five transitions between 300 and 306 nm in the optical spectrum of the iron atom. The data were obtained by means of high-resolution laser spectroscopy utilizing frequency doubling into the ultraviolet. The data have been examined by means of a King plot. Field shifts factors have been obtained allo...

Laser spectroscopy of a thermal atomic beam of natural lanthanum has been performed. An active filtering technique has been used to remove spurious cavity modes from the laser output, leading to unambiguous identification of hyperfine structure associated with 138La. Hyperfine structure coefficients and isotope shifts for several transitions of the...

A major objective of the laser-IGISOL program has been realized with the first ever on-line observation of collinear laser induced fluorescence from an ion of a refractory element. The measurements demonstrate that the IGISOL can be operated in a mode that produces ion beams of good emittance with reasonable extraction efficiency. The technique has...

Ultraviolet spectroscopy of 233U and 232U, in the form of uranium oxide dissolved in 3M nitric acid, has revealed a number of spectral lines with widths of less than 6 nm from the 233U source but no detectable narrow lines from the 232U source. These lines could possibly be attributed to the decay of the 229Th isomeric state at an energy of around...

This chapter explains positron emission tomography (PET) technique and presents some of its non-medical applications. PET is an emission technique that uses radioactive tracers that decay via the emission of a positron. The result of this decay is the production of two back-to-back γ-rays. By detecting both of these γ -rays simultaneously with posi...

The RAL/Birmingham Positron Camera consists of a pair of MWPCs for detecting the pairs of back-to-back 511 keV photons arising from positron-electron annihilation. It was constructed in 1984 for the purpose of applying PET to engineering situations, and has been widely used for the non-invasive imaging of flow, including extensive studies on geolog...

Laser spectroscopy on the atomic or ionic states of radioactive nuclei can be used to obtain information on the most fundamental properties of the nucleus. Enhancements in the techniques of collinear laser spectrocopy have been developed by us at Daresbury Laboratory and these enhancements have enabled us to perform measurements on very short lived...