| 1. |
- Gao, Yan, 1995, et al.
(författare)
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Compact lithium niobate microring resonators in the ultrahigh Q/V regime
- 2023
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 48:15, s. 3949-3952
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Tidskriftsartikel (refereegranskat)abstract
- Lithium niobate (LN) is a promising material for future complex photonic-electronic circuits, with wide applications in such fields as communications, sensing, quantum optics, and computation. LN took a great stride toward compact photonic integrated circuits (PICs) with the development of partially etched LN on insulator (LNOI) waveguides. However, integration density is still limited for future highly compact PICs, owing to the partial etching nature of their waveguides. Here, we demonstrate a fully etched LN PIC platform, which, for the first time to our knowledge, simultaneously achieves ultralow propagation loss and compact circuit size. The tightly confined fully etched LN waveguides with smooth sidewalls allow us to bring the bending radius down to 20 μm (corresponding to 1 THz free spectral range). We have achieved compact high Q microring resonators with Q/V of 8.7 × 104 μm−3, almost one order of magnitude larger than previous demonstrations. The statistical mean propagation losses of our LN waveguides is 8.5 dB/m (corresponding to a mean Q factor of 4.9 × 106), even with a small bending radius of 40 μm. Our compact and ultralow-loss LN platform shows great potential in future miniaturized multifunctional integration systems. As complementary evidence to show the utility of our platform, we demonstrate soliton microcombs with an ultrahigh repetition rate of 500 GHz in LN.
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| 2. |
- Helgason, Òskar Bjarki, 1989, et al.
(författare)
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Power-efficient soliton microcombs in anomalous-dispersion photonic molecules
- 2022
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Ingår i: Optics InfoBase Conference Papers.
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Konferensbidrag (refereegranskat)abstract
- We demonstrate a microcomb with power conversion efficiency exceeding 50%. It originates from a single dissipative Kerr soliton circulating in an anomalous-dispersion microresonator whose pump resonance is shifted through linear coupling with an auxiliary cavity.
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| 3. |
- Helgason, Òskar Bjarki, 1989, et al.
(författare)
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Surpassing the nonlinear conversion efficiency of soliton microcombs
- 2023
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Ingår i: Nature Photonics. - 1749-4885 .- 1749-4893. ; 17:11, s. 992-999
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Tidskriftsartikel (refereegranskat)abstract
- Laser frequency combs are enabling some of the most exciting scientific endeavours in the twenty-first century, ranging from the development of optical clocks to the calibration of the astronomical spectrographs used for discovering Earth-like exoplanets. Dissipative Kerr solitons generated in microresonators currently offer the prospect of attaining frequency combs in miniaturized systems by capitalizing on advances in photonic integration. Most of the applications based on soliton microcombs rely on tuning a continuous-wave laser into a longitudinal mode of a microresonator engineered to display anomalous dispersion. In this configuration, however, nonlinear physics precludes one from attaining dissipative Kerr solitons with high power conversion efficiency, with typical comb powers amounting to ~1% of the available laser power. Here we demonstrate that this fundamental limitation can be overcome by inducing a controllable frequency shift to a selected cavity resonance. Experimentally, we realize this shift using two linearly coupled anomalous-dispersion microresonators, resulting in a coherent dissipative Kerr soliton with a conversion efficiency exceeding 50% and excellent line spacing stability. We describe the soliton dynamics in this configuration and find vastly modified characteristics. By optimizing the microcomb power available on-chip, these results facilitate the practical implementation of a scalable integrated photonic architecture for energy-efficient applications.
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| 4. |
- Helgason, Òskar Bjarki, 1989, et al.
(författare)
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Thermally stable initiation of dissipative Kerr solitons in photonic molecules
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023.
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Konferensbidrag (refereegranskat)abstract
- Dissipative Kerr solitons (DKSs) have been heavily researched in the last decade. These are robust waveforms that are generated in a single anomalous-dispersion microresonator. Microcombs corresponding to a single DKS circulating in a microcavity have been demonstrated to be robust, enabling multiple different applications, such as spectroscopy and telecommunications [1]. However, the fact that the continuous-wave (CW) laser has to be operated far red-detuned from resonance leads to practical limitations. One such limitation is low conversion efficiency, due to much of the pump bypassing the cavity. A second limitation is a challenging DKS initiation, which is a consequence of the red side of resonance being thermally unstable in the majority of integration materials, often requiring time-sensitive control schemes [2], or auxiliary cooling lasers [3], to enable the initiation. In a recent work, we addressed the limited conversion efficiency by shifting the pumped resonance via an avoided mode-crossing enabled by linear coupling to an auxiliary cavity [4]. Here, we show that this coupled-cavity arrangement (a photonic molecule) allows the initiation process, including the final DKS state, to be operated with the CW laser consistently located on the blue side of the pumped resonance. This thermal stabilization leads to a robust initiation scheme, which is not readily available for DKSs in single anomalous-dispersion cavities.
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| 5. |
- Hu, Xiaonan, 1988, et al.
