Single-mode Laser Research Articles

27% slope efficiency in a WGM microcavity enabled by an Yb:YAG crystalline film.

The choice of a laser gain medium is crucial in achieving efficient and high-power outputs of optically stimulated WGM microcavity lasers. This work employs an Yb:YAG crystalline film as the gain medium for the microdisk laser. The Yb:YAG crystalline film is exfoliated from a bulk of a Yb:YAG crystal by the ion-implantation-enhanced etching method. The crystalline film is shaped into a microdisk through focused ion beam milling. This Yb:YAG microdisk laser achieves a single-mode laser output (with a side-mode-suppression ratio of 27.8 dB) under a 946 nm laser pumping. The maximum slope efficiency reaches 27% with a maximum output power of 1.1 mW.

Switchable whispering gallery mode lasing via phase transition.

Combining phase-transition materials with optical microcavities may advance the applications of whispering-gallery mode (WGM) lasing in performance customization, sensing, and optical switching. In this study, switchable WGM lasing based on phase transition is reported. The device is designed by introducing the phase-transition hydrogel into the capillary microcavity. After approaching the phase-transition point in hydrogel, the number of WGM lasing modes decreases sharply with a significant blueshift in the wavelength. The phenomenon is caused by the increase in light scattering and decrease in effective refractive index of the device. Furthermore, single-mode lasing is obtained by manipulating the phase transition, which exhibits superior reversibility. This study may pave the way for designing and multifunctioning of novel WGM lasing in photonic devices.

Robust design of mid-infrared GaSb-based single-mode laser diode fabricated by standard photolithography with socketed ridge-waveguide modulation.

In this paper, we put up a robust design of a stable single-mode-operated GaSb-based laser diode emitting around 1950nm. This novel design structure with socketed ridge-waveguide enables a simple fabrication and batch production of mid-infrared laser diodes on account of the mere usage of standard photolithography. By introducing micron-level index perturbations distributed along the ridge waveguide, the threshold gains of different FP modes are modulated. Four geometrical parameters of the perturbations are systematically optimized by analyzing the reflection spectrum to get a robust single-mode characteristic. Based on the optimized geometrical parameters, 1-mm long uncoated lasers are carried out and exhibit a stable single longitudinal mode from 10 °C to 40 °C with a maximum output power of more than 10 mW. Thus, we prove the feasibility of the standard photolithography to manufacture the monolithic single-mode infrared laser source without regrowth process or nanoscale lithography.

2.2 kW single-mode narrow-linewidth laser delivery through a hollow-core fiber

Antiresonant hollow-core fibers (AR-HCFs) have opened up exciting possibilities for high-energy and high-power laser delivery because of their exceptionally low nonlinearities and high damage thresholds. While these fiber designs offer great potential for handling kilowatt-class powers, it is crucial to investigate their performance at multi-kW power levels. Until now, transmission of narrow-linewidth single-mode lasers at multi-kW power levels through a HCF has not been demonstrated, to our knowledge. Here, we present the delivery of a record 2.2 kW laser power with an input spectral linewidth of 86 GHz, centered at 1080 nm, while maintaining 95% transmission efficiency and beam quality (M2) of 1.03. This was achieved via a 104.5 m single-mode five-tube nested AR-HCF with 0.79 dB/km loss. Furthermore, we show power delivery of 1.7 kW with a spectral linewidth as narrow as 38 GHz through the same fiber. Our results could lead to a new generation of fiber-based laser beam delivery systems with applications in precision machining, nonlinear science, directed energy, and power beaming over fiber.

Delta interferometer: A polarization sensitive interferometer

Abstract A new type of polarization sensitive interferometer is proposed, which is named as Delta interferometer due to the geometry of the simplest interferometer of this type looks like Greek letter, Delta. The main difference between Delta interferometer and other existed interferometer, such as Michelson interferometer, Mach-Zehnder interferometer, Young’s double-slit interferometer, is that the two interfering paths are asymmetrical in Delta interferometer. The visibility of the first-order interference pattern observed in Delta interferometer is dependent on the polarization of the incidental light. Optical coherence theory is employed to interpret the phenomenon and single-mode continuous-wave laser light is employed to verify the theoretical predictions. The theoretical and experimental results are consistent. Delta interferometer provides a perfect tool to study the reflection of electromagnetic field in different polarizations and may find applications in polarization sensitive scenarios.

