Ultrabroadband Supercontinuum Generation and Frequency-Comb Stabilization Using On-Chip Waveguides with Both Cubic and Quadratic Nonlinearities

Hickstein, Daniel D.; Jung, Haemyeong; Carlson, David R.; Lind, Alex; Coddington, Ian; Srinivasan, Kartik; Ycas, Gabriel; Cole, Daniel C.; Kowligy, Abijith S.; Fredrick, Connor; Droste, Stefan; Lamb, Erin S.; Newbury, Nathan R.; Tang, Hong X.; Diddams, Scott A.

doi:10.1103/physrevapplied.8.014025

Cited by 111 publications

(66 citation statements)

References 56 publications

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“…We also observed a second-harmonic generation (SHG) peak near 830 nm for almost all input power levels. This results from phase-mismatched conversion over short lengths on the chip and has been observed in other waveguide platforms possessing nonzero χ (2) [42,43]. We confirmed this by polarizing the output spectrum in vertical (TM) or horizontal (TE) directions in Fig.…”

Section: Near-ir-pumped Supercontinuum Generationsupporting

confidence: 82%

Multifunctional integrated photonics in the mid-infrared with suspended AlGaAs on silicon

Chiles¹,

Nader²,

Stanton³

et al. 2019

Optica

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The microscale integration of mid-and longwave-infrared photonics could enable the development of fieldable, robust chemical sensors, as well as highly efficient infrared frequency converters. However, such technology would be defined by the choice of material platform, which immediately determines the strength and types of optical nonlinearities available, the optical transparency window, modal confinement, and physical robustness. In this work, we demonstrate a new platform, suspended AlGaAs waveguides integrated on silicon, providing excellent performance in all of these metrics. We demonstrate low propagation losses within a span of nearly two octaves (1.26 to 4.6 µm) with exemplary performance of 0.45 dB/cm at λ = 2.4 µm. We exploit the high nonlinearity of this platform to demonstrate 1560 nm-pumped second-harmonic generation and octave-spanning supercontinuum reaching out to 2.3 µm with 3.4 pJ pump pulse energy. With mid-IR pumping, we generate supercontinuum spanning from 2.3 to 6.5 µm. Finally, we demonstrate the versatility of the platform with mid-infrared passive devices such as low-loss 10 µm-radius bends, compact power splitters with 96 ± 1% efficiency and edge couplers with 3.0 ± 0.1 dB loss. This platform has strong potential for multi-functional integrated photonic systems in the mid-IR. arXiv:1905.01380v1 [physics.app-ph] 3 May 2019 have suitable optical transparency [23], and strong optical nonlinearities are also required for the generation or broadening of frequency combs in the mid-IR [15]. While significant Kerr nonlinearity is present in silicon, germanium and chalcogenide materials, they lack intrinsic second-order optical nonlinearities for highly efficient frequency conversion [6,7,24,25] and electro-optic modulation [26].Alternatively, group III-V materials possess many desirable properties for multi-functional integrated photonic systems including a high refractive index, strong second-and third-order optical nonlinearities, and wide optical transparency windows into the LWIR. A practical advantage of these materials is the ability to grow a chemically selective etch stop underneath a high-quality epitaxial device (donor) film, enabling wafer or chip-bonding film transfer techniques for heterogeneous integration [27,28]. This has enabled high-index-contrast III-V waveguides on other substrates such as oxidized silicon and sapphire [29][30][31][32][33]. However, to take full advantage of the broad transparency window supported by III-V semiconductors, it is necessary to pursue alternative geometries such as air-clad suspended waveguides. But even this approach requires a degree of caution, as most materials readily form surface oxide layers that also introduce absorption. Undercut etching has been used to suspend GaAs waveguides engineered for mid-IR difference frequency generation [34]. While this represents a promising step in the development of nonlinear mid-IR photonics with III-V materials, many issues remain, such as the propagation loss in the mid-IR region, atmospheric stabilit...

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Section: Near-ir-pumped Supercontinuum Generationsupporting

confidence: 82%

Multifunctional integrated photonics in the mid-infrared with suspended AlGaAs on silicon

Chiles¹,

Nader²,

Stanton³

et al. 2019

Optica

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“…SCG has numerous applications, including self-referencing frequency combs [4][5][6], microscopy [7], spectroscopy [8], and tomography [9]. SCG is traditionally accomplished using bulk crystals or nonlinear fiber, but recently, "photonic waveguides" (on-chip waveguides produced using nanofabrication techniques) have proven themselves as a versatile platform for SCG, offering small size, high nonlinearity, and increased control over the generated spectrum [10][11][12][13][14][15][16][17][18][19]. The spectral shape and efficiency of SCG is determined by the input pulse parameters, the nonlinearity of the material, and the refractive index of the waveguide, which determines the phasematching conditions.…”

