Mr. Abdel-Sattar M. Gadallah Profile

Abdel-Sattar M. Gadallah

at Univ Ulm

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Proceedings Article | 28 April 2010 Paper

High-power single-higher-order-mode VCSELs for optical particle manipulation

Abdel-Sattar Gadallah, Anna Bergmann, Rainer Michalzik

Proceedings Volume 7720, 77201Y (2010) https://doi.org/10.1117/12.854319

KEYWORDS: Vertical cavity surface emitting lasers, Particles, Polarization, Etching, Optical manipulation, Microfluidics, Quantum wells, Crystals, Singular optics, Optical tweezers

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We report the design, fabrication and characterization of oxide-confined large-area rectangular-shaped VCSELs that emit a single higher-order transverse mode. The mode selection mechanism is based on an inverted surface relief. In this method, extra losses are induced by a quarter-wavelength-thick antiphase layer, into which a multi-spot pattern is etched in a single step. The main parameters that control the selected mode, such as the threshold gain and the three-dimensional confinement factor, are calculated as a function of the active aperture dimensions for various structures, patterns, and aspect ratios, aiming to achieve single-higher-order transverse mode emission. Based on the design rules, 850 nm wavelength top-emitting GaAs/AlGaAs VCSELs have been fabricated and characterized. Devices with an aperture area of about 6 × 68 μm² show high output powers of 12 mW in the (8, 1) order mode and differential resistances of only 18 ohms. In addition, the asymmetric transverse cavity can be used to achieve oscillation on a single polarization. Optical manipulation of micro-particles is a promising biophotonic application area for the investigated VCSELs. In an optical tweezers setup, a multi-spot VCSEL is positioned under an angle of about 25 degrees with respect to the fluidic flow direction. Lateral all-optical deflection of flowing 10 μm diameter polystyrene particles is achieved, which is of particular interest for non-mechanical sorting in a microfluidic chip. With the multi-spot VCSEL, the distance between the intensity spots is 9 μm, which cannot be easily achieved with conventional linear VCSEL arrays. Trapping and stacking of polystyrene microspheres are also shown.

Proceedings Article | 8 May 2008 Paper

Oblong-shaped VCSELs with pre-defined mode patterns

Abdel-Sattar Gadallah, Andrea Kroner, Ihab Kardosh, Fernando Rinaldi, Rainer Michalzik

Proceedings Volume 6997, 69971R (2008) https://doi.org/10.1117/12.781099

KEYWORDS: Vertical cavity surface emitting lasers, Refractive index, Etching, Oxides, Mirrors, Optical manipulation, Semiconductor lasers, Resistance, Numerical analysis, Laser damage threshold

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We report on the theoretical analysis and fabrication of a novel type of vertical-cavity surface-emitting laser (VCSEL) that provides selection of a certain higher-order transverse mode. This selection is based on a spatial variation of the threshold gain by adding an antiphase layer with an etched relief structure. The field intensity profile emitted from this laser is calculated numerically as well as with an analytical approach. The main factors that control the selected mode such as the threshold gain, the confinement factor, and the phase parameter are calculated as a function of the active aperture, aiming to achieve single higher-order transverse mode emission. For a given aspect ratio of a rectangular oxide aperture, the threshold gain difference between the selected and neighboring modes is maximized via the relief diameter and the size of the aperture. The fabrication process involves selective etching of the antiphase layer, passivation of the relief, oxidation of an AlAs layer to the desired aperture after reaching this layer using wet-chemical etching. N- and p-metalization processes are applied, followed by polyimide passivation. Finally, bondpad metalization is carried out for electrical contacting. Mode selection is successfully achieved. Attractive applications for such devices are found in optical manipulation of micro-particles such as sorting and separation.

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