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HCG VCSELs

Lupe

The VCSEL is a modern laser concept with devices emitting continuous wave at room temperature were reported. GaAs-based VCSELs have been intensely studied since the mid-1990s, and are now widely used in optical systems ranging from the laser mouse to optical interconnects. Due to the vertical emission behavior, the devices can be fully processed and characterized on-wafer without prior cleaving. Another interesting property of VCSELs, evolving from the very short optical cavity is the longitudinal single mode emission. Further, e.g. for sufficiently small apertures, VCSELs are also transverse single-mode. The modal behavior can be altered by many kinds of mode filters integrated into the cavity.

With the advances in semiconductor fabrication technologies, nanostructures could not only be utilized by crystal growth, but also by means of nanomachining. By imbedding nanostructures with high refractive index contrast in the VCSEL design, the light in the laser cavity can be confined.

Especially for VCSELs, polarization stability has been a challenge, as the structure does not have an intrinsic polarization preference. For effective polarization control, a mode filter is needed. Gratings with a high refractive index contrast to the surrounding media (HCG, high-contrast grating) can provide high reflectivity for only one polarization and provide reflectivities > 99.9%.

Moreover, a HCG cannot only be employed to control the polarization VCSEL emission, but it can even suppress the higher-order traverse modes of large aperture devices.

Recent works at the center of nanophotonics at TU Berlin focus on fabrication of high quality HCG to be embedded with the successful conventional VCSEL designs as depicted in Figure. Energy efficient, polarization stable, high-power, high-speed VCSELs are expected making use of the advances made in the nanofabrication and nanostructuring technologies.

The HCG design requires a large effort of numeric. Utilizing the Finite-difference time-domain method, some design parameters should be chosen carefully for a later reliable performance.

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Betreuer: Wissam Hamad

Ansprechpartner: Prof. Werner Hofmann

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