(författare)
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Passive Si3N4 photonic integrated platform at 1μm for short-range optical interconnects
- 2019
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Ingår i: 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019. - 2162-2701. ; Part F140-CLEO_Europe 2019
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Konferensbidrag (refereegranskat)abstract
- With the increasing development of cloud services, a large number of high-speed optical interconnects are needed in large-scale datacenters. Future datacenters will require short-range links with multi-Tb/s interconnect capacity, i.e. more than an order of magnitude higher than what is available today with vertical-cavity surface-emission lasers (VCSELs) or silicon photonics. In addition, large-scale datacenters will require longer (> 1km) transmission links. Single-mode GaAs VCSELs today provide transmission speeds ∼ 100 Gb/s, close to their fundamental limit. The recent development of high-speed GaAs VCSELs at a slightly longer wavelength of opens a path forward for low-energy dissipation, high-speed, long-reach optical interconnects because the chromatic dispersion and attenuation in fibers are significantly reduced compared to shorter wavelengths [1]. In order to meet the future capacity prospects, we envision the use of multi-wavelength GaAs VCSEL arrays at 1 μm with advanced multi-fiber cables. This vision requires the use of a low-cost, low-loss passive integrated photonic platform for laser integration, multiplexing, and fiber interfacing, as sketched in Figure (a). Here, we present a silicon nitride (henceforth SiN) platform that can meet these requirements.
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| 6. |
- Hu, Xiaonan, 1988, et al.
(författare)
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Si3N4 photonic integration platform at 1 µm for optical interconnects
- 2020
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 28:9, s. 13019-13031
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Tidskriftsartikel (refereegranskat)abstract
- Vertical-cavity surface-emitting lasers (VCSELs) are the predominant technology for high-speed short-range interconnects in data centers. Most short-range interconnects rely on GaAs-based multi-mode VCSELs and multi-mode fiber links operating at 850 nm. Recently, GaAs-based high-speed single-mode VCSELs at wavelengths > 1 µm have been demonstrated, which increases the interconnect reach using a single-mode fiber while maintaining low energy dissipation. If a suitable platform for passive wavelength- and space-multiplexing were developed in this wavelength range, this single-mode technology could deliver the multi-Tb/s interconnect capacity that will be required in future data centers. In this work, we show the first passive Si3N4 platform in the 1-µm band (1030-1075 nm) with an equivalent loss < 0.3 dB/cm, which is compatible with the system requirements of high-capacity interconnects. The waveguide structure is optimized to achieve simultaneously single-mode operation and low bending radius, and we demonstrate a wide range of high-performance building blocks, including arrayed waveguide gratings, Mach-Zehnder interferometers, splitters and low-loss fiber interfaces. This technology could be instrumental in scaling up the capacity and reducing the footprint of VCSEL-based optical interconnects and, thanks to the broad transparency in the near-infrared and compatibility with the Yb fiber amplifier window, enabling new applications in other domains as optical microscopy and nonlinear optics.
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| 7. |
- Lei, Fuchuan, 1987, et al.
(författare)
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Hyperparametric Oscillation via Bound States in the Continuum
- 2023
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 130:9
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Tidskriftsartikel (refereegranskat)abstract
- Optical hyperparametric oscillation based on the third-order nonlinearity is one of the most significant mechanisms to generate coherent electromagnetic radiation and produce quantum states of light. Advances in dispersion-engineered high-Q microresonators allow for generating signal waves far from the pump and decrease the oscillation power threshold to submilliwatt levels. However, the pump-to-signal conversion efficiency and absolute signal power are low, fundamentally limited by parasitic mode competition and attainable cavity intrinsic Q to coupling Q ratio, i.e., Qi/Qc. Here, we use Friedrich-Wintgen bound states in the continuum (BICs) to overcome the physical challenges in an integrated microresonator-waveguide system. As a result, on-chip coherent hyperparametric oscillation is generated in BICs with unprecedented conversion efficiency and absolute signal power. This work not only opens a path to generate high-power and efficient continuous-wave electromagnetic radiation in Kerr nonlinear media but also enhances the understanding of a microresonator-waveguide system - an elementary unit of modern photonics.
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| 8. |
- Lei, Fuchuan, 1987, et al.
(författare)
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Optical linewidth of soliton microcombs
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Understanding noise dynamics in frequency combs is crucial for applications. Here, the authors study the phase noise dynamics and the linewidth of soliton microcombs, revealing that some comb lines can be more quiet than the pump laser itself. Soliton microcombs provide a versatile platform for realizing fundamental studies and technological applications. To be utilized as frequency rulers for precision metrology, soliton microcombs must display broadband phase coherence, a parameter characterized by the optical phase or frequency noise of the comb lines and their corresponding optical linewidths. Here, we analyse the optical phase-noise dynamics in soliton microcombs generated in silicon nitride high-Q microresonators and show that, because of the Raman self-frequency shift or dispersive-wave recoil, the Lorentzian linewidth of some of the comb lines can, surprisingly, be narrower than that of the pump laser. This work elucidates information about the physical limits in phase coherence of soliton microcombs and illustrates a new strategy for the generation of spectrally coherent light on chip.
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| 9. |
- Lei, Fuchuan, 1987, et al.
(författare)
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Power-efficient hyperparametric oscillation via bound states in the continuum
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023.
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Konferensbidrag (refereegranskat)abstract
- Optical hyperparametric oscillation (h-OPO) emerges in a driven Kerr cavity because of modulation instability. Two pump photons are converted into a pair of two correlated photons at new wavelengths. For many realistic applications, efficient operation of h-OPO is required, especially at high-power regime. Currently, the pump-to-signal conversion efficiency is fundamentally limited mainly by two factors: parasitic mode competition [1] and attainable cavity intrinsic Q (Qi) to coupling Q (Qc) ratio [2].
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| 10. |
- O'Malley, Nathan P., et al.
(författare)
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RF Stabilization of Vernier Dual-microcombs
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics, CLEO 2023.
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Konferensbidrag (refereegranskat)abstract
- Leveraging the Vernier dual-comb method, we self-reference a THz octave-spanning microcomb with fCEO ~100 GHz - normally too high for typical detection equipment - and translate the stability of an RF reference to optical frequencies.
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