Two-mode Laser Research Articles

Dynamics of two-mode laser light beams coupled to vacuum reservoir

Dynamics of two-mode laser light beams coupled to vacuum reservoir

Tracing the origins of mode coupling for beam quality optimization in high-power fiber laser delivery systems

Abstract Suppressing mode degradation is the key issue for high-power laser delivery; however, diagnosing mode degradation in its entirety, ranging from the contents and origins to locations, has always been a major obstacle. Here, a versatile approach for tracing the origins of mode coupling is demonstrated through addressing the differential intermodal dispersions of fiber modes. Full recognition for modal contents and the origins of mode degradation are experimentally completed in a two-mode fiber laser delivery system, which assists a significant improvement of beam quality M2 from 1.35 to 1.15 at the highest power of over 300 W. This method yields a quantitative characterization for manipulating the individual mode of dual-mode coupling origins or their combinations. This work points toward a promising strategy for the online tracing of mode coupling in cascade fiber links, thus enabling further pursuit of seeking extreme beam quality in high-power fiber laser systems.

Single-mode quasi PT-symmetric laser with high power emission

Large-area lasers are practical for generating high output powers. However, this often comes at the expense of lower beam quality due to the introduction of higher-order modes. Here, we experimentally demonstrate a new type of electrically pumped, large-area edge-emitting lasers that exhibit a high power emission (∼0.4 W) and a high-quality beam (M2∼1.25). These favorable operational characteristics are enabled by establishing a quasi PT-symmetry between the second-order mode of a large area two-mode laser cavity and that of a single-mode auxiliary partner cavity, i.e., by implementing a partial isospectrality between the two coupled cavities. This in turn enlarges the effective volume of the higher-order modes. As a result, a selective pump applied via current injection into the main laser cavity can provide a stronger modal gain to the fundamental mode, and thus lead to lasing in the single mode regime after filtering out higher order transverse modes. The reported experimental results confirm this intuitive picture and are in good agreement with both theoretical and numerical analysis. Above all, the employed material platform and fabrication process are compatible with the industrial standards of semiconductor lasers. This work provides the first clear demonstration, beyond previous proof-of-concept studies, of the utility of PT-symmetry in building laser geometries with enhanced performance and, at the same time, useful output power levels and emission characteristics.

Inside Front Cover: Observation of Robust Polarization Squeezing via the Kerr Nonlinearity in an Optical Fiber (Adv. Quantum Technol. 3/2023)

The cover shows the evolution of the state of the light field represented on the Poincaré sphere (green) due to the nonlinear Kerr interaction described in article number 2200143 by Nikolay Kalinin, Gerd Leuchs, and co-workers. The quantum uncertainty of the initial coherent two-mode laser field is the small grey sphere on the larger Poincaré sphere which develops into the orange squeezed ellipsoid.

Effects of thermal fluctuation when an optical cavity possesses neutral atoms and a two-mode laser system

Quantum-based experiments and their applications in lasers and magnetic fields have long been paramount, yet how to achieve exact stability for a long time is a merely answered question. This article develops a coupled laser map with cavity loss via a one-dimensional laser map, where complex phenomena in the newly developed mathematical model, dynamical properties with coupling delay, and thermal fluctuation of the lasing system are discussed numerically and analytically. It is deduced that the intensity of the laser beam can be controlled and stabilized for a long time, and large values of the effective gain coefficient can be reached when thermal noise exists in the optical cavity and when a nonlinear feedback loop is provided with coupling delay. Utilizing noise and coupling delay as a nonlinear feedback loop to the coupled laser map, we observed non-autonomous behaviour at different growth rate values. In contrast, symmetrical and phase-entrained synchronized mirror imaged orthogonal strange attractors and fractals were seen at the same growth rate values. At specific values of the controlling parameters, the peculiar attractors experience cyclic collisions with their basin boundaries, which break symmetry and synchronization and cause irregular behaviour.

