| 1. |
- Chen, XÍ, et al.
(author)
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TDHQ Enabling Fine-granularity Adaptive Loading for SSB-DMT Systems
- 2018
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In: IEEE Photonics Technology Letters. - : Institute of Electrical and Electronics Engineers Inc.. - 1041-1135 .- 1941-0174. ; 30:19, s. 1687-1690
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Journal article (peer-reviewed)abstract
- In this letter, we introduce time domain hybrid quadrature amplitude modulation (TDHQ) for the single sideband (SSB) discrete multi-tone (DMT) systems. Experimental results reveal that with a single precoding set and the proposed adaptive loading algorithm, the TDHQ scheme can achieve finer granularity and therefore smoother continuous growth of data rate than that with the conventional quadrature amplitude modulation (QAM). Besides, thanks to the frame construction and the tailored mapping rule, the scheme with TDHQ has an obviously better peak to average power ratio (PAPR).
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| 2. |
- Chen, Zexin, et al.
(author)
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Transmitter optimization for PS-QAM signal in high spectral efficiency metro-transmission
- 2023
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In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 41, s. 1-10
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Journal article (peer-reviewed)abstract
- Probabilistic constellation shaping (PCS) brings unprecedented flexibility to future optical networks. However, PCS combined with higher-order modulation formats and higher symbol rates puts more demands on the transmitter. For metro-transmission with high spectral efficiency (SE), transmitter impairments are responsible for a major portion of the system constraints. To address this issue, in this work we study the impact of transmitter impairments on probabilistically shaped quadrature amplitude modulation (PS-QAM) signals. First, we investigate the impact of transmitter impairments and radio frequency (RF) amplifier noise on the optimum shaping factor and the modulation depth within a fiber link. Then, we explore how generalized mutual information (GMI) and the shaping factor are affected by the noise from the transmitter. Next, we first jointly optimize the arcsine swing and the clipping ratio, in order to mitigate the transmitter impairments for the PS-QAM signal, when the modulation depth, the noise from the transmitter, the noise from the fiber optical channel, and the shaping factor are fixed. Then, we verify its validity for various configurations of transmission system. The optimized parameters primarily depend on the noise from the transmitter and turn out to be insensitive to the noise from the fiber optical link and the shaping factor. Finally, we experimentally verify the optimization strategy with PS-256QAM in back-to-back (B2B) transmission.
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| 3. |
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| 4. |
- Feng, Zhenhua, et al.
(author)
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Multicore-Fiber-Enabled WSDM Optical Access Network With Centralized Carrier Delivery and RSOA-Based Adaptive Modulation
- 2015
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In: IEEE PHOTONICS JOURNAL. - : Institute of Electrical and Electronics Engineers (IEEE). - 1943-0655. ; 7:4
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Journal article (peer-reviewed)abstract
- We proposed and experimentally demonstrated a wavelength-space division multiplexing (WSDM) optical access network architecture with centralized optical carrier delivery utilizing multicore fibers (MCFs) and adaptive modulation based on reflective semiconductor amplifier (RSOA). In our experiment, five of the outer cores are used for undirectional downstream (DS) transmission only, whereas the remaining outer core is utilized as a dedicated channel to transmit upstream (US) signals. Optical carriers for US are delivered from the optical line terminal (OLT) to the optical network unit (ONU) via the inner core and then transmitted back to the OLT after amplification and modulation by the RSOA in the colorless ONU side. The mobile backhaul (MB) service is also supported by the inner core. Wavelengths used in US transmission should be different from that of the MB in order to avoid the Rayleigh backscattering effect in bidirectional transmission. With quadrature phase-shift keying-orthogonal frequency-division multiplexing (QPSK-OFDM) modulation format, the aggregation DS capacity reaches 250 Gb/s using five outer cores and ten wavelengths, and it can be further scaled to 1 Tb/s using 20 wavelengths modulated with 16 QAM-OFDM. For US transmission, 2.5 Gb/s QPSK-OFDM transmission can be achieved just using a low-bandwidth RSOA, and adaptive modulation is applied to the RSOA to further enhance the US data rate to 3.12 Gb/s. As an emulation of high-speed MB transmission, 48 Gb/s inphase and quadrature (IQ) modulated popularization division multiplexing (PDM)-QPSK signal is transmitted in the inner core of MCF and coherently detected in the OLT side. Both DS and US optical signals exhibit acceptable performance with sufficient power budget.
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| 5. |
- Feng, Zhenhua, et al.
