Compact Light Source Research Articles

Analysis of the impact of non-sinusoidal voltage levels in the power grid of apartment buildings on the reliability and efficiency of transformers

The effects of mass implementation of energy-saving lighting on the permissible level of loading of the supply transformer were analyzed. The influence of non-sinusoidal voltages and currents on transformer wear was analyzed. Distortions of sinusoidal shape of voltages and currents lead to additional power losses in transformer. They cause heating of the insulation and windings of the transformer, increased losses and accelerated wear and tear. Higher harmonic components of voltage and current in a 0.4 kV network are caused by the presence of various energy-saving lighting lamps with non-linear volt-ampere characteristic, which include compact fluorescent and LED light sources. As a result, the transformer designed to operate at a frequency of 50 Hz experiences an additional adverse effect in the form of power losses and accelerated wear of electrical insulation, which leads not only to the deterioration of its technical and economic performance characteristics, but also to a significant decrease in reliability associated with the influence of higher harmonic components of voltage and current on equipment failure. It is shown that the lack of power factor correction schemes for low-power compact fluorescent and LED lamps causes the growth of nonsinusoidal voltage and current as they spread, which in turn causes the need to adjust the limit load of transformers to ensure their rated thermal mode. One way to maintain operational reliability under such conditions is to limit the transformer load depending on the level of higher harmonics in the network, as well as to predict the residual life of the operating transformer. Measuring the values of current transformer load and current levels of higher harmonic components of voltage and current will allow not only to calculate an acceptable load factor of the transformer (for the condition of insulation wear), but also to estimate the current residual life of transformer equipment using a neural network model.

Photonic flatband resonances for free-electron radiation.

Flatbands have become a cornerstone of contemporary condensed-matter physics and photonics. In electronics, flatbands entail comparable energy bandwidth and Coulomb interaction, leading to correlated phenomena such as the fractional quantum Hall effect and recently thosein magic-angle systems. In photonics, they enable properties including slow light1 and lasing2. Notably, flatbands support supercollimation-diffractionless wavepacket propagation-in both systems3,4. Despite these intense parallel efforts, flatbands have never been shown to affect the core interaction between free electrons and photons. Their interaction, pivotal for free-electron lasers5, microscopy and spectroscopy6,7, and particle accelerators8,9, is, in fact, limited by a dimensionality mismatch between localized electrons and extended photons. Here we reveal theoretically that photonic flatbands can overcome this mismatch and thus remarkably boost their interaction. We design flatband resonances in a silicon-on-insulator photonic crystal slab to control and enhance the associatedfree-electron radiation by tuning their trajectory and velocity. We observe signatures of flatband enhancement, recording a two-order increase from the conventional diffraction-enabled Smith-Purcell radiation. The enhancement enables polarization shaping of free-electron radiation and characterizationof photonic bands through electron-beam measurements. Our results support the use of flatbands as test beds for strong light-electron interaction, particularly relevant for efficient and compact free-electron light sources and accelerators.

Programmable freeform optics with extended white light sources: possibilities and limitations.

Freeform optics can be used in lighting applications to generate accurate prescribed illumination patterns from compact light sources such as LEDs. When targeting dynamic illumination systems, a time-variable optical functionality is needed. Phase-only spatial light modulators (SLMs) have been used in the past for various dynamic beam shaping applications with monochromatic, zero-étendue illumination under paraxial conditions. Such limitations can no longer hold when considering lighting applications. In this paper, a novel algorithm for the calculation of smooth phase shift patterns is presented in order to generate arbitrary target patterns from arbitrary incident wave fronts for non-paraxial conditions. When applying such phase shift patterns to SLMs, these devices can be considered as programmable freeform optics. The experimental performance of the calculated phase patterns is analyzed on a real SLM, with a maximal phase shift of 6π, for collimated laser beams and white LEDs. The possibilities and limitations of generating accurate prescribed target patterns are critically discussed in terms of the angular extent of the target pattern, the consider spectrum of the light source and the étendue of the incident light beam.

