| 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. |
- Brajato, Giovanni, et al.
(författare)
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Bayesian filtering framework for noise characterization of frequency combs
- 2020
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 28:9, s. 13949-13964
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Tidskriftsartikel (refereegranskat)abstract
- Amplitude and phase noise correlation matrices are of fundamental importance for studying noise properties of frequency combs. They include information about the origin of noise sources as well as the scaling and correlation of the noise across the comb lines. These matrices provide an insight that is essential for obtaining low-noise performance which is important for, e.g., applications in optical communication, low–noise microwave signal generation, and distance measurements. Estimation of amplitude and phase noise correlation matrices requires highly–accurate measurement technique which can distinguishes between noise sources coming from the frequency comb and the measurement system itself. Bayesian filtering provides a theoretically optimum approach for filtering of measurement noise and thereby, the most accurate measurement of phase and amplitude noise. In this paper, a novel Bayesian filtering based framework for joint estimation of amplitude and phase noise of multiple frequency comb lines is proposed, and demonstrated for phase noise characterization. Compared to the conventional approaches, that do not employ any measurement noise filtering, the proposed approach provides significantly more accurate measurements of correlation matrices, operates over a wide range of signal–to–noise–ratios and gives an insight into comb’s dynamics at short scales (<10−8 s). © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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| 3. |
- Brajato, Giovanni, et al.
(författare)
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Optical frequency comb noise characterization using machine learning
- 2019
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Ingår i: IET Conference Publications. ; 2019:CP765
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Konferensbidrag (refereegranskat)abstract
- A novel tool, based on Bayesian filtering framework and expectation maximization algorithm, is numerically and experimentally demonstrated for accurate frequency comb noise characterization. The tool is statistically optimum in a mean-square-error-sense, works at wide range of SNRs and offers more accurate noise estimation compared to conventional methods.
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| 4. |
- Lundberg, Lars, 1989
(författare)
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Aspects of Power Consumption in Coherent Fiber-Optical Communication Systems
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The power consumption of coherent fiber-optical communication systems is becoming increasingly important, for both environmental and economical reasons. The data traffic on the Internet is increasing at a faster pace than that at which optical network equipment is becoming more energy efficient, which means that the overall power consumption of the Internet is increasing. In addition, wasted energy leads to higher costs for network operators, through increased electricity expenses but also because the heat generated in the equipment limits how closely it can be packed. This thesis includes power consumption modelling, trade-off studies and investigations of novel schemes that may lead to an improved energy efficiency in future systems. In particular, the power consumption of optical amplifiers is modelled and connected to a performance model based on the Gaussian-noise model. Using these models, the trade-offs between amplifier power consumption and the choice of modulation format and forward-error-correction (FEC) scheme is studied. We find that 16-ary quadrature-amplitude modulation (16QAM) has a lower energy consumption per bit than quadrature phase-shift keying (QPSK) due to its higher spectral efficiency, and that using a shorter amplifier spacing to improve signal quality may be more energy efficient than using a powerful FEC.Furthermore, the power consumption for a coherent link with minimal digital signal processing (DSP) is studied. We find that when the DSP is minimized, it accounts for below 10% of the power consumption, which is dominated by the optical components.Finally, we demonstrate that the phase-coherence of optical frequency comb lines can be utilized to simplify the carrier-recovery by joint processing of multiple wavelength channels. We use the phase-drift from one wavelength channel to compensate the phase-drift of another one spaced up to 275GHz away with negligible penalty.
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| 5. |
- Lundberg, Lars, 1989, et al.
