33 results found
Eldeeb HB, Eso E, Jarchlo EA, et al., 2021, Vehicular VLC: A Ray Tracing Study Based on Measured Radiation Patterns of Commercial Taillights, IEEE PHOTONICS TECHNOLOGY LETTERS, Vol: 33, Pages: 904-907, ISSN: 1041-1135
Eso E, Ghassemlooy Z, Zvanovec S, et al., 2021, Vehicle-to-Vehicle Relay-Assisted VLC With Misalignment Induced Azimuth or Elevation Offset Angles, IEEE PHOTONICS TECHNOLOGY LETTERS, Vol: 33, Pages: 908-911, ISSN: 1041-1135
Eso E, Ghassemlooy Z, Zvanovec S, et al., 2021, Fundamental Analysis of Vehicular Light Communications and the Mitigation of Sunlight Noise, IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, Vol: 70, Pages: 5932-5943, ISSN: 0018-9545
Eso E, Ghassemlooy Z, Zvanovec S, et al., 2021, Performance of Vehicular Visible Light Communications under the Effects of Atmospheric Turbulence with Aperture Averaging, SENSORS, Vol: 21
Eso E, Jarchlo EA, Ghassemlooy Z, et al., 2021, Performance Analysis of Indoor Vehicular VLC Links for Autonomous Driving, 32nd IEEE Annual International Symposium on Personal, Indoor and Mobile Radio Communications (IEEE PIMRC), Publisher: IEEE
Sathian J, Abadi MM, Damzen MJ, et al., 2020, Communication characteristics of high-brightness light sources based on luminescence concentration
Communication characteristics of high-brightness solid-state light sources based on luminescence concentration generated using blue emitting InGaN light emitting diode arrays are demonstrated here for the first time. The proposed device is used as a transmitter in visible light communications, and its performance is evaluated.
Damzen M, Sathian J, Tawy G, et al., 2020, Non-astigmatic Alexandrite ring laser design with wavelength-tunable single-longitudinal-mode operation, Journal of the Optical Society of America B: Optical Physics, Vol: 37, Pages: 2185-2192, ISSN: 0740-3224
This work presents a study of a fully nonastigmatic design of a single-longitudinal-mode, wavelength-tunable, unidirectional alexandrite ring laser cavity and assessment of its performance compared to more complex laser design requiring astigmatism compensation. A “displaced mode” nonastigmatic laser cavity design eliminating astigmatic cavity elements is developed around an alexandrite crystal end-pumped by a low-brightness, high-power red diode laser pump system. Single-longitudinal-mode, continuous-wave operation is demonstrated with output power of 700 mW with an excellent TEM00 mode (M2<1.1) across a wide pump power range. Wavelength tuning from 748–773 nm is produced using a birefringent filter plate. The nonastigmatic alexandrite laser design achieves better spatial quality and resilience to maintain TEM00 operation across wide variation in pump-induced lensing compared to the astigmatic design. To the best of our knowledge, this is the first wavelength-tunable, single-longitudinal-mode operation of a unidirectional alexandrite ring system in a fully nonastigmatic cavity regime.
Eso E, Pesek P, Chvojka P, et al., 2020, A Relay-Assisted Vehicular Visible Light Communications Network, IEEE Photonics Conference (IPC), Publisher: IEEE, ISSN: 2374-0140
Eldeeb HB, Eso E, Uysal M, et al., 2020, Vehicular Visible Light Communications: The Impact of Taillight Radiation Pattern, IEEE Photonics Conference (IPC), Publisher: IEEE, ISSN: 2374-0140
Sathian J, Minassian A, Alford NM, et al., 2019, Enhancing performance of Ce:YAG luminescent concentrators for high power applications
High power scaling of an LED pumped luminescent concentrator (LC) can address significant excitation and illumination applications, including laser pumping and medical light therapy [1-3]. However, heat deposited into the luminescent material is critical and was already a serious issue in our prior systems  where forced air cooling of the Ce:YAG LC light-guide was employed but limited power and/or duration of operation. Here we report the successful demonstration of a temperature controlled Ce:YAG LC pumped with blue InGaN LEDs.
