Semiconductor Laser Arrays Research Articles

Optimal Design and Analysis of Wide-Band Near-Infrared Hybrid Dielectric Gratings with High Transmission Efficiency

Since surface relief transmission gratings have very strict requirements on operators and use environment, according to the semiconductor laser external cavity spectral beam combining system, this paper proposes a design scheme for a semiconductor laser array spectral beam combining system based on the grating-external cavity. The finite element approach was used to create a wideband, high-efficiency fill-in multilayer dielectric transmission grating structure for a high-power spectrum beam combining system. The incidence angle, ridge height, duty cycle, and sidewall inclination angle of the transmission grating were tuned and evaluated, and a link between the transmission grating’s diffraction efficiency and grating characteristics was discovered. The calculated design of the high-power fused silica transmission grating has a negative first-order peak diffraction efficiency of 99.5% in the 800 nm range. In the spectral region of 765–872 nm, the transmission grating’s diffraction effectiveness exceeds 92%. The filled ultra-high diffraction efficiency multilayer dielectric transmission grating design addresses the issue of resistance to high-power lasers under complicated operating settings. It is intended to maintain a high diffraction efficiency even after several cleaning cycles, and it is an ideal component for high-power spectrum beam combining systems.

Coupling multi-beam laser diode to multimode fiber by wedge prism combiner

For high-power fiber-lasers, high power and high brightness have always been the goals pursued in the field of industry and defense. Based on the beam propagation principle, a novel lens combination of right-angle prisms and trapezoidal prisms is designed to realize the homogenized alignment of two rows of semiconductor laser array spots. The beam propagation and coupling efficiency of the system are analysed in detail using numerical analysis and ZEMAX, respectively. The results show that the output power of the fiber-laser reaches 620.9 W at 35 A current with 86.24 % coupling efficiency, which matches the simulation result of 89.65 %. Furthermore, the effects of the variations of different degrees of freedom of the optical elements on the coupling efficiency, such as angle and displacement, are further analysed to provide a reliable basis for the development of coupling devices.

Spectral analysis of beam-combining-systems based on laser array with smile effect

The smile effect in semiconductor laser arrays can cause spectral deterioration in spectral beam combining (SBC) systems. We analyze this effect using position error and pointing deviation and propose a coupled-cavity resonance model based on the external-cavity optical feedback and the multibeam interference theory to study locked spectra. Our results indicate that the central emitter exhibits excellent spectral purity, and the edge emitters show side peaks and a decrease in peak intensity. With the increase in the position error and pointing deviation, the emitters experience an obvious spectral shift and an expansion of the spectral width. Pointing deviation has a greater impact on wavelength locking and array spectral width than position errors. Increasing the focal length and incident angle can reduce shifts and spectral width. Furthermore, adopting a grating with a large line density can also decrease its center wavelength shift and compress the spectral width of the combined beam.

Improvement on the topological localized interface enabled by chiral symmetry

Zero-energy topological states, which are protected by chiral symmetry against certain perturbations topologically, localize at interfaces between trivial and non-trivial phases in the Su–Schrieffer–Heeger (SSH) chain model. Here, we propose and demonstrate a method to manipulate chiral symmetry itself to improve the localized interfaces and enlarge the mode volume of topological states in the SSH model, thus optimizing the lasing performance of localized interfaces. As multiple defects corresponding to off-diagonal perturbations in an eigenmatrix are introduced, the topological state expands and extends to extra defects at the topological interface without breaking chiral symmetry. We apply the proposed method in electrical pumping semiconductor laser arrays to verify our theoretical prediction and optimize the output characteristics of the devices. The measured results of the proposed multi-defect SSH laser array show that the output power has been increased by 27%, and the series resistance and far-field divergence have been reduced by half compared to the traditional SSH laser array, establishing a high-performance light source for integrated silicon photonics, infrared light detection and ranging, and so on. Our work demonstrates that the proposed method is capable of improving topological localized interfaces and redistributing zero-energy topological states. Furthermore, our method can be applied to other platforms and inspire optimizations of more devices in broader areas.

Single Transverse-Mode Semiconductor Laser Arrays by Parity-Time Symmetry Breaking

Single Transverse-Mode Semiconductor Laser Arrays by Parity-Time Symmetry Breaking

Narrow linewidth semiconductor multi-wavelength DFB laser array simultaneously self-injection locked to a single microring resonator.

