Tunable Source Research Articles

Electrical Control of Electroluminescence in 2D Semiconductor Light Emitting Device through Synchronous Injection of Electrons and Holes

AbstractAchieving efficient electroluminescence (EL) in 2D materials requires precise control over the injection and recombination of charge carriers—electrons and holes. In this study, a method is introduced to improve charge carrier injection in using transition metal dichalcogenides (TMDCs) based light emitting devices driven by alternating current (AC), achieved through dual pulse injection. The dual pulse device exhibits a notable enhancement in EL intensity, displaying a substantial increase as compared to the single pulse device, achieving an approximate sixfold improvement. The proposed dual pulse operated device configuration enables the independent control of electron and hole injection, facilitating the fine‐tuning of carrier recombination processes to improve the EL emission efficiency. Phase delay dependent EL characteristics are observed featuring a maximum integrated EL at a phase delay of 180° indicating an enhanced EL emission during out‐of‐phase pulse operation between the electrodes. Moreover, the dual pulse device exhibited a ≈3.5‐fold improvement in the device EL external efficiency (ηe) when compared to the device operated with a single pulse. Manipulating carrier recombination in TMDCs‐based LEDs opens up new opportunities to enhance their performance, enabling practical applications in display technology, lighting, optical communication, and electrically tunable light sources.

Memristor‐Based Reconfigurable True Time Delay Circuit

ABSTRACTA memristor‐controlled CMOS reconfigurable true time delay circuit is introduced in this paper. The delay circuit includes three stages of ‐C all‐pass filter delay elements connected in cascade and memristor‐based tunable DC voltage sources. The memristor value variation changes the DC bias voltage inputs of the delay elements and thus controls the delay time indirectly: The memristor resistance changes in analogue from 10 to 17 k, changing the tunable DC voltage source output from 584‐ to 711‐mV DC voltage and the delay from 269 to 632 ps. The delay circuit can work in a frequency range from 50 MHz to 1.6 GHz with gain ripple smaller than 3 dB. The resolvable delay time step across the delay range is < 8.7 ps, troughing at as low as 0.4 ps. A delay circuit working in the MHz region is also designed to compare the performance with the GHz circuit, and a memristor‐programming circuit is built to change the resistance levels of memristors.

6.7-8.1 µm tunable single-frequency difference frequency generation in ZGP for high-resolution spectroscopy.

Difference frequency generation (DFG) based tunable single-frequency mid-infrared (MIR) light sources are desirable for high-resolution spectroscopy, sensing, and imaging. In this work, we demonstrate a continuous-wave (CW) single-frequency DFG in a ZnGeP2 (ZGP) crystal driven by all-fiber near-infrared (NIR) fiber lasers, for the first time to our knowledge. The all-fiber NIR laser sources consist of a 1.5 µm erbium-doped fiber amplifier seeded by a CW tunable fast scanning single-frequency laser and a 1.9 µm CW tunable single-frequency thulium-doped fiber laser. Taking advantage of the high nonlinear coefficient and large birefringence of the ZGP crystal, single-frequency DFG in ZGP achieves a broad spectral tuning range from 6.7 to 8.1 µm, with an output power at the 10 µW level. Precise detection of C2H2 gas by continuously scanning the DFG source across a spectral range of 1.1 THz (∼34 cm-1) is also presented, highlighting the potential of the tunable DFG source for high-resolution optical spectroscopy applications. We anticipate this work will provide what we believe to be a new platform for spectroscopy in the molecular fingerprint spectral region.

High range resolution spectral-scanning LiDAR based on optical frequency-domain reflectometry.

Spectral scanning, which utilizes the dispersive effect of light, is a simple and robust method for solid-state beam steering in light detection and ranging (LiDAR) applications. Powered by a tunable laser source, optical frequency-domain reflectometry (OFDR) is a high-precision measurement scheme that is inherently compatible with spectral scanning. Here, we propose a spectral-scanning LiDAR based on OFDR technology and demonstrate that, by connecting the measured spectral reflectivity and group delay of the targets with the dispersion equation, their cloud point data can be obtained. Moreover, compared to the spectral-scanning LiDAR based on the frequency-modulated continuous-wave (FMCW) ranging method, our proposed LiDAR scheme offers a more than tenfold improvement in range resolution with a large number of angular pixels. This enhancement enables high-resolution 3D imaging along both the angular and range axes.