Sathian J, Tawy G, Sheng X, et al., 2019, Compact non-astigmatic alexandrite ring laser with unidirectional single-longitudinal-mode operation
Progress in single frequency and precise wavelength tunable lasers are essential to address future demands in high resolution spectroscopy, metrology and quantum technology systems. Alexandrite lasers with wide tunability in near-IR spectral region when pumped by low cost red diodes provide a good prospect as a cost effective precision laser source. This was demonstrated in our earlier work  using a tunable single-frequency bow-tie cavity with Brewster-cut Alexandrite crystal. The astigmatism of the Brewster cut gain medium and need for angled curved mirrors for astigmatic compensation, whilst being well established [2,3] also places some complexity on the design and can be compromised by astigmatic thermal lensing . Here we report the investigation and successful operation of a non-astigmatic compact design of a unidirectional wavelength tunable Alexandrite ring laser with single frequency operation.
Sathian J, Jonathan Breeze BB, Frangeskou A, et al., 2019, Quantification of NV-centres in diamond for room-temperature maser
MASERs are devices that exploit stimulated emission to amplify electromagnetic waves at microwave frequencies. Their principal advantage over conventional (semiconductor-based) electronic amplifiers is lower noise. An optically-pumped, solid-state pentacence maser operating at room temperature in pulsed mode was demonstrated . This was followed by the recent demonstration of a continuous maser at room temperature using colour centres (NV) in diamond  paving the way for a new class of masers that could find new applications in medicine, security and sensing, quantum computing/information processing.
Sathian J, Lian W, Minassian A, et al., 2019, Brightness-enhanced solid-state light sources: From kaleidoscope effect to uniform illumination
Luminescent concentrators (LCs) are systems that can increase the brightness of lambertian light sources such as an LED. Applications considered for LED-pumped LCs include laser pumping, general lighting and medical illumination [1-3]. Most studies consider the output power, spectrum and efficiency of the LC system. Here we explore the spatial nature of the output of the LCs under both laser and LED illumination.
Sathian J, Breeze J, Ben B, et al., 2019, Quantification of NV-centres in Diamond for Room-Temperature Maser, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Sathian J, Minassian A, Alford NM, et al., 2019, Enhancing Performance of Ce:YAG Luminescent Concentrators for High Power Applications, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Sathian J, Tawy G, Shen X, et al., 2019, Compact Non-Astigmatic Alexandrite Ring Laser with Unidirectional Single-Longitudinal-Mode operation, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Sathian J, Lian W, Minassian A, et al., 2019, Brightness-Enhanced Solid-State Light Sources: From Kaleidoscope Effect to Uniform Illumination, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Sheng X, Tawy G, Sathian J, et al., 2018, Unidirectional single-frequency operation of a continuous-wave Alexandrite ring laser with wavelength tunability, Optics Express, Vol: 26, Pages: 31129-31136, ISSN: 1094-4087
High resolution spectroscopy, metrology and quantum technologies (e.g. trapping and cooling) require precision laser sources with narrow linewidth and wavelength tunability. The widespread use of these lasers will be promoted if they are cost-effective, compact and efficient. Alexandrite lasers with a broad tuning band pumped efficiently by low-cost red diodes are a potential candidate, but full performance as a precision light source has not been fully achieved. We present in this work the first continuous-wave (CW) and single-frequency operation of a unidirectional diode-end-pumped Alexandrite ring laser with wavelength tunability. An ultra-compact bow-tie ring cavity is developed with astigmatic compensation and a novel ‘displaced mode’ design producing CW output power > 1 W in excellent TEM00 mode (M2 < 1.2) when using a low brightness pump (M2 ≥ 30). Wavelength tuning from 727 - 792 nm is demonstrated using a birefringent filter plate. This successful operation opens the prospects of precision light source applications.
Qin H, Wu D, Sathian J, et al., 2018, Tuning the upconversion photoluminescence lifetimes of NaYF4:Yb3+, Er3+ through lanthanide Gd3+ doping, Scientific Reports, Vol: 8, ISSN: 2045-2322
The multiplexing capacity of conventional fluorescence materials are significantly limited by spectral overlap and background interference, mainly due to their short-lived fluorescence lifetimes. Here, we adopt a novel Gd3+ doping strategy in NaYF4 host materials, realized tuning of upconversion photoluminescence (UCPL) lifetimes at selective emissions. Time-correlated single-photon counting (TCSPC), was applied to measure the photoluminescence lifetimes accurately. We demonstrated the large dynamic range of lifetimes of upconversion nanoparticles with good upconversion quantum yields, mainly owing to the dominance of high efficient energy transfer upconversion mechanism. The exceptional tunable properties of upconversion materials allow great potential for them to be utilized in biotechnology and life sciences.
