Yingxiong Song

On stress-induced voltage hysteresis in lithium ion batteries: impacts of material property, charge rate and particle size

The effects of mechanical stresses on the voltage hysteresis of a lithium ion battery during charge–discharge cycles are theoretically investigated. A diffusion–reaction-stress coupling model has been established. It is found that a compressive stress in the electrode surface layer would impede lithium intercalation. Therefore, a higher overpotential is needed to overcome the intercalation barrier induced by stresses. The stress difference between charge and discharge made contribution to the voltage hysteresis which depends on charge rate, electrode particle radius, as well as a combined parameter that reflects the influence of material properties including elastic modulus, partial molar volume, capacity and diffusivity. Calculations show that the stress-induced overpotentials are several orders of magnitude higher in silicon electrodes compared to those in graphite and LiMn2O4 electrodes. Finally, a relaxation simulation shows that the stress variation from a thermodynamically non-equilibrium state to an equilibrium state leads to the relaxation of the electrode potential under an open-circuit operation. This serves as a proof that battery performance is affected by stresses.

Cost-effective sampling clock synchronisation scheme with its implementation in optical orthogonal frequency division multiplexing systems

A cost-effective scheme for sampling clock synchronisation based on the interpolation algorithm is proposed and implemented via field programmable gate array (FPGA). This scheme can provide a simpler and more economical achievement than the schemes that utilise expensive external clock recovery circuits. Low system complexity is another advantage of the proposed scheme due to the utilisation of the results of the frame synchronisation. Besides, a novel fractional sampling interval calculating algorithm which aims to calculate the fractional sampling time offset in a sampling interval is also proposed and this simpler operation algorithm based on least squares method is proved to fully satisfy the multi-subcarrier characteristic of orthogonal frequency division multiplexing (OFDM) symbol. The design and experimental results of a 2.5 Gb/s FPGA-based optical OFDM receiver by using the scheme that was proposed earlier are presented here. A major improvement in this scheme for sampling clock synchronisation is demonstrated to be suitable for practical application.

Flat frequency comb generation based on Mach-Zehnder modulator and phase modulator

A method to generate flat optical frequency comb is proposed and demonstrated which is based on Mach-Zehnder modulator and phase modulator cascade. Utilizing this method, we have analyzed flat optical frequency comb generation in the condition of different RF driving voltages. We also illustrate and correct the optimal operation condition for generating flat optical comb lines through the modulators.

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.

Low-complexity joint symbol synchronization and sampling frequency offset estimation scheme for optical IMDD OFDM systems.

A low-complexity joint symbol synchronization and SFO estimation scheme for asynchronous optical IMDD OFDM systems based on only one training symbol is proposed. Numerical simulations and experimental demonstrations are also under taken to evaluate the performance of the mentioned scheme. The experimental results show that robust and precise symbol synchronization and the SFO estimation can be achieved simultaneously at received optical power as low as -20dBm in asynchronous OOFDM systems. SFO estimation accuracy in MSE can be lower than 1 × 10-11 under SFO range from -60ppm to 60ppm after 25km SSMF transmission. Optimal System performance can be maintained until cumulate number of employed frames for calculation is less than 50 under above-mentioned conditions. Meanwhile, the proposed joint scheme has a low level of operation complexity comparing with existing methods, when the symbol synchronization and SFO estimation are considered together. Above-mentioned results can give an important reference in practical system designs.

Performance analysis of flat optical comb generation based on recirculating frequency shifter

The performance of the optical frequency comb generation based on the re-circulating frequency shifter has been analyzed and demonstrated in this paper. We have theoretically analyzed the condition for flatness of the optical frequency comb and the relative intensity noise influence. And the resulting performance analysis has been confirmed by a successfully generated 16 comb lines, which are stable and flat with spacing 12.5 GHz.

Encoding and decoding by the states of vector modes for vortex beams propagating in air-core fiber

In order to enhance the channel capacity and spectrum efficiency, the technology of space division multiplexing (SDM) has become research hotspot in optical communications. In this paper, a new encoding/decoding concept is proposed by the states of vector modes (polarized direction, rotational direction of phase and topological charge) for vortex beam propagating. To support encoded vector modes propagating in fiber, an OAM fiber with air-core structure is designed for encoding/decoding. Meanwhile, a new mode recognition method of judging states of the received vector modes is presented by the technology of digital image processing and digital signal processing (DSP). To verify the feasibility of encoding/decoding, an experimental platform to verify that encoded 16-QAM signal (0010_1100_1110_1010) is established. The vector modes of OAM beams can be propagated in OAM fiber with the length of 80 cm, and the received signal can be decoded to 16-QAM by image processing successfully. In addition, we also evaluate and analyze the influence factor (OAM fiber length and bit rate) on the transmitting performance in terms of BER, crosstalk and constellation figures.

Dual-drive Mach–Zehnder modulator-based reconfigurable and transparent spectral conversion for dense wavelength division multiplexing transmissions

Abstract. A digital signal process enabled dual-drive Mach–Zehnder modulator (DD-MZM)-based spectral converter is proposed and extensively investigated to realize dynamically reconfigurable and high transparent spectral conversion. As another important innovation point of the paper, to optimize the converter performance, the optimum operation conditions of the proposed converter are deduced, statistically simulated, and experimentally verified. The optimum conditions supported-converter performances are verified by detail numerical simulations and experiments in intensity-modulation and direct-detection-based network in terms of frequency detuning range-dependent conversion efficiency, strict operation transparency for user signal characteristics, impact of parasitic components on the conversion performance, as well as the converted component waveform are almost nondistortion. It is also found that the converter has the high robustness to the input signal power, optical signal-to-noise ratio variations, extinction ratio, and driving signal frequency.

A Single Pilot Subcarrier-Based Sampling Frequency Offset Estimation and Compensation Algorithm for Optical IMDD OFDM Systems

A sampling frequency offset (SFO) estimation and compensation scheme for asynchronous optical intensity-modulation and direct-detection orthogonal frequency division multiplexing (OFDM) systems by using one single pilot subcarrier is proposed. Experimental demonstrations are also under taken to evaluate the performance of the mentioned scheme, and results show that precise SFO estimation with an accuracy of <; ±0.2 ppm can be achieved under the SFO range from -1000 to 1000 ppm after 25 km standard single mode fiber (SSMF) transmission. Meanwhile, an SFO compensation method by extending the channel response with the phase shift correction term is also presented; more than 1000 and 400 ppm SFO effects can be compensated by using the phase shift correction term and its approximation, respectively.

Performance of optical OFDM transmission over RoF system with Mach-Zehnder modulator

This paper is concerned with the effect of the nonlinearity of an MZM (Mach-Zehnder modulator) on optical OFDM signal distortion. The optical OFDM signal output from the MZM is expressed as a Taylor series including third-order and fifth-order nonlinear distortion terms, by which we can easily establish a mathematical model of the optical OFDM signals in different formats and rates. According to the model, we can get the EVM at the optimized point. Moreover, the proposed theoretical model is proved in good agreement with experiment results of the RoF (Radio over Fiber) system.