Metrology-grade spectroscopy source based on an optical parametric oscillator

Continuous-wave optical parametric oscillators (OPOs) are widely tunable and powerful sources of narrow-linewidth radiation. These properties make them suitable for a wide range of spectroscopic studies - but so far not at the metrological level. Indeed, although important technical OPO developments occurred more than two decades ago, and commercial devices have been available for nearly as long, the long-hoped-for the potential of these devices, providing simultaneously ultralow linewidth, ultrahigh frequency stability, ultrahigh frequency accuracy, and wide wavelength coverage has not yet become a reality. Here, we present an OPO metrology system suitable for optical spectroscopy with ultra-high resolution and accuracy in the 2.2 - 3.9 μm range. The system relies on the second-harmonic generation of the idler wave to bridge the gap to the near-infrared regime where frequency combs are readily available. By actively controlling the pump laser frequency, the idler radiation is phase-locked to an optically stabilized frequency comb, enabling a full transfer of the frequency comb’s spectral properties to the idler radiation and measuring the idler frequency with ultra-high precision. We reach fractional line widths and Allan deviations of the idler radiation at the level of 4 × 10−14 and 1 × 10−14, respectively. We also perform a thorough characterization of the stabilized OPO via a comparison with a second, independent optically stabilized frequency comb and thereby determine an overall idler frequency systematic uncertainty of less than 1.2 × 10−14. Sources of residual frequency noise are identified. The system delivered excellent results in high-accuracy spectroscopy.

Mid-infrared enhanced Raman soliton generation in an erbium-doped ZBLAN with record energy and peak power

The advancement of tunable ultrafast sources in the mid-infrared spectrum would bring about significant progress in various scientific fields. This study suggests a gain-modulation technique to increase the peak power and pulse energy of mid-infrared tunable Raman solitons. By utilizing a high-power 2-2.23 µm Raman soliton pulse as a pump source, mid-infrared Raman solitons within the 2-3.2 µm tuning range can be generated in a segment of Er3+: ZBLAN fiber. Additionally, the introduction of 976 nm pump light into the Er3+: ZBLAN fiber leverages the gain of Er3+ to amplify the frequency shift velocity and pulse energy of the Raman soliton. Consequently, the frequency shift range of the Raman soliton is extended to 3.5 µm, with peak power and pulse energy reaching 0.93 MW and 107 nJ, respectively. These achievements represent the highest peak power and energy levels of Raman solitons generated in mid-infrared fibers to date.

Development of wavelength dispersion measurement method using Fresnel reflection of fiber under test at both end faces

The phase shift method is generally used for wavelength (chromatic) dispersion measurement of optical fibers. However, the phase shift method requires a long fiber under test (FUT) of several hundred meters or more to obtain high temporal resolution. Therefore, measuring specialty fibers with short production lengths and amplification fibers that absorb light at specific wavelengths used for fiber lasers is difficult with this method. We have developed a method to measure the beat spectrum, by incident, an incoherent tunable light source (I-TLS) composed of amplified spontaneous emission (ASE) to a FUT. The FUT constitutes a Fabry–Perot resonator using Fresnel reflections at both end faces of the fiber. Chromatic dispersion can be calculated from the wavelength dependence of the refractive indices of the FUT, enabling measurement with short fiber lengths. The standard deviation of the chromatic dispersion @1550 nm was 0.352 ps/(nm km) based on five measurements of a FUT of approximately 3 m. The error between the manufacturer's measurement of chromatic dispersion @1550 nm, and the average value measured in this study was measured at 0.56%, indicating that it can be measured with very high accuracy.

Small tunable X-ray sources may have large impact

Small tunable X-ray sources may have large impact

Tunable 30 GHz laser frequency comb for astronomical spectrograph characterization and calibration.

