Single-mode Laser Research Articles

Lasing properties and carrier dynamics of CsPbBr3 perovskite nanocrystal vertical-cavity surface-emitting laser

Abstract All-inorganic lead halide perovskite nanocrystals (NCs) have been widely investigated as highly promising optical gain materials due to their compelling electrical and optical properties. Although many efforts have been carried out, a deep understanding of perovskite NC vertical-cavity surface-emitting lasers (VCSELs) is elusive, which is very important in the development of photoelectronic integrated circuits. Along these lines, in this work, a low lasing threshold (22 μJ/cm2) single-mode VCSEL consisting of CsPbBr3 NCs film and two distributed Bragg reflectors was successfully constructed. The CsPbBr3 NCs were synthesized by using the supersaturated recrystallization method. Interestingly, benefiting from the strong coupling between the active layer and the optical field in the cavity, a single-mode lasing at 527 nm was demonstrated under femtosecond optical pumping. The carrier dynamics of the perovskite NC VCSEL was also thoroughly investigated by performing pump intensity-dependent time-resolved photoluminescence measurements. The typical gain-switching phenomenon was observed with an ultrafast decay of the laser pulse of ∼10 ps. Our work provides valuable insights for the implementation of the CsPbBr3 NC VCSEL for various optoelectronic applications.

Increasing the Q-Contrast in Large Photonic Crystal Slab Resonators Using Bound-States-in-Continuum

Photonic-crystal surface-emitting lasers (PCSELs) have shown promise for large-area single-mode lasers. However, the difficulty in increasing PCSEL area while preserving single-mode operation has hindered the progress of achieving ultralarge-area PCSELs. The physical origin of the scaling challenge lies in the diminishing quality-factor (Q) contrast between the fundamental mode and higher-order modes as the lateral size of the crystal increases. Here, we show that the existence of bound states in the continuum (BIC) can overcome this challenge. The presence of BIC enables large and constant Q-contrast that is independent of the lateral size of the crystal. Such a Q-contrast should guarantee size-invariant single-mode operation, which is the key to realize ultralarge-area PCSEL. We develop an analytical theory to elucidate the underlying physics of the size-invariant Q-contrast enabled by BIC and verify it with full-wave simulations. Furthermore, we show that the Q-contrast can be further increased by introducing specific spatial nonuniformities. Our findings provide theoretical guidance and open new possibilities for designing ultralarge-area PCSEL.

Divergence of the Variance of the Optical Phase in Gain-Switched Semiconductor Lasers Described by Stochastic Rate Equations

We report a theoretical study of the phase diffusion in a gain-switched single-mode semiconductor laser. We use stochastic rate equations for the electric field to analyze the phase statistics of the gain-switched laser. Their use avoids the instabilities obtained with rate equations for the photon number and optical phase when the photon number is small. However, we show that a new problem appears when the field equations are integrated: the variance of the optical phase becomes divergent. This divergence cannot be observed with the numerical integration of the commonly used equations for the photon number and optical phase because of the previous instabilities. The divergence of the phase variance means that this quantity does not reach a fixed value as the integration time step is decreased. We find that the phase variance increases as the integration time step decreases, with no sign of saturation behavior even for tiny steps. We explain the divergence by making the analogy of our problem with two-dimensional Brownian motion. The fact that the divergence appears is not surprising because in 1940 Paul L\`evy demonstrated that the variance of the polar angle in two-dimensional Brownian motion is a divergent quantity. Our results show that stochastic rate equations for the photon number and phase are not appropriate for describing the phase statistics when the photon number is small. Simulation of the stochastic rate equations for the electric field are consistent with L\`evy's results but gives unphysical results since an infinite value is obtained for a quantity that can be measured.

High side-mode suppression ratio with a Vernier effect single-mode laser using triple coupled microrings

The development of single-mode lasers with a high side-mode suppression ratio (SMSR) is challenging but highly desirable for integrated photonics devices and long-distance communications due to their high spectral purity and stability. Here, we demonstrate a single-mode laser with a high side-mode suppression ratio based on size-mismatched triple-coupled microrings. With the exact engineering of several key parameters of the structure like air gap and radii of microrings for controlling the free spectral range (FSR), a predominant mode is selected to lase in amplified spontaneous emission (ASE) of the gain material and all side and high order modes are suppressed by Vernier effect. In this work, we show that a single-mode operation is efficiently generated with an improved side-mode suppression ratio of over 20 dB in a three-ring-coupled microcavity laser. The single-frequency output persists for a wide power range. The theoretical calculations and numerical simulations’ results confirm the validity of the experimental results. Our structural engineering creates new opportunities in a variety of frontier applications in single-mode lasers and high-quality sensors.