All-optical tuning of the frequency of Yb3+/Er3+ co-doped microsphere WGM laser pumped by 1 µm ASE light source

In this paper, the laser generated by Yb3+/Er3+ co-doped silica microspheres excited and tuned by amplified spontaneous emission (ASE) light source was studied. The adoption of ASE light avoids the synchronous adjustment of the coupling condition of the microcavity during broadband tuning process, and facilitates the actual application of the microcavity-based tunable laser. The stable single-mode laser at approximate 1595 nm was generated in the Yb3+/Er3+ co-doped silica microsphere due to the polarization insensitivity of the ASE light source with a center wavelength of 1 µm. For the all-optical modulation of laser mode, a thin layer of copper film was coated on the spherical crown of the microsphere by magnetron sputtering. Controllable heating of the microsphere and linear tuning of laser mode were realized through the absorption of ASE light by the copper film injecting from the stem of the microsphere. The tuning range reached 190 GHz.

On the Dynamics of a Single-Mode Laser with an Additional Mirror

On the Dynamics of a Single-Mode Laser with an Additional Mirror

Solidification Crack Free Welding Strategy via Ultra High Precision Laser Scanning at a Single Grain of Directionally Solidified and Single Crystal Superalloys

In this study, possibility of solidification crack-free welding of directionally solidified CM247LC and single crystal CMSX-4 superalloys was metallurgically investigated using single-mode fiber laser scanning. The key metallurgical factors of solidification cracking have been identified as the formation of highly misoriented solidification grain boundaries (low level of epitaxial growth behavior) at the fusion zone that affects the repulsive force between two adjacent dendrites and dendrite coalescence undercooling at the terminal stage of weld solidification. In particular, under extremely low heat input and ultra-high-speed laser beam scan conditions (welding speed: 1,000 mm/s, heat input: 2 J/mm, and energy density: 65 J/mm<sup>2</sup>), an effective fusion zone could be achieved within a single directionally solidified grain of CM247LC alloy owing to the characteristics of single-mode fiber laser. The fusion zone successfully showed a 99.9% of epitaxial growth achievement ratio (that is, low fraction of highly misoriented solidification grain boundaries at the fusion zone) without solidification cracking. Based on these results on CM247LC alloy, solidification crack-free welds could be successfully achieved using quadruple-pass and square-type weld geometries.

Ionic Solvent-Assisted MAPbBr3 Perovskite Film for Two-Photon Pumped Single-Mode Laser.

Miniaturized coherent light sources on the nanoscale are highly desired for on-chip photonics integration. However, when approaching the diffraction limit, the sub-wavelength-scale all-dielectric lasers are difficult to realize due to the trade-off between lasing performance and physical size. Especially for a thin-film laser, usually an externally complex cavity is required to provide the necessary optical feedback. Herein, we successfully shrink the MAPbBr3 perovskite thin-film laser to sub-wavelength scale (300 nm) with simplified cavity design using only an ultraviolet glue layer and a quartz glass. The morphology quality and the gain properties of the film are enhanced by introducing ionic liquid. Consequently, the stable and low-threshold single-mode laser with a highly linear polarization degree of 78.6% and a narrow line width of 0.35 nm is achieved under two-photon excitation. The excellent single-mode laser with sub-wavelength scale and ultrasimplified structure could provide a facile and versatile platform for future integrated optoelectronic devices.

