Efficient extraction of terahertz wave totally reflected at semiconductor surface by double metal gratings

We propose double metal grating as a way of extracting terahertz (THz) wave which is totally reflected at the surface of THz emitter such as quantum cascade lasers, THz parametric oscillators, etc. By tuning the grating parameters, efficiencies as high as 60% for vertical output and 70% for tilted output is predicted assuming practical material loss. The high efficiency is realized by the control of Fano resonance between the direct and resonant scatterings, the latter introduced as the Fabry-Perot resonance between the two gratings. Then, the results are analyzed using temporal coupled mode theory, to show how the high efficiency is realized.

I. Introduction

For the applications of terahertz (THz) waves, compact and easy-to-use emitter with sufficient output power is strongly required. Quantum cascade lasers (QCLs) including a type based on difference-frequency-generation (DFG)[1] and THz parametric oscillators (TPOs)[2] or generators (TPGs)[3] are the good candidates. In these devices, the extraction of THz waves not via the side facets but via the top or bottom surface would be beneficial to avoid the reabsorption of the THz waves inside the device. For such purpose, grating or prism is necessary [4]. Here we consider the gratings which can be fabricated by a standard lithographic method.