Continuous-wave Lasing Research Articles

Stable continuous-wave lasing from discrete cesium lead bromide quantum dots embedded in a microcavity.

All-inorganic cesium lead bromide (CsPbBr3) quantum dots (QDs) with high photoluminescence (PL) quantum efficiency have been reported as ideal gain materials for high-performance lasers. Nevertheless, isolated CsPbBr3 QDs have not achieved lasing emission (LE) due to finite absorption cross-section. Here, we demonstrate continuous-wave lasing of isolated CsPbBr3 QDs embedded in a microcavity. Distributed Bragg reflectors (DBRs), together with isolated CsPbBr3 QDs in a polymer matrix, are introduced to construct a vertical-cavity surface-emitting laser (VCSEL), which exhibits stable single-mode lasing emissions with an ultra-low threshold of 8.8 W cm-2 and a high Q factor of 1787. Such perovskite-based microcavity structures sustain highly stable excitons at room temperature and can provide an excellent experimental platform to further study the single-particle nano-lasers and quantum physics frontiers such as exciton-polariton condensation, single-photon emission, and optical quantum communication.

Key temperature-dependent characteristics of AlGaN-based UV-C laser diode and demonstration of room-temperature continuous-wave lasing

Although the pulsed operation of AlGaN-based laser diodes at UV-C wavelengths has been confirmed in the previous studies, continuous oscillation without cooling is difficult because of the high operating voltage. In this study, the temperature dependence of key parameters was investigated and their impact on achieving continuous-wave lasing was discussed. A reduction in the threshold voltage was achieved by tapering the sides of the laser diode mesa and reducing the lateral distance between the n- and p-electrodes. As a result, continuous-wave lasing at room temperature was demonstrated at a threshold current density of 4.2 kA/cm2 and a threshold voltage of 8.7 V.

GaAs on (001) Si templates for near-infrared InP quantum dot lasers

We investigated the effects of thermal cycle annealing (TCA) at high temperatures on the defect density and morphology of GaAs epilayers grown on (001) Si substrates. Several types of TCA combined with dislocation filter layers (DFLs) were introduced to reduce the defect densities in the GaAs grown on Si substrates. Plan-view transmission electron microscopy shows that the defect density of a 2.7 μm-thick GaAs/Si template with optimized TCA and DFLs is 1.4 × 107 cm−2, lower than a 1.1 μm-thick GaAs/Si template by a factor of 40. The surface roughness of the optimized GaAs/Si template is 1.3 nm after insertion of the DFLs. Additionally, optically pumped InP quantum dot micro-disk lasers (MDLs) were fabricated on these GaAs/Si templates to evaluate the template quality. Room-temperature continuous-wave lasing of 1.5 μm-diameter MDLs was observed, with ultralow lasing thresholds ranging from 0.5 to 2 μW.

Continuous-Wave Current Injected InGaN/GaN Microdisk Laser on Si(100)

GaN-based microdisk laser on Si can be adopted as an efficient on-chip laser source for Si photonics. However, most of the reported microdisk lasers are integrated on Si(111), which is not fully compatible with cost-effective mainstream complementary metal-oxide-semiconductor (CMOS) foundries. In this study, GaN-based microdisk laser monolithically integrated on Si(100) is carefully designed and fabricated thorough wafer bonding and substrate removal. Moreover, it shows 66.5% lower junction temperature due to reduced electric injection power and thermal resistance as compared with the reported conventional GaN-based microdisk lasers grown on Si(111). The result is the room-temperature continuous-wave current-injected lasing of GaN-based microdisk laser on Si(100), showing a narrow spectral line width of about 0.16 nm and an obvious turning point in the optical output power versus injection current curve.

Continuous-wave Tm:YLF laser with ultrabroad tuning (1772-2145 nm).

We report detailed experimental data aiming for rigorous investigation of Tm:YLF laser performance, especially with a focus on tuning behavior. Continuous-wave (cw) lasing performance of Tm:YLF crystals with thulium dopings in the 2-6% range is investigated under diode and Ti:Sapphire pumping at 792 nm and 780 nm, respectively. While employing the c-axis, we have achieved cw lasing thresholds below 20 mW, laser output power up to 1.42 W, and laser slope efficiencies as high as 70% with respect to absorbed pump power. The passive loss of the Tm:YLF crystal is estimated to be as low as 0.05% per cm, corresponding to a crystal figure of merit above 10000. Via employing this low-loss crystal and a 2-mm thick off-surface optical axis birefringent filter (BRF) with strong sideband rejection, a record cw tuning range covering the 1772-2145 nm interval is demonstrated (except a small gap between 1801-1815nm region). Detailed lifetime and emission cross section measurements have been performed to explain the observed performance, and strategies for further performance enhancement are discussed.