(author)
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Performance-Enhanced Direct Detection Optical OFDM Transmission With CAZAC Equalization
- 2015
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In: IEEE Photonics Technology Letters. - 1041-1135 .- 1941-0174. ; 27:14, s. 1507-1510
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Journal article (peer-reviewed)abstract
- Direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) transmission with constant amplitude zero autocorrelation (CAZAC) sequence equalization is proposed and experimentally demonstrated. Simulation results show that more than 2-dB peak-to-average power ratio (PAPR) reduction can be realized using CAZAC equalization, and 50-km standard single mode fiber (SSMF) transmission of 4.11-Gb/s QPSK-OFDM can be achieved with bit-error rate (BER) under forward error correction limit. Transmission performance of QPSK-based DDO-OFDM system is analyzed in both OB2B configuration and fiber link with and without CAZAC equalization. More than 2.5-dB optical receiver sensitivity improvements can be obtained thanks to the PAPR reduction enjoyed by CAZAC equalization. Signal-to-noise ratio for every subcarrier derived from error vector magnitude is estimated and its flatness is confirmed to be much improved with CAZAC equalization. The performance improvements brought by CAZAC equalization can be extended to other modulation formats, and 8.22-Gb/s 16-quadratic-amplitude modulation-OFDM signals transmission using CAZAC equalization is demonstrated with over 1.5 dB enhancement in receiver sensitivity.
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| 6. |
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| 7. |
- Gao, Jitao, et al.
(author)
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Active Mode-Selective Conversion Enabled by an Elliptical-Core Highly Nonlinear Few-Mode 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 design an elliptical-core highly nonlinear few-mode fiber to achieve mode-selective conversion without parasitic wavelength conversion, using intermodal four-wave mixing. The proposed mode converter can be used in optical cross-connects over the C-band.
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| 8. |
- Gao, Jitao, et al.
(author)
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Elliptical-Core Highly Nonlinear Few-Mode Fiber Based OXC for WDM-MDM Networks
- 2021
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In: IEEE Journal of Selected Topics in Quantum Electronics. - 1558-4542 .- 1077-260X. ; 27:2
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Journal article (peer-reviewed)abstract
- In order to realize an optical cross-connect (OXC) converting wavelengths and spatial modes into one-dimensional switching ports, we propose an active mode selective conversion without parasitic wavelength conversion, based on the intermodal four-wave mixing (FWM) arising in a few-mode fiber (FMF). First, we design a dispersion-engineered elliptical-core highly nonlinear FMF (e-HNL-FMF) with a graded refractive index (RI) profile, which can independently guide 3 linearly polarized (LP) spatial modes. Meanwhile, a high doping concentration of germanium in the core leads to relatively high intermodal nonlinear coefficients of 3.23 (W·km)-1 between LP01 and LP11a modes and 3.14 (W·km)-1 between LP01 and LP11b modes. Next, we propose an e-HNL-FMF based OXC scheme for wavelength division multiplexing-mode division multiplexing (WDM-MDM) networks. After optimizing both the e-HNL-FMF length and pump power, we can realize either active mode selective conversion over the designated wavelength-band or three-wavelength to three-mode superchannel conversion for 100 Gbaud 16-quadratic-amplitude modulation (16-QAM) signals over the C-band. Due to excellent characteristics of the e-HNL-FMF, both cost and configuration complexity of the OXC can be reduced, showing great potentials for all-optical signal processing in the future WDM-MDM networks.
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| 9. |
- Gao, J. T., et al.
(author)
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Design, fabrication, and characterization of a highly nonlinear few-mode fiber
- 2019
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In: Photonics Research. - 2327-9125. ; 7:11, s. 1354-1362
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Journal article (peer-reviewed)abstract
- We present the design, fabrication, and characterization of a highly nonlinear few-mode fiber (HNL-FMF) with an intermodal nonlinear coefficient of 2.8 (W · km)−1, which to the best of our knowledge is the highest reported to date. The graded-index circular core fiber supports two mode groups (MGs) with six eigenmodes and is highly doped with germanium. This breaks the mode degeneracy within the higher-order MG, leading to different group velocities among corresponding eigenmodes. Thus, the HNL-FMF can support multiple intermodal four-wave mixing processes between the two MGs at the same time. In a proof-of-concept experiment, we demonstrate simultaneous intermodal wavelength conversions among three eigenmodes of the HNL-FMF over the C band.
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| 10. |
- Gao, Jitao, et al.
(author)
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Vector mode inter-modal wavelength conversion in a dispersion tailored highly nonlinear few-mode fibre
- 2019
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In: IET Conference Publications. - : Institution of Engineering and Technology. ; 2019:CP765
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Conference paper (peer-reviewed)abstract
- We present the design and fabrication of a dispersion tailored highly nonlinear few-mode fibre with an inter-modal nonlinear coefficient of 2.81 (W · km)-1, the highest reported to date. Inter-modal wavelength conversion between the HE21 and TE01 vector modes is demonstrated in the fibre.
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