Design and Analysis of Si/CaF<sub>2</sub> Near-Infrared (λ∼1.7µm) DFB Quantum Cascade Laser for Silicon Photonics

We have designed a near-infrared wavelength Si/CaF2 DFB quantum cascade laser and investigated the possibility of single-mode laser oscillation by analysis of the propagation mode, gain, scattering time of Si quantum well, and threshold current density. As the waveguide and resonator, a slab-type waveguide structure with a Si/CaF2 active layer sandwiched by SiO2 on a Si (111) substrate and a grating structure in an n-Si conducting layer were assumed. From the results of optical propagation mode analysis, by assuming a λ/4-shifted bragg waveguide structure, it was found that the single vertical and horizontal TM mode propagation is possible at the designed wavelength of 1.70 μm. In addition, a design of the active layer is proposed and its current injection capability is roughly estimated to be 25.1 kA/cm2, which is larger than required threshold current density of 1.4 kA/cm2 calculated by combining analysis results of the scattering time, population inversion, gain of quantum cascade lasers, and coupling theory of a Bragg waveguide. The results strongly indicate the possibility of single-mode laser oscillation.

Optimizing Optical Potentials With Physics-Inspired Learning Algorithms

We present our experimental and theoretical framework, which combines a broadband superluminescent diode with fast learning algorithms to provide speed and accuracy improvements for the optimization of on-dimensional optical dipole potentials, here generated with a digital micromirror device. To characterize the setup and potential speckle patterns arising from coherence, we compare the superluminescent diode to a single-mode laser by investigating interference properties. We employ machine-learning tools to train a physics-inspired model acting as a digital twin of the optical system predicting the behavior of the optical apparatus including all its imperfections. Implementing an iterative algorithm based on iterative learning control we optimize optical potentials an order of magnitude faster than heuristic optimization methods. We compare iterative model-based ``offline'' optimization and experimental feedback-based ``online'' optimization. Our methods provide a route to fast optimization of optical potentials, which is relevant for the dynamical manipulation of ultracold gases.

Self-injection locking of a low-noise erbium-doped random fiber laser by a random fiber grating ring.

We demonstrate a self-injection locking (SIL) in an Er-doped random fiber laser by a high quality factor (high-Q) random fiber grating ring (RFGR) resonator, which enables a single-mode narrow-linewidth lasing with ultra-low intensity and frequency noise. The RFGR resonator includes a fiber ring with a random fiber grating to provide random feedback modes and noise suppression filters with self-adjusted peak frequency adaptable to small perturbations allowing single longitudinal mode over 7000 s with frequency jitter below 3.0 kHz. Single-mode operation is accomplished by carefully controlling phase delays and mode coupling of resonant modes between main ring and RFGR with a side-mode suppression ratio of 70 dB and narrow linewidth of 1.23 kHz. The relative intensity noise is -140 dB/Hz above 100 kHz and the frequency noise is 1 Hz/Hz1/2 above 10 kHz.

Ultra-low threshold continuous-wave quantum dot mini-BIC lasers

Highly compact lasers with ultra-low threshold and single-mode continuous wave (CW) operation have been a long sought-after component for photonic integrated circuits (PICs). Photonic bound states in the continuum (BICs), due to their excellent ability of trapping light and enhancing light-matter interaction, have been investigated in lasing configurations combining various BIC cavities and optical gain materials. However, the realization of BIC laser with a highly compact size and an ultra-low CW threshold has remained elusive. We demonstrate room temperature CW BIC lasers in the 1310 nm O-band wavelength range, by fabricating a miniaturized BIC cavity in an InAs/GaAs epitaxial quantum dot (QD) gain membrane. By enabling effective trapping of both light and carriers in all three dimensions, ultra-low threshold of 12 μW (0.052 kW cm−2) is achieved at room temperature. Single-mode lasing is also realized in cavities as small as only 5 × 5 unit cells (~2.5 × 2.5 μm2 cavity size) with a mode volume of 1.16(λ/n)3. The maximum operation temperature reaches 70 °C with a characteristic temperature of T0 ~93.9 K. With its advantages in terms of a small footprint, ultra-low power consumption, and adaptability for integration, the mini-BIC lasers offer a perspective light source for future PICs aimed at high-capacity optical communications, sensing and quantum information.

