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In the field of optical communication, laser and its modulation bandwidth and modulation rate are very important for optical wireless communication. There are two main modulation modes for semiconductor laser signal: internal modulation and external modulation. These two modulation technologies have their own characteristics and are suitable for different fields of optical fiber communication. Internal modulation laser, also known as direct modulation laser, has become a cost-effective light source for the Fifth Generation Mobile Communication Technology (5G) fronthaul and data center because of its high-speed transmission and low cost. There is no additional Chirp of light source in external modulation laser, so the Composite Second Beat (CSB) distortion caused by fiber dispersion can be effectively overcomed. On the basis of reviewing the development history of communication laser and its modulation technology, this paper introduces the work and main progress made by Xi’an University of Technology in this field. This paper discusses the internal and external factors of nonlinear distortion of semiconductor laser, simulates the effects of various parameters of response characteristics, linearization compensation method and power control system on the output light source of light emitting device, and analyzes the influence of temperature fluctuation on the output power of laser and modulation device. Based on the basic theory of refractive index ellipsoid and numerical analysis, the variation trend of emitted light intensity with temperature is discussed under the longitudinal and transverse modulation, respectively. The results show that the variation trend of outgoing light intensity with temperature under longitudinal modulation is only related to the refractive index of Lithium Niobate (LN) crystal. Under transverse modulation, the variation trend of outgoing light intensity with temperature is affected not only by the refractive index of the crystal, but also by the crystal size and its expansion coefficient. Therefore, the special size crystal can be used to improve the temperature stability of the electro-optic modulator.

【Objective】Deformable Mirror(DM) is a key device in adaptive optics system for wavefront correction, and its performance directly determines the wavefront correction capability of the system. By studying DM and their control algorithm, the wavefront correction capability of adaptive optics system can be continuously improved. On one hand, the accuracy and response speed of DM can be enhanced to better correct various complex wavefront distortions. On the other hand, the control algorithm can be improved to increase the efficiency and accuracy of the correction. These studies will directly affect the imaging quality and performance of adaptive optics system. Therefore, investigating the DM and their control algorithm is of great significance for improving the wavefront correction capability, expanding application fields, and enhancing imaging quality and performance of adaptive optics system.【Methods】The article aims to summarize the research progress on DM and their control algorithm both domestically and internationally, as well as analyze the correction accuracy of different control algorithm for wavefront distortion, establishing the groundwork for the advancement of adaptive optics. Firstly, several typical DMs are used as examples to model the DM and provide detailed introductions to the structures and working principles of separate actuator DM, splicer DM, thin film DM, dual piezoelectric DM, Micro Electromechanical System (MEMS) DM and voice coil DM. Then, several control algorithms such as the Prandtl-Ishlinskii (PI) hysteresis model-based control algorithm, decoupled control algorithm, and sparse sampling control algorithm are analyzed.【Results】Summarized the work done by Xi'an Technological University in this field, and finally pointed out the future technological breakthroughs and improvement directions in this field.【Conclusion】The research progress on DM and their control algorithm lays the foundation for the development of adaptive optics, enabling its application in more fields and further improving the performance of adaptive optics system. This will help improve imaging quality and drive the development of adaptive optics technology.

Liquid Crystal-Spatial Light Modulators (LC-SLM) control the optical path by modulating the refractive index of liquid crystal, and play an important role in adaptive optics. This paper sorts out the development status of LC-SLM at home and abroad, and introduces the working principle and phase calibration principle of LC-SLM in detail. Aiming at the application of LC-SLM in adaptive optics, the research status of key technologies of LC-SLM at home and abroad is discussed. The experimental research in this field of Xi'an University of Technology is analyzed and summarized. Finally, the application status of LC-SLM is prospected.

【Objective】Coherent optical communication is a high-speed, high-quality, and highly secure communication method, and coherent detection plays an extremely important role in coherent optical communication. High sensitivity coherent detection systems can significantly increase the distance of coherent optical communication. By studying the factors that affect the sensitivity of coherent detection, targeted corrections can be made to improve the detection sensitivity.【Methods】This paper first briefly describes the principle of the coherence detection, and summarizes the research progress in this field at home and abroad. Then the paper analyzes the influence of thermal noise, shot noise, wavefront distortion, polarization loss, spot size deviation, optical axis deflection, coupling efficiency, detector performance, preamplifier and other aspects on coherence detection sensitivity of wireless optical coherence detection system.【Results】The results show that the influence of the thermal noise and shot noise of the system on the detection sensitivity can be minimized by controlling the local oscillator power. The wavefront distortion of signal light can be suppressed by adding an adaptive correction system. The polarization control compensation device can be used to compensate the polarization mismatch between signal light and local oscillator light. The deviation of spot size and optical axis deviation requires improving the processing level of hardware to reduce this error. The use of new detectors can improve the performance of detectors to a certain extent. The pre-amplifier can amplify weak signal light, which is crucial for improving detection sensitivity.【Conclusion】This article analyzes the factors that affect the sensitivity of wireless optical coherent detection, and summarizes the methods used by domestic and foreign scholars to improve detection sensitivity in recent years. It provides theoretical reference for improving the sensitivity of detection systems in practice, which has important significance for improving the performance of coherent optical communication systems.