Unidirectional emission of GaN-on-Si microring laser and its on-chip integration

Abstract GaN-based microring lasers grown on Si are promising candidates for compact and efficient light sources in Si-based optoelectronic integration and optical interconnect due to their small footprints, low mode volume, low power consumption, and high modulation rate. However, the high symmetry of circular microcavity leads to isotropic emission, which not only reduces the light collection efficiency, but also affects other adjacent devices during data transmission. In this study, the unidirectional lasing emission of room-temperature current-injected GaN-based microring laser was realized by coating metal Ag on the microring sidewall and integrating a direct coupled waveguide. The light was efficaciously confined in the cavity and only emitted from the waveguide, which avoided optical signal crosstalk with other adjacent devices. Furthermore, we integrated a microdisk at the other end of the waveguide as a photodetector, which could effectively detect the output power of the microring laser from the direct coupled waveguide. Therefore, a preliminary on-chip integration of GaN-based microring laser, waveguide and photodetector on Si substrate was successfully demonstrated for the first time, opening up a new way for on-chip integration and optical interconnect on a GaN-on-Si platform.

An efficient LiSrGaF6:Cr3+ fluoride phosphor with broadband NIR emission towards sunlight-like full-spectrum lighting.

Sunlight-like full-spectrum phosphor-converted light-emitting diodes (pc-LEDs) require near-infrared (NIR) emission bands to fill the spectrum gap and consequently propel their widespread applications. Although fluoride NIR phosphors have been increasingly investigated, balancing high quantum efficiency (QE), high thermal stability, and wideband NIR emission to obtain excellent overall performance in a single system is still a challenge for Cr3+-doped fluoride NIR phosphor and is significant for direct utilization. Herein, a high-efficiency and thermally stable broadband NIR emission was realized in a novel LiSrGaF6:Cr3+ fluoride phosphor benefitting from a relatively weak crystal field and electron-phonon coupling effect. Upon blue light excitation, the ultra-broad NIR luminescence ranging from 650 to 1150 nm can be achieved with an FWHM of 149 nm peaking at ∼813 nm. Furthermore, this system possesses a high QE of up to 76.88% and its emission intensity at 423 K still maintains 61.62% of its initial intensity at room temperature. An NIR output power of 42.82 mW and photoelectric conversion efficiency of 14.27% of NIR pc-LED devices have also been presented based on this NIR phosphor, demonstrating its possible application in compact nonvisible light sources. In addition, a highly continuous sunlight-like vis-NIR pc-LED was further constructed by employing a blue chip with commercial cyan (BaSi2O2N2:Eu2+), yellow (Y3Al5O12:Ce3+), red (CaAlSiN3:Eu2+), and this LiSrGaF6:Cr3+ NIR phosphor. The as-obtained pc-LED exhibits an ultra-broad spectrum ranging from 400 nm to 1000 nm, exhibiting a higher color reproduction with a color rendering index (CRI) of 95.1 and luminous efficiency (LE) of 50.22 lm W-1. These results indicate that LiSrGaF6:Cr3+ phosphor can be a promising NIR phosphor candidate for high-quality sunlight-like full-spectrum lighting and infrared night vision technology.

Characterization of the electron beam visualization stations of the ThomX accelerator

We present an overview of the diagnostics screens stations - named SSTs - of the ThomX compact Compton source. ThomX is a compact light source based on Compton backscattering. It features a linac and a storage ring in which the electrons have an energy of 50 MeV. Each SST is composed of three screens, a YAG:Ce screen and an Optical Transition Radiation (OTR) screen for transverse measurements and a calibration target for magnification and resolution characterisation. The optical system is based on commercial lenses that have been reverse-engineered. An Arduino is used to control both the aperture and the focus remotely, while the magnification must be modified using an external motor. We report on the overall performance of the station as measured during the first steps of beam commissioning and on the optical system remote operations.

