Single-mode Semiconductor Lasers Research Articles

High continuous-wave power surface emitting terahertz lasers integrated with multimode interferometer

Distributed feedback (DFB) surface emitting semiconductor laser realizes power extraction by periodic photonic heterostructure. A direct method to increase the output power is scaling up the area of active region, however, the length of the device is restricted by the coupling strength of the DFB grating. Herein we develop a high-power single-mode surface emitting scheme by monolithically integrating second-order DFB terahertz quantum cascade laser and a multimode interferometer, which can significantly enhance the optical power by increasing photon density and altering field distribution in the grating region. Application of this concept leads to high continuous-wave (CW) surface emitting power of 55 mW, with single-lobed far-field pattern and single-mode operation at about 3.9 THz, which is among the best reported results. Such an integrated scheme can be combined with any one-dimensional photonic heterostructure, which has great potential in further improving the pulsed and CW output power of single-mode semiconductor lasers.

Advances in Semiconductor Lasers Based on Parity-Time Symmetry.

Semiconductor lasers, characterized by their high efficiency, small size, low weight, rich wavelength options, and direct electrical drive, have found widespread application in many fields, including military defense, medical aesthetics, industrial processing, and aerospace. The mode characteristics of lasers directly affect their output performance, including output power, beam quality, and spectral linewidth. Therefore, semiconductor lasers with high output power and beam quality are at the forefront of international research in semiconductor laser science. The novel parity-time (PT) symmetry mode-control method provides the ability to selectively modulate longitudinal modes to improve the spectral characteristics of lasers. Recently, it has gathered much attention for transverse modulation, enabling the output of fundamental transverse modes and improving the beam quality of lasers. This study begins with the basic principles of PT symmetry and provides a detailed introduction to the technical solutions and recent developments in single-mode semiconductor lasers based on PT symmetry. We categorize the different modulation methods, analyze their structures, and highlight their performance characteristics. Finally, this paper summarizes the research progress in PT-symmetric lasers and provides prospects for future development.

High-power and high-beam-quality photonic-crystal surface-emitting lasers: a tutorial

Realization of single-mode, high-power and high-beam-quality (namely, high-brightness) semiconductor lasers, which can rival or even replace bulky lasers such as gas, solid, and fiber lasers, is one of the ultimate goals of laser physics and photonics. The demand for such ultimate single-mode high-brightness semiconductor lasers is increasing for a wide variety of emerging applications including next-generation remote sensing for smart mobility and high-precision laser processing for smart manufacturing. Photonic-crystal surface-emitting lasers (PCSELs) show promise to meet these demands, based on their broad-area coherent two-dimensional (2D) resonance at a singularity (Γ) point of their 2D photonic band structure. In this tutorial paper, the lasing principle, theoretical analysis, and experimental demonstration of PCSELs are described. Recent progress in PCSEL development, including the formulation of a design guideline for realizing 100-W-to-kW-class single-mode operation, the experimental demonstration of a brightness of 1 GW cm–2 sr–1, and an extension of the lasing wavelengths to telecommunication and mid-infrared wavelengths are also covered.

High single-mode selectivity V-cavity tunable semiconductor laser based on GaAs

With the progress of integrated optoelectronic devices over recent decades, the semiconductor research has increasingly focused on tunable semiconductor lasers featuring a compact structure and simplified fabrication. In this manuscript, we present a proposal for a V-Cavity tunable semiconductor Laser (VCL) at a center wavelength of 940 nm. The theoretical analysis encompasses the threshold conditions of the laser, considering various cavity length differences within the waveguide layer structure. Moreover, we showcase a VCL with a waveguide width of 3 μm and a channel interval of 0.6 nm. Through the optimization of polynomial parameters associated with the curved waveguide, the VCL attains a transmittance exceeding 99.4 %. Additionally, we address the determination of optimal parameter ranges and solve the optical field distribution within the half-wave coupler. The simulation results exhibit that the half-wave coupler, employing optimized parameters, achieves remarkable single-mode selectivity when operating at a central wavelength of 940 nm. Notably, a maximum side mode suppression ratio (SMSR) of 47.9 dB is attainable with a half-wave coupler length of 45 μm and a waveguide gap of 1.7 μm.

