Transversely distorted high-contrast gratings for tailoring the optical field in vertical-cavity microlasers: enabling lithographically defined wavelength tuning and removing high-speed bottlenecks

Research Project, 2012 – 2015

This project will investigate the use of a transversely oriented high contrast grating (HCG) as a feedback element in a vertical cavity surface emitting microlaser (VCSEL). It builds on the unique properties of HCGs: the extremely high reflectance (>99.5%) that can be achieved, and the recently realized fact that the high-reflectance mechanism is surprisingly local, allowing for the HCG to be distorted by a spatial variation of grating parameters over the extension of the HCG. This leads to a variation in the phase of the reflected wave which allows for functions such as wavelength tuning or/and focusing to be built into the grating. The vertical cavity is very convenient for realizing such HCGs by microlithography. Moreover, the compact reflection in the HCG makes the mode volume in the VCSEL smaller, which allows for higher modulation speed. Based on all these observations high-speed lasers will be designed and fabricated using HCGs that strongly enforce single mode operation without additional elements for optical confinement. This enables more efficient electrical and thermal transport, further improving the high speed properties. We will also develop arrays of HCG-VCSELs, with individually designed HCGs causing the lasers to emit at different, precisely specified, wavelengths although they all share the same epitaxial structure. This should be a precursor of a monolithic wavelength division multiplexing (WDM) chip with single-channel modulation speeds beyond 40 Gb/s.

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