Smaller Stokes Shift Induced Highly Efficient Broadband Near Infrared Garnet Phosphor

AbstractBroadband near‐infrared (NIR) phosphor converted light emitting diodes (pc‐LEDs) are novel compact light sources that enable portable devices for substance detection. However, to achieve such efficient pc‐LEDs is still a challenge due to lack of efficient phosphors. In this paper, Stokes shift as an efficiency predictor is emphasized. In Cr3+ activated Ca2LuZr2Al3O12 (CLZA) garnet phosphor, Stokes shift decreases from 2990 to 2854 cm−1 upon substituting Ca‐Zr with Lu‐Al. As a result, electron–phonon coupling related nonradiative process is reduced. The external quantum efficiency is significantly enhanced to 47.4%, and the as fabricated NIR pc‐LED offers 33.7% @10 mA electro‐optical efficiency. The results can advance the development of efficient NIR phosphors.

Pentavalent Manganese Luminescence: Designing Narrow-Band Near-Infrared Light-Emitting Diodes as Next-Generation Compact Light Sources

Pentavalent Manganese Luminescence: Designing Narrow-Band Near-Infrared Light-Emitting Diodes as Next-Generation Compact Light Sources

Development of compact entangled photon-pair sources for satellites

Satellites are expected to play a significant role in the future of global quantum networks. Small satellites such as those following CubeSat standards may enable space-based quantum networks. CubeSat type satellites require less resources to develop and deploy and can be used to rapidly qualify technologies in orbit. The constraints of small satellites drive the development of compact quantum light sources, which will be useful even if the final satellite volume is large due to transmitter aperture requirements. In this article, we discuss the state-of-the-art in compact entangled photon-pair sources and suggest challenges that must be met by new source designs.

Spatiotemporal singular value decomposition for denoising in photoacoustic imaging with a low-energy excitation light source.

Photoacoustic (PA) imaging is an emerging hybrid imaging modality that combines rich optical spectroscopic contrast and high ultrasonic resolution, and thus holds tremendous promise for a wide range of pre-clinical and clinical applications. Compact and affordable light sources such as light-emitting diodes (LEDs) and laser diodes (LDs) are promising alternatives to bulky and expensive solid-state laser systems that are commonly used as PA light sources. These could accelerate the clinical translation of PA technology. However, PA signals generated with these light sources are readily degraded by noise due to the low optical fluence, leading to decreased signal-to-noise ratio (SNR) in PA images. In this work, a spatiotemporal singular value decomposition (SVD) based PA denoising method was investigated for these light sources that usually have low fluence and high repetition rates. The proposed method leverages both spatial and temporal correlations between radiofrequency (RF) data frames. Validation was performed on simulations and in vivo PA data acquired from human fingers (2D) and forearm (3D) using a LED-based system. Spatiotemporal SVD greatly enhanced the PA signals of blood vessels corrupted by noise while preserving a high temporal resolution to slow motions, improving the SNR of in vivo PA images by 90.3%, 56.0%, and 187.4% compared to single frame-based wavelet denoising, averaging across 200 frames, and single frame without denoising, respectively. With a fast processing time of SVD (∼50 µs per frame), the proposed method is well suited to PA imaging systems with low-energy excitation light sources for real-time in vivo applications.

Ka-band linearizer structure studies for a compact light source

The CompactLight design for a next-generation x-ray free-electron laser utilizes a C-band injector. This requires that the harmonic system used to linearize the beam's phase space must operate at X-band rf or higher. We investigate the optimum frequency for the harmonic system in the range of frequencies from 12 to 48 GHz. We describe the reasoning behind selecting 36 GHz (Ka-band) as our working harmonic frequency. The full linearizer system design including the power source, pulse compressor, and linearizing structure, along with options, is considered and presented. These designs are compared in terms of rf and beam dynamics performance. Two potential MW-level rf sources are discussed; a multibeam klystron and a gyro-klystron, while a klystron-based upconverter with an X-band driver is briefly discussed as an alternative path if even higher peak powers are needed. To further increase peak power, novel options for pulse compressors at Ka-band are discussed. Traveling and standing wave solutions for the structure are presented.