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.

Development of small form factor packaged single-mode semiconductor laser for spectroscopic applications at 689 nm

We report on the development of a compact packaged semiconductor laser capable of spectroscopy applications at 689 nm. The key component is an optical isolator that is small enough to fit inside a package that is compatible with standard 14-pin butterfly packages. We present a threshold current of 33 mA, a forward voltage of 2.5 V at 50 mA, long term reliability study for over 12,500 h, a relative intensity noise below −145 dBc/Hz, and a linewidth of 1.4 MHz. The relative intensity noise and the frequency noise spectra verify continuous-wave lasing and frequency stability of the packaged laser.

Effect of Scattering Parameter on Small Signal analysis in Direct Modulated Dynamic Semiconductor Lasers

Effect of scattering parameter is that the effect which it is effected on the operating characteristics of direct modulated semiconductor lasers by small signal analysis for injection current density , where this parameter is effected on amount of quantum confinement carriers density where the part of this carriers density is lost in the active region. The scattering parameter leads to appear the nonlinear gain effects which they are reduced the response frequency of the direct modulation process. We use the rate equations of the single-mode semiconductor lasers and that they have characteristics are used to continuous-wave small-signal modulation. We can presented this effect and discussion it by the simple two-port device.

Independent Control of Mode Selection and Power Extraction in Terahertz Semiconductor Lasers

Mode selection and power extraction are the core of single-mode semiconductor lasers, but generally, they restrict each other. A large gain area with high radiation efficiency is necessary for high output power but will induce more competitive modes and increase the threshold gain of the desired mode. Here, we demonstrate a novel laser cavity─an active distributed Bragg reflector (ADBR) and a grating coupler (GC) are monolithically integrated into a laser ridge─enabling independent control of mode selection and power extraction. The ADBR features a reflection peak with an extremely narrow bandwidth that releases the constraint on the cavity length, while the GC provides a controllable high radiation efficiency. The concept is implemented onto terahertz quantum cascade lasers, exhibiting robust single-mode emission with high output power and high operating temperature. Given the universality of the ADBR and GC, our concept can be utilized in different material systems at different wavelengths.

Spontaneous emission rate and phase diffusion in gain-switched laser diodes

Quantum random number generation (QRNG) has become a topic of growing interest in recent years due to important applications in cryptography and simulations. Interferometric detection of phase diffusion in gain-switched single-mode semiconductor lasers is one of the main generation techniques. In this paper, we study experimentally and theoretically the phase diffusion in gain-switched discrete mode laser diodes. We derive a stochastic rate equations model for the laser electric field that avoids numerical instabilities that appear when simulating amplitude and phase equations. Measurements are performed in order to extract the parameters of our semiconductor laser. Spontaneous emission rate coupled into the lasing mode is measured as a function of the carrier number for bias currents below threshold. A quadratic dependence is obtained that permits us to evaluate the validity of the linear approximations that have been used to describe laser phase diffusion in QRNG. The good agreement between experiments and theory permits us to give a realistic quantitative description of the dynamical evolution of the phase statistics in this type of QRNGs.

High-Resolution Simulation of Externally Injected Lasers Revealing a Large Regime of Noise-Induced Chaos

We present comprehensive numerically simulated scans of the spectral evolution of the output from a single-mode semiconductor laser diode undergoing external light injection. The spectral scans are helpful to understand the different regimes of operation as well as the system evolution between each state: i.e., locked state, four-wave mixing, pulsations, chaos. We find that, when under strong injection, when the injected power equals about half of the laser power, two distinct regions of chaotic behaviour are observed. One of the chaotic regions arises due to the usual period-doubling route to chaos; the other chaotic region is a blurring of what would be higher-order period pulsations whose periodicity is broken by spontaneous emission and the laser spectrum is chaotic. Eliminating spontaneous emission in our simulations confirms the latter chaotic region becomes a region with higher-order pulsations.

