Narrow Linewidth Research Articles

61‐1: Invited Paper: Polaritonic OLEDs with Assistant Strong‐coupling Layers: A New Approach to Sub‐20nm Emission Linewidth in OLED Displays

With ever more stringent color‐gamut requirements in displays (e.g., BT.2100), there is growing demand for OLEDs with narrowband emission. However, many efficient emitters reported to date show spectrally broad luminescence. Micro‐cavity OLEDs offer narrow linewidth but suffer from changes in spectrum with observation angle. To overcome these limitations, we hybridize microcavity and exciton states in an efficient OLED, thus creating strongly coupled polariton states that inherit the angle insensitivity of excitons and the narrow linewidth of the microcavity. Using assistant strong‐coupling layers located away from the recombination zone yields efficient OLEDs with FWHM <20 nm and angle shift <10 nm @60° tilt.

Ultra-narrow linewidth in continuous-wave external cavity diamond Raman laser

A continuous-wave narrow linewidth diamond Raman laser based on an intracavity frequency doubling structure was demonstrated. Linewidth narrowing and power enhancement were realized by tuning the phase matching in the second-harmonic generation element through temperature control. A maximum output power of 5 W at 592 nm with a linewidth of 72 MHz was obtained using a Yb doped fiber laser with a power of 40 W and a linewidth of >4 GHz, an enhancement of the linewidth by a factor of about 65. The results indicate that high-power and narrow linewidth lasers can be produced utilizing diamond Raman conversion combined with the phase matching in the second-harmonic generation element.

Efficient, Color-Stable, Pure-Blue Light-Emitting Diodes Based on Aromatic Ligand-Engineered Perovskite Nanoplatelets.

Perovskite nanoplatelets (NPLs) show great potential for high-color-purity light-emitting diodes (LEDs) due to their narrow line width and high exciton binding energy. However, the performance of perovskite NPL LEDs lags far behind perovskite quantum dot-/film-based LEDs, owing to their material instability and poor carrier transport. Here, we achieved efficient and stable pure blue-emitting CsPbBr3 NPLs with outstanding optical and electrical properties by using an aromatic ligand, 4-bromothiophene-2-carboxaldehyde (BTC). The BTC ligands with thiophene groups can guide two-dimensional growth and inhibit out-of-plane ripening of CsPbBr3 NPLs, which, meanwhile, increases their structural stability via strongly interacting with PbBr64- octahedra. Moreover, aromatic structures with delocalized π-bonds facilitate charge transport, diminish band tail states, and suppress Auger processes in CsPbBr3 NPLs. Consequently, the LEDs demonstrate efficient and color-stable blue emissions at 465 nm with a narrow emission line width of 17 nm and a maximum external quantum efficiency (EQE) of 5.4%, representing the state-of-the-art CsPbBr3 NPL LEDs.

Efficient Perovskite Nanograin Light-Emitting Diodes in Green-to-Blue Gamut with Co-Additive Engineering.

Perovskite nanograins exceeding the Bohr exciton diameter show great potential for high-performance light-emitting diodes (LEDs) owing to their bandgap homogeneity, spatial charge confinement, and nonlocal interaction. However, it is challenging to directly synthesize proper nanograins along with reduced crystal defects on functional substrate, and the corresponding high-efficiency perovskite LEDs (PeLEDs) have rarely been reported. In this study, crystallization modulation for perovskites with an effective co-additive system, including lithium bromide, p-fluorophenethylammonium bromide, and 18-crown-6, is performed. Furthermore, it is demonstrated that the proposed co-additive system can synergistically retard perovskite crystallization and reduce crystal defects. Consequently, high-quality perovskite nanograin solids (≈22.8nm) are obtained with a high photoluminescence quantum yield (≈88%). These superior optical properties contribute to developing efficient green PeLEDs with a champion external quantum efficiency (EQE) of 28.4% and an average EQE of 27.1%. The co-additive system can be universally applied to mixed-halide perovskite nanograin LED, presenting a maximum EQE of 24.4%, 21.6%, 17.5%, and 11.1% for the blue device at 496, 488, 478, and 472nm, respectively, along with a narrow spectral linewidth (17-14nm) and stable color. These results supplement the research on high-efficiency perovskite nanograin LEDs for multicolor displays and lighting.

