Characterization of Active Regions for InP-Based MEMS-VCSELs

Examensarbete för masterexamen
Master Thesis
Engineering Physics (300 hp)
Haglund, Erik
Widely tunable MEMS-VCSELs with a tuning range exceeding 50 nm are currently being developed for applications in reconfigurable optical networks and sensor systems. The tuning range of MEMS-VCSELs is today mainly limited by the width and magnitude of the gain spectra. In order to design new devices with improved performance, especially improved tuning range, detailed knowledge of the gain properties is required. Due to the difficulties associated with performing reliable gain spectra imulations, this thesis is concerned with implementing an experimental procedure to determine the gain haracteristics of an active region. An MBE-grown active region with two AlGaInAs quantum wells was characterized. The gain spectra of the active region was determined by measuring the ASE-spectra and using the Hakki-Paoli method to compute the gain [1]. Care was taken to reduce the influence of the OSA limited linewidth. The Hakki-Paoli method can not be applied directly on a VCSEL, due to its very long free spectral range. The active region was therefore characterized by measurements on edge-emitting Metal-Clad Ridge-Waveguide (MCRW) laser diodes. The lasers had ridge widths of 2-30 μm and lengths of 300-1500 μm. The laser wavelength was 1.5 μm. Due to the lack of lateral current confinement nderneath the ridge, the lasers showed a lateral carrier diffusion with almost 20% of the injected current flowing outside of the ridge at threshold for 5 μm wide ridges. To be able to predict the VCSEL gain from the gain measured in the MCRW lasers, the empirical material gain parameter g0 was calculated from the measurements. Only the relevant fundamental TE mode was measured by coupling the light into the OSA using a smallaperture polarization maintaining fiber with an in-fiber polarizer. The influence of the current density and heatsink temperature on the gain peak wavelength, FWHM and gain magnitude was investigated. A g0=1441 cm¡1 was measured at 15oC. The peak gain was red-shifted with 0.77 nm/K, and blue shifted with 0.91 nm/mA. The peak net gain was found to decrease with 0.49 cm¡1/K.
Informations- och kommunikationsteknik , Nanovetenskap och nanoteknik , Fotonik , Nanoteknik , Information & Communication Technology , Nanoscience & Nanotechnology , Photonics , Nano Technology
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