The maser—the microwave progenitor of the optical laser—has been confined to relative obscurity owing to its reliance on cryogenic refrigeration and high-vacuum systems. Despite this, it has found application in deep-space communications and radio astronomy owing to its unparalleled performance as a low-noise amplifier and oscillator. The recent demonstration of a room-temperature solid-state maser that utilizes polarized electron populations within the triplet states of photo-excited pentacene molecules in a p-terphenyl host1,2,3 paves the way for a new class of maser. However, p-terphenyl has poor thermal and mechanical properties, and the decay rates of the triplet sublevel of pentacene mean that only pulsed maser operation has been observed in this system. Alternative materials are therefore required to achieve continuous emission: inorganic materials that contain spin defects, such as diamond4,5,6 and silicon carbide7, have been proposed. Here we report a continuous-wave room-temperature maser oscillator using optically pumped nitrogen–vacancy defect centres in diamond. This demonstration highlights the potential of room-temperature solid-state masers for use in a new generation of microwave devices that could find application in medicine, security, sensing and quantum technologies.
Sathian J, Oxborrow M, 2017, A Light Source
There is provided a light source arranged to output light at a first wavelength. The light source comprises a luminescent concentrator having a slab-shaped geometry. The luminescent concentrator comprises: an input port arranged to receive light and define a first area; an output port arranged to transmit light and define a second area which is smaller than the first area; and surfaces arranged to direct light inside the luminescent concentrator to the output port. The luminescent concentrator further comprises lumophores arranged to receive light at a second wavelength and emit light at the first wavelength; and a pump light supply coupled to the input port and arranged to illuminate the input port with light at the second wavelength.
Parali U, Sheng X, Minassian A, et al., 2017, Diode-pumped Alexandrite laser with passive SESAM Q-switching and wavelength tunability, Optics Communications, Vol: 410, Pages: 970-976, ISSN: 0030-4018
We report the first experimental demonstration of a wavelength tunable passively Q-switched red-diode-endpumped Alexandrite laser using a semiconductor saturable absorber mirror (SESAM). We present the results ofthe study of passive SESAM Q-switching and wavelength-tuning in continuous diode-pumped Alexandritelasers in both linear cavity and X-cavity configurations. In the linear cavity configuration, pulsed operation upto 27 kHz repetition rate in fundamental TEM00 mode was achieved and maximum average power was 41 mW.The shortest pulse generated was 550 ns (FWHM) and the Q-switched wavelength tuning band spanned wasbetween 740 nm and 755 nm. In the X-cavity configuration, a higher average power up to 73 mW, and obtainedwith higher pulse energy 6.5 J at 11.2 kHz repetition rate, in fundamental TEM00 mode with excellent spatialquality M2 < 1.1. The Q-switched wavelength tuning band spanned was between 775 nm and 781 nm.
Breeze JDB, Salvadori E, Sathian J, et al., 2017, Room-temperature cavity quantum electrodynamics with strongly-coupled Dicke states, npj Quantum Information, Vol: 3, ISSN: 2056-6387
The strong coupling regime is essential for efficient transfer of excitations between states in different quantum systems on timescales shorter than their lifetimes. The coupling of single spins to microwave photons is very weak but can be enhanced by increasing the local density of states by reducing the magnetic mode volume of the cavity. In practice, it is difficult to achieve both small cavity mode volume and low cavity decay rate, so superconducting metals are often employed at cryogenic temperatures. For an ensembles of N spins, the spin–photon coupling can be enhanced by N−−√N through collective spin excitations known as Dicke states. For sufficiently large N the collective spin–photon coupling can exceed both the spin decoherence and cavity decay rates, making the strong-coupling regime accessible. Here we demonstrate strong coupling and cavity quantum electrodynamics in a solid-state system at room-temperature. We generate an inverted spin-ensemble with N ~ 1015 by photo-exciting pentacene molecules into spin-triplet states with spin dephasing time T∗2~3T2*~3 μs. When coupled to a 1.45 GHz TE01δ mode supported by a high Purcell factor strontium titanate dielectric cavity (Vm~0.25Vm~0.25 cm3, Q ~ 8,500), we observe Rabi oscillations in the microwave emission from collective Dicke states and a 1.8 MHz normal-mode splitting of the resultant collective spin–photon polariton. We also observe a cavity protection effect at the onset of the strong-coupling regime which decreases the polariton decay rate as the collective coupling increases.
