Broad-area Laser Research Articles

Surfactant effect of Bi on InAs quantum dot laser diode

In this study, InAs multiple-stacked quantum dot lasers were investigated in the 1.55 μm band using the Bi surfactant effect. The Bi surfactant effect increased the size of the quantum dot and changed the emission wavelength from 1522 to 1554 nm. Moreover, the surfactant effect enhanced the internal quantum efficiency of the fabricated broad-area laser from 33% to 54%.

48 W Continuous-Wave Output From a High- Efficiency Single Emitter Laser Diode at 915 nm

Improving the power and efficiency of 9xx-nm broad-area laser diodes has a great help in reducing the cost of laser systems and expanding applications. This letter presents an optimized epitaxial structure with high power and conversion efficiency. Laser diodes with 230 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> emitter width and 5 mm cavity length deliver continuous-wave output power up to 48.5 W at 48 A, 30 °C, the highest power reported for 9xx-nm single emitter lasers so far. The slope efficiency is as high as 1.23 W/A due to a low internal optical loss of 0.31 cm−1 and a high internal efficiency of 96%. The maximum power conversion efficiency reaches 72.6% at 15.3 W and 67.3% at the operating power of 30 W under a heatsink temperature of 25 °C. Life test results show no failure in 1000 hours for 55 laser diodes.

Catastrophic optical damage in 808 nm broad area laser diodes: a study of the dark line defect propagation

We present a study of the propagation of dark line defects (DLDs) in catastrophically damaged 808 nm laser diodes, based on cathodoluminescence (CL) measurements and laser mode propagation simulations. Room temperature CL images show blurred DLDs running parallel to the laser cavity. Remarkably, low temperature images reveal their true morphology: the blurred lines are resolved as parallel narrow discontinuous DLDs. This morphology does not match the usually reported molten front scenario of DLD propagation. Low temperature images show that DLDs consist of a sequence of catastrophic optical damage (COD) events separated a few micrometers from each other. Consequently, a different propagation scheme is proposed. The points where the CODs occur suffer a temperature increase and these hot spots play a capital role in the propagation of the DLDs. Their influence on the beam distribution is modelled using finite element methods. The calculations evidence changes on the intensity distribution of the laser that qualitatively reproduce the DLD shapes. Additionally, the COD events result in the generation of defects in the region that surrounds them. The successive CODs in the discontinuous DLDs are rationalized in terms of the enhanced laser absorption in these sensitized regions where the laser beam is concentrated by thermal lensing.

High-power laser diode at 9xx nm with 81.10% efficiency.

In this study, a low-resistance, low-loss, continuously gradual composition extreme double asymmetric (CGC-EDAS) epitaxial structure is designed to improve efficiency. The structure and facet reflectivity of the broad area (BA) lasers are optimized to maximize the power conversion efficiency (PCE). In the experiment, the peak PCE of 75.36% is measured at 25°C. At 0°C, a peak PCE of 81.10% is measured and the PCE can still reach 77.84% at an output power of 17.10 W, which, to the best of our knowledge, is the highest value to date for any BA lasers.

Extreme Double/Triple Asymmetric Epitaxial Structure Based Diode Lasers for High Powers and High Efficiencies

In edge-emitting high power laser diodes, the longitudinal spatial hole burning (LSHB) effect induced by the inhomogeneous photon and carrier distributions and the non-linear process, two-photon absorption (TPA), are demonstrated to the key causes of power saturation at the high injection level even in the absence of thermal roll-over. Laser diodes based on extreme, double/triple asymmetric (EDAS/ETAS) epitaxial structures show great potentials in high-power and high-efficiency applications owing to the reduced series resistance, low optical loss, and suppressed power saturation. In this paper, a novel semi-analytical calculation method is proposed to systematically analyze the impact of LSHB and TPA effects on the output characteristics of EDAS/ETAS-based broad area lasers (BALs). By leveraging the feature that it is flexible to adjust the confinement factor of ETAS epitaxial structure without compromising the internal loss and resistance level, the laser parameters are first optimized to minimize power saturation of ETAS-based BALs under pulsed and Continuous Wave (CW) operation.