We experimentally demonstrate a narrow linewidth semiconductor multi-wavelength distributed feedback (DFB) laser array by simultaneously injection locking each laser to the corresponding resonance of a single on-chip microring resonator. The white frequency noises of all the DFB lasers is reduced by more than 40 dB once they are simultaneously injection locked to a single microring resonator with a quality factor (Q-factor) of 2.38 million. Correspondingly, the instantaneous linewidths of all the DFB lasers are narrowed by a factor of 104. In addition, frequency combs originating from non-degenerate four-wave mixing (FWM) between the locked DFB lasers are also observed. Simultaneously injection locking multi-wavelength lasers to a single on-chip resonator may enable the possibilities of integrating a narrow-linewidth semiconductor laser array on a single chip and having multiple microcombs in a single resonator, which are in high demand in wavelength division multiplexing coherent optical communication systems and metrological applications.

Electrically driven supersymmetric semiconductor laser arrays with single-lobe far-field patterns.

Semiconductor laser arrays based on the third-order supersymmetric (SUSY) transformation are proposed to increase the mode discrimination between fundamental supermode and high-order supermodes. The distance between the edge waveguide of the main array and that of the superpartners is optimized. Then, the electric field distributions of different modes are also calculated, which show that, except for the fundamental supermode, the high-order supermodes penetrate deeper into the superpartner arrays, which accounts for the increased loss of high-order supermodes. The fabricated third-order SUSY laser array can emit light with a single-lobe far-field pattern under an injection current of 70 mA, which is a promising candidate for optical couplings between lasers and optical elements.

Analysis of physical mechanism of beam crosstalk in semiconductor laser array spectral-beam-combined system

In spectral beam combining systems based on a grating-external cavity, due to some factors such as the “smile” effect of the semiconductor laser array and the error of the optical components in the external cavity, the beam from one emitter transmits into the external cavity and then can return to other emitters, thereby forming beam crosstalk between the two emitters. In this work, in order to investigate the physical mechanism of beam crosstalk and the influence of beam crosstalk on beam properties such as locked spectra and beam combining efficiency, based on the optical feedback semiconductor rate equation, the beam modes that can stably oscillate in the coupling cavity are derived, and the coupling cavity oscillating model is built. With the consideration of the mode competition mechanism in the coupling cavity, the effects of different crosstalk between two emitters with different intervals on the locked spectra are analyzed in detail. The results show that crosstalk leads to the shift of the peak of locked spectrum and the generation of sub-peak. The crosstalk between two closer emitters has a more serious influence on the beam spectrum structure, combined beam spot, and combining efficiency. The combining efficiencies influencing the 1<sup>st</sup>, 2<sup>nd</sup> and 3<sup>rd</sup> crosstalk are 45.5%, 50.2%, and 63.8%, respectively (When there is no crosstalk, the efficiency is 80.1%). Finally, the results of the theoretical analysis are verified experimentally, and the experimentally observed spectra under the influence of crosstalk show phenomena such as peak degradation, peak shift, edge burrs, and side lobes in spectra, which are consistent with the theoretical predictions. Moreover, according to the simulation results and experimental observations, it is found that the crosstalk can be suppressed to a certain extent by increasing the spacing between emitters, and the Galileo telescope system is suggested to suppress crosstalk and optimize the spectral structure and beam combining efficiency. Compared with the Kepler telescope structure, the Galileo telescope does not have a real focal point, which can prevent the local power from being too high, thereby damaging the optical components.

Wideband tunable REC-DFB laser array using thin-film heaters on the submount

A wideband wavelength-tunable 4×5 distributed feedback (DFB) semiconductor laser array based on the reconstruction-equivalent-chirp (REC) technique using a simple tuning scheme is demonstrated. It consists of 20 DFB lasers with 4×5 matrix interleaving distributions, two-level cascaded Y-branch optical combiners, and one active semiconductor optical amplifier (SOA), all in-series integrated on one chip. Unlike the traditional thermal-electric cooler (TEC)-based wavelength-tuning scheme, the tunable 4×5 REC-DFB laser array achieves a faster and broader continuous wavelength-tuning range using TaN thin-film heaters integrated on the AlN submount. By changing the injection current of the TaN resistor from 0 to 190 mA, the proposed tunable laser achieves a wavelength-tuning range of ∼2.5 nm per channel and a total tuning of over 50 nm. This study opens up new avenues for realizing cost-effective and wide-tuning-range semiconductor lasers.

