| 91. |
- He, Zonglong, 1994, et al.
(författare)
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Inter-Channel Interference Cancellation for Long-Haul Superchannel System
- 2024
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 42:1, s. 48-56
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Tidskriftsartikel (refereegranskat)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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| 92. |
- He, Zonglong, 1994, et al.
(författare)
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Periodicity-Enabled Size Reduction of Symbol Based Predistortion for High-Order QAM
- 2022
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 40:18, s. 6168-6178
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Tidskriftsartikel (refereegranskat)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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| 93. |
- Hedekvist, Per Olof E, 1967, et al.
(författare)
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Fiber four-wave mixing demultiplexing with inherent parametric amplification
- 1997
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Ingår i: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 15:11, s. 2051-2058
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Tidskriftsartikel (refereegranskat)abstract
- We present an all-optical time-division demultiplexer with 22 dB conversion efficiency, using four-wave mixing (FWM) at 1550 nm in a single-mode dispersion-shifted fiber. Error-free demultiplexing of 20 Gb/s data to 10 Gb/s is obtained, with 1.4 dB power penalty at BER = 10-9. We also derive theoretical expressions for the conversion efficiency, the maximum bit rate that is possible to demux and the shape of the switching window. In particular we emphasize the importance of phase-matching in order to achieve a flat switching window. Furthermore the pump must remain undepleted to avoid a detrimental reduction of the extinction ratio due to instantaneous parametric gain saturation.
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| 94. |
- Hedekvist, Per Olof E, 1967, et al.
(författare)
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Microwave Harmonic Frequency Generation utilizing the properities of an Optical Phase Modulator
- 2004
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 22:3, s. 882-886
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Tidskriftsartikel (refereegranskat)abstract
- New techniques to generate a harmonic microwave frequency modulated on an optical carrier are presented. All these techniques utilize the polarization-dependent properties of a LiNbO3-phase modulator and manage to achieve 40-GHz modulation using only 10-GHz electronics. The signal quality of the generated frequency is mainly determined by the 10-GHz signal generator, and the suppression of undesired lower order harmonic frequencies exceeds 30 dB.
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| 95. |
- Hellström, E., et al.
(författare)
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Third-order dispersion compensation using a phase modulator
- 2003
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 20:5, s. 1188-1197
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Tidskriftsartikel (refereegranskat)abstract
- Compensation of third-order dispersion in a fiber-optic transmission system using a phase modulator is studied both theoretically and experimentally. A sinusoidal signal is used as modulation function, where the amplitude and phase delay are optimized. The 2-ps input pulses (160-Gb/s compatible) were transmitted through a 626-km fiber link, where the characteristic oscillating tail was measured with a 1.6-ps resolution optical sampling system. When applying the phase modulation, the oscillating tail was significantly suppressed. The pulses were also used in a 160-Gb/s transmission experiment, where the eye diagrams were measured with the sampling system. Numerical simulations and practical experiments showed excellent agreement.
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| 96. |
- Hey Tow, Kenny, et al.
(författare)
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Graphene-material based nanocomposite-coated optical fibres : a multi-functional optical fibre for improved distributed sensing performance in harsh environment
- 2024
-
Ingår i: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers Inc.. - 0733-8724 .- 1558-2213.
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Tidskriftsartikel (refereegranskat)abstract
- The optical fibre coating is essential to ensure high performance and reliability of the optical fibre. Out of all polymer-coated fibres, polyimide coatings provide the highest temperature rating, typically rated for use in optical fibre sensing applications at 300˚C (in air), with short excursion to 350˚C. In this communication, we assess whether the inclusion of graphene-based nanoparticles, such as graphene and graphene oxide, in a polyimide coating can enhance the durability of optical fibres at high temperatures. Draw tower fabrication of optical fibres with nanocomposite polymer coating is described. Tensile strength tests, performed on aged nanocomposite-coated optical fibres, are used as an indication of their performance at harsh conditions. The results are validated and quantified by distributed temperature and humidity sensing tests performed using these fibres. The results show that this novel class of fibre is more robust to high-temperature ageing and moisture-induced strain than standard polyimide-coated fibres, when used for distributed sensing. The electrical conductivity of the nanocomposite coating is also used in a multi-sensing approach, together with distributed optical fibre sensing, to measure temperature in a reliable way using the same optical fibre.
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| 97. |
- Hu, R., et al.
(författare)
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A Small Polymeric Ridge Waveguide With a High Index Contrast
- 2008
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Ingår i: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 26:13-16, s. 1964-1968
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, an optimal design of a small polymeric ridge waveguide with a high index contrast is presented. In order to reduce the leakage to the substrate and pure bending losses, the buffer layer of the present waveguide is etched partially. The single-mode condition, the bending characteristics, and the birefringence of the present small polymeric ridge waveguide are also studied. By adjusting the core width and the core height, it is possible to obtain a polarization-insensitive small polymer ridge waveguide. For the bending loss, the numerical results show that the dominant part is the transition loss between the straight and bending sections (other than the pure bending loss) and the transition loss could be reduced greatly by introducing a lateral offset. However, the transition loss is still too large to obtain a very small bending radius (e.g., 10 mu m). When only the pure bending loss is necessary to consider in some special case (e.g., microrings without any transitions), one can have a bending radius less than 10 mu n due to the possibility of low pure bending loss.