Sathian J, Breeze J, Richards B, et al., 2017, Solid-state source of intense yellow light based on a Ce:YAG luminescent concentrator, Optics Express, Vol: 25, Pages: 13714-13727, ISSN: 1094-4087
A luminescent concentrator functioning as a bright source of yellow light is reported. It comprises a waveguide made of cerium-doped YAG crystal, in the form of a long-thin rectangular strip, surrounded by flowing air and optically pumped from both sides with blue light from arrays of high-efficiency InGaN LEDs. Phosphor-converted yellow light, generated within the strip, is guided to a glass taper that is butt-coupled to one of the strip’s end faces. Up to 20 W of optical power, centered on 575 nm with a linewidth of 76 nm, can be continuously radiated into air from the taper’s 1.67 mm × 1.67 mm square output aperture. The intensity of the outputted light is significantly greater than what any yellow (AlGaInP) LED can directly produce (either singly or arrayed), with only a modest increase in linewidth. Furthermore, the wall-plug efficiency of the source exceeds that of any yellow laser. The concept allows for further substantial increases in intensity, total output power and wall-plug efficiency through scaling-up and engineering refinements.
Salvadori E, Breeze JD, Tan K-J, et al., 2017, Nanosecond time-resolved characterization of a pentacene-based room-temperature MASER, Scientific Reports, Vol: 7, ISSN: 2045-2322
The performance of a room temperature, zero-field MASER operating at 1.45 GHz has been examined. Nanosecond laser pulses, which are essentially instantaneous on the timescale of the spin dynamics, allow the visible-to-microwave conversion efficiency and temporal response of the MASER to be measured as a function of excitation energy. It is observed that the timing and amplitude of the MASER output pulse are correlated with the laser excitation energy: at higher laser energy, the microwave pulses have larger amplitude and appear after shorter delay than those recorded at lower laser energy. Seeding experiments demonstrate that the output variation may be stabilized by an external source and establish the minimum seeding power required. The dynamics of the MASER emission may be modeled by a pair of first order, non-linear differential equations, derived from the Lotka-Volterra model (Predator-Prey), where by the microwave mode of the resonator is the predator and the spin polarization in the triplet state of pentacene is the prey. Simulations allowed the Einstein coefficient of stimulated emission, the spin-lattice relaxation and the number of triplets contributing to the MASER emission to be estimated. These are essential parameters for the rational improvement of a MASER based on a spin-polarized triplet molecule.
Perera C, Vernon K, Cheng E, et al., 2016, Highly compact refractive index sensor based on stripe waveguides for lab-on-a-chip sensing applications, Beilstein Journal of Nanotechnology, Vol: 7, Pages: 751-757, ISSN: 2190-4286
In this paper we report the design and experimental realisation of a novel refractive index sensor based on coupling between three nanoscale stripe waveguides. The sensor is highly compact and designed to operate at a single wavelength. We demonstrate that the sensor exhibits linear response with a resolution of 6 × 10−4 RIU (refractive index unit) for a change in relative output intensity of 1%. Authors expect that the outcome of this paper will prove beneficial in highly compact, label-free and highly sensitive refractive index analysis.
Breeze J, Tan K-J, Richards B, et al., 2015, Enhanced magnetic Purcell effect in room-temperature masers, Nature Communications, Vol: 6, Pages: 1-6, ISSN: 2041-1723
Recently, the world’s first room-temperature maser was demonstrated. The maser consisted of a sapphire ring housing a crystal of pentacene-doped p-terphenyl, pumped by a pulsed rhodamine-dye laser. Stimulated emission of microwaves was aided by the high quality factor and small magnetic mode volume of the maser cavity yet the peak optical pumping power was 1.4 kW. Here we report dramatic miniaturization and 2 orders of magnitude reduction in optical pumping power for a room-temperature maser by coupling a strontium titanate resonator with the spin-polarized population inversion provided by triplet states in an optically excited pentacene-doped p-terphenyl crystal. We observe maser emission in a thimble-sized resonator using a xenon flash lamp as an optical pump source with peak optical power of 70 W. This is a significant step towards the goal of continuous maser operation.
Sathian J, Jaatinen E, 2013, Dependence of residual amplitude noise in electro-optic phase modulators on the intensity distribution of the incident field, JOURNAL OF OPTICS, Vol: 15, ISSN: 2040-8978
Sathian J, Jaatinen E, 2013, Reducing residual amplitude modulation in electro-optic phase modulators by erasing photorefractive scatter, OPTICS EXPRESS, Vol: 21, Pages: 12309-12317, ISSN: 1094-4087
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