Laser Diode Array Research Articles

Monolithic 45 Degree Deflecting Mirror as a Key Element for Realization of 2D Arrays of Laser Diodes Based on AlInGaN Semiconductors

In this study, we propose a solution for realization of surface emitting, 2D array of visible light laser diodes based on AlInGaN semiconductors. The presented system consists of a horizontal cavity lasing section adjoined with beam deflecting section in the form of 45° inclined planes. They are placed in the close vicinity of etched vertical cavity mirrors that are fabricated by Reactive Ion Beam Etching. The principle of operation of this device is confirmed experimentally; however, we observed an unexpected angular distribution of reflected rays for the angles lower than 45°, which we associate with the light diffraction and interference between the vertical and deflecting mirrors. The presented solution offers the maturity of edge-emitting laser technology combined with versatility of surface-emitting lasers, including on-wafer testing of emitters and addressability of single light sources.

The Effect of Cooling Layer Thickness and Coolant Velocity on Crystal Thermodynamic Properties in a Laser Amplifier.

Laser diode pumped solid-state lasers (DPSSLs) have been widely used in many fields, and their thermal effects have attracted more and more attention. The laser diode (LD) side-pumped amplifier, as a key component of DPSSLs, is necessary for effective heat dissipation. In this paper, instead of the common thermal analysis based only on a crystal rod model, a fluid-structure interaction model including a glass tube, cooling channel, coolant and crystal rod is established in numerical simulation using ANSYS FLUENT for the configuration of an LD array side-pumped laser amplifier. The relationships between cooling layer thickness, coolant velocity and maximum temperature, maximum equivalent stress, inlet pressure and the convective heat transfer coefficient are analyzed. The results show that the maximum temperature (or maximum equivalent stress) decreases with the increase in the coolant velocity; at low velocity, a larger cooling layer thickness with more coolant is not conductive enough for improved heat dissipation of the crystal rod; at high velocity, when the cooling layer thickness is above or below 1.5 mm, the influence of the cooling layer thickness on the maximum temperature can be ignored; and the effect of the cooling layer thickness on the maximum equivalent stress at high velocity is not very significant. The comprehensive influence of various factors should be fully considered in the design process, and this study provides an important reference for the design and optimization of a laser amplifier and DPSSL system.

Исследование однородности распределения накачки в активном элементе в виде стержня мощных квантронов с диодной накачкой

Experimental investigations and calculations of various optical schemes of high-power DPSS and solid-state lasers with cylindrical active elements and transverse pumping by laser diode arrays are presented. Numerical simulations were used to solve hydrodynamic problems and problems of geometric optics for DPSS with rod active elements pumping by quasi-continuous laser diode arrays. The dependencies of the uniformity of active element illumination on the geometry of the optical scheme were studied, as well as the influence of the uniformity of coolant flows over different pump arms on the uniformity of the luminescence distribution pro-file from the end of the active element. An optical pumping scheme for active element of a high-power DPSS with an optimal geometry is proposed and implemented.

Design of high-brightness, fiber-coupled, beam shaping system based on a multichip 2D green laser diode array

Small size, high-brightness fiber-coupled laser modules have always been the ultimate goal that all researchers are pursuing. A high-brightness 525 nm wavelength fiber-coupled system is designed and evaluated. Based on a multichip 2D green laser diode array, fast-axis collimators are set inside the light source, and a beam shaping system that can rearrange the beam and improve the beam quality in both axes is designed. The simulation results indicate that 24 single emitters are coupled into a 50μm / 0.15 NA optical fiber successfully and the output power is 22.55 W. The brightness of 16.25 MW / ( cm2 · sr ) is calculated with fiber coupling efficiency is 97%.

A photoacoustic patch for three-dimensional imaging of hemoglobin and core temperature

Electronic patches, based on various mechanisms, allow continuous and noninvasive monitoring of biomolecules on the skin surface. However, to date, such devices are unable to sense biomolecules in deep tissues, which have a stronger and faster correlation with the human physiological status than those on the skin surface. Here, we demonstrate a photoacoustic patch for three-dimensional (3D) mapping of hemoglobin in deep tissues. This photoacoustic patch integrates an array of ultrasonic transducers and vertical-cavity surface-emitting laser (VCSEL) diodes on a common soft substrate. The high-power VCSEL diodes can generate laser pulses that penetrate >2 cm into biological tissues and activate hemoglobin molecules to generate acoustic waves, which can be collected by the transducers for 3D imaging of the hemoglobin with a high spatial resolution. Additionally, the photoacoustic signal amplitude and temperature have a linear relationship, which allows 3D mapping of core temperatures with high accuracy and fast response. With access to biomolecules in deep tissues, this technology adds unprecedented capabilities to wearable electronics and thus holds significant implications for various applications in both basic research and clinical practice.

