Efficient power extraction in surface-emitting semiconductor lasers using graded photonic heterostructures

Xu, Gangyi; Colombelli, R.; Khanna, Suraj P.; Belarouci, Ali; Letartre, Xavier; Li, Lianhe; Linfield, E. H.; Davies, A. G.; Beere, Harvey E.; Ritchie, D. A.

doi:10.1038/ncomms1958

Cited by 125 publications

(90 citation statements)

References 47 publications

(54 reference statements)

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“…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.…”

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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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“…On one hand, this is a promising architecture for polaritonic LEDs. On the other hand, with the appropriate lifetime engineering, the occupation number of the ground state could be improved and even reach the value of 1, necessary for the final state stimulation process [16].…”

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Mid-infrared intersubband polaritons in dispersive metal-insulator-metal resonators

Manceau¹,

Zanotto

Ongarello³

et al. 2014

Applied Physics Letters

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We demonstrate room-temperature strong-coupling between a mid-infrared (λ=9.9 µm) intersubband transition and the fundamental cavity mode of a metal-insulator-metal resonator. Patterning of the resonator surface enables surface-coupling of the radiation and introduces an energy dispersion which can be probed with angle-resolved reflectivity. In particular, the polaritonic dispersion presents an accessible energy minimum at k=0 where potentially polaritons can accumulate. We also show that it is possible to maximize the coupling of photons into the polaritonic states andsimultaneously -to engineer the position of the minimum Rabi splitting at a desired value of the in-plane wavevector. This can be precisely accomplished via a simple post-processing technique. The results are confirmed using the temporal coupled mode theory formalism and their significance in the context of the concept of strong critical coupling is highlighted.Light emitting devices based on microcavity polaritons have experienced a tremendous development in the last two decades with the successful demonstration of electroluminescent diodes and optically pumped "bosonic lasers" operating at near-infrared wavelengths 1,2 . The extension of such devices to mid-infrared (mid-IR) and Terahertz (THz) wavelengths (λ > 10µm) has been recently explored, taking advantage of the design flexibility offered by intersubband (ISB) transitions in semiconductor quantum wells. The strong coupling between an ISB transition (or more precisely an ISB plasmon 3 ) and a microcavity photonic mode was first demonstrated in the mid-IR 4 and then in the THz range 5 . Devices based on microcavity ISB polaritons hold great potential since in the strong-coupling regime a periodic energy exchange between the light and matter degrees of freedom takes place on an ultrafast time scale (the Rabi oscillation time). On one hand, ISB polaritons can in principle exhibit radiatiave decay times faster than a bare ISB transition. This effect could yield more efficient electroluminescent devices at such wavelengths 6,7 . On the other hand, due to their bosonic nature, ISB polaritons are subject to final state stimulation, as it is also the case for their excitonic counterparts, and they can potentially lead to the demonstration of bosonic mid-IR or THz lasers 8-10 , which would not rely on population inversion. Quantum cascade structures embedded in microcavities have been used to demonstrate electrically pumped light emitting polaritonic devices in the mid-IR 11 . Furthermore, phonon-assisted polariton scattering processes have been observed 12 . This constitutes an encouraging step towards the development of efficient electroluminescent polaritonic devices, since it is possible to rely on a proven scattering process.However, in the polaritonic light emitting devices (LED) demonstrated to date a key parameter is missing. It is not possible with a total internal reflection cavity geometry to obtain an energy minimum at very low in-plane wavevector (k ) values, where the density of states...

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“…Recently, however, non-periodic feedback gratings have been engineered and investigated in an attempt to overcome some of the inherent limitations of standard DFBs, in terms of output beam quality and optical power. [20][21][22][23] In this letter, we report on the development of THz QCLs employing feedback gratings with a doubleperiodicity. By exploiting two unrelated spatial frequencies, independent control of both the frequency at which optical feedback occurs, and the angle at which radiation is coupled out of the cavity is obtained, without the need to match the effective mode index to a particular value.…”

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confidence: 99%

Distributed feedback terahertz frequency quantum cascade lasers with dual periodicity gratings

Castellano

Zanotto

et al. 2015

Applied Physics Letters

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We have developed terahertz frequency quantum cascade lasers that exploit a double-periodicity distributed feedback grating to control the emission frequency and the output beam direction independently. The spatial refractive index modulation of the gratings necessary to provide optical feedback at a fixed frequency, and simultaneously, a far-field emission pattern centered at controlled angles, was designed through use of an appropriate wavevector scattering model. Single mode terahertz (THz) emission at angles tuned by design between 0 and 50 was realized, leading to an original phase-matching approach for highly collimated THz quantum cascade lasers. Terahertz (THz) frequency quantum cascade lasers (QCLs) have undergone rapid development in performance since their first demonstration, 1 finding potential application in a number of fields including astronomy, security screening, biomedicine, and cultural heritage, inter alia. 2,3 Operating across the 1.2-5 THz range, QCLs can provide high peak output powers (1 W), 4 a high spectral purity, 5,6 frequency, phase and amplitude stability, 7-9 and an ultrabroadband gain spanning an octave in frequency 10,11 at temperatures 199 K. 12 Most of the mentioned applications require sources with a low divergent spatial profile in the far-field as well as a fine spectral control of the emitted radiation. However, the double-metal waveguides conventionally employed to maximize the THz QCL operating temperature 12 suffer from a lack of efficient extraction and a poor collimation of the output radiation, 13 owing to the sub-wavelength dimensions of the resonant cavities. Also, the strong longitudinal confinement provided by such microstrip waveguide configuration typically induces the laser to operate in a multimode regime.Distributed feedback (DFB) is commonly employed in semiconductor lasers to tailor the shape, symmetry, and frequency of the optical resonator eigenmodes, while simultaneously allowing stable single-mode operation. A DFB operates by introducing a periodic refractive index modulation along the propagation direction, which provides scattering between two guided states (feedback) or between a guided state and a radiative one (extraction), so that distributed optical feedback is achieved by coupling two counterpropagating modes through one of the spatial harmonics of a refractive index modulation. In fact, the latter is never purely sinusoidal and a grating with periodicity L contains spatial harmonics with wavevector k n ¼ n/L. Depending on whether the first, second, or third harmonic is used for feedback (n ¼ 1, 2, 3), the grating is described to be of the first, second or third order, respectively. 14 In the case of second 15,16 and third order 17 gratings, although a high spatial harmonic is used for optical feedback (k fb ¼ k 2 , k 3… ), the fundamental frequency is employed for radiation extraction (k e ¼ k 1 ). The ratio between the feedback wavevector k fb and the extraction wavevector k e determines the behavior of the laser: second order gratings emit...

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Efficient power extraction in surface-emitting semiconductor lasers using graded photonic heterostructures

Cited by 125 publications

References 47 publications

Random lasers for broadband directional emission

Random lasers for broadband directional emission

Mid-infrared intersubband polaritons in dispersive metal-insulator-metal resonators

Distributed feedback terahertz frequency quantum cascade lasers with dual periodicity gratings

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