Electrically pumped quantum-dot lasers grown on 300 mm patterned Si photonic wafers

Monolithic integration of quantum dot (QD) gain materials onto Si photonic platforms via direct epitaxial growth is a promising solution for on-chip light sources. Recent developments have demonstrated superior device reliability in blanket hetero-epitaxy of III–V devices on Si at elevated temperatures. Yet, thick, defect management epi designs prevent vertical light coupling from the gain region to the Si-on-Insulator waveguides. Here, we demonstrate the first electrically pumped QD lasers grown by molecular beam epitaxy on a 300 mm patterned (001) Si wafer with a butt-coupled configuration. Unique growth and fabrication challenges imposed by the template architecture have been resolved, contributing to continuous wave lasing to 60 °C and a maximum double-side output power of 126.6 mW at 20 °C with a double-side wall-plug efficiency of 8.6%. The potential for robust on-chip laser operation and efficient low-loss light coupling to Si photonic circuits makes this heteroepitaxial integration platform on Si promising for scalable and low-cost mass production.

Room-temperature continuous-wave indirect-bandgap transition lasing in an ultra-thin WS2 disk

Room-temperature continuous-wave indirect-bandgap transition lasing in an ultra-thin WS2 disk

Simultaneous ultraviolet, visible, and near-infrared continuous-wave lasing in a rare-earth-doped microcavity

Microlaser with multiple lasing bands is critical in various applications, such as full-color display, optical communications, and computing. Here, we propose a simple and efficient method for homogeneously doping rare earth elements into a silica whispering-gallery microcavity. By this method, an Er-Yb co-doped silica microsphere cavity with the highest quality (Q) factor (exceeding 108) among the rare-earth-doped microcavities is fabricated to demonstrate simultaneous and stable lasing covering ultraviolet, visible, and near-infrared bands under room temperature and a continuous-wave pump. The thresholds of all the lasing bands are estimated to be at the submilliwatt level, where both the ultraviolet and violet continuous wave upconversion lasing from rare earth elements has not been separately demonstrated under room temperature until this work. This ultrahigh-Q doped microcavity is an excellent platform for high-performance multiband microlasers, ultrahigh-precision sensors, optical memories, and cavity-enhanced light–matter interaction studies.

Toward Continuous-Wave Pumped Metal Halide Perovskite Lasers: Strategies and Challenges.

Reliable and efficient continuous-wave (CW) lasers have been intensively pursued in the field of optoelectronic integrated circuits. Metal perovskites have emerged as promising gain materials for solution-processed laser diodes. Recently, the performance of CW perovskite lasers has been improved with the optimization of material and device levels. Nevertheless, the realization of CW pumped perovskite lasers is still hampered by thermal runaway, unwanted parasitic species, and poor long-term stability. This review starts with the charge carrier recombination dynamics and fundamentals of CW lasing in perovskites. We examine the potential strategies that can be used to improve the performance of perovskite CW lasers from the materials to device levels. We also propose the open challenges and future opportunities in developing high-performance and stable CW pumped perovskite lasers.

Broadly tunable (993-1110 nm) Yb:YLF laser.

We have investigated room-temperature continuous-wave (cw) lasing performance of Yb:YLF oscillators in detail using rod-type crystals with low Yb-doping (2%). The laser is pumped by a low-cost, high brightness, 10 W, 960 nm single-emitter multimode diode. Laser performance is acquired in both E//a and E//c configurations, using 12 different output couplers with transmission ranging from 0.015% to 70%. We have estimated the passive loss of the Yb:YLF crystal as 0.06% per cm, corresponding to an impressive crystal figure of merit above 4000. The low-doping level not only reduces the system losses but also minimizes the thermal load as the low doped crystals enable distribution of heat load in a greater volume. Using the advantages of lower loss and improved thermal behavior, we have achieved cw output power above 4 W, cw slope efficiencies up to 78%, and a record cw tuning range covering the 993-1110 nm region (117 nm). The output power performance achieved in this initial work is limited by the available pump power, and future room-temperature Yb:YLF systems have the potential to produce higher output power levels.