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confidence: 99%

Quasi-Phase-Matched Supercontinuum Generation in Photonic Waveguides

et al. 2018

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Supercontinuum generation in integrated photonic waveguides is a versatile source of broadband light, and the generated spectrum is largely determined by the phase-matching conditions. Here we show that quasi-phase-matching via periodic modulations of the waveguide structure provides a useful mechanism to control the evolution of ultrafast pulses during supercontinuum generation. We experimentally demonstrate quasi-phase-matched supercontinuum to the TE20 and TE00 waveguide modes, which enhances the intensity of the SCG in specific spectral regions by as much as 20 dB. We utilize higher-order quasi-phase-matching (up to the 16 th order) to enhance the intensity in numerous locations across the spectrum. Quasi-phase-matching adds a unique dimension to the design-space for SCG waveguides, allowing the spectrum to be engineered for specific applications. Supercontinuum generation (SCG) is a χ(3) nonlinear process where laser pulses of relatively narrow bandwidth can be converted into a continuum with large spectral span [1][2][3]. SCG has numerous applications, including self-referencing frequency combs [4][5][6], microscopy [7], spectroscopy [8], and tomography [9]. SCG is traditionally accomplished using bulk crystals or nonlinear fiber, but recently, "photonic waveguides" (on-chip waveguides produced using nanofabrication techniques) have proven themselves as a versatile platform for SCG, offering small size, high nonlinearity, and increased control over the generated spectrum [10][11][12][13][14][15][16][17][18][19]. The spectral shape and efficiency of SCG is determined by the input pulse parameters, the nonlinearity of the material, and the refractive index of the waveguide, which determines the phasematching conditions. Specifically, when phase-matching between a soliton and quasi-continuous-wave (CW) light is achieved, strong enhancements of the intensity of the supercontinuum spectrum can occur in certain spectral regions. These spectral peaks are often referred to as a dispersive waves (DWs) [2,[20][21][22], and they are often crucial for providing sufficient spectral brightness for many applications. The soliton-DW phase-matching condition is typically satisfied by selecting a material with a favorable refractive index profile and engineering the dimensions of the waveguide to provide DWs at the desired wavelengths [15,16]. However, there are limitations to the refractive index profile that can be achieved by adjusting only the waveguide cross-section. Quasi-phase-matching (QPM) takes a different approach, utilizing periodic modulations of the material nonlinearity to achieve an end-result similar to true phase-matching [23][24][25][26]. QPM is routinely employed to achieve high conversion efficiency for nonlinear * danhickstein@gmail.com FIG. 1.a,b) Quasi-phase-matching (QPM) of supercontinuum generation in on-chip photonic waveguides can be achieved via waveguide-width modulation (a) or claddingmodulation (b). c) When the effective index of the soliton in the TE00 mode ("soliton index") intersects the ...

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“…Attempts to transfer such microcombs into UV regimes are usually hampered by the strong normal material dispersion and large waveguide attenuation therein. Photonic chip-based supercontinua are equally important for serving as ultra-broadband comb sources in various photonic platforms [15][16][17][18][19][20], where soliton-induced dispersive waves * hong.tang@yale.edu are employed for coherent spectral transfer into visible (VIS) and mid-infrared regions. Nonetheless, UV supercontinuum microcombs are still in its infancy, and have only been demonstrated in silica-based waveguides [21] owing to its small material dispersion and flexible waveguide fabrication for tailoring a zero-integrated dispersion in the UV region.…”

Section: Introductionmentioning

confidence: 99%

Beyond 100 THz-spanning ultraviolet frequency combs in a non-centrosymmetric crystalline waveguide

Liu

Bruch

et al. 2019

Nat Commun

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Ultraviolet frequency combs enable applications ranging from precision spectroscopy to atomic clocks by addressing electronic transitions of atoms and molecules. Access to ultraviolet light via integrated nonlinear optics is usually hampered by the strong material dispersion and large waveguide attention in ultraviolet regions. Here we demonstrate a simple route to chip-scale ultraviolet comb generators, simultaneously showing a gap-free frequency span of 128 terahertz and high conversion efficiency. This process relies on adiabatic quadratic frequency translation of a near-visible supercontinuum sourced by an ultrafast fiber laser. The simultaneous cubic and quadratic nonlinear processes are implemented in single-crystalline aluminum nitride thin films, where chirp-modulated taper waveguides are patterned to ensure a broad phase matching. The heterodyne characterization suggests that both the near-visible and ultraviolet supercontinuum combs maintain high coherence. Our approach is also adaptable to other non-centrosymmetric photonic platforms for ultrafast nonlinear optics with scalable bandwidth.

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Ultrabroadband Supercontinuum Generation and Frequency-Comb Stabilization Using On-Chip Waveguides with Both Cubic and Quadratic Nonlinearities

Cited by 111 publications

References 56 publications

Multifunctional integrated photonics in the mid-infrared with suspended AlGaAs on silicon

Multifunctional integrated photonics in the mid-infrared with suspended AlGaAs on silicon

Quasi-Phase-Matched Supercontinuum Generation in Photonic Waveguides

Beyond 100 THz-spanning ultraviolet frequency combs in a non-centrosymmetric crystalline waveguide

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