The search for Earth-like exoplanets with the Doppler radial velocity (RV) technique is an extremely challenging and multifaceted precision spectroscopy problem. Currently, one of the limiting instrumental factors in reaching the required long-term 10-10 level of radial velocity precision is the defect-driven subpixel quantum efficiency (QE) variations in the large-format detector arrays used by precision echelle spectrographs. Tunable frequency comb calibration sources that can fully map the point spread function (PSF) across a spectrograph's entire bandwidth are necessary for quantifying and correcting these detector artifacts. In this work, we demonstrate a combination of laser frequency and mode spacing control that allows full and deterministic tunability of a 30 GHz electro-optic comb together with its filter cavity. After supercontinuum generation, this gives access to any optical frequency across 700-1300 nm. Our specific implementation is intended for the comb deployed at the Habitable-Zone Planet Finder (HPF) spectrograph and its near-infrared Hawaii-2RG array, but the techniques apply to all laser frequency combs (LFCs) used for precision astronomical spectrograph calibration and other applications that require broadband tuning.

Electro-optically Modulated Nonlinear Metasurfaces.

Electrically reconfigurable nonlinear metasurfaces provide dynamic control over nonlinear phenomena such as second-harmonic generation (SHG), unlocking novel applications in signal processing, light switching, and sensing. Previous methods, like electric-field-induced SHG in plasmonic metasurfaces and Stark-tuned nonlinearities in quantum well metasurfaces, face limitations due to weak SHG responses from metals and mid-infrared constraints of quantum wells, respectively. Addressing the need for efficient SHG control in the visible and near-infrared ranges, we present a novel approach using the electro-optic (EO) effect to modulate SHG. By leveraging the exceptional EO and SHG properties of lithium niobate (LN), we integrate the EO effect with SHG within a metasurface framework for the first time. Our LN metasurface achieves an 11.3% modulation depth in SHG amplitude under a ±50 V alternating voltage. These results open new avenues for reconfigurable photonic applications. including tunable nonlinear light sources, quantum optics, and nonlinear information processing.

Electrophotocatalysis for Organic Synthesis.

Electrocatalysis and photocatalysis have been the focus of extensive research efforts in organic synthesis in recent decades, and these powerful strategies have provided a wealth of new methods to construct complex molecules. Despite these intense efforts, only recently has there been a significant focus on the combined use of these two modalities. Nevertheless, the past five years have witnessed rapidly growing interest in the area of electrophotocatalysis. This hybrid strategy capitalizes on the enormous benefits of using photons as reagents while also employing an electric potential as a convenient and tunable source or sink of electrons. Research on this topic has led to a number of methods for C-H functionalization, reductive cross-coupling, and olefin addition among others. This field has also seen the use of a broad range of catalyst types, including both metal and organocatalysts. Of particular note has been work with open-shell photocatalysts, which tend to have comparatively large redox potentials. Electrochemistry provides a convenient means to generate such species, making electrophotocatalysis particularly amenable to this intriguing class of redox catalyst. This review surveys methods in the area of electrophotocatalysis as applied to organic synthesis, organized broadly into oxidative, reductive, and redox neutral transformations.

Comment on “Recovering noise-free quantum observables”

Zero-noise extrapolation (ZNE) stands as the most widespread quantum error mitigation technique used in the recovery of noise-free expectation values of observables of interest by means of noisy intermediate-scale quantum (NISQ) machines. Recently, Otten and Gray proposed a multidimensional generalization of polynomial ZNE for systems where there is no tunable global noise source [M. Otten , ]. Specifically, the authors refer to multiqubit systems where each of the qubits experiences several noise processes with different rates, i.e., a nonidentically distributed noise model. The authors proposed a hypersurface method for mitigating such noise, which is technically correct in the sense that if the required samples are obtained, the observable can be mitigated. However, the proposed method presents an excessive experiment repetition overhead, making it impractical, at least from the perspective of quantum computing. Specifically, we discuss that in order to perform a simple mitigation task to multinomial order 3 considering 100 qubits, there, 2.5 years or over a million quantum processors running in parallel would be required. In this Comment, we show that the traditional extrapolation techniques can be applied for such a nonidentically distributed noise setting consisting of many different noise sources, implying that the measurement overhead is practical. In fact, we discuss that the previous mitigation task can be resolved in the order of minutes using a single quantum processor by means of standard ZNE. To do so, we clarify what it is meant by a tunable global noise source in the context of ZNE, a concept that we consider important to be clarified for a correct understanding of how and why these methods work. Published by the American Physical Society 2024

Effects of dim-evening lighting optimised for geographical orientation versus standard lighting on mental health: protocol paper for a quasiexperimental study in a psychiatric hospital

IntroductionResearch has provided novel insights into how light stimulates circadian rhythms through specialised retinal ganglion cells to the suprachiasmatic nucleus. In addition, there has been a revolution in light-emitting diode...