Method of Suppressing Solidification Cracking by Laser Surface Melting and Epitaxial Growth Behavior for Directionally Solidified 247LC Superalloy

In this study, the relationship between solidification cracking and epitaxial growth behavior with the high-speed laser surface melting of a directionally solidified 247LC superalloys was fundamentally and metallurgically investigated, to develop a successful welding procedure for the next generation of gas turbine blades. Under typical laser surface melting conditions (scan speed: 50 mm/s, heat input: 40 J/mm), severe solidification cracking phenomena occurs. The key metallurgical factors of solidification cracking have been identified as solidification segregation-assisted pipeline diffusion behavior at the solidification grain boundary, and in the randomly formed polycrystalline melting zone microstructure. In addition, under extremely low heat input and high-speed laser beam scan conditions (scan speed: 1000 mm/s, heat input: 2 J/mm), an effective surface melting zone can be obtained within a single directionally solidified grain under a relatively high-energy beam density (65 J/mm2) using the characteristics of single-mode fiber lasers. Results reveal that the laser melting zone successfully shows a 99.9% epitaxial growth achievement ratio. Because of the superior epitaxial growth ratio within the laser surface melting zone, and the rapid solidification phenomena, formation of a solidification grain boundary and solidification segregation-assisted pipeline diffusion behavior can be suppressed. Finally, a solidification crack-free laser melting zone can thus be achieved.

28.1: Invited Paper: A Review of Optical source by using μLED and Single mode Laser Diodes for HMD, AR/VR Glasses

Expansion of devices to access the virtual world is expected due to much attention to Metaverse in recent years. In particular, head mount display (HMD), smart glasses and AR glasses have been attracting attention as next‐generation mobile devices that will replace smart phones. Laser diodes and μLEDs are developed in various research institutes and companies as light sources for those devices. In this paper, we describe the development status of the laser diodes and the μLEDs, the technical problems of optimal adaptation to smart glasses, and introduce one of the solutions when using the laser diodes.

Diode-pumped mode-locked Yb:Sc2SiO5 laser generating 38 fs pulses.

We report on sub-40 fs pulse generation from a Yb:Sc2SiO5 laser pumped by a spatially single-mode fiber-coupled laser diode at 976 nm. A maximum output power of 545 mW was obtained at 1062.6 nm in the continuous-wave regime, corresponding to a slope efficiency of 64% and a laser threshold of 143 mW. A continuous wavelength tuning across 80 nm (1030 -1110 nm) was also achieved. Implementing a SESAM for starting and stabilizing the mode-locked operation, the Yb:Sc2SiO5 laser delivered soliton pulses as short as 38 fs at 1069.5 nm with an average output power of 76 mW at a pulse repetition rate of ∼79.8 MHz. The maximum output power was scaled to 216 mW for slightly longer pulses of 42 fs, which corresponded to a peak power of 56.6 kW and an optical efficiency of 22.7%. To the best of our knowledge, these results represent the shortest pulses ever achieved with any Yb3+-doped rare-earth oxyorthosilicate crystal.

A chiral microchip laser using anisotropic grating mirrors for single mode emission

Abstract A pair of nanostructured mirrors made of a diffraction grating inscribed in the top layer of a Bragg mirror are designed such that a phase shift near π and different reflected amplitudes exist between transverse electric (TE) and magnetic (TM) reflected polarization states at normal incidence. When a standing wave laser resonator is formed with two such mirrors and the two mirrors’ principal axes are twisted one with respect to the other, this phase shift condition suppresses multiple longitudinal mode emission arising from axial spatial hole burning. In addition, the different amplitudes of TE and TM reflected polarizations create polarization eigenstates with different round-trip losses, suppressing one polarization eigenstate. Laser experiments made with a Yb3+-doped Y3Al5O12 active material reveal enhanced purity of the emission spectrum compared to similar lasers using conventional laser mirrors. The proposed design enables a miniature single mode laser, replacing more complex designs usually needed to achieve that goal.