Bulged CH3NH3PbBr3 Microwires for Single‐Mode Lasing

Herein, the lasing action of fabricated bulged CH3NH3PbBr3 microwires is demonstrated with features of a low threshold, narrow linewidth, single‐mode operation, and high intensity. Benefiting from the bulged end facets, the CH3NH3PbBr3 microwires are feasible for constructing a high‐brightness, whispering‐gallery‐mode(WGM)‐type, and single‐mode laser while suppressing Fabry–Pérot‐type multi‐mode lasing. Numerical simulation unveils that the bulged end facets result in the significantly reduced reflectivity of fundamental waveguided modes. The obtained microlasers require neither complex structures (such as distributed Bragg reflector) nor careful pumping adjustment, suggesting the practical feasibility of a higher single‐mode lasing intensity than conventional WGM perovskite microlasers. The results provide new routes to realize high‐performance perovskite microlasers and their potential application in sensing refractive index.

Photoluminescence of Monolayer WSe2 Enhanced by the Exciton Funnel Effect and the Interfacial Carrier Tunneling Effect When Integrated with 3D Si Wrinkled Structures

Quantum optics and photonic quantum-information technologies require emitters that have good stability and brightness, coupled with fabrication scalability and on-chip integrability. Most quantized emitters are presently based on 1D and 3D sources. Recently, monolayer transition metal dichalcogenides (TMDCs) hosting spatially localized excitons with narrow linewidths have garnered great interest. Advantages such as large binding energies and long room-temperature lifetimes of intralayer excitons suggest that TMDCs are promising candidates for use in optical devices. Here, we propose an emitter based on a 2D WSe2 semiconductor monolayer integrated with a periodic 3D Si-based wrinkled pattern. Carriers confined within the wrinkled pattern can be electrically and optically pumped, and funneled, to boost emission from the 2D WSe2 layer. This in turn acts as a monochromated quantum light source for the Si or any Si-based quantum optic and photonic information technologies. The brightness of the emission is enhanced by a factor greater than 40 compared with monolayer WSe2 on conventional flat SiGe. Moreover, these monolayer 2D/3D semiconductor composite heterostructures are fully scalable and promisingly efficient chip-integrated emitters.

Wavelength selective beam-steering in a dual-mode multi-layer plasmonic laser

Due to its improved localization and confinement of light in single or multiple wavelength modes, nanolasers based on plasmonic crystals have grown in popularity in recent years. However, the lasing modes are not spatially separated, making applying different modes to different applications difficult. This work demonstrates an effective technique for spatially separating the two modes of a merged lattice metal nanohole array-based dual-mode plasmonic laser. A flat dielectric metasurface-based beam-splitter that exploits phase gradient profiles on the interfaces has been added to the laser to separate the modes into distinct spatial beams. The proposed structure successfully separates two modes by ∼23°, and the separation can be raised to ∼63° by tuning structural parameters such as the radius of the nanocylinders and the number of supercell rows. In addition, multiple beams can be generated, allowing for manual beam steering. This approach has a high emission output with a narrow linewidth, clarity, and a substantial degree of future tunability potential. The proposed integrated structure will provide a novel means of device miniaturization and may also serve advanced optical applications such as optical communication, quantum optics, interferometry, spectroscopy, and light detection and ranging (LiDAR).

Narrow Linewidth, Arbitrarily Tuning DFB Laser Using 3×3 Optical Coupler-Based Fully Digital Feedback

Narrow Linewidth, Arbitrarily Tuning DFB Laser Using 3×3 Optical Coupler-Based Fully Digital Feedback

Physics package based on intracavity laser cooling 87Rb atoms for space cold atom microwave clock

Abstract This article proposes a new physics package to enhance the frequency stability of the space cold atom clock with the advantages of a microgravity environment. Clock working processes, including atom cooling, atomic state preparation, microwave interrogation, and transition probability detection, are integrated into the cylindrical microwave cavity to achieve a high-performance and compact physics package for the space cold atom clock. We present the detailed design and ground-test results of the cold atom clock physics package in this article, which demonstrates a frequency stability of 1.2 × 10−12 τ −1/2 with a Ramsey linewidth of 12.5 Hz, and a better performance is predicted with a 1 Hz or a narrower Ramsey linewidth in microgravity environment. The miniaturized cold atom clock based on intracavity cooling has great potential for achieving space high-precision time-frequency reference in the future.

