| 1. |
- Torres Company, Victor, 1981, et al.
(författare)
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Laser Frequency Combs for Coherent Optical Communications
- 2019
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 37:7, s. 1663-1670
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Tidskriftsartikel (refereegranskat)abstract
- Laser frequency combs with repetition rates on the order of 10 GHz and higher can he used as multi-carrier sources in wavelength-division multiplexing (WDM). They allow replacing tens of tunable continuous-wave lasers by a single laser source. In addition, the comb's line spacing stability and broadband phase coherence enable signal processing beyond what is possible with an array of independent lasers. Modern WDM systems operate with advanced modulation formats and coherent receivers. This introduces stringent requirements in terms of signal-to-noise ratio, power per line, and optical linewidth which can be challenging to attain for frequency comb sources. Here, we set quantitative benchmarks for these characteristics and discuss tradeoffs in terms of transmission reach and achievable data rates. We also highlight recent achievements for comb-based superchannels, including >10 Tb/s transmission with extremely high spectral efficiency, and the possibility to significantly simplify the coherent receiver by realizing joint digital signal processing. We finally discuss advances with microresonator frequency combs and compare their performance in terms of flatness and conversion efficiency against state-of-the-art electro-optic frequency comb generators. This contribution provides guidelines for developing frequency comb sources in coherent fiber-optic communication systems.
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| 2. |
- Fülöp, Attila, 1988, et al.
(författare)
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High-order coherent communications using mode-locked dark-pulse Kerr combs from microresonators
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Microresonator frequency combs harness the nonlinear Kerr effect in an integrated optical cavity to generate a multitude of phase-locked frequency lines. The line spacing can reach values in the order of 100 GHz, making it an attractive multi-wavelength light source for applications in fiber-optic communications. Depending on the dispersion of the microresonator, different physical dynamics have been observed. A recently discovered comb state corresponds to the formation of mode-locked dark pulses in a normal-dispersion microcavity. Such dark-pulse combs are particularly compelling for advanced coherent communications since they display unusually high power-conversion efficiency. Here, we report the first coherent-transmission experiments using 64-quadrature amplitude modulation encoded onto the frequency lines of a dark-pulse comb. The high conversion efficiency of the comb enables transmitted optical signal-to-noise ratios above 33 dB, while maintaining a laser pump power level compatible with state-of-the-art hybrid silicon lasers.
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| 3. |
- Girardi, Marcello, 1991, et al.
(författare)
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3D Integration of Microcombs
- 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
- Microcombs based on silicon nitride are a promising technology in applications such as sensing, metrology and telecommunication [1]. These applications often require to combine a nonlinear waveguide with a linear integrated processor on the same chip to perform functionalities such as splitting, demultiplexing, and optical buffering. However, there is a fundamental performance tradeoff between linear and nonlinear waveguides. For microcomb generation, thick waveguide cores are necessary to achieve the desired anomalous dispersion, while for linear operation a thin core improves the loss of a single mode (SM) waveguide [2]. The dissimilar requirements in waveguide thickness brings challenges for planar integrated technologies. Here, we propose and demonstrate wafer-level three-dimensional integration of microcombs using two different Si3N4 core thicknesses: a thick core featuring dispersion-engineered microcombs and a thinner core for linear processing (see Fig. 1a). This technology breaks off the fundamental tradeoff between loss and confinement in thick waveguides and opens the door to combine high-performance microcombs with ultra-low-loss silicon nitride waveguide technology [3]. We demonstrate this approach by efficiently coupling a microcomb between two layers of Si3N4 and demultiplexing a few lines with an arrayed waveguide grating (AWG) (Fig 1b).
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| 4. |
- Girardi, Marcello, 1991, et al.
(författare)
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Multilayer integration in silicon nitride: decoupling linear and nonlinear functionalities for ultralow loss photonic integrated systems
- 2023
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 31:19, s. 31435-31446
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Tidskriftsartikel (refereegranskat)abstract
- Silicon nitride is an excellent material platform for its extremely low loss in a large wavelength range, which makes it ideal for the linear processing of optical signals on a chip. Moreover, the Kerr nonlinearity and the lack of two-photon absorption in the near infrared enable efficient nonlinear optics, e.g., frequency comb generation. However, linear and nonlinear operations require distinct engineering of the waveguide core geometry, resulting in a tradeoff between optical loss and single-mode behavior, which hinders the development of high-performance, ultralow-loss linear processing blocks on a single layer. Here, we demonstrate a dual-layer photonic integration approach with two silicon-nitride platforms exhibiting ultralow optical losses, i.e., a few dB/m, and individually optimized to perform either nonlinear or linear processing tasks. We demonstrate the functionality of this approach by integrating a power-efficient microcomb with an arrayed waveguide grating demultiplexer to filter a few frequency comb lines in the same monolithically integrated chip. This approach can significantly improve the integration of linear and nonlinear optical elements on a chip and opens the way to the development of fully integrated processing of Kerr nonlinear sources.
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| 5. |
- Helgason, Òskar Bjarki, 1989, et al.