1300 nm Semiconductor Optical Amplifier Compatible With an InP Monolithic Active/Passive Integration Technology

In monolithic photonic integrated circuits (PICs), an optimized active/passive integration is needed to provide efficient coupling and low amount of interface reflections between amplifiers and passive components. A 1300 nm semiconductor optical amplifier (SOA) on InP substrate and optimized for butt-joint reflections is investigated. Material performance were assessed from measurements of broad area lasers. Room temperature operation reveals 1.2 W single facet output power with threshold current around 100 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> per well. Characteristic temperatures of T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 75 K and T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> = 294 K were obtained. A compact model description of the SOA, suitable for the design of PICs and rate equation analysis, was applied to parametrize the unsaturated gain measurements. Current injection efficiency of 0.65, transparency carrier density of 0.57 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> , and free carrier absorption losses up to 15 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> were extracted from fitting the data. The model is verified with measurements of optical gain saturation. A modal gain of 15 dB for a 600 μm long narrow ridge SOA leads to output saturation power higher than 30 mW at 7 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . This building block contributes to the development of an InP monolithic integration technology in the 1300 nm range, which can enable the use of photonic integrated circuits in many kind of applications.

Spectral linewidth narrowing of broad-area blue diode bar in V-shape external Talbot cavity.

A 1-D linear array of 23 high-power broad-area laser diode (BALD) beams in the blue spectral region (447 nm) is combined employing a V-shape external Talbot cavity in Littrow configuration. A surface grating provides optical feedback via self-imaged diffractive coupling to the diode bar and induces all the emitters to lase at a common central wavelength. The external cavity reduces the spectral linewidth of the free-running laser diode bar from several nm to 20-50 pm (FWHM) with the power level of 11.8 W. The narrow spectrum of the external cavity stabilized laser can be tuned in the range of 3-4 nm by adjusting the tilt angle of the grating while the laser diode bar is operated in constant current mode at a temperature of 20°C.

Stable Lateral Far Field of Highly Dense Arrays of Uncoupled Narrow Stripe Ridge Waveguide 1060 nm Lasers

In order to stabilize the lateral far-field profile of a broad area laser diode at high pump currents, the design of an asymmetric InGaAs&#x002F;AlGaAs&#x002F;GaAs laser heterostructure was developed. Lasers with an aperture formed by ten optically uncoupled ridge waveguides (each 6.5 &#x03BC;m wide) were developed on its basis. To maintain the single-mode operation of each ridge waveguide without coupling between emitters, a High Dense Microstripe Array (HDMSA, the pitch is 13.5 &#x03BC;m) and a Low Dense Microstripe Array (LDMSA, the pitch is 40 &#x03BC;m) were fabricated with a coupling parameter between adjacent lateral waveguides of 2&#x00B7;10^&#x2212;5 and 3&#x00B7;10^&#x2212;19, respectively. The maximum optical output power was 5 W (HDMSA) in CW mode and 25 W (HDMSA) and 26 W (LDMSA) in pulsed mode (130ns&#x002F;1kHz). It is shown that in both CW and pulsed modes, lasers of both designs provide a stable Gaussian-like distribution in the lateral far field (LFF) with a FWHM of 8&#x2013;11 degrees for HDMSA and 6.5&#x2013;10 degrees for LDMSA. It was found that the LFF broadens with a pump current in the range of low currents and stabilizes in the range of high currents for both designs. Studies of the near field in both operating modes at any pump currents showed no array modes and the uncoupling mode is maintained for ridge waveguide arrays.

Dual-wavelength emission from a high-order Bragg gratings integrated broad-area laser diode

This paper presents a broadband distributed Bragg reflection laser diode with dual-wavelength emission. The waveguide of the laser diode is integrated with a 95-um high-order Bragg grating (HOBG) region. Thus, the longitudinal mode of the broadband laser diode can be partially filtered by the HOBGs. As the gain peak of the active region can cover nearly four modes, two modes with nearly the same gain value can be emitted simultaneously. Moreover, two wavelengths with an interval of 0.25 nm are obtained, and the centre wavelength is near 958 nm. The maximum output power of the dual-wavelength emission can reach 411 mW at an operating current of 1.16 A. A stable dual-wavelength emission can be maintained when the operating current is changed from 1.02 A to 1.16 A. In particular, the spacing between the two wavelengths barely varies. Thus, dual-wavelength emission can be used for multi-wavelength continuous tuning applications.

