Effect of transverse mode structure on the far field pattern of metal-metal terahertz quantum cascade lasers

Gellie, P.; Maineult, W.; Andronico, A.; Leo, Giuseppe; Sirtori, Carlo; Barbieri, Stefano; Chassagneux, Yannick; Coudevylle, Jean-René; Colombelli, R.; Khanna, Suraj P.; Linfield, E. H.; Davies, A. G.

doi:10.1063/1.3043795

Cited by 15 publications

(8 citation statements)

References 15 publications

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“…However, an accurate characterization of this effect will require integration of the output power across the entire laser far-field pattern, which is hard to quantify owing to the diffuse nature of the output beam from edge-emitting metalmetal waveguides. 15 In conclusion, we have demonstrated that the strong vertical mode confinement in metal-metal waveguides allows the reduction in the thickness of both mid-IR and THz QCL ARs far below the effective wavelength without a large increase in J th for THz devices. This result may considerably ease the demanding growth conditions for QCL ARs for which high power output is not a priority.…”

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confidence: 71%

Vertical subwavelength mode confinement in terahertz and mid-infrared quantum cascade lasers

Strupiechonski

Grassani

Fowler

et al. 2011

Applied Physics Letters

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We exploit the modal confinement properties of metal-metal ridge waveguides to investigate the effect of reducing the thickness of the active laser cores in both terahertz and mid-infrared quantum cascade lasers. Devices with active regions over 55 times thinner than the free-space emission wavelength are demonstrated. They show only a modest increase in threshold current density compared with conventional-thickness devices. The limited increase in threshold is possibly due to a parasitic current channel in addition to the radiative current channel. These structures could be useful for the development of ultra-low volume lasers.

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confidence: 71%

Vertical subwavelength mode confinement in terahertz and mid-infrared quantum cascade lasers

Strupiechonski

Grassani

Fowler

et al. 2011

Applied Physics Letters

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“…In contrast to the work reported in Ref. [20,21,22,23] we introduce a set-back along with additional losses given by a thin metallic layer, which is deposited onto functional devices, instead of using a highly-doped epitaxial layer. Finite element simulations are used to obtain frequency dependent optical losses in order to choose the right set-back width with respect to the laser waveguide width.…”

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confidence: 99%

Short pulse generation and mode control of broadband terahertz quantum cascade lasers

Bachmann

Rösch

Süess

et al. 2016

Optica

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We report on a waveguide engineering technique that enables the generation of a bandwidth up to ∼ 1 THz and record ultra-short pulse length of 2.5 ps in injection seeded terahertz quantum cascade lasers. The reported technique is able to control and fully suppress higher order lateral modes in broadband terahertz quantum cascade lasers by introducing side-absorbers to metal-metal waveguides. The side-absorbers consist of a top metalization set-back with respect to the laser ridge and an additional lossy metal layer. In continuous wave operation the side-absorbers lead to octave spanning laser emission, ranging from 1.63 to 3.37 THz, exhibiting a 725 GHz wide flat top within a 10 dB intensity range as well as frequency comb operation with a bandwidth of 442 GHz. Numerical and experimental studies have been performed to optimize the impact of the side-absorbers on the emission properties and to determine the required increase of waveguide losses. Furthermore, these studies have led to a better understanding of the pulse formation dynamics of injection-seeded quantum cascade lasers.

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“…However, the consequent sub-wavelength vertical light confinement leads to highly divergent output beams from the laser facets [5]. Several strategies have been investigated to achieve more directional light output, in either edge or surface-emitting configurations, while maintaining low threshold current densities (J th ) and high T max [6][7][8].…”

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Continuous-wave operation of 2.7 THz photonic crystal quantum cascade lasers

Sevin

Fowler

et al. 2010

Electron. Lett.

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Continuous-wave laser action has been achieved in a 2.7 THz quantum cascade device operating on the modes of a two-dimensional photonic crystal resonator. The photonic structure is patterned into the device top metal contact layer. The emission is obtained from the device surface. It is single lobed and highly directional. At cryogenic temperatures the output power is ≃300 mW.Introduction: Since their inception in 2002 [1], advances in long wavelength (60-300 mm) quantum cascade laser (QCL) designs have rapidly established this technology as the leading candidate for compact semiconductor sources of coherent terahertz radiation. While improvements in the design and performance of the QCL active region (AR) have slowed in recent years, leading to a stagnation of the maximum operation temperature T max of 186 K [2], constant refinement of the applied waveguide technology is addressing other important aspects of the device performance, in particular, the quality of the output beam pattern.Currently, the most efficient solution for a terahertz QCL waveguide relies on the tranverse magnetic (TM)-polarised plasmonic modes at the upper and lower interfaces between the dielectric semiconductor AR and metallic contact layers [3,4], in so-called metal -metal waveguides. However, the consequent sub-wavelength vertical light confinement leads to highly divergent output beams from the laser facets [5]. Several strategies have been investigated to achieve more directional light output, in either edge or surface-emitting configurations, while maintaining low threshold current densities (J th ) and high T max [6][7][8]. One such approach is the photonic crystal resonator in which single frequency surface emission can be achieved by patterning the upper metallic contact layer, at the expense of generally slightly higher waveguide losses and thus lower T max compared with standard FabryPerot ridge resonators [9 -11].Continuous-wave (CW) laser operation is dependent on the dissipation of heat through the relatively high thermal resistance material of the QCL device, such that the effective temperature within the AR does not exceed T max . Thus, CW laser action may be promoted not only by improving the heat flow within the device, but also by reducing the J th of a laser, either by refining the AR energy band structure or by enhancing the overall Q factor of the resonator.In this Letter, we implement a refined PhC design which allows CW singlemode laser operation at n ¼ 2.7 THz up to a heatsink temperature of 39 K, whilst maintaining highly directional and monochromatic surface emission. The target application of these devices is local oscillators for heterodyne detection, typically for astronomic detection applications [12], where cryogenic operation and hundreds of mW of output power are acceptable performance constraints. Fig. 1 Typical emission spectra of lasers under CW operation. Measurements performed at T ¼ 20 K, with Fourier transform infrared spectrometer (resolution: 0.125 cm 21 ) and DTGS detector Inset: Surface view of ...

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Effect of transverse mode structure on the far field pattern of metal-metal terahertz quantum cascade lasers

Cited by 15 publications

References 15 publications

Vertical subwavelength mode confinement in terahertz and mid-infrared quantum cascade lasers

Vertical subwavelength mode confinement in terahertz and mid-infrared quantum cascade lasers

Short pulse generation and mode control of broadband terahertz quantum cascade lasers

Continuous-wave operation of 2.7 THz photonic crystal quantum cascade lasers

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