Lateral distributed-feedback gratings for single-mode, high-power terahertz quantum-cascade lasers

M Wienold,K Biermann,L Schrottke,H T Grahn,R Sharma,X Lü,R Hey,A Tahraoui

doi:10.1364/oe.20.011207

Abstract

We report on terahertz quantum-cascade lasers (THz QCLs) based on first-order lateral distributed-feedback (lDFB) gratings, which exhibit continuous-wave operation, high output powers (>8 mW), and single-mode emission at 3.3-3.4 THz. A general method is presented to determine the coupling coefficients of lateral gratings in terms of the coupled-mode theory, which demonstrates that large coupling strengths are obtained in the presence of corrugated metal layers. The experimental spectra are in agreement with simulations of the lDFB cavities, which take into account the reflective end facets.

Highlights

Terahertz quantum-cascade lasers (THz QCLs) have been proposed and demonstrated for applications such as local oscillators in heterodyne receivers [1,2,3,4,5] above 2 THz. This requires THz QCLs, which operate in continuous-wave mode with a high output power in a single spectral mode
An alternative approach is the use of lateral DFB gratings [14,15,16], which allow for a closed top metallization such as for Fabry-Perot THz QCLs
THz QCLs with first-order lateral DFB (lDFB) gratings and sub-mW output powers have already been demonstrated for metal-metal waveguides [15], for which the optical mode is confined between two metal layers

Summary

Introduction

Terahertz quantum-cascade lasers (THz QCLs) have been proposed and demonstrated for applications such as local oscillators in heterodyne receivers [1,2,3,4,5] above 2 THz. The two conventional approaches for obtaining single-mode QCLs have been distributed-feedback (DFB) gratings and external-cavity setups [7,8]. An alternative approach is the use of lateral DFB (lDFB) gratings [14,15,16], which allow for a closed top metallization such as for Fabry-Perot THz QCLs. The advantages of lateral gratings are a homogeneous current injection and the possibility of using a larger number of bonding wires, which reduces the current load for each wire and the risk of failure in the case of cw operation. THz QCLs with first-order lDFB gratings and sub-mW output powers have already been demonstrated for metal-metal waveguides [15], for which the optical mode is confined between two metal layers. Experimental results are discussed and compared to simulations of the lDFB cavities

Modeling of lateral gratings

Experimental results and discussion

Summary and conclusions