Effects of Thermal Fluctuation When an Optical Cavity Possesses Neutral Atoms and a Two-Mode Laser System

Effects of Thermal Fluctuation When an Optical Cavity Possesses Neutral Atoms and a Two-Mode Laser System

Quantum Entanglement and its Quantification in a Two-Mode Cascade Laser

In this paper, quantum entanglement of correlated two-mode light generated by a three-level laser coupled to a two-mode squeezed vacuum reservoir is thoroughly analyzed using different inseparability criteria, using the master equation, we obtain the stochastic dierential equation and the correlation properties of the noise forces associated with the normal ordering. Next, we study the photon entanglement by considering different inseparability criteria. In particular, the criteria applied are Duan-Giedke-Cirac-Zoller (DGCZ) criterion, logarithmic negativity, Hillery-Zubairy, and Cauchy-Schwartz inequality and we found that the presence of the squeezing parameter leads to an increase in the degree of entanglement. Moreover, the linear gain coecient significantly achieved the degree of entanglement for the cavity radiation

Enhanced Squeezing and Entanglement in Nondegenerate Three-Level Laser Coupled to Squeezed Vacuum Reservoir

Squeezing and entanglement of a two-mode cascade laser, produced by a three-level atom which is initially prepared by a coherent superposition of the top and bottom levels then injected into a cavity coupled to a two-mode squeezed vacuum reservoir is discussed. I obtain stochastic differential equations associated with the normal ordering using the pertinent master equation. Making use of the solutions of the resulting differential equations, we determined the mean photon number for the cavity mode and their correlation, EPR variables, smallest eigenvalue of the symplectic matrix, intensity difference fluctuation, and photon number correlation. It is found that the squeezed vacuum reservoir increases the degree of the statistical and nonclassical features of light produced by the system. Furthermore, using the criteria developed by logarithm negativity and Hillery-Zubairy criteria, the quantum entanglement of the cavity mode is quantified. It is found that the degree of the entanglement for the system under consideration increases with the squeezing parameter of the squeezed vacuum reservoir.

Electrically Pumped Two-Mode Laser Dynamics

The statistical and squeezing properties of the cavity light produced by a three-level laser are studied. In the laser, N three-level atoms in an open cavity are coupled with a two-mode vacuum reservoir and are pumped to the top level by means of the electron bombardment. Applying the steady-state solutions of the equations of evolution of the expectation values of the atomic operators and the quantum Langevin equations for the cavity mode operators, we have obtained the global and local photon statistics for single-mode cavity light beams and for two-mode cavity light. It is found that the global mean photon number and the global photon-number variance of the light emitted from the top are greater than those for the light emitted from intermediate level. The cavity lights emitted from the top and intermediate levels can be separately in a chaotic state under certain conditions. However, the two-mode cavity light is in a squeezed state under certain conditions. We have established that the maximum quadrature squeezing of the two-mode cavity light to be about 46% below the coherent-state level. The presence of the vacuum reservoir noise has the effect of increasing the photon-number variance and decreasing the quadrature squeezing of the cavity light but has no effect on the mean photon number. We have shown that the local mean photon number and photon number variance of the cavity light approach the global mean photon number and photon number variance of the cavity light as the frequency interval increases.

Generation of entanglement from a two-mode cascade laser

We analyse the entanglement of the light produced by a three-level laser whose cavity contains a parametric amplifier, with the cavity mode driven by the coherent light and coupled to a squeezed vacuum reservoir. Employing stochastic differential equations associated with the normal ordering resulted from the pertinent master equation, the quadrature variances and entanglement of the two-mode light are obtained and photon statistics of the two-light modes is discussed. It is found that the three-level laser generates squeezed light under certain conditions, with maximum intracavity squeezing being 89.7% below the coherent state level. We also show that the parametric amplifier enhances the mean photon number and photon number correlation.