Influence of transverse carrier diffusion on two-dimensional optical rogue waves in broad-area semiconductor lasers with a saturable absorber

The statistics and dynamics of two-dimensional rogue waves in a broad-area semiconductor laser with an intracavity saturable absorber are numerically investigated under the effect of transverse carrier diffusion. We show that lateral diffusion of carriers alters the statistics of rogue waves by enhancing their formation in smaller ratios of carrier lifetimes in active and passive materials while suppressing them when the ratio is larger. The temporal dynamics of the emitted rogue waves is also studied and show that the finite nonzero transverse carrier diffusion coefficient gives them a longer duration. To further approach a realistic experimental situation, we also investigate the statistics and dynamics of rogue waves by simulating a circular disk-shape pump which replaces the flat pump profile typically used in numerical simulations of broad-area lasers. We show that a finite pump shape reduces the number of emitted rogue waves per unit area both below and above the laser threshold for every carrier lifetime ratio. The temporal width of the emitted rogue waves is also shown to decrease as a consequence of removing the nonphysical effects of the infinite flat pump on carrier dynamics.

Observation of Spatial Coherence Collapse in High-Power, Broad-Area Lasers Using Fiber-Assisted Self-Heterodyning

In this work, a high-resolution, self-heterodyne,RF measurement of a broad-area laser is spatially resolved using an optical fiber at a range of power levels. Three separate spatial regimes of operation are revealed as power is increased: conventional modes, spatial coherence collapse, and cavity-assisted filamentation.

Gallium Arsenide Photonic Integrated Circuit Platform for Tunable Laser Applications

An active-passive integration technique for operation near a wavelength of 1030 nm has been developed on a gallium arsenide (GaAs) photonic integrated circuit platform. The technique leverages quantum wells (QWs) that are slightly offset vertically from the center of the waveguide, and selectively removed prior to upper cladding regrowth to form active and passive regions. The active region consists of indium gallium arsenide (InGaAs) QWs, gallium arsenide phosphide (GaAsP) barriers, GaAs separate confinement heterostructure layers, and aluminum gallium arsenide (AlGaAs) cladding. Fabry Perot lasers with various widths were fabricated and characterized, exhibiting high injection efficiency of 98.8%, internal active loss of 3.44 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , and internal passive loss of 4.05 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> for 3 μm wide waveguides. The 3 μm, 4 μm, and 5 μm wide lasers demonstrated greater than 50 mW output power at 100 mA continuous wave (CW) current and threshold current as low as 9 mA. 20 μm wide broad area lasers demonstrated 240 mW output power, 35.2 mA threshold current under CW operation, and low threshold current density of 94 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for 2 mm long lasers. Additionally, these devices exhibit transparency current density of 85 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and good thermal characteristics with T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 205 K, and T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">η</sub> = 577K.

Room‐temperature laser operation of a (Ga,In)As/Ga(As,Bi)/(Ga,In)As W‐type laser diode

The ongoing pursuit for laser device emitting in the near-infrared spectral region on GaAs substrates has led to various material systems and device concepts. Alloys containing dilute amounts of Bismuth are promising candidates due to the already substantial band gap shift when incorporating low molar fractions of Bi in the GaAs host lattice. However, devices emitting at technologically essential wavelengths of 1.3 and 1.55 μm have yet to be demonstrated using this material system. Especially the non-equilibrium nature of the growth conditions required to grow the metastable material makes epitaxial growth with high molar fractions of Bi challenging. An alternate approach to reach the desired wavelengths exploits a type-II band alignment between two materials to push the emission wavelength further into the telecom bands. Here, room-temperature laser operation of the first type-II structure employing Ga(As,Bi) as hole confining layer and (Ga,In)As as electron confining layer is demonstrated. Sample growth is conducted by low-pressure metalorganic vapour phase epitaxy. Broad area laser devices are processed and characterized by electroluminescence measurements. A threshold current density of 3.86 kA/cm2 and emission wavelength of 1037 nm are observed, showing this device concept's potential for future lasers in the telecom bands.