Sub-mm resolution tomographic imaging in turbid media by an ultra-high density multichannel approach.

We demonstrate an ultra-high-density source-detector (SD) diffuse optical tomography system scalable to thousands of combinatorial SD pairs per cm3 of total voxel volume. We demonstrate the imaging of dynamic targets (including phantom arteries) with 100 um resolution at over 10 Hz frame rate within turbid media (> 60 MFP). Further, as a step toward a wearable mobile imager, we introduce monolithic mm-size dense semiconductor laser array chips as sources for potential unobtrusive epidermal tomographic use.

Transverse photonic crystal semiconductor laser arrays

Transverse photonic crystal (TPC) laser arrays are designed by effective index method and transfer matrix method, and fabricated by the process of standard photolithography. The fundamental supermode of the TPC laser array possesses a larger optical confinement factor in the active region than those of high-order supermodes, because the propagation constant of the fundamental supermode lies in the forbidden band of the TPC while all the propagation constants of the high-order supermodes lie in the allowed band of the TPC. Therefore, the fundamental supermode can lase firstly near the threshold when the laser is injected with currents. The fabricated TPC laser achieves a single-lobe horizontal far-field pattern under an injection current of 0.3 A, and the corresponding near-field pattern is well confined to the center five waveguides injected with currents. The TPC semiconductor laser array may be a good candidate for optical sources with narrow horizontal divergence angles.

Extreme events in two laterally-coupled semiconductor lasers.

Rogue waves (RWs) are extreme and rare waves that emerge unexpectedly in many natural systems and their formation mechanism and prediction have been extensively studied. Here, we numerically demonstrate the appearance of extreme events (EEs) for the first time, to the best of our knowledge, in the chaotic regimes of a two-element coupled semiconductor laser array. Based on coupled-mode theory, we characterize the occurrence of EEs by calculating the probability distribution, which confirms the RW-type feature of the intensity pulses, i.e., non-Gaussian distribution. Combining with the results of the 0-1 test for chaos, we confirm that EEs originate from deterministic nonlinearities in coupled semiconductor laser systems. We show that EEs can be predicted with a long anticipation time. Furthermore, simulation results manifest that the occurrence probability of EEs can be flexibly tuned by tailoring the coupling parameter space. With the help of two-dimension maps, the effects of key parameters, i.e., the waveguide structure and the pump level, on the formation of EEs are discussed systematically. This work provides a new platform for the research of EEs in a highly integrated structure and opens up a novel investigation field for coupled semiconductor laser arrays.

Research Progress of Monolithic Integrated DFB Laser Arrays for Optical Communication

Photonic integrated circuits (PICs) play a leading role in modern information and communications technology. Among the core devices in PICs is the distributed feedback (DFB) multi-wavelength semiconductor laser array. Multi-wavelength semiconductor laser arrays can be integrated on a single chip and have the advantages of high stability, good single-mode performance, and narrow line width. The wavelength tuning range has been expanded through the design of the DFB laser array, which is an ideal light source for wavelength-division multiplexing systems. The preparation of DFB laser arrays with a large number of channels, ease of mass production, and accurate emission wavelengths has become an important field of research. The connection methods of lasers in DFB laser arrays are introduced systematically and the current methods of manufacturing multi-wavelength DFB laser arrays covering the perspective of technical principles, technical advantages and disadvantages, main research progress, and research status are summarized.

Non-Hermitian laser arrays with tunable phase locking.

Inspired by the idea of non-Hermitian spectral engineering and non-Hermitian skin effect, a novel, to the best of our knowledge, design for stable emission of coupled laser arrays with tunable phase locking and strong supermode competition suppression is suggested. We consider a linear array of coupled resonators with asymmetric mode coupling displaying the non-Hermitian skin effect and show that, under suitable tailoring of complex frequencies of the two edge resonators, the laser array can stably emit in a single extended supermode with tunable phase locking and with strong suppression of all other skin supermodes. The proposed laser array design offers strong robustness against both structural imperfections of the system and dynamical instabilities typical of semiconductor laser arrays.

