Lasing Polarization Research Articles

Dynamic Physical Unclonable Function Relying on Lasing Polarization

Dynamic Physical Unclonable Function Relying on Lasing Polarization

Controllable Optical Features of Multiple‐Layered Axial Heterostructure Nanorods for Multicolor Polariton Nanolasers

AbstractThe optical features of multiple‐layered axial heterostructures composed of III‐nitride semiconductors (GaN, InGaN, and AlGaN) are investigated to realize tunable nanolasers. The optical confinement effects develop exciton‐polariton in nanorods, leading to polariton lasing with distinctive dispersion. The lasing characteristics in the heterostructure are similar to those in the homostructure, although the carrier transfer between layers influences the optical gain. The energy‐dependent property of polariton changes the mode spacing of lasing peaks. The alloyed systems of InGaN can tune the color of lasing in the visible region, while the lasing of AlGaN is also achievable in the optimized configuration. The polarization of lasing indicates the predominant contribution of the fundamental transverse mode. Therefore, in the multiple‐layered heterostructure, controllable triple‐color lasing using the feature of polariton, modulation of band gap energy, and the amplification process of the waveguide is demonstrated for the first time, with the tunable color over a wide range of the visible region. Multicolor polariton nanolasers offer a promising path to diverse nanophotonic devices with controllable optical characteristics.

Control over polarization of vertically emitting random lasers based on dye doped nematic liquid crystals by applying a transverse electric field locally

Flexible control over random lasers (RLs) is highly desired. In this manuscript, a control over the polarization of random lasing emitted vertically from dye doped nematic liquid crystal (NLC) cell by the transverse component of a local ac electric field was demonstrated. The polarizing direction of the RL could be tuned continuously and monotonously with the increase of the field strength, from the direction along the NLC director without an applied electric field. The maximum rotation angle of the polarizing direction reached nearly 90° at the applied voltage of 200 V (root-mean-square value) across the 230 μm wide slit. The degree of polarization declined from 1 at zero voltage, and after reaching the minimum rose with the field strength. The lasing spectrum consists of sharp spikes corresponding to the resonant modes for all the applied voltages. The mechanisms responsible for electrically tuning the polarization of the RL were discussed. Optimizing the voltage characteristic of the polarization tunability was suggested by the preliminary experimental results.

Thermal treatment effect on the random lasing polarization of polymer optical fiber

Influences of annealing process on silica optical fiber have been widely reported, while the thermal treatment effect on polymer optical fiber is still given less concern. In order to explore the application of polymer fiber random laser in magneto-optic effect, in this paper, polymer optical fibers doped with ferromagnetic nanoparticles and laser dye were fabricated. Polarization is a key parameter in magneto-optic effect, while the polarization degree of random laser may be affected or even degraded in thermal environment, so the effect of thermal treatment on polarization degree of random polymer optical fiber laser was verified. Anisotropic scattering leads to random lasing emission with high polarization degree. Experimental results show that the average polarization degree is up to 0.88 before the thermal treatment. The polarization degree remains high and increases to 0.99 after annealing, which indicates that random lasers with stable and high polarization degree have been realized.

Low-latency deep-reinforcement learning algorithm for ultrafast fiber lasers

The application of machine learning to the field of ultrafast photonics is becoming more and more extensive. In this paper, for the automatic mode-locked operation in a saturable absorber-based ultrafast fiber laser (UFL), a deep-reinforcement learning algorithm with low latency is proposed and implemented. The algorithm contains two actor neural networks providing strategies to modify the intracavity lasing polarization state and two critic neural networks evaluating the effect of the actor networks. With this algorithm, a stable fundamental mode-locked (FML) state of the UFL is demonstrated. To guarantee its effectiveness and robustness, two experiments are put forward. As for effectiveness, one experiment verifies the performance of the trained network model by applying it to recover the mode-locked state with environmental vibrations, which mimics the condition that the UFL loses the mode-locked state quickly. As for robustness, the other experiment, at first, builds a database with UFL at different temperatures. It then trains the model and tests its performance. The results show that the average mode-locked recovery time of the trained network model is 1.948 s. As far as we know, it is 62.8% of the fastest average mode-locked recovery time in the existing work. At different temperatures, the trained network model can also recover the mode-locked state of the UFL in a short time. Remote algorithm training and automatic mode-locked control are proved in this work, laying the foundation for long-distance maintenance and centralized control of UFLs.

Inducing lasing in organic materials with low optical gain by three-dimensional plasmonic nanocavity arrays.

Lasing in organic media with very low gain has been pursued for a long time in optoelectronics. Here, we experimentally demonstrate that plasmonic lasing in the visible regime at room temperature can be achieved by hybridizing active media of very low optical gain such as ionic liquid and polymethylmethacrylate with three-dimensional (3D) plasmonic metamaterials. The 3D nanostructure consists of a double-layer N-shaped silver wire-hole array with strongly coupled multiple hot spots densely packed in each unit cell. These hot spots overlap perfectly with the gain media, allowing efficient gain-plasmon coupling in subwavelength volumes. The periodic arrangement of hot spots, as the metal and dielectric are distributed in an alternate manner along both transverse and vertical directions, results in ultrastrong suppression of scattering losses. In addition, the lasing characteristics, including threshold, intensity and polarization can be controlled by the lattice constant and geometry of metamaterials. Such a plasmonic nanolaser proves to be of low threshold and low gain requirement, providing an essential step towards easy-processing organic based optoelectronics.