Numerical investigation of relative intensity noise in frequency-doubled multimode fiber lasers

In this paper, we study the intensity noise performance of frequency-doubled lasers. In particular, we investigate how the relative intensity noise (RIN) of multimode fiber lasers is affected by the second harmonic generation process. We first develop an analytical approach and show that, in contrast with a single-mode laser, the low frequency RIN (or excess noise) of a two-mode laser can increase of more than 6 dB after the frequency-doubling operation. This occurs when the intensities of both modes are different and this is explained by a nonlinear coupling between noise and intensity of modes. To deal with more commonly-used multimode fiber lasers, we have extended our study to any number of modes. For this purpose, we have developed a model to numerically simulate the dynamics of a multimode fiber laser. This model includes noise sources and mode competition dynamics due to spatial hole burning. It gives access to the complex amplitude of the electric field of the laser. Using this model, we have confirmed that the excess noise of frequency-doubled multimode fiber lasers can be more than 6 dB higher than the excess noise of the laser before frequency-doubling.

Formation and Evolution of Soliton in Two-Mode Fiber Laser

High-order mode fiber lasers are gathering the rising attentions from fundamental researches to practical applications due to their distinctive spatial and temporal properties. Here, we demonstrate a carbon nanotube mode-locked two-mode fiber laser and investigate the formation and evolution process of the soliton based on the time-stretch dispersive Fourier transform method. Stable single pulse and bound-state pulses are observed at pump powers of 32.0 and 41.3 mW, respectively. Attributing to the coexistence of fundamental mode and first group high-order modes, the optical spectrum exhibits slight intensity modulations and the autocorrelation trace shows additional small side lobes. Similar to that of single-mode fiber lasers, the buildup process of soliton includes the relaxation oscillation, beating behavior, and stable mode-locking state. However, owing to the interplay between two transverse modes in the two-mode fiber laser, the duration and fluctuation intensity of the relaxation oscillation are much larger than that of single-mode fiber lasers.

Influence of time-dependent losses on operation of two-mode random laser

In this paper, we investigated the influence of time-dependent losing coefficient on the characteristics of the laser mode by solving the rate equations system which describe the variation in photon density of two-mode random laser. The results showed that when the losing coefficient depends on the time of the characteristics of the modes such as the photon density, the time to reach the maximum value of the photon density and the pulse duration of the emitting mode were changed. The received results give us more knowledge about the influence of time-dependent losses on the operation of the two-mode random laser.

Исследование аномальной генерации вертикально-излучающих лазеров спектрального диапазона 850 nm с двойной оксидной токовой апертурой при большой величине спектральной расстройки

The static characteristics of 850 nm-range vertical-cavity surface-emitting lasers (VCSEL) based on strained InGaAs/AlGaAs quantum wells were studied in the wide range of oxide current aperture sizes and the origins of their anomalous behavior at large gain-to-cavity detuning was analyzed. The higher-order modes localized at the periphery of the oxide current aperture can appear in the studied VCSELs due to the lateral carrier spreading in the quantum wells and the specific profile of the oxide aperture (leading to the formation of a two-stage effective waveguide). Inhomogeneous carrier injection over the current aperture area in wide-aperture lasers leads anomalous start of lasing via high-order transverse modes, and the subsequent transition to the classical lasing via low-order modes with an increase in the current is due to a change of the gain-to-cavity detuning with an increase in the internal laser temperature. Anomalous lasing via higher-order modes in the case of narrow-aperture VCSELs becomes possible due to the increase in diffraction losses at the edge of the oxide current aperture for the fundamental mode, while the subsequent switching to the two-mode lasing is due to not only a decrease in the gain-to-cavity detuning, but also the thermal lens effect.

Modulational instability and soliton trains in a model for two-mode fiber ring lasers

A model of orthogonally polarized two-field fiber ring laser with a linear gain is considered, with emphasis on the continuous-wave stability and the existence of soliton trains. The continuous-wave stability analysis is carried out within the framework of the modulational-instability approach, the variations of the gain spectrum with the modulation frequency and characteristic parameters of the model give rise to a rich variety of stability features including single-band and multiband stability regions. Seeking for pulse structures of the model, the two coupled cubic complex Ginzburg–Landau equations describing individual mode propagations are transformed into a set of coupled, first-order nonlinear ordinary-differential equations for the amplitudes and phases of the two modes. Numerical simulations of the last set of coupled equations indicate that in the anomalous dispersion regime, envelopes of the two fields are periodic trains of pulses the amplitudes of which are affected by the linear gain.

