| 1. |
- Eliasson, Henrik, 1985, et al.
(author)
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Phase-sensitive amplifier link with distributed Raman amplification
- 2018
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In: Optics Express. - 1094-4087 .- 1094-4087. ; 26:16, s. 19854-19863
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Journal article (peer-reviewed)abstract
- We demonstrate long-haul transmission using a hybrid amplifier approach combining distributed Raman amplification and lumped phase-sensitive amplification. Aside from the well-known resulting SNR improvement, distributed Raman amplification is included in an effort to improve the nonlinearity mitigation capability of the phase-sensitive amplifiers. When changing from phase-insensitive operation to phase-sensitive operation in a link employing distributed Raman amplification, the transmission reach at BER = 10−3is increased from 15 to 44 spans of length 81 km while simultaneously increasing the optimal launch power by 2 dB.
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| 2. |
- Foo, Benjamin, 1991, et al.
(author)
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Analysis of nonlinearity mitigation using phase-sensitive optical parametric amplifiers
- 2019
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In: Optics Express. - 1094-4087 .- 1094-4087. ; 27:22, s. 31926-31941
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Journal article (peer-reviewed)abstract
- Phase-sensitive optical parametric amplifiers (PSAs) can provide low-noise optical amplification while simultaneously mitigating nonlinear distortions caused by the Kerr effect. However, nonlinearity mitigation using PSAs is affected by link parameters, and imperfect link design results in residual nonlinear distortions. In this paper, we use first-order perturbation theory to describe these residual nonlinear distortions, and develop a way to mitigate them using a modified third-order Volterra nonlinear equalizer (VNLE) in the receiver. Using numerical simulations, we show that our proposed VNLE reduces the residual nonlinear distortions in links using in-line PSAs for several combinations of symbol rates and modulation formats, and can increase the maximum transmission distance by up to 80%. We also perform a proof-of-concept experiment and confirm that our modified VNLE can mitigate the residual nonlinear distortions on a 10-Gbaud 16QAM signal after transmission through a 10×80-km link with in-line PSAs.
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| 3. |
- Foo, Benjamin, 1991, et al.
(author)
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Combining phase-sensitive amplifiers with DSP for enhanced nonlinearity mitigation
- 2019
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In: IET Conference Publications. ; 2019:CP765
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Conference paper (peer-reviewed)abstract
- We investigate combining phase-sensitive optical amplifiers (PSAs) with a static Volterra nonlinear equalizer (VNLE) to mitigate residual nonlinear distortions. Experiments show that the VNLE reduces penalties from link design and improves QBER by 0.4 dB for a 10-GBaud 16QAM signal in a 10×80-km PSA-amplified link.
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| 4. |
- He, Zonglong, 1994, et al.
(author)
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Inter-Channel Interference Cancellation for Long-Haul Superchannel System
- 2024
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In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 42:1, s. 48-56
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Journal article (peer-reviewed)abstract
- Optical frequency combs enable superchannel systems with dense channel spacing by providing equally-spaced lines to overcome the relative frequency drifts of free-running lasers, achieving high spectral efficiency. However, strong inter-channel interference is induced in densely spaced systems due to imperfect pulse-shaping, preventing the further improvement of system throughput. By including the spectra information from the adjacent channels, comb-based multi-channel equalization has been previously validated in a back-to-back and 80 km transmission system for linear crosstalk mitigation. In this case, the limiting factor of the system was the effective number of bits (ENOB). Here, we investigate the influence of amplified spontaneous emission noise and the effectiveness of joint equalization in long-haul transmission systems. We show that the performance of the multi-channel equalizer (MCE) is significantly degraded when reducing the optical-signal-to-noise ratio (OSNR), especially for high-order modulation formats, in both noise-loading and long-distance transmission experiments. Moreover, the ASE noise from the neighboring channels can be coupled into the systems by the MCE, degrading the performance improvement. We find that a large-tap MCE can maximize the system performance in the high OSNRs, whereas MCE with a smaller tap should be applied in low OSNRs to alleviate the effect of ASE noise. After transmission of 800 km, an AIR increase of more than 0.1 bits/s/Hz is enabled by the optimized MCE for 16-QAM and 64-QAM. Our results confirm the validity of the joint equalization gain for short-distance transmission but also clearly demonstrate the performance penalty originating from transmission optical noise. Moreover, the equalizer tap number needs to be optimized for each OSNR to maximize the performance of joint equalization. We believe this limitation is also valid for other impairments such as optical noise in the comb and electrical noise in the transceiver.
