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Intersubband Polariton Emitters

The investigation of the strong coupling regime between intersubband transitions (ISB) in semiconductor quantum wells and cavity photons has enormous potential in the mid- and far-infrared for improving device performance and creating fundamentally new types of devices.  Photonic devices based on ISB transitions in quantum wells, such as the quantum cascade laser and quantum well infrared photodetectors, are examples of successful ISB devices.  Electrically injected optical devices incorporating ISB polaritons could be the next game-changing device in the infrared.

To realize polariton exicitation process, materials with ISB properties such as InP and GaAs are designed based on active region – multi-layered quantum wells. Most of the researchers have concentrated on edge-emitting structures due to the intrinsic transverse-magnetic (TM) polarization of ISB transitions. However, surface emission with two-dimensional photonic crystals which can be used to create localized microcavity light sources is becoming particularly appealing because of properties like high Q factor, high-power, low loss due to periodic Bragg mirror structure as well as flexibility of the designers. 

In this research, a strategy is proposed to achieve mid-infrared ISB polariton light emission based on 1D and 2D photonic crystal cavities. With plane wave expansion (PWE) analysis and FDTD analysis, a honeycomb lattice for creating 2D photonic crystal polarition emitter structure is designed for mid-infrared wavelength. A full 2D optical bandgap for TM polarization can be obtained and localized modes can be generated through creating a defect in 2D photonic crystal structure. By tuning the defect size and layered defect quantum well region, a tailored wavelength light can be excited with possible lateral electrical injection. In addition, several 1D tapered photonic crystal structures are also discussed to make comparisons and provide fabrication simplicity. 

Simulation results have shown well-localized modes in both 2D and 1D photonic crystal cavity structures. Fig.1 shows that  light can be generated in semiconductor defect region by tuning air hole size – lattice constant ratio. While Fig.2 shows that 3 times 3 expansion of 1D tapered defect region with localized modes.