Liquation crack-free welding strategy for 247LC DS superalloy by control of pipeline diffusion via ultra-high-speed laser beam scanning

Under completely suppressed constitutional liquation of MC carbide, unexplored 247LC superalloy single-mode fibre laser welds experience unexpected liquation cracking. These cracks continuously propagate from a solidification crack, particularly at highly misoriented and epitaxially grown solidification grain boundaries, and dominated by pipeline diffusion of impurities. Two novel metallurgical preconditions were identified which, if satisfied, ensure complete suppression of liquation cracking of 247LC superalloy welds. These preconditions are (i) the constitutional liquation of MC carbide at the heat-affected zone and (ii) pipeline diffusion of impurities at the fusion zone. It is also highly recommended that the welding is carried out in a single directionally solidified grain under scanning conditions, avoiding the formation of highly misoriented solidification grain boundaries.

Organic Synthetic Photonic Systems with Reconfigurable Parity-Time Symmetry Breaking for Tunable Single-Mode Microlasers.

Synthetic photonic materials exploiting the quantum concept of parity-time (PT) symmetry lead to an emerging photonic paradigm-non-Hermitian photonics, which is revolutionizing the photonic sciences. The non-Hermitian photonics dealing with the interplay between gain and loss in PT synthetic photonic material systems offers a versatile platform for advancing microlaser technology. However, current PT-symmetric microcavity laser systems only manipulate imaginary parts of the refractive indices, suffering from limited laser spectral bandwidth. Here, an organic composite material system is proposed to synthesize reconfigurable PT-symmetric microcavities with controllable complex refractive indices for realizing tunable single-mode laser outputs. A grayscale electron-beam direct-writing technique is elaborately designed to process laser dye-doped polymer films in one single step into microdisk cavities with periodic gain and loss distribution, which enables thresholdless PT-symmetry breaking and single-mode laser operation. Furthermore, organic photoisomerizable compounds are introduced to reconfigure the PT-symmetric systems in real-time by tailoring the real refractive index of the polymer microresonators, allowing for a dynamically and continuously tunable single-mode laser output. This work fundamentally enhances the PT-symmetric photonic systems for innovative design of synthetic photonic materials and architectures.

Single-Mode Tunable Interband Cascade Laser Emitting at 3.4 μm With a Wide Tuning Range Over 100 nm

We report a widely tunable monolithically integrated V-coupled cavity interband cascade laser (ICL) emitting near <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.4~\mu \text{m}$ </tex-math></inline-formula> . The mode selection is achieved using a half-wave V-coupler designed for the ICL in the mid-infrared range without any grating. The side-mode suppression ratio is demonstrated up to 35.7 dB. In the heat-sink temperature range from 130 K to 140 K, single-mode wavelength tuning range of over 100 nm from 3329.9 nm to 3431.3 nm has been attained by adjusting both current and temperature. These results show that the V-coupled cavity ICLs are very promising for multi-species trace gas absorption spectroscopy with a high sensitivity.

Perovskite quantum dot one-dimensional topological laser

Various topological laser concepts have recently enabled the demonstration of robust light-emitting devices that are immune to structural deformations and tolerant to fabrication imperfections. Current realizations of photonic cavities with topological boundaries are often limited by outcoupling issues or poor directionality and require complex design and fabrication that hinder operation at small wavelengths. Here we propose a topological cavity design based on interface states between two one-dimensional photonic crystals with distinct Zak phases. Using a few monolayers of solution-processed all-inorganic cesium lead halide perovskite quantum dots as the ultrathin gain medium, we demonstrate a lithography-free, vertical-emitting, low-threshold, and single-mode laser emitting in the green. We show that the topological laser, akin to vertical-cavity surface-emitting lasers (VCSELs), is robust against local perturbations of the multilayer structure. We argue that the design simplicity and reduction of the gain medium thickness enabled by the topological cavity make this architecture suitable for low-cost and efficient quantum dot vertical emitting lasers operating across the visible spectral region.