Objective To independently verify and compare the accuracy of 2 cardiovascular risk prediction models, Framingham model and New Zealand Diabetes Cohort Study (DCS) model in Chinese patients with type 2 diabetes mellitus (T2DM). Methods A total of 48 063 T2DM patients aged from 30 to 74 who had medical records but no cardiovascular diseases (CVD) in the Chinese electronic health records research in Yinzhou (CHERRY) were enrolled from January 1, 2010 to December 31, 2018. Kaplan Meier method was used to calculate the actual risk of CVD in following 5 years, and the recalibrated Framingham model and DCS model were adopted to estimate the predicted 5-year risks of the diseases. The performance of the models was assessed in terms of discrimination and calibration degrees, using C-index and Hosmer-Lemeshow Chi-square value respectively. Results Through a median follow-up of 5.9 years, 2 867 new CVD cases were observed among the subjects. However, both the Framingham and the DCS models underestimated the risk of subjects, by 3.6% (Framingham) and 21.1% (DCS) in males, and by 21.0% (Framingham) and 20.9% (DCS) in females, respectively. For males, the DCS model (C-index=0.716, 95%CI: 0.702~0.730) had a better discriminative ability than the Framingham one (C-index=0.662, 95%CI: 0.648~0.677), though the performance of calibration was not ideal in both models (P < 0.05). For females, C-index was 0.743 in DCS (95%CI: 0.730~0.756) and 0.686 in Framingham models (95%CI: 0.673-0.700), both showing poor performance on calibration (P < 0.05). Conclusion Both Framingham model and DCS model are confirmed inapplicable to CVD risk prediction in Chinese population with T2DM.

In free-space optical communication, the transmission of signal light and beacon light of differing wavelengths through the same atmospheric channel encounters variations in how the atmospheric refractive index absorbs and scatters light. This leads to distinct degrees of wavefront aberrations between the signal and beacon lights. In this study, we employed statistical optics to derive wavefront phase structure functions for both signal and beacon lights under conditions of strong turbulence. We explored how wavefront distortion varies among beams of different wavelengths after propagation through such turbulent conditions. Our findings revealed that as the turbulence outer scale escalates, the difference in wavefront distortion between signal and beacon lights stabilizes after an initial increase, assuming constant wavelengths. Furthermore, we observed significant changes in the relative wavefront aberrations when the inner scale of turbulence surpasses the separation between two points on the receiving apertures. As the disparity in wavelength decreases, so does the difference in wavefront aberrations. Finally, we propose a method for correcting wavefront aberrations based on coefficients of Zernike polynomials corresponding to beams with different wavelengths. This approach is validated through simulation and experimentation, demonstrating an 11% enhancement in the signal-to-optical Strehl ratio and a 0.072 increase in spot energy after the addition of correction coefficients compared with before their inclusion. These results solidify the efficacy of our method in improving adaptive optics correction accuracy. [ABSTRACT FROM AUTHOR]

Four-level pulse amplitude modulation (PAM4) can transmit more information in the same symbol interval, effectively improving the information transmission rate and frequency band utilization of visible light communication (VLC). This paper proposes a method for encoding and decoding the PAM4 signal based on FPGA. The PAM4 signal is studied and analyzed under different channel noise models. The research results show that the bit error rate (BER) performance of the PAM4 signal is the best under the additive noise model. The influence of the multiplicative noise on the BER of the PAM4 signal is much greater than that of the additive noise. The BER performance of the PAM4 signal depends on the variance of the noise data. The greater the variance, the worse the BER performance. At the same time, an indoor VLC system based on PAM4 is designed. The simulation results verify that the system scheme is feasible and provides a way to further realize high-speed signal transmission. [ABSTRACT FROM AUTHOR]

This correction notice addresses two errors in the original publication titled "Experimental Study on Chromaticity Control in Visible Light Communication Systems." The first error is in the legend for Figure 21, which mistakenly labeled the image as an experiment using low-power LEDs instead of high-power LEDs. The second error is regarding the affiliations of the authors, which were listed in the wrong order. The authors assure that these errors do not affect the scientific conclusions of the study. The correction has been approved by the Academic Editor and the original publication has been updated. [Extracted from the article]

In dual-wavelength free-space optical communication systems, the wavefront distortion differences caused by the wavelength difference of the signal and beacon lights cannot be completely corrected. In this study, according to the method of geometric optics, the relationship between the wavefront phases of the signal and beacon lights is analyzed by establishing a mathematical model of the cross-correlation ratio of the arrival-angle fluctuation and phase relationship of different Gaussian-beam wavelengths under weak turbulence near the surface. The numerical results show that after Gaussian beams of different wavelengths propagate through the same atmospheric channel, the cross-correlation number of the arrival-angle fluctuation decreases with an increase in the wavelength difference, waist radius, and turbulence intensity, and increases with an increase in propagation distance. The beam-wavefront phase difference increases with an increasing wavelength difference. Finally, a wavefront distortion correction experiment of a dual-wavelength adaptive optical system verified the correctness of the wavefront phase-difference relationship between the signal light and beacon light established in this study. [ABSTRACT FROM AUTHOR]