An optical modulator includes an emitter layer with N-type doping having a first bandgap energy; a base layer with P-type doping having a second bandgap energy; a sub-emitter layer disposed between the emitter layer and the base layer, wherein the sub-emitter layer has a third bandgap energy that is less than both the first bandgap energy and the second bandgap energy. The sub-emitter layer provides a barrier to electrons flowing from the emitter layer, while allowing photo-generated holes to recombine in the sub-emitter layer thereby mitigating current amplification.

A nonlinear metasurface structure including a multi-quantum-well layer designed for a nonlinear response for a desired nonlinear optical process and an array of nanoantennas coupled to the intersubband transitions of the multi-quantum-well layer. Each nanoantenna in the array is designed to have electromagnetic resonances at or close to all input and output frequencies of a given nonlinear optical process. Nanoantennas allow efficient coupling of any incident and outgoing light polarizations to intersubband transitions. Nanoantennas may further provide significant field enhancement in the multi-quantum-well layer. As a result, the nonlinear metasurface structure can be designed to produce a highly nonlinear response for any polarization and angle of incidence of incoming and outgoing waves in a nonlinear optical process. Due to their very larger nonlinear response, efficient frequency conversion can be produced in these metasurfaces without the stringent phase-matching constraints of bulk nonlinear crystals.

A nonlinear metasurface structure including a multi-quantum-well layer designed for a nonlinear response for a desired nonlinear optical process and an array of nanoantennas coupled to the intersubband transitions of the multi-quantum-well layer. Each nanoantenna in the array is designed to have electromagnetic resonances at or close to all input and output frequencies of a given nonlinear optical process. Nanoantennas allow efficient coupling of any incident and outgoing light polarizations to intersubband transitions. Nanoantennas may further provide significant field enhancement in the multi-quantum-well layer. As a result, the nonlinear metasurface structure can be designed to produce a highly nonlinear response for any polarization and angle of incidence of incoming and outgoing waves in a nonlinear optical process. Due to their very larger nonlinear response, efficient frequency conversion can be produced in these metasurfaces without the stringent phase-matching constraints of bulk nonlinear crystals.