The far-field of metal-metal terahertz quantum cascade lasers is greatly improved through integrated and stable planar horn antennas on top of the QCL ridge. The antenna structures introduce a gradual change in the high modal confinement of metal-metal waveguides and permit an improved far-field, showing a five times increase in the emitted output power. The two dimensional far-field patterns are measured at 77K and compared to electromagnetic simulations. The influence of parasitic high order transverse modes are restricted through the engineering of antenna structure (ridge and antenna width) to couple out the fundamental mode only

Colombelli, R

Davies, AG

Dhillon, SS

Kundu, I

Li, L

Linfield, EH

Mangeney, J

Moumdji, S

Tignon, J

Wang, F

White Rose Research Online

Far-field engineering of metal -metal terahertz quantum cascade lasers with integrated horn antennas

F. Wang

I. Kundu

L. Li

E. H. Linfield

A. G. Davies

S. Moumdji

R. Colombelli

J. Mangeney

J. Tignon

S. S. Dhillon

Crossref

Far-field engineering of metal-metal terahertz quantum cascade lasers with integrated horn antennas

This is a repository copy of Far-field engineering of metal -metal terahertz quantum cascade lasers with integrated horn antennas.White Rose Research Online URL for this paper:http://eprints.whiterose.ac.uk/87405/Version: Accepted VersionProceedings Paper:Wang, F, Kundu, I, Li, L et al. (7 more authors) (2015) Far-field engineering of metal -metalterahertz quantum cascade lasers with integrated horn antennas. In: 2015 40th International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz). International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 23-28 Aug 2015, Hong Kong. IEEE . ISBN 9781479982721 https://doi.org/10.1109/IRMMW-THz.2015.7327479eprints@whiterose.ac.ukhttps://eprints.whiterose.ac.uk/Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version - refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher’s website. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Abstract— The far-field of metal-metal terahertz quantum cascade lasers is greatly improved through integrated and stable planar horn antennas on top of the QCL ridge. The antenna structures introduce a gradual change in the high modal confinement of metal-metal waveguides and permit an improved far-field, showing a five times increase in the emitted output power. The two dimensional far-field patterns are measured at 77K and compared to electromagnetic simulations. The influence of parasitic high order transverse modes are restricted through the engineering of antenna structure (ridge and antenna width) to couple out the fundamental mode only. I. INTRODUCTION erahertz (THz) quantum cascade laser (QCL) are semiconductor sources based on intersubband transitions and permit laser emission over a large portion of the THz spectrum. THz QCLs have shown considerable advancements with high power output and high temperature operation. However, typically these two parameters cannot be demonstrated simultaneously. The highest temperature operation of 200K has been demonstrated with metal-metal (MM) waveguides, where the high modal confinement permits a high modal gain. However, a disadvantage of the latter is a highly diffracted beam and a large facet reflectivity leading to weak directionality and low output powers, respectively. Several monolithic methods have been proposed and realized to resolve this problem. These are based on second-order grating or photonic structures for surface emission [1] but are inherently mono-frequency and thus not adapted for broadband emission. The latter is interesting in the case of modelocking or frequency comb generation. Most broadband techniques, however, have been based manual positioning techniques such as silicon laser placed on the facet or suspended antenna structures [2]. A promising technique has been recently demonstrated where planar horn antennas (PHAs) are etched onto the top of the QCL surface, permitting the confined mode to be better matched to a radiative mode [3]. This has allowed a considerable increase in the output power without effecting greatly the temperature performance of the QCL. This greatly simplified approach has proven to be stable and broadband. Indeed injection seeding of bound-to-continuum QCLs have been recently demonstrated taking advantage of the inherent broadband characteristics of the antenna structure [3]. However, no control of the far-field was demonstrated with only one-dimensional profiles of the far field investigated. In this work, we demonstrate how the far-field can be controlled by engineering the transverse modes and the geometry of the horn antenna and ridge. We show two dimensional far field patterns and compare these with electromagnetic simulations that show a good agreement, as shown in figure 1 for a QCL operating at 3.2THz and held at a temperature of 77K. As shown, there is a good agreement between simulated (right) and measured (left) far-fields with the horn antennas extracting more power from the cavity. We also show that the ridge width is an inportant factor with the large ridge coupling out a high order bi-lobe mode of the QCL while a thin ridge allows coupling of the only the fundamental mode.    Fig. 1. Simulated far-field patterns (right side) of metal-metal THz QCLs and theirs corresponding far-field patterns measured at 77K (left). (a) 40µm-wide metal-metal THz QCL (b) 80µm-wide metal-metal THz QCL. a) and b) are with ~150µm-long planar horn antennas integrated onto QCL top metal at both side of the facet. (c) 60µm-wide metal-metal THz QCL without any planar horn antenna. REFERENCES [1]. G. Xu et al. "Efficient power extraction in surface-emitting semicon lasers using graded photonic heterostructures", Nat. Comm 3, 952 (2012). [2]. W. Maineult et al, "Metal-metal THz QCL with micro-transverse-electromagnetic-horn antenna", Appl, Phys. Lett.  93, 18 508 (2008).  [3]. A. Brewer et al, “Coherent detection of metal-metal terahertz quantum cascade lasers with improved emission characteristics” Appl, Phys. Lett.  104, 081107 (2014)  F. Wang1, I. Kundu3, L. Li3, E. H. Linfield3, A. G. Davies3, S. Moumdji2, R. Colombelli2, J. Mangeney1, J. Tignon1 & S. S. Dhillon1 1Laboratoire Pierre Aigrain, Ecole Normale Supérieure-PSL Research University, CNRS, Université Pierre et Marie Curie-Sorbonne Universités, Université Paris Diderot-Sorbonne Paris Cité, 75231 Paris, France 2Institut d’Electronique Fondamentale, Université Paris Sud, CNRS, UMR 8622, 91405 Orsay, France 3School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds LS29JT, UK Far-field engineering of metal-metal terahertz quantum cascade lasers with integrated horn antennas T 

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Far-field engineering of metal -metal terahertz quantum cascade lasers with integrated horn antennas

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