Nonlinear Dynamics of a Single-Mode Semiconductor Laser with Long Delayed Optical Feedback: A Modern Experimental Characterization Approach

Semiconductor lasers can exhibit complex dynamical behavior in the presence of external perturbations. Delayed optical feedback, re-injecting part of the emitted light back into the laser cavity, in particular, can destabilize the laser’s emission. We focus on the emission properties of a semiconductor laser subject to such optical feedback, where the delay of the light re-injection is large compared to the relaxation oscillations period. We present an overview of the main dynamical features that emerge in semiconductor lasers subject to delayed optical feedback, emphasizing how to experimentally characterize these features using intensity and high-resolution optical spectra measurements. The characterization of the system requires the experimentalist to be able to simultaneously measure multiple time scales that can be up to six orders of magnitude apart, from the picosecond to the microsecond range. We highlight some experimental observations that are particularly interesting from the fundamental point of view and, moreover, provide opportunities for future photonic applications.

Phase diffusion in gain-switched semiconductor lasers for quantum random number generation.

In this paper, we report a theoretical and experimental study of the phase diffusion in a gain-switched single-mode semiconductor laser. Our modelling includes nonlinear dependencies of the carrier recombination rate and the semiconductor material gain on the carrier number. Also a comparison with the results obtained with linear models is performed. We focus on the below threshold operation, that is, the regime where most of the phase diffusion occurs in quantum random number generators based on the above mentioned system. Using the extracted parameters for our laser and simple analytical expressions for the laser linewidth, we show that logarithmic material gain and cubic carrier recombination dependence on the carrier number must be considered for a good agreement between experiments and theory. In this way we show that consideration of these nonlinearities is essential for obtaining a good quantitative description of the phase diffusion when using rate equations modelling.

High-power single-mode triple-ridge waveguide semiconductor laser based on supersymmetry

To achieve a high-power single-transverse mode laser, we here propose a supersymmetry-based triple-ridge waveguide semiconductor laser structure, which is composed of an electrically pumped main broad-ridge waveguide located in the middle and a pair of lossy auxiliary partner waveguides. The auxiliary partner waveguides are designed to provide dissipative modes that can phase match and couple with the higher-order modes in the main waveguide. By appropriately manipulating the gain–loss discrimination of the modes in the laser cavity, one can effectively suppress all the undesired higher-order transverse modes while keeping the fundamental one almost unaffected, thereby ensuring stable single-mode operation with a larger emitting aperture and accordingly a higher output power than a conventional single-transverse-mode ridge waveguide diode laser.

STUDY OF DIRECT LASER RECORDING OF MICRO-RELIEF ON A TWO-LAYER a-Si/Ag STRUCTURE

This paper presents the results of direct laser recording on a two-layer amorphous silicon / silver structure deposited on a glass substrate by magnetron sputtering. The absorption spectra of a-Si films of various thicknesses and a glass substrate are investigated. A method is proposed for direct laser recording of microstructures by focused radiation of a single-mode semiconductor laser with a wavelength of λ = 405 nm on a two-layer a-Si / Ag medium from the side of a glass substrate. The formation of the micro relief is studied during direct recording by semiconductor laser pulses with λ = 405 nm on the a-Si layer. Parameters of two-layer structure a-Si / Ag for direct laser recording are optimized.

A Directly Modulated Laterally Coupled Distributed Feedback Laser Array Based on SiO2 Planarization Process

Low-cost and high-speed single-mode semiconductor lasers are increasingly required as wide-band access fiber communication expands in recent years. Here, a high-speed laterally coupled distributed feedback (LC-DFB) laser array is achieved based on a SiO2 planarization process. The device exhibits low threshold currents of about 12 mA and high slope efficiencies over 0.26 W/A. Stable single mode operation and high-speed performance are realized with side mode suppression ratios (SMSR) over 45 dB, and 3-dBe bandwidths exceed 14 GHz for all four channels. Such a high-speed and process simple LC-DFB laser array shows great potential to the low-cost fiber communication networks.

Dirac-vortex topological cavities.

