Superchannel Signal Research Articles

Compensation Schemes for Transmitter- and Receiver-Based Pattern-Dependent Distortion

A nonlinear pre-distorter (NLPD) at the transmitter, and a maximum-a-posteriori probability (MAP) detector, time-domain Volterra nonlinear equalizer (VNLE), or sparse-VNLE at the receiver are compared for compensation of the pattern-dependent distortion that can occur in high baud rate transmitters and receivers. Experimental results are presented for a 1.206-Tb/s dual-polarization 16-ary quadrature amplitude-modulation (16-QAM) superchannel signal with three subcarriers. The NLPD with iterative calculation of the pre-distortion provides the best performance in back-to-back systems and transmission systems followed by the MAP detector, VNLE, and sparse-VNLE. At the FEC threshold of 1.9 × 10 -2 , the NLPD provides an increase in the transmission distance of 300 km compared with the sparse-VNLE, VNLE, and MAP detector. For transmission over 1500 km of SMF, the VNLE and MAP detector exhibit additional optical signal-to-noise ratio margins of 0.16 and 0.47 dB relative to the sparse-VNLE. Compared with the VNLE, the sparse-VNLE exhibits a 55% reduction in number of kernel coefficients.

Transmission Performance of 448 Gb/s Single-Carrier and 1.2 Tb/s Three-Carrier Superchannel Using Dual-Polarization 16-QAM With Fixed LUT Based MAP Detection

Transmission of single-carrier 448 Gb/s dual-polarization 16-ary quadrature-amplitude-modulation (DP 16-QAM) electrical time-division multiplexed (ETDM) signal and a 1.206 Tb/s three-carrier superchannel ETDM signal using DP 16-QAM is demonstrated by applying a fixed look-up table (LUT) based on maximum-a-posteriori (MAP) detection. The MAP detector is used to mitigate the effect of pattern dependent distortion in the transmitted signal arising from the high symbol rates. Different decision rules for the MAP detector are considered based on multiple observations of the same symbol as the detection window advances through the received symbol sequence. The back-to-back optical signal-to-noise ratios for a bit error ratio of $\mathbf {10^{-3}}$ are 26.9 and 26.4 dB for the 448 Gb/s signal (12% overhead with 7% for forward error correction (FEC) coding overhead) and 1.206 Tb/s superchannel signal (20% overhead with 15% for FEC coding overhead), respectively. Compared to conventional MAP detection, a seven-symbol minimum distance MAP detector reduces the required OSNR by about 0.8 and 1 dB at the FEC thresholds of $\mathbf {3.8\times 10^{-3}}$ and $\mathbf {1.9\times 10^{-2}}$ for the 448 Gb/s signal and 1.206 Tb/s superchannel signal, respectively. Transmission over 1200 and 1500 km of standard single-mode fiber with EDFA amplification is achieved for the 448 Gb/s signal and 1.206 Tb/s superchannel signal, respectively.

A numerical and experimental comparison of a wavelength conversion for a 200 Gbit/s super-channel in a periodically poled lithium niobate waveguide

Tunable all optical wavelength conversion of a 200 Gbit/s super-channel data signal based on the cascaded of sum-frequency generation and different frequency generation in a periodically poled lithium niobate waveguide is demonstrated. This principle of wavelength conversion has been proposed, theoretically analyzed and the numerical results have been compared with the experimental ones.

Real-Time Ethernet to Software-Defined Sliceable Superchannel Transponder

Optical Ethernet gains great success in varied optical domains. Ethernet while providing the elastic allocation of bandwidth per flow is currently restricted to being transported over fixed-rate fixed-grid optical channels. However, as data transmission and switching in optical networks is becoming more flexible, the current Ethernet to optical interface with fixed functions and fixed design face great challenges for applications in an elastic optical network. In addition, the coexisted Ethernet standards in optical networks also need a converter to transform low-capacity Ethernet signals to high-capacity Ethernet signals. In this paper, we propose a real-time Ethernet to software-defined programmable sliceable transponder based on network function programmable Ethernet to elastic optical networks (ETH-EON) interface, multiformat supported transmitter and architecture-on-demand (AoD)-based superchannel signal processor. The transponder parses the Ethernet traffic and then transports it over a number of optical carriers with the appropriate baud-rate, modulation format and associated spectral bandwidth. Software-defined reconfigurability of both electronic (i.e., FPGA) and optics (AoD) allow for a flexible transponder to offer high Ethernet to optical transport efficiency. Ethernet capacities from 40 Gbit/s to 2.88 Tbit/s can be provided by reconfiguring the modulation formats and the used optical carrier number. The modulation format adaptability also provides a tradeoff between transmission capacity and transmission distance, to optimize network performance. The designed software-defined sliceable elastic transponder aggregate multiple Ethernet traffic flows and send spectral-efficient signals through the elastic optical network with simple Ethernet protocols, avoiding using complex and expensive OTN technologies. Finally, we demonstrate the converter in elastic optical networks for several application scenarios.