Tunable, High-Power, Narrow-Linewidth Diode Laser for Potassium Alkali Metal Vapor Laser Pumping

This work proposes a method of compressing spectral linewidth and tuning the central wavelength of multiple high-power diode laser arrays in an external cavity feedback structure based on one volume Bragg grating (VBG). Through the combination of beam collimation and spatial beam technologies, a diode laser source producing 102.1 W at an operating current of 40 A is achieved. This laser source has a central wavelength of 766 nm and a narrow spectral linewidth of 0.164 nm. Moreover, a tuning central wavelength ranging from 776–766.231 nm is realized by precisely controlling the temperature of the VBG, and the locked central wavelength as a function of temperature shifts at the rate of approximately 0.0076 nm/°C. The results further prove that the smile under 1 μm can restrain the self-excitation effect of the emitting laser, which can influence the efficiency of the potassium alkali metal vapor laser pumping.

Modal characteristics of coupled vertical cavity surface emitting laser diode arrays

The modal characteristics of dual-element coupled vertical cavity surface emitting laser (VCSEL) arrays are analyzed numerically and experimentally. A photonic crystal pattern etched into the top mirror optically defines the two elements of the array that are independently electrically biased. Using a two-dimensional complex waveguide analysis, we incorporate the effects of varying temperature and electron plasma-induced index suppression arising from asymmetric injection. The simulations are compared to experimental characterization of output power, lasing spectra, and far-field beam profile as a function of the two independent injection currents. Three distinct operating regimes are identified for the arrays: single independent local mode; a region of two modes that are primarily localized into a specific cavity; and a region of two supermodes whose fields extend across both elements. This analysis provides a physical intuition for the behavior of the dual-element coupled VCSEL array across its full operating range for emerging applications.

Color quality consideration when switching from FL to LED

Color quality consideration when switching from FL to LED

Amplification of high repetition-rate, picosecond laser pulses using a zig-zag slab configuration

Laser sources which generate high peak-pulse energy, picosecond pulse duration outputs at high repetition rates are of particular interest for applications including laser ignition and space fragment detection. In this work, we demonstrate the design and operation of a zig-zag slab, solid-state master oscillator power amplifier (MOPA) which yields high energy amplification. The system uses a weakly-doped Nd:YAG slab as the amplifier medium, to amplify laser pulses from a passively Q-switched microchip seed laser. The seed laser beam undergoes four passes of the slab amplifier resulting in an amplified output pulse with hundreds of picoseconds pulse duration. We investigate the relationship between the angle of incidence of the seed laser beam into the amplifier slab and its effect on the slab fill-factor and overall laser field amplification. We also investigate the impact that the temperature of the laser diode array (LDA) which is used to pump the slab amplifier, has on the amplification efficiency of the MOPA. Experimentally, we demonstrate an amplification factor of ∼90 times from the optimized slab amplifier, and a resultant output laser field with a pulse energy of 99.58 mJ, a pulse duration of 491 ps, and a repetition rate of 200 Hz. We believe that this work will pave the way towards the development of novel all-solid-state amplifier designs for the generation of high-energy, high repetition frequency, sub-nanosecond laser outputs.

High Brightness Diode Lasers Based on Beam Splitting and Polarization Combining

A new method to improve the brightness of diode lasers based on beam-waist splitting and polarization combining was proposed and demonstrated. The beam waist was split by a precisely cut prism into two parts and combined with a polarization beam combiner. The advantages of simple setup, high efficiency, brightness, and universality were presented. The slow axis M2 factor of a broad-area diode laser with a ridge beam width of 180 μm was reduced from 18.5 to 9.8, and a brightness of 42.4 MW cm−2 sr−1 was realized; this brightness was a 84.21% improvement of the same emitter at 8 A. The slow axis M2 factor of a commercial broad-area diode laser array combined by spectral beam combining was reduced from 9.08 to 4.78, and 80.6% improvement of brightness was realized on the same commercial broad-area diode laser array. A brightness of 195.8 MW cm−2 sr−1 was realized at 36 A by this diode laser array. This method can be applied in a highly polarized light source to improve the beam quality and brightness.