(författare)
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Bidirectional initiation of dissipative solitons in photonic molecules
- 2021
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Ingår i: 2021 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2021. - 9781665418768 ; June 2021
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Konferensbidrag (refereegranskat)abstract
- Dissipative solitons (DSs) can be generated in microresonators featuring Kerr nonlinearities via continuous wave (CW) pumping, forming a frequency comb in the spectral domain. While single cavity DSs have been thoroughly investigated in the last years, recent efforts have moved towards photonic molecules (linearly coupled cavities). These arrangements give rise to exotic physical phenomena and practical improvements in terms of conversion efficiency and tuneable comb dynamics. In a recent study of normal dispersion photonic molecules, we found that DSs can be generated in absence of intracavity CW bistability. Here, we show that this feature enables the CW initiation of DSs, tuning the laser into resonance either from the blue side or the red side. While DS initation from the red side has been demonstrated with the photorefractive effect, this is the first demonstration of bidirectional initiation that only requires a Kerr nonlinear medium.
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| 6. |
- Helgason, Òskar Bjarki, 1989, et al.
(författare)
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Dark-pulse Kerr combs in linearly coupled microring structures
- 2020
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Ingår i: Optics InfoBase Conference Papers. - 2162-2701. - 9781943580767 ; Part F183-CLEO-SI 2020
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Konferensbidrag (refereegranskat)abstract
- The generation of dissipative Kerr solitons in microresonators became a milestone in the quest towards a chip-scale frequency comb source. Although successful demonstrations in diverse fields have been made, one outstanding issue with dissipative Kerr solitons is their poor power conversion efficiency. This has a fundamental origin in the need to operate the soliton microcomb at a large frequency detuning. The limited conversion efficiency is a crucial aspect when considering co-integration with chip-scale laser sources or applications that demand higher power per line, such as optical communications.
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| 7. |
- Helgason, Òskar Bjarki, 1989
(författare)
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Dissipative Kerr solitons in normal dispersion waveguides
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The microresonator comb (microcomb) is a laser source which generatesequally spaced coherent lines in the spectral domain. Having a miniaturefootprint and the potential of being low cost, it has attracted attention inmultiple applications. Demonstrations have included high-speed opticalcommunications, light detection and ranging, calibrating spectrographsfor exoplanet detection and optical clocks. These experiments relied onthe generation of dissipative Kerr solitons (DKS) which circulate in themicroresonator. The development of such waveforms is paramount forfurther advancement of the micrcomb.This thesis studies the dynamics of DKS in microresonators aim-ing at developing a low-cost, reliable and high-performing microcombsource. The investigation will cover both dark and bright DKS’s, whichare found respectively in normal and anomalous dispersion microres-onators. The dark DKS will be in center focus since it can providea relatively high comb power compared to other waveforms. The per-formance of microcombs in terms of line power is numerically exploredfor telecommunication purposes. The initiation of dark DKS from lin-early coupled microcavities is investigated, showing efficient, low-powergeneration from silicon nitride microresonators that are reproducible infabrication. These studies could facilitate reliable, low-powered, energy-efficient microcombs.
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| 8. |
- Helgason, Òskar Bjarki, 1989, et al.
(författare)
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Dissipative solitons in photonic molecules
- 2021
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Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 15:4, s. 305-310
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Tidskriftsartikel (refereegranskat)abstract
- Many physical systems display quantized energy states. In optics, interacting resonant cavities show a transmission spectrum with split eigenfrequencies, similar to the split energy levels that result from interacting states in bonded multi-atomic—that is, molecular—systems. Here, we study the nonlinear dynamics of photonic diatomic molecules in linearly coupled microresonators and demonstrate that the system supports the formation of self-enforcing solitary waves when a laser is tuned across a split energy level. The output corresponds to a frequency comb (microcomb) whose characteristics in terms of power spectral distribution are unattainable in single-mode (atomic) systems. Photonic molecule microcombs are coherent, reproducible and reach high conversion efficiency and spectral flatness while operated with a laser power of a few milliwatts. These properties can favour the heterogeneous integration of microcombs with semiconductor laser technology and facilitate applications in optical communications, spectroscopy and astronomy.
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| 9. |
- Helgason, Òskar Bjarki, 1989
(författare)
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High-efficiency dissipative Kerr solitons in microresonators
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The microresonator comb (microcomb) is a laser source that generates equally spaced coherent lines in the spectral domain. Having a chip-scale size and the potential of being low cost, it has attracted attention in multiple applications. Demonstrations have included high-speed optical communications, light detection and ranging, calibrating spectrographs for exoplanet detection and, optical clocks. These experiments typically rely on the generation of a dissipative Kerr soliton (DKS) --- a temporal waveform that circulates the microresonator without changing shape. However, these DKS states have thus far been limited in certain technical aspects, such as energy efficiency, which are essential for realizing commercial microcomb solutions. This thesis studies the dynamics of DKSs in microresonators aiming at developing a reliable and high-performing microcomb source. The investigation will cover DKSs found both in the normal and anomalous dispersion regime of silicon nitride microresonators. The performance of microcombs in terms of line power is numerically explored in single-cavity arrangements for telecommunication purposes. DKSs generated in linearly coupled microcavities are investigated, revealing exotic dynamics and improved performance in terms of power efficiency and DKS initiation. These studies facilitate reliable energy-efficient microcombs, bringing the technology a step closer to commercial use.
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| 10. |
- 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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