High-Precision Microdisk Laser Particles by Active Photoelectrochemical Etching for Cell Barcoding

To study the spatio-temporal evolution of individual cells in an intact tissue or other specific microenvironment, organic fluorophores are widely used. Owing to the broad emission linewidth (full width at half maximum exceeding 50 nm) of the organic fluorophore molecules, only limited number of fluorophores with non-overlapping spectral signatures can be simultaneously observed on the spectral range of the spectrometer. Thus there is a need of optical probes of deterministic colors with non-overlapping narrow spectral signatures. In the recent past, a new class of biophotonic tool – called laser particles – has emerged, which is unique in terms of its narrow spectral linewidth arising from lasing. In the previous studies, however, the lasing wavelength of the individual laser particles has been random. In this presentation, we shall report the first step towards addressing this, by demonstrating fabrication of InGaAsP microdisk laser particles by active photoelectrochemical etching to lase in distinct deterministic narrow-band “colors”. The experimental pathway supported by a theoretical model to explain the results, would be presented. By careful choice of the material system coupled with the design of the disk geometry, we were able to demonstrate multiple unique “color bands” of single-mode lasing of all microdisks simultaneously emitting in the same narrow spectral band. Transferring these wavelength-tuned microdisks onto a PDMS substrate, we create free-standing precision laser particles. This technology could potentially open up a viable avenue to simultaneously identify and image over 20 unique biomarkers in the same spectral bandwidth as currently provided by 4 organic fluorophores.

Rydberg State Single-Mode Polariton Lasing with Ultralow Threshold via Symmetry Engineering.

Symmetry plays an essential role in the fundamental properties of a physical system. In this work, we report on the realization of tunable single-mode polariton lasing from highly excited Rydberg states via symmetry engineering. By breaking the symmetry of the polaritonic wave function through potential wells and controlling the spatial overlap between the gain region and the eigen mode, we are able to generate single-mode polariton lasing, reversibly and dynamically, from quantized polariton states. Increasing the asymmetry of the potential well, single-mode lasing can be achieved even for the highly excited Rydberg state with a principle quantum number of N = 14. Moreover, as a result of the excellent reservoir-eigen mode overlap and efficient spatial confinement, the threshold of lasing can be reduced up to 6 orders of magnitude, compared with those conventional pumping schemes. Our results present a new strategy toward the realization of thresholdless polariton lasing with dynamical tunability.

Lasing in Zn-doped GaAs nanowires on an iron film

In this work, we demonstrate optically pumped lasing in highly Zn-doped GaAs nanowires (NWs) lying on an iron film. The conically shaped NWs are first covered with an 8 nm thick Al2O3 film to prevent atmospheric oxidation and mitigate band-bending effects. Multimode and single-mode lasing have been observed for NWs with a length greater or smaller than 2 μm, respectively. Finite difference time domain calculations reveal a weak electric field enhancement in the Al2O3 layer at the NW/iron film interface for the lasing modes. The high Zn acceptor concentration in the NWs provides enhanced radiative efficiency and enables lasing on the iron film despite plasmonic losses. Our results open avenues for integrating NW lasers on ferromagnetic substrates to achieve new functionalities, such as magnetic field-induced modulation.

Metasurface reflector enables room-temperature circularly polarized emission from VCSEL

While most lasers are linearly polarized, circularly polarized laser sources are crucial components for many optical applications such as biosensing, quantum technologies, and AR/VR. However, conventional methods for generating chiral light have limitations in device miniaturization. Vertical-cavity surface-emitting lasers (VCSELs), with their small footprint and surface emission feature, can be integrated with ultrathin metasurfaces for light manipulation, offering an opportunity to realize ultracompact chiral lasers. Here we report, to our knowledge, the first demonstration of chiral lasing from electrically pumped VCSELs at room temperature, without spin injection. This is enabled by incorporating a high-contrast chiral metasurface reflector as the VCSEL top mirror, favoring one specific circular polarization for lasing. Our demonstrated 940 nm VCSELs show stable single-mode chiral lasing and achieve a circular-polarization degree of up to 59%. This study provides a scalable approach for circular-polarization control of VCSELs and holds great promise for applications that desire ultracompact chiral emitters.

