- enabling lithographically defined wavelength tuning and removing high-speed bottlenecks
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