500-nm broadband light generation in highly nonlinear dispersion shifted fiber by soliton laser

A compact and robust broadband light source is desirable for frequency combs, and broadband infrared microscopy. To address these demanding problems, we report the generation of broadband spectroscopy using highly nonlinear dispersion-shifted fiber (HNL-DSF) in an all-fiber system without any free-space optics instruments. However, due to the damage to the glass material by a large number of photons at high power, the ability of the fiber to widen will weaken over time. Therefore, the seed pulse used in this paper is the traditional soliton mode-locked pulse, which has lower energy than other types of mode-locked pulse. After two-stage amplification, the peak power, pulse width, and pulse energy of the soliton pulse are about 2 kW, 10 ps, and 18.79 nJ respectively. Amplifying the power of a low-energy pulse to pump the dispersion-shifted fiber, the ultra-wideband spectrum of more than 500 nm can be obtained without damaging the fiber, which is an efficient method to generate a wide spectrum. This method can be potentially used in astronomy, industry, medicine, etc.

Self-probed ptychography from semiconductor high-harmonic generation.

We demonstrate a method to image an object using a self-probing approach based on semiconductor high-harmonic generation. On the one hand, ptychography enables high-resolution imaging from the coherent light diffracted by an object. On the other hand, high-harmonic generation from crystals is emerging as a new source of extreme-ultraviolet ultrafast coherent light. We combine these two techniques by performing ptychography measurements with nanopatterned crystals serving as the object as well as the generation medium of the harmonics. We demonstrate that this strong field in situ approach can provide structural information about an object. With the future developments of crystal high harmonics as a compact short-wavelength light source, our demonstration can be an innovative approach for nanoscale imaging of photonic and electronic devices in research and industry.

Model resolution matrix based deconvolution improves over non-quadratic penalization in frequency-domain photoacoustic tomography.

Frequency domain photoacoustic tomography is becoming more attractive due to low-cost and compact light-sources being used; however, frequency-domain implementation suffers from lower signal to noise compared to time-domain implementation. In this work, we have developed a non-quadratic based penalization framework for frequency-domain photoacoustic imaging, and further proposed a two-step model-resolution matrix based deconvolution approach to improve the reconstruction image quality. The model-resolution matrix was developed in the context of different penalty functions like l2-norm, l1-norm, Cauchy, and Geman-McClure. These model-resolution matrices were then used to perform the deconvolution operation using split augmented Lagrangian shrinkage thresholding algorithm in both full-view and limited-view configurations. The results indicated that the two-step approach outperformed the different penalty function (prior constraint) based reconstruction, with an improvement of about 20% in terms of peak signal to noise ratio and 30% in terms of structural similarity index measure. The improved image quality provided using these algorithms will have a direct impact on realizing practical frequency-domain implementation in both limited-view and full-view configurations.

Spontaneous parametric down-conversion in bottom-up grown lithium niobate microcubes

Nonclassical light sources are highly sought-after as they are an integral part of quantum communication and quantum computation devices. Typical sources use bulk nonlinear crystals that rely on stringent phase-matching conditions, limiting the operating wavelength and bandwidth. In this work, we demonstrate the generation of photon pairs from a free-standing lithium niobate microcube at the telecommunication wavelength of 1.56 µm through the spontaneous parametric down-conversion process. The maximum photon pair generation rate obtained from a single microcube with the size of 3.6 µm is 490 Hz, resulting in an efficiency of 20.6 GHz/Wm, which is three orders of magnitude larger than the efficiency of biphoton generation in bulk nonlinear crystals. The microcubes are synthesized through a solvothermal method, offering the possibility for scalable devices via bottom-up assembly on any substrates. Our work constitutes an important step forward in the realization of compact nonclassical light sources with a wide bandwidth for various quantum applications.