A review: Rise of PT-symmetry for laser applications

In quantum mechanics, with the groundbreaking discovery of parity-time symmetry (PT-symmetry), Bender and Boettcher unfold the nature of the non-Hermitian Hamiltonian to exhibit real eigenvalues. This opened a new doorway to efficiently explore all the previously ignored quantum non-Hermitian systems. The analogy between the Schrödinger equation in quantum mechanics and the paraxial wave equation in optics spurred researchers to apply the concept of PT-symmetry to optical systems. On exploring the PT-symmetric optics experimentally, by engineering loss and gain in the system, a lot of applications have been reported. It includes single-mode lasers, coherent perfect absorber lasers (CPA lasers), exceptional point sensors (EPS), spectral and spatial filters, etc. In addition to linear theoretical models on PT-symmetry, nonlinear theoretical models and the corresponding experimental results have also been reported in the last few decades. This review article begins with the fundamental idea of PT-symmetry for beginners. Subsequently, we elucidate its advancements in the field of optics. Besides, we present the recent developments of various laser systems using PT-symmetry. Thus, this review intends to focus on novel theoretical and experimental works on PT-symmetry.

Single-mode lasing in diode-pumped passive Q-switch lasers based on neodymium-doped yttrium aluminate and ytterbium-erbium glass active elements

Single-mode lasing in diode-pumped passive <i>Q</i>-switch lasers based on neodymium-doped yttrium aluminate and ytterbium-erbium glass active elements

Single-Mode-VCSEL With a Ring-Shaped Self-Aligned Recessed Metal Mode Filter

This article presents a single-mode vertical-cavity surface-emitting laser (VCSEL) using a novel ring-shaped self-aligned recessed metal (SARM) mode filter on the emitting window as a means of transverse mode control. The SARM structure acts as a spatial filter to suppress the higher-order transverse modes through selective recessed-etching of the top mirror and the self-aligned deposition of the p-type contact metals for cavity tuning and blocking the higher-order modes. The SARM mode filter could be a potentially high-yield alternative technique for the mass production of single-mode VCSELs, demonstrating a single-mode emission with 1.55-mW power and a 30.7-dB side mode suppression ratio.

Cost-Effective Half-Duplex Transceivers for Fiber-to-the-Room Network Enabled by Optical Feedback Resistant Single-Mode Lasers

Cost-Effective Half-Duplex Transceivers for Fiber-to-the-Room Network Enabled by Optical Feedback Resistant Single-Mode Lasers

High-Power, Large-Mode 1.3-μm Lasers Based on Supermode Screening

A high-power, single-mode laser structure based on screening of supermodes in vertically coupled waveguides is proposed and demonstrated in the 1.3 μm wavelength range. This supermode-screening (SuMoS) laser operates in a single large mode with low ellipticity that is ideal for optical coupling and high optical power at the facet. Fabricated Fabry-Pérot lasers demonstrated low loss (~1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ), high power (>500 mW), reasonable power conversion efficiency (>20%), and good coupling to a lensed optical fiber (>80%).

Tunable, coherent optical comb source via on-chip bidirectional coupling.

A tunable comb source is demonstrated through gain switching on a three-sectioned photonic integrated circuit (PIC). The PIC consists of two mutually coupled lasers connected by a passive waveguide. One of these is a tunable, two-section, single mode laser. The second laser is a simple Fabry-Perot cavity laser which can be phase-locked with the single mode laser via bidirectional coupling. Frequency combs are produced by gain switching the Fabry-Perot laser by applying a high-power radio frequency signal. Combs are generated with line spacings ranging from 3.5 to 8 GHz. The on-chip bidirectional coupling causes the comb to also be generated in the two-section device. Despite the lack of on-chip optical isolation between the lasers, the resulting combs are stable. Numerical simulations using a delay-differential model reproduce the results and reveal the important role played by the short delay times inherent to on-chip integration in this stability.

Ultrasmall InGa(As)P Dielectric and Plasmonic Nanolasers.

Nanolasers have great potential for both on-chip light sources and optical barcoding particles. We demonstrate ultrasmall InGaP and InGaAsP disk lasers with diameters down to 360 nm (198 nm in height) in the red spectral range. Optically pumped, room-temperature, single-mode lasing was achieved from both disk-on-pillar and isolated particles. When isolated disks were placed on gold, plasmon polariton lasing was obtained with Purcell-enhanced stimulated emission. UV lithography and plasma ashing enabled wafer-scale fabrication of nanodisks with an intended random size variation. Silica-coated nanodisk particles generated stable subnanometer spectra from within biological cells across an 80 nm bandwidth from 635 to 715 nm.