808 nm broad-area laser diodes designed for high efficiency at high-temperature operation

Semiconductor lasers with high power conversion efficiency (PCE) and output power are heavily investigated driven by more energy-efficient commercial applications. In this paper, an asymmetric broad area laser (A-BAL) design is studied and compared with a conventional symmetric broad area laser (S-BAL) design for 808 nm single emitter laser diodes. We present a comparative theoretical and experimental investigation by studying the thermal effects on the laser parameters. The output characteristics and efficiency loss paths for the designs were analyzed. The leakage of carriers was identified as the primary source of the PCE reduction with temperature. Suppressing this leakage by optimization of the A-BAL design, a record continuous-wave PCE of 68% at 25 °C and 60.4% at 75 °C were achieved for a single emitter laser with 10 W output power. These devices deliver high efficiency at high temperatures with reliable operation achieving 2000 h of an accelerated aging lifetime without failures.

High Power 980-nm Broad-Area Lasers with Distributed Bragg Reflection Grating

High-power and highly stable 980 nm semiconductor lasers are widely used in fiber laser pumping and instrumentation applications. We report on a distributed Bragg reflector (DBR) semiconductor laser manufactured on the waveguide structure of an asymmetric large optical cavity. Wavelength stabilization is achieved using a 500-µm-long DBR with a sixth-order Bragg grating, which is fabricated using a combination of electron beam lithography and inductively coupled plasma etching. When the device injection current is 22 A, the output power ranges up to 16 W, the slope efficiency is 0.73 W/A, and a spectral linewidth of 1.4 nm is achieved.

Spatiotemporal Dynamics of Broad-Area Lasers with the Pump Modulation and Injection of External Optical Radiation

Spatiotemporal Dynamics of Broad-Area Lasers with the Pump Modulation and Injection of External Optical Radiation

Boosting the output power of large-aperture lasers by breaking their circular symmetry

Breaking the spatial symmetry in optical systems has become a key approach to the study of nonlinear dynamics, wave chaos, and non-Hermitian physics. Moreover, it enables tailoring of the spatiotemporal properties of such systems. Breaking the circular symmetry of lasers yields a more uniform light intensity profile within the optical aperture and makes uniform the spectral distribution of the optical states (modes). Those effects are known to enhance spontaneous as well as stimulated emission and consequently suppress undesired nonradiative recombination in the active region, but their importance for laser emission is not fully understood so far. In this paper, using the example of vertical-cavity surface-emitting lasers, we show that intentionally deformed optical apertures induce a more uniform light intensity distribution within the optical aperture, related to wave chaos, and a higher density of optical states, enhancing stimulated emission as predicted by quantum electrodynamics theory. These two phenomena contribute to increasing the optical output power by more than 60% and quantum efficiency by more than 10%. The results of this study are of significant importance for a variety of lasers, showing a clear link between the fundamentals of their operation and quantum electrodynamics and providing a general, robust method of enhancing emitted power for high-power broad-area lasers.

Spatially modulated broad-area lasers for narrow lateral far-field divergence.

A novel laser design is presented that combines a longitudinal-lateral gain-loss modulation with an additional phase tailoring achieved by etching rectangular trenches. At 100 A pulsed operation, simulations predict a far-field profile with 0.3° full width at half maximum (Θ F W H M =0.3 ∘ ) where a 0.4°-wide main lobe contains 40% of the emitted optical output power (Θ 40% =0.4 ∘ ). While far-field measurements of these structured lasers emitting 10 ns long pulses with 35 W peak power confirm a substantial enhancement of radiation within the central 1∘ angular range, the measured far-field intensity outside of the obtained central peak remains high.

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.

Spectral linewidth narrowing of two broad-area blue laser diodes (445 nm) with a common external cavity.

Two watt-level broad-area laser diodes were simultaneously locked into a common external cavity made using a surface grating in a Littrow configuration. The spectral linewidth of the combined laser beam was narrowed down from over a nanometer to 10-15 pm (FWHM), and the output power was the sum of the power of the individually locked laser diodes. The spectrum of the combined laser beam can be tuned over a range of 2-3 nm by changing the tilt angle of the grating and varying the injection currents of each laser diode.