Complex-coupled photonic crystal THz lasers with independent loss and refractive index modulation

Hua Zhang,Romuald Houdré,Mattias Beck,Jérôme Faist,Giacomo Scalari

doi:10.1364/oe.19.010707

Abstract

Compared to near infra-red photonic crystal (PhC) band-edge lasers, achieving vertical emission with quantum cascade (QC) material operating in the THz range needs dedicated engineering because the TM polarized emission of QCLs favors in-plane emitting schemes and the currently used double plasmon waveguide, prevents vertical light extraction. We present an approach with independent refractive index and extraction losses modulation. The extraction losses are obtained with small extracting holes located at appropriate positions. The modal operation of the PhC is shown to critically depend on the external losses introduced. Very high surface emission power for optimum loss extractor design is achieved.

Highlights

Surface emission is always a challenging task for semiconductor lasers [1,2], especially with quantum cascade (QC) active material operating in the terahertz (THz) range
Compared to near infra-red photonic crystal (PhC) band-edge lasers, achieving vertical emission with quantum cascade (QC) material operating in the THz range needs dedicated engineering because the TM polarized emission of QCLs favors in-plane emitting schemes and the currently used double plasmon waveguide, prevents vertical light extraction
Such approach can be used as a general tool for the development of both electrical and optical pumped devices at any frequencies based on index modulation devices

Summary

Introduction

Surface emission is always a challenging task for semiconductor lasers [1,2], especially with quantum cascade (QC) active material operating in the terahertz (THz) range. We will focus on an approach based on deeply etched pillars that provide a full TM gap, and excellent performances in terms of drive current and high temperature operation thanks to propagation losses reduction combined with the benefit that only the area with a large field overlap is pumped [12] Such devices do not allow surface emission as the slow light mode lies outside of the light cone [12]. Compared to near infra-red PhC band-edge lasers, achieving vertical emission with quantum cascade (QC) [13] material operating in the THz range [14,15] needs dedicated engineering because, even if the operating Bloch states lies within the light cone, the TM polarized emission of QCLs favors in-plane emitting schemes and secondly because the currently used [16] double plasmon waveguide, which provides nearly unitary mode confinement, prevents vertical light extraction [12] unless the top metal layer is appropriately turned semi-transparent. These holes introduce periodic losses to the existing system while barely disturbing the overall dispersion

Design

Device fabrication and characterization

Conclusion