A dual parallel Mach–Zehnder modulator linearization scheme based on 90° phase shifters

In this paper, a dual-drive dual-parallel Mach–Zehnder Modulator based linearization scheme is implemented by utilizing only two phase shifters and comprehensively demonstrated for a photonic transmission link. Third order intermodulation distortion is suppressed by adjusting angles of electrical phase shifters i.e. π/2 and−π/2 and a non-linear distortion immune system can be proposed for microwave photonic link. A complete suppression in intermodulation terms and 20.8 dB enhancements are found in spurious free dynamic range (SFDR). SFDR reaches 135.6 dB Hz4/5 by suppressing major spurious contributors of third order intermodulation distortions in optical domain only which ensures the improvement in performance of link against non-linear terms.

Performances enhancement of underwater wireless optical communications (UWOC) using pulse position modulation

In this work, we study the performance analysis of underwater optical wireless communication (UOWC) transmission link by incorporating optical code division multiple access (OCDMA) using pulse position modulation (PPM) to enhance the channel range and cardinality. Bit error rate (BER) variations are examined versus the range, modulation type (on–off keying (OOK), quadrature amplitude modulation (QAM), etc.), number of users as well as the channel attenuation caused by different water types. The power and transmitter inclination angle limitation, of the enhanced system, are also presented in order to determine the threshold for which the minimum BER 10−9 is achievable.

The Differences in Mean and Volatility Shock Transmission among Bitcoin, Currencies from Developed Countries, and Currencies from Emerging Countries

This paper studied the mean and volatility transmission among Bitcoin as the most prominent cryptocurrency, exchange rates from developed countries/regions, and exchange rates from emerging countries/regions. Using daily returns between January 1, 2015, and December 31, 2018, and Bivariate VAR - Diagonal VECH models. The empirical results suggest there was no mean transmission between USD/EUR and USD/BTC. However, there was a unidirectional mean shock transmission link from USD/CNH, USD/MAD, and USD/IDR to USD/BTC. The results also suggested the existence of a bidirectional cross-volatility persistence link between bitcoin and all the exchange rates, except for USD/IDR and a bidirectional cross-volatility spillover link between USD/BTC and USD/CNH. A critical implication of these results is that they will be of use to investors, speculators, risk managers, and policymakers in understanding the degree of integration in terms of volatility and return among Bitcoin, currencies from developed, and currencies from emerging countries.

Fiber nonlinearity compensation using optical phase conjugation in dispersion-managed coherent transmission systems

In the discretely amplified transmission systems with erbium-doped fiber amplifiers, the system performance of nonlinearity-compensated optical transmission based on pre-dispersed spectral inversion (PSI) is investigated numerically. We find that PSI offers more significant performance improvement in dispersion-managed (DM) links than that in non-dispersion-managed (noDM) links. On the other hand, the DM link is more sensitive to the span offset from the center of the transmission link than noDM link. The performance difference between DM and noDM links is 1 dB if the span offset equals four spans in 20 × 90 km nonlinear transmission. Furthermore, we show that for the dispersion-managed transmission, in order to obtain the best system performance, the amount of pre-dispersion of the PSI, should be optimized over different dispersion maps.

Chained Data Acquisition and Transmission System Protype for Cabled Seafloor Earthquake Observatory

Seafloor observatories can provide long-term, real-time submarine monitoring data, which has great significance for the study of major scientific technology in marine science, especially in the seafloor earthquake observation. The chained submarine data sampling and transmission system is the prototype and foundation of cabled seafloor earthquake observatories. This paper designs and builds a chained data sampling and transmission system (SQSTS) based on Zynq-7000 Soc (System on chip) and clock synchronization. At the beginning, we realized high-precision submarine data (24 bit) sampling based on Zynq-7000 Soc and ADS 1256. Using the PPS (Pulse per second) signal provided by the P88 1588 PTP (Precise time protocol) clock synchronization board and the inner crystal oscillator of the Zynq-7000 Soc, the time stamp up to the microsecond level, for the seismic data sampled in each seismometer node can support subsequent inversion of seismic data. In addition, a high-speed data transmission link connecting nodes in SQSTS, which is based on the Gigabit transceiver and optical cable, has been investigated. The transmission link has been realized by using the Aurora IP core. The theoretical calculations indicate that the data transmission bus bandwidth can reach 4 Gbps, while in the meantime its reliability has been proved by experiments. The experimental results show that the system owns the characteristics of high data sampling accuracy, stable and reliable high-speed transmission, and has promising application prospects.

Investigation of the Scattering Noise in Underwater Optical Wireless Communications

In underwater optical wireless communications (UOWC), scattering of the propagating light beam results in both intensity and phase variations, which limit the transmission link range and channel bandwidth, respectively. Scattering of photons while propagating through the channel is a random process, which results in the channel-dependent scattering noise. In this work, we introduce for the first time an analytical model for this noise and investigate its effect on the bit error rate performance of the UOWC system for three types of waters and a range of transmission link spans. We show that, for a short range of un-clear water or a longer range of clear water, the number of photons experiencing scattering is high, thus leading to the increased scattering noise. The results demonstrate that the FEC limit of 3×10−3 and considering the scattering noise, the maximum link spans are 51.5, 20, and 4.6 m for the clear, coastal, and harbor waters, respectively.