Continuous-wave lasing of AlGaN-based ultraviolet laser diode at 274.8 nm by current injection

We demonstrated continuous-wave lasing of an AlGaN-based ultraviolet laser diode, fabricated on a single-crystal AlN substrate when operating at 5 °C. The threshold current density and device series resistance were reduced by improvements to the epitaxial structure and electrode arrangement. A peak wavelength of 274.8 nm was observed for lasing at a drive current over 110 mA, which corresponded to a threshold current density of 3.7 kA cm−2. The operating voltage at the threshold current was as low as 9.6 V.

Ultra-short optical pulse generation in micro OLEDs and the perspective of lasing

We report experimental and theoretical investigations with an in-house fabricated tris(8‐hydroxyquinoline)‐aluminum (Alq3)-based high-speed micro-organic light-emitting diodes (μ-OLEDs) and demonstrate very promising optical pulse responses as short as 400 ps. With a model for an electrically pumped OLED, we simulate the emission of sub-nanosecond optical pulses. The model includes field-dependent (Poole-Frenkel) Langevin recombination and reabsorption of photons by singlets (Stokes-shifted), and by triplets (TA). The good agreement between the measurement and the simulation is the basis for further study of the prospects on the ps time scale, i.e. stimulated emission and conditions for laser operation. For an Alq3-based micro-OLED with high-Q optical cavity, we predict pulsed laser operation with damped relaxation oscillations in the GHz regime and several orders of magnitude linewidth narrowing, but only during 3 ns at most. The simulated current density threshold values vary from 10 kA cm−2 for Q= 500 to less than 1 kA cm−2 for Q = 1000. No continuous-wave (CW) lasing is found due to the accumulation of triplet excitons for t > 5 ns, which has two deteriorating effects, (a) suppression of the gain-providing singlet excitons due to singlet-triplet absorption and (b) suppression of the photon density due to photon absorption by triplets (TA). Prospects for CW-lasing with other organic molecules are discussed.

Numerical Study of Triplet Dynamics in Organic Semiconductors Aimed for the Active Utilization of Triplets by TADF under Continuous-Wave Lasing.

The limitation of lasing duration less than nanosecond order has been a major problem for realizing organic solid-state continues-wave (CW) lasers and organic semiconductor laser diodes. Triplets accumulation under CW excitation has been well recognized as a critical inhibiting factor. To overcome this issue, the utilization of thermally activated delayed fluorescence (TADF) emitters is a promising mechanism because of efficient reverse intersystem crossing. Herein, we model the triplet accumulation processes under lasing and propose the active utilization of TADF for lasing based on our simulation analysis. We used the rate constants experimentally determined from the optical properties of a boron difluoride curcuminoid fluorophore showing both TADF and lasing. We demonstrate that the intersystem crossing efficiency is gradually increased after the convergence of relaxation oscillation, i.e., terminating laser oscillation. In addition, we found that when the reverse intersystem crossing rate is close to the intersystem crossing rate, CW lasing becomes dominant.

Experiment and modeling of the pulsed lasing in a diode-pumped argon metastable laser

Diode-pumped metastable rare gas lasers are showing their potential for high-energy laser systems with intensive investigations carried out to understand their lasing characteristics. Here, we demonstrated pulsed lasing of a diode-pumped argon metastable laser based on a pulsed DC glow discharge in argon and helium mixtures for different discharge voltages and pressures. A transient rate equation model was established and solved to explain the cause of the pulsed lasing in our experiment. The insufficient production rate of argon metastable atoms (1s5) and the slow transfer rate out of the 1s4 state in the plasma during the lasing process were found to be the key reasons. This work may shed some light on the future design of plasma sources that have higher metastable atom production rates to achieve highly efficient continuous wave lasing.

Ultra-low threshold lasing through phase front engineering via a metallic circular aperture

Semiconductor lasers with extremely low threshold power require a combination of small volume active region with high-quality-factor cavities. For ridge lasers with highly reflective coatings, an ultra-low threshold demands significantly suppressing the diffraction loss at the facets of the laser. Here, we demonstrate that introducing a subwavelength aperture in the metallic highly reflective coating of a laser can correct the phase front, thereby counter-intuitively enhancing both its modal reflectivity and transmissivity at the same time. Theoretical and experimental results manifest a decreasing in the mirror loss by over 40% and an increasing in the transmissivity by 104. Implementing this method on a small-cavity quantum cascade laser, room-temperature continuous-wave lasing operation at 4.5 μm wavelength with an electrical consumption power of only 143 mW is achieved. Our work suggests possibilities for future portable applications and can be implemented in a broad range of optoelectronic systems.