(författare)
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Frequency Comb-Based WDM Transmission Systems Enabling Joint Signal Processing
- 2018
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 8:5
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Tidskriftsartikel (refereegranskat)abstract
- We review the use of optical frequency combs in wavelength-division multiplexed (WDM) fiber optic communication systems. In particular, we focus on the unique possibilities that are opened up by the stability of the comb-line spacing and the phase coherence between the lines. We give an overview of different techniques for the generation of optical frequency combs and review their use in WDM systems. We discuss the benefits of the stable line spacing of frequency combs for creating densely-packed optical superchannels with high spectral efficiency. Additionally, we discuss practical considerations when implementing frequency-comb-based transmitters. Furthermore, we describe several techniques for comb-based superchannel receivers that enables the phase coherence between the lines to be used to simplify or increase the performance of the digital carrier recovery. The first set of receiver techniques is based on comb-regeneration from optical pilot tones, enabling low-overhead self-homodyne detection. The second set of techniques takes advantage of the phase coherence by sharing phase information between the channels through joint digital signal processing (DSP) schemes. This enables a lower DSP complexity or a higher phase-noise tolerance.
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| 6. |
- Lundberg, Lars, 1989, et al.
(författare)
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In-Band OSNR Monitoring of PM-QPSK Using the Stokes Parameters
- 2015
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Ingår i: 2015 Optical Fiber Communications Conference and Exhibition, OFC 2015, Los Angeles, United States, 22-26 March 2015. - Washington, D.C. : OSA. - 9781557529374 ; , s. 7122095-
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Konferensbidrag (refereegranskat)abstract
- We discuss OSNR monitoring using low bandwidth Stokes parameter analysis. OSNR levels reaching 23dB are experimentally estimated within ±1dB. Simulations show resilience to chromatic dispersion, corresponding to 1000km of SMF for the experimental setup.
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| 7. |
- Lundberg, Lars, 1989, et al.
(författare)
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Joint Carrier Recovery for DSP Complexity Reduction in Frequency Comb-Based Superchannel Transceivers
- 2017
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Ingår i: European Conference on Optical Communication, ECOC.
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Konferensbidrag (refereegranskat)abstract
- We experimentally demonstrate a master-slave carrier recovery scheme by joint processing of 10 GBd PM-64QAM phase-locked wavelength carriers. We measure negligible penalty up to a frequency spacing of 275 GHz, showing the potential for effective resource utilization among many wavelength channels.
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| 8. |
- Lundberg, Lars, 1989, et al.
(författare)
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Master-slave carrier recovery for M-QAM multicore fiber transmission
- 2019
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 27:16, s. 22226-22236
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Tidskriftsartikel (refereegranskat)abstract
- Master-slave carrier recovery is a digital signal processing technique that uses correlated phase noise in multi-channel receivers to eliminate redundant carrier recovery blocks. In this paper we experimentally investigate the performance of master-slave carrier recovery for multicore fiber transmission in the presence of inter-channel nonlinear interference. Using a triple parallel loop setup we jointly receive three spatial channels in a 7-core fiber for transmission distances of up to 1600 km. We find that an increased launch power causes a moderate penalty on the slave channels. Furthermore, we study the penalty from a non-zero inter-core skew.
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| 9. |
- Lundberg, Lars, 1989, et al.
(författare)
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Phase-coherent lightwave communications with frequency combs
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Fiber-optical networks are a crucial telecommunication infrastructure in society. Wavelength division multiplexing allows for transmitting parallel data streams over the fiber bandwidth, and coherent detection enables the use of sophisticated modulation formats and electronic compensation of signal impairments. Optical frequency combs can replace the multiple lasers used for the different wavelength channels. Beyond multiplexing, it has been suggested that the broadband phase coherence of frequency combs could simplify the receiver scheme by performing joint reception and processing of several wavelength channels, but an experimental validation in a fiber transmission experiment remains elusive. Here we demonstrate and quantify joint reception and processing of several wavelength channels in a full transmission system. We demonstrate two joint processing schemes; one that reduces the phase-tracking complexity and one that increases the transmission performance. © 2020, The Author(s).
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| 10. |
- Lundberg, Lars, 1989, et al.
(författare)
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Phase Correlation Between Lines of Electro-Optical Frequency Combs
- 2018
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Ingår i: Optics InfoBase Conference Papers. - 2162-2701.
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Konferensbidrag (refereegranskat)abstract
- Simultaneous measurement of the phase noise from 49 electro-optical frequency comb lines show a correlation of over 99.99% between lines. Additionally, the phase noise difference between line pairs is correlated, verifying theoretical predictions.
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