Epsilon-Near-Zero Enhancement of Nonlinear Responses from Intersubband Transitions in the Mid-Infrared

摘要

Many applications of photonics require efficient nonlinear optical interactionswith low power and small footprints. However, the current needs for longinteraction lengths and strong laser sources of nonlinear optical devices makethem unsuitable for nanophotonic integrated optics. New materials anddevices with stronger nonlinear properties have been developed using variousapproaches in the past few years. One of the largest nonlinear opticalresponses reported to date has been realized with engineered intersubbandtransitions in n-doped multiple quantum wells (MQWs) semiconductors.Here, this work proposes to improve further the nonlinear properties of aMQW heterostructure by tailoring its permittivity to reach near-zero values.Materials with vanishing permittivity, called epsilon-near-zero (ENZ)materials, have exotic nonlinear features which can be explored to achieve thisgoal. To prove this point, this work makes use of In_(0.53)Ga_(0.47)As/Al_(0.48)In_(0.52)As,designs an ultrathin multilayer structure, and couples the designed structurewith metasurfaces. Unprecedented nonlinear efficiency within subwavelengthpropagation lengths is obtained. Such structure with strong second harmonicgeneration (SHG) enables efficient frequency conversion, while the tunabilityoffered by the metasurface provides new degrees of freedom to control theamplitude, phase, and polarization of the nonlinear light.