Narrow-line coherently combined tapered laser diodes in a Talbot external cavity with a volume Bragg grating

We present the phase locking of an array of index-guided tapered laser diodes. An external cavity based on the self-imaging Talbot effect has been built. A volume Bragg grating is used as the output coupler to stabilize and narrow the spectrum at 976 nm. A power of 1.7 W is achieved in the in-phase single main lobe mode with a high visibility. We have checked that each emitter is locked to the Bragg wavelength with a 100 pm spectrum linewidth. The experimental results compare well with numerical simulations performed with two-dimensional wide-angle finite difference beam propagation method

Double-pass amplification of picosecond pulses with a tapered semiconductor amplifier

Double-pass amplification of picosecond pulses is demonstrated and compared with single-pass amplification. This was achieved using a two-section tapered semiconductor optical amplifier with a chirped quantum-dot active region and a mode-locked laser diode as a seed. Across the range of biasing conditions common to both configurations, an enhancement in signal gain of up to 7 dB and output power by a factor of 4.1 was seen in the double-pass amplifier, compared to the single-pass. Only marginal increases in pulse duration were observed in the double-pass regime compared to the single-pass amplifier, meaning that enhancements in output power were well translated into peak power. Furthermore, the two-section contact layout of the SOA allowed the pulse duration to be optimised for a given fixed output power, giving additional flexibility to the amplifier. These results demonstrate the suitability of this simple and versatile technique, which could become the new standard in amplification of ultrashort pulses

Wide and tunable spectral asymmetry between narrow and wide facet outputs in a tapered quantum-dot superluminescent diode

A wide spectral asymmetry between the front and rear facets of a tapered chirped quantum dot multi-section superluminescent diode is reported. The spectral asymmetry between the two facet outputs was found to be tunable and highly dependent on the bias asymmetry between the two contact sections, with a spectral mismatch of up to 14 nm. Numerical simulations confirmed a relationship between this spectral asymmetry and the non-uniform filling of the quantum dots’ confined states when different current densities are applied to the device electrodes. The results from this investigation open up an additional degree of freedom for multi-section superluminescent diodes, which could pave the way for optical bandwidth engineering via multiplexing the spectral output from both facets, using only a single device

Widely Tunable Quantum-Dot Source Around 3 μm

We propose a widely tunable parametric source in the 3 μm range, based on intracavity spontaneous parametric down conversion (SPDC) of a quantum-dot (QD) laser emitting at 1.55 μm into signal and idler modes around 3.11 μm. To compensate for material dispersion, we engineer the laser structure to emit in a higher-order transverse mode of the waveguide. The width of the latter is used as a degree of freedom to reach phase matching in narrow, deeply etched ridges, where the in-plane confinement of the QDs avoids non-radiative sidewall electron-hole recombination. Since this design depends critically on the knowledge of the refractive index of In1−xGaxAsyP1−y lattice matched to InP at wavelengths where no data are available in the literature, we have accurately determined them as a function of wavelength (λ = 1.55, 2.12 and 3 μm) and arsenic molar fraction (y = 0.55, 0.7 and 0.72) with a precision of ±4 × 10−3. A pair of dichroic dielectric mirrors on the waveguide facets is shown to result in a continuous-wave optical parametric oscillator (OPO), with a threshold around 60 mW. Emission is tunable over hundreds of nanometers and expected to achieve mW levels

