Interband Cascade Lasers, from Fabry-Pérot Waveguides to Subwavelength Cavities

Abstract

This research in centered around engineering approaches to improve the electro-optical performance of interband cascade lasers. The enhancement strategies are ranging from empirical design optimizations and fabrication and packaging techniques to design and application of optical coating. These improvements resulted in room temperature (RT) CW optical powers of 40 mW, as well as, internal loss and threshold current densities as low as 4.9 cm^-1 and 365 A/cm^2 respectively. Moreover, additional improvements resulted in devices with threshold current density as low as 320 A/cm^2 and wall plug efficiency reaching up to 5.9% for a 1 mm device producing 20.3 mW CW RT output power. Application of Antireflection (AR) coatings to interband cascade lasers not only led to identification of several promising material combinations for AR coatings in Mid-Infrared (Mid-IR) region of the spectrum, but was also used to study the fundamental laser parameters such as internal efficiency and leakage current. AR coatings ranging from 0.15 to 7E-4 were designed and fabricated on ICL waveguide facets. By monitoring the laser performance before and after coating a direct relation between carrier concentration and leakage currents was observed and an optimal reflectivity value of 9.6E-3 was experimentally extracted in order to achieve the maximum slope efficiency for a 1 mm device. As the next step toward utilization of the Mid-IR ICLs a systematic approach to design of sub-wavelength cavities was developed with universal applications in active plasmonic cavities. Key parameters such as quality factor, confinement factor, and threshold gain have been calculated and their dependence of cavity parameters are demonstrated which enables a flexible design for various applications. In particular a coaxial cavity with energy confinement factor of 84% and mode volume of 0.14 λ/2n^3 and quality factor of Q=515 was designed at 3.55 λm. The dependence of the emission wavelength to the surrounding refractive index was also demonstrated with potential sensing applications.