Vibrothermography for NDT : dynamic control of thermal sources by acoustic fields

Among the plethora of Non-Destructive Evaluation (NDE) techniques, the coupling of acoustic/vibration and thermography has emerged as a powerful method, more particularly denoted as sonothermography, utilizing the principle of energy conversion from acoustic waves to thermal heat sources to reveal structural abnormalities or create tunable volumic sources in materials. The calculation of the displacement field induced by acousto-vibrational excitations, using the analytical expression of energy conversion, has led to the generation and modeling of localized thermal sources in space over time within a material. By manipulating the input parameters of acoustic signals (frequency, phase, amplitude), we have demonstrated that it is possible to strategically position these sources in space and optimize the dissipation of thermal energy. The variation of parameters (creating a phase shift, a beat, a reversal law, etc.) makes it possible to control and move these internal heat sources to scan the material (in numerical approach and in the near future experimentally). The analysis of the resulting fields (acoustic-vibration and thermal), using inverse methods, opens up new possibilities for measuring the physical properties (mechanical, thermal) or characterizing defects in a material.

Topological-charge-tunable and wavelength- switchable vortex laser enabled by a helically twisted high-absorption few-mode erbium-doped fiber.

Vortex beams carrying orbital angular momentum (OAM) offer a solution for enhancing spatial degrees of freedom, particularly in conjunction with wavelength division multiplexing, which can significantly boost data capacity for optical communication. Addressing the increasing demand for high information-carrying capacity, we present a dynamically tunable OAM laser source in this study. We demonstrate a ring-cavity vortex fiber laser employing intra-cavity mode conversion through a helically twisted high-absorption few-mode erbium-doped fiber (HA-FM-EDF). The constructed vortex fiber laser exhibits wavelength switchability via an integrated Sagnac loop, facilitated by a homemade ring-core fiber. Furthermore, topological-charge tunability is achieved through the utilization of twisted HA-FM-EDF with varying helical pitches. To our knowledge, this marks the first successful implementation of two-dimensional multiplexing of wavelength and OAM in a vortex fiber laser. The OAM laser serves as a versatile vortex source with high tunability and flexibility, holding significant potential for deployment in ultrahigh-speed/ultrahigh-capacity communications, ultrahigh-resolution imaging, and ultrahigh-sensitivity sensing applications.

Design and development of a portable tuneable radiation source from UV to IR for in situ calibration of radiometers measuring atmospheric aerosol properties.

Abstract We present the results of development of a portable tuneable radiation source (TuPS II) covering the broad spectral range from 300 nm up to 1700 nm. It was developed to provide SI-traceable in-situ calibration of bandpass functions of radiometers measuring both sky radiance and sky irradiance in the surface-based remote sensing networks for column integrated atmospheric aerosol properties. The TuPS II provides quasi-monochromatic radiation with spectral bandwidth smaller than 0.2 nm and central wavelength uncertainty lower than 0.05 nm for a specified number of aerosol wavelength bands ranging from to 300 nm to 1700 nm. In its design it represents an evolution with extended spectral capabilities of the TuPS (Smid, M. et al., 2021) that was successfully used to characterize Dobson spectrophotometers in the UV spectral range.

Radiometric characterization of daytime luminescent materials directly under the solar illumination

The materials efficiently emitting photoluminescence (PL) under solar irradiation could find broad applications in passive radiative cooling of buildings, urban heat mitigation, and solar energy harvesting. In this work, we discuss the limitations of common laboratory characterization of such materials (using tunable light sources or solar simulators) and propose a methodology for direct outdoor characterization of PL efficiency under full solar irradiation. A simple, portable radiometry setup with an integrating sphere is described, and its capability of rapid determination of the spectral distribution of the absorbed and emitted power, as well as the overall PL power efficiency and quantum yield, is demonstrated. By characterization of three materials developed for daytime radiative cooling applications, we reveal deviations of obtained parameters caused by the replacement of the real solar irradiation by that of solar simulators. The described method is suitable for studies of long-term stability, photo-induced degradation, or thermal effects.