Simple microwave photonic downconversion channelizer based on multi-wavelength laser sources.

This work presents a simple microwave photonic downconversion channelizer based on multi-wavelength laser sources. The design of two laser diode (LD) arrays enables signal multiplexing and simultaneous multichannel downconversion processing, which provide stable, relatively flat, and strong multi-frequency combs. A proof-of-concept experiment was taken, showing that 14.375-17.75 GHz broadband radio frequency (RF) signals were successfully downconverted to the same intermediate frequency (IF) and were sliced into four subchannels with 875 MHz bandwidth showing excellent image rejection and channel uniformity, which agrees with the simulation results. The spurious free dynamic range (SFDR) of the proposed RF channelizer is 100dBHz2/3, the image rejection is over 28 dB, and the frequency measurement error is less than ±6MHz. Replacing optical filters with electrical filters, the proposed simple optoelectronic hybrid reconfigurable microwave photonic channelizer system acquits stable performance and high maturity and meets the application requirements, behaving with stupendous potential in fields such as radar, satellite communication, electronic warfare, and others.

A High Brightness GaN Laser Array With Lateral-Corrugated Waveguides

A high brightness GaN laser diode array with an output power of 78 W and an average lateral beam-quality factor of 3.5 for 38 emitters has been realized by the new design method of lateral-corrugated waveguides (LCWGs). The LCWG we propose was optimized by calculating both output power and beam-quality so as to maximize lateral brightness. As a result, the maximum output power of 117 W was obtained and a lateral brightness increased 1.6 times compared to the previous LCWG array. Finally, a high brightness GaN laser source was achieved by combining the beams from 38 emitters for GaN laser processing.

Optimization of Tunable Diode Laser Arrays for Inlet Mass Capture Measurement

Multibeam tunable diode laser absorption spectroscopy (TDLAS) sensors are used to measure mass flow in a complex, inhomogeneous flowfield with limited optical access. The cost and complexity of a TDLAS array increases with the number of beams, but adding beams does not necessarily improve accuracy. A technique to optimize the location and orientation of multiple laser beams for mass flow sensing in a 3D flow path geometry is developed and presented. We devised a statistical objective function that minimizes the uncertainty of estimates using a novel, linear formulation of absorption tomography with velocimetry (LATV). Beam arrangements that minimize the uncertainty of LATV reconstructions consequently maximize confidence in mass flow rate estimates; such arrangements are identified, subject to physical constraints on the pitch and catch optics. Our metric provides general guidance for the arrangement of a multibeam TDLAS mass flow sensor and does not require the use of tomographic reconstruction.

Dynamics of mutual injection phase-locking of laser diode array with interference effect

In this paper, an effective method to realize almost in-phase mode phase-locked output on laser diode array (LDA) chip is proposed by using a one-half period lateral shift face-to-face mutual injection Talbot cavity. The phase-locking model is complemented by involving interference effect to modify mutual injection ratios between laser elements. Based on the modified mutual injection Lang–Kobayashi (L–K)rate equation, the phase-locking process under different fill factors (FFs), coupling coefficients (CCs) and wavelength detunings (Δλs) is comprehensively analyzed. As a result, the allowable wavelength detuning range is obviously expanded, and the robust in-phase mode phase-locked output can be obtained theoretically under specific configuration of FF and CC.

Towards rainbow portable Cytophone with laser diodes for global disease diagnostics

In vivo, Cytophone has demonstrated the capability for the early diagnosis of cancer, infection, and cardiovascular disorders through photoacoustic detection of circulating disease markers directly in the bloodstream with an unprecedented 1,000-fold improvement in sensitivity. Nevertheless, a Cytophone with higher specificity and portability is urgently needed. Here, we introduce a novel Cytophone platform that integrates a miniature multispectral laser diode array, time-color coding, and high-speed time-resolved signal processing. Using two-color (808 nm/915 nm) laser diodes, we demonstrated spectral identification of white and red clots, melanoma cells, and hemozoin in malaria-infected erythrocytes against a blood background and artifacts. Data from a Plasmodium yoelii murine model and cultured human P. falciparum were verified in vitro with confocal photothermal and fluorescent microscopy. With these techniques, we detected infected cells within 4 h after invasion, which makes hemozoin promising as a spectrally selective marker at the earliest stages of malaria progression. Along with the findings from our previous application of Cytophone with conventional lasers for the diagnosis of melanoma, bacteremia, sickle anemia, thrombosis, stroke, and abnormal hemoglobin forms, this current finding suggests the potential for the development of a portable rainbow Cytophone with multispectral laser diodes for the identification of these and other diseases.