Room-temperature electrical control of polarization and emission angle in a cavity-integrated 2D pulsed LED

Devices based on two-dimensional (2D) semiconductors hold promise for the realization of compact and versatile on-chip interconnects between electrical and optical signals. Although light emitting diodes (LEDs) are fundamental building blocks for integrated photonics, the fabrication of light sources made of bulk materials on complementary metal-oxide-semiconductor (CMOS) circuits is challenging. While LEDs based on van der Waals heterostructures have been realized, the control of the emission properties necessary for information processing remains limited. Here, we show room-temperature electrical control of the location, directionality and polarization of light emitted from a 2D LED operating at MHz frequencies. We integrate the LED in a planar cavity to couple the polariton emission angle and polarization to the in-plane exciton momentum, controlled by a lateral voltage. These findings demonstrate the potential of TMDCs as fast, compact and tunable light sources, promising for the realization of electrically driven polariton lasers.

The generation of broadband photosource in fiber amplifier with different seed lasers - soliton and dissipative soliton pulse

Soliton and dissipative soliton have different pulse width, pulse energy, and propagation behaviors. The results are quite different for the generation of broadband photosource. In this work, broadband photosource with a wide spectral range based on two pulsed seed lasers is investigated. A high flatness spectrum with a bandwidth greater than 300 nm and predicted spectrum up to 2000 nm covering Er and Tm emission regime has been obtained by amplifying soliton pulsed laser. 370-mW higher average power broadband photosource has been obtained based on the amplification of dissipative soliton lasers. The proposed broadband photosource does not need to add further nonlinear medium in case of introducing unnecessary losses. These results pave the way for the realization of broadband, high flatness spectrum, compact light sources, and the use of all-fiber optic structure to lay the foundation for integration and detection applications, etc.

Heterogeneously integrated quantum-dot emitters efficiently driven by a quasi-BIC-supporting dielectric nanoresonator

Bound states in the continuum (BICs) can make subwavelength dielectric resonators sustain low radiation leakage, paving a new way to minimize the device size, enhance photoluminescence, and even realize lasing. Here, we present a quasi-BIC-supporting GaAs nanodisk with embedded InAs quantum dots as a compact bright on-chip light source, which is realized by heterogeneous integration, avoiding complex multilayered construction and subsequent mismatch and defects. The emitters are grown inside the nanodisk to match the mode field distribution to form strong light–matter interaction. One fabricated sample demonstrates a photoluminescence peak sustaining a quality factor up to 68 enhanced by the quasi-BIC, and the emitting effect can be further promoted by improving the epilayer quality and optimizing the layer-transferring process in the fabrication. This work provides a promising solution to building an ultracompact optical source to be integrated on a silicon photonic chip for high-density integration.

(INVITED)Infrared luminescence of chalcogenide glasses doped with rare earth ions and their potential applications

This article deals with sulfur and selenium-based glasses doped with rare earth ions. It reviews the most significant glass compositions and their related thermal and mechanical properties, with emphasis given to optical and spectroscopic properties in the infrared domain. Optical transparency, multiphonon relaxations, luminescence in optical fibers and planar waveguides doped with trivalent rare earth ions are presented in details. Applications as new compact light sources and lasers, especially for the mid-IR domain, are shown.

Quasi‐Bound States in the Continuum Enhanced Second‐Harmonic Generation in Thin‐Film Lithium Niobate

AbstractThis work reports the second‐harmonic generation (SHG) in a z‐cut thin‐film lithium niobate (LN) under nearly normal‐incident linearly‐polarized pumping. To utilize the largest nonlinear term which is along the out‐of‐plane direction in the z‐cut LN film, the film is patterned with a 2D periodic array to support symmetry‐protected bound states in the continuum (BICs) bearing strong out‐of‐plane electric field component. Enabled by such optical resonances near the BIC condition at the pumping wavelength, significant enhancement in SHG compared to an unpatterned film is observed. This approach, combining transparent thin‐film nonlinear materials with tailored BICs, offers prospects for engineering compact coherent light sources in a broad wavelength range.