10G-class Optics Research Articles

Demonstration of all-digital burst clock and data recovery for symmetrical 50 Gb/s/[formula omitted] PON based on low-bandwidth optics

We experimentally demonstrated all-digital burst clock and data recovery (BCDR) for symmetrical single-wavelength 50 Gb/s four-level amplitude modulation (PAM-4) passive optical network (PON) over the same fiber link at O-band, with the using of 10G-class optics and simple digital signal processing (DSP). The uplink burst frame and BCDR algorithm is used for accurately evaluating PON uplink transmission performance. The results show that over 26 dB link loss budget for continuous-mode uplink transmission and over 25 dB for burst-mode uplink transmission at a bit error rate of 3.8 × 10−3 can be achieved, respectively. For symmetrical 50 Gb/s/λ PON uplink burst-mode, there are 1 dB power budget loss less than uplink continuous-mode.

Low complexity Volterra nonlinear equalizer based on weight sharing for 50 Gb/s PAM4 IM/DD transmission with 10G-class optics

In this paper, an improved Volterra nonlinear equalizer with low computational complexity and good performance is proposed to compensate the distortions caused by bandwidth limitation and optical devices. The performance of the equalizer is improved by introducing one-hot encoding, and the complexity is reduced by using absolute operations and weight sharing based on k-means clustering. We employ the k-means clustering algorithm to replace some weights that are close in value with another similar weight, which greatly reduces the multiplications of this equalizer. Finally, we experimentally demonstrate a 50 Gb/s PAM4 IM/DD transmission with 10G-class optics using this proposed equalization scheme. The results show that, compared with the conventional 3rd-order Volterra nonlinear equalizer, the sensitivity of the proposed scheme is improved by > 2 dB, and the number of multiplication operations is reduced by ∼81.2%.

Simplified Soft-Output Direct Detection FTN Algorithm for 56-Gb/S Optical PAM-4 System Using 10G-Class Optics

In this paper, a simplified soft-output direct detection faster than Nyquist (SO-DD-FTN) algorithm is proposed to eliminate severe inter-symbol interference in optical interconnects. The feasibility of the proposed algorithm is verified in a C-band 56-Gb/s 4-ary pulse amplitude modulation (PAM-4) system using 10G-class optics, and the 3-dB system bandwidth is only 5.5 GHz. Compared to conventional SO-DD-FTN, the simplified SO-DD-FTN not only reduces 90% multiplication complexity and 80% addition complexity, but also has almost no performance degradation. Experimental results show that, for the back-to-back case, the achieved receiver sensitivity using simplified SO-DD-FTN has 4.5-dB improvement compared with conventional direct detection faster than Nyquist (DD-FTN). As for 20-km standard single-mode fiber (SSMF) transmission application, since the system suffers from both optical/electronic bandwidth limitation and dispersion-induced power fading, the conventional DD-FTN cannot achieve the bit error rate (BER) threshold of 10 -3 , while the simplified SO-DD-FTN can achieve the BER threshold at received optical power of -14.5 dBm. In conclusion, the proposed simplified SO-DD-FTN algorithm achieves superior performance with low computational complexity and has the potential for applying to optical interconnects.

Machine learning classifier based on FE-KNN enabled high-capacity PAM-4 and NRZ transmission with 10-G class optics

Modified by special feature engineering, a powerful and low-order equalizer based on K-nearest neighbors (KNN) classifier is applied to improve performance of high-speed system with bandwidth-limited optics. The feature construction and feature weighting are specially designed to conduct an appropriate a feature engineering-based KNN (FE-KNN) scheme, which contains more data characteristics to enhance the equalization performance. Experimental comparisons of KNN classifier with/without feature engineering, decision feedback equalizer (DFE) and feed-forward equalizer (FFE) are implemented to prove the feasibility of our scheme in both 25-Gb/s NRZ and 50-Gb/s PAM-4 transmission experiments with 10-G optics system. The corresponding results show that, without the feature engineering, the performance achieved by the common KNN is not improved even in the case of hard decision (HD). In contrast, compared to the common 11-taps DFE, the performance achieved by FE-KNN with only 5 taps is improved by 1-dB at KP4-FEC threshold (BER=2.2E-4) for 25-Gb/s NRZ transmission. While, for 50-Gb/s PAM-4 case, 0.5-dB sensitivity improvement is achieved by our scheme compared to the common 11-taps DFE under the HD-FEC limit (BER=3.8E-3).

A Powerful Equalizer Based on Modified SVM Classifier Without Nonlinear Kernel Enabled 100-Gb/s NG-EPON System With 10-G Class

For the future high-speed next-generation Ethernet passive optical network (NG-EPON) system, the low-cost system could be kept by adopting low bandwidth devices. To compensate for the signal distortion and improve the performance of high-speed bandwidth limited system, we propose a special feature vector construction to achieve a new equalizer scheme based on support vector machines (SVM) classifier. For the first time, we mathematically analyze the model of the bandwidth-limited optical transmission system and theoretically derive the linear separability of the proposed feature vector formed linear hyperplane in 100-Gb/s NG-EPON system. Furthermore, 4 × 25-Gb/s non-return to zero (NRZ) and 2 × 50-Gb/s four-level pulse amplitude modulation (PAM-4) per wavelength transmission experiments with 10-G class optics system are demonstrated to prove the feasibility of our scheme. The experimental results show that, for 25-Gb/s/λ NRZ transmission, compared to the decision feedback equalizer (DFE) and feed-forward equalizer (FFE), the receiver sensitivity achieved by our scheme can be improved by about 0.5-dB @BER=3.8e-3 with limited training sequence. For the 50-Gb/s/λ PAM-4 case, the SVM-based equalization method improves the receiver sensitivity for about 1-dB.

