Influence of the facet type on the performance of terahertz quantum cascade lasers with double-metal waveguides

Brandstetter, Markus; Krall, Michael; Deutsch, C.; Detz, Hermann; Andrews, A. M.; Schrenk, W.; Strasser, G.; Unterrainer, K.

doi:10.1063/1.4811124

Cited by 17 publications

(14 citation statements)

References 20 publications

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“…However, for typically used THz QCL waveguides the output aperture is on the order of 10 µm, while the emission wavelength is about 100 µm. This, in fact, leads to a very divergent output beam, which is additionally distorted by interference effects [10,11]. Since external optical elements such as lenses or antennas are difficult to handle on a large scale [12,13], several monolithic concepts have been pursued to address this issue.…”

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confidence: 99%

Random lasers for broadband directional emission

Schönhuber

Brandstetter

Hisch

et al. 2016

Optica

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Broadband coherent light sources are becoming increasingly important for sensing and spectroscopic applications, especially in the mid-infrared and terahertz (THz) spectral regions, where the unique absorption characteristics of a whole host of molecules are located. The desire to miniaturize such light emitters has recently lead to spectacular advances with compact on-chip lasers that cover both of these spectral regions. The long wavelength and the small size of the sources result in a strongly diverging laser beam that is difficult to focus on the target that one aims to perform spectroscopy with. Here, we introduce an unconventional solution to this vexing problem relying on a random laser to produce coherent broadband THz radiation as well as an almost diffraction limited far-field emission profile. Our random lasers do not require any fine-tuning and thus constitute a promising example of practical device applications for random lasing.Various spectroscopic techniques rely on the specific absorption features of numerous molecules within the midinfrared and terahertz (THz) spectral regions, which allow their unambiguous identification. Although broadband coherent sources of radiation are already available within these frequency regions [1][2][3][4][5], a compact size and electrically pumped operation are additionally desired for actual applications. These criteria are fulfilled by quantum cascade lasers (QCLs), semiconductor sources which are able to provide broadband emission at mid-infrared [6,7] and THz [8,9] frequencies. However, for typically used THz QCL waveguides the output aperture is on the order of 10 µm, while the emission wavelength is about 100 µm. This, in fact, leads to a very divergent output beam, which is additionally distorted by interference effects [10,11]. Since external optical elements such as lenses or antennas are difficult to handle on a large scale [12,13], several monolithic concepts have been pursued to address this issue. To improve the far-field for facet emission, e.g., a 3rd order distributed feedback (DFB) grating can be used [14]. Another approach is to coherently emit from a large area on the laser surface. In contrast to interband semiconductor lasers, QCLs can only generate in-plane radiation due to intersubband selection rules, preventing the realization of VCSELtype resonators. Thus several concepts have been developed to couple out the in-plane cavity mode in vertical direction, including 2nd order DFB gratings [15,16] , and photonic crystal (PhC) cavities [17]. Recently, also non-periodic resonator structures such as graded photonic heterostructures [18], or quasicrystal cavities [19,20] have been developed. However, all on-chip techniques providing surface emission demonstrated so far are designed to support a single laser mode only, while for many spectroscopic applications a broadband coherent light source is necessary. To achieve the objective of a broadband and at the same time very collimated laser light emission in the THz regime, we propose here a radical ...

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confidence: 99%

Random lasers for broadband directional emission

Schönhuber

Brandstetter

Hisch

et al. 2016

Optica

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“…Only the emission from one end of the QCL was modeled in the simulation. We thus neglect any fringes in the far-field that originate from the interference of the emission between the opposite facets [26]. The total efficiency, which is defined as the radiated power (integrated over all angles) divided by the input power, of the MMHS waveguide is calculated to be 2.2 times that obtained for the MM waveguide at a frequency of 2.5 THz.…”

Section: Introductionmentioning

confidence: 99%

Improving the Out-Coupling of a Metal-Metal Terahertz Frequency Quantum Cascade Laser Through Integration of a Hybrid Mode Section into the Waveguide

Fobbe

Nong

Schott

et al. 2016

J Infrared Milli Terahz Waves

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“…In terms of sources, despite their need for cryogenic cooling, THz quantum cascade lasers (QCL) [1,2] are the only high spectral purity [3] solid state sources that can provide hundreds of mW levels of power in the 2-5 THz band [4,5]. One of the key issues in THz QCL technology is, however, the divergence of the outcoming beams: in a standard edge emitting configuration the radiation is emitted in a beam with approximately 30° divergence for single-plasmon waveguides [6], whereas an almost isotropic emission, rich in fringes, is seen for the case of double-metal [7] waveguides. This is principally due to diffraction at the subwavelength-sized laser facet, and interference between emissions from the two cleaved facets.…”

Section: Introductionmentioning

confidence: 99%

THz waveguide adapters for efficient radiation out-coupling from double metal THz QCLs

Castellano¹,

Li²,

Linfield³

et al. 2015

Opt. Express

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Abstract:We report the development of on-chip optical components designed to improve the out-coupling of double-metal terahertz (THz) frequency quantum cascade lasers (QCLs). A visible reshaping of the optical beam is achieved, independent of the precise waveguide configuration, by direct incorporation of cyclic-olefin copolymer (COC) dielectric optical fibers onto the QCL facet. A major improvement is further achieved by incorporating a micromachined feed-horn waveguide, assembled around the THz QCL and integrated with a slit-coupler. In its first implementation, we obtain a ± 20° beam divergence, offering the potential for high-efficiency radiation coupling from a metal-metal waveguide into optical fibers.

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Influence of the facet type on the performance of terahertz quantum cascade lasers with double-metal waveguides

Cited by 17 publications

References 20 publications

Random lasers for broadband directional emission

Random lasers for broadband directional emission

Improving the Out-Coupling of a Metal-Metal Terahertz Frequency Quantum Cascade Laser Through Integration of a Hybrid Mode Section into the Waveguide

THz waveguide adapters for efficient radiation out-coupling from double metal THz QCLs

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