The optimization problem of the shaped knife profiling

Проаналізовано переваги та недоліки процесу гарячого поділу безперервнолитої квадратної заготовки на ножицях з фасонними ножами. Відзначається доцільність проведення теоретичних досліджень розділових операцій на ножицях з використанням методу скінченних елементів (МСЕ). Метою даної роботи було визначення оптимальної форми профілювання фасонного ножа для поділу квадратної заготовки в гарячому стані шляхом математичного моделювання на базі МСЕ. Представлено методику проведення досліджень, що включали два етапи. На першому етапі використовували математичне моделювання відповідно до плану повного факторного експерименту 24 згідно виробничих умов реалізації процесу з ножами що мали значення кута розкриття ножів 90…98° та ухилу контактних поверхонь 3…11°. При обробці даних моделювання були отримані три відносних параметра, два з яких характеризують зминання (затяжка) і загин кінців розкату, і ще один – ромбічність торцевої поверхні. Для кожного з параметрів, отримані лінійні рівняння регресії як функція температури різання та розмірів заготовок, величини кута розкриття ножів та ухилу контактних поверхонь. На другому етапі дослідження вирішували оптимізаційну задачу пошуку мінімуму цільової функції – ромбічності. За результатами відзначено, що оптимальні значення профілювання ножів залежать від вимог, що висуваються до якості зрізу. Введено фактор граничного відхилення зминання і загину кінців, встановлений діапазон його значень та проаналізовано вплив на оптимальні параметри. Запропоновано величини кута розкриття ножів та ухилу контактних поверхонь, за умови мінімізації граничного відхилення зминання і загину кінців у досліджуваних діапазонах температур та розмірів заготовок. Отримано залежності параметрів профілювання ножів від граничного відхилення зминання і загину кінців заготовок після поділу. Результати роботи можуть бути рекомендовані для використання при прийнятті проектно-конструкторських і технологічних рішень в питаннях гарячого розділення безперервнолитої квадратної заготовки фасонними ножами на кут.The advantages and disadvantages of the process of separation in hot condition of billet with square shape by special profiled knives were analyzed. There is expediency of carrying out theoretical researches the separating operations by shears based on finite elements method (FEM) is noted. The purpose of the work was to determine the optimal shape for make form a profiled knife for separating a square billet in a hot state by simulating based on the FEM. A methodology of study realization consisting of two stages is presented. At the first stage, simulating was used in accordance with the plan of the full factorial experiment 24 according to the technological environment for the process implementation with knives having a knife opening angle of 90...98° and a contact surface inclination of 3...11°. At the processing the simulation results, three relative parameters were obtained. Two parameters characterize the crumpling (tightening) and bending of the billet ends, and one more – the rhomboidity of the end surface. For each of the parameters, the linear regression equations obtained as a function of cutting temperature and billet sizes, the knife opening angle and contact surface inclination. At the second stage of the study, the optimization problem of determining the minimum of the objective function – rhomboidity – was solved. According to the results, it was noted that the optimal values of the profiling of knives depend on the requirements for the quality of the cut. The factor of the maximum deviation of crumpling and bending of the ends is introduced. The range of its values is established and the influence on the optimal parameters is analyzed. The values of the knife opening angle and contact surface inclination are proposed, provided that the maximum deviation of the crumpling and bending of the ends, at the studied temperature ranges and sizes of the billets, is minimized. The dependences of the optimal parameters of the profiling of knives on the maximum deviation of the crumpling and bending of the ends of the billets after separation are obtained. Results of work can be recommended for use to get solutions in design and technology questions of hot separation square billet by profiled knife on the angle

Coherence function control of Quantum Dot Superluminescent Light Emitting Diodes by frequency selective optical feedback.

Low coherent light interferometry requires broad bandwidth light sources to achieve high axial resolution. Here, Superluminescent Light Emitting Diodes (SLDs) utilizing Quantum Dot (QD) gain materials are promising devices as they unify large spectral bandwidths with sufficient power at desired emission wavelengths. However, frequently a dip occurs in the optical spectrum that translates into high side lobes in the coherence function thereby reducing axial resolution and image quality. We apply the experimental technique of frequency selective feedback to shape the optical spectrum of the QD-SLD, hence optimizing the coherence properties. For well-selected feedback parameters, a strong reduction of the parasitic side lobes by a factor of 3.5 was achieved accompanied by a power increase of 40% and an improvement of 10% in the coherence length. The experimental results are in excellent agreement with simulations that even indicate potential for further optimizations

Two-dimensional carrier density distribution inside a high power tapered laser diode

The spontaneous emission of a GaAs-based tapered laser diode emitting at lambda = 1060 nm was measured through a window in the transparent substrate in order to study the carrier density distribution inside the device. It is shown that the tapered geometry is responsible for nonuniform amplification of the spontaneous/stimulated emission which in turn influences the spatial distribution of the carriers starting from below threshold. The carrier density does not clamp at the lasing threshold and above it the device shows lateral spatial hole-burning caused by high stimulated emission along the cavity center. (C) 2011 American Institute of Physics. (doi: 10.1063/1.3596445

Monolithic integration of a high power semiconductor master oscillator power amplifier

We present a high power semiconductor Master Oscillator Power Amplifier monolithically integrated on InP, which includes a modulation section. This device can be used for random-modulation-continuous wave lidar systems or free-space communications