THz quantum cascade lasers based on a hyperuniform disordered optical cavity design

A terahertz quantum cascade laser has been realized from an isotropic disordered hyperuniform design. Such a system presents a photonic band-gap (PBG) although it is characterized by an efficient depletion of long range order, which is counterintuitive. In this work, a hyperuniform distribution pattern, which is characterized by the total suppression of density fluctuations for long wavelengths [1] was investigated. The statistical properties of the distribution are globally isotropic while locally the system is anisotropic. Hyperuniform disordered patterns allow greater versatility in engineering band gaps in comparison to standard photonic-crystal and quasi-crystal designs. In fact, these PBGs can be tuned by acting a priori on an order parameter which regulates the degree of disorder in the system. The procedure for the realization of a 2D hyperuniform pattern has been done according to Ref. [1] and is based on a 2D scatterers distribution. The final design consists of a hyperuniform distribution of disks arranged in a hexagonal tile. This pattern was transferred in a finite element method solver (Comsol Multiphysics v4.2), where the eigenmodes are computed using the effective index approximation, in order to simulate the real device. The system presents a PBG as large as 17%. The highest Q-factor modes lies at the lower edge of the PBG and are localized, as shown in Fig. 1 a). The device fabrication is similar to the process described in [2] for the fabrication of photonic crystal THz QCL. An active region design with center emission frequency around at 3.1 THz, was processed into a disordered hyperuniform distribution of pillars, whose size have been scaled in order for the lower edge of the PBG to match the gain profile of the active region.