Dynamic exploration of laser linewidth compression in resonant feedback external-cavity laser

An external-cavity laser with resonant optical feedback is a common and mature method to achieve narrow linewidth lasers. Since the proposal of optical feedback in 1964, a series of studies on resonant optical feedback have been reported. Although longer feedback length leads to narrower linewidth, it also introduces coupling of environmental noise and causes instability in the laser cavity, which is detrimental to high-speed tuning of the laser wavelength. With such a challenge, current research on resonant optical feedback primarily focuses on the static results of laser linewidth compression. In order to obtain narrow linewidth high-speed tuned external-cavity lasers, further research on the laser dynamics is required to obtain dynamic tuning of narrow linewidth external-cavity lasers. In this work, we construct an external-cavity laser based on resonant optical feedback, and utilize a coherent detection method to measure the dynamic process of laser linewidth compression and wavelength tuning. Based on resonant optical feedback from the external cavity, the linewidth of the main-cavity laser can be compressed from near 100 kHz to the 100 Hz level, with the frequency noise compressed from the order of 104 to the 102 Hz2/Hz level. Since the wavelength switching process includes frequency shift process, linewidth compression process, and frequency stabilization process, etc., we first conduct a research on laser linewidth compression dynamics. In the results of linewidth compression dynamics, we discover that using a shorter fiber ring results in shorter linewidth compression time, which is advantageous for laser dynamic tuning. We subsequently carry out the laser wavelength switching process with a main-cavity switching time in milliseconds. In the wavelength switching process, while undergoing the frequency shift process of fast tuning transient laser frequency, the laser first undergoes the linewidth broadening process, then enters the main-cavity laser frequency stabilization process and undergoes the linewidth compression process at the same time. The experimental results show that the 100 m feedback fiber ring will not significantly increase the external-cavity laser wavelength switching time under the condition that linewidth compression is faster than main-cavity laser switching, while a longer fiber ring will introduce a strong noise. Our work experimentally demonstrates that shorter feedback ring lengths lead to faster compression, which provides valuable insights for the development of high-speed and high-precision tunable narrow linewidth external-cavity lasers.

Electrohydrodynamic Inkjet Printing of Three-Dimensional Perovskite Nanocrystal Arrays for Full-Color Micro-LED Displays.

Perovskite nanocrystal (PeNC) arrays are showing a promising future in the next generation of micro-light-emitting-diode (micro-LED) displays due to the narrow emission linewidth and adjustable peak wavelength. Electrohydrodynamic (EHD) inkjet printing, with merits of high resolution, uniformity, versatility, and cost-effectiveness, is among the competent candidates for constructing PeNC arrays. However, the fabrication of red light-emitting CsPbBrxI(3-x) nanocrystal arrays for micro-LED displays still faces challenges, such as low brightness and poor stability. This work proposes a design for a red PeNC colloidal ink that is specialized for the EHD inkjet printing of three-dimensional PeNC arrays with enhanced luminescence and stability as well as being adaptable to both rigid and flexible substrates. Made of a mixture of PeNCs, polymer polystyrene (PS), and a nonpolar xylene solvent, the PeNC colloidal ink enables precise control of array sizes and shapes, which facilitates on-demand micropillar construction. Additionally, the inclusion of PS significantly increases the brightness and environmental stability. By adopting this ink, the EHD printer successfully fabricated full-color 3D PeNC arrays with a spatial resolution over 2500 ppi. It shows the potential of the EHD inkjet printing strategy for high-resolution and robust PeNC color conversion layers for micro-LED displays.

Spin and charge interactions between nanographene host and ferrocene.

Ferrocene (FeCp2) was introduced as a non-magnetic guest molecule to activated carbon fibers (ACFs) as a nanographene-based host having localized spins originating from zigzag edges of graphene. The introduction of the guest molecule was confirmed by FTIR for ACFs-FeCp2 introduced at 55 (150) °C (FeCp2-ACFs-55(150)). The appearance of satellite Fe2p peaks and the increase in shake-up peak intensity of the C1s in the XPS spectrum proved the emergence of charge-transfer host-guest interaction in FeCp2-ACFs-150, supported by the red-shift of the G-band in the Raman spectrum. The six-times enhancement in the spin concentration in FeCp2-ACFs-150 compared with ACFs indicates the spin magnetism of the non-magnetic guest FeCp2+ molecule induced by a charge-transfer host-guest interaction in the nanographene host. The larger ESR linewidth than that expected from the dipolar interaction estimated by the localized spin concentration suggests the exchange interaction between the nanographene and FeCp2 spins. The narrowing of the ESR linewidth of FeCp2-ACFs-55 upon higher excitation microwave power suggests the inhomogeneity of the environment for FeCp2+ molecules in the nanographene host. The observed induction of spin magnetism by the interfacial interactions between the nanographene host and the guest molecules will be a promising strategy for developing a new class of molecular magnets.