Half-Ring Microlasers Based on InGaAs Quantum Well-Dots with High Material Gain

We report on half-ring lasers that are 100–200 µm in diameter and are fabricated by cleaving the initial full rings into halves. Characteristics of the half-ring and half-disk lasers fabricated from the same wafer are compared. The active area of the microlasers is based on the quantum heterostructures of mixed (0D/2D) dimensionality, referred to as quantum well-dots with very high material gain. Half-ring lasers show directional light emission and single-mode lasing near the threshold. A maximal continuous-wave output power of 76 mW is achieved for a half-ring that is 200 µm in diameter. Half-rings demonstrate better wall-plug efficiency as compared to half-disks. Lasing in pulse mode is observed up to 140 °C, the characteristic temperature is 100–125 K, depending on the half-ring size. P-side down bonding onto Si-board significantly improves power and temperature characteristics. In CW mode, lasing is maintained up to 97 °C, limited by active-area overheating.

New insight into microstructure and mechanical properties of heterostructures 7075 Al joint prepared via single mode laser welding

The application of lightweight and high-strength Al alloys are crucial to reduce energy consumption and emissions in today's world. The lightweight and high strength 7 series aluminum alloy is widely used in aerospace, but its poor welding performance has been a bottleneck restricting the further lightweight of structural parts. In this work, a lightweight and high-strength Al joint with a tensile strength of ∼400 MPa was successfully prepared by single mode laser beam welding using non-weldable 7075 aluminum alloy as the experimental mode. The superfine laser beam reduces the volume of molten pool and increases the solidification rate of molten pool, which significantly inhibits the growth behavior of each microstructure, thus refining the microstructure. The geometrically necessary dislocations (GND) density of each microstructure of 7075 joint after tensile test was: 1.32 × 1014 m−1 for EZ, 1.21 × 1014 m−1 for CLZ, HAZ is 1.17 × 1014 m−1 for HAZ. The synergistic effect of heterogeneous microstructure and work hardening enhanced the tensile strength of 7075 joint. Furthermore, TEM, FIB and EBSD were used to characterize the fracture behavior of the 7075 joint in detail. TEM images showed that the discordant interface between α-Al grain boundary and SiO2 particle was the potential source of crack initiation. The microstructure refinement design and technical selection strategy of the work provide a new insight for laser welding of lightweight and high strength 2xxx/7xxx aluminum alloy.

On‐Chip Multiwavelength Single‐Mode Lasers with CdSe Nanoribbons‐Embedded Microcavities

Single-Mode Lasers In article number 2200367, Shaowei Wang and co-workers propose on-chip multi-wavelength single-mode lasers with CdSe nanoribbons embedded in microcavities. The number and wavelength of integrated lasers can be easily controlled by the thickness of the microcavities. It paves a way for new type of nanolaser chips which can be applied in integrated optics and other fields.

Relative phase locking of a terahertz laser system configured with a frequency comb and a single-mode laser

Stable operation is one of the most important requirements for a laser source for high-precision applications. Many efforts have been made to improve the stability of lasers by employing various techniques, e.g., electrical and/or optical injection and phase locking. However, these techniques normally involve complex experimental facilities. Therefore, an easy implementation of the stability evaluation of a laser is still challenging, especially for lasers emitting in the terahertz (THz) frequency range because the broadband photodetectors and mature locking techniques are limited. In this work, we propose a simple method, i.e., relative phase locking, to quickly evaluate the stability of THz lasers without a need of a THz local oscillator. The THz laser system consists of a THz quantum cascade laser (QCL) frequency comb and a single-mode QCL. Using the single-mode laser as a fast detector, heterodyne signals resulting from the beating between the single-mode laser and the comb laser are obtained. One of the heterodyne beating signals is selected and sent to a phase-locked loop (PLL) for implementing the relative phase locking. Two kinds of locks are performed by feeding the output error signal of the PLL, either to the comb laser or to the single-mode laser. By analyzing the current change and the corresponding frequency change of the PLL-controlled QCL in each phase-locking condition, we, in principle, are able to experimentally compare the stability of the emission frequency of the single-mode QCL (fs) and the carrier envelope offset frequency (fCEO) of the QCL comb. The experimental results reveal that the QCL comb with the repetition frequency injection locked demonstrates much higher stability than the single-mode laser. The work provides a simple heterodyne scheme for understanding the stability of THz lasers, which paves the way for the further locking of the lasers and their high-precision applications in the THz frequency range.