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| 5. |
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| 6. |
- He, Zonglong, 1994, et al.
(author)
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Periodicity-Enabled Size Reduction of Symbol Based Predistortion for High-Order QAM
- 2022
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In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; In press
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Journal article (peer-reviewed)abstract
- We experimentally demonstrate a novel size reduction approach for symbol-based look-up table (LUT) digital predistortion (DPD) of the transmitter impairments taking advantage of the periodicity in the pattern-dependent distortions. Compared to other reduced-size LUT schemes, the proposed method can significantly lessen the storage memory requirements with negligible performance penalty for high-order modulation formats. To further alleviate the storage memory restriction, a twice reduced-size LUT scheme is proposed to provide further size reduction. Importantly, given a targeted memory length, we verify the importance of averaging over sufficient occurrences of the patterns to obtain a well-performing LUT. Moreover, it is necessary to evaluate the performance of LUT-based DPD using random data. Finally, we demonstrate a neural network (NN) based nonlinear predistortion technique, which achieves nearly identical performance to the full-size LUT for all employed constellations and is robust against a change of modulation format. The proposed techniques are verified in a back-to-back transmission experiment of 20 Gbaud 64-QAM, 256-QAM, and 1024-QAM signals considering 3 and 5 symbol memory. The performance of the LUT-based DPD is further validated in a noise loading experiment.
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| 7. |
- He, Zonglong, 1994, et al.
(author)
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Symbol-Based Supervised Learning Predistortion for Compensating Transmitter Nonlinearity
- 2021
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In: 2021 European Conference on Optical Communication, ECOC 2021. - 9781665438681
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Conference paper (peer-reviewed)abstract
- We experimentally demonstrate a symbol-based nonlinear digital predistortion (DPD) technique utilizing supervised learning, which is robust against a change of modulation format. Back-to-back transmission of 30 Gbaud 32, 64 and 256QAM confirms that our scheme significantly outperforms the baseline of arcsine-based predistortion.
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| 8. |
- Mirani, Ali, 1992, et al.
(author)
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Comparison of Physical Realizations of Multidimensional Voronoi Constellations in Single Mode Fibers
- 2022
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In: European Conference on Optical Communication, ECOC.
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Conference paper (peer-reviewed)abstract
- We investigate experimentally and numerically the impact of using different fiber dimensions to spread out the 32-dimensional Voronoi constellations. We find similar performance in experiments and less than 5.4% reach improvements in long-haul transmission simulations by spreading the constellation dimensions over time slots compared to wavelengths
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| 9. |
- Mirani, Ali, 1992, et al.
(author)
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Experimental Demonstration of 8-Dimensional Voronoi Constellations with 65,536 and 16,777,216 Symbols
- 2021
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In: 2021 European Conference on Optical Communication, ECOC 2021. - 9781665438681
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Conference paper (peer-reviewed)abstract
- We experimentally demonstrate high-cardinality, low-complexity Voronoi constellations based on the E8 lattice over multiple time slots with OSNR and launch power gains of up to 1.7 and 2.4 dB for back-to-back and 80 km fiber transmission, respectively, compared to QAM formats.
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| 10. |
- Mirani, Ali, 1992, et al.
(author)
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Physical Realizations of Multidimensional Voronoi Constellations in Optical Communication Systems
- 2023
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In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 41:17, s. 5557-5563
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Journal article (peer-reviewed)abstract
- Abstract:Multidimensional geometric shaping has been shown to outperform uniform quadrature amplitude modulation (QAM) in optical communication systems but the complexity of symbol decision and bit mapping can often be significant as dimensionality increases. In this paper, a low-complexity geometric shaping method based on multidimensional lattices is investigated both in experiments and simulations. The modulation formats designed based on this method are called Voronoi constellations (VCs) and we study them in 8, 16, and 32 dimensions. We obtain transmission reach improvements of up to 22 and 70% for VCs compared to 4QAM and 16QAM, respectively, in nonlinear long-haul fiber transmission. Moreover, we compare different physical realizations of multidimensional VCs over wavelengths, polarizations, and time slots in both the Gaussian and nonlinear fiber channels. We demonstrate that different physical realizations perform similarly in the fiber-optic back-to-back channel. However, in long-haul transmission systems, spreading the dimensions over time slots can increase the transmission reach up to 4% compared to wavelengths and polarizations. Furthermore, the mutual information and generalized mutual information are estimated and compared to QAM formats at the same spectral efficiencies.
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