We have recently demonstrated that mid-infrared saturable-absorber mirrors and optical power limiters can be constructed using the concept of intersubband polaritonic metasurfaces – devices in which intersubband transitions in a semiconductor heterostructure are strongly coupled with optical modes in nanoresonators. Our original demonstration produced only relatively small (~20%) variation in reflection between low and high intensity illumination. We have now optimized the metasurface design, relying on a GaAsSb-InGaAs heterostructure that provides narrower-linewidth intersubband transitions, increased doping density, and utilized transitions between excited states to significantly improve the experimentally-measured reflectivity contrast, which now spans from 80% to 10% for different illumination intensities.
Nonlinear metasurfaces based on coupling of intersubband transitions in n-doped semiconductor heterostructures with optical modes in nanoresonators provide the largest known second-order nonlinear response in condensed matter systems in the mid-infrared spectral range. However, these giant nonlinearities are only present at relatively low pumping intensities which limits the maximum achievable frequency conversion efficiency. We experimentally investigate a new nonlinear intersubband metasurface design for second harmonic generation based on two-level nonlinear intersubband system that provides high nonlinearity combined with significantly reduced intensity saturation compared to the intersubband metasurfaces based on three-level intersubband systems demonstrated so far.
In this talk, we discuss our recent progress in the area of non-reciprocal photonics, discussing approaches to break reciprocity without magnetic bias, using temporal modulation schemes or nonlinearities. We will discuss our progress in the synthesis of non-reciprocal devices based on these principles, and arrays of them to enable topological bandgaps with non-reciprocal response.
The time-bandwidth limit refers to the trade-off between the time delay that can be applied to a signal as it travels through a device and its bandwidth. Recently, there have been several studies showing that this bound can be broken in nonreciprocal nano-structures, including nonreciprocal cavities and terminated unidirectional waveguides. Here, we explore the physical mechanisms involved in these structures, and explore the opportunities offered by non-reciprocal elements to control the delay applied to an impinging signal.
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