Lasing Polarization Characteristics in 1.55- $\mu \text{m}$ Spin-Injected VCSELs

Circular polarization characteristics in vertical-cavity surface-emitting lasers (VCSELs) with InAlGaAs quantum wells injected by spin-polarized electrons were investigated. A degree of circular polarization of 10% was obtained in a reduced birefringence VCSEL at a lasing wavelength of 1544 nm at room temperature under optical pumping of spin-polarized electrons. Strong birefringence originally introduced to stabilize the lasing polarization was confirmed to be undesirable for a high degree of circular polarization in spin-injected VCSELs. A spin-flip rate equation analysis fairly reproduced the experimental results and supported our conclusions.

Polarization-dependent coupling between a polarization-independent high-index-contrast subwavelength grating and waveguides

We investigated the optical coupling between a polarization-independent high-index-contrast subwavelength grating (HCG) and two orthogonal in-plane waveguides. We fabricated the HCG with waveguides on a silicon-on-insulator substrate and demonstrated that a waveguide with a strong output is switched by changing the polarization of light injected into the HCG. The light coupled more strongly to the waveguide in the direction perpendicular to the polarization of the incident light than to that in the parallel direction. If this waveguide-coupled HCG is incorporated into a polarization bistable vertical-cavity surface-emitting laser (VCSEL), the output waveguide can be switched by changing the lasing polarization of the VCSEL.

Lasing in optimized two-dimensional iron-nail-shaped rod photonic crystals

We demonstrated lasing at the Γ-point band-edge (BE) modes in optimized two-dimensional iron-nail-shaped rod photonic crystals by optical pulse pumping at room temperature. As the radius of the rod increased quadratically toward the edge of the pattern, the quality factor of the Γ-point BE mode increased up to three times, and the modal volume decreased to 56% compared with the values of the original Γ-point BE mode because of the reduction of the optical loss in the horizontal direction. Single-mode lasing from an optimized iron-nail-shaped rod array with an InGaAsP multiple quantum well embedded in the nail heads was observed at a low threshold pump power of 160 μW. Real-image-based numerical simulations showed that the lasing actions originated from the optimized Γ-point BE mode and agreed well with the measurement results, including the lasing polarization, wavelength, and near-field image.

Study of the Characteristics of a Laser Based on the Cr2+−Ion Doped ZnS Polycrystal Obtained by the Method of Chemical Vapor Deposition

We study the lasing characteristics of the Cr2+:ZnS-crystal laser pumped by the pulsed-periodic Tm3+:YLF laser, as well as the lasing polarization properties. The Cr2+:ZnS sample was obtained by chemical vapor deposition of zinc sulfide doped by the chrome ions in the hightemperature isostatic processing. Total efficiency of the pump-power conversion to lasing power at a level of 33% was reached, which corresponds to a laser differential efficiency of about 55% in terms of the absorbed power.

Photochromic Composite for Random Lasing Based on Porous Polypropylene Infiltrated with Azobenzene-Containing Liquid Crystalline Mixture.

We report on a new low-cost and easily fabricated type of liquid crystalline polymer composites demonstrating low threshold random lasing, which can be used as a cheap and simple mirror-less laser source. The composite is based on mass-producible commercially available porous polypropylene (Celgard 2500) infiltrated with low-molar-mass liquid crystal material doped with Rhodamine 800 laser dye. Excitation with red nanosecond laser (630 nm) induces random lasing with the emission peak in NIR spectral range (804 nm) with noticeable degree of linear polarization. The possibility to control the lasing threshold and polarization of the output light with UV radiation through photoswitching of liquid crystal phase from nematic to isotropic is demonstrated. The photocontrollable phase switching is achieved by reversible E/Z isomerization of the azobenzene dopant introduced to the nematic host matrix. It is revealed that the isotropic state of liquid crystal provides more efficient random lasing with lower threshold due to significant scattering of the ordinary wave.

Polarization of Lasing in ZnO Nanowires#

Polarization of Lasing in <scp>ZnO</scp> Nanowires^#

Plasmonic lasing of nanocavity embedding in metallic nanoantenna array.

Plasmonic nanolasers have ultrahigh lasing thresholds, especially those devices for which all three dimensions are truly subwavelength. Because of a momentum mismatch between the propagating light and localized optical field of the subwavelength nanocavity, poor optical pumping efficiency is another important reason for the ultrahigh threshold but is normally always ignored. On the basis of a cavity-embedded nanoantenna array design, we demonstrate a room-temperature low-threshold plasmonic nanolaser that is robust, reproducible, and easy-to-fabricate using chemical-template lithography. The mode volume of the device is ∼0.22(λ/2n)(3) (here, λ is resonant wavelength and n is the refractive index), and the experimental lasing threshold produced is ∼2.70MW/mm(2). The lasing polarization and the function of nanoantenna array are investigated in detail. Our work provides a new strategy to achieve room-temperature low-threshold plasmonic nanolasers of interest in applications to biological sensoring and information technology.

