Diastereoselective Three-Component 1,3-Dipolar Cycloaddition to Access Functionalized ß-Tetrahydrocarboline- and Tetrahydroisoquinoline-Fused Spirooxindoles.

A chemselective catalyst-free three-component 1,3-dipolar cycloaddition has been described. The unique polycyclic THPI and THIQs were creatively employed as dipolarophiles, which led to the formation of functionalized ß-tetrahydrocarboline- and tetrahydroisoquinoline-fused spirooxindoles in 60-94% of yields with excellent diastereoselectivities (10: 1->99: 1 dr). This reaction not only realizes a concise THPI- or THIQs-based 1,3-dipolar cycloaddition, but also provides a practical strategy for the construction of two distinctive spirooxindole skeletons.

High-security and low-complexity OCDM transmission scheme based on GAN enhanced chaotic encryption.

We report a low-complexity and high-security orthogonal chirp division multiplexing (OCDM) transmission scheme based on generative adversarial networks (GAN) enhanced chaotic encryption. Our investigation focuses on the security and efficiency of the communication system. To successfully apply GAN for the encryption scheme, we design our networks with new network architectures and modify the loss functions to improve the adversarial training performance of the networks. In the experiment, a weakly coupled seven cores fiber of 2 km was applied to achieve a 70 Gb/s transmission system. The results reveal that our proposed scheme has a maximum receiver sensitivity gain of about 1.26dB than traditional OFDM transmission system, and our encryption scheme has a large keyspace at about 1 × 10202 against brute force cracking by illegal optical network units with only 0.63% running time compared with the traditional chaotic scheme. The results highlight that the proposed encryption scheme has a remarkable reduction in complexity and improvement in security, which is a promising candidate for next-generation PONs.

Chaotic constant composition distribution matching for physical layer security in a PS-OFDM-PON.

This paper proposes a probabilistic shaping orthogonal frequency division multiplexing passive optical network (PS-OFDM-PON) based on chaotic constant composition distribution matching (CCDM). With the implementation of a four-dimensional hyperchaotic Lv system, probabilistic shaping and chaotic encryption are realized with low complexity on the process of signal modulation, so as to enhance the system performance in the presence of bit error rate (BER) and security. An 8.9 Gb/s encrypted PS-16 quadrature amplitude modulation (QAM)-OFDM signal transmission over a 25 km standard single mode fiber (SSMF) is experimentally demonstrated. And experimental results indicate that compared with conventional uniform 16QAM-OFDM, the encrypted PS-16QAM-OFDM can obtain a 1.2 dB gain in receiver sensitivity at a BER of 10-3 under the same bit rate. Moreover, the key space of the proposed scheme is 1.98 × 1073, which is a large enough number to effectively guard against any malicious attacks from illegal optical network units (ONUs). The combined superiority of BER and security performance enables a promising prospect for the proposed PS chaotic encryption scheme in a future low-cost optical access network.

Security-enhanced OFDM-PON with two-level coordinated encryption strategy at the bit-level and symbol-level.

A novel security-enhanced scheme combining improved deoxyribonucleic acid (DNA) encoding encryption at the bit-level with matrix scrambling at the symbol-level is proposed in OFDM-PON for the first time in this paper. In our proposed scheme, firstly each subcarrier is encrypted by improved DNA encoding encryption, which includes the functioning of key base series and the cross interchange. And the selected encoding rules, decoding rules, key base series, operating principles and the positions of cross interchange are dynamically changing, which enhances the robustness against malicious attacks by illegal attackers. Then during the matrix scrambling process, the non-equal-length quadrature amplitude modulation (QAM) matrix is divided into several squares of equal length according to an optimum method. At the same time, the times of matrix scrambling can be determined randomly. With the multi-fold encryption of the proposed scheme, the achieved key space can reach up to 10154, which can sufficiently ensure the physical layer security. Experimental verification of the proposed security-enhanced strategy was demonstrated in an 8 Gb/s 16QAM orthogonal frequency division multiplexing passive optical network (OFDM-PON) system over 25-km standard single-mode fiber (SSMF). The experimental results prove that the two-level coordinated encryption at the bit-level and symbol-level using chaos and encryption can effectively protect data from violent attacks, differential attacks, etc.

All-optical 3R regeneration for DPSK signal based on a semiconductor optical amplifier scheme.

This paper presents experimental demonstration of an all-optical 3 R (re-amplification, re-shaping, re-timing) regeneration scheme for differential phase-shift keying (DPSK) signals, which consists of a clock recovery module and a phase-regeneration module. The clock recovery module is based on a mode-locked fiber laser, and the optical clock is extracted with low timing jitter of 29 ps from a degraded 10 Gb/s DPSK signal. The phase regenerator consists of a one-bit delay interferometer demodulation stage and a semiconductor optical amplifier in which cross-phase modulation and nonlinear polarization rotation occur simultaneously. The results show that, after 3 R regeneration, the receiver sensitivity is improved by more than 1.6 dB for a bit error rate of 1 E-9.