Zhennan Zheng

1.76Tb/s Nyquist PDM 16QAM signal transmission over 714km SSMF with the modified SCFDE technique.

Nyquist pulse shaping is a promising technique for high-speed optical fiber transmission. We experimentally demonstrate the generation and transmission of a 1.76Tb/s, polarization-division-multiplexing (PDM) 16 quadrature amplitude modulation (QAM) Nyquist pulse shaping super-channel over 714km standard single-mode fiber (SSMF) with Erbium-doped fiber amplifier (EDFA) only amplification. The superchannel consists of 40 subcarriers tightly spaced at 6.25GHz with a spectral efficiency of 7.06b/s/Hz. The experiment is successfully enabled with the modified single carrier frequency domain estimation and equalization (SCFDE) scheme by performing training sequence based channel estimation in frequency domain and subsequent channel equalization in time domain. After 714km transmission, the bit-error-rate (BER) of all subcarriers are lower than the forward error correction limit of 3.8 × 10(-3).

Orthogonal-band-multiplexed offset-QAM optical superchannel generation and coherent detection.

Nowadays the Internet not only has fast growing data traffic, but also has a fast growing number of on-line devices. This leads to high demand of capacity and flexibility of the future networks. The conventional Orthogonal Frequency Division Multiplexing (OFDM) and Nyquist pulse shaping signals have the advantage of high spectral efficiency when consisting of superchannels in the Wavelength-Division-Multiplexing (WDM) way. However, they face a cost issue when the spectral granularity of the superchannel is decreased to support more users. This paper proposes for the first time the scheme of Orthogonal-band-multiplexed offset-Quadrature Amplitude Modulation (OBM-OQAM) superchannel. OBM-OQAM superchannel provides large capacity and high spectral efficiency. Furthermore, it has the advantage of offering subbands of variable symbol rate without changing the system configuration. We provide a proof-of-principle demonstration of OBM-OQAM superchannel transmission. In our experiment, 400 Gbps 16 Quadrature Amplitude Modulation (QAM) OBM-OQAM superchannel transmission over 400 km Standard Single Mode Fiber (SSMF) is conducted. The experimental results show that the OBM-OQAM signal has low penalty in multi-band aggregation.

1 λ × 1.44 Tb/s free-space IM-DD transmission employing OAM multiplexing and PDM

We report the experimental demonstration of single wavelength terabit free-space intensity modulation direct detection (IM-DD) system employing both orbital angular momentum (OAM) multiplexing and polarization division multiplexing (PDM). In our experiment, 12 OAM modes with two orthogonal polarization states are used to generate 24 channels for transmission. Each channel carries 30 Gbaud Nyquist PAM-4 signal. Therefore an aggregate gross capacity record of 1.44 Tb/s (12 × 2 × 30 × 2 Gb/s) is acheived with a modulation efficiency of 48 bits/symbol. After 0.8m free-space transmission, the bit error rates (BERs) of all the channels are below the 20% hard-decision forward error correction (HD-FEC) threshold of 1.5 × 10(-2). After applying the decision directed recursive least square (DD-RLS) based filter and post filter, the BERs of two polarizations can be reduced from 5.3 × 10(-3) and 7.3 × 10(-3) to 2.2 × 10(-3) and 3.4 × 10(-3), respectively.

Fiber Nonlinearity Mitigation in 32-Gbaud 16QAM Nyquist-WDM Systems

Fiber nonlinearity distortion limits the achievable transmission distance and channel capacity of optical transmission systems. In this paper, we demonstrate an experiment of 1400-km standard single mode fiber transmission of 11 × 32 Gbaud 16-ary quadrature amplitude modulation signals with an emphasis on nonlinearity mitigation. Based on the first-order perturbation theory, we present the nonlinearity mitigation principle of the conjugate data repetition (CDR) scheme in a polarization division multiplexed wavelength division multiplexed scenario. Then, we apply several nonlinearity mitigation methods such as CDR, phase-conjugated twin waves (PCTW), digital back propagation (DBP), and the recursive least-squares (RLS) algorithm based filtering to the experiment, respectively. Optical Kerr effects of self-phase modulation, intra- and interchannel cross-phase modulation are considered. The experimental results show that CDR demonstrates similar performance to PCTW. By introducing the CDR scheme, the average bit error rate is reduced from 1.92 × 10-2 to 1.76 × 10-3 at the cost of halving the data rate. This corresponds to 3.2-dB Q2 factor promotion, including 1.5 dB improvement in nonlinearity mitigation. In contrast, 1.0-dB Q2 factor promotion is achieved by employing RLS-based filtering and DBP together without sacrificing the data rate.

Coherent Detection-Based Automatic Bias Control of Mach–Zehnder Modulators for Various Modulation Formats

In this paper, a method to automatically control the bias voltages of LiNbO3 Mach-Zehnder modulator (MZM) is proposed and demonstrated experimentally. The automatic bias control (ABC) method is based on low cost coherent detection employing 3 × 3 optical coupler, which enhances the dither detection sensitivity. By minimizing the monitored dither frequency components which represents the residual carrier component in the optical signal, the modulator biases are optimized. A 0-π/2 square-wave phase modulation is introduced to mitigate the detection fluctuation induced by the imbalance of 3 × 3 coupler and improve the monitoring accuracy. Experiments show that the proposed method is universal for different modulation formats. High bias control precision is achieved for inner in-phase/quadrature (I/Q) branches and outer phase bias of optical quadrature modulator. The penalty caused by the proposed ABC is negligible for both single carrier (SC) modulation and optical orthogonal frequency division multiplexing modulation. The tolerance to temperature disturbance is also demonstrated.

Unrepeatered 447Gb/s Nyquist PDM-64QAM transmission over 160km SSMF with backward Raman amplification

We experimentally demonstrate Nyquist superchannel transmission of 447 Gb/s (8×55.97Gb/s) PDM-64QAM over single span of 160 km SSMF with backward Raman amplification. We achieve a record distance of unrepeatered transmission for the spectral efficiency (SE) as high as 8.95b/s/Hz.

High spectral efficiency Nyquist optical superchannel transmission

In this paper, we briefly review high spectral efficiency optical superchannel transmission with Nyquist pulse shaping. Afterwards we present the principle of coherent optical Nyquist single carrier (SC) systems with frequency domain channel estimation and time domain equalization (FDTDE) with nonlinear compensation scheme coordinated. With this technique, Terabit polarization division multiplexed (PDM) 32 quadrature-amplitude modulation (QAM) superchannel with Nyquist pulse shaping is generated and transmitted experimentally.