Joint Hartley-domain and time-domain equalizer for a 200-G (4×56-Gbit/s) optical PAM-4 system using 10G-class optics.

In this paper, we experimentally demonstrate a 200-G (4×56-Gbit/s) optical 4-level pulse-amplitude modulation (PAM-4) system using 10G-class optics over 10-km standard single-mode fiber and propose a joint Hartley-domain equalizer (HDE) and time-domain equalizer (TDE) algorithm for efficiently compensating the serious high-frequency distortions caused by the bandwidth-limited devices. To the best of our knowledge, the first HDE based on Hartley transform is designed for an optical PAM-4 system. Owing to the real-valued and self-inverse properties of the Hartley transform, the HDE has advantages in processing the real-valued PAM-4 signal. The experimental results show that the joint HDE and TDE algorithm has a better performance than only the HDE or only the TDE. Meanwhile, for obtaining a desired bit error rate, the computational complexity of the joint HDE and TDE algorithm is approximately 6% that of only the TDE with larger tap number. In conclusion, the joint HDE and TDE algorithm shows great potential for high-speed and cost-sensitive optical PAM-4 systems.

Power budget of 25-Gb/s digital orthogonal filter multiple access PONs with 10G-class optics

Abstract Power budget is a key factor that should be considered in intensity modulation and direct detection (IM/DD) passive optical networks (PONs). Based on the low-cost 10G-class electro-absorption modulated laser (EML) operating at C-band, we not only experimentally and theoretically investigate the interplay between the chromatic dispersion, the chirp of EML, and the self-phase modulation (SPM), but also explore the influences of the resolution and timing jitter of the analog to digital converter (ADC). Both theoretical and experimental results show that high power budget can be effectively achieved by making full use of the high launch power induced SPM effect and EML-induced frequency chirp. Based on the 10-G transmitter optical sub-assembly (TOSA) and receiver optical sub-assembly (ROSA), we successfully realize 25 Gb/s signal transmission at C-band over 25 km standard single mode fiber (SSMF) in IM/DD PON system. Even the worst performing bands can still achieve 25 dB power budget. The proposed scheme in this work has a potential application in future cost-effective optical access networks.

Design and analysis of high-speed optical access networks in the O-band with DSP-free ONUs and low-bandwidth optics.

In this paper, we demonstrate and investigate high-speed passive optical networks (PON) in the O-band without using any digital signal processing (DSP) at the ONU side, meanwhile still adopting cost-effective low-bandwidth optics. We show that with commercial 10G-class optics including DML and PIN-TIA, 50Gb/s PAM4 PON with a power budget up to 29dB is achieved under the HD-FEC BER limit. We present the detailed design procedure of the DSP including the downlink Nyquist pulse shaping and pre-equalization and uplink post-equalization, and conduct a comprehensive study on this system including DSP complexity, DAC/ADC sampling rate requirement and tolerance to the response diversity of ONU receivers. We conclude that, 1) 55 and 35 taps are sufficient for downlink and uplink digital filters to approach the BER floor; 2) the minimum required DAC and ADC sampling rate are respectively 33.75GS/s and 32GS/s to achieve the optimal performance; and 3) with 1dB sensitivity penalty at the HD-FEC BER limit, the allowable response diversity of ONU receivers can be from -2.2dB/10GHz to 1.8dB/10GHz. Furthermore, we explore and demonstrate the suitable data rate based on on-off keying and duobinary modulation formats in this system and present corresponding results.

Experimental Demonstration of 40-Gb/s I-SC-FDM With 10G-Class Optics and Low-Complexity DSP for Next-Generation PON

Low cost and low energy consumption are two important issues for the upgrade of next-generation passive optical network (PON). In this paper, we experimentally demonstrated a 40-Gb/s PON downstream transmission employing interleaved single carrier frequency-division multiplexing (I-SC-FDM) modulation and joint frequency-time domain equalization. At the transmitter, low peak-to-average power ratio and low-complexity signal is generated using simplified encoding structure of phase rotation and complex-to-real transform. At the receiver, the digital signal processing is of low computational complexity since very few taps of joint equalization are needed. 10G-class optics are used both in transmitter and receiver to maintain a low-cost system. Experimental results indicate that total 28.6 dB link power budget over 20 km transmission in C-band was successfully achieved without using any optical amplifier or optical dispersion compensation fiber, which supports up to $1:256$ optical splitter ratio in PON systems. The proposed scheme is of great reference significance in the next-generation PON systems.

Investigation on the equalization techniques for 10G-class optics enabled 25G-EPON.

High speed modulation based on bandwidth limited devices is desired for cost-effective PON capacity upgrade. In this paper, we investigate the equalization techniques for enabling 25-Gb/s transmission with 10G-class optics. A comparison between FFE and DFE based equalizer and MLSE based digital equalizer is made, where 13-tap FFE and 3-tap DFE are required to obtain similar performances with MLSE based detection. In addition, to verify the cost introduced by the ADC, the demand for the ADC parameters in the MLSE based detector, including the sampling rate, resolution, and timing jitter is investigated. Experimental results show that using a 25-GS/s ADC with 4-bit resolution, 25-Gb/s transmission is realized using 10-G TOSA and ROSA, and 28-/30-dB loss budget can be achieved in C-/O-band respectively.