Lasing properties and their anisotropy of Yb:CaWO[formula omitted] crystal

Continuous-wave lasing properties of the tetragonal Yb:CaWO4 crystal were investigated with a- and c-cut crystals under 976-nm diode pumping, revealing a strong anisotropy in many output characteristics. Depending on the resonator output coupling, the laser oscillation realized with the a-cut crystal could be σ- or π-polarized; it could also consist of σ and π polarization states simultaneously. An output power of 2.01 W was generated at 1025.1–1027.8 nm in dual-polarization laser operation, with an optical-to-optical efficiency of 24.1% and a slope efficiency of 28%; the σ- and π-polarized components were measured to be 1.05 and 0.96 W, respectively. The laser emission generated with the c-cut crystal could only be unpolarized; while the maximum output power, which was limited by the output saturation behavior, amounted only to 1.61 W.

Low threshold lasing from silicon Mie resonators

The unique electromagnetic response of high-index dielectric resonators with Mie resonances facilitates the selective enhancement and confinement of light, holding great promise for nanoscale lasing. However, up to now, nanolasing exploiting Mie resonances of individual Si nanowires has been limited to theoretical proposals. Here, we demonstrate a strategy to realize nanolasing with Si nanowires in the SOI platform. It is found that, by carefully tailoring the sizes of the Si nanowires, the Mie resonances of Si nanowires enhance the pumping/emission fields, leading to continuous-wave lasing at room temperature with low threshold in the visible range. The lasing of a dye at the wavelength of 523 nm assisted by the Mie resonances of Si nanowire is demonstrated experimentally. It is shown that the lasing wavelength changes with the width of nanowire due to the different scattering peak from Mie theory. In addition, the quality factor Q of lasing modes can be affected by the thickness of silica shell which determines the interaction volume of the pumping light and dyes. The proposed strategy paves the way towards practical integrated nanolasers for single-photon sources and micro-display, which have potential applications of on-chip optoelectrical devices.

High average output power from a backside-cooled 2-µm InGaSb VECSEL with full gain characterization.

We compare the gain and continuous wave lasing properties of two InGaSb-based vertical external cavity surface emitting lasers (InGaSb VECSEL) with different heat management approaches operating at a center wavelength of around 2μ m. To date, intracavity heatspreaders have been required for good average output power, which have many trade-offs, especially for passive modelocking. Here we demonstrate a record high average output power of 810 mW without an intracavity heatspreader using a backside-cooled non-resonant VECSEL chip optimized for modelocking. In addition, we introduce and demonstrate an optical characterization for a wavelength range of 1.9 to 3μ m to precisely measure wavelength-dependent gain saturation and spectral gain. Gain characteristics are measured as a function of wavelength, fluence, pump power and temperature. Small signal gain of more than 5%, small saturation fluences and broad gain bandwidths of more than 90 nm are demonstrated. In comparison to a commercial VECSEL chip with an intracavity heatspreader, we have obtained similar average output power even though our VECSEL chip is designed for antiresonance.

Low-Threshold Continuous-Wave Anti-Stokes Raman Lasing in Silicon Racetrack Resonators

Low-Threshold Continuous-Wave Anti-Stokes Raman Lasing in Silicon Racetrack Resonators

Lanthanide Upconverted Microlasing: Microlasing Spanning Full Visible Spectrum to Near-Infrared under Low Power, CW Pumping.

The miniaturization of lasers holds promise in ultradense data storage and biosensing, but greater pump power is required to reach the lasing thresholds to overcome increased optical losses with reduced resonant cavity sizes. Here, the whispering galley mode (WGM) of Yb3+ /Tm3+ doped upconversion nanoparticles (UCNPs) coupled with microcavities (≈5µm) is used to achieve ultralow threshold upconverted lasing at 800nm with excitation fluences as low as 4Wcm-2 . The continuous-wave (CW) upconverted lasing, with a Q factor on the order of 103 , can remain stable for more than 6 h. In addition, ultralow threshold upconverted microlasers spanning the full visible spectrum from Yb3+ /Er3+ , Yb3+ /Ho3+ , and Yb3+ /Tm3+ doped UCNPs are obtained with the same WGM cavity design. These upconverted microlasers working under low power CW 980nm laser will enable promising applications in biosensing and imaging.