Design of enhanced broadband optical couplers for long-infrared quantum well infrared photodetectors

Abstract

Quantum-well infrared photodetectors (QWIPs) have emerged as a promising technology for broadband detection, particularly used in highly uniform large area focal plane array (FPA) imaging systems. However, one of the main challenges for broadband QWIPs is to design broadband optical couplers. In this paper, we propose a broadband optical scheme suited for the long-wavelength infrared quantum-well (QW) active layers. Our design features a multiple-stairstep reflection grating, which operates as a resonant waveguide in conjunction with the semiconductor layers. Surface plasmon polariton and transverse magnetic waveguide modes are effectively excited and regulated to match the active region. Over 40% absorption efficiency of the quantum wells is achieved across the entire range from 9 to 12 μm. Moreover, the structure demonstrates excellent fabrication tolerance and can be well compatible with FPAs, which is favored for practical applications.