Cavity design is crucial for single-mode semiconductor lasers such as the ubiquitous distributed feedback and vertical-cavity surface-emitting lasers. By recognizing that both of these optical resonators feature a single mid-gap mode localized at a topological defect in the one-dimensional lattice, we upgrade this topological cavity design concept into two dimensions using a honeycomb photonic crystal with a vortex Dirac gap by applying the generalized Kekulé modulations. We theoretically predict and experimentally show on a silicon-on-insulator platform that the Dirac-vortex cavities have scalable mode areas, arbitrary mode degeneracies, vector-beam vertical emission and compatibility with high-index substrates. Moreover, we demonstrate the unprecedentedly large free spectral range, which defies the universal inverse relation between resonance spacing and resonator size. We believe that our topological micro-resonator will be especially useful in applications where single-mode behaviour is required over a large area, such as the photonic-crystal surface-emitting laser.

Reconstruction of parameters and unobserved variables of a semiconductor laser with optical feedback from intensity time series

We propose a method for the reconstruction of time-delayed feedback systems having unobserved variables from scalar time series. The method is based on the modified initial condition approach, which allows one to significantly reduce the number of starting guesses for an unobserved variable with a time delay. The proposed method is applied to the reconstruction of the Lang-Kobayashi equations, which describe the dynamics of a single-mode semiconductor laser with external optical feedback. We consider the case where only the time series of laser intensity is observable and the other two variables of the model are hidden. The dependence of the quality of the system reconstruction on the accuracy of assignment of starting guesses for unobserved variables and unknown laser parameters is studied. The method could be used for testing the security of information transmission in laser-based chaotic communication systems.

Reconstruction of Systems with Delays and Hidden Variables

We propose a method for reconstruction of dynamical systems with delayed feedback, which have several hidden variables including a hidden variable with a time delay. The method is based on the original approach allowing one to significantly reduce the number of the starting guesses for a hidden variable with a delay. The method is used for reconstructing the model system of the Lang–Kobayashi equations, which describes the dynamics of a single-mode semiconductor laser with time-delayed feedback, using periodic and chaotic time series. The dependence of the systemreconstruction quality on the accuracy of specifying the starting guesses for unknown parameters and hidden variables is studied.

Динамика двух лазеров, связанных взаимной модуляцией добротности

В приближении скоростных уравнений построена математическая модель синхронизации двух одномодовых полупроводниковых лазеров. Модель представляет собой систему нелинейных обыкновенных дифференциальных уравнений для концентраций электронов и плотностей фотонов в обоих лазерах. Особенность модели состоит в характере связи между лазерами — она устроена так, что удельные потери каждого лазера пропорциональны интенсивности излучения другого. Помимо того, в уравнениях учитываются нелинейные (квадратичные) потери излучения. Система исследована методами теории бифуркаций и многих масштабов. Показано, что модель проявляет различное поведениепри сильной и слабой связи между лазерами. При сильной связи в системе нет колебаний, и в то же время возможны бистабильность и гистерезис. При слабой связи в системе возможно возникновение предельного цикла и пичковых релаксационных колебаний. Выявлено, что синхронные колебания плотности фотонов в лазерах происходят в антифазе. Сделан вывод о возможности применения предложенной схемы синхронизации для получения длиннопериодических осцилляций.

Parity–Time Symmetry in Bidirectionally Coupled Semiconductor Lasers

We report on the numerical analysis of intensity dynamics of a pair of mutually coupled, single-mode semiconductor lasers that are operated in a configuration that leads to features reminiscent of parity–time symmetry. Starting from the rate equations for the intracavity electric fields of the two lasers and the rate equations for carrier inversions, we show how these equations reduce to a simple 2 × 2 effective Hamiltonian that is identical to that of a typical parity–time (PT)-symmetric dimer. After establishing that a pair of coupled semiconductor lasers could be PT-symmetric, we solve the full set of rate equations and show that despite complicating factors like gain saturation and nonlinearities, the rate equation model predicts intensity dynamics that are akin to those in a PT-symmetric system. The article describes some of the advantages of using semiconductor lasers to realize a PT-symmetric system and concludes with some possible directions for future work on this system.