Brillouin light storage for 100 pulse widths

Signal processing based on stimulated Brillouin scattering (SBS) is limited by the narrow linewidth of the optoacoustic response, which confines many Brillouin applications to continuous wave signals or optical pulses longer than several nanoseconds. In this work, we experimentally demonstrate Brillouin interactions at the 150 ps time scale and a delay for a record 15 ns which corresponds to a delay of 100 pulse widths. This breakthrough experimental result was enabled by the high local gain of the chalcogenide waveguides as the optoacoustic interaction length reduces with pulse width. We successfully transfer 150 ps-long pulses to traveling acoustic waves within a Brillouin-based memory setup. The information encoded in the optical pulses is stored for 15 ns in the acoustic field. We show the retrieval of eight amplitude levels, multiple consecutive pulses, and low distortion in pulse shape. The extension of Brillouin-based storage to the ultra-short pulse regime is an important step for the realization of practical Brillouin-based delay lines and other optical processing applications.

Reliable intracavity reflection for self-injection locking lasers and microcomb generation

Self-injection locking has emerged as a crucial technique for coherent optical sources, spanning from narrow linewidth lasers to the generation of localized microcombs. This technique involves key components, namely a laser diode and a high-quality cavity that induces narrow-band reflection back into the laser diode. However, in prior studies, the reflection mainly relied on the random intracavity Rayleigh backscattering, rendering it unpredictable and unsuitable for large-scale production and wide-band operation. In this work, we present a simple approach to achieve reliable intracavity reflection for self-injection locking to address this challenge by introducing a Sagnac loop into the cavity. This method guarantees robust reflection for every resonance within a wide operational band without compromising the quality factor or adding complexity to the fabrication process. As a proof of concept, we showcase the robust generation of narrow linewidth lasers and localized microcombs locked to different resonances within a normal-dispersion microcavity. Furthermore, the existence and generation of localized patterns in a normal-dispersion cavity with broadband forward–backward field coupling is first proved, as far as we know, both in simulation and in experiment. Our research offers a transformative approach to self-injection locking and holds great potential for large-scale production.

Single-Photon Emission from Point Defects in Hexagonal Boron Nitride Induced by Plasma Treatment.

Solid-state quantum emitters are gaining significant attention for many quantum information applications. Hexagonal boron nitride (h-BN) is an emerging host material for generating bright, stable, and tunable single-photon emission with narrow line widths at room temperature. In this work, we present a facile and efficient approach to generate high-density single-photon emitters (SPEs) in mechanically exfoliated h-BN through H- or Ar-plasma treatment followed by high-temperature annealing in air. It is notable that the postannealing is essential to suppress the fluorescence background in photoluminescence spectra and enhance emitter stability. These quantum emitters exhibit excellent optical properties, including high purity, brightness, stability, polarization degree, monochromaticity, and saturation intensity. The effects of process parameters on the quality of quantum emitters were systematic investigated. We find that there exists an optimal plasma power and h-BN thickness to achieve a high SPE density. This work offers a practical avenue for generating SPEs in h-BN and holds promise for future research and applications in quantum photonics.

Recent Developments in Quantum Dot Patterning Technology for Quantum Dot Display

Colloidal quantum dot (QDs) have emerged as a crucial building block for LEDs due to their size-tunable emission wavelength, narrow spectral line width, and high quantum efficiency. Tremendous efforts have been dedicated to improving the performance of quantum dot light-emitting diodes (QLEDs) in the past decade, primarily focusing on optimization of device architectures and synthetic procedures for high quality QDs. However, despite these efforts, the commercialization of QLEDs has yet to be realized due to the absence of suitable large-scale patterning technologies for high-resolution devices., This review will focus on the development trends associated with transfer printing, photolithography, and inkjet printing, and aims to provide a brief overview of the fabricated QLED devices. The advancement of various quantum dot patterning methods will lead to the development of not only QLED devices but also solar cells, quantum communication, and quantum computers.

