Proposal of an optical modulator based on resonant tunneling and intersubband transitions

We propose and analyze an optical modulator based on intersubband transitio ns. The absorption is modulated by modulating the carrier density in the gr ound state of a quantum well (QW). Electrons are injected resonantly into t his subband from a QW reservoir subband through a single barrier. When the two states are tuned out of resonance, the electrons are rapidly evacuated by means of the optical held, A waveguide based on surface plasmons is assu med in order to have a high optical mode overlap. Calculations are performe d for a cascaded structure with four periods, assuming InGaAs-InAlAs QWs, T he considered modulator structure operates at lambda =6.0 mum and is RC lim ited to 27 GHz, An extinction ratio of it is obtained with a low applied vo ltage of 0.6 V, At larger applied voltages, the absorption is bistable, Abs orption at shorter/longer wavelengths can be obtained by using materials wi th a larger/smaller conduction band offset. We also assess resonant tunneli ng from a 2-D electron gas reservoir into an array of quantum dots and comp are it to the 2-D-2-D tunneling resonance.