KEYWORDS: Quantum wells, Waveguides, Semiconducting wafers, Semiconductor lasers, Optical tweezers, Signal attenuation, High power lasers, Lab on a chip, Refractive index, Cladding
Record values for the rollover power and rollover linear power densities of 9xx nm devices, obtained by simultaneous
scaling of length and d/Γ, are reported. The values for d/Γ lay in the range 0.8 μm to 1.2 μm with corresponding cavity
lengths from 3.5 mm to 5 mm. The transversal structures were asymmetric, with a higher refractive index on the n side.
An optical trap was helpful in reducing the radiation extension on the p side and the overall thickness. The highest
rollover linear power densities were 244 mW/μm for structures without an optical trap and 290 mW/μm for those that
included an optical trap
Two double-waveguide 940 nm asymmetric structures with 8 nm InxGa1-xAs quantum well (x = 0.13) are presented. They consist of an active region waveguide that includes a QW and an optical trap waveguide on the n side of the active region. The second structure has a supplementary optical wall in the p - clad that further pushes the optical field from the active region and reduces the confinement factor. The nominal lengths were chosen as 2.8 mm and 4 mm and the design values for the d/gamma ratio were 0.8 μm and 1.14 μm, respectively. Devices were fabricated with 100 μm apertures and yielded threshold current densities of 0.2 kA/cm2 and 0.17 kA/cm2 with corresponding slope efficiencies of 0.76 W/A and 0.85 W/A. At high current levels devices presented a power saturation behavior. The highest power values were 9.7 W (rollover) and 11.5 W (CMOD), respectively.
High d/G allows high total emitted power and avoids high power density in the active QW layer where power induced degradation processes occur. d/G is scaled up to 0.84 micrometers in a series of four 7 nm thick single QW AlGaAs structures, designed for 810 nm wavelength. Two structures have an asymmetric design that includes an optical trap next to the active region. The optical trap captures a part of the total radiation flux and reduces the confinement factor. One of asymmetrical structures includes an optical wall built into the p cladding layer that further pushes the radiation flux toward the trap. Device lengths are inversely proportional to the confinement factor; therefore all lasers optimally operate at the same current density. All have approximately the same threshold current density equal to 250 A/cm2. For the 0.84 micrometers d/G case, the nominal length is 2.8 mm, the attenuation coefficient is 0.7 cm-1 and the slope efficiency is 0.96 W/A. The thermal rollover maximum power is greater than 8 W/100micrometers .
Iulian Petrescu-Prahova, Manuela Buda, Gheorghe Iordache, Fouad Karouta, Barry Smalbrugge, Theo van de Roer, L. Kaufmann, Joachim Wolter, Willem van der Vleuten
Low confinement laser diode structure permits lower modal gain, longer devices and wider stripes. The optimum value of the confinement factor is correlated with the modal attenuation coefficient. For an 1 cm-1 modal attenuation coefficient, the optimum operation is obtained in 12 micrometers stripe and 0.007 confinement factor. In such structures, fundamental lateral mode is preserved at power higher than 1 W.
Designing of laser diodes needs waveguide parameter optimization and testing. In order to maximize the emitted power of a laser diode an important design parameter is the optical confinement factor (Gamma) of the active region and the reduced confinement factor g equals G/d, where d is the active region thickness. This paper presents a measurement method of the reduced confinement factor by correlating changes in absorption loss with the current density of injected free carriers, for a LPE fabricated double heterostructure single quantum well laser diode with the active region thickness of about 0.1 micrometers . A reduced confinement factor of 8.5 10-2 micrometers -1 and waveguide absorption coefficient of 1.8 cm-1 of the laser diode are reported.
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