Efficient and widely tunable mid-infrared sources using GaAs and AlGaAs integrated platforms for second-order frequency conversion.

Integrated coherent mid-infrared (mid-IR) sources are crucial for spectroscopy and quantum frequency conversion (QFC) to facilitate scalable fiber-based application of single photons. Direct mid-IR emission with broad tunability poses fundamental challenges from the gain media and mirror components. This paper presents a characterization of a second-order nonlinear platform. It showcases a mid-IR parametric coherent source with a continuous tuning range exceeding 230 nm centered around 2425 nm, achieved through difference-frequency generation (DFG). The nonlinear coefficient d14 of gallium arsenide (GaAs) and aluminum gallium arsenide (AlGaAs) on insulator is experimentally determined via second-harmonic generation (SHG) in waveguides of various lengths, and the tolerance of the process is investigated. These materials are explored for their high conversion efficiency, utilizing monolithic epitaxial quantum dots and integrated waveguides for QFC. The results demonstrate efficient and tunable mid-IR emission suitable for compact, scalable quantum emitters, with applications in environmental and health monitoring.

Tunable broadband luminescence of the novel Sn2+ doped oxyfluoride glass and glass-ceramics for W-LEDs

The demand for white-light luminescent materials for the white-light-emitting diodes (W-LEDs) field has been growing in modern life. In this work, a series of Sn2+ and Mn2+ ions co-doped highly transparent white-light emitting oxyfluoride glasses (precursor glass, PG) and Sr2LuF7 glass-ceramics (GC) were successfully prepared by the melt-quenching technique. Their luminescent and structural properties were investigated by the transmission spectra, excitation and emission spectra at different temperatures (300-500 K), luminescent decay curves, XRD, and TEM characterizations. Upon excitation with ultraviolet (UV) light, tunable broadband blue-white light emissions of Sn2+ were obtained by adjusting the concentration of Sn2+ ions. A conspicuous energy transfer process from Sn2+ to Mn2+ was observed in Sn2+/Mn2+ co-doped samples. Tunable broadband luminescence between blue-white light and orange-red light regions and nearly pink-white light emission was realized by varying Mn2+ concentration. Furthermore, compared to PG samples, the emissions were enhanced in GC samples due to the crystallization of Sr2LuF7 nanocrystals. Excellent thermal stability was also performed in these Sn2+ doped PG and GC samples with a recovering value of 96 % and 98.8 %, respectively. Simultaneously, Sn2+ doped PG and GC samples also own good optical thermal sensitivities with an SA value of 2.28 % and 2.47 % K-1, respectively. Our results indicate that these Sn2+/Mn2+ co-doped PG and GC may serve as tunable light sources under UV excitation and have prospects on the ratiometric optical thermometry fields.

Mid-infrared ultrafast soliton molecules from a few-cycle Cr:ZnS laser

Soliton molecules, or soliton bound states, are envisioned to make far-reaching changes in both fundamental research and applications. Here, we report on the generation and precision manipulation of soliton molecules based on a Kerr-lens mode-locked single-crystal Cr:ZnS laser at 2.4 µm. In the classical soliton regime, self-starting near-transform-limited pulses with a duration of 37 fs, less than 5 optical cycles, have been obtained at a repetition frequency of 173 MHz and an average output power of 572 mW. By fine-tuning the cavity group-delay dispersion profile, bi-soliton states with pulse durations between 55 fs and 98 fs with temporal separations between 348 fs and 604 fs have been observed and characterized. These are the shortest pulse duration and separation of soliton molecules reported so far in the mid-infrared region, to the best of our knowledge. With the ability of precision manipulation of soliton molecules generated on a sub-100-fs timescale, the tunable mid-infrared soliton molecule source paves the way for applications in the fields of telecommunications and ultrafast laser technologies.