Experimental Investigation of Lasing Modes in Double-Lattice Photonic-Crystal Resonators and Introduction of In-Plane Heterostructures

Photonic-crystal surface-emitting lasers (PCSELs) are attractive for a wide range of applications such as material processing and remote sensing owing to their advantage of broad-area coherent lasing supported by a 2-D photonic crystal. Recently, we proposed double-lattice photonic-crystal resonators and achieved 10-W-class high-power and high-beam-quality (namely, high-brightness) operation. To further increase the brightness, it is important to understand the lasing mode behavior of PCSELs in detail. In this article, we experimentally investigate the change in the lasing mode depending on the current injection levels and compare the results with a theoretical analysis that accounts for the change in refractive index and gain distributions due to the current injection. We observed a transition from single-mode lasing to two-mode lasing at high injection currents. We develop a technique for resolving the near-field profiles of individual lasing modes and show that these profiles coincide with theoretical predictions. A comparison of experimental and theoretical results reveals that high-order modes appear due to a bandgap confinement effect induced by a change in the refractive index in the carrier injection area. To effectively remove this confinement effect and suppress the oscillation of high-order modes, we incorporate an in-plane heterostructure into the PCSEL.

The Influence of Wide-Band Frequency Modulation on the Competition of Orthogonally Polarized Modes in a Two-Mode Laser

Competitive interaction of orthogonally polarized modes in a two-mode laser operating in a regime of wide-band frequency modulation has been numerically simulated. This modulation was implemented by means of the corresponding variation of the laser cavity length. Parameters of the active medium adopted in the numerical model were characteristic of He–Ne lasers with an inhomogeneously broadened gain line. It is established that negative consequences of the mode competition can be significantly reduced at certain values of the modulation frequency and frequency deviation.

Improvement of intermodal frequency stability of two-mode HeNe laser

A method of improving intermodal frequency stability of two-mode helium-neon laser has been developed. The approach is based on using in the stabilization circuit a signal processor for real-time analysis of data from an LF amplitude and an HF frequency detector. We propose to use the signal from the LF detector in the initial phase of the stabilization process and the signal from the HF detector afterwards. Experiments proved that with the suggested design it is possible to obtain frequency stability of the intermodal frequency better than 100 Hz or 2*10-10 for 1000s averaging. In the paper we also show the influence the intermodal frequency stability on the absolute stability of the laser frequency.

Preservation of Gaussian state entanglement in a quantum beat laser by reservoir engineering

Quantum beat lasers have been considered as sources of entangled radiation in continuous variables such as Gaussian states. In order to preserve entanglement and to minimize entanglement degradation due to the system’s interaction with the surrounding environment, we propose to engineer environment modes through insertion of another system in between the laser resonator and the environment. This makes the environment surrounding the two-mode laser a structured reservoir. It not only enhances the entanglement among two modes of the laser but also preserves the entanglement for sufficiently longer times, a stringent requirement for quantum information processing tasks.

Cavity-induced mirror-mirror entanglement in a single-atom Raman laser

We address an experimental scheme to analyze the optical bistability and the entanglement of two movable mirrors coupled to a two-mode laser inside a doubly resonant cavity. With this aim we investigate the master equations of the atom-cavity subsystem in conjunction with the quantum Langevin equations that describe the interaction of the mirror cavity. The parametric amplification-type coupling induced by the two-photon coherence on the optical bistability of the intracavity mean photon numbers is found and investigated. Under this condition, the optical intensities exhibit bistability for all large values of cavity laser detuning. We also provide numerical evidence for the generation of strong entanglement between the movable mirrors and show that it is robust against environmental thermalization.