High power semiconductor laser array with single-mode emission

The semiconductor laser array with single-mode emission is presented in this paper. The 6-μm-wide ridge waveguides (RWGs) are fabricated to select the lateral mode. Thus the fundamental mode of laser array can be obtained by the RWGs. And the maximum output power of single-mode emission can reach 36 W at an injection current of 43 A, after that, a kink will appear. The slow axis (SA) far-field divergence angle of the unit is 13.65°. The beam quality factor M 2 of the units determined by the second-order moment (SOM) method, is 1.2. This single-mode emission laser array can be used for laser processing.

Using Disorder to Overcome Disorder: A Mechanism for Frequency and Phase Synchronization of Diode Laser Arrays

Noise and disorder are known, in certain circumstances and for certain systems, to improve the level of coherence over that of the noise-free system. Examples include cases in which disorder enhances response to periodic signals, and those where it suppresses chaotic behavior. We report a new type of disorder-enhancing mechanism, observed in a model that describes the dynamics of external cavity-coupled semiconductor laser arrays, where disorder of one type mitigates (and overcomes) the desynchronization effects due to a different disorder source. Here, we demonstrate stabilization of dynamical states due to frequency locking and subsequently frequency locking-induced phase locking. We have reduced the equations to a potential model that illustrates the mechanism behind the misalignment-induced frequency and phase synchronization.

Study on bonding of single bar high power semiconductor lasers

Due to the mismatch between the thermal expansion coefficients of semiconductor laser chip and heat sink, giant thermal stresses will be generated after eutectic bonding. Immoderate thermal stress will cause the devices to produce the smile effect, making the coupling efficiency low. In this paper, we propose an approach to reduce thermal stress and improve the near-field linearity for semiconductor laser arrays. We optimize the eutectic bonding process by controlling the semiconductor laser chip and heat sink in different temperature fields through independent heat sources, to achieve the purpose of matching the shape variables earlier than welding. The heating temperature is determined by Suhir’s deformation formula (Suhir E. Stresses in Bi-metal thermostats. J Appl Mech. 1986;53(3):657–660; Suhir E. Stresses in adhesively bonded Bi-material assemblies used in electronic packaging. MRS Proc. 1986;72). Then, finite element Analysis (FEA) was used for simulation verification.

Non-Hermitian arrangement for stable semiconductor laser arrays.

We propose and explore a physical mechanism for the stabilization of the complex spatiotemporal dynamics in arrays (bars) of broad area laser diodes taking advantage of the symmetry breaking in non-Hermitian potentials. We show that such stabilization can be achieved by specific pump and index profiles leading to a PT-symmetric coupling between nearest neighboring lasers within the semiconductor bar. A numerical analysis is performed using a complete (2 + 1)-dimensional space-temporal model, including transverse and longitudinal spatial degrees of freedom and temporal evolution of the electric field and carriers. We show regimes of temporal stabilization and light emission spatial redistribution and enhancement. We also consider a simplified (1 + 1)-dimensional model for an array of lasers holding the proposed non-Hermitian coupling with a global axisymmetric geometry. We numerically demonstrate a two-fold benefit: the control over the temporal dynamics over the EELs bar and the field concentration on the central lasers leading to a brighter output beam, facilitating a direct coupling to an optical fiber.

Design and Implementation of High Precision Synchronization Controller for Gated Imaging

In this paper, we have designed a high-precision synchronization controller for gated imaging. The design scheme is proposed according to the semiconductor laser arrays overall range-gated imaging system composition and working principle. The programming of control logic is illustrated in detail from the main time counter, mode control logic, key control decoder, pulse generator, automatic frequency generator and display control. Finally, a synchronization controller with precision of 80 ns and frequency of 12 khz was developed. The whole system joint debugging test shows that the indicators of the synchronization controller have reached the expected goal, and have met the current technical requirements of gated imaging within 3 km in the atmospheric environment.

Research on Heat Dissipation of Diode Laser Array with Sharp-angle Sink

The project is designed and analyzed for the heat sink of the semiconductor laser array, and the heat dissipation performance of the heat sink with a sharp-angled channel is simulated by the finite element method. The results show that: compared with the traditional cylindrical cavity, the sharp-angle shape cavity has a stronger heat dissipation capacity. By designing a gradual flow channel inlet and outlet size, the flow channel inlet and outlet two of the large-size and multi-bar array laser are significantly reduced. The chip junction temperature difference at the end makes the array chip wavelength difference controlled within 1.9nm, which effectively improves the absorption uniformity and efficiency of the Nd:YAG crystal in this type of pump module.