Thermoelastic stresses in high-power CW diode laser arrays assembled on CuW and AlN submounts

Comparative results are presented of 3D-calculation for thermoelastic stress (TES) profiles in diode laser arrays (LDAs) assembled on CuW and AlN submounts (temperature compensators) and operating at a continuous-wave (CW) thermal power load of up to 220 W. For the first time, the simulation has revealed substantial differences in the maximal TES values for the arrays assembled on CuW and AlN submounts, as well as pronounced features of TES distribution in LDA assemblies, in particular, near the rear (highly reflecting) mirror of the laser diode cavity in similar geometries of temperature compensators. Results of the numerical simulation qualitatively agree with thorough measurements of spectral distributions over the LDA emitting aperture. The obtained results are interesting for mastering the production technologies of high-power devices aimed at improving their output parameters and service life.

Spectrum-locked high-power volume Bragg grating external-cavity diode laser

Spectrum-locked high-power diode lasers are extremely sought after in many fields. Here, we establish the volume Bragg grating external-cavity diode laser model and investigate the impact of facet reflectivity on the output spectrum. The simulation results emphasize that optimizing reflectivity can realize better spectrum-locking and side-mode suppression ratio. To prove the feasibility, we built a diode laser array with 20 single emitters. Three different facet reflectivity are prepared, 0.1%, 0.5%, and 0.8%. As a result, the output spectrums of the array are improved obviously with the decrease in reflectivity. In the case of 0.1%, the side-mode is well suppressed under injection current up to 16 A, and the calculated current-spectrum shift is around 0.07 nm A−1. After beam combining and fiber coupling, an output power of 243.4 W and a brightness of about 11.2 MW cm−2-str is attained.

A Low-Cost High-Resolution Solid-State Lidar With Wavelength Division Multiplexed Components and Interleaved Orthogonal Polarization Grating Couplers

Laser diodearray and photo diode array combined through coarse wavelength division multiplexed (CWDM) are widely used in short-reach optical communication within massive web-scale data center. Those components can be used in solid-state photonics-based Lidar built upon silicon-on-insulator (SOI) waveguide as well, achieving significant cost saving. Beam steering can be naturally achieved through diffraction in output grating couplers. However, current design is hampered by low angular resolution. We demonstrate a novel design by combining outputs of two grating couplers with orthogonal polarizations in an interleaving manner. This scheme effectively doubles the angular resolution of on-chip Lidar.

New Design of Two-Dimensional Array of Laser Diodes With Direct Convective Cooling

New Design of Two-Dimensional Array of Laser Diodes With Direct Convective Cooling

Standalone portable xenon-129 hyperpolariser for multicentre clinical magnetic resonance imaging of the lungs.

ObjectivesDesign and build a portable xenon-129 (129Xe) hyperpolariser for clinically accessible 129Xe lung MRI.MethodsThe polariser system consists of six main functional components: (i) a laser diode array and optics; (ii) a B0 coil assembly; (iii) an oven containing an optical cell; (iv) NMR and optical spectrometers; (v) a gas-handling manifold; and (vi) a cryostat within a permanent magnet. All components run without external utilities such as compressed air or three-phase electricity, and require just three mains sockets for operation. The system can be manually transported in a lightweight van and rapidly installed on a small estates footprint in a hospital setting.ResultsThe polariser routinely provides polarised 129Xe for routine clinical lung MRI. To test the concept of portability and rapid deployment, it was transported 200 km, installed at a hospital with no previous experience with the technology and 129Xe MR images of a diagnostic quality were acquired the day after system transport and installation.ConclusionThis portable 129Xe hyperpolariser system could form the basis of a cost-effective platform for wider clinical dissemination and multicentre evaluation of 129Xe lung MR imaging.Advances in knowledgeOur work successfully demonstrates the feasibility of multicentre clinical 129Xe MRI with a portable hyperpolariser system.