Focusing metasurface quantum-cascade laser with a near diffraction-limited beam

Xu, Luyao; Chen, Daguan; Itoh, T.; Reno, John L.; Williams, Benjamin S.

doi:10.1364/oe.24.024117

Cited by 34 publications

(18 citation statements)

References 32 publications

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“…One disadvantage of the focusing design is that it is less amenable to broadband frequency tuning as the desired phase curvature is only present at a single frequency. The design principles and tradeoffs of such a focusing metasurface are described in detail in Ref [ 2 ]…”

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confidence: 99%

Terahertz quantum-cascade patch-antenna VECSEL with low power dissipation

Curwen

Reno

Williams

2020

Applied Physics Letters

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We report a terahertz quantum-cascade vertical-external-cavity surface-emitting laser (QC-VECSEL) based upon a metasurface consisting of an array of gain-loaded resonant patch antennas. Compared with the typical ridge-based metasurfaces previously used for QC-VECSELs, the patch antenna surface can be designed with a much sparser fill factor of gain material, which allows for reduced heat dissipation and improved thermal performance. It also exhibits larger amplification thanks to enhanced interaction between the incident radiation and the QC-gain material. We demonstrate devices that produce several milliwatts of continuous-wave power in a single mode at ~4.6 THz, and dissipate less than 1 W of pump power. Use of different output couplers demonstrates the ability to optimize device performance for either high power, or high operating temperature. Maximum demonstrated power is 6.7 mW at 4 K (0.67% wall-plug efficiency (WPE)), and 0.8 mW at 77 K (0.06% WPE). Directive output beams are measured throughout with divergence angles of ~5°. THE MANUSCRIPT The terahertz (THz) quantum-cascade (QC) vertical-external-cavity surface-emitting laser (VECSEL) is a recently developed approach for designing THz QC-lasers with scalable output power and high-quality beam patterns. 1 The enabling component of the QC-VECSEL is an amplifying metasurfacea reflectarray of resonant antenna-coupled THz QC-gain elements with subwavelength spacing that exhibits a reflectance R greater than unity across some finite gain bandwidth. The antenna elements are unable to lase on their own due to high surface radiation losses, but instead, the metasurface is used as the amplifying element of an external cavity laser. The external cavity mode effectively phase locks the antenna elements, and because the metasurface can be made large relative to the lasing wavelength, near-diffraction-limited beams with high power have been observed. 2 The external-cavity allows one to more easily modify the outcoupling efficiency and cavity resonant frequency, 3 while the metasurface offers unique opportunities such as engineering of "flat-optics" focusing 2 and polarization switchability. 4 The typical metasurface design consists of a 1D sub-wavelength array of narrow metal-metal ridges of width w and period Λ that are coupled to surface radiation via the TM01 cutoff resonances of the ridges. 5,6 This design has been used to realize many high-performance VECSELs operating between 3-4 THz. 3,7,8

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Terahertz quantum-cascade patch-antenna VECSEL with low power dissipation

Curwen

Reno

Williams

2020

Applied Physics Letters

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“…Therefore, many techniques have been proposed to enhance the Q-factor of photonic-crystal-based cavities for engineering light sources, such as introducing a small disorder or a defect into the crystal [7,12], using photonic-crystal heterostructures [9,13], and by locally modulating the width of the photonic-crystal waveguide [14,15]. Recent advances in developing optical lasers rely on engineering the response of the cavity structures by employing plasmonic nanocavities [16][17][18], photonic band-edges [19][20][21][22][23][24][25], Parity-Time (PT)-symmetry breaking [26][27][28][29][30][31][32], or by exploiting unique structural topologies including metamaterials [33][34][35][36] and metasurfaces [37,38].…”

Section: Introductionmentioning

confidence: 99%

Degenerate band edge laser

et al. 2018

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We propose a novel class of lasers based on a fourth order exceptional point of degeneracy (EPD) referred to as the degenerate band edge (DBE). EPDs have been found in Parity-Time-symmetric photonic structures that require loss and/or gain, here we show that the DBE is a different kind of EPD since it occurs in periodic structures that are lossless and gainless. Because of this property, a small level of gain is sufficient to induce single-frequency lasing based on a synchronous operation of four degenerate Floquet-Bloch eigenwaves. This lasing scheme constitutes a light-matter interaction mechanism that leads also to a unique scaling law of the laser threshold with the inverse of the fifth power of the laser-cavity length. The DBE laser has the lowest lasing threshold in comparison to a regular band edge laser and to a conventional laser in cavities with the same loaded quality (Q) factor and length. In particular, even without mirror reflectors the DBE laser exhibits a lasing threshold which is an order of magnitude lower than that of a uniform cavity laser of the same length and with very high mirror reflectivity. Importantly, this novel DBE lasing regime enforces mode selectivity and coherent single-frequency operation even for pumping rates well-beyond the lasing threshold, in contrast to the multifrequency nature of conventional uniform cavity lasers.

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“…Therefore, it is attainable to manipulate the outcoupling of mode energy by monolithically integrating side-emitter structures. [84] The configuration characteristics of THz VECSELs, that is, efficient energy outcoupling of the gain cavities and scalable array size, contribute to good performance including single-mode emission, small beam divergence (≈3° × 3°), [138,139] high power (1.35 W at 6 K and 830 mW at 77 K in pulse mode), [101] and high efficiency (PSE ≈ 767 mW A −1 and WPE ≈ 2%). [55,92] By coupling one reflector along with the antenna loop to control the lasing mode propagating direction, unidirectional emission was achieved along the waveguide with an enhancement of WPE (≈1%) in the predefined direction.…”

Section: Power Efficiencymentioning

confidence: 99%

“…In THz VECSELs, the external FP cavity ensures the phase coherence among the QC wires (work effectively as antenna emitters). [84] The configuration characteristics of THz VECSELs, that is, efficient energy outcoupling of the gain cavities and scalable array size, contribute to good performance including single-mode emission, small beam divergence (≈3° × 3°), [138,139] high power (1.35 W at 6 K and 830 mW at 77 K in pulse mode), [101] and high efficiency (PSE ≈ 767 mW A −1 and WPE ≈ 2%). [101,140]…”

Section: Power Efficiencymentioning

confidence: 99%