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| 98. |
- Hu, Wenxiu, et al.
(författare)
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High-Dimensional Feature Based Non-Coherent Detection for Multi-Intensity Modulated Ultraviolet Communications
- 2022
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Ingår i: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 40:7, s. 1879-1887
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Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet communication (UVC) has been regarded as a promising supplement for overloaded conventional wireless communications. One challenge lies in the communication deterioration caused by the UV-photon scattering induced intersymbol-interference (ISI), which will be even worse when encountering multilevel pulse amplitude modulation (multi-PAM) symbols. To address this ISI, traditional coherent detection methods (e.g., maximum-likelihood sequence detection, MLSD) require high computational complexities for UV channel estimation and sequential detection space formation, thereby making them less attractive. Current non-coherent detection, which simply combines the ISI-insensitive UV signal features (e.g., the rising edge) into a one-dimensional (1D) metric, cannot guarantee reliable communication accuracy. In this work, a novel high-dimensional (HD) non-coherent detection scheme is proposed, leveraging a HD construction of the ISI-insensitive UV signal features. By doing so, we transform the ISI caused sequential detection into an ISI-released HD detection framework, which avoids complex channel estimation and sequential detection space computation. Then, to compute the detection surface, a UV feature based unsupervised learning approach is designed. We deduce the theoretical bit error rate (BER), and prove that the proposed HI) non-coherent detection method has a lower BER than that of the current 1D non-coherent scheme. Simulation results validate our results, and more importantly, demonstrate a BER that approaches that of the state-of-the-art coherent MLSD (<1 dB in SNR at BER = 4.5 x 10(-8), the 7% overhead forward-error-correction limit), and also a reduction of computational complexity by at least two orders of magnitude.
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| 99. |
- Hu, Wenxiu, et al.
(författare)
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Non-Coherent Detection for Ultraviolet Communications With Inter-Symbol Interference
- 2020
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Ingår i: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 38:17, s. 4699-4707
-
Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet communication (UVC) serves as a promising supplement to share the responsibility for the overloads in conventional wireless communication systems. One difficulty lies in how to address the inter-symbol-interference (ISI) from the strong scattering nature and the time-varying channel response. This is more challenging for the energy-constrained scenarios (e.g., underwater UV), as existing coherent schemes (i.e., requiring exact channel information for signal detection) become less attractive given the computational and storaging complexity for repeated time-varying channel estimation and statistical signal detection. In this work, a novel non-coherent paradigm is proposed, via the exploration of the UV signal features that are insensitive to the ISI. By optimally weighting and combining the extracted features to minimize the bit error rate (BER), the optimally-weighted non-coherent detection (OWNCD) is proposed, which converts the signal detection with ISI into a binary detection framework, with a heuristic weight updating approach for time-varying channel. As such, the proposed OWNCD avoids the complex channel estimation and guarantees the detection accuracy. Compared to the state-of-the-art coherent maximum likelihood sequence detection (MLSD) in the cases of static and time-varying channel response, the proposed OWNCD can gain similar to 1 dB and similar to 8 dB in signal-to-noise-ratio (SNR) at the 7% overhead forward-error-correction (FEC) limit (BER of 4.5 x 10(-3)), respectively, and can also reduce the computational complexity by 4 order of magnitude.
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| 100. |
- Hu, Wenxiu, et al.
(författare)
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Tapping Eavesdropper Designs Against Physical Layer Secret Key in Point-to-Point Fiber Communications
- 2023
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Ingår i: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 41:5, s. 1406-1414
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Tidskriftsartikel (refereegranskat)abstract
- With the growing demand for service access and data transmission, security issues in optical fiber systems have become increasingly important and the subject of increased research. Physical layer secret key generation (PL-SKG), which leverages the random but common channel properties at legitimate parties, has been shown to be a secure, low-cost, and easily deployed technique as opposed to computational-based cryptography, quantum, and chaos key methods that rely on precise equipment. However, the eavesdropper (Eve) potential for current PL-SKG in fiber communications has been overlooked by most studies to date. Unlike wireless communications, where the randomness comes from the spatial multi-paths that cannot be all captured by Eves, in fiber communications, all the randomness (from transmitted random pilots or channel randomness) is contained in the signals transmitted inside the fiber. This, therefore, enables a tapping Eve to reconstruct the common features of legitimate users from its received signals, and further decrypt the featured-based secret keys. To implement this idea, we designed two Eve schemes against polarization mode distortion (PMD) based PL-SKG and the two-way cross multiplication based PL-SKG. The simulation results show that our proposed Eves can successfully reconstruct the legitimate common feature and the secret key relied upon, leading to secret key rate (SKR) reductions of between three and four orders of magnitude in the PL-SKG schemes studied. As a result, we reveal and demonstrate a novel eavesdropping potential to provide challenges for current physical layer secret key designs. We hope to provide more insightful vision and critical evaluation on the design of new physical layer secret key schemes in optical fiber links, to provide more comprehensively secure, and intelligent optical networks.
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