| 1. |
- Girardi, Marcello, 1991, et al.
(author)
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3D Integration of Microcombs
- 2023
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In: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023.
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Conference paper (peer-reviewed)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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| 2. |
- Girardi, Marcello, 1991, et al.
(author)
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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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In: Optics Express. - 1094-4087 .- 1094-4087. ; 31:19, s. 31435-31446
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Journal article (peer-reviewed)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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| 3. |
- Helgason, Òskar Bjarki, 1989, et al.
(author)
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Dissipative solitons in photonic molecules
- 2021
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In: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 15:4, s. 305-310
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Journal article (peer-reviewed)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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| 4. |
- Jorgensen, A. A., et al.
(author)
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Petabit-per-second data transmission using a chip-scale microcomb ring resonator source
- 2022
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In: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 16:11, s. 798-802
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Journal article (peer-reviewed)abstract
- Optical fibre communication is the backbone of the internet. As essential core technologies are approaching their limits of size, speed and energy-efficiency, there is a need for new technologies that offer further scaling of data transmission capacity. Here we show that a single optical frequency-comb source based on a silicon nitride ring resonator supports data capacities in the petabit-per-second regime. We experimentally demonstrate transmission of 1.84 Pbit s–1 over a 37-core, 7.9-km-long fibre using 223 wavelength channels derived from a single microcomb ring resonator producing a stabilized dark-pulse Kerr frequency comb. We also present a theoretical analysis that indicates that a single, chip-scale light source should be able to support 100 Pbit s–1 in massively parallel space-and-wavelength multiplexed data transmission systems. Our findings could mark a shift in the design of future communication systems, targeting device-efficient transmitters and receivers.
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| 5. |
- Kong, D., et al.
(author)
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Single Dark-Pulse Kerr Comb Supporting 1.84 Pbit/s Transmission over 37-Core Fiber
- 2020
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In: Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS. - 1092-8081. ; 2020-May
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Conference paper (peer-reviewed)abstract
- We show that a single dark-pulse Kerr comb can generate high enough OSNR to carry 1.84 Pbit/s data, achieved by 223 WDM spectral lines modulated with 32-Gbaud, SNR-adapted probabilistically shaped DP-QAM, over a 37-core fiber.
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| 6. |
- Torres Company, Victor, 1981, et al.
(author)
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Laser Frequency Combs for Coherent Optical Communications
- 2019
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In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 37:7, s. 1663-1670
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Journal article (peer-reviewed)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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| 7. |
- Twayana, Krishna Sundar, 1986, et al.
(author)
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Differential phase reconstruction of microcombs
- 2022
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In: Optics Letters. - : Optica Publishing Group (formerly OSA). - 0146-9592 .- 1539-4794. ; 47:13, s. 3351-3354
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Journal article (peer-reviewed)abstract
- Measuring microcombs in amplitude and phase provides unique insight into the nonlinear cavity dynamics, but spectral phase measurements are experimentally challenging. Here, we report a linear heterodyne technique assisted by electro-optic downconversion that enables differential phase measurement of such spectra with unprecedented sensitivity (−50 dBm) and bandwidth coverage (>110 nm in the telecommunications range). We validate the technique with a series of measurements, including single-cavity and photonic molecule microcombs. © 2022 Optica Publishing Group
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| 8. |
- Twayana, Krishna Sundar, 1986, et al.
(author)
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Frequency-Comb-Assisted Swept-Wavelength Interferometry
- 2021
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In: 2021 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2021.
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Conference paper (peer-reviewed)abstract
- Swept-wavelength interferometry (SWI) is a highly sensitive and versatile technique implemented in a diverse array of industrial and scientific applications. SWI uses a continuously tunable laser to capture the magnitude and phase response of a device under test (DUT). The prevalent non-linear tuning of the laser calls for an auxiliary interferometer for the calibration of the laser frequency on the fly [1]. However, this approach is susceptible to environmental perturbations, and the inherent dispersion of the interferometer introduces systematic errors. Laser frequency combs can be used as optical rulers against which to calibrate tunable lasers with high- precision and, when self-referenced, with high accuracy [2]. Here, we apply this comb-based calibration approach in the context of SWI for the first time and illustrate its relevance for the characterization of high-Q microresonators.
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| 9. |
- Twayana, Krishna Sundar, 1986, et al.
(author)
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Frequency-comb-calibrated swept-wavelength interferometry
- 2021
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In: Optics Express. - 1094-4087 .- 1094-4087. ; 29:15, s. 24363-24372
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Journal article (peer-reviewed)abstract
- Lasers are often used to characterize samples in a non-destructive manner and retrieve sensing information transduced in changes in amplitude and phase. In swept wavelength interferometry, a wavelength-tunable laser is used to measure the complex response (i.e. in amplitude and phase) of an optical sample. This technique leverages continuous advances in rapidly tunable lasers and is widely used for sensing, bioimaging and testing of photonic integrated components. However, the tunable laser requires an additional calibration step because, in practice, it does not tune at a constant rate. In this work, we use a self-referenced frequency comb as an optical ruler to calibrate the laser used in swept-wavelength interferometry and optical frequency domain reflectometry. This allows for realizing high-resolution complex spectroscopy over a bandwidth exceeding 10 THz. We apply the technique to the characterization of low-loss integrated photonic devices and demonstrate that the phase information can disentangle intrinsic from coupling losses in the characterization of high-Q microresonators. We also demonstrate the technique in reflection mode, where it can resolve attenuation and dispersion characteristics in integrated long spiral waveguides.
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| 10. |
- Twayana, Krishna Sundar, 1986, et al.
(author)
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Linear Broadband Differential Phase Measurement of Soliton Microcombs
- 2022
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In: Optics InfoBase Conference Papers. - 9781957171050
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Conference paper (peer-reviewed)abstract
- We demonstrate complex (amplitude and phase) spectral characterization of a 100 GHz repetition rate microcomb over a bandwidth exceeding C and L bands using a linear stepped heterodyne technique.
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