Berlin 2008 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 34: Semiconductor Laser
HL 34.7: Talk
Wednesday, February 27, 2008, 16:00–16:15, EW 202
Tapered Quantum Cascade Lasers — •Julia Semmel1, Lars Nähle2, Wolfgang Kaiser1, Sven Höfling1, and Alfred Forchel1 — 1Technische Physik Universität Würzburg, Am Hubland, 97074 Würzburg — 2Nanoplus GmbH, Oberer Kirschberg 4, 97218 Gerbrunn
Quantum Cascade Lasers (QCLs) are unipolar devices that have shown excellent performance in the mid-infrared wavelength range. For most applications, however, the beam divergence of the devices is a limiting factor, since it affects the coupling efficiency and resolution. In order to improve the horizontal far field characteristics, gain guided tapered sections have been introduced in 1996 [1]. They allow the fundamental mode to expand towards a broader output facet, which leads to a narrow far field.
In QCLs the gain guided approach can not be realized, since the laser structure displays an anisotropic electrical conductivity, which makes etching through the whole active region a necessity.
We report on index guided quantum cascade tapered lasers, which are based on a 2LO-Phonon-Resonace design [2]. The one-step dry-etching process provides etching depths of up to 12 µ m with smooth, perpendicular edges. The output power of the tapered lasers at room temperature is as high as 300 mW and the FWHM angle of the horizontal far field scan is as small as 6.6 ∘ for a device with a 100 µ m wide output facet.
References: [1] J. N. Walpole, Optical and Quantum Electronics, 28 (1996) 623; [2] Liu et al., Phot. Technol. Lett., 18 (2006) 1347