Scalable narrow linewidth high power laser for barium ion optical qubits

The linewidth of a laser plays a pivotal role in ensuring the high fidelity of ion trap quantum processors and optical clocks. As quantum computing endeavors scale up in qubit number, the demand for higher laser power with ultra-narrow linewidth becomes imperative, and leveraging fiber amplifiers emerges as a promising approach to meet these requirements. This study explores the effectiveness of thulium-doped fiber amplifiers (TDFAs) as a viable solution for addressing optical qubit transitions in trapped barium ion qubits. We demonstrate that by performing high-fidelity gates on the qubit while introducing minimal intensity noise, TDFAs do not significantly broaden the linewidth of the seed lasers. We employed a Voigt fitting scheme in conjunction with a delayed self-heterodyne method to accurately measure the linewidth independently, corroborating our findings through quadrupole spectroscopy with trapped barium ions. Our results show linewidth values of 160 ± 15 Hz and 156 ± 16 Hz, respectively, using these two methods, underscoring the reliability of our measurement techniques. The slight variation within the error-bars of the two methods can be attributed to factors such as amplified spontaneous emission in the TDFA or the influence of 1/f noise within the heterodyne setup delay line. These contribute to advancing our understanding of laser linewidth control in the context of ion trap quantum computing as well as stretching the availability of narrow linewidth, high-power tunable lasers beyond the C-band.

Topologically protected subradiant cavity polaritons through linewidth narrowing enabled by dissipationless edge states

Cavity polaritons derived from strong light–matter interaction provide a basis for efficient manipulation of quantum states via cavity field. Polaritons with narrow linewidth and long lifetime are appealing in applications, such as quantum sensing and storage. Here, we propose a prototypical arrangement to implement a whispering-gallery-mode resonator with one-dimensional topological atom mirror, which allows to boost the lifetime of cavity polaritons over an order of magnitude. This considerable enhancement attributes to the coupling of polaritonic states to dissipationless edge states protected by the topological bandgap of atom mirror that suppresses the leakage of cavity modes. When exceeding the width of Rabi splitting, topological bandgap can further reduce the dissipation from polaritonic states to bulk states, giving arise to subradiant cavity polaritons with extremely sharp linewidth. The resultant Rabi oscillation experiences decay rate lower than the free-space decay of a single quantum emitter. Inheriting from the topologically protected properties of edge states, the subradiance of cavity polaritons can be preserved in disordered atom mirror with moderate perturbations involving the atomic frequency, interaction strengths and location fluctuations. Our work opens up a new paradigm of topology-engineered quantum states with robust quantum coherence for future applications in quantum computing and network.

Narrow linewidth fiber laser using compound-ring cavity filter and self-injection locked mechanism

Narrow linewidth erbium-doped fiber lasers (EDFLs) hold in significant potential optical fiber sensing, wavelength multiplexing transmission, and optical fiber communication. However, many EDFLs produced outputs with linewidth in several kHz level. Therefore, a high optical signal-to-noise ratio (OSNR), narrow linewidth single-longitudinal-mode (SLM) EDFL was proposed and investigated in this work. The EDFL utilized a combination of compound-ring cavity filter and a self-injection locked mechanism to generate a stable SLM output with an OSNR greater than 72 dB. The maximum wavelength drift and maximum peak power fluctuation over 60 min were maintained at low values of 0.0041 nm and 0.16 dB. Moreover, a narrow linewidth of 1.82 kHz at a measuring time of 0.002 s was realized. Furthermore, the research also investigated output power variations with different pump powers, relaxation oscillation, and the dependence of output central wavelength on the axial strain.

Measuring non-linear Faraday rotation in cold atoms in presence of persistent transverse fields using tunable differential imaging

Non-linear Faraday rotation in cold atoms promises precision magnetometry due to narrower magnetic resonance linewidth compared to the linear Faraday effect. Imaging techniques based on linear Faraday effect have emerged as a tool to characterize the dynamics of ultracold atomic clouds. Using a camera instead of balanced detectors, we can obtain the spatial distribution of polarization rotation in a uniformly intense optical beam. However, the finite dynamic range of the imaging device limits the sensitivity to measure non-linear Faraday rotation at a given incident power. Here, we experimentally demonstrate a differential imaging technique in which we can tune parameters to improve contrast and the sensitivity to the non-linear Faraday rotation signal by a factor of ≈7 over existing imaging methods. The atomic cloud experiences a uniform optical field even when shifted by persistent magnetic fields making the method robust. This allows us to study the effect of transverse fields on non-linear Faraday rotation in ultra-cold atoms, paving the way toward spatially resolved vector magnetometry.