Wired and wireless convergent extended-reach optical access network using direct-detection of all-optical OFDM super-channel signal

We propose and demonstrate the feasibility of using all-optical orthogonal frequency division multiplexing (AO-OFDM) for the convergent optical wired and wireless access networks. AO-OFDM relies on all-optically generated orthogonal subcarriers; hence, high data rate (> 100 Gb/s) can be easily achieved without hitting the speed limit of electronic digital-to-analog and analog-to-digital converters (DAC/ADC). A proof-of-concept convergent access network using AO-OFDM super-channel (SC) is demonstrated supporting 40 - 100 Gb/s wired and gigabit/s 100 GHz millimeter-wave (MMW) ROF transmissions.

Transmission of 1 Tb/s Unique-Word DFT-Spread OFDM Superchannel Over 8000 km EDFA-Only SSMF Link

Conventional coherent optical orthogonal frequency-division multiplexed (CO-OFDM) system has inferior nonlinear tolerance due to high peak-to-average power ratio (PAPR). Discrete Fourier transform spread OFDM (DFTS-OFDM) has recently been proposed as a promising candidate that possesses similar spectral characteristics as conventional CO-OFDM, but has much better nonlinear tolerance. We demonstrate experimentally the transmission of 1.0 Tb/s unique-word DFTS-OFDM superchannel signal over 8000 km standard single-mode fiber with 80 km span engineering and erbium-doped fiber amplification (EDFA) using quadrature phase shift keying (QPSK) modulation, representing a record spectral efficiency and reach product in transmission systems compatible with most of the deployed links.

Transmission of 1936 Tb/s (11 × 176 Gb/s) DP-16QAM superchannel signals over 640 km SSMF with EDFA only and 300 GHz WSS channel

With an improved receiver-side spectral shaping technique by introducing and optimizing one tap coefficient in the intermediate response, we successfully transmitted 1.936 Tb/s (11 × 176 Gb/s) DP-16QAM superchannel signal over 8 × 80 km SSMF with EDFA-only and two 280 GHz wavelength selective switches (WSSs) in support of future 1.6 Tb/s Ethernet with up to 20% forward error correction overhead. The 280 GHz 3-dB bandwidth of the WSS passband permits a sufficient guardband if the 1.936 Tb/s superchannel signals are placed in a 300 GHz WSS channel.

Building up low-complexity spectrally-efficient Terabit superchannels by receiver-side duobinary shaping

Recently, an increasing interest has been put on spectrally-efficient multi-carrier superchannels for beyond 100G. Apart from orthogonal frequency-division multiplexing (OFDM) and Nyquist wavelength-division multiplexing (WDM), another low-complexity WDM approach based on transmitter-side pre-filtering and receiver-side duobinary shaping is proposed to build up multi-carrier superchannels. This approach is referred to as receiver-side duobinary-shaped WDM (RS-DBS-WDM). Generation and transmission of a 1.232-Tbit/s 11-carrier superchannel is experimentally demonstrated. The superchannel signal can be well fit inside the passband of multiple 300-GHz reconfigurable optical add and drop multiplexers (ROADMs). In the superchannel scenario, the proposed RS-DBS-WDM is qualitatively compared with OFDM and Nyquist-WDM in terms of implementation complexity. In sum, the proposed RS-DBS-WDM approach features high transceiver analog-bandwidth efficiency, high spectral-efficiency, the absence of specific spectral manipulation, compatibility with conventional WDM technologies and coherent detection algorithms, and comparable implementation penalty.

1.96 Tb/s (21$\,\times\,$100 Gb/s) OFDM Optical Signal Generation and Transmission Over 3200-km Fiber

A novel scheme to generate coherent 21 optical subcarriers with fixed frequency of 25 GHz is proposed and experimentally demonstrated. Using these optical subcarriers, we have successfully generated 1.96 Tb/s (21 × 100 Gb/s) polarization-multiplexing optical orthogonal frequency multiplexed (PM-OFDM) polarization multiplexed quadrature phase-shift keying (QPSK) optical superchannel signal with optical signal-noise ratio of each subchannel larger than 30 dB (0.1-nm bandwidth). We have transmitted this 1.96-Tb/s optical OFDM superchannel over 3200-km SMF-28 with amplification span of 80 km with erbium-doped fiber amplifier-only.