Exploring lasing modes and polarization characteristics in broad-area square-shaped vertical-cavity surface emitting lasers with frequency detuning

We experimentally explore the polarization characteristics of broad-area square-shaped vertical-cavity surface emitting lasers with the cryogenic cooling to achieve a wide range of frequency detuning. At room temperature the lasing modes are subject to thermal effects and exhibit the phenomenon of polarization switching. For operating temperatures below 260 K, the transverse modes are confirmed to be mainly controlled by the lateral oxide boundary and usually do not display polarization switching. Near the maximum frequency detuning, the lasing modes are well localized on the ray trajectories and display a remarkable frequency-locking phenomenon from single-frequency to multi-frequency operation for the injected current changing from near to far above lasing threshold.

A Research Paper on the Performance Analysis of a Self-Mode Locking High Power Linearly Polarised Fiber Laser

In this research a design for high power linearly polarized all-fiber linear cavity lasers with self-mode-locking is presented, and a new theoretical model based on a Nonlinear Schrodinger Equation (NLSE) is developed and implemented on the MATLAB platform. For the design of cavity, Polarization Maintaining (PM) fibers for both the gain medium and the Fiber Bragg Gratings (FBGs) is implemented. The FBG pairs are used to select the lasing wavelength and polarization. The fiber lasers incorporate specially designed FBGs to achieve an extinction ratio larger than 23 dB. The proposed configuration is based on Non-Linear Polarization (NPR) using PM Yb-doped active fiber and two matching FBGs to form the laser cavity. The combination of nonlinearity, gain, and birefringence in the cavity made the laser generate mode-locked pulses in the picosecond range and with high average output power. Experimental data and numerical simulations of the self-mode-locking fiber laser are presented. Main parameters affecting mode-locked pulses and its envelope are identified. The model proposed here explains the self-mode-locking mechanism and the source of the pulse envelope. In this model, it is proven that self-phase modulation (SPM) plays an essential role in pulse formation and shaping.

GaN-based high contrast grating surface-emitting lasers

GaN-based high contrast grating surface-emitting lasers (HCG SELs) with AlN/GaN distributed Bragg reflectors were reported. The device exhibited a low threshold pumping energy density of about 0.56 mJ/cm2 and the lasing wavelength was at 393.6 nm with a high degree of polarization of 73% at room temperature. The specific lasing mode and polarization characterisitcs agreed well with the theoretical modeling. The low threshold characteristics of our GaN-based HCG SELs faciliated by the Fano resonance can serve as the best candidate in blue surface emitting laser sources.

Square-wave switching in vertical-cavity surface-emitting lasers with polarization-rotated optical feedback: Experiments and simulations

We study experimentally the dynamics of vertical-cavity surface-emitting lasers (VCSELs) with polarization-rotated (PR) optical feedback, such that the natural lasing polarization of a VCSEL is rotated by 90 deg and then is reinjected into the laser. We observe noisy, square-wave-like polarization switchings with periodicity slightly longer than twice the delay time, which degrade to (or alternate with) bursts of irregular oscillations. We present results of simulations that are in good agreement with the observations. The simulations demonstrate that close to threshold the regular switching is very sensitive to noise, while well above threshold is less affected by the noise strength. The frequency splitting between the two polarizations plays a key role in the switching regularity, and we identify wide parameter regions where deterministic and robust switching can be observed.

Circularly polarized lasing over wide wavelength range in spin-controlled (1 1 0) vertical-cavity surface-emitting laser

We investigated the emission wavelength dependence of the lasing polarization in a (110)-oriented vertical-cavity surface-emitting laser (VCSEL) with GaAs/AlGaAs quantum wells under optical spin injection at room temperature. Lasing was observed in the one circularly polarized mode over a wide wavelength range from 838 to 857nm, in which a degree of circular polarization higher than 0.8 was maintained. The optical gain spectrum that contributed to the circularly polarized lasing is discussed based on the optical selection rules and the measured polarization-resolved photoluminescence spectra of the active layers.

Anisotropic polarization of radiation in quantum-confinement whispering-gallery-mode lasers

The polarization of lasing and spontaneous emission from half-disk- and disk-shaped quantum-confinement lasers operating on whispering-gallery modes with wavelengths within 2.18–2.28 μm has been studied. It is established that electric vector E of output radiation is oriented predominantly in the p-n junction plane, which is explained by the fact that radiation is generated due to electron-heavy hole transitions. Modulation of the polarized spontaneous radiation spectra has been observed.

Numerical characterization of transient polarization square-wave switching in two orthogonally coupled VCSELs

We study the dynamics of two vertical-cavity surface-emitting lasers (VCSELs) mutually coupled such that the natural lasing polarization of each laser is rotated by 90 degrees and then is injected into the other laser. Simulations based on the spin-flip model show transient square-wave polarization switchings before a stationary state is reached. The influence of various model parameters on the duration